The Monsoon Rainband from

Satellite and Reanalysis Data

New high-resolution satellite data reveal south Asian monsoon rainband structure and movement.

Movement of Bay of Bengal rainband related to structure of surface wind vis-à-vis Rain

MT Workshop, SAC Ahmedabad 19 October 2005

D Sengupta, D S Anitha, CAOS IISc Bangalore

Global Precipitation Climatology Project (GPCP) - Rain

TRMM Microwave Imager (TMI) - Rain

QuikSCAT Scatterometer - Surface Wind

ECMWF Reanalysis ERA 40 - Rain

Data

1ox1o 1998-2003 Daily

0.25ox0.25o 1998-2003 Three-day

0.25ox0.25o July1999-2003 Daily

2.5ox2.5o 1998-2002 Daily

Structure and Movement:

JJAS 1998-2003 Composites based on 28 rain events (84 days)

GP

CP

Rai

n, d

/dt(

GP

CP

Rai

n)

(mm

day

-1)

Positive curl north and west, negative curl south and east of rainband.

wE= 1 (curl s)f

Conclusions:

The summer monsoon rainband in the Bay of Bengal is a northwest-southeast (NW-SE) tilted structure

It moves “sideways”, the rain growing to the NW and decaying in the SE (fast movement)

On longer time scales, the rainband moves parallel to itself, the rain growing in the north and decaying to the south (slow movement)

The movement of reanalysis rain is consistent with data, although reanalysis rain has bias

The slow movement of the rainband is consistent with the structure of the wind field, and Ekman pumping due to stress curl

+22

GPCP Rain (mm day –1)

Moisture: