NOPR Collection:

Evaluation of GPS PDOP from elevation and azimuth of satellites

Mon, 01 Apr 1996 00:00:00 GMT

Title: Evaluation of GPS PDOP from elevation and azimuth of satellites Authors: Banerjee, P; Bose, Anindya Abstract: Evaluation of position dilution of precision (PDOP) is very important for optimum selection of visible GPS satellites in order to get good accuracy I position fixing. A formulation to evaluate PDOP only from the knowledge of elevation and azimuth of GPS satellites has been developed. A program has been developed to compute PDOP with the above formulation. The PDOP thus computed matches well with the data available in GPS receiver. This formulation will be useful to plan many common view GPS experiments. Page(s): 110-113

Unusually low amplitude anisotropic wave train events in cosmic ray intensity

Mon, 01 Apr 1996 00:00:00 GMT

Title: Unusually low amplitude anisotropic wave train events in cosmic ray intensity Authors: Kumar, Santosh; Chauhan, M L Abstract: The exceptionally low amplitude anisotropic wave train events (LAEs) have been investigated using the neutron monitoring cosmic ray intensity data during the period 1981-90. It has been observed that for majority of the LAEs, the phase of the diurnal anisotropy remains in the corotational direction. However, for some of the LAEs, the shift in the phase of the diurnal anisotropy has been observed to early hours. Further, the LAEs have been observed to be dominant during the period of minimum solar activity. The interplanetary magnetic field (IMF) and solar wind plasma (SWP) parameters and also different features at solar disc have been investigated. The results indicate that the LAEs are the consequence of the accumulated effect of the multiple probable sources acting in such a way that the amplitude remains low continuously for the successive days and phase in the corotational direction; or the amplitude remains low regularly for the number of days, but the phase shifts to earlier hours. Page(s): 106-109

Quasi-biennial oscillations in quiet-day ranges of low latitude geomagnetic H component

Mon, 01 Apr 1996 00:00:00 GMT

Title: Quasi-biennial oscillations in quiet-day ranges of low latitude geomagnetic H component Authors: Kane, R P Abstract: After correcting for long-term variations, the geomagnetic H ranges at Trivandrum, Kodaikanal, Annamalainagar (equatorial electrojet region, India) for 1972-90 showed strong QBOs (Quasi-biennial oscillations) while Alibagh (low latitude, India) showed weak QBO. Sunspots showed very weak QBO. The geomagnetic QBO matched very roughly with QBO of stratospheric (50 mb) equatorial zonal winds, which, in turn, seems to be linked with tropospheric weather cycles Page(s): 101-105

Periodicities and spread-F associated with large-scale travelling ionospheric disturbances

Mon, 01 Apr 1996 00:00:00 GMT

Title: Periodicities and spread-F associated with large-scale travelling ionospheric disturbances Authors: Bowman, G G Abstract: Spread-F associated with large-scale travelling ionospheric disturbances (LS-TIDS) has been discussed and examined by considering fixed-frequency phase-path information for an event on October 24/25, 1990 at Bribie Island, near Brisbane, Australia. The results suggest that radiowave reflections from the titled isoionic surfaces, which are produced by LS-TIDs with certain periodicities, are not responsible for the spread. Instead, it seems likely that the wave amplitudes of medium-scale travelling ionospheric disturbances (MS-TIDs), which are also present at these times, are enhanced when the LS-TID macroscale height changes occur. It is suggested that these wave amplitudes are sufficiently enhanced (due to lower neutral densities) to allow the significant off-vertical reflections which are responsible for the spread. Also, during the equinoctial periods of some sunspot-maximum years, it is shown using phase-path rates of change of the main trace of the F₂ layer that the LS-TIDs have preferred periodicities of 35 and 17 min. Page(s): 93-100