International Workshop on Atmospheric Composition and the Asian Summer Monsoon Bangkok 8th-10th June 2015 Effects Of On Indian Summer Monsoon Rainfall During El Niño Suvarna Fadnavis, CHAITRI ROY, Ashok Karumuri, Ayantika Dey Choudhury, Sabin T.P Indian Institute of Tropical Meteorology, Pune, India.
SCIENCE QUESTION To investigate the influence of pre-monsoonal & monsoonal aerosol loading on ISM during CONTEXT Context Indian summer monsoon precipitation serves as a lifeline to the society is a key factor for suppressing ISM associated with droughts An early onset and intensification of ISM rainfall - due to buildup of premonsoon absorbing aerosols - Elevated Heat pump Hypothesis Recent observations (AERONET) shows high BC and dust in the IGP during pre-monsoon (Mar-May) Interaction of pre-monsoon aerosols and Effects on ISM
JUN - SEP MEAN OF TOMS AEROSOL INDEX 1979 to 2005 1972, 1977, 1982, 1991, 1994, 1997, 2002, 2004 APR-MAY MEAN OF TOMS AEROSOL INDEX High aerosol loading during
JUN - SEP MEAN OF ZONAL WIND CIRCULATION (m/s) FROM NCEP REANALYSIS, AVERAGED OVER 15 30 N Strong upward motion over the IGP, foothills of Himalayas as well as TP Anomalous subsidence in the Indian region associated with the El Niño
TIME SERIES PLOT (LON: 70-90E; LAT: 20-30N) OF DAILY TOMS AI (RED) & ALL INDIA RAINFALL (BLUE) Increase in AOD from April through June AOD decrease during monsoon Corr = 0.54, lag of 3 months role of pre-monsoon aerosols in increasing rainfall over IGP
MODEL SIMULATIONS We designed sensitivity experiments using a state-of-the-art fully interactive aerosol chemistry climate model ECHAM5-HAMMOZ Horizontal Spectral Resolution : T42 (2.8 X 2.8 ) Vertical Resolution : 31 hybrid sigma-p levels from 1000hPa to 10 hpa 8 Sensitivity Experiments (10 membered ensembles) atology Expt ( Aero-On-May, Aero-Off-May, Aero-On-Mar, Aero-Off-Mar) El Niño Expt ( Aero-On-May, Aero-Off-May, Aero-On-Mar, Aero-Off-Mar) May Monsoon March Pre-monsoon
MODEL SIMULATED JUN - SEP MEAN RAINFALL (mm/day) & WINDS (m/s) AT 850 hpa Monsoon The general spatial pattern of rainfall is reasonably well simulated in the model. Low level monsoon circulation is clearly seen ENSO simulation with monsoon aerosols produces relatively less precipitation over the Indian region.
MODEL SIMULATED MEAN AOD JUN SEP Contribution of BC, OC, sea salt Monsoon MODEL SIMULATED MEAN AOD APR- MAY Higher AOD over IGP Pre-Monsoon Sea salt contribution
MODEL SIMULATED JUN - SEP MEAN RAINFALL ANOMALY (mm/day) Monsoon On Off Pre-Monsoon On Off Aerosol induced negative rainfall anomalies El- Niño effect reinforced by monsoon aerosols Positive rainfall anomalies over Northern India Positive rainfall anomalies over North, North-East India
MODEL SIMULATED ZONAL WIND ANOMALY (m/s) FOR JUN - SEP, AVERAGED OVER 15 30 N Monsoon On Off Strong anomalous upward motion over IGP, foothills &TP in Weakening of upward vertical velocities over IGP, TP & foothills during Pre-Monsoon On Off (EN) Increase in midtropospheric upward motion over foothills & TP due to premonsoon aerosols Increased convection
MODEL SIMULATED TEMPERATURE ANOMALY, AVERAGED OVER 70 100 E JUN SEP Monsoon On Off Low UT warming over TP Strong subsidence during El Niño over N. India El Niño inhibits the lifting of aerosols to UT MODEL SIMULATED TEMPERATURE ANOMALY, AVERAGED OVER 70 100 E APR- MAY Pre-Monsoon On Off Elevated level of aerosols during premonsoon during El Niño Enhanced UT warming
CONCLUSION TOMS observations indicates higher-than-normal aerosol loading over IGP during JJAS with a concurrent El-niño Sensitivity experiments with ECHAM5-HAMMOZ also shows similar finding - El-niño induced negative rainfall anomalies over India Analysis shows anomalously high aerosols over IGP during premonsoon of El-niño years. Pre-monsoon aerosol loading reduces severity of drought during El-niño
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