[P-EM12] Coupling Processes in the Atmosphere-Ionosphere System

[PEM12-P14] The Occurrence Characteristics of Daytime Spread F in the Low Latitude Regions During 2013-2020 Observed by Puer Ionosonde

*Lehui Wei^1,2、Chunhua Jiang¹、Tatsuhiro Yokoyama² (1.School of Electronic Information, Wuhan University, Wuhan, Hubei, China、2.Research Institute for Sustainable Humanosphere, Kyoto University, Uji, Japan)

キーワード：Daytime Ionospheric Irregularities/Spread F, Low Latitude Ionosphere, Ionosphere Electrodynamic Effect

Spread F-like irregularities are usually known as being generated at nighttime and disappear before sunrise. However, there are a few reported cases that suggested these spread F irregularities structures could be observed during the daytime period. Due to the rarity of daytime spread F (DSF), and the difficulty in determining when and where these daytime F-region irregularities are initially generated, their generation mechanism and occurrence characteristics remain unresolved. Using the Puer (22.7°N, 101.05°E, dip lat.13.21°N) ionosonde, F-region diffuse echoes were observed on the daytime ionograms from local sunrise to local sunset during 2013-2020. The observation results show that DSF could appear at any time from early morning to late afternoon, with a maximum occurrence rate near the local sunrise terminator. Regarding the morphological type of DSF, daytime F-region diffuse echoes on the ionograms are mainly frequency spread F (FSF), rarely mix spread F (MSF) or range spread F (RSF). The occurrence characteristic of DSF is characterized by a high occurrence rate in the summer months, especially in the June solstice. Statistical analysis of solar and geomagnetic activities during 2013-2020 and the date of DSF occurrences found that DSF is closely dependent on solar and geomagnetic activities, and DSF prefers to occur in the background of geomagnetic disturbance and higher solar activity. In addition, observations of DSF events also showed that the local time dependence of DSF varied with seasons, geomagnetic and solar activities. In equinox, with active geomagnetic conditions and high solar activity, DSF occurs only in the morning to noon with a high occurrence rate near sunrise. However, in summer, with quiet geomagnetic conditions and low solar activity, DSF appears more frequently in the afternoon hours with a high occurrence rate near sunset. Compared with observation characteristics of nighttime SF and associated irregularities in the low latitudes, some similarities in occurrence characteristics illustrate that the origin of DSF could primarily be the remnant of nighttime plasma bubbles. At the same time, the influence of traveling ionospheric disturbances (TIDs)/atmosphere gravity waves (AGWs) and penetration electric fields on a small fraction of newly generated DSFs during the daytime cannot be ignored.