α‐Chapman Scale Height: Longitudinal Variation and Global Modeling

Abstract

AbstractScale height measures the altitude gradient of the electron density profile and relates with the ionospheric chemistry and dynamics, while its longitudinal variation has not been fully investigated in both statistical analyses and empirical modelings. In this study, 11‐year electron density profiles from Constellation Observing System for Meteorology, Ionosphere, and Climate radio occultations are collected to retrieve the α‐Chapman scale height (Hm) from the lower topside ionospheric electron density profile (within 200‐km altitudes above the peak height of F2 layer [hmF2]) by fitting α‐Chapman function with a constant scale height. The Hm shows evident longitudinal variations at midlatitudes, and its zonal structure shows a consistency with that of hmF2 during daytime, which indicates neutral winds change the ionospheric height and shape at the same time. Further, a global modeling of Hm named 2PCAFourier‐Hm is built based on a two‐layer Principle Component Analysis combined with Fourier regression analysis of its coefficients under low and moderated solar activity. Longitudinal variation is considered in the Hm's modeling, along with the variations of local time, latitude, day of the year, and solar activity. Overall, the model well captures the temporal and spatial variations of Hm with a root‐mean‐square error of 2.25 km and a correlation coefficient of 0.97 with respect to the Constellation Observing System for Meteorology, Ionosphere, and Climate observations.