Solar- Terrestrial Predictions in regard to Ionospheric Absorption of Radio Waves

Abstract

The AI-ionospheric radiowave absorption, <i>L_dB</i>, measured on three different frequencies, viz. 1.8, 2.2 and 2.5 MHz at Ahmedabad (Iat., 23^ᵒN; long., 72.6 E; mag. dip 34°N) during the 9-yr period (1972-1980) of the solar cycle 20-21 is studied for finding its relationship with solar activity at different times of the day or solar zenith angles (SZA) <img src='/image/spc_char/lembda.gif' border=0> for each month of the year. It is found that the cos <img src='/image/spc_char/lembda.gif' border=0> -index, <i>n</i>, for diurnal variation of absorption does not undergo much change with solar activity and it remains at a mean value of about 0.8 with a scatter of up to ±0.3 depending on the season. The variation of absorption is more sensitive to solar activity at higher SZA both in respect of the time of the day and the season. The smoothed 12-monthly running average of <i>L_dB</i> and R: show that the former increases by a factor of about √2 when the latter goes up to 110, beyond which the rate of increase of absorption slows down, finally stopping to increase any further. Two examples are given to illustrate the method of prediction of diurnal variation of absorption in different seasons for a specified solar activity, and application of these in practical radio communication. The predicted values are found to be in good agreement with the observed values of absorption.