The paper preseots thtd seasonal variations and distribution of atmospherio'density in the upper air over Indian region. The study reveals the density gradient has a down slope from North to South during winter and South to North, upto 200 mb level in summer. At 850 mb level the ieopycnir: lines form tl shallow trough over East aoast and at 700 mb level over Bombay-Poona region while over the rest of the country the isopy 'nice show no spacial fcaturea: At 500 mb level there is a well marked trough of density over North Western India. Above 200 mb level an altogether di-'ertmt picture throughout the year is noticed.One of the meteorological parameters which has received scant attention in the field of Indian meteo-. rological literature is the study of upper air density and variations in it in different seasons. It is well known that density is directly proportional to pressure. The latter has been thoroughly investigated and plays a key role in the field of Meteorology. The authors' attention was drawn to the study of density variation in the upper-air of India in the course of studying the variation in thunderstorm frequencies over North India, The mean monthly data given in Normals of Climat-Temp. based on radiosonde data. for the years 1951-65 were used in this study1. The data relate to the mandatory levels, like surface, 850 mb, 700 mb, 500 mb, 300 mb, 150 rnb and 100 mb and those for-14 stations in Indian: sub-continent have been used in this study. T H E O R E T I C A L C O N S I D E R A T I O N SIt is well-known that the density equation p = PIRT is valid for completely dry air. But in the atmosphere water vapour will alway5 be present. Therefore, the total presswe of a parcel of unsaturated air may be regarded as the sum of the partial pressure which would be exelted by the dry air and the water vapour independently.Since the value of gas constant for water vapour is 815 times that of dry air, the density of water vapour is given by the formula p, = 5e/8RT wherein e=vapour pressure in mb. Density of dry air is given by the equation, pd = p -e/ltT. Thus the density of a parcel of unsaturated air or a parcel of mixture of dry air and water vapour can be written as :where p , = density of unsaturated air in gm/m3, R = gas constant, T = tehp in K O and p = pressure in mb.Starting with this generalised form of equation, air densities from surface upto 100 mb level were computed for 14 stations for twelve months. For such computations, the monthly means of pressure,. 31

Meteorological analysis or stem-borer attack on paddy crop at Pattambi (Kerala State) shows that both in pre-sowing season and the actual crop season, temperature, relative humidity and sunshine hours at some critical periods account for most or the variations in the percentage of infestation, Thus forewarning or the stem-borer attack on paddy crop at Pattambi from weather data appears feasible.