NOPR Collection:

Evaluation of capacitance matrix of artificial orbiting satellites

2015-12-01T00:00:00Z

Title: Evaluation of capacitance matrix of artificial orbiting satellites Authors: Alad, Rizwan H; Chakrabarty, S B Abstract: The paper presents the evaluation of capacitance matrix of an artificial orbiting satellite considering a composite metallic structure of a parabolic reflector antenna with cuboid and plates. Integral equations are formed by relating the unknown charge density on the metallic conductor and are solved using the Method of Moments (MoM) in which the pulse functions are used as basis functions and the delta functions are used as testing functions. The surfaces of the conducting structure are meshed using non-uniform triangular patches. The matrix equations are solved by iterative generalized minimum residual (GMRES) algorithm. The numerical data on the capacitance matrix and charge distribution of these structures have been presented. The capacitance of a metallic cuboid is computed to validate the approach. Page(s): 199-204

Equatorial electrojet in the African sector

2015-12-01T00:00:00Z

Title: Equatorial electrojet in the African sector Authors: Rastogi, R G; Chandra, H Abstract: Hourly values of the deviations in the geomagnetic X and Y field at two equatorial electrojet stations in Africa, viz. Freetown (FTN) on the western part and Addis Ababa (AAE) on the eastern part, are studied for three years 1962-64. The declination is almost along the geographic N-S at AAE and 14° towards west of the geographic N-S at FTN. The annual mean daily range in X is around 80 nT at FTN and 70 nT at AAE with peak around 1100 hrs LT. Deviations in Y at FTN show a broad minimum of about -20 nT around noon while the decrease is much smaller at AAE with a minimum of -5 nT at noon. Seasonal mean variations of the daily range in X show almost equal peaks during December solstice and equinox at FTN but at AAE it is highest during equinoctial months and lowest during June solstice. The seasonal asymmetry at FTN could be due to large declination. The equinoctial peak in March - April is higher than the peak in September - October at both the stations. Another notable feature at FTN is the steady increase in deviation in X from about -10 nT at 1800 hrs LT to 10 nT at 0600 hrs LT. The direction of the H vector is aligned almost along the geographic N-S for December solstice and equinox at AAE and along 12° W of north during June solstice. At FTN, it is aligned along about 5° W of north during D and E-months and to about 20° W of north during June solstice. Page(s): 187-198

Spread F at tropical latitude stations in India

2015-12-01T00:00:00Z

Title: Spread F at tropical latitude stations in India Authors: Rastogi, R G; Chandra, H Abstract: Regular radio soundings of the ionosphere over Ahmedabad were started in 1953 and several studies describe the various features of the ionosphere close to the equatorial ionization anomaly crest. Finer characteristics of the spread F echoes could not be studied earlier due to the very wide pulse of the transmitter. The characteristics of the spread F at Ahmedabad are described in the present paper using the recordings of recently installed Digisonde during June - July 2012. The spread F echoes at Ahmedabad are not due to the in situ produced irregularities as at an equatorial station Thumba. The spread F echoes at Ahmedabad during the June solstices of 2012 are due to reflection (not scattering) from the off-vertical direction that produce multiple traces from off-vertical direction overlapping over the main (vertical) h'-f trace, sometimes giving an appearance of diffuse echoes near the critical frequencies. Presence of medium scale traveling ionospheric disturbances (TIDs) could be a possibility to account for such off-vertical reflections. Page(s): 177-186

Study of O⁺(²P-²D) 732.0 nm dayglow emission under geomagnetic storm conditions

2015-12-01T00:00:00Z

Title: Study of O⁺(²P-²D) 732.0 nm dayglow emission under geomagnetic storm conditions Authors: Dharwan, Maneesha; Singh, Vir Abstract: The effect of geomagnetic storms on O⁺(²P-²D) 732.0 nm dayglow emission is studied using recently updated photochemical model of Thirupathaiah et al. [An updated model of O⁺(²P) 7320 Å dayglow emission, Indian J Radio Space Phys, 44 (2015), 7]. Three geomagnetic storms, which occurred on 23-27 August 2005, 13-17 April 2006 and 1-5 February 2008 are chosen in the present study. A negative correlation is found between the volume emission rate (VER) and the Dst index for all the three geomagnetic storms. The present study shows that the relative variation of VER with respect to the initial value of VER (before the onset of a geomagnetic storm) during the main phase increases above 260 km. It is also found that the altitude of the peak emission rate does not show any appreciable variation with the activity of geomagnetic storm. A positive correlation is found between the zenith intensity and the atomic oxygen number density. The atomic oxygen number density obtained from NRLMSISE-00 model is compared with the measurements of Earle et al. [Low latitude thermospheric responses to magnetic storms, J Geophys Res (USA), 118 (2013), 3866] during a geomagnetic storm. This comparison shows that the atomic oxygen number density as provided by NRLMSISE-00 model is significantly lower than the measured value. Consequently, the atomic oxygen number density is treated as a variable parameter in the photochemical model and its effect on the VER of 732.0 nm dayglow emission is further studied. The zenith intensity is found to increase about 70% even in the case of weakest storm when the atomic oxygen number density is doubled. The latitudinal effect on the VER and zenith intensity of 732.0 nm is also studied. It is found that the VER decreases as the latitude increases. The decrease in VER from low to mid latitudes is due to the decrease in atomic oxygen number density with latitude. The zenith intensity at the maximum geomagnetic activity is about 12% higher than the zenith intensity before the start of the geomagnetic storm in equatorial region. However, no appreciable change in the zenith intensity is found at higher latitudes. Page(s): 167-176

NOPR Collection:

Evaluation of capacitance matrix of artificial orbiting satellites

Equatorial electrojet in the African sector

Spread F at tropical latitude stations in India

Study of O+(2P-2D) 732.0 nm dayglow emission under geomagnetic storm conditions

Study of O⁺(²P-²D) 732.0 nm dayglow emission under geomagnetic storm conditions