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Foreword During the pre-summer rainy season (April-June), Southern China often experiences frequent
occurrences of extreme rainfall, leading to severe flooding and inundations. To improve the
quantitative precipitation forecast of the pre-summer rainy season rainfall, the China
Meteorological Administration (CMA) initiated a nationally coordinated research project, the
Southern China Monsoon Rainfall Experiment (SCMREX). With the participation and strong
support of international experts, SCMREX was approved by the World Meteorological
Organization (WMO)’s World Weather Research Programme (WWRP) as a WWRP Research and
Development Project (RDP). The SCMREX RDP (2013-2018) consists of four major components:
field campaign, database management, studies on physical mechanisms of heavy rainfall events,
and convection-permitting numerical experiments including data assimilation, evaluation and
improvement of model physics, and ensemble prediction.
International Workshop of SCMREX, 12-13 April 2017 in Beijing, China, is organized by the
WWRP/WGTMR Monsoon Panel and is hosted by the State Key Laboratory of Severe Weather
(LaSW) of the Chinese Academy of Meteorological Sciences (CAMS), CMA. This volume is the
collection of abstracts of papers presented in the workshop.
The objective of this workshop is to bring together researchers and forecasters to review the
progress of the SCMREX RDP and to discuss topics of mutual interests. Through these
discussions we hope to identify research results that can be transferred to operational applications
in National Meteorological and Hydrological Services (NMHSs).
We would like to thank all authors for their contributions to the workshop, and to thank Ms.
Nanette Lomarda of the WWRP office at WMO for her strong support of the workshop. We would
also like to thank the capable colleagues of LaSW/CAMS for their excellent efforts in the
preparation of the workshop. Yali Luo (Chinese Academy of Meteorological Sciences) Chair, International Organizing Committee Chih-Pei Chang (NPS, USA) Yihong Duan (CAMS, China) Co-Chairs, International Organizing Committee
2
Committees International Organizing Committee: Chih-Pei Chang (Co-Chair) Yihong Duan (Co-Chair) Richard Johnson Dong-In Lee Yali Luo (Chair) Zhiyong Meng Hiroshi Uyeda Local Organizing Committee: Xudong LIANG (Chair) Wei WEI Rujun XING Dan YAO Haoyue ZHANG Yan ZHAO
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International Workshop of the Southern China Monsoon Rainfall
Experiment (SCMREX)
Beijing, China, 12-13 April 2017
Date Time Program Speaker Chair
Wednesday
12 April
8:30-9:00 Opening ceremony, Group photo Yali LUO
(CAMS)
9:00-9:25 Introduction to SCMREX Yali LUO
(CAMS)
Yali LUO
(CAMS)
9:25-9:45
Observation and Data Analysis of Cloud
and Precipitation at Longmen Station in
2016 SCMREX
Zheng RUAN
(CAMS)
9:45-10:05
Statistical Characteristics of the
Raindrop Size Distributions and their
Retrieved Polarimetric Parameters
During SCMREX
Xiantong LIU
(GITMM)
10:05-10:25
CPOL Radar Detection and Preliminary
Analysis of Heavy Rainfall in South
China
Bin WANG
(WIHR)
10:25-10:45
The Optimized Hydrometeor
Classification Algorithm for
Polarimetric Radars in South China
Chong WU
(CAMS)
10:45-11:00 Coffee break
11:00-11:20 Observation and Parameterization of
Cloud Microphysical Processes
Xueliang
GUO
(CAMS)
Wai Kin
WONG
(HKO)
11:20-11:40 Introduction of FY-4 Satellite and the
Developing Convection Product
Danyu QIN
(NSMC/CMA)
11:40-12:00
Tropical Cyclones-pacific Asian
Research Campaign for Improvement of
Intensity Estimations/Forecasts
(T-PARCII): A Research Plan of
Typhoon Aircraft Observations in Japan
Kazuhisa
Tsuboki
(Nagoya U
/Japan)
12:00-12:20
Recent Progress in Monitoring and
Forecasting Techniques of Significant
Weather in Southern China
Wai Kin
WONG
(HKO)
12:20-14:00 Lunch
14:00-14:20
Synoptic and Mesoscale Processes
Associated with Extreme Convective
Rainfall
Richard H.
Johnson
(CSU/USA)
Richard H.
Johnson
(CSU/USA)
5
Date Time Program Speaker Chair
14:20-14:40
Stage-dependent Predictability of a
Heavy-rainfall Event in South China:
An Ensemble-based Analysis
Zhiyong
MENG
(PKU)
14:40-15:00
Operational QPF Progress and Scientific
Research on Heavy Rainfall in South
China during the Pre-summer Rainy
Season
Zhiping
ZONG
(NMC/CMA)
15:00-15:20
Mesoscale Observational Analysis of
Lifting Mechanism of a Warm-Sector
Convective System Producing the
Maximal Daily Precipitation in China
Mainland during Pre-summer Rainy
Season of 2015
Mengwen WU
(CAMS)
15:20-15:40
An Extreme Rainfall Event Associated
with a Mesoscale Outflow Boundary
and Multiple Rainbands over
Guangdong Coastal Areas during
SCMREX-2014
Xi LIU
(NUIST)
15:40-15:55 Coffee Break
15:55-16:15 Analysis of Heavy Rainfall Events over
India
Ajit Tyagi
(IMS/India)
Ben Jong-Dao
JOU
(PSA)
16:15-16:35 Evaluation of the Met Office Unified
Model for a SCMREX Case Study
Kalli Furtado
(UK Met Office)
16:35-16:55
Lightning Activity Characteristics as
Indicated by Lightning Location System
in Guangdong
Dong ZHENG
(CAMS)
16:55-17:15 Diurnal Variations of Pre-Summer
Rainfall over Southern China
Zhina JIANG
(CAMS)
17:15-17:35
A Comparison and Relationship
Between Two Consecutive
Heavy-rainfall Events during
SCMREX-2014
Yangruixue
CHEN
(CAMS)
Thursday
13 April
8:30-8:50 Key Microphysical Factors Impact the
Simulation of Squall Lines
Yanluan LIN
(Tsinghua U)
Zhiyong
MENG
(PKU)
8:50-9:10
Application of a Convection- permitting
Ensemble Prediction System to QPF over
Southern China: Preliminary Results
during SCMREX
Xubin
ZHANG
(GITMM)
9:10-9:30
Cloud-resolving Heavy-rainfall
Quantitative Precipitation Forecasts and
Ensemble Strategy
Chung-Chieh
WANG
(PSA)
6
Date Time Program Speaker Chair
9:30-9:50 Stochastic Physics for Ensemble
Forecast and Its Application
Yuejian ZHU
(NCEP/USA)
9:50-10:10
The Characteristics of GRAPES-REPS
Model and its Sensitivity for a Heavy
Rainfall Case in Southern China
Jing CHEN
(NMC/CMA)
10:10-10:30
Influence of Monsoonal Wind Speed
and Moisture Content on Intensity and
Diurnal Variations of the Meiyu Season
Coastal Rainfall over South China
Kun ZHAO
(NJU)
10:30-10:45 Coffee Break
10:45-11:05
Evaluation and Application of the High
Resolution Models from the 2013-2016
NMC TESTBED Warm-season
Experiments
Xiaoling
ZHANG
(NMC/CMA)
Yuejian ZHU
(NCEP/USA)
11:05-11:25
Evaluation of Quantitative Precipitation
Forecast by TIGGE Ensembles for
South China during the Pre-summer
Rainy season
Ling HUANG
(CAMS)
11:25-11:45
A High Resolution Weather Forecast
Regime in India: Focus on Extreme
Events
Parthasarathi
Mukhopadhyay
(IITM/India)
11:45-12:05
Assimilating Doppler Radar
Observations with an Ensemble Kalman
Filter for Convection-permitting
Prediction of Convective Development
in a Heavy Rainfall Event during the
Pre-summer Rainy Season of South
China
Xinghua BAO
(CAMS)
12:05-12:25
Impact of Assimilating Wind Profiling
Radar Observations on
Convection-permitting QPFs during
SCMREX
Xubin
ZHANG
(GITMM)
12:25-14:00 Lunch
14:00-17:30 Discussion
Yali LUO
(CAMS),
Xudong
LIANG
(CAMS)
7
Contents 1. The Southern China Monsoon Rainfall Experiment (SCMREX) ..................................... 9
2. Observation and Data Analysis of Cloud and Precipitation at Longmen Station in 2016
SCMREX ........................................................................................................................................ 10
3. Statistical Characteristics of the Raindrop Size Distributions and their Retrieved
Polarimetric Parameters During SCMREX .................................................................................... 11
4. CPOL Radar Detection and Preliminary Analysis of Heavy Rainfall in South China .... 12
5. The Optimized Hydrometeor Classification Algorithm for Polarimetric Radars in South
China ........................................................................................................................................ 13
6. Observation and Parameterization of Cloud Microphysical Processes ........................ 14
7. Introduction of FY-4 Satellite and the Developing Convection Product......................... 15
8. Tropical Cyclones-pacific Asian Research Campaign for Improvement of Intensity
Estimations/Forecasts (T-PARCII): A Research Plan of Typhoon Aircraft Observations in Japan . 16
9. Recent Progress in Monitoring and Forecasting Techniques of Significant Weather in
Southern China ................................................................................................................................ 18
10. Synoptic and Mesoscale Processes Associated with Extreme Convective Rainfall ..... 19
11. Stage-dependent Predictability of a Heavy-rainfall Event in South China: An
Ensemble-based Analysis ................................................................................................................ 20
12. Operational QPF Progress and Scientific Research on Heavy Rainfall in South China
