GLOBAL NATURAL BACKGROUND NOISE VARIATION AT TOPSIDE OF IONOSPHERE OBSERVED BY SATELLITES IN THE LAST DECADE

摘要

The author observed the global distribution of the background noise levels on the topside of the ionosphere. The observations were conducted by means of two Japanese satellites, in the time interval between 1990 and 2001. They were conducted on frequencies: VLF (1-10 kHz), LF (180 kHz of Aurora Kilometric Radiation -AKR), and VHF (46 MHz). The noise intensity variations were measured at 160 observation points, and analyzed considering such phenomena as (1) Solar Activity, (2) Kp and AE index, (3) Seasonal and (4) Daily variations. The local variation effects appeared obvious in the noisy area spread over the northern Canada, north-eastern coast and west coast region of USA, and over north-western European Zone. Power line radiation data on 50 and 60 Hz show a good correlation with the density of the population inhabitance, as described in a recent paper [1]. The highest noisy area in the VLF and LF wave ranges appeared in both hemispheres at the latitudes few degrees higher than the aurora oval. The maximum VLF wave noise levels are shifted by approximately 6 to 10 degrees towards lower latitudes than usual. Their positions correspond very well to positive coherence with AE (and Kp) index variations. Results of these noise waves measurements, taken in various geophysical conditions, will be presented in this paper.