1 / 20

Ocean and Atmosphere Biases on Land Precipitation during Indian Summer Monsoon in CFS Forecasts

This study explores the role of ocean and atmosphere biases on land precipitation during the Indian summer monsoon in CFS forecasts. It examines the impacts on local Hadley circulation, biases in equatorial crossing of ITCZ, biases in Findlater jet and monsoon precipitation, spatial structure of forecast biases, and precipitation pattern correlations over the land and in the Bay of Bengal.

bjenkins
Download Presentation

Ocean and Atmosphere Biases on Land Precipitation during Indian Summer Monsoon in CFS Forecasts

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 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

  2. 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

  3. 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

  4. 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.chikyu.ac.jp/ precip/

  5. 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)

  6. 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)

  7. Mass flux stream function (averaged over 60E-110E) CFSR CFS TG#2 CFS TG#1 CFS TG#3 The Y-axis shows pressure in hPa

  8. 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) N. Eq. : Eq-5oN; 70o-95oE CI : 16.5o-26.5oN; 74.5o-86.5oE In the March-initialized April forecast, the ITCZ is mostly stuck around Equator and results in excess precipitation during May. The land-biases grew into JJA.

  9. The ITCZ averaged averaged 50o-70oE and 90o-110oE Averaged over 90o-110oE Averaged over 50o-70oE (shading units in mm day-1)

  10. 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

  11. Biases (CFS-OBS) in precipitation, SST, Zonal Wind in March-initialized forecasts SST bias (oC) in shading Precip bias (mm day-1) in shading

  12. Biases in zonal wind grew with long-lead forecasts

  13. Signature of off-equatorial Rossby-wave and equatorial Kelvin wave in D20's annual-harmonic

  14. Mar initialized d20 climatologies show deepening of thermocline in the SWEIO in MAM

  15. And Kelvin-wave signature in EIO in early summer

  16. GPCP correlations in BoB Similar to Meehl et al. (2012)

  17. Same, but for April-initialized forecasts

  18. 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

  19. Differences in JJA forecast biases ENSO biases-Non-ENSO biases Precip bias mm day-1 in shading

  20. 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 Easterly wind biases + Ekman pumping south of the Equator (spring) 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)

More Related