• A global model of Ne profile in F region ionosphere was constructed based on the α-Chapman function • The model gives 3-D Ne as well as five key parameters of Ne profile, including NmF2, hmF2, Hm and its change rates with height • The model reasonably reproduces the equatorial ionization anomaly and midlatitude trough Accepted Article This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as

Scale 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. Plain Language Summary Scale height is the logarithmic altitude gradient of the electron density profile and tightly relates with ionospheric dynamics, plasma thermal structure, and composition. However, longitudinal dependence of scale height has not been fully investigated especially at midlatitudes. Longitudinal variation is such that ionospheric parameters show evident zonal difference at the same local time. Moreover, nearly no empirical models of scale height include the longitude as a variable though Liu et al. (2008, https://doi.org/10.1029/2008JA013490) found equatorial scale height has evident wave-like longitudinal variation.In this study, more than 4,100,000 samples of α-Chapman scale height (Hm) were retrieved from 11-year electron density profiles of Constellation Observing System for Meteorology, Ionosphere, and Climate. We found the midlatitude Hm has evident longitudinal variation, and its zonal structure is tightly relates with neutral winds' dynamics during daytime. Moreover, a five-dimensional (latitude, local time, longitude, day of year, and solar activity) empirical model of Hm is built based on a two-layer Principle Component Analysis combined with Fourier regression analysis of its coefficients. An executable MATLAB live code of this model is also provided in the supporting information.

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