K R Ramanathan
Articles written in Proceedings – Section A
Volume 1 Issue 5 November 1934 pp 308-314
Volume 1 Issue 11 May 1935 pp 822-829
Volume 29 Issue 5 May 1949 pp 330-348
Observations of the light scattered from the clear blue zenith sky were made with Dobson’s photo-electric spectrophotometer at Delhi (28° 35′ N.) and Poona (18° 31′ N.) during the periods November 1945 to March 1947 and February–March 1948, and these have been used to determine the height distributions of atmospheric ozone at these places. After using Dobson’s method A in an exploratory way, the more detailed method B was used to calculate the vertical distributions from the observed Umkehr curves. Agreement between the observed and calculated points was obtained by trial and error at various zenith angles of the sun in the range 50°–90° where the effect of large particle scattering is negligible.
Distributions of ozone are given for total ozone amounts varying from 0·155 cm. to 0·217 cm. at Delhi, the average heights of ozone for these being from 26·3 km. to 25·1 km. A decrease in the total ozone amount is found to cause a rise in the centre of gravity. At Poona, distributions for ozone amounts 0·164 cm. and 0·174 cm. give a more or less fixed height of 28·0 km. for the centre of gravity.
The paper concludes with a brief survey of the distribution of ozone in the earth’s atmosphere both in the horizontal and the vertical and shows that it is easier to understand the regional, seasonal and day-to-day variations of ozone if we separately consider the contributions to total ozone content over any place from the photo-chemical action of sunlight and from transport in the horizontal and vertical directions of the accumulated ozone below the level of primary ozone formation.
Volume 37 Issue 2 February 1953 pp 321-331
The paper contains a summary of the results of the height distribution of ozone in the atmosphere obtained at Motmt. Abu with a Dobson Speetrophotometer during the period October 1951 to April 1952, when western disturbances affect North Indian weather. The observations show that there is very little ozone in the atmosphere below 18 km., that the ozone amount above 27 km. show very little systematic change with total amount, and that most of the changes take place in the layer 18 to 27 km. These results are compared with those obtained at Delhi, Kodaikanal, New Mexico (with V2 rockets), Arosa (in Switzerland) and Tromsϕ (Norway). In middle and high latitudes, there are substantial amounts of ozone below 18 km., and the larger the total amount, the larger is the proportion in the lower levels. For high ozone amounts in high latitudes, nearly hall the total amount may be below 20 km.
These results are discussed in relation to the variations of ozone with latitude and season, connecting them with the photo-chemical formation of ozone in the atmosphere above 27 km., the existence of a shelter-region for ozone between 27 km. and the tropopause and the destruction of ozone by mixing it with water-vapour and oxidisable matter carried up in the troposphere by convective activity.
It is concluded that the problem of variations of atmospherie ozone is one of large-scale turbulence and circulation in the upper troposphere and lower stratosphere.
Volume 43 Issue 2 February 1956 pp 67-78
Volume 43 Issue 5 May 1956 pp 306-308
Volume 43 Issue 6 June 1956 pp 394-399
The paper contains an analysis of the variation of the midday values of foF2, h′F2 and hpF2 with lunar phase at Ahmedabad during the years 1954 and 1955 and of foF2 alone at Bombay, Madras and Tiruchirapalli during 1954. It is found that while the semidiurnal lunar tidal variations at Ahmedabad and Bombay agree in phase with those observed at middle latitudes, the phase reverses in direction between Bombay and Madras. The results are compared with those relating to Huancayo and Singapore.
Volume 43 Issue 6 June 1956 pp 400-400 Erratum
Volume 65 Issue 1 January 1967 pp 38-44
Continuous recording of the field strength of 164 Kc/s CW transmission from Tashkent (42° N, 69° E) has been going on at Ahmedabad (23° 01′ N, 72° 36′ E) since March 1960. The present communication deals with a delayed effect of S.I.D.’s which has been observed on the 164 Kc/s transmissions.
Volume 66 Issue 1 July 1967 pp 60-67
The paper summarises the results of observations on the field strength of 164 kHz radio-waves received at Ahmedabad from Tashkent during the period 1960–65. There is a general increase in field strength with decrease in solar activity. From the end of 1965 when we began to receive X-ray data from N.R.L. satellites, it has been noticed that increases in the intensity of 0–8 Å at satellite level, are associated with daytime decreases in the field strength of 164 kHz waves received at Ahmedabad. As may be expected, the enhancement of 0–8 Å X-rays is also associated in a general way with an increased emission from the sun of 10·7 cm. radio-waves. Examples are given.
Volume 71 Issue 2 February 1970 pp 69-81
Volume 75 Issue 6 June 1972 pp 249-261
The comparison of X-ray flares observed in satellites and their manifestation in the field-strength records of 164 kHz radio waves received at Ahmedabad from Tashkent show that almost all the flares between 0200–1200 hr U.T. during the period 27 October to 3 November, 1968, were able to influence the signal intensity. The starting time and peak time of the X-ray flare and the sudden changes in 164 kHz radio signal agreed within a few minutes. The flare effect on the signal strength persists for a longer time than the flare itself.
The effects of even small X-ray flares on 164 kHz field-strength can be seen at Ahmedabad and Poona whereas only bigger flares show up at Delhi often with a pronounced initial dip. This suggests that the distance between the transmitter and receiver plays an important role in the observable effects on LF propagation; the longer the distance, the better is the effect observed. The details of the X-ray flux variations during a flare and the associated changes in radio signal intensities (164 kHz) at Ahmedabad and Delhi are under further study.