NOPR Collection:

Slow Ion Acoustic Double Layers with Non-isothermal Electron Distributions

2016-10-28T10:16:41Z

Title: Slow Ion Acoustic Double Layers with Non-isothermal Electron Distributions Authors: Das, S Sutradhar; Bujarbarua, S Abstract: The existence of slow ion acoustic double layer in the presence of reflected ions and non-isothermal electrons has been pointed out. The conditions for the existence of this type of double layer have been discussed. The results may be applicable to the recent observations in the auroral plasma. Page(s): 73-74

Vertical Distribution of Water Vapour over Hyderabad Characteristic Infrasonic Waves Associated with Depressions & Cyclones in the Bay of Bengal

2016-10-28T10:15:36Z

Title: Vertical Distribution of Water Vapour over Hyderabad Characteristic Infrasonic Waves Associated with Depressions & Cyclones in the Bay of Bengal Authors: Venkatachari, R; Saha, A K; Srivastava, B J Abstract: Observations of atmospheric waves generated by cyclone centres in the Bay of Bengal using microbarographs at Delhi, Hyderabad and Calcutta are presented. There appears to be a cause-and-effect relationship between infrasonic pressure variations and microseisms generated d1¥ing a cyclone. The possibility of using a suitably deployed system for cyclone detection and monitoring is discussed. Page(s): 69-72

Vertical Distribution of Water Vapour over Hyderabad

2016-10-28T10:14:22Z

Title: Vertical Distribution of Water Vapour over Hyderabad Authors: Jayaraman, A; Subbaraya, B H Abstract: Under the Indian Middle Atmosphere Program (lMAP), a balloon carrying PRL's sun-tracking multichannel photometer was launched from Hyderabad Ba1loon Facility on 22 Oct. 1985. Radiation measurements were made in the wavelength regions of 215,290, 310,450,600 and 800 nm. The vertical distributions of zone, aerosol and water vapour concentrations are derived. The data analysis technique used and the results obtained on the atmospheric water vapour concentration are presented. The water vapour mixing ratio profile thus obtained in the altitude region of 10-31 km shows a broad minimum (called hygropause) around 16 km with a mixing ratio value of 2.82 ppmv. Page(s): 63-68

Salient Features of Amplitude Scintillations & Faraday Polarization Fluctuations at VHF Observed at Delhi

2016-10-28T10:12:18Z

Title: Salient Features of Amplitude Scintillations & Faraday Polarization Fluctuations at VHF Observed at Delhi Authors: Vijayakumar, P N; Tyagi, T R; Gupta, J K Abstract: Nighttime ionospheric scintillation phenomena of transionospheric VHF satellite signals observed at Delhi during the ascending phase of solar activity reveal certain interesting features. There is a marked difference between the scintillations observed in the premidnight period and those observed in the postmidnight period. The former is associated with explosive growth (SI > 60%) with fading rates of 10 to 15 fades/min and often, found to cause saturation of amplitude fluctuations accompanied by strong Faraday polarization fluctuations (FPFs). In contrast, the latter is of a weak nature (SI < 50%) with fading rates of 3 to 5 fades/min and often continues up to presunrise period. These may be classified as class I and class II types, respectively, similar to their counterparts observed at magnetic equator bearing distinct relationship with postsunset bottomside spread-F. Under the influence of ascending solar activity, clear seasonal trends are present in the occurrence of FPFs, with peaks in the equinoctial months, increasing with solar activity. In contrast, the occurrence of class II type scintillation shows negative correlation with solar activity in summer and equinoctial months and is independent of solar activity in the winter months. Also, it is found that the occurrence of FPFs at Delhi is conditional to their prior occurrence at a low latitude station like Hyderabad, while they die out first at Delhi and later at Hyderabad. It is concluded that class I type of scintillation and FPFs are important manifestations of a strong magnetic equator coupling in the postsunset period in the Indian sector especially during high solar activity. The scale of irregularities which cause FPFs are distinct from those that cause general class I type scintillations. Finally, the class II type observed at Delhi may be of a different origin. Page(s): 58-62