Research Article

Responding trends of ionospheric F₂-layer to weaker geomagnetic activities

¹ Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, PR China
² Innovation Academy for Earth Science, CAS, Beijing 100029, PR China
³ Beijing National Observatory of Space Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, PR China
⁴ College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, PR China
⁵ Heilongjiang Mohe Observatory of Geophysics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, PR China

^* Corresponding author: chenyd@mail.iggcas.ac.cn

Received: 18 September 2021
Accepted: 22 February 2022

Abstract

Geomagnetic activities frequently occur in varying degrees. Strong geomagnetic activities, which have been widely investigated, occur occasionally; they can cause distinguishable and significant disturbances in the ionosphere. Weaker geomagnetic activities frequently appear, whereas their effects are generally difficult to be distinguished from complex ionospheric variations. Weaker geomagnetic activities play important roles in ionospheric day-to-day variability thus should deserve further attention. In this study, long-term (longer than one solar cycle) measurements of the F₂-layer critical frequency (f_oF₂) were collected to statistically investigate ionospheric responses to weaker geomagnetic activities (Ap < 60). The responding trends of low- to high-latitude f_oF₂ to increasing geomagnetic activity are presented for the first time; they are statistically evident. Both increasing and decreasing trends can occur, depending on latitudes and seasons. The trend gradually transits from high-latitude decreasing trends to equatorial increasing trends with decreasing latitude, and this transition is seasonally dependent. As a result, the trend has a seasonal difference at mid-latitudes. The responding trend is generally more distinct at higher latitudes and in the equatorial region than at mid-latitudes, and the responding intensity is largest at higher latitudes. Although theoretically, geomagnetic activities can disturb the ionosphere through multiple mechanisms, the morphology of the trend suggests that the frequent weaker geomagnetic activities modulate the high- to low-latitude ionosphere mainly through disturbing high-latitude thermospheric composition and further altering the thermospheric background circulation.