Intra-seasonal oscillation of north east monsoon over southern peninsular India-an investigation

When illustratively went through the NE rainfall pattern of southern peninsular India enclosed within latitudes of 8 ̊N and 13 ̊N, longitudes 75 ̊E and 82 ̊E for last 5 decades demonstrated no long term trend in it. At the same time there is a prominent inter-annual variation in the seasonal mean rainfall as well as its sub seasonal distribution, which cannot be correlated to anything in a simple style. Effort is done to decode the length of different spells of precipitation found within the season and attention is given to individual years that displayed similar sub seasonal distribution. Thus it became necessary to consider various forcing factors of inter-annual variability such as ENSO, IOD which drive the variability of Boreal Fall Monsoon precipitation over southern peninsular India to unravel the mystery behind different oscillations. The evolution of MISOs in the equatorial region of Boreal Summer Season and its passage across the SP towards north and its potential to modify the intraseasonal variability of Boreal Summer Monsoon is widely discussed in many of the earlier studies. The capacity of the Madden Julian Oscillation to drive Ocean Atmosphere coupled dynamic processes in tropics during Boreal Winter is also well documented. The Boreal fall season lies in annual cycle during the transition from Boreal Summer to Boreal Winter and where the synoptic activities are as strong as the low frequency Intra Seasonal Oscillations (ISO). Southern Peninsular India and Sri Lanka, which get benefited by Boreal Fall Monsoon are positioned in between the two poles of Indian Ocean Dipole mode can give its own impact to the year to year variation of the rain fall pattern and that is also considered. The part of ocean that can impart more sensible changes and can modulate the intraseasonal rain variation of SP is located and the possibility as well as the potential of that particular area is kept under special scrutiny throughout the study. To get a clear picture of the frequently found paces of rain, FFT analysis is carried out for strong and weak NE monsoon, positive and negative IOD years, El Nino and La Nina years and their composites. Paper agrees to an earlier approved fact like IOD can affect intra-seasonal modes of variability whereas ENSO can modify long term inter-annual changes. Obviously the proximity of IOD to the experimental region and the probable lag in executing the effect of ENSO on the concerned area can be the reason for it. It invariably points out the local and remote effect of the ocean to modify the climate outweighing the role of atmosphere in doing the same. 1-5 days Synoptic changes, 10-20 days mode oscillations, as well as 20-60 days low frequent intra seasonal oscillations are found to be equally prominent within the season. SST, SLP and wind parameters found in and around equatorial Indian Ocean region are examined to get a better understanding. Identifying the part of ocean that can more creatively and directly influence the rainfall pattern is located. The SST of Bay of Bengal and South China Sea as well as SLP gradient from Philippines Sea to Arabian Sea are nominated as the most important parameters in modifying the Boreal Fall Monsoon (BFM) Season of Southern Peninsular India (George et al 2011).