The interannual fluctuations in the Southern Oscillation indices (Wright, 1975) and their relations to the Indian monsoon (June-September) rainfall have been examined for the period of 106 years from 1875 to 1980. The monsoon rainfall is significantly (99.9 per cent level) correlated with the Southern Oscillation indices for the seasons: MJJ (069), A S 0 (0.67), NDJ (0.53), and FMA of the following year (0.38). The fluctuations in the Southern Oscillation index for the A S 0 season appear strongly related to the nearly simultaneous monsoon rainfall of India. This implies that the large positive (negative) value of the Southern Oscillation index, signifying strengthening (weakening) of the Walker circulation coincides with large excess (deficient) monsoon rainfall over India. The coherence spectrum reveals that the Southern Oscillation index and the monsoon rainfall are highly correlated in the period range of about 2-2.5 years and 4-6 years. The first of these periods corresponds with the Quasi-Biennial Oscillation and the latter agrees with the features of the Southern Oscillation, suggesting a strong link between Indian monsoon rainfall and these two phenomena. The striking feature of the composites of the Southern Oscillation index averaged for all the drought years and for all the flood years is the simultaneous occurrence of low (high) Southern Oscillation index and droughts (floods) in India. However, this association has limited use in long-range prediction. A preliminary study suggests that a nearly simultaneous occurrence of major climatic anomalies of the tropics, such as droughts in India and El Nirio off the coast of Peru, are linked to the Southern Oscillation, indicating some kind of time dependent zonal east-west circulation, i.e. Walker circulation.

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The technique of screening-regression analysis is applied to forecasting the monsoon performance (percentage rainfall departure) over India from the immediately preceding May's meteorological variables. The resulting prediction equation with five variables performed well, with a few exceptions, on independent data. The forecasting scheme shows some promise of providing a useful forecast of monsoon rainfall departures over India before the beginning of the season.

H E quest for the possible relationships between sunspots and weatherlclimate T began even before Schwabe, a German astronomer, discovered the sunspot cycle in 1843. In spite of the controversy surrounding the claimed effects of sunspot cycles on weather and climate, consideration is being given to the possible implication for climatological forecasts. In recent years there has been a major revival of interest on the problems of the sun-weathedclimate relationships. New statistical methods and modem computers are being used to tackle hitherto unmanageable calculations in order to test the reality of the effects and put this in proper perspective.It has been argued that there is little or no reliable evidence for significant correlations of either the 11-or 22-year sunspot cycles with variations of weather or climate (Gerety et al. 1977;Pittock 1978). However, among the long-term solar effects, evidence for an approximately 22-year cycle, twice the period of the sunspot cycle, has been found in several climatological variables (Mitchell et al. 1979;Dicke 1979;Hancock and Yarger 1979;Bhalme and Mooley 1980;Weinbeck and Yarger 1981;Williams 1981). The 22-year cycle is supposed to arise as a result of the alternate changes in the polarity of the leading sunspots in a given solar hemisphere in successive 11-year cycles. Thus the true sunspot cycle is 22 years rather than 11 years when the altematioil of sign of spot magnetic fields is considered. The 22-year quasi-cycle of sunspot activity is often termed the double sunspot cycle or Hale sunspot cycle. A recent work by Bhalme and Mooley (1981) provides evidence of an approximately 22-year cycle in the fluctuations of flood area indices over India for the 89-year period 1891-1979, showing strong coherence with the double (Hale) sunspot cycle. Furthermore, they were able to demonstrate the consistent occurrence of large-scale flood events in the major sunspot cycle by harmonic dial analysis. This finding receives support from the study of Ananthakrishnan and Parthasarathy (1983) who found statistically significant excess rainfall years around the peak phase of alternate sunspot cycles.The present note illustrates the association found between the occurrences of large-scale flood events in India and the double (Hale) sunspot cycle by separating drought and Aood years in a single diagram of the sunspot curve and by statistical analysis of the data. METHOD FOR IDENTIFICATION OF DROUGHTS AND FLOODSBhalme and Mooley (1980) developed an objective numerical drought index, based on the monthly monsoon (June-September) rainfall over an area and a duration for assessment of drought intensity. The basic assumption in the development of the index is that plant life and established human activities are geared to the long-term mean monthly rainfall of the area of the specific period and that the deviation from the mean monthly rainfall determines the drought characteristics. The drought index equation is I k = 0.5 Ik-1 + Mk/48.55(1)where Ik, Ik-1 are the drought intensities of the kt...

