shallow orographic heavy rainfall in the asian monsoon region...

Shallow orographic heavy rainfall in the Asian monsoon region observed by TRMM PR

Shoichi Shige1 & Christian D. Kummerow2 1Graduate School of Science, Kyoto University

2Dept. of Atmospheric Science, Colorado State University

Background

APHRODITE

PR GSMaP GPROF

GSMaP-PR GPROF−PR

India [Shige et al. 2014] June–August 2007

Precipitation Radar PR

TRMM Microwave Imager TMI

mature stage cumulus stage dissipating stage

Wallace & Hobbs (2006) [Adapted from Byers and Braham (1949)]

MWR rainfall algorithms assume that heavy rainfall results from deep clouds.

Background (Continued)

Weak Scattering ↓

Light Rainfall

Strong Scattering ↓

Heavy Rainfall

Background (Continued)

mature stage cumulus stage

Wallace & Hobbs (2006) [Adapted from Byers and Braham (1949)]

However, heavy rainfall can be caused by shallow orographic convection in moist Asian monsoon regions.

mature stage Obs. TB

Est. Rain

Underestimate

Orographic Original

LUT@85 GHz

Background

APHRODITE

PR GSMaP

GSMaP-PR

June–August 2007 India [Shige et al. 2014]

Land Ocean

yhv

xhu

DtDhw

¶¶

+¶¶

==

Orographically Forced Upward Motion

Background

APHRODITE

PR GSMaP GSMaP(revised)

GSMaP-PR GSMaP(revised)−PR

India [Shige et al. 2014] June–August 2007

What environmental thermodynamic parameters constrain the depth of orographic rain clouds?

??? ???

Mexico

Cardamom

Bilauktaung

Arakan Yoma

Annam Cordillera

Phillipines

Western Ghats

Murakami & Matsumoto (1994, JMSJ)

Mexico

Cardamom

Bilauktaung

Arakan Yoma

Annam Cordillera

Phillipines

Western Ghats

I II V VI

Logtitude-height sections of the 5-year unconditional mean Q1-QR for the June-August season

18oN

Fig. 2: Schematic of target region and upstream region.

ERA-Interim 0.75o

Low-level upstream

region

Target region

hDtDhw Ñ×== Horo V

z = 4.5 km

z = 2.5 km

TRMM PR: 0.05o ERA-Interim: 0.75o

SRTM30: the original 1-km resolution data averaged within the horizontal length scale of 50km

Mid-level upstream

region

z = 7.5 km

The 7-yr conditional mean Q1 − QR and RH profiles stratified with dp/dt at 500 hPa averaged over the ocean, associated with (a) all rain, for all rain averaged over the grids with SST of

28.0°–29.0°C. (Takayabu et al. 2010 JC)

Q1 − QR RH

DRY MOIST Ocean

Fig. 6: Precipitation profiles with heavy near-surface rain rates (10 mm h-1 < R ≤ 40 mm h-1) and upward motion (woro > 0 m s-1) as a function of RHlow. Contours indicate values of the confidence interval for the mean at the 95 % level with Student’s t test.

-0.91 -0.71 -0.80

-0.75 -0.97 -0.19

RHlow Correlation coefficients with PTH(1 mm h-1)

Fig. 6: Precipitation profiles with heavy near-surface rain rates (10 mm h-1 < R ≤ 40 mm h-1) and upward motion (woro > 0 m s-1) as a function of RHmid. Contours indicate values of the confidence interval for the mean at the 95 % level with Student’s t test.

-0.94 -0.68 -0.76

-0.77 -0.39 -0.68

RHmid Correlation coefficients with PTH(1 mm h-1)

MOIST DRY

What determines deep or shallow?

DRY MOIST Ocean

Mountain

-0.90 -0.90 -0.61

-0.83 -0.78 -0.92

Fig. 10: As in Fig. 3 but for precipitation profiles with near-surface rain rates of 10 mm h-1 < R ≤ 40 mm h-1 and upward motion (woro > 0 m s-1) as a function of dT/dzlow.

dT/dzlow Correlation coefficients with PTH(1 mm h-1)

Fig. 9: As in Fig. 3 but for precipitation profiles with heavy near-surface rain rates (10 mm h-1 < R ≤ 40 mm h-1) and upward motion (woro > 0 m s-1) as a function of dT/dzmid.

-0.95 -0.71 -0.82

-0.83 -0.97 -0.89

dT/dzmid Correlation coefficients with PTH(1 mm h-1)

I II V VI

Fig. 13: Jun-Aug climatology (2004-2008) of dT/dzmid with horizontal winds at z=5.5 km (top) and function of dT/dzlow with horizontal winds at z=2.5 km (bottom) from ERA Interim.

dT/dzmid dT/dzlow

Low-level or mid-level static stability determines precipitation depths?

Summary • Heavy rainfall can be caused by shallow convection over mountain

ranges of the Asian monsoon regions, which differs from the assumptions of MWR algorithms.

