rongqian yang, ken mitchell, jesse meng impact of different land models & different initial land...
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Rongqian Yang, Ken Mitchell, Jesse Meng
Impact of Different Land Models & Different Initial Land States
on CFS Summer and Winter Reforecasts
Acknowledgment to : S. Saha, S. Moorthi, W. Wang, C. Thiaw
This development is sponsored by CPPA Program of the NOAA Climate Program Office
4th Annual Climate Test Bed Science Advisory Board Meeting11-12 September 2008
Project Sponsorship
This work is funded by the Climate Prediction Program for the Americas (CPPA) of the NOAA Climate Program Office.
No funding was received from the Climate Test Bed (CTB) program for this work, but the experimental design and importance was evaluated positively by CTB technical advisory group.
The CFS experiments were executed in the CTB partition of the NOAA Research Computer at NCEP.
Objective of this project:
Upgrade the land physics and initial land states of the CFS and assess the impact on T126 CFS summer and winter season reforecasts.
Motivation: While SST anomalies are believed to be the foremost source of seasonal predictability in coupled global models, land surface anomalies are generally believed to be the second most important source of seasonal predictability (e.g. anomalies of soil moisture, snowpack, vegetation cover)
Land Model Upgrade: In CFS experimentsNoah LSM (new) versus OSU LSM (old):
• Noah LSM– 4 soil layers (10, 30, 60, 100 cm)– Frozen soil physics included– Surface fluxes weighted by snow
cover fraction– Improved seasonal cycle of
vegetation cover– Spatially varying root depth– Runoff and infiltration account for
sub-grid variability in precipitation & soil moisture
– Improved soil & snow thermal conductivity
– Higher canopy resistance– More
• OSU LSM– 2 soil layers (10, 190 cm)– No frozen soil physics– Surface fluxes not weighted by
snow fraction– Vegetation fraction never less than
50 percent– Spatially constant root depth– Runoff & infiltration do not account
for subgrid variability of precipitation & soil moisture
– Poor soil and snow thermal conductivity, especially for thin snowpack and moist soils
Noah LSM replaced OSU LSM in operational NCEP medium-rangeGlobal Forecast System (GFS) in late May 2005
Initial Land States: Two Sources GLDAS/Noah & Global Reanalysis 2 (GR2/OSU):
• GLDAS: an uncoupled land assimilation system driven by observed precipitation analyses (CPC CMAP analyses)– Executed using same grid, land mask, terrain field and
four-layer Noah LSM as in experimental CFS forecasts– Non-precipitation land forcing is from GR2– Executed retrospectively from 1979-2006 (after spin-up)
• GR2: a coupled atmosphere/land assimilation system wherein land component is driven by model predicted precipitation– applies the OSU LSM with two soil layers– nudges soil moisture based on differences between
model and CPC CMAP precipitation
Observed 90-dayPrecipitation Anomaly(mm) valid 30 April 99
GLDAS/Noah (top ) versus GR2/OSU (bottom)
2-meter soil moisture (% volume)
May 1st Climatology 01 May 1999 Anomaly
Left column: GLDAS/Noah soil moisture climo is generally higher then GR2/OSUMiddle column: GLDAS/Noah soil moisture anomaly pattern agrees betterthan that of GR2/OSU with observed precipitation anomaly (right column: top)
GLDAS/Noah GLDAS/Noah
GR2/OSU GR2/OSU
Monthly Time Series (1985-2004) of Area-mean
Illinois 2-meter Soil Moisture [mm]:
Observations (black), GLDAS/Noah (purple), GR2/OSU (green)
Climatology
The climatology of GLDAS/Noah soil moisture is higher and closer to the observed climatology than that of GR2/OSU.
