Characteristics of Enhanced and Low Amplitude Anisotropic Wave Trains and Interplanetary Transients

The occurrence of a large number of high and low amplitude anisotropic wave train events over the years 1981–1994 has been examined along with the different solar features. The results indicate that the time of maximum of diurnal variation significantly remains in the 18-h direction for majority of the high and low amplitude wave trains. The amplitude of diurnal anisotropy remains significantly high and phase shifts towards earlier hours as compared to the quite day annual average values for majority of the HAEs. The diurnal amplitude remains significantly low and phase shifts towards earlier hours as compared to the quiet day annual average values for majority of the LAEs. The occurrence of these enhanced/low amplitude events is found to be dominant during the positive polarity of the Bz component of the interplanetary magnetic field. The amplitude of the diurnal anisotropy of these events is found to increase on the days of magnetic cloud as compared to the days prior to the event and it found to decrease during the later period of the event as the cloud passes the Earth. The high-speed solar wind streams do not play any significant role in causing these types of events. The interplanetary disturbances (magnetic clouds) are also effective in producing cosmic ray decreases.