NOPR Collection:

High amplitude anisotropic wave train events in the cosmic ray intensity during 1981-90

2016-10-13T06:39:47Z

Title: High amplitude anisotropic wave train events in the cosmic ray intensity during 1981-90 Authors: Kumar, Santhosh; Chauhan, M L Abstract: The high amplitude anisotropic wave train events (HAEs) in cosmic ray (CR) intensity have been investigated during the period 1981-90 using the neutron monitoring data for different latitudes. In all, 21 HAEs have been studies. It has been observed that the phase of the diurnal anisotropy remains in the same co-rotational direction for majority of the events. On the other hand, the phase of the diurnal anisotropy changes to later hours in some of the events. Further, the amplitude of the semi-diurnal anisotropy for HAEs remains statistically the same, but the phase of the semi-diurnal anisotropy has been found to shift to later hours for all events. Furthermore, the HAEs occur dominantly during the declining phase of the solar activity. The geomagnetic activity index (Ap) has been observe to remain low during the period of each HAE. The possible sources to cause the enhanced daily variation have been proposed to occur on the backside of the sun. Page(s): 232-235

Solar radio burst on 30 September 1993

2016-10-13T06:38:03Z

Title: Solar radio burst on 30 September 1993 Authors: Vats, Hari Om; Deshpande, M R; Iyer, K N; Kondo, T; Isobe, T Abstract: The metrewave observations of a type-III radio burst which occurred on 30 Sep. 1993 have been described. The spectrum of the burst was obtained by new Hiraiso radio spectrograph (HiRAS) and time-resolved single frequency observations were made by two 103 MHz radio telescopes located at Thaltej and Rajkot. The burst peaked at ~ 165 MHz. The burst spikes appeared to be caused by relativistic beam of particles having velocities in the range of 0.1 – 0.3 c, where c is the velocity of light. Page(s): 228-231

Generation of perturbation electric field suitable for triggering of equatorial spread-F by gravity waves in the E-region and zonal winds in the F-region

2016-10-13T06:35:24Z

Title: Generation of perturbation electric field suitable for triggering of equatorial spread-F by gravity waves in the E-region and zonal winds in the F-region Authors: Prakash, S Abstract: A new mechanism for the generation of perturbation electric fields which can produce irregularities in the electron density in the F-region, which in turn can act as seed irregularities suitable for the growth of equatorial spread-F is described. The mechanism involves (i) gravity wave winds in the E-region producing electron density irregularities which in turn make the flux tube integrated Pedersen and Hall conductivities non-uniform in this region, (ii) eastward winds in the base of F-region and in the intermediate region which give rise to downward electric fields through dynamo action, (iii) these downward electric fields transport the plasma from 130 km region into the lower E-region and thus enhance the Hall conductivity in the E-region, (iv)the eastward electric fields transport the ionization upwards, thereby decreasing the conductivity in the region between 130 km and the base of the F-region, and, (v) the zonal currents, driven by the electrojet fields and the F-region dynamo fields while flowing in the non-uniformly conducting E-region give rise to the required perturbation electric fields. Using realistic values of various parameters, the amplitudes of perturbations in the vertical plasma drift velocities was found to be as large as 6.5 ms^-1. This amplitude is much larger than 1.3 ms^-1 required to produce 5% perturbation in the electron density near the base of the F-region normally used in the simulation of the equatorial spread-F. Page(s): 211-227

Atmospheric total ozone content from spectral extinction measurements

2016-10-13T06:28:55Z

Title: Atmospheric total ozone content from spectral extinction measurements Authors: Satheesh, S K; Moorthy, K K Abstract: The estimation of columnar content of atmospheric ozone from multispectral solar extinction measurements in the visible and near infra-red range is described and has been applied to the ground-based multiwavelength solar radiometer (MWR) data for the period December 1993-May 1995 at the coastal station, Trivandrum (8.55°N, 77°E). The estimated values of total ozone content compare well, on an average, with the climatological monthly means obtained from the other measurements, except during the monsoon months. The disagreement during monsoon months appears to be the manifestations of local meteorological processes which cause significant changes in the aerosol size distribution and hence the spectral variation of aerosol optical depths. Page(s): 204-210