NOPR Collection:

Size distribution of radar echoes from convective clouds around Delhi during monsoon season

Sat, 01 Jun 1996 00:00:00 GMT

Title: Size distribution of radar echoes from convective clouds around Delhi during monsoon season Authors: Chatterjee, R N; Ali, K; Prakash, Prem; Majumdar, S C Abstract: The size distributions of radar echoes from convective clouds observed in Delhi region during each monsoon season of the 6-year period from 1967 to 1972 have been investigated. It has been found that the size distribution of about 99 per cent of the total echoes in each monsoon season and covering echoes up to diameter 35 km (30 km in 1972) are well represented by the exponential distribution N_D = a exp (-b), where N_D is the number of echoes in the diameter interval D to D + D, is the mid-value of the interval, i.e. D + D/2, and a and b are the coefficients to describe the exponential distribution. The possibility of using these results in connection with the estimation of rain attenuation for millimeter wave propagation has been discussed. Page(s): 124-128

Measurement of field intensity of radio signals, atmospheric noise and UV radiation during the total solar eclipse of 24 October 1995

Sat, 01 Jun 1996 00:00:00 GMT

Title: Measurement of field intensity of radio signals, atmospheric noise and UV radiation during the total solar eclipse of 24 October 1995 Authors: Bhattacharya, A B; Kar, S K; Bhattacharya, R; Basak, J Abstract: During the period of the solar eclipse of 24 October 1995, both MF and HF band signal strengths were noticeable increased while the VLF atmospherics showed a fading pattern presumably due to ionospherics showed a fading pattern presumably due to ionospheric irregularities at such times. It was also observed that the UV-A intensity was sharply reduced during the peak phase of the eclipse. Page(s): 173-174

Association of fire-hose instability and geomagnetic activity in the plasma sheet

Sat, 01 Jun 1996 00:00:00 GMT

Title: Association of fire-hose instability and geomagnetic activity in the plasma sheet Authors: Bindu, S; Renuka, G; Venugopal, C Abstract: During maximum solar activity years (1978-79) and at low geomagnetic activity, the temperature of plasma sheet (PS) in the tail region of earth’s magnetosphere is found to be decreasing. The heating of the plasma sheet ions can occur both adiabatically and non-adiabatically. The strong ion heating associated with substorm-onset occurs in a non-adiabatic fashion with a strong increase of specific entropy, and this heating is found to be localized since both low and high entropy plasmas are present in the plasma sheet. During high activity periods, plasma sheets was found to be surviving against particle loss and heat transport. The chaotic behaviour of the plasma sheet during the selected substorm events is also discussed. Page(s): 168-172

Daytime amplitude scintillations at a low latitude station, Calcutta

Sat, 01 Jun 1996 00:00:00 GMT

Title: Daytime amplitude scintillations at a low latitude station, Calcutta Authors: Das, S K; Chakrborty, S K; Das, A Abstract: The paper deals with ionospheric scintillations of the 136 MHz signal from the geostationary satellite ETS-II observed during daytime at Calcutta (23°N; 88.5°E; 32°N dip) which is situated well outside the equatorial electrojet region. Observations over a solar cycle (1977-1986) show that daytime scintillation occurrence with sunspot number. Simultaneous record of Faraday polarization angle of the satellite signal shows that all the cases of daytime scintillations occur when there are definite signatures of travelling ionospheric disturbances (TIDs) which are manifestations of atmospheric gravity waves. However, the reverse is not true. There are days when the Faraday rotation record exhibited periodic structures but no scintillation in amplitude was observed. Page(s): 163-167