S. K. Dhaka

Ionospheric absorption on October 24, 1995 solar eclipse

The ground based vertical radio wave propagation experiment was conducted at the frequency of 2.5 MHz to study variations in ionospheric radio wave absorption during partial solar eclipse that occurred on October 24, 1995 at Delhi (28.6°N, 77.2° E). It was observed that the minimum in absorption data was four minutes earlier than the ground level eclipse totality, and an anomaly was accompanied by an abnormal sharp rise (shock-like wave structure) in absorption data around 30 minutes after the eclipse totality. Absorption during post-eclipse control days was higher compared to those on pre-eclipse control days.

PLANETARY WAVE EFFECT ON IONOSPHERIC ABSORPTION

Abstract A relationship is examined between quasi-periodic fluctuations in absorption data at ionospheric altitudes and wave perturbations in wind data at tropospheric, stratospheric and lower mesospheric heights at Indian latitudes. The spectral analyses using Maximum Entropy Method (MEM) reveal almost the same band of periodicities in both the parameters. The important band of frequencies of 6–8 days and between 20–25 days in wind data are found to propagate up to mesospheric heights and are well reflected in absorption data. These fluctuations in absorption data are thought to be due to the vertical propagation of Rossby waves on different time scales. The correlation coefficient between absorption and wind data are found to be of the order of 0.5 to 0.75 at 95% confidence level in most of the cases at a lag of 1 to 5 days with lower stratospheric zonal winds. The lag reduces considerably when the correlation coefficient was computed at 60 km altitude using rocket data. Another important finding is that when the QBO is in the easterly phase the long-period band preferably shows a predominance of 20–25 days, while during the westerly phase of the QBO, this band of periods extends to 30–45 days, which is consistently observed in quasi-periodic fluctuations of both absorption and wind data. This may have possible implications of coupling between the stratosphere and mesosphere through the QBO.