during the Pre-summer Rainy Season ............................................................................................. 21
13. Mesoscale Observational Analysis of Lifting Mechanism of a Warm-Sector Convective
System Producing the Maximal Daily Precipitation in China Mainland during Pre-summer Rainy
Season of 2015 ................................................................................................................................ 22
14. An Extreme Rainfall Event Associated with a Mesoscale Outflow Boundary and
Multiple Rainbands over Guangdong Coastal Areas during SCMREX-2014 ................................ 23
15. Analysis of Heavy Rainfall Events over India ................................................................ 25
16. Evaluation of the Met Office Unified Model for a SCMREX Case Study ..................... 26
17. Lightning Activity Characteristics as Indicated by Lightning Location System in
Guangdong ...................................................................................................................................... 27
18. Diurnal Variations of Pre-Summer Rainfall over Southern China .................................. 29
19. A Comparison and Relationship Between Two Consecutive Heavy-rainfall Events
during SCMREX-2014 ................................................................................................................... 30
20. Key Microphysical Factors Impact the Simulation of Squall Lines ............................... 32
21. Application of a Convection- permitting Ensemble Prediction System to QPF over
Southern China: Preliminary Results during SCMREX ................................................................. 33
8
22. Cloud-resolving Heavy-rainfall Quantitative Precipitation Forecasts and Ensemble
Strategy ........................................................................................................................................ 34
23. Stochastic Physics for Ensemble Forecast and Its Application ....................................... 35
24. The Characteristics of GRAPES-REPS Model and its Sensitivity for a Heavy Rainfall
Case in Southern China ................................................................................................................... 36
25. Influence of Monsoonal Wind Speed and Moisture Content on Intensity and Diurnal
Variations of the Meiyu Season Coastal Rainfall over South China ............................................... 37
26. Evaluation and Application of the High Resolution Models from the 2013-2016 NMC
TESTBED Warm-season Experiments ........................................................................................... 38
27. Evaluation of Quantitative Precipitation Forecast by TIGGE Ensembles for South China
during the Pre-summer Rainy season ........................................................................................... 39
28. A High Resolution Weather Forecast Regime in India: Focus on Extreme Events ........ 40
29. Assimilating Doppler Radar Observations with an Ensemble Kalman Filter for
Convection-permitting Prediction of Convective Development in a Heavy Rainfall Event during
the Pre-summer Rainy Season of South China ............................................................................... 41
30. Impact of Assimilating Wind Profiling Radar Observations on Convection-permitting
QPFs during SCMREX ................................................................................................................... 42
9
The Southern China Monsoon Rainfall Experiment (SCMREX)
Yali Luo
State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing 100081, China
Abstract
During the pre-summer rainy season (April-June), South China often experiences frequent
occurrences of extreme rainfall, leading to severe flooding and inundations. To expedite the efforts
in improving the quantitative precipitation forecast (QPF) of the pre-summer rainy season rainfall,
the China Meteorological Administration (CMA) initiated a nationally coordinated research
project, namely, the Southern China Monsoon Rainfall Experiment (SCMREX) that was endorsed
by the World Meteorological Organization (WMO) as a Research and Development Project (RDP)
of the World Weather Research Programme (WWRP). The SCMREX RDP (2013-2018) consists
of four major components: field campaign, database management, studies on physical mechanisms
of heavy rainfall events, and convection-permitting numerical experiments including impact of
data assimilation, evaluation/improvement of model physics, and ensemble prediction. The field
campaigns were carried out during early May to mid-June of 2013-16. This paper: (i) describes the
scientific objectives, 2013-16 field campaigns, and data sharing of SCMREX; (ii) provides an
overview of heavy rainfall events during the intensive observing periods; (iii) presents examples
of research results; (iv) explains future research opportunities and 2017-18 field campaigns.
10
Observation and Data Analysis of Cloud and Precipitation at
Longmen Station in 2016 SCMREX
Ruan Zheng1 Liping Liu 1 Feng Li 1 Jiafeng Zheng 2
1. State Key Laboratory of Severe Weather，Chinese Academy of Meteorological Sciences, Beijing,
2. Chengdu University of Information Technology, School of Atmospheric Sciences, Chengdu
Abstract
From April to September, 2016, the SCMREX was carried out and comprehensive
measurements of water vapor, clouds, and precipitation were conducted at Longmen Guangdong
province. The most vertical radars and instruments, such as Ka-Band millimeter-wave cloud radar,
Ku-Band micro-rain radar, C-Band frequency modulated continuous wave radar(C-FMCW) and
lidar, and microwave radiometer and disdrometer were deployed to observe high spatial-temporal
resolution vertical structures of clouds and precipitation. The work of Longmen observation
station in 2016 includes the operation environment construction，portable instruments installation
and calibrate, data compared between the different wavelength radars. All the data processed and
data submitted for sharing after experiment.
The data analysis of experiment are include the data of C-FMCW and Cloud radar analysis
respectively and data merging. The C-FMCW data anslysis is using a case of precipitation to give
the characteristics of convective, stratiform and mix cloud in pre-summer rainy season. And the
difference of vertical structure characteristics of precipitation cloud in Tibetan Plateau, jianghuai
meiyu and south China are analysis. After analyze the consistency between cloud radar
measurements with the three modes, a cloud radar data merging algorithm for the three modes is
also proposed. Finaly, Constructing a cloud–precipitation radar dataset by merging observations
from a ka-Band cloud radar, C-FMCW and a ceilometer for analysis of summer time cloud
characteristics in South China.
11
Statistical Characteristics of the Raindrop Size Distributions and
their Retrieved Polarimetric Parameters During SCMREX
Xiantong Liu1* Huijun Huang1 YaLi Luo2 QiLin Wan1
Hong Wang1 Hui Xiao1 Lu Feng1
1. Institute of Tropical and Marine Meteorology, CMA, Guangzhou 510080, China
2. Chinese Academy of Meteorological Science, Beijing 100081, China
Abstract
The characteristics of raindrop size distributions (DSDs) and polarimetric radar parameters
retrieved by T-matrix are studied using PARSIVEL disdrometers measurements during the field
campaign of the SCMREX (Southern China Monsoon Rainfall Experiment) project from 2014 to
2016. According to the rain rate and its temporal variation, the observational spectra are divided
into convective and stratiform precipitation. The measured DSDs during summer monsoon season
in Southern China indicate higher values of mass-weighted mean diameter of raindrops (Dm) and
lower values of generalized intercept parameters (log10 Nw) for both stratifrom and convective rain
types. The convective precipitation was composed of larger raindrop sizes and higher raindrop
concentrations than those of the stratiform precipitation. The averaged DSDs of both rain types are
in good agreement with gamma distributions. The shape(μ)-slope(Λ) relationships of the gamma
distribution derived for convective rain are similar to that found in Nanjing (Chen et al., 2013) and
Yangjiang (Tang et al., 2014), compared to the Florida relation (Zhang et al., 2003). The values of
radar reflectivity factor (ZH) derived by T-matrix are in good agreement with those derived by
PARSIVEL for both rain types, with correlation coefficients all above 0.998. There are
exponential relationships between differential reflectivity (ZDR) and ZH, as well as the relations
between specific differential phase (KDP) and ZH. The Z-R relationships derived in this study are
found to be closer to the observed rain rate compare with the classic Z-R relationships (Z=300R1.4).
The polarimetric rainfall estimated relationships R(ZH, ZDR) and R(KDP) are both have better
performances than the Z-R relationships. The R(KDP) relationships have the best performance,
especially in heavy rainfall situations.
