Intraseasonal monsoon fluctuations seen through 25 years of Indian radiosonde observations

Abstract

Radiosonde records for 12, major Indian cities have been checked and analyzed for intraseasonal set type sonal activity in the monsoon, After forming time series with two observation per day removing bad values, and filling data gaps with linear interpolation, the time series have been plotted with and without filtering and have  been subjected to spectral analysis to reveal the nature of intraseasonal fluctuations and their interannual variability. Spectra were estimated from the time, series using the maximum entropy method (MEM) which fits an autoregresslve; (AR) model to the time series. M.EM spectra bases on tenth order AR models show that most of the variance In monsoon weather comes from intra seasonal activity with periods longer than 10 days, but do not show separate peaks at 10.20 and/or 30-50 day time scales for the majority of summers.