Extratropical Rossby Wave breaking a cause for Indian

Extratropical Rossby Wave breaking: a cause for Indian summer monsoon failure Mihir Kumar Dash*, Dhrubajyoti Samanta* and P. C. Pandey** * Indian Institute of Technology, Kharagpur * Indian Institute of Technology, Bhubaneswar

Indian Institute of Technology, Kharagpur Outline �Introduction �Data and Methodology �Rossby wave breaking and circulation over the West Asia � Convective inhibition over the Indian subcontinent � Summary

Introduction Ø Westerly Jet or wave guide Ø High Pressure regions Major 200 -h. Pa circulation anomalies accompanied with climatological zonal wind (shading >15 m) from June to September. The dotted line indicates the zero zonal wind line in 200 -h. Pa Adopted from Ding Q. 2008 Indian Institute of Technology, Kharagpur

Indian Institute of Technology, Kharagpur • Low over WCI • Blocking high over south eastern china Krishnan et al. 2009

Indian Institute of Technology, Kharagpur Western Asia Dry Air Incursion 18 June 2009 16 th July 2002 4 th August 2009 30 th August 2001 Ten-day back trajectories from central India. Dry spell for trajectories terminating at 850 (green) and 700 (red) h. Pa (from Krishnamurti et al, 2010)

Indian Institute of Technology, Kharagpur Rossby Wave Breaking Overturning of PV event at 350 -K PV (a) Anticyclonic (b) Cyclonic. contoured every 2 potential vorticity units. From Strong and Magnusdottir, 2009

Data and Methodology �

Indian Institute of Technology, Kharagpur Climatology of Isentropic Potential Vorticity and horizontal wind at 350 K Level

Indian Institute of Technology, Kharagpur Sample cases of Rossby Wave Breaking and intensification of circulation over the western India

Potential Vorticity and Wind Field anomalies at 350 K Over Asia and Africa

Geopotential Height and Temperature anomalies at 500 h. Pa Over Asia and Africa

Indian Institute of Technology, Kharagpur

Meridional Cross-section of Specific humidity over Central India

Thermodynamics of the upper-troposphere

Thermodynamics of the upper-troposphere

Hadley Circulation during Breaking condition

Summary Rossby Wave Breaking over the Western/Western Central Asia Formation of blocking high over Western Central Asia Descending of dry air from western and central Asia forming a inversion layer over Indian subcontinent Modification of Hadley circulation over the Indian Subcontinent Suppression of convection over the Indian – subcontinent and Drought

THANK YOU