The onset of the southwest monsoon over Kerala: 1901-1980

Utilising daily mean rainfall from dense rain gauge networks, the dates of onset of the southwest monsoon over south and north Kerala have been derived on the basis of objective criteria for the years 1901 to 1980. These dates have been compared with the onset dates as per records of the India Meteorological Department. Statistics of the onset dates are presented. The mean onset date for south Kerala is found to be 30 May and for north Kerala 1 June with a standard deviation of about 9 days in both cases. The sharp increase in rainfall that heralds the onset of the monsoon is highlighted by superposed epoch analysis. The prevailing notion that rainfall from pre-monsoon thunderstorms progressively increases and merges with the monsoon rainfall is shown to be not valid

Statistical distribution of daily rainfall and its association with the coefficient of variation of rainfall series

The study focuses attention on the normalized rainfall curve (NRC) depicting the association between cumulated percentage rain amount (x) and cumulated percentage number of rain days (y) of the rainfall series. It is shown that the NRC is uniquely determined by the coefficient of variation (CV) of the rainfall series. There is no universal NRC that can represent all rainfall regimes. The equation x=y exp-b(100-y)c, where b and c are two empirical constants, gives a good analytical representation of the NRCs over a wide range of CV values of the rainfall series. This analytical equation is able to account for the occurrence of high rainfall intensities towards the upper extremity of the NRC for rainfall series with high values of CV

Some features of the south-west monsoon rainfall of Cochin and Minicoy ( India).

Several characteristics of the SW monsoon rainfall of the low latitude stations of Cochin (coastal) and Minicoy (island) have been studied using the hyetograms of these stations for the 10yr period 1973-1982. Both stations exhibit diurnal variations of rainfall with maximum activity in the post-midnight hours and minimum in the afternoon hours. The amplitude of the diurnal variation increases for rain events of increasing intensities. The integrated duration of the seasonal rainfall is about 250h at Cochin and 110h at Minicoy. Half the total rain from heavy falls is received in a 5th of the total duration; half the total duration accounts for only a 5th of the total rain from light falls

The onset of the southwest monsoon in 1990

statistics relating to the date of onset of the southwest monsoon over kerala for the 100 year period 1891-1990 reveal that the mean and median dates of onset for south kerala are 31 May and 1 June with standard deviation of 8.5 day

On the northward advance of the ITCZ and the onset of the southwest monsoon rains over the southeast Bay of Bengal ( Kerala).

It is found that at the island stations south of 10oN the summer monsoon rains set in on the average towards the end of April which is a month in advance of the onset of the monsoon over the south Kerala coast of peninsular India. At the island stations to the north of 10oN the onset occurs about the first week of May. These dates are ahead of those shown in the existing diagrams giving the average onset dates of the summer monsoon over the SE Bay of Bengal. -from Author

Atmospheric tidal oscillations. Part I : Historical Development

The invention of the barometer in the seventeenth century lead to the discovery of Atmospheric tidal oscillations with a pronounced solar semi-diurnal component

Giant Meterwave Radio Telescope observations of an M2.8 flare: insights into the initiation of a flare-coronal mass ejection event

We present the first observations of a solar flare with the GMRT. An M2.8 flare observed at 1060 MHz with the GMRT on Nov 17 2001 was associated with a prominence eruption observed at 17 GHz by the Nobeyama radioheliograph and the initiation of a fast partial halo CME observed with the LASCO C2 coronograph. Towards the start of the eruption, we find evidence for reconnection above the prominence. Subsequently, we find evidence for rapid growth of a vertical current sheet below the erupting arcade, which is accompanied by the flare and prominence eruption.Comment: Accepted for publication in Solar Physic

Atmospheric tidal oscillations. Part 2 : Diurnal variation of pressure over India

Hourly surface pressure data (annually and monthly) over a network of Indian stations have been harmonically analyzed