Affect of ENSO + IOD on snowfall in Western Himalayas.
The past three winters we had an extended La-Nina phase of the ENSO cycle.
What we saw was below average snowfall in Western Himalaya. Storms were not very strong and were interlaced with long dry spells.
A stronger El-Nino phase is set to occur through the upcoming fall and winter.
And what could it mean.
There have been years when it has positively and negatively impacted winter precipitation.
It all depends on which part of the pacific is heated during the El-Nino and which part of the Indian Ocean Dipole(heating of Indian Ocean) is occurring.
We basically require a subsistence of the Hadley cell over central India to sufficiently move the sub tropical jet streams to direct western disturbances.
A warming of the western Indian Ocean can do this.
As for be ENSO cycle, the winter precipitation depends upon the warming of the eastern Pacific (EP) El Nino rather than the central Pacific (CP) El Nino.
The EP El Nino warms the western Indian Ocean during the winter season which intensifies the Hadley cell with its subsidence over central India.
The sinking motion over central India shifts and intensifies the sub-tropical westerly jet (SWJ) over northern India.
The SWJ intensifies the frequent surges in mid-latitude, called western disturbances (WDs) which, results in excess precipitation over the north and central India.
Also, the subsidence over central India leads to lower level cyclonic circulation over central Indian landmass, which converges winds from warm Arabian Sea to north India supplying with abundant moisture for the WDs.