SummaryModified Palmer drought indices for six district areas, two each from arid, semi-arid and dry subhumid climatic regions of tropical India, have been examined for the fluctuations of drought indices series covering a period of 70 years (1901 1970). Power spectrum analysis of the drought indices series revealed statistically significant quasi-periodicities of 3.3, 6.6, 10 and 20 years with regional preferences. The first two of these periods are close to the two modal peaks of the Southern Oscillation suggesting that the oscillations of the drought indices may be connected to the large-scale atmospheric pressure in the Indo-Pacific region. The other two periods 10 and 20 years are close to the 11-year sunspot cycle and the 22-year double sunspot cycle. The influences of solar activity and the Southern Oscillation on the Indian climate seem to be causal features for introducing these quasi-periodic cycles in drought indices fluctuations. ZusammenfassungGr6ssere quasiperiodische Schwankungen der Trockenheitsindizes Modifizierte Trockenheitsindizes nach Palmer wurden ftir sechs Gebiete im tropischen Indien, je zwei mit aridem, mit semiaridem und mit subhumidem Klima, auf Schwankungen in den eine Periode von 70 Jahren umfassenden Reihen der Trockenheitsindizes untersucht. Die Spektralanalyse der Reihen der Trockenheitsindizes ergab statistisch signifikante Quasiperiodizit~iten von 3,3, 6,6, 10 und 20 Jahren mit regionaler Bevorzugung. Die ersten zwei dieser Perioden liegen eng bei Spitzenwerten der Stidtichen Oszillation und weisen darauf hin, dat~ die Schwankungen der Trockenheitsindizes mit der grof~r~iumigen Dmckverteilung im indisch-pazifischen Raum verbunden sein dtirften. Die anderen zwei Perioden von 10 und 20 Jahren sind dem 1 ljiihrigen Sonnenfleckenzyldus und dem 22j~,ihrigen Sonnenfleckenzyklus fast gleich. Der Einfluss der Sonnenaktivitiit und der Siidlichen Oszillation scheinen die Haupteinflussfaktoren auf die Bildung der quasiperiodischen Schwankungen der Trockenheitsindizes zu sein.

In the present paper performance of the monthly sub-divisional summer monsoon rainfall is studied in association with the position of the Low Pressure System (LPS) over the Indian region. Existence of the LPS over a particular location increases the rainfall activities in certain parts of the country while decreases in some other parts. For this study, the Indian region (5°-35° N and 60° -100° E) is divided into 5°  Lat. ´ 5° Long. grids. The duration of LPS is taken in terms of LPS days with respect to the location of LPS in a particular grid. Monthly total number of LPS days in each of the grids are computed during the summer monsoon season, June to September for the period 1891 – 1990. Maximum number of LPS days (more than half of the total) are observed in the latitude belt between 20°-25°N. The percentages of total LPS days in this area are higher in July and August which are peak monsoon months as compared to June and September. When there is a LPS are in the area 20°-25° N and 80°-90° E, there is significant increase in the rainfall activities in the sub-divisions along mean monsoon trough while northeast India and southeast peninsular India experience significant decrease in rainfall in the months of July and August. Owing to the movement of LPS from east to west through central India, most parts of the country, excluding northeast India and south peninsular India get good rainfall activity. Correlation coefficients between monthly LPS days over the different grids and monthly sub-divisional rainfall are computed to study the relationships. The performance of sub-divisional rainfall mostly related with the occurrence of LPS in certain grid- locations. The correlation field maps may give some useful information about rainfall performance due to LPS in a particular grid locations.

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