12
CPOL Radar Detection and Preliminary Analysis of Heavy
Rainfall in South China
Bin Wang Muyun Du Liang Leng ZhiKang Fu WenGang Zhang
Institute of Heavy Rain, CMA, Wuhan, China
Abstract
A mobile C-band polarimetric Doppler weather radar owned by the Institute of Heavy Rain,
CMA was employed in the SCMREX field campaign in 2016. The CPOL radar was fulfilled
enhanced detection with one month stage in May and obtained a dataset including 4 heavy rainfall
processes. Besides a lot of conventional VOL scans, intense RHI scans were operated and
emphasized on purpose of detecting high temporal and spatial resolution vertical cross-section
characteristics of hydrometeors and precipitation. On the basis of radar data quality control, the
preliminary study is carried out to analyze vertical profiling characteristics of dual polarimetric
variables and their relation to precipitation development.
13
The Optimized Hydrometeor Classification Algorithm for
Polarimetric Radars in South China
Chong Wu Liping Liu
State Key Lab of Severe Weather, Chinese Academy of Meteorological Science, Beijing, China
Abstract
A modified Hydrometeor Classification Algorithm(HCA) has been developed in this study
for Chinese polarimetric radars. This algorithm is based on the U.S. operational HCA, and the
methodology of statistics-based optimization is proposed, including calibration checking, datasets
selection, membership functions modification, computation thresholds modification, and effect
verification. The above procedures are applied to Zhuhai radar which is the first operational
polarimetric radar in South China. No significant calibration bias is found, but the reliability of
Zhuhai radar measurements deteriorates when the Signal Noise Ratio(SNR) is low, and ρhv within
the melting layer is usually lower than that of the U.S. WSR-88D radar. Through the modification
based on the statistical analysis of polarimetric variables, the localized HCA specially for Zhuhai
is obtained, and it performs well over a one-month test by contrasting with sounding and surface
observations. Then, this algorithm is utilized for analysis of a squall line case on 11 May 2014.
The horizontal and vertical structures indicate that the algorithm can provide reasonable details,
and the results of HCA, especially the rain-hail mixture region, could reflect the life cycle of
squall line. Moreover, the difference between radar-detected hail regions and surface hail reports is
also analyzed. False alarm of HCA seems inevitable due to the hail melting below the minimum
radar-detectable altitude. Results of this study provided evidence for the improvement of the
hydrometeor classification algorithm that is specifically developed for China.
14
Observation and Parameterization of Cloud
Microphysical Processes
Xueliang Guo Shichao Zhu Guangxian Lu Chungang Fang
Chinese Academy of Meteorological Sciences, Beijing, China
Abstract
Cloud dynamical and microphysical processes are critical to the weather forecast, climate
change and water cycle. However, the well understanding and parameterizing of clouds and
precipitation processes are still a challenge issue. So far, the main problem is a lack of quantitative
observation of these processes.
Cloud microphysical processes including ice crystal habits, growth and size distribution in
mixed-phase clouds were observed by multiple aircraft in 2009 during the Beijing Cloud
Experiment (BCE) and compared with those simulated by WRF model. The results show that both
riming and aggregation processes played critical roles in the broadening of particle size
distributions (PSDs), and these processes were more active in embedded convection regions than
in stratiform regions. Both in embedded convection and stratiform region the particle size
distributions simulated and observed are not fully consistent. There was an obvious discrepancy
for the parameterization of microphysical processes between the observed and simulated,
especially at the growth and change of ice particles. The simulated broadening rate of PSDs was
smaller than observations. In particular, the simulated snow mass concentration was higher than
that observed. This study show that there is an uncertainty about the PSDs parameterization of
cloud ice processes in WRF model, especially at the growth and change of ice particles. The
further improvement of these processes based on observations for typical cloud system are
necessary.
15
Introduction of FY-4 Satellite and the Developing
Convection Product
Danyu Qin Fenglin Sun Bo Li
National Satellite Meteorological Center, Beijing, China
Abstract
China new-generation meteorological satellite, FY-4 was launched on 11 December 2016. It
is first satellite of CMA's (China Meteorological Administration) three-axis stabilized,
geostationary meteorological satellite series. Four new instruments are onboard, namely,
Advanced Geosynchronous Radiation Imager (AGRI), Geosynchronous Interferometric Infrared
Sounder (GIIRS), Lightning Mapping Imager (LMI) and Space Environment Package (SEP). For
the first time in the world, the GIIRS is an hyper-spectral vertical atmospheric sounding payload，
which could conducting a high-precision observation of atmosphere over China and
neighborhoods. The observation system is more capable than the current system, thus is bound to
significantly enhance weather warning and forecasting capability. As a result, FY-4 can serve
multispectral, high-precision and quantitative observation data and images. Furthermore, users are
expected to investigate the details inside typhoon, rainstorm, flood, forest fire, sand storm and
space weather.
Base on FY-4 AGRI, the developing convection product is introduced for nowcasting purpose.
It uses a multi spectral thresholding technique, which tracks convective clouds with cloud top
temperature keeping cooling, and monitor their spectral characteristics. If its cloud top cooling
rate(CTC) threshold is exceeded, then the pixels within the cloud object are flagged for
developing convection（DC）. The DC product concerning not only convective initiation but also
vigorous deep convective clouds and cloud systems. The DC algorithm is tested by using the
simulated AGRI data, FY-2 6min observation data and Himawari-8 data, results show the
encouraging applications on monitoring the convective cloud systems.
16
Tropical Cyclones-pacific Asian Research Campaign for
Improvement of Intensity Estimations/Forecasts (T-PARCII): A
Research Plan of Typhoon Aircraft Observations in Japan
Kazuhisa Tsuboki
Institute for Space-Earth Environmental Research (ISEE), Nagoya University
Furo-cho, Chikusa-ku, Nagoya, 464-8601 Japan
e-mail: [email protected]
Abstract
Typhoons are the most devastating weather system occurring in the western North Pacific
and the South China Sea. Violent wind and heavy rainfall associated with a typhoon cause huge
disaster in East Asia including Japan. In 2013, Supertyphoon Haiyan struck the Philippines caused
a very high storm surge and more than 7000 people were killed. In 2015, two typhoons
approached the main islands of Japan and severe flood occurred in the northern Kanto region.
Typhoons are still the largest cause of natural disaster in East Asia. Moreover, many researches
have projected increase of typhoon intensity with the climate change. This suggests that a typhoon
risk is increasing in East Asia. However, the historical data of typhoon include large uncertainty.
In particular, intensity data of the most intense typhoon category have larger error after the US
aircraft reconnaissance of typhoon was terminated in 1987.The main objective of the present study
is improvements of typhoon intensity estimations and of forecasts of intensity and track. We will
perform aircraft observation of typhoon and the observed data are assimilated to numerical models
to improve intensity estimation. Using radars and balloons, observations of thermodynamical and
cloud-microphysical processes of typhoons will be also performed to improve physical processes
of numerical model.
In typhoon seasons (mostly in August and September), we will perform aircraft observations
of typhoons. Using dropsondes from the aircraft, temperature, humidity, pressure, and wind are
measured in surroundings of the typhoon inner core region. The dropsonde data are assimilated to
a cloud-resolving model which has been developed in Nagoya University and named the Cloud
Resolving Storm Simulator (CReSS). Then, more accurate estimations and forecasts of the
typhoon intensity will be made as well as typhoon tracks. Furthermore, we will utilize a
ground-based balloon with microscope camera, X-band precipitation radar, Ka-band cloud radar,
aerosol sonde, and a drone to observe typhoon-associated clouds and precipitation. After a test
17
flight in June 2017, typhoon observations will be made for the snext 4 years; 2017-2020. The main
target area of observation is the south of Okinawa where a typhoon reaches the maximum
intensity and often changes its moving direction.
This research will advance aircraft observation technique of typhoon in Japan. The aircraft
observation will be a breakthrough to improve typhoon intensity estimations. Assimilation of the
aircraft observation data to the cloud-resolving model will improve intensity estimations and
forecasts of typhoons. This is the first step for the future advanced aircraft observation and will
contribute to prevention or reduction of typhoon disasters.
18
Recent Progress in Monitoring and Forecasting Techniques of
Significant Weather in Southern China
Wai Kin Wong
Hong Kong Observatory, Hong Kong, China
Abstract
In Hong Kong Observatory, recent years have seen progressive enhancements in weather
observations that provide indispensable sources of data in monitoring and modelling of significant
weather processes. For instance, a dropsonde measurement system was successfully deployed for
a couple of experimental trials during passage of tropical cyclones over South China Sea in 2016
using a newly replacement aircraft of the Government Flying Services. With the flight data probe
on-board providing in-situ measurements, high resolution profiles of wind, temperature and
humidity can be collected to help understand the dynamical and physical mechanisms of the
significant weather due to tropical cyclone and monsoonal precipitation. Planning of observation
strategy in support of tropical cyclone monitoring and related WMO research projects will be
discussed. In very-short-term forecasts of significant convection over the coastal areas of
southern China, the Observatory’s SWIRLS nowcasting system using radars in Hong Kong and
Guangdong has been extended to incorporate the data of Himawari-8 satellite for estimation and
very-short-range prediction of precipitation. Multispectral Advanced Himawari Imager data are
utilized to retrieve equivalent reflectivity based on machine-learning technique. Verification
results reveal that the satellite-derived reflectivity provides a useful estimate to improve the spatial
and temporal coverage of the precipitation nowcast. More sophisticated cloud analysis
algorithms are under development to retrieve the characteristics of cloud properties using the
real-time NWP model forecasts and radiative transfer model. Potential applications of
satellite-derived reflectivity and retrieval products of significant convection to benchmark NWP
model performance and provide seamless blending forecasts for high-impact weather will also be
discussed.
