Quiet-time seasonal behaviour of the ionosphere measured by the Ionosphere PhotoMeter (IPM) on the Chinese meteorological satellite FY-3D compared with the IRI2016 model predictions

Abstract

In this paper, we examine the climatology structure of the mid-night ionosphere at approximately two o’clock local time of a low-solar-activity year and discrepancies between Ionosphere PhotoMeter (IPM) observations and IRI (International Reference Ionosphere) model-2016 predictions using (1) a global structure for the F2 layer peak electron density (NmF2) for four seasons, (2) the mean NmF2 values at different latitudes by month, and (3) the monthly distribution of the global average of NmF2. The data is collected by the IPM, a far-ultraviolet nadir- viewing photometer that has been aboard the second-generation, polar-orbiting Chinese meteorological satellite Feng-Yun 3D (FY-3D) since its launch on November 25th, 2017 and has provided excellent opportunities for many scientific investigations of the ionosphere. We collected night glow data under low geomagnetic activity (KP ≤ 4) during 2018, and the data obtained five days before and after a full-moon night were removed to prevent the influence of stray light. Before analysing the climatology of the ionosphere and comparing the results with those obtained from IRI2016, the accuracy of NmF2 measured by IPM was evaluated by comparison with data from ground-based ionosondes. A statistical comparative analysis of NmF2 measured by IPM and ionosonde indicated a difference of 20% at middle latitudes and 28% at low latitudes. The global behaviour of NmF2 measured by IPM and IRI for four seasons shows that the IRI model generally captures the morphology of the latitudinal structure and hemispheric asymmetry in NmF2 observed by IPM. A comparison between IPM-measured NmF2 and IRI-predicted NmF2 indicates that the former is systematically lower than the latter. The difference in the measurements and predictions can be as large as 300%.