An improved model of energetic electron precipitation providing a long-term ionization data set for CMIP7

Abstract

Medium-energy electron precipitation (MEE; energies between about 30 keV and 1 MeV) in the upper atmosphere is a source of a chain of chemical reactions which ultimately affect temperature and circulation in the lower atmosphere, and is therefore a significant component to be taken into account in chemistry climate models. In this paper, a new electron precipitation model is presented, offering several upgrades and improvements over earlier versions. The model was developed using the electron flux observations of the Polar-orbiting Operational Environmental Satellites (POES) from 1998-2023. The electron content of the bounce loss cone was derived from both the 0-degree and 90-degree channels of the latest generation of the instrument onboard POES in combination with a theoretical model of pitch-angle diffusion. The data were corrected and calibrated for proton contamination and instrument sensitivity. The electron fluxes are modelled separately in three separate energy ranges (30-100, 100-300 and 300-1000 keV), with a 1-day time resolution, as functions of corrected geomagnetic latitude and of time series of the geomagnetic index Ap. In the model, the Ap index is integrated over a convolution function in time, to account for a latitude- and energy-dependent delay in response to geomagnetic disturbances. The energy spectrum between 30 and 1000 keV was constructed from these three modelled energy bins by fitting a two-section power-law model. The resulting energy-flux spectra are used to calculate atmospheric ionization rates, which provide the solar forcing from medium-energy electrons, to serve as input into long-term atmosphere and climate simulations.