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The role of ocean and atmosphere biases on land
precipitation-biases during Indian Summer Monsoon
in CFS forecasts Bala Narapusetty1,2, Raghu
Murtugudde1, Arun Kumar3, Hui Wang3 2015-Feb18-22
1 ESSIC, UMD 2 Hydrological Sciences
Laboratory, NASA/GSFC 3 NOAA Climate Prediction
Center
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Outline

• 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

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Details of datasets used in this study

• 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

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Precipitation averaged over Central India
The x-axis shows forecast month as target
CI (16.5o-26.5oN 74.5o-86.5oE)
Obs. Precip. APHRODITE (1982-2007) http//www.ch
ikyu.ac.jp/ precip/
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Precipitation averaged over Eastern equatorial
Indian Ocean
The x-axis shows forecast month as target
Averaged over (5oS-5oN 90o-110oE)
Obs. Precip CPC (1982-2011)
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Precipitation averaged over Western equatorial
Indian Ocean
The x-axis shows forecast month as target
Averaged over (5oS-5oN 50o-70oE)
Obs. Precip CPC (1982-2011)
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Mass flux stream function (averaged over
60E-110E)
CFSR
CFS TG2
CFS TG1
CFS TG3
The Y-axis shows pressure in hPa
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The Equatorial crossing of ITCZ in the month of
Apr/May is crucial for Monsoon rainfall
Averaged over 70o-95oE
(shading units in mm day-1)
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The ITCZ averaged averaged 50o-70oE and 90o-110oE
Averaged over 90o-110oE
Averaged over 50o-70oE
(shading units in mm day-1)
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Negative biases in Findlater jet grew with
longer-lead forecasts and so the dry-land biases
mm day-1
NWEIO Findlater Jet 5o-20oN 50o-70oE CI
16.5o-26.5oN 74.5o-86.5oE
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Biases (CFS-OBS) in precipitation, SST, Zonal
Wind in March-initialized forecasts
SST bias (oC) in shading
Precip bias (mm day-1) in shading
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Biases in zonal wind grew with long-lead forecasts
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Signature of off-equatorial Rossby-wave and
equatorial Kelvin wave in D20's annual-harmonic
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Mar initialized d20 climatologies show
deepening of thermocline in the SWEIO in MAM
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And Kelvin-wave signature in EIO in early summer
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GPCP correlations in BoB Similar to Meehl et al.
(2012)
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Same, but for April-initialized forecasts
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Unlike in observations, the ENSO years' JJA
forecasts are wetter over CI in CFS long-lead
forecasts
CFS (ENSO-NONENSO)
CPC (ENSO-NONENSO)
Precip difference (mm day-1) in shading
Precip difference (mm day-1) in shading
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Differences in JJA forecast biases ENSO
biases-Non-ENSO biases
Precip bias mm day-1 in shading
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Summary
High-level view of bias propagation
development of Large-scale cyclonic system in the
mid-Arabia sea (Summer)
Negative biases in Findlater jet weak upwelling
on West Arabian-sea (late spring early summer)
Negative Precip. Bias in Central India
Changes in local Hadley circulation
Biases in ITCZ Eq-crossing (Mid and late spring)
Enhanced Kelvin wave propagates warmer SSTs to
Tropical EEIO (summer)
SST increase due to d20 increase in SWEIO WEIO
(late spring)