19
Synoptic and Mesoscale Processes Associated with
Extreme Convective Rainfall
Richard H. Johnson
Colorado State University, Fort Collins, USA
Abstract
Extreme convective rainfall, often leading to flash flooding, accounts for substantial property
damage and loss of life worldwide, both in monsoon/tropical regions and at midlatitudes. The
primary environmental factors contributing to heavy convective rainfall are abundant moisture,
instability, a lifting mechanism, and in many cases a low-level jet. However, in order for extreme
rainfall to occur, apart from orographically produced precipitation, something other than just
favorable environmental factors must exist. In particular, heavy rainfall is often associated with a
unique pattern of behavior of convective cells: they are either quasi-stationary, regenerate in the
same location, repeatedly pass over the same location, or exhibit some combination of these
behaviors.
Studies of United States extreme summertime rainfall events have determined that these
events are most frequently associated with mesoscale convective systems (MCSs). In particular,
they have been found to be connected to specific modes of organization of MCSs. Three
prominent modes of organization have been identified for United States heavy rain events:
training line/adjoining stratiform precipitation systems, MCSs with back-building cells on the
upstream end, and squall lines with trailing stratiform systems where the southern end becomes
approximately aligned with the overall system motion. Similar patterns of organization have
been recently documented in association with heavy rainfall along the Meiyu front in China.
Back-building convection has also been observed within tropical cyclones, as occurred during the
historic floods associated with 2009 typhoon Morakot.
Another mesoscale phenomenon contributing to heavy rainfall is the mesoscale convective
vortex (MCV). In studies of MCVs over the United States, it has been determined that heavy
rainfall is favored on the downshear side of the vortex where there is dynamic lifting and an
interaction between a low-level jet and the vortex itself.
20
Stage-dependent Predictability of a Heavy-rainfall Event in
South China: An Ensemble-based Analysis
Murong Zhang Zhiyong Meng
Department of Atmospheric and Oceanic Sciences, Peking University, China
Abstract
Persistent heavy rainfall during warm-season sometimes presents a stage-dependent
predictability, which make it a big challenge for operational forecasting. Based on ensemble
forecast, this study investigated the key influencing factors of two different rainfall stages with
different predictability in a persistent heavy rainfall in South China, Guangdong Province during
29-31 March 2014, aiming at explaining the lower predictability in S1 of this rainfall event.
By applying ensemble-based sensitivity analysis (ESA) on operational global ensemble
forecasts from the European Centre for Medium-Range Weather Forecasts (ECMWF), different
key factors of the two rainfall stages were diagnosed by correlating accumulated precipitation of
each stage to atmospheric state variables at respective times. The precipitation in both stages was
found to be strongly correlated with the low-level vortex and the low-level jet on the southeast
flank of the vortex. The key influencing factor in earlier stage S1 was the location of the low-level
jet. A more to the southeast low-level vortex resulted in a more to the southeast low-level jet,
leading to more precipitation in Guangdong. In later stage S2, with the relatively accurate
low-level jet location, the width of the jet became more important. A narrower low-level jet
associated with a weaker low-level vortex was found to be favorable for heavy rainfall to occur
because the moisture from the southwest can be concentrated over Guangdong rather than
transported more to the north in this situation.
The stage-dependent precipitation predictability in this case can be attributed to the different
predictability of low-level jet over stages, which might be relevant to the juxtapositions between
orientation of the low level jet and the direction of low-level vortex movement in the target area.
The locations of low-level jet axis in S1 were very diverse among ensemble members, while in S2
were more concentrated and better captured by model. The lower predictability of precipitation in
S1 was strongly associated with the less accurate low-level jet location in ensemble forecast. In
this stage, the low-level vortex moved southeast perpendicular to the low level jet, the uncertainty
of the geopotential height in the target area was large within the ensemble, resulting in wide
ensemble spread of the jet location. In stage 2, however, the low-level vortex moved
northeastward parallel to the low level jet, leading to small height uncertainty in the target area
and thus the jet locations were more concentrated and well predicted.
21
Operational QPF Progress and Scientific Research on Heavy
Rainfall in South China during the Pre-summer Rainy Season
Zhiping Zong Tao Chen
National Meteorological Center, Beijing, China
Abstract
In recent years significant progress has been achieved in the modernization of forecast
operation in National Meteorological Center with improving forecast skills in Quantative
Precipitation Forecast (QPF) during warm seasons in China. Based on operational high-resolution
mesoscale numerical model and ensemble model forecasts, kinds of objective precipitation
forecast products include Probability Matching (PM), Optimum Percentage (OPF) have been
testified in QPF operation in results of higher Threat Scores and lower bias compared with direct
numerical model output. In future, a more intellectual, automated of forecast operation process
will be designed facing challenge of higher extreme weather events occurrence frequency.
However, due to obvious forecast bias still existed in pre-summer seasons in South China, several
science research projects have been applied in NMC. Fifty eight events of Heavy Rain over the
Warm Sector (referred as WSHR events) in South China during the pre-summer months of 2008 ~
2014 were analyzed statistically from perspective of precipitation, synoptic situations,
environmental conditions, especially the characteristics of heavy-rain-producing Mesoscale
Convective Systems. Three synoptic types of WSHR events are categorized as pre-frontal (PF)
type, warm and moist airflow (WF) type, and low-level vortex (LV) type. In most of WSHR
events deep moist layer and intensive CAPE was pre-existing in the environment, with weak
vertical shear in mid-level layer, as well as active Low Level Jet below 925 hPa. Clear diurnal
variation was found in the climax MCS activities in afternoon and secondary peak in evening to
the early morning of second day. Three classes of MCS organization can be identified as simple
linear MCS, complex MCS and slow evolving MCS with low-level vortex in WSHR evens.
Mesoscale topographic lifting is convinced to be an important triggering mechanism of for the
simple linear MCS. Weak warm advection forcing due to synoptic systems played important roles
in preconditioning of environment in warm sector, also the organizing process for the complex
MCS.
22
Mesoscale Observational Analysis of Lifting Mechanism of a
Warm-Sector Convective System Producing the Maximal Daily
Precipitation in China Mainland during Pre-summer Rainy
Season of 2015
Mengwen Wu Yali Luo
State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing, China
Abstract
A long-lived, quasi-stationary mesoscale convective system (MCS) producing extreme
rainfall (maximum of 542 mm) over the eastern coastal area of Guangdong Province on 20 May
2015 is analyzed by using high-resolution surface observations, sounding data, and radar
measurements. New convective cells are continuously initiated along a mesoscale boundary at the
surface, leading to formation and maintenance of the quasi-linear-shaped MCS from about 2000
BT 19 to 1200 BT 20 May. The boundary is originally formed between a cold dome generated by
previous convection and southwesterly flow from the ocean carrying higher equivalent potential
temperature (θe) air. The boundary is subsequently maintained and reinforced by the contrast
between the MCS-generated cold outflow and the oceanic higher-θe air. The cold outflow is weak
(wind speed ≤5 m s−1), which is attributable to the characteristic environmental conditions, i.e.,
high humidity in the lower troposphere and weak horizontal winds in the middle and lower
troposphere. The low speed of the cold outflow is comparable to that of the near surface southerly
flow from the ocean, resulting in very slow southward movement of the boundary. The boundary
features temperature contrasts of 2–3℃ and is roughly 500-m deep. Despite its shallowness, the
boundary appears to exert a profound influence on continuous convection initiation because of the
very low level of free convection and small convection inhibition of the near surface oceanic air,
building several parallel rainbands (of about 50-km length) that move slowly eastward along the
MCS and produce about 80% of the total rainfall. Another MCS moves into the area from the
northwest and merges with the local MCS at about 1200 BT. The cold outflow subsequently
strengthens and the boundary moves more rapidly toward the southeast, leading to end of the
event in 3 h.
