DIURNAL-VARIATION IN-DIFFUSION COEFFICIENT AND OCCURRENCE RATE OF RADIO METEOR TRAILS

The daily variation in the occurrence rate (per hour) of radio meteors observed by the 54.95 MHz radar operated at Trivandrum (8.5 degrees N , 77 degrees E) during each month of the year is discussed. From. the exponential amplitude decay rate of 62,081 carefully selected underden se meteor trails, the ambipolar diffusion coefficients (D) in the 80-1 05 km altitude region of the atmosphere have been determined. The D va lues have been used to study the diurnal (d), semi-diurnal (sd) and te r-diurnal (td) variations of the hourly mean diffusion coefficient of the atmosphere which corresponds to an altitude close to 92 km. These diurnal and its sub-harmonic variations have been interpreted in terms of the temperature oscillations of the mesopause region. It is found that the annual mean d oscillation of the mesopause temperature is of amplitude 21.8 K while sd and td oscillation amplitudes are both equal to 3.5 K. These results have been compared with the results from theo retical models and the scantly available observations using rockets. I t is significant to note that td mesopause temperature oscillation is as significant as sd oscillation.