CLIMATE FORECAST SYSTEM

INDIAN SUMMER MONSOON PREDICTION IN THE NCEP CLIMATE FORECAST SYSTEM (CFS)
Catherine Thiaw(1) Suranjana Saha(2) Diane Stokes(2) Stephen Lord(2)
(1) IMSG for EMC/NCEP/NWS/NOAA (2) EMC/NCEP/NWS/NOAA
CFS Retrospective Forecasts
CLIMATOLOGY (1981-2004)
OBJECTIVES OF THE STUDY
To study the CFS (T62L64) prediction of
the CLIMATOLOGY of Rainfall, Lower
Level Winds, Winds Stress and SST in the
Indian Region, and compare it with the
observational Climatology.
AREAS OF STUDY
•SOMALI JET : winds at 850 hPA
•ARABIAN SEA and BAY OF BENGAL
areas: winds at 850 hPA and SST
•All India Rainfall
CFS
OBS
CFS
OBS
SST (C)
Bay of Bengal
OBS
CFS
Arabian Sea
CFS
OBS
CFS
CFS - OBS
CFS - OBS
CFS - OBS
JUN
INITIAL CONDITIONS
May 00GMT from R-2 for 24 years from
1981-2004 (the sample size is 24x5)
All 5 atmospheric states (9-13 May) have
the same GODAS ocean initial condition
for the 11th of May 00GMT for 1981-2004.
VERIFICATION DATA
Precipitation :
• CMAP Rainfall Estimates for Monthly
and Pentad means from Xie-Arkin
SST : OIv2 Reynolds SST data
Wnd850 : Reanalysis-2 data
SST: From May to August,
CFS-OBS < 2 C
Arabian Sea and Bay of Bengal
Wnd850 hPa (m/s) : from May 16 to Sep 2:
Little difference between CFS and Observations
OBS
CFS Retrospective Forecasts
ANOMALIES
JUL
5 m/s
1:3
5 m/s
1:3
JUN
Upwelling brings cool
water to surface
Precipitation rate (mm/day) over India:
CFS usually shows less rain than the observations
AC skill up to 50% in some area
OBS
JUN
CFS
OBS
OBS
CFS
Somali Jet
JUL
CFS
OBS
Wnd850 (hPa)
Bay of Bengal
CFS
OBS
CFS - OBS
10-14
22-26
CFS - OBS
CFS - OBS
AC SKILL (%)
AC SKILL (%)
JUL
SUMMARY & CONCLUSIONS
SST CLIMATOLOGY
Arabian Sea Bay of Bengal
CFS forecast model climatology is realistic but
has some problem areas:
•Somali jet is too weak and the onset is late
•Bay of Bengal wind climatology is too weak
10-15
WIND 850 hPa CLIMATOLOGY
Somali Jet Area Bay of Bengal Area
•SST too warm in Arabian Sea (wind forcing is
too weak)
•Rainfall over India begins 2 weeks late and is
too weak at the peak
•Precipitation anomaly shifted north over Nepal
•Some skill in interannual precipitation anomaly
over SE Asia
•Marginal skill over India
45-50
•ONSET as defined by Somali Jet
Winds at 850 hPa and All India
Rainfall in the CFS is about 2
weeks late.
All India:
Rainfall
Anomalies
Future Developments
Rainfall Climatology
All India
Improvements to the CFS T62L64 is underway. These include higher resolution,
T126L64 for the atmospheric model, and a new ocean model MOM4, along with
changes to the physics and numerics. Hopefully this will lead to better results.
OBS
CFS(x2)
CFS