Quantitative estimates of relationships between geomagnetic activity and equatorial spread-F as determined by TID occurrence levels
© The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences. 2000
Received: 11 June 1999
Accepted: 29 May 2000
Published: 6 June 2014
Using a world-wide set of stations for 15 years, quantitative estimates of changes to equatorial spread-F (ESF) occurrence rates obtained from ionogram scalings, have been determined for a range of geomagnetic activity (GA) levels, as well as for four different levels of solar activity. Average occurrence rates were used as a reference. The percentage changes vary significantly depending on these subdivisions. For example for very high GA the inverse association is recorded by a change of −33% for Rz ≥ 150, and −10% for Rz < 50. Using data for 9 years for the equatorial station, Huancayo, these measurements of ESF, which indicate the presence of TIDs, have also been investigated by somewhat similar analyses. Additional parameters were used which involved the local times of GA, with the ESF being examined separately for occurrence pre-midnight (PM) and after-midnight (AM). Again the negative changes were most pronounced for high GA in Rz-max years (−21%). This result is for PM ESF for GA at a local time of 1700. There were increased ESF levels (+31%) for AM ESF in Rz-min years for high GA around 2300 LT. This additional knowledge of the influence of GA on ESF occurrence involving not only percentage changes, but these values for a range of parameter levels, may be useful if ever short-term forecasts are needed. There is some discussion on comparisons which can be made between ESF results obtained by coherent scatter from incoherent-scatter equipment and those obtained by ionosondes.