23
An Extreme Rainfall Event Associated with a Mesoscale
Outflow Boundary and Multiple Rainbands over Guangdong
Coastal Areas during SCMREX-2014
Xi LIU1,3 Yali LUO1,2＊ Zhaoyong GUAN1,3 Da-Lin ZHANG2,4
1. Key Laboratory of Meteorological Disasters of China Ministry of Education (KLME), Nanjing University of
Information Science &Technology, Nanjing, China
2. State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing, China
3. Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters (CIC-FEMD), Nanjing
University of Information Science &Technology, Nanjing, China
4. Department of Atmospheric and Oceanic Science, University of Maryland, College Park, College Park,
Maryland, USA
* Corresponding author (E-mail: [email protected])
Abstract
This study investigates an extreme rainfall event (up to 451 mm accumulated precipitation)
that occurred in the middle coastal area of Guangdong Province (hereafter the control region) on
11 May 2014, using dual-Doppler radar wind retrieval and high-resolution observations collected
during the Southern China Monsoon Rainfall Experiment (SCMREX) field campaign. The
synoptic conditions over South China during the event were characterized by a mid-tropospheric
trough, a northeast-southwest oriented shear line in the lower troposphere, and a surface front to
the north of the control region, with significant warm advection in the planetary boundary layer
(PBL) in the warm sector. The extreme rainfall was mostly produced by two linear-shaped
mesoscale convective systems (MCSs) that were initiated in the west-coastal area at 0100 BST
(Beijing Standard Time; BST = UTC + 8h) and 0800 BST, respectively, and both moved eastward
along the coastline, contributing 37% and 57% to the total accumulated precipitation over the
control region in the warm sector.
It is found that both MCSs (MCS1, MCS2) were initiated with the influence of near surface
convergence along the coastline and the mesoscale orographic lifting of near surface oceanic
southerly flow. However, the initiation of the MCS1 was enhanced by a weak mesoscale outflow
boundary (MOB) at the leading edge of a shallow cold pool (about 500 m depth) left behind by an
MCS occurred during the previous afternoon-to-midnight hours. This MOB also played an
important role in lifting high-θe air carried by near surface oceanic southerly flows.
Of more relevance to the extreme precipitation event is the generation of another MOB along
24
the coastline resulting from evaporative cooling and cloud shielding during the maintenance stages
of the MCS1 (0500-1200 BST 11 May) and MCS2 (1200 BST 11 May-0000 BST 12 May).
Combined with surface observations, an analysis of the retrieved Dual-Doppler winds reveals that
the extreme precipitation occurred as the southerly high-θe air overran the along-coastline
quasi-stationary MOB and triggered continuously convection at several locations along the MOB.
The subsequent northeastward “echo training” of these convective elements under the influence of
the southwesterly environmental flow led to the formation of northeast-southwest-oriented
meso-β-scale rainbands (with reflectivity > 40 dBZ). As compared with the MCS1, the MCS2
lasted longer with stronger convective intensity and more abundant convective cores producing
larger rain rates, due to the development of more meso-β-scale rainbands and the presence of
stronger local frontogenesis.
It is the slow movement of the multiple meso-β-scale rainbands, especially in the afternoon,
that contributed to the production of extreme precipitation. The formation of the distinct banded
structures could be attributed partly to inhomogeneous convergence along the MOB, and partly to
the development of two bow-shaped rainbands observed during about 1318-1354 BST and
1536-1612 BST, respectively. Both bow-shaped rainbands were transformed from a near-straight
rainband each, and accompanied by a strong rear-to-front descending flow in their central
segments. This descending flow appeared to be associated with convective downdrafts that
originated from evaporative cooling and hydrometeor loading in the convective regions with large
reflectivity. The descending flow generated strong eastward outflows at the surface that penetrated
the rainband and initiated convection ahead, subsequently building a new rainband forward to the
east, i.e., a forward rainband building process was observed. In contrast, the southern portion of
the bow-shaped rainband moved much slower than the central segment and became detached from
the latter, due to the lack of rear-to-front penetrating flow. The detached southern portion soon
became another new rainband due to the southwestward backbuilding of convective cells at the
MOB, which also played an important role in the formation of the new rainband ahead of the
central segment of the previous bow-shaped rainband.
In conclusion, the quasi-stationary and quasi-stagnant state and long duration of the MOB led
to continuous southwestward backbuilding of convective cells that affected the same inshore area
(i.e., the control region) for about 20 hours, while the forward (eastward) rainband building
combined with the southwestward cell building resulted in establishment of multiple rainbands
that poured extreme precipitation to the north of the MOB.
25
Analysis of Heavy Rainfall Events over India
Ajit Tyagi1 Kamaljit Ray2 P. Guhathakurta3 Someshwar Das4
1. Indian Meteorological Society, New Delhi, India
2. Indian Meteorological Department, New Delhi, India
3. Indian Meteorological Department, Pune, India
4. Central University of Rajasthan, Kishangarh, India
Abstract
India experiences long period of monsoon weather under the influence of Southwest
Monsoon (June–September) and Northeast Monsoon (October-December). With in the monsoon
season, rainfall shows wide spatial and temporal variability in terms of intensity. In this paper
attempt has been made to analyse the rainfall days in terms of different intensity of rainfall and
identify regions having higher number of heavy rainfall days. It is observed that orography plays
dominant role in causing heavy rainfall under favourable synoptic conditions, The paper discusses
different synoptic situations favourable for heavy rainfall over the different parts of the country.
Most of heavy rainfall events over India occur during Southwest Monsoon period. In the
main monsoon zone over central and western India, heavy rainfall is mainly associated with
monsoon systems. These occur during active to strong phase of the monsoon. Over northern plains
most of the heavy rainfall spells occur either with more northerly course of monsoon systems or
oscillation of monsoon trough., where as over mountainous region it is because of interaction of
mid-latitude system with monsoon systems. Himalayan region are also affected by localised
intense rainfall, land slides and flash floods.
In the southern parts of peninsula and along east coast of India heavy rainfall events occur
during Northeast Monsoon associated with Bay of Bengal systems moving across lower latitudes.
The paper presents analysis of very heavy rainfall event (15-18th June 2013) in Uttrakhand
state of India and adjoining Nepal which resulted in floods and extensive loss of human lives and
property
26
Evaluation of the Met Office Unified Model for a
SCMREX Case Study
Kalli Furtado 1 Yali Luo 2
1. Met Office, Exeter, UK
2. State Key Lab of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing, China
Abstract
Complexity in cloud-microphysics schemes arises from the number of microphysical
processes, and the level of `sophistication', or physical detail, to which those processes are
modeled. Greater differentiation of cloud-species, and more prognostic variables, increase both
physical realism and computational cost but it is not obvious what the effects of this additional
complexity are, or where the balance between costs and benefits lies. To understand the effects
of cloud-microphysics complexity on simulations of organized deep-convection during the East
Asian Summer Monsoon, we evaluate a set of convection-permitting model-configurations of the
Met Office Unified Model against radar observations of the 20 May 2016 heavy-rainfall case from
SCMREX, and against satellite-derived estimates of clouds and precipitation. In particular, the
effects of different numbers of prognostic moments, and the relative importance of cloud-fraction
diagnosis, are identified. The sensitivity tests show differences in surface rainfall and the radiative
properties of clouds, which are related to the distribution of condensed water between
hydrometeor species. Model biases in outgoing short-wave radiation are shown to be dominated
by low clouds: the use of a diagnostic cloud-scheme, with a critical relative-humidity less than one,
therefore reduces these biases. Outgoing long-wave biases are dominated by high clouds, and are
shown to be influenced by the microphysical properties of ice crystals. Differences in radar
reflectivity-factor between the configurations are shown to be due to the number concentration of
rain droplets in single- and double-moment representations of the rain-droplet size spectrum; this
information is used to improve the simulated radar reflectivity in a single-moment configuration.
27
Lightning Activity Characteristics as Indicated by Lightning
Location System in Guangdong
Dong Zheng1 Yijun Zhang1 Yang Zhang1
Weitao Lu1 Lvwen Chen2 Dongdong Shi1
1. State Key Laboratory of Severe Weather / Laboratory of Lightning Physics and Protection Engineering, Chinese
Academy of Meteorological Sciences, Beijing 100081, China
2. Guangzhou Institute of Tropical and Marine Meteorology, CMA, Guangzhou 510080, China
Abstract
Three systems severing for the detection of lightning activities in Guangdong are introduced.
Their performances are evaluated by referring to the artificially triggered lightning and the
lightning striking to the skyscrapers. The Guangdong cloud-to-ground (CG) Lightning Location
System (GDLLS) operated by the power department represents the detection efficiency of 94% for
lightning flash and 60% for return stork, with a mean location error of 710 m and a mean absolute
percentage error of peak current of 16.3%. The counterparts for the Guangdong-Hongkong-Macao
Lightning Location System (GHMLLS) constructed jointly by the meteorological departments in
Guangdong, Hongkong and Macao are 96%, 89%, 532 m and 25%, respectively. A new 3-D total
lightning location system named as Low-Frequency E-field Detection Array (LFEDA) and
developed by Chinese Academy of Meteorological Sciences show the detection efficiency of 100%
for triggered lightning flashes and 95% for return strokes of triggered lightning, with an average
plane location error of 102 m.
