NOPR Collection:

Whistlers at Low Latitudes

Wed, 01 Mar 1972 00:00:00 GMT

Title: Whistlers at Low Latitudes Authors: Somayajulu, V.V.; Rao, M.; Tantry, B.A.P. Abstract: The contributions made by Indian workers towards a better appreciation of the low latitude ground observations of whistlers are reviewed. Though some routine results are included, the main emphasis is on those results which, the authors believe, elucidate some physical processes occurring in the magnetosphere. An example of such results is the experimental evidence for the duct formation and decay during geomagnetic disturbances. We also attempt to explain the riser, low dispersion and twin whistlers observed for the first time at ground stations, with the help of ray tracing in model magnetospheres, Elementary theoretical considerations are included only to make the presentation complete. Electron density estimates obtained from the whistler data are given to show the consistency of the observations. More accurate estimates require nose frequency data which, unfortunately, are not easily obtained at low latitudes. Directions for further researches in the field are indicated. Page(s): 102-118

Sudden Ionospheric Disturbances

Wed, 01 Mar 1972 00:00:00 GMT

Title: Sudden Ionospheric Disturbances Authors: Mitra, A.P.; Subrahmanyam, C.V. Abstract: A brief review of the recent results of the sudden ionospheric disturbances (SID) caused, by solar flares has been presented; no attempt has been made to cover the whole literature on the subject. Some of the areas covered include SID phenomenology, ionization and loss processes during times of SIDs. The implications on the ion chemistry of the D-region are also discussed. Page(s): 93-101

Cosmic Radio Noise Absorption in the Ionosphere: If Review of Results for the First Two Decades of Riometry at Low Latitudes

Wed, 01 Mar 1972 00:00:00 GMT

Title: Cosmic Radio Noise Absorption in the Ionosphere: If Review of Results for the First Two Decades of Riometry at Low Latitudes Authors: Sarma, S. B. S. S.; Mitra, A. P. Abstract: In the past two decades since the original work of A. P. Mitra and C. A. Shain [J. atmos. terr. Phys., 4 (1953),204] on cosmic noise absorption, giving information about the ionospheric absorption of radio waves, the riometer technique has been used extensively, because of its importance in radio commutations and its implications in geophysical research. During IGY, a breakthrough in this technique resulted from the development of the riometer. This paper summarizes the state of knowledge, at the end of 1971, on cosmic radio noise absorption as applicable to low and equatorial latitudes, with emphasis on the Indian contribution towards the development and use of this technique. Due to the advantageous location of the Indian stations, riometer observations have provided meaningful results. Page(s): 84-92

Rocket Measurements of D-Region Electron Densities at the Equator

Wed, 01 Mar 1972 00:00:00 GMT

Title: Rocket Measurements of D-Region Electron Densities at the Equator Authors: Somayajulu, Y. V.; Avadhanulu, M. B. Abstract: The D-region electron density profiles at the equator measured by rocket techniques are summarized. It is noted that these profiles are consistent with the current concepts of the ionizing sources and loss mechanisms which control the equilibrium electron densities in the D-region. However, there appease to be some discrepancy regarding the cosmic ray contribution, the actual values observed below 70 km. being somewhat higher than the expected values. Page(s): 81-83