In May 1974 a new era in satellite radio beacon studies of the ionosphere opened with the ATS-6 Radio Beacon Experiment. The history of radio beacon studies up to that time is reviewed briefly and the particular features of the ATS-6 beacon are discussed together with the basic theory required to interpret the measurements. The main emphasis is on the ATS-6 beacon experiment but other beacon data are discussed which provide the necessary background. The diurnal and seasonal variations of the total electron content and the plasmaspheric content are presented for the U.S.A. and Europe. In winter the plasmaspheric content over the Western Hemisphere maximizes at night while in Europe and the Pacific it appears to peak near noon. This is thought to be caused by flow of plasma from the local and conjugate ionospheres. Night maxima of total electron content are found showing that they do not arise from depletions of the plasmaspheric content. The plasmaspheric content is highly sensitive to solarterrestrial disturbance, it reaches a minimum on the third day of a storm and may take between 10 and 20 days of partial filling and emptying to recover. Traveling disturbances in U.S.A., Europe, and India show similarities of speeds but not of direction. Beacon observations of micropulsations in total content, tropospheric fluctuations and Fresnel diffraction by intense ionospheric irregularities are discussed together with radio wave scintillations and some applications of beacon radio data to communications and navigation.

Recent progress in satellite radio beacon studies with particular emphasis on the ATS-6 radio beacon experiment

Night-time ionospheric scintillations at the magnetic equator

[1] Using the mesosphere-stratosphere-troposphere (MST) radar observations in the troposphere and lower stratosphere at a tropical station, Gadanki, the rate of turbulent kinetic energy dissipation ϵ, as estimated by the spectral width method, the power method, and the variance method, has been compared It is found that ϵ from the spectral width method and variance method agree quite well under low background wind conditions, whereas under high background wind conditions, ϵ from the spectral width method appears to be an underestimate The ϵ from the power method is generally lower than that from the other two methods Adopting the variance method, the turbulence parameters ϵ and the eddy diffusivity for momentum Km have been estimated for tropospheric and lower stratospheric regions over Gadanki for the period 18 January 1999 to 5 March 1999, making use of the vertical wind observations from MST radar on each night for ∼2 hours Average altitude profiles of ϵ and Km for the winter season are presented The turbulence parameter profiles reveal a prominent peak in the upper troposphere From Richardson number considerations the observed turbulence is attributed mainly to wind shear

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2000JD000146

Turbulence parameters in the tropical troposphere and lower stratosphere

Lidar observations of cirrus cloud near the tropical tropopause: temporal variations and association with tropospheric turbulence

. Altitude profiles of temperature in the stratospheric and mesopheric region from lidar observations at NARL, Gadanki, India, during December 2002–April 2005, as part of ISRO's Middle Atmospheric Dynamics – "MIDAS (2002–2005)" program are used to study the characteristics of gravity waves and their seasonal variation. Month-to-month variation of the gravity wave activity observed during the period of December 2002–April 2005 show maximum wave activity, with primary peaks in May 2003, August 2004 and March 2005 and secondary peaks in February 2003 and November 2004. This month-to-month variation in gravity wave activity is linked to the variation in the strength of the sources, viz. convection and wind shear, down below at the tropospheric region, estimated from MST radar measurements at the same location. Horizontal wind shear is found to be mostly correlated with wave activity than convection, and sometimes both sources are found to contribute towards the wave activity.

/pdf/seasonal-variation-of-gravity-waves-in-the-equatorial-middle-nddlmym1bu.pdf

Seasonal variation of gravity waves in the Equatorial Middle Atmosphere: results from ISRO's Middle Atmospheric Dynamics (MIDAS) program

THE fluctuations in the signal strength of v.h.f. and u.h.f. transmissions from satellites received at ground level contain valuable information about ionospheric irregularities. These fluctuations, usually called scintillations, depend on the frequency of transmission, characteristics of the irregularities and the angle of incidence. At equatorial latitudes, there have as yet been few such observations, and there are reasons to expect the scintillation characteristics at equatorial latitudes to be quite different from those at higher latitudes because the ionospheric irregularities (mainly spread F irregularities) responsible for scintillations differ widely in their characteristics with latitude. It is also well recognised that the equatorial region is a strong scintillation zone. At Trivandrum (dip 0°57′S, geographic longitude 76°57′E), a station close to the magnetic equator, amplitude and phase scintillations of the radio beacon transmissions on 40, 140 and 360 MHz as well as the amplitude scintillations of the 860–MHz television downlink from the geostationary satellite ATS–6 have been recorded since August 1975. Here we present preliminary results on the frequency variation of the scintillation index.

Frequency variation of equatorial ionospheric scintillations

Aerosol clouds about 2 km below the trop opa use are studi ed usin g th e data from lidar and MST radar at Gadan ki. The cloud shows nuctuation s with time scales as short as 'h h in the backsca tt er ratio. Depolarization factor indicates ic.: crys tal formation when th e cloud is str ong. The MST radar wind data show stro ng turbulence below the cloud level indi ca ti ng. probably, turbulent mixin g /tran sport of wate r vapou r from lower height s to clmJd hei ght s facilitatin g cloud form ation.

http://nopr.niscair.res.in/bitstream/123456789/25988/1/IJRSP%2029%284%29%20245-248.pdf

Thin aerosol clouds at tropopause level

In this paper, 246 Rayleigh lidar observations covering the altitude range of stratosphere and mesosphere collected during the period March 1998 - December 2001 (37 months) using Indo-Japanese Lidar at National MST Radar Faculty (NMRF), Gadanki (138°N, 792°E), India are presented The atmospheric density profiles were derived Using the limited database, a climatological structure of temperature over a tropical site giving seasonal variations of upper stratosphere and mesospheric region is also presented It has been observed over Gadanki, that the stratopause is quite broad and occurred in the range of 43-58 km with the temperature maximum observed in winter and equinox periods A semi-annual variation is seen clearly around 70 km with maxima at May/June and Dec/Jan Mesospheric temperature shows strong inversion very often The average climatology over 37 months period is found to compare well with a reference atmosphere model (MSISE 90) The observed temperature is, in general, colder throughout the year in the 30-45 km range and warmer in summer at 70-80 km as compared to the model derived values The present study suggests that the 45-55 km region is less affected by temperature variability, which is well suited for the detection of possible temperature trends

http://nopr.niscair.res.in/bitstream/123456789/25730/1/IJRSP%2033%281%29%2050-57.pdf

K. Krishna Murthy

Papers

Frequency variation of equatorial ionospheric scintillations

Thin aerosol clouds at tropopause level

Lidar observations of middle atmosphere temperature variability over low latitude