Comparison of Ozone Amounts Measured at Delhi (28I/2°N), Srinagar (34°N) and Tateno (36°N) in 1957~58

Abstract

A new ozone station was established in Kashmir (34°N) in 1955 in a region where double tropopauses are frequent in winter and spring. In this paper, a comparison is made of the ozone amounts measured at Delhi (281/2°N) and Srinagar (34°N) in India and at Tateno (36°N) in Japan in 1957-58. The ozone amounts at Tateno are much larger than at Srinagar although the latitude of Tateno is only 2° greater than that of Srinagar. It is recalled that at Zi-Ka-Wei and Cairo, which are at lower latitndes than Srinagar, significantly higher ozone values had been recorded in winter. It is thus evident that there is a large geographical influence on the total ozone amount measured at a place. Apparently, the Himalayas and the Indian summer monsoon exert a strong depressing influence on the ozone amount south of the Himalayas and incursions of the cold Siberian anti-cyclone tend to bring with it larger amounts of ozone over China and Japan. The seasonal variation of ozone over N. India was of an unusual character in 1957. A summary of the results of the ozone measurements made in India prior to 1954 was given by RAMANATHAN (1954) at the Rome Meeting of the International Association of Meteorology. The day-to-day variations of ozone are small during most of the year and surface weather conditions do not seem to affect them. In December to April, however, there are significant variations of ozone over Mt. Abu and New Delhi, this being the period when active western disturbances move across N. India. The transition from the autumn minimum of ozone to the comparatively high values in winter and spring takes place in a succession of surges, the first surge approximately coinciding with the onset of strong upper westerlies over N. India. Some pronounced surges are associated with the passage of deep troughs of low pressure at 6 and 9 km. The rise of ozone during a surge takes place when northwesterly winds are replacing the southwesterlies, but once the northwesterlies get settled, the ozone amount begins to fall. However, ozone fluctuations could not be * Paper presented at the International Ozone Symposium at Oxford in July 1959. 86R. N. Kulkarni, P. D. Angreji and K. R. Ramanathan Vol. X No. 2 explained in terms of shifts in wind direction at pilot balloon levels. Middle latitude variations of ozone associated with waves in the upper atmosphere are observable even at latitudes down to 20°N in winter and spring. The association of ozone changes with western disturbances was confirmed from later observations made at Delhi, Mt. Abu and Quetta. Since 1955, observations on the total amount of ozone and its vertical distribution have been made at Srinagar (34°N) at a latitude where double tropopauses are frequent. An ozone observing station was established at Srinagar in May 1955 by transferring a DOBSON'S spectrophotometer there. The optical wedges of the spectrophotometer were recalibrated and the constants determined. Frequent checks of calibration were made in the subsequent period. The present paper contains a summary of the results of the ozone observations so far analysed. It was decided to use the afternoon ozone amounts observed on the wavelength pair 3114/3324 (CC') for the present study. The ozone values were calculated and corrected for haze in the manner suggested by RAMANATHAN and KARANDIKAR (1949) . All the ozone values have been converted to VIGROUX'S level of ozone absorption coefficient a for uniformity. 1. Day-to-day variation of ozone In Fig. 1 the daily ozone values over three Indian stations, Mt. Abu (24°N), New Delhi (28V2°N) and Srinagar (34°N) for the year 1957-58 are given. The daily ozone amounts over Tateno (36°N) (1957-58) in Japan have also been included in the diagram. 1959 Comparison of Ozone Amounts Measured in 1957-58 87 A striking feature of this diagram is that although the latitude of Tateno differs only by 2° from that of Srinagar, the ozone values over Tateno are much higher than those over Srinagar in the winter and spring months. The fluctuations in the ozone content over Tateno are also markedly larger than those over Srinagar. In August to October, however, the ozone content over Tateno is only a little larger than that over the north Indian stations. The Tateno ozone starts separating from the Indian values in December and the difference increases rapidly. 2. Seasonal variation of ozone Fig. 2 gives the ten-day mean ozone values at Tateno, Srinagar, New Delhi and Mt. Abu from July 1955 to December 1958. (1) In general, the seasonal variation conforms to the normal variation appropriate to middle latitudes with maxima in winter and spring and minima in summer