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Ionospheric Electron Content Measurements at Bombay, a Station Close to Appleton Anomaly Peak Region

1987-12-01T00:00:00Z

Title: Ionospheric Electron Content Measurements at Bombay, a Station Close to Appleton Anomaly Peak Region Authors: Koparkar, Pramila Abstract: The salient features of ionospheric electron content (lEC) at Bombay, a station close to the equatorial F region anomaly during low sunspot year 1984 (mean R_z = 51), are described. The daytime values of lEC show systematic increase with 10.7 cm solar flux and equatorial electrojet strength even on day-to-day basis. No clear effect of magnetic activity was seen on lEC. The daytime values of lEC in 1984 were about twice compared to those in 1975-76. Page(s): 408-410

Precipitation of Resonant Particles by ELF Waves at Low Latitudes

1987-12-01T00:00:00Z

Title: Precipitation of Resonant Particles by ELF Waves at Low Latitudes Authors: Prakash, Ram Abstract: Diffusion of particles of different energies and pitch angles resonating with ELF emissions at low latitudes is studied. The results show that the energy change required for particle precipitation increases with the increase in both the wave frequency and the L-value, implying that the resonant particles easily fall into loss cone to be precipitated into the lower region of the ionosphere due to the pitch. angle and energy changes induced by lower frequency waves towards the lower L-values. Page(s): 405-407

Effect of Lossy Ground on Radiation Characteristics of Helical Antenna Array

1987-12-01T00:00:00Z

Title: Effect of Lossy Ground on Radiation Characteristics of Helical Antenna Array Authors: Singh, D P; Dey, K K Abstract: The results of a methematical analysis of the field radiation pattern of helical antenna array of staggered halfwave dipole radiators arranged above a flat lossy ground are reported. The individual radiators are thin, linear and centre-driven dipoles. The radiation patterns for various types of lossy grounds have been obtained. The height of the antenna array above the lossy ground influences the radiation pattern and this aspect has also been studied. The ground reflection coefficients for vertically polarized fields have been obtained for different types of lossy grounds. Page(s): 401-404

Some Characteristics of Zonal Wind in the Middle Atmosphere Over India

1987-12-01T00:00:00Z

Title: Some Characteristics of Zonal Wind in the Middle Atmosphere Over India Authors: Kumar, Somesh; Nagpal, O P Abstract: Monthly averaged values of the tropospheric and lower stratospheric wind fields for 15 months period May 1982-July 1983 obtained by high altitude balloons at ten Indian stations, along with the rocket observed winds for the parallel period (1982-83) at two rocket ranges in the country are analyzed to obtain the height-latitude and time variation of zonal winds over Indian region, encompassing a latitude range of 8-28°N. The monthly mean values are also used to bring out the amplitudes and phases of the semi-annual oscillation (SAO) and annual oscillation (AO), thus providing an opportunity to obtain a first ever picture of their latitudinal variations. Similarly, a study of quasi-biennial oscillation (QBS) is made with the help of 7-year data (1977-83) at Hyderabad station (17.2°N, 78.3°E). Results show that there is easterly flow during summer months. between 10 and 15 km with a strong easterly jet of 50-60 m/s at tropopause heights during monsoonal months. The winds turn to westerlies during winter months and there is an indication that this reversal starts first at high latitude stations and at lower heights and moves equatorward ascending with time to higher altitudes. The reversal of westerlies to easterlies, on the other hand, takes place at higher altitudes (~ 50 km) and at low latitudes, descending downward with time to lower levels and moving northward. The occurrence of strong tropospheric easterly jet seems to be negatively correlated with the monsoonal activity. The SAO has an amplitude of about 5 m/s or less below 30 km altitude up to about 20ᵒN latitude, increasing to 12 m/s at 26.5ᵒN at 32 km. At higher heights, its amplitude becomes significant reaching 30 m/s at 54 kmat Thumba and 20 m/s at 50 km at Balasore. The annual oscillation, on the other hand, has a well defined peak at the tropopause height at all the stations, maximizing at about 20ᵒN latitude with an amplitude of 30 m/s. The QBO at Hyderabad station has an amplitude maximum of 8 m/s at about 25 km, reducing to about 2 m/s at 17 km. The observed features of SAO, AO and QBO in zonal winds are discussed in relation to earlier observations and some significant differences noted. Page(s): 390-400