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[en] Complete text of publication follows. A solar terminator wave has been revealed in thermospheric wind and density simultaneously observed by CHAMP. The wind terminator wave is out of phase with the density terminator wave. But both have wavefronts about 30 circ$ inclined to the terminator line at low latitudes, and wavelengths ranging between 3000-5000 km. They show a clear dawn-dusk asymmetry, with more pronounced wave signatures forming at dusk. Terminator wave is indiscernible in the dawnside wind. Most wave structures are observed at night, with some extension to the sunlit region around solstices. The midnight density maximum is seen to be closely connected to terminator wave structures, hence indicating a possible role of terminator waves in its formation.
[en] The electrojet field in the Indian region, on days when counter-electrojet afternoon event occurs, is considered to be composed of two components, a normal quiet-day electrojet field and an additional field superposed on it. The additional field in horizontal intensity, deduced from the data, shows a northward field with its maximum at about 1000 LT followed by a rapid decay and reversal of direction shortly after local noon. The northward additional field in the forenoon appears to be present on most of the days of counter-electrojet afternoon event and on some days it is greater than the southward field in the early afternoon. The early afternoon southward field, with its peak, value around 1500 LT, also decays rapidly and vanishes well before the sunset. Associated vertical force effects at a station, about 2.50 to the north of the dip equator, support these features of the additional field
[en] The long term variation of diurnal anisotropy has been investigated on geomagnetically quiet days (QD) using the experimental data of the cosmic ray intensity from the world-wide neutron monitoring stations. It is found that the characteristics of the annual average diurnal anisotropy on QD is similar to that observed when all days are considered. The similarity continued even during 1971 and onwards where the diurnal time of maximum has shifted very significantly to earlier hours. This conclusion is also valid, in general, on monthly average basis. Nevertheless, during July-Sept. 1976, the diurnal anisotropy on QD is observed in the early morning hours with almost insignificant amplitude. The diurnal amplitude for all days during July-Sept. 1976 is also small, however, the phase is in normal direction. These are compared with the values so obtained for July-Sept. 1954, 22 years ago. It is suggested that for examining the nature of the diurnal anisotropy either on long or short term basis, the QD are more informative
[en] Complete text of publication follows. We investigate the day-to-day variability of the plasma bubble activity by analyzing the TIMED/GUVI, ROCSAT-1, DMSP, and CHAMP satellite data. The pre-reversal enhancement (PRE) is known as the most important single parameter for the onset of plasma bubbles but we do not know yet to what extent the day-to-day variability of the bubble activity can be attributed to the PRE. We will obtain the magnitude of the PRE from ROCSAT-1 and the occurrence of bubbles in relation to the PRE will be investigated by using the coincident observations of bubbles from TIMED/GUVI, DMSP, and CHAMP. By conducting one-to-one comparison of the PRE characteristics with the bubble occurrence we will examine the role of the PRE in the onset of bubbles.
[en] Harmonic analyses of the monthly average daily variations observed with the neutron monitors are carried out for all the stations compiled in WDC-C2 for Cosmic Rays during the period 1964-74. Besides usual harmonic coefficients, three kinds of amplitude errors are estimated. The internal error is estimated from the total counts analyzed. The external error is obtained from the residual variation after the daily variation is fitted to a sine curve with higher harmonics. It is shown that the external errors are slight but significantly greater than the internal errors. This indicates that there still remain variations which can not be simulated by the harmonics. Some of them arise from anomalous sudden variations such as Ground Level Enhancements and great Forbush decreases. It is found that the errors obtained from scatters of monthly diurnal vectors are nearly constant regardless of the internal errors. It means there are significant month to month variations in diurnal variations
[en] The data of cosmic-rays for about three solar cycles are analysed to study the long term changes of the solar diurnal variations on the base of the model of the two-ways anisotropy of cosmic-rays in the interplanetary space. As a result, it is revealed that one of the two anisotropies lies in the day side in the interplanetary space and the other lies in the nightside; furthermore, it is shown that the direction of each anisotropy varies in the period of double solar cycle as follows: they lie in around 3 hr. L.T. direction and around 15 hr. L.T. direction, respectively, for the period of expected negative polarity of the magnetic field of the sun while they lie in the directions of around midday and midnight, respectively, for the expected positive polarity, where the polarity of the magnetic field of the sun is defined as positive when the solar general magnetic field is away from the sun at the north pole of the sun and negative polarity for the opposite direction