• Depth of heavy orographic rainfall decreases with RH in opposition to what has been observed for oceanic convection.

• Depth of heavy orographic rainfall also decreases with the low-level and mid-level static stability.

• Mid-level static stability, which inhibit cloud growth and promotes cloud detrainment, is inferred to be a key parameter determining precipitation depths.

• Low-level static stability, however, might be more effective to improve microwave radiometer rainfall algorithms, because of a result of shallow convection and their strong links.

Fig. 11 Comparison of correlation coefficients between candidate thermodynamic quantities and precipitation top heights

Fig. 8: Two dimensional histogram of grid with heavy rain rates (10 mm h-1 < R ≤ 40 mm h-1) as function of woro and RHmid for Western Ghats, Arakan Yoma, and Bilauktaung.

Fig. 8: Two dimensional histogram of grid with heavy rain rates (10 mm h-1 < R ≤ 40 mm h-1) as function of woro and RHmid for Western Ghats, Arakan Yoma, and Bilauktaung.

Mexico

Cardamom

Bilauktaung

Arakan Yoma

Annam Cordillera

Phillipines

Western Ghats

I II V VI III IV I V

I II

III IV I V

V VI

I: Western Ghats II: Arakan Yoma III: Bilauktaung IV: Cardamom V: Annam Cordillera VI: Phillipines

MOIST STABLE

DRY UNSTABLE

What determines deep or shallow?

DRY MOIST Ocean

Mountain

Kato et al. (2007, JMSJ)

The relatively stable atmospheric condition around the Japan Islands, found when the LNB appears at the MP, is mainly caused by the advection of a middle-level air that is warmed through convective activities over upstream regions, especially the China Continent.

Murakami & Matsumoto (1994, JMSJ)

Kummar et al. (2014, CD)

Jun-Jul

Aug-Sep

Deeper clouds appear more frequently over the Myanmar coast, while shallower clouds over the Western Ghats.

Mexico

Cardamom

Bilauktaung

Arakan Yoma

Annam Cordillera

Phillipines

Western Ghats

Look-up table: Relationship between Tbs and rain rates

Obs. TB

Est. Rain

Underestimate

Ice

Water

Ice

Water

Original

Orographic Typhoon

Namtheun

Orographic Original

LUT@85 GHz

Shige et al. (2013, JAMC)

Retrieval

Original LUTs

Orographic LUTs

Yes No

GANAL

w > 0.1 Q > 0.5×10-6

SRTM30

Retrieval

Orographic/Non-Orographic Rainfall Classification Scheme

Land Ocean

yhv

xhu

DtDhw

¶¶

+¶¶

==

( ) ( )÷÷ø

öççè

æ¶

¶+

¶¶

-=yvq

xuqQ

Convergence of Surface Moisture Flux

Orographically Forced Upward Motion

Shige et al. (2013, JAMC) Taniguchi et al. (2013, JH)

Typhoon Namtheun (2004) over Japan (Kubota et al. 2009, JMSJ)

PR

GSMaP

GPROF PR PTH (km)

TMI PCT85 Radar-AMeDaS

Mexico

Cardamom

Bilauktaung

Arakan Yoma

Annam Cordillera

Phillipines

Western Ghats

Wang & LinHo (2002, JC)

Fig. 1: Location of mesoscale mountain ranges (Western Ghats, Arakan Yoma, Bilauktaung, Cardamom, Annam Cordillera and the Phillipines) of the South Asian monsoon region (Fig 1a) and Mexico for comparison (Fig. 1b).

Baja California

Cardamom

Bilauktaung

Arakan Yoma

Annam Cordillera

the Phillipines

Western Ghats

Fig. 11

-0.72

-0.84 -0.85

-0.69

-0.89

-0.78

Typhoon Morakot (2009) over Taiwan: Taniguchi et al. (2013, JHM)

hDtDhw Ñ×== Horo V

Background:

(a) (b)

(c) (d)

PR SRTM30

TRMM satellite overpass of Typhoon Morakot over Taiwan (Taniguchi et al. 2013, JHM)

Precipitation Radar PR

TRMM Microwave Imager TMI

TRMM (Nov 1997~)

http://www.boston.com/bigpicture/2009/08/typhoon_morakot.html

Background:

(a) (b)

(c) (d)

PR

GSMaP (TMI) GPROF (TMI)

SRTM30

TRMM satellite overpass of Typhoon Morakot over Taiwan (Taniguchi et al. 2013, JHM)

Precipitation Radar PR

TRMM Microwave Imager TMI

TRMM (Nov 1997~)

Typhoon Morakot (2009) over Taiwan Taniguchi et al. (2013, JHM)

Applied orographic profile

PR _ Near Surface Rain

SRTM30_Topography

GSMaP_TMI_Surface Rain (orig.) GSMaP_TMI _Surface Rain

Orographic Forced Lifting Convergence of Surface Moisture Flux

w > 0.1 (ms-1) Q > 0.5 ×10-6 (s-1)