S. C. Garg

Results of foF2 and Ne-h profiles at low latitude using recent digital ionosonde observations and their comparison with IRI-2000

Abstract Using digital ionosonde observations at low-latitude station, Delhi (28.6 N, 77.2 E, mag. dip 42.4 N), the diurnal and seasonal variations of the critical frequency of F2 layer (foF2) are analyzed from August 2000 to July 2001 during a high solar activity period. Also, noontime bottomside electron density (Ne-h) profiles, below the F2-peak, are derived from ionogram, using the POLAN (Report UAG-93, WDC-A, for Solar Terrestrial Physics, Boulder, Co.) program during the same period, and these profiles are then normalized to the peak height and density (hmF2, NmF2) of the F2-region. These observations are used to assess the predictability of the International Reference Ionosphere, IRI-2000 model (Radio Sc. 36(2) (2001) 261). Results show in general, a large variability, (1σ, σ is standard deviation), in foF2 during nighttime than daytime during winter and equinox, the variability of foF2 about the mean is about ±25% by night and ±15% by day. The IRI model shows a fairly good agreement with foF2 observations during daytime, however during nighttime, the discrepancies between the two exist. Comparative studies of the normalized observed profiles with those obtained with the IRI model (Bilitza, 2001) using both the options namely: Gulyaevas (Adv. Space Res. 7 (1987) 39) model and B0-Table (Adv. Space Res. 25(1) (2000) 89), show that during all the seasons, in general, the B0-Tab option, reveals a better agreement with the observations, while the IRI model using Gulyaevas option, overestimates the electron density distribution during summer and equinox, however, during winter, the model is close to the observations. The comparisons of average profile shape parameters (B0,B1) derived from noontime observed profiles, with those obtained, using B0-Tab option, in the IRI model, show a good agreement during all the seasons. However, B0, B1 obtained, using Gulyaevas option in the IRI model, show a disagreement with the derived B0, B1 values during all the seasons, except during winter, for B0 parameter.

Evening enhancements in F-region electron temperature at subtropical latitudes during June solstice in the Indian SROSS C2 RPA data

Abstract In-situ measurments of the topside F-region ionospheric electron and ion temperatures are very few over the low and equatorial latitudes during the last two solar cycles, particularly in the Indian sector. The SROSS C2 satellite has provided some valuable data on the thermal structure of the topside ionosphere over the Indian region. This article reports a typical evening enhancement in the topside F-region electron temperatures around 18:00 IST observed in the subtropical latitudes of 15–20°N. These enhancements that are seen during the low sunspot activity periods show a latitudinal difference with an early and sharp peak at higher latitudes (23°N). The observed features are explained on the basis of equatorial plasma dynamics associated with the Appleton ionization anomaly.

A Phased Array Acoustic Wind Profiler for Remote Atmospheric Wind Measurement

Abstract A phased array acoustic atmospheric wind profiler has been developed. The system has the capability to remotely measure atmospheric horizontal and vertical winds from 70 m to 770 m within the earth’s atmospheric boundary layer. This system is being operated at the National Physical Laboratory (NPL), which is located in the middle of a highly noisy environment of the city of Delhi. Moreover, due to the rich green surroundings, there are plenty of birds whose calls make measurements at acoustic frequencies very difficult. In spite of the above two limitations, the system has been successfully used to make wind measurements in the height range of 70 m to 455 m.

Design of a simple low cost tethersonde data acquisition system for meteorological measurements

A tethersonde instrument for vertical sounding in the lowest height region of the atmosphere designed using commercially available solid state sensors is presented. This instrumentation which was developed for high-resolution measurements of the vertical profiles of atmospheric temperature, humidity, and pressure to study the evolution of radiation fog in winter over Delhi, measures the pressure (800–1100milli-bar), temperature (0–35°C), and relative humidity (0–100% RH) and includes an eight-channel 12bit data acquisition unit and a low-power digital, FM telemetry system operating at 173MHz and uses a PC printer port connection for real-time data logging and operates from a single 9V supply. It is capable of providing data to high resolutions of better than 0.01°C for temperature, 0.07mb for pressure, 0.1% for the relative humidity, and the system has a response time of ∼50s. The sonde can accommodate up to six different sensors according to sounding requirements. The data are serially streamed into the ...

Clock Synchronization Experiment in India Using Symphonie Satellite

A recent clock synchronization experiment between the National Physical Laboratory (NPL), New Delhi and Space Applications Centre (SAC), Ahmedabad via geostationary satellite symphonie-II, stationed at 49°E longitude, is reported in this paper. As only one satellite transponder was available for this experiment, the two-way transmission of the clock pulses was carried out by switching the transmit—receive roles at the two stations at 5 minute intervals to achieve a nearly simultaneous two-way transmission. Taking into account all the additional delays, the results demonstrated a clock—synchronisation accuracy of better than 0.5 μs. A crystal-based portable clock flown aboard an aircraft confirmed this clock-synchronization to within a microsecond.