The CG lightning data from the GDLLS are used to study the lightning activity across
Guangdong. There are two areas of high lightning density are identified in Guangdong: one over
the Pearl River Delta, and the other to the north of Leizhou Peninsula. The frequency of total CG
lightning shows a main peak in June and a second peak in August. The rain yield per flash is on
the order of 107–108 kg per flash, and its spatial distribution is opposite to that of lightning density.
The large-current CG (LCCG) lightning and small-current CG (SCCG) lightning are found to be
different from each other in the geographical and seasonal distributions. It is revealed that
thunderstorms with relatively weak convection and large precipitation areas are more likely to
produce the LCCG lightning, and the positive LCCG lightning is well correlated with mesoscale
convective systems in the spatial distribution during nonrainy season.
The 3-D lighting data from the LFEDA can provide the information on the initiation and the
28
propagation of lightning channels and help to identify the main charge region involved in the
lightning discharge. The special analysis focusing on the characteristics during the initial stage of
lightning in two thunderstorms show that the average heights where the lightning is initiated are
6.8 and 8.4 km for upward-initiated lightning and downward-initiated lightning, respectively.
Their average velocity is on the order of 105 m s-1, and display the trend to decrease with the
increase of height. The difference between the characteristics during the initial stage of lightning
within the convection core region and those out of the convection core region are also
investigated.
29
Diurnal Variations of Pre-Summer Rainfall over Southern China
Zhina Jiang Da-Lin Zhang Rudi Xia Tingting Qian
State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing, China
Abstract
In this study, the presummer diurnal cycle of rainfall (DCR) over southern China is examined
using the merged 0.18-resolution gridded hourly rain gauge and satellite rainfall dataset and the
National Centers for Environmental Prediction Final Global Analysis during April to June of
2008–2015. Results show pronounced diurnal variations in rainfall amount, frequency, and
intensity over southern China, with substantially different amplitudes from southwestern to
southeastern China, and from the pre- to post-monsoon-onset period. Southwestern China often
encounters significant nocturnal-to-morning rainfall under the influence of enhanced nocturnal
low-level southwesterly winds. Southeastern China is dominated by afternoon rainfall, as a result
of surface heating, likely aided by local topographical lifting. Both the pre- and
post-monsoon-onset periods exhibit two diurnal rainfall peaks: one in the early morning and the
other in the late afternoon. But the latter shows the two peaks with nearly equal amplitude whereas
the former displays a much larger early morning peak than that in the late afternoon. Three
propagating modes accounting for the presummer DCR are found: (i) an eastward- or
southeastward-propagating mode occurs mostly over southwestern China that is associated with
enhanced transport of warm and moist air from tropical origin and the induced low-level
convergence, (ii) a quasi-stationary mode over southeastern China appears locally in the warm
sector with weak-gradient flows, and (iii) an inland propagating mode occurs during the daytime
in association with sea breezes along the southern coastal regions, especially evident throughout
the post-monsoon-onset period.
30
A Comparison and Relationship Between Two Consecutive
Heavy-rainfall Events during SCMREX-2014
Yangruixue Chen1,2 Yali Luo1,3＊ Da-Lin Zhang1,4
1. State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing, China 2University of Chinese Academy of Sciences, Beijing, China
3. Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of
Information Science and Technology, Nanjing, China
4. Department of Atmospheric and Oceanic Science, University of Maryland, College Park, Maryland, USA
Corresponding author: Dr. Yali Luo, Chinese Academy of Meteorological Sciences, Beijing, China (Email:
Abstract
Two heavy-rainfall events that occurred consecutively on 22 and 23 May 2014 over
Guangdong Province in South China are studied using high-resolution observations collected
during the Southern China Monsoon Rainfall Experiment (SCMREX) field campaign and a series
of convection-permitting model simulations. Observational analyses reveal significant differences
in the characteristics of heavy-rain-producing mesoscale convective systems (MCSs) between the
two days. Heavy rainfall on 22 May was overspread, and has a distinct center of about 300 mm
over the northern mountainous regions that were produced by a quasi-stationary MCS and the
passage of a southeastward-moving quasi-linear MCS in the early morning hours. The two MCSs
merged to form a larger MCS at noon, which exhibited a classic mesoscale structure of the leading
convective line and trailing stratiform precipitation. This merged MCS produced well-organized
cold outflow boundaries, where new convective elements were continuously initiated, accounting
for its continued southeastward movement. Of significance is that this MCS left behind a
mesoscale northwest-southeast oriented cold pool on the windward side of the northern mountains
during the early evening hours. Convective elements, albeit much less intense than those occurring
during the daytime, began to be continuously initiated over the “old” cold pool around midnight.
At the same time, weak convective elements were initiated over the sloping mountains on the
northwest of the cold pool and then moved over the cold pool, leading to the formation of a
northwest-southeast oriented MCS in a few hours. The MCS at the mature stage consisted of
multiple convective rainbands that were embedded in stratiform precipitation regions. Little
evidence of cold outflows could be observed at the surface, suggesting the presence of elevated
convection associated with the rainbands. Despite its weaker convective intensity, as suggested by
both lightning flashes and vertical profiles of reflectivity in convective cores, this MCS persisted
31
locally for about 20 hours, producing more than 300 mm precipitation on the windward side of the
mountains in central Guangdong on May 23.
Both heavy rainfall events occurred under favorable large-scale settings including high
precipitable water (about 60 mm), a high θe tongue from the South China Sea, southerly low-level
jets (LLJs), and warm advection in the planetary boundary layer (PBL). However, the
environmental dynamics and thermodynamics of the two events differ in a few ways. On 22 May
there was a northeast-southwest oriented shear line in the lower troposphere extending to north
Guangxi, where the moving MCS was initiated. The MCS’s subsequent growth and movement
were driven by convectively generated cold outflow boundaries associated with middle-level dry
intrusions. In contrast, the heavy-rain-producing MCS on 23 May was significantly influenced by
the “old” cold pool (depth of 1~1.5km) that facilitated the continuous lifting of high-θe air of
tropical origin from the southerly LLJ, and the generation of elevated convection with little cold
downdraft air.
The above observation-based understanding, especially the connection between the two
events, is supported by a series of numerical simulations. Results confirm that the formation,
long-duration, and stagnation of the heavy-rain-producing MCS on 23 May are attributable partly
to the cold dome left behind by the 22 May MCSs and partly to its own convective feedbacks (i.e.,
rain evaporative cooling and cloud shielding). The northeastern mountains in Guangdong tended
to block the MCS’s movement, accounting for the stagnation of the 23 May MCS. Moreover, the
weakening of the LLJ in the evening hours of 23 May seems to play an important role in the
dissipation of the MCS.
32
Key Microphysical Factors Impact the Simulation of
Squall Lines
Yanluan Lin Qifeng Qian Xi Zhao
Tsinghua University, Beijing, 100084
Abstract
Monsoon heavy rainfall events are generally associated with convective systems, such as
squall lines and mesoscale convective systems. Forecast and simulation of these convective
systems are still far from satisfactory. A series of sensitivity simulations of a squall line in the
SCMREX using various microphysical schemes are conducted. The performance of the simulation,
including the longevity, strength, morphology and precipitation spatial distribution of the
simulated squall line depend strongly on the details of a few key microphysical process
parameterizations. Specifically, rain evaporation and graupel melting dominate the cold pool
strength, which is critical for the movement and intensity of the squall line. The trailing stratiform
precipitation is highly related to the assumed characteristics of snow and graupel in the schemes,
especially the fall speed and size distribution od snow.
A double moment version of the SBU_YLIN microphysics scheme is developed and
compared with the single moment version of the scheme for this case. It is found that the double
moment version predicts a better rain drop size distribution with observational measurements than
the single moment. As a result, the rain evaporation magnitude is better captured and thus the
movement and morphology of the simulated squall line. Double moment approach also provides a
tool for the consideration of aerosol impacts on the storm development and precipitation.
Microphysical processes impact the distribution of diabatic heating and cooling, which strongly
interacts with the dynamics of the squall line. The study indicates that the interaction between
microphysical processes and squall line internal dynamics is essential for realistic simulations.
Future work will investigate the indirect aerosol impacts on the simulation of this squall line.
