1. Pg. 1 The role of ocean and atmosphere biases on land precipitation-biases during Indian Summer Monsoon in CFS forecasts Bala Narapusetty 1,2, Raghu Murtugudde 1, Arun Kumar 3, Hui Wang 3 2015-Feb18-22 1 – ESSIC, UMD 2 – Hydrological Sciences Laboratory, NASA/GSFC 3 – NOAA Climate Prediction Center

2. 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

3. 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 0.25 o 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. 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: (16.5 o -26.5 o N; 74.5 o -86.5 o E)

5. Pg. 5 Precipitation averaged over Eastern equatorial Indian Ocean Obs. Precip: CPC (1982-2011) The x-axis shows forecast month as target Averaged over: (5 o S-5 o N; 90 o -110 o E)

6. Pg. 6 Precipitation averaged over Western equatorial Indian Ocean Obs. Precip: CPC (1982-2011) The x-axis shows forecast month as target Averaged over: (5 o S-5 o N; 50 o -70 o E)

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

8. The Equatorial crossing of ITCZ in the month of Apr/May is crucial for Monsoon rainfall (shading units in mm day -1 ) Averaged over 70 o -95 o E N. Eq. : Eq-5 o N; 70 o -95 o E CI : 16.5 o -26.5 o N; 74.5 o -86.5 o E 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. Pg. 8

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

10. Negative biases in Findlater jet grew with longer-lead forecasts and so the dry-land biases Pg. 10 mm day -1 NWEIO: Findlater Jet: 5 o -20 o N; 50 o -70 o E CI : 16.5 o -26.5 o N; 74.5 o -86.5 o E

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

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

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

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

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

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

17. Same, but for April-initialized forecasts Pg. 17

18. 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

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

20. SST increase due to d20 increase in SWEIO + WEIO (late spring) Pg. 20 Negative Precip. Bias in Central India Changes in local Hadley circulation High-level view of bias propagation Summary Negative biases in Findlater jet + weak upwelling on West Arabian-sea (late spring + early summer) 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) development of Large- scale cyclonic system in the mid-Arabia sea (Summer)