For the past few years in succession India has witnessed extreme flooding events caused by monsoonal troughs colloding with what appears transitory mid latitude disturbances and these appear to trigger flash floods. Case in point - http://en.wikipedia.org/wiki/2013_North_India_floods and http://en.wikipedia.org/wiki/2014_India%E2%80%93Pakistan_floods. My question relates to the physics of such interactions.
Following are my questions:
1) The northward propagating waves emanating at the 850 hPa level from the MJO(BSISO) appear to be damped at the Himalayan foothills(30 N latitude). Following orographic interactions I presume the 850 hpA 's geopotential height appears to be raised. Is that an accurate statement i.e. in the mountains the 850 hPa monsoonal trough's geopotential height is higher(much higher) than at sea levels?
2) Then the planetary wave at the 500 hPa level then appears to be dipping down in the tropics and interacting with monsoonal troughs. How does a upper level trough "propagate" down ? Is this due to quasi geostropic theory?