Seasonal and annual surface air temperature of Delhi has been analysed for 90-year period (1901-1990) for finding trends and periodicities. The analysis revealed that frequency distribution of all the four seasons as well as of annual time series is normal. Markov linear-type of persistence is observed in pre and post-monsoon seasons. Recent period {1961-1990) averages of temperature are significantly lower than the long period means in respect of annual, monsoon and pre-monsoon seasons.

more »

... ing trend is noticed in monsoon and annual temperature time series. Low-pass filter analysis suggests that the trend is not linear but oscillatory consisting periods of 10 years or more.