Diurnal Variations of Atmospheric Noise in the Evening Transition Period

The analysis of atmospheric noise burst level data collected at Delhi for one complete year by Aiya´s method during the evening transition period shows that there are large systematic diurnal variations in all the parameters, viz., the proportion of days on which the noise is received in the burst form, the median noise levels, and the upper decile noise leyels. These have been related to the characteristics of sources and propagation. The comparison of Delhi data with the data collected at Bangalore and Poona by the same method shows good agreement. However, it is noted that the activity remains constant during 16-20 h at Bangalore, whereas it decays with time at Delhi. This is attributed to the difference in thunderstorm activity at two places because of the difference in their latitudes. The data were also compared with the data collected previously at Delhi by using standardized recording equipment (the ARN-2 radio noise recorder) developed by the National Bureau of Standards (NBS). The trends of variations are similar. As there are large systematic variations, it is suggested that for 16-20-h time period, hourly values may be given in the predictions of atmospheric noise data.