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

OutlineIntroduction

Data and Methodology

Rossby wave breaking and circulation over the West Asia

Convective inhibition over the Indian subcontinent

Summary

Indian Institute of Technology, Kharagpur

IntroductionIndian Institute of Technology, Kharagpur

Major 200-hPa circulation anomalies accompanied with climatological zonal wind (shading >15m) from June to September . The dotted line indicates the zero zonal wind line in 200-hPa Adopted from Ding Q. 2008

Westerly Jet or wave guide

High Pressure regions

Indian Institute of Technology, Kharagpur

Krishnan et al. 2009

• Low over WCI

• Blocking high over south eastern china

Ten-day back trajectories from central India. Dry spell for trajectories terminating at 850 (green) and 700 (red) hPa (from Krishnamurti et al, 2010)

18 June 2009

4th August 2009

16th July 2002

30th August 2001

Indian Institute of Technology, Kharagpur

Western Asia Dry Air Incursion

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

Daily wind fields (u, v, w) and temperature fields at eleven different pressure levels at a resolution of 2.5° × 2.5° from NCEP-NCAR reanalysis

Geopotential height from NCEP –NCAR reanalysis Precipitation from TRMM

𝛁T + 𝛚

Indian Institute of Technology, Kharagpur

Climatology of Isentropic Potential Vorticity and horizontal wind at 350K 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 350K Over Asia and Africa

Geopotential Height and Temperature anomalies at 500hPa 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 sub-continent

Modification of Hadley circulation over the Indian Subcontinent

Suppression of convection over the Indian –subcontinent and Drought

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