33
Application of a Convection- permitting Ensemble Prediction
System to QPF over Southern China: Preliminary
Results during SCMREX
Xubin Zhang
Institute of Tropical and Marine Meteorology/Guangdong Provincial Key Laboratory of Regional Numerical
Weather Prediction, CMA, Guangzhou, China
Abstract
The Convection-Permitting Ensemble Prediction System (CPEPS) based on
GRAPES-MESO is developed, implemented and run for improving the quantitative precipitation
forecasts (QPFs) skill in South China. It consists of 1 control member and 16 perturbation
members at 0.03° resolution over Southern China and North of the South China Sea. The blending
of downscaling (DSC), ensemble of data assimilation (EDA), and time-lagged (TLA) technique is
used as the initial condition (IC) perturbation of CPEPS, and the blending of downscaling and
balanced random perturbation (BR) technique is used as the lateral boundary conditions (LBCs)
perturbation. Especially, the downscaling perturbations are from the Mesoscale Ensemble
Prediction System (MSEPS). Additionally, the terrain height and surface temperature are also
added perturbations. The model uncertainty is represented by the combination of Multi-physics
(MP), Parameter Perturbation (PP) and Stochastically Perturbed Parameterization Tendencies
(SPPT). CPEPS is initialed at 0000/1200 UTC, with a forecast length of 12 hours. The control
member of CPEPS is the deterministic forecast with the operational settings for physical
parameterization and without IC and LBCs perturbations.
The impact of CPEPS on the QPFs in Southern China was evaluated over the period of
Southern China Monsoon Rainfall Experiment (SCMREX) in May 2014. The half-month batch
experiment (8-23 May, 2014) was implemented, and results showed that the probability-matching
forecasts of CPEPS perturbation members are superior to the ones of CPEPS control member for
the heavy rainfall. The impact of different perturbation methods on QPFs were also discussed to
reveal their importance in the CPEPS, by a case study.
34
Cloud-resolving Heavy-rainfall Quantitative Precipitation
Forecasts and Ensemble Strategy
Chung-Chieh Wang
Pacific Science Association
Abstract
During the past several years, high skill of heavy- to extreme-rainfall quantitative
precipitation forecasts (QPFs) by the 2.5-km Cloud-Resolving Storm Simulator (CReSS), within
the range of 3 days, has been demonstrated for both typhoons and mei-yu events in Taiwan. For
example, for all 29 typhoons in 2010-2015, the overall threat scores (TSs) of day-1 (0-24 h) QPFs
at thresholds of 100, 350, and 500 mm (per 24 h) are 0.45, 0.28, and 0.18. For the most-rainy top 5%
typhoon periods, the TSs are even higher, at 0.72, 0.39, and 0.25 on day 1, at 0.70, 0.38, and 0.21
on day 2 (24-48 h), and at 0.53, 0.25, and 0.12 on day 3 (48-72 h), respectively. Similarly, for top
4% mei-yu events (May-June) in 2012-2014, the overall TSs at 100, 350, and 500 mm are 0.31,
0.21, and 0.16 on day 1, and 0.31, 0.07, and 0.07 on day 2, respectively. The above high skills
arise mainly from topographic rainfall in the mountains where the model, with high resolution, can
handle well when the strong, moisture-rich flow impinges on the steep terrain of Taiwan. Such a
scenario of forced uplift has relatively high predictability (at where the total rainfall tends to be
higher). On the other hand, much of the rainfall over the flat, coastal areas is from migratory
systems that have relatively low predictability (in exact timing and location) due to the
nonlinearity of the atmosphere, regardless of the ability of the model. Thus, our results indicate
that it is not only possible to significantly improve heavy-rainfall QPFs in Taiwan (in the
mountains), but such an improvement is a certainty using the CReSS model.
Also, in this study, the strategy and performance of the time-lagged ensemble QPF system for
Taiwan, with a sufficiently high (cloud-resolving) resolution, a large domain of 1860 1360 km2,
and an extended range of 8 days, is evaluated and discussed. The strategy allows for realistic
rainfall scenarios into the medium range (over one week), and thus extended time for early
preparation for possible hazards.
35
Stochastic Physics for Ensemble Forecast and Its Application
Yuejian Zhu
Juhui Ma*# Wei Li and Xiaqiong Zhou
Environmental Modeling Center
NCEP/NWS/NOAA *North Carolina State University, NC, USA
#Nanjing University of Information Sciences, Nanjing, China
Abstract
Ensemble forecast has been widely used as daily numerical weather guidance to service
general public. However, a quality of forecast will be argued if single model initial perturbed
ensemble system has less spread (or under dispersion) when compared to their forecast error.
Theoretically, initial perturbations, such as using singular vector method, breeding method and
EnKF, can not provide sufficient forecast spread to represent forecast uncertainty, such as
precipitation and surface temperature. A stochastic physics is common method to generate realistic
model uncertainty in many ensemble systems except for using multi-physics or multi-model
approach.
This investigation will focus on heavy precipitation events those are from Southern China
Monsoon Rainfall Experiment (SCMREX) and Continental of United States (CONUS) extreme
(heavy) rainfall cases. The experiments will use NCEP latest Global Ensemble Forecast System
(GEFS) and NCAR Weather Research and Forecast (WRF) model through introducing stochastic
physics, such as SPPT (Stochastically Perturbed Parametrization Tendencies), to enhance
probabilistic forecast capability for heavy rainfall. An improvement of precipitation forecast
reliability would be demonstrated through increasing model resolution, using dynamic
downscaling, adding stochastic perturbation schemes and testing new scale-aware (SA)
convection scheme.
36
The Characteristics of GRAPES-REPS Model and its Sensitivity
for a Heavy Rainfall Case in Southern China
Jing CHEN 1 Jingzhuo WANG 2 Zhaorong ZHUANG 3 Jing WANG 2
1.National Meteorological Centr, CMA,Beijing, 100081
2. Chinese Academy of Meteorological Sciences, Beijing 100081
3. Chengdu University of Information Technology，Chengdu,610025
Abstract
Based on GRAPES-REPS(Global and Regional Assimilation and Prediction Enhanced
System-Regional Ensemble Prediction System) model, the ensemble forecast experiments of
10km and 15km horizontal resolution model by use of Ensemble Transform Kalman Filter (ETKF)
are conducted from 1 to 15 JUN 2015 The Characteristics of Initial perturbation structures and its
growth rates were analysed.Then the sensetivity of ETKF and Stochastic Perturbation of Physics
Tendency (SPPT) for a heavy rainfall in 9 Jun, 2015 was studie.The results showed that:
(1) The perturbation field derived from ETKF initial perturbation schemes is mainly
large-scale with a flow dependent structure. The total energy of initial perturbations and ensemble
spread can keep appropriate growth rates in all forecast lead times, And the temperature forecast
variance is larger than ensemble variance, especially with the increase of forecast lead time.The
increase of horizontal resolution can better capture the large-scale perturbation uncertainty of mid
and high levels. The internal perturbation energy in low levels showed obvious diurnal variation
characteristics, especially centered on Qinghai Tibet Plateau.So,Improving low-level perturbations
are essential.
(2) Increasing the density of observation data of ETKF can significantly improve the
ensemble mean prediction error, especially during the period from 12 to 48h. For SPPT method,
four spatial scales (750km, 500km, 300km and 250km) showed that scale of 300km can
significantly improve the maximum center of heavy rainfall. The main improvement come from
sub grid scale precipitation.
Key words: regional ensemble forecast, GRAPES model, heavy rainfall, perturbation method,
forecast sensetivity.
37
Influence of Monsoonal Wind Speed and Moisture Content on
Intensity and Diurnal Variations of the Meiyu Season Coastal
Rainfall over South China
Kun Zhao1 Xingchao Chen1,2 Fuqing Zhang2
1. Key Laboratory for Mesoscale Severe Weather, Ministry of Education, and School of Atmospheric Science,
Nanjing University, Nanjing, China
2. Department of Meteorology, and Center for Advanced Data Assimilation and Predictability Techniques, The
Pennsylvania State University, University Park, Pennsylvania, USA
Abstract
This study examines the the influence of monsoonal onshore wind speed and moisture
content on the intensity and diurnal variations of coastal rainfall over South China during the
Mei-yu seasons using 3 years of operational Doppler radar data in the region and the Weather
Research and Forecasting (WRF) model. The radar observation reveals that convection near the
coast occurs preferentially on days when a southerly low-level jet (LLJ) exists during the Meiyu
season. A pair of 10-day WRF simulations with diurnally varying cyclic lateral boundary
conditions averaged over the high versus low onshore wind speed days of the 3-yr Mei-yu seasons
show that the pattern of coastal rainfall spatial distribution is mostly controlled by the ambient
onshore wind speed. During the high-wind days, strong coastal rainfall is concentrated along the
coastline and reaches its maximum in the early morning. The coastal lifting induced by the
differential surface friction and small hills is the primary cause for the strong coastal rainfall,
while land breeze enhances coastal lifting and precipitation from evening to early morning. In the
low-wind days, on the other hand, coastal rainfall is mainly induced by the land-sea breeze fronts,
which has apparent diurnal propagation perpendicular to the coastline. With stronger land-sea
temperature contrast, the land-sea breeze is stronger during the low-wind days. Both in the
high-wind and low-wind days, the coastal rainfall intensity is sensitive to the incoming moisture in
the upstream oceanic airflow, especially to the moisture content in the boundary layer (below 1
km).