Choice of Land Model
Choice of
LandInitial
Conditions
GR2/OSU (CONTROL)GLDAS/Noah
GLDAS/Noah--CLIMO
GR2/OSU
CFS/Noah CFS/OSU
Summer CFS Experiments: all 4 configurations above (A, B, C, D) 25-year (1980-2004) summer reforecasts (10 member ensembles) from mid April and early May initial conditions
Winter Land Related Experiments: top 2 configurations in table (A & C) 24-year (1981-2004) winter reforecasts (10 member ensembles) from late Nov and Dec initial conditions
Four configurations of T126 CFS:A) CFS/OSU/GR2: - OSU LSM, initial land states from GR2 (CONTROL)B) CFS/Noah/GR2: - Noah LSM, initial land states from GR2C) CFS/Noah/GLDAS: - Noah LSM, initial land states from T126 GLDAS/NoahD) CFS/Noah/GLDAS-Climo: - Noah LSM, initial land states from GLDAS/Noah climo
CFS Experiment Design: four configurations
Summer Results
25-year (1980-2004) summer reforecasts (10 member ensembles) from mid April and early May initial conditions
Partition 25 summers (80-04) intoNeutral & Non-neutral samples
using MJJ Nino3.4 SST anomaly0.7C as a threshold
10 non-neutral summers:82,83,87,88,91,92,93,97,99,02 (red: warm, blue: cold)
15 neutral summers:80,81,84,85,86,89,90,94,95,96,98,00,01,03,04
10 non-neutral years: CONUS JJA precipitation AC score
WorstCase
15 neutral years: CONUS JJA precipitation AC score
WorstCase
Significance test (T-statistic) shows differences wrt third bar arenot significant at 90% confidence.
Significance test (T-statistic) showsdifferences wrt third bar aresignificant at 90% confidence.
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
OSU/GR2 Noah/GR2 Noah/GLDAS Noah/GLDAS C
Non-Neutral Years
-0.06
-0.05
-0.04
-0.03
-0.02
-0.01
0
0.01
0.02
0.03
0.04
OSU/GR2 Noah/GR2 Noah/GLDAS Noah/GLDAS C
Neutral Years
CONUS-average JJA precipitation AC score
0.18
0
0.04
-0.06
Winter Results
Only two of four configurations were executed:
-- OSU/GR2 (Control)-- Noah/GLDAS
24-year (1981-2004) winter reforecasts (10 member ensembles) from late Nov and Dec initial conditions
Partition 24 winters (1981-2004) intoNeutral & Non-neutral samples
using JFM Nino3.4 SST anomaly0.5C as a threshold
14 non-neutral winters:83, 85, 86, 87, 88, 89, 92, 95, 96, 98, 99, 00, 01, 03
10 neutral winters:81, 82, 84, 90, 91, 93, 94, 97, 02, 04
14 Non-neutral Years: CONUS JFM Precipitation AC Score:83, 85, 86, 87, 88, 89, 92, 95, 96, 98, 99, 00, 01, 03
10 Neutral Years: CONUS Domain JFM Precip AC Score:81, 82, 84, 90, 91, 93, 94, 97, 02, 04
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
Noah/GLDAS OSU/GR2
CONUS-average JFM precipitation AC scoreNon-neutral Years
I
Significance test (T-statistic) shows differences are not significant at 90% confidence
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
Noah/GLDAS OSU/GR2
Neutral Years
Significance test (T-statistic) shows differences are not significant at 90% confidence
0.2
0.2
0
0
Conclusions• When upgrading land surface model of coupled CFS, it is
imperative to upgrade to the same land surface model in the supporting data assimilation system
• Positive impact of land surface upgrade on CFS seasonal forecast skill for precipitation is very modest– Significant only for summer season in neutral ENSO years (and
then only very small positive impact)– Essentially neutral impact for winter season and non-neutral
ENSO summers
• For a given land configuration, differences in CONUS precipitation skill between neutral and non-neutral years appears larger than differences between two different land configurations for given sample of years– Confirming that impact of SST anomaly is indeed substantially
greater than impact of land surface configuration