Time and scale size of planetary wave signatures in the ionospheric F region:: Role of the geomagnetic activity and mesosphere/lower thermosphere winds -: art. no. 1403

The time and scale size of planetary wave signatures (PWS) in the mid latitude F region ionosphere of the Northern Hemisphere and the main pattern of their possible sources of origin are presented. The PWS involved in this study have periods of about 2-3, 5-6, 10, 13.5, and 16 days. The PWS in the ionosphere are large scale phenomena. PWS with periods of about 2-3 and 5-6 days have a typical longitudinal size of 80degrees, they are coherent some 6000 km apart, and they occur about 12% and 14% of the entire observational record respectively. The typical longitudinal size of PWS with periods of about 10 and 13 days is 100degrees, they are coherent some 7500 km apart, and they occur about 24% and 22% of the entire observational record respectively. PWS with periods of about 16 days seem to be global scale phenomena, and they occur about 30% of the entire observational record. The results estimate that geomagnetic activity variations play the most important role for driving PWS in the ionosphere. The geomagnetic activity variations can drive at least 20-30% of the PWS with periods of about 2-3, 5-6, 10 and 16 days, but even up to 65-70% for the PWS with periods of about 10 and 16 days, and they practically drive 100% of the PWS with periods of about 13.5 days. The planetary wave activity in the mesosphere/lower thermosphere (MLT) winds can drive about 20-30% of the PWS with periods of about 2-3, 5-6, 10 and 16 days. There is a significant percentage of existence of PWS in the F region apparently 'independent' from the geomagnetic activity variations and of the MLT winds. The latter is better expressed for PWS with shorter period. PWS with periods of about 13.5 days are an exception to that. A candidate mechanism for the 'independent' events may be the non linear interaction or the amplitude modulation between different PWS.