38
Evaluation and Application of the High Resolution Models from
the 2013-2016 NMC TESTBED Warm-season Experiments
Xiaoling Zhang Jie Sheng Wenjian Zhu Jian Lin Qingtao Meng
National Meteorological Center of China Meteorological Administration, Beijing, China,
Abstract
The warm-season experiments focus on meso-scale convective weather was started by the
NMC TESTBED in 2013. The NMC forecasters have evaluated and applied the high resolution
regional models (the operational GRAPES-10km model and the experimental GRAPES-3km
model from Numerical Weather Prediction Center of China Meteorological Administration, the
research WRF-4km model from Najing University, the operational WRF-9km model from
Shanghai Typhoon Institute of China Meteorological Administration) in the 2013-2016
warm-season experiments.
The statistics and cases evaluation reported that all the high resolution regional models did
better job on heavy rainfall (≥50 mm/24h) simulation than those the global determinate models of
ECWMF, NCEP-GFS and CMA T639 did. And furthermore, the high resolution regional models
provided at least 1-h interval reflectivity factor, 1-h accumulated precipitation and cloud
microphysics parameters, which is benefit to forecast severe convective weather and heavy
rainfall. Thus, based on the evaluated high resolution models but WRF-4km from Nanjing
University, NMC developed the up-scaling, ensemble forecasting techniques and applied them
into severe convective weather forecasting in 2016.
39
Evaluation of Quantitative Precipitation Forecast by TIGGE
Ensembles for South China during the
Pre-summer Rainy season
Ling Huang1 Yali Luo1,2
1. State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing, China
2. Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of
Information Science and Technology, Nanjing, China
Abstract
Based on The Observing System Research and Predictability Experiment (THORPEX)
Interactive Grand Global Ensemble (TIGGE) dataset, this study evaluates the performance of five
global ensemble prediction systems (EPSs) from the European Centre for Medium-Range Weather
Forecasts (ECMWF), US National Centers for Environmental Prediction (NCEP), Japan
Meteorological Agency (JMA), Korean Meteorological Administration (KMA), and China
Meteorological Administration (CMA), respectively, on predicting the pre-summer rainy season
(April-June) precipitation in South China. Evaluation for the 36-h forecasts in three seasons
(2013−2015) indicates higher skill of the probability matching forecast than the simple ensemble
mean and deterministic forecast, overestimation of light-to-heavy rainfall (0.1 to 15mm/6h) by the
EPSs with CMA being the worst, underestimation of heavier rainfall (> 15mm/6h) especially near
the coastal lines by the EPSs with JMA being the worst, and degradation in the forecast of
precipitation in the afternoon by CMA and KMA.
By analyzing the synoptic situations predicted by the identified skillful (ECMWF) and less
skillful (JMA) EPSs and the ensemble sensitivity for four representative torrential rainfall cases,
the low-level southwesterly flow upstream of the torrential rainfall regions that transports warm,
moist air to South China is found to be a key synoptic factor that controls the QPF. The results
also suggest that prediction of the locally produced torrential rainfall is more challenging than the
more extensively distributed torrential rainfall, for which a slight improvement in the performance
by shortening the forecast lead-time from 30−36h to 18−24h and to 6−12h is noticed but not the
locally produced cases.
40
A High Resolution Weather Forecast Regime in India:
Focus on Extreme Events
P. Mukhopadhyay1 R. Phani Murali Krishna1 Medha Deshpande1
Malay Ganai1 Tanmoy Goswami1 Snehlata Tirkey1
Sahadat Sarkar1 Kumar Roy1 V. S. Prasad2 R. Ashrit2
1. Indian Institute of Tropical Meteorology, Pune, India
2. National Center for Medium Range Weather Forecast, Noida, India
Abstract The National Center for Environmental Prediction’s Global Forecast System (GFS) model
has been adopted by IITM, Pune to initiate and establish the short range ensemble forecast system
(Probabilistic forecasting system) and a high-resolution (12 km) deterministic weather forecast in
the country. To start the initiative, the forecasting system has been configured and established at
IITM for an experimental forecast for the monsoon season of 2016. The high resolution GFS (with
horizontal resolution 12.5 km) replaces the low resolution (25 km) operational GFS model of IMD
for deterministic forecast. The short range ensemble prediction system based on GFS was lacking
in the country for probabilistic forecast application. The GEFS T574 (Global Ensemble Forecast
System model) fulfils the need and would provide forecast of percentage probability of rainfall,
temperature and other relevant parameters. The GEFS T574 system is presently being
experimentally run and 10 days forecast being generated in IITM. Based on the deterministic
forecast performance of GFS T1534 (12.5 km) for recent extreme events of 2016, it has been
made operational at IMD and forecast being issued daily twice based on initial condition at 0000
and 1200 UTC. GFST 1534 shows reasonable skill in forecasting extreme events.
41
Assimilating Doppler Radar Observations with an Ensemble
Kalman Filter for Convection-permitting Prediction of
Convective Development in a Heavy Rainfall Event during the
Pre-summer Rainy Season of South China
Xinghua Bao1 Yali Luo1,2* Jiaxiang Sun3
1. State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing, China
2. Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University
of Information Science and Technology, Nanjing, China
3. CAAC East China Regional Air Traffic Administration, Shanghai, China
Abstract
This study examines the effectiveness of an ensemble Kalman filter based on the Weather
Research and Forecasting model to assimilate Doppler radar radial velocity observations for
convection-permitting prediction of convection evolution in a high-impact heavy rainfall event
over coastal areas of South China during the pre-summer rainy season. An ensemble of forty
deterministic forecast experiments with the data assimilation (DA) is conducted, in which the DA
starts at the same time but lasts for different time spans (up to 2h) with the time intervals being
6-min, 12-min, 24-min, and 30-min, respectively. Another experiment is conducted without the
DA.
It is found that the DA experiments generally improve the convection prediction. The
probabilistic forecast of the inland heavy-rain-producing mesoscale convective system (MCS) and
the MCS over the ocean is quite close to the radar observations, despite slight displacement biases.
Compared with the experiments using the longer DA time intervals, the experiments with 6-min
interval tend to produce better forecasts although a shorter interval (e.g., 12-min) does not always
help. The experiment with the shortest DA time interval and maximum DA window shows the best
performance, as it corrects errors in the simulated convection evolution over both the inland and
offshore areas. The improved representation of the initial state leads to dynamic and
thermodynamic conditions that are more conducive to the earlier initiation of the inland MCS and
the longer maintenance of the offshore MCS.
42
Impact of Assimilating Wind Profiling Radar Observations on
Convection-permitting QPFs during SCMREX
Xubin Zhang
Institute of Tropical and Marine Meteorology/Guangdong Provincial Key Laboratory of Regional Numerical
Weather Prediction, CMA, Guangzhou, China
Abstract
To improve the prediction of heavy rainfall in Southern China during the pre-rainy season,
horizontal wind data from the wind profile radar (WPR) were assimilated in the partial-cycle data
assimilation (DA) system based on three-dimensional variational method for use with the
convective-scale global/regional assimilation and prediction system (GRAPES) model. The
impact of assimilating WPR data on the quantitative precipitation forecast (QPF) in Southern
China was evaluated over the period of Southern China Monsoon Rainfall Experiment (SCMREX)
in May 2014, by comparing the results of the control experiment with WPR data assimilated and
the denial one without that.
Positive impact of WPR DA was significant on the forecasts of atmospheric variables in the
vertical and diagnostic fields at the surface, especially those of surface wind fields in the 0–6 h
range. It also improved the QPF skill of light and heavy rainfall throughout the 12-h forecast
period by reducing the predicted spurious precipitation and thereby alleviating overestimations
and false alarms, with the largest improvement in 6-h heavy rainfall forecasts. WPR DA
considerably alleviated the spin-up problem, remarkably improving the QPF of heavy rainfall
(especially rainstorm). Moreover, the benefits of WPR DA depended on the synoptic situation,
with most primary ones on the days characterized by local heavy rainfall with low predictability,
weak synoptic/subsynoptic forcing, and moderate southwest monsoons. The improved
representations of wind and moisture at lower levels in the analyses due to WPR DA were the
physical causes of the QPF improvement, which was illustrated in a case study.