Upload
charles-owen
View
219
Download
0
Tags:
Embed Size (px)
Citation preview
•Pg. 1
The role of ocean and atmosphere biases on land precipitation-biases during Indian Summer Monsoon in
CFS forecastsBala Narapusetty1,2, Raghu Murtugudde1, Arun
Kumar3, Hui Wang3
2015-Feb18-22
1 – ESSIC, UMD2 – Hydrological Sciences Laboratory, NASA/GSFC3 – NOAA Climate Prediction Center
Outline
Pg. 2
• Motivation: Systematic dry-precipitation bias over
land and wet-bias over Eastern-Equatorial Indian Ocean• Analysis
• Impacts on local Hadley circulation• Biases in equatorial crossing of ITCZ in April/May• Biases in Findlater jet and Monsoon precipitation• Spatial structure of March-initialized forecast biases in
precipitation, SST and zonal wind.• Precipitation pattern correlations over the land and in
BoB
• Results and conclusions• Overall-picture: Schematic-view of bias propagation• Summary
Details of datasets used in this study
Pg. 3
• Forecast data:• CFSv2 monthly-mean forecasts (up to 11 lead-
months) obtained by initializing around the beginning of each month from 1982-January to 2011-March.
• 24 ensemble forecasts each month.
• Observations• Precipitation: APHRODITE
Gauge-based and 0.25o spatial-resolution (http://www.chikyu.ac.jp/precip)CPC and GPCP : As needed
• SST : NOAA Optimum Interpolated (OISST; Reynolds et al., 2002)
• 10-m zonal and meridional winds : CCMP 3.5
Pg. 4
Precipitation averaged over Central India
Obs. Precip.: APHRODITE(1982-2007)http://www.chikyu.ac.jp/precip/
The x-axis shows forecast month as target
CI: (16.5o-26.5oN; 74.5o-86.5oE)
Pg. 5
Precipitation averaged over Eastern equatorial
Indian Ocean
Obs. Precip: CPC(1982-2011)
The x-axis shows forecast month as target
Averaged over: (5oS-5oN; 90o-110oE)
Pg. 6
Precipitation averaged over Western equatorial
Indian Ocean
Obs. Precip: CPC(1982-2011)
The x-axis shows forecast month as target
Averaged over: (5oS-5oN; 50o-70oE)
Pg. 7
Mass flux stream function (averaged over 60E-110E)
CFSR
CFSTG#1
CFSTG#3
CFSTG#2
The Y-axis shows pressure in hPa
The Equatorial crossing of ITCZ in the month of
Apr/May is crucial for Monsoon rainfall
(shading units in mm day-1)
Averaged over 70o-95oE
N. Eq. : Eq-5oN; 70o-95oECI : 16.5o-26.5oN; 74.5o-86.5oE
In the March-initialized April forecast, the ITCZ is mostly stuckaround Equator and results in excess precipitation during May.The land-biases grew into JJA.
Pg. 8
(shading units in mm day-1)
Averaged over 50o-70oE
Pg. 9
Averaged over 90o-110oE
The ITCZ averaged averaged 50o-70oE and 90o-110oE
Negative biases in Findlater jet grew with longer-lead
forecasts and so the dry-land biases
Pg. 10
mm day-1
NWEIO: Findlater Jet: 5o-20oN; 50o-70oECI : 16.5o-26.5oN; 74.5o-86.5oE
Biases (CFS-OBS) in precipitation, SST, Zonal Wind
in March-initialized forecasts
Pg. 11
Precip bias (mm day-1)in shading
SST bias(oC)
in shading
Biases in zonal wind grew with long-lead forecasts
Pg. 12
Signature of off-equatorial Rossby-wave and equatorial Kelvin wave in D20's annual-
harmonic
Pg. 13
Mar initialized d20 climatologies show deepening
of thermocline in the SWEIO in MAM
Pg. 14
And Kelvin-wave signature in EIO in early summer
Pg. 15
GPCP correlations in BoBSimilar to Meehl et al. (2012)
Pg. 16
Same, but for April-initialized forecasts
Pg. 17
Unlike in observations, the ENSO years' JJA forecasts are wetter over CI in CFS long-lead
forecasts
Pg. 18
CPC (ENSO-NONENSO)
CFS (ENSO-NONENSO)
Precip difference (mm day-1)in shading
Precip difference (mm day-1)in shading
Differences in JJA forecast biasesENSO biases-Non-ENSO biases
Pg. 19
Precip bias mm day-1 in shading
SST increase due to d20 increasein SWEIO + WEIO (late spring)
Pg. 20
Negative Precip. Bias inCentral India
Ch
ang
es i
n l
oca
lH
adle
y ci
rcu
lati
on
High-level view of bias propagation
Summary
Negative biases in Findlater jet + weakupwelling on West Arabian-sea (late spring + early summer)
Easterly wind biases + Ekman pumping south of the Equator (spring)
Biases in ITCZEq-crossing (Mid and late spring)
Enhanced Kelvin wave propagates warmer SSTs to Tropical EEIO(summer)
development of Large-scale cyclonic systemin the mid-Arabia sea(Summer)