SummaryThe results of thunderstorm observations made with local lightning flash counters at Poona during 1967--1969 are presented. A positive correlation between the average total count when the count exceeds 20 per hour on a 5V/m counter, and the number of days per month when thunder is heard has been established. The diurnal and seasonal variations in thunderstorm actNity are described. It is seen that although a single isolated storm can vitiate the normal pattern of thunderstorm activity in a month or season, a long term statistical average can be taken with a greater degree of confidence as a better index of electrical activity than the current aural method of observation of thunderstorms.
Zusammenfassung
Untersuchung der elektrischen Aktivit~it yon Gewittern mit BlitzzfihlernErgebnisse yon in der Zeit yon 1967--1969 in Poona mit 6rtlichen Blitzziihlern durchgefiihrten Gewitterbeobachtungen werden vorgelegt. Wenn je Stunde mehr als zwanzig Impulse auf einem 5 V/m-Z~ihler registriert werden, kann eine positive Korrelation zwischen der durchschnittlichen Gesamtimpulszahl und der Anzahl der Tage, an denen Donner geh6rt wurde, festgestellt werden. Es wird gezeigt, dat~, obwohl ein einzelnes isoliertes Gewitter das normale Bild der Gewittert~itigkeit in einem Monat oder in einer Jahreszeit verfalschen kann, ein langfristiger statistischer Durchschnitt mit gr6t~erer Zuverl~issigkeit als besserer Index fiir elektrische Aktivifiit genommen werden kann als die gegenw{irtige ,,akustische" Methode der Gewitterbeobachtung. * Dedicated to the memory of Prof. Hans Israel. 298 G.P. Srivastav~ et aI.
The paper describes a satellite automatic picture transmission (APT) ground receiving station, designed and developed at the Instruments Division, Meteorological, Office, Poona. The station has been in operation at Poona for over six months and has provided good quality Visible and infrared pictures from meteorological satellites ESSA.2, ESSA.8, Nlmbus.3 and ITOS.
The station uses a high gain right circularly polarized helical antenna, a highly sensitive and selective FM receiver and a Mufax facsimile recorder modified suitably to record the satellite cloud pictures. The paper highlights the design details of the antenna and the FM receiver and also described the necessary modifications to the 'Mufax' facsmile recorder for recording correct satellite pictures. Future development plans are also briefly discussed.
A series of measurements of the electrical conductivity of air in the atmosphere up to a height of 20-25 km was made at Poona during 1971- 72 using balloon borne conductivity sondes developed and constructed in the Instrument Research Laboratories of the Meteorological Office at Poona.
During July and September conductivity increases monotonically with height in agreement with theory, while during winter months it shows a sharp fall after about 18 km. The main cause for the differences in conductivity would appear to be the changes in aerosol content in the lower stratosphere due to changes in the circulation patterns.
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