Toward the Reconstruction of Substorm‐Related Dynamical Pattern of the Radiowave Auroral Absorption

Abstract

In addition to existing empirical models describing the average distributions of energetic electron precipitation into the auroral ionosphere at different activity levels, we develop and test a semiempirical approach to construct dynamical models describing the recurrent features of spatiotemporal development of auroral absorption in the ionosphere during individual substorms. Its key ingredients are (a) usage of linear prediction filter technique to extract from riometer data the response function to the injection of unit magnitude and (b) characterization of injection parameters by midlatitude magnetic variations caused by the substorm current wedge. Using global riometer network we test the method performance for stations in the middle of auroral zone (at corrected geomagnetic latitudes of 65–67°) where generally the absorption amplitude is largest. In this paper we use the midlatitude positive bay index, recently developed by X. Chu and R. McPherron, to drive the model. We evaluate the model performance, discuss the dynamical properties of energetic electron precipitation as revealed by the linear prediction filter response function analyses, and finally, we discuss possible future improvements of this method intended for both science and applications.

Ionospheric Electron Density and Conductance Changes in the Auroral Zone During Substorms

“…It is also useful to identify the isolated substorms, which are preferred in our statistical study intended to identify the systematic response to substorms. Moreover, in our companion paper, the MPB index was shown to provide a good ordering of substorm‐related precipitation into the lower ionosphere as reflected in the cosmic noise absorption measured by auroral zone riometers (Sergeev et al., 2020, hereafter referred to as Paper 1). Like in Paper 1, we chose 5 min as optimal time resolution based on observation by Nagai et al.…”

“…To identify isolated substorms, we apply recently developed midlatitude positive bay (MPB) index (Chu et al., 2015; McPherron & Chu, 2017), which is suitable to identify and characterize the time intervals and magnitudes of substorm‐related magnetic field dipolarization, closely related to intense energy injections into the inner magnetosphere and ionosphere. To reconstruct the response in substorm time and take into account different intensities of contributing substorms, we exploit the linear prediction filter (LPF) technique, which recently proved to be useful for substorm studies (Sergeev et al., 2020). In addition to the ionization at particular altitudes, we also consider the changes of important height‐integrated quantities, the ionospheric Pedersen and Hall electric conductance (Σh and Σp), which control the substorm‐related auroral electric currents.…”

Study of Substorm‐Related Auroral Absorption: Latitudinal Width and Factors Affecting the Peak Intensity of Energetic Electron Precipitation

“…In view of close relationship between equatorial and precipitating energetic electrons, it is natural that sharp nightside CNA variations with short rise time accompany the dispersionless injections (Spanswick et al., 2007), whereas the morningside CNA events are characterized by delayed gradual appearance, longer duration and eastward drifting CNA features (Kellermann, 2021). Statistical reconstructions of CNA azimuthal dynamics during substorms (Berkey et al., 1974; Sergeev et al., 2020) confirmed close dynamical coupling between nightside and morningside regions, with auroral absorption being suddenly intensified in localized region near the midnight at substorm onset, and then continuously expanding eastward. Electron flux depletion over noon and low fluxes in the afternoon sector are contributed by combined effect of precipitation losses and adiabatic flux variations on the dayside, caused by electron deceleration in the dawn‐dusk convection electric field (Korth et al., 1999; Shukhtina & Sergeev, 1996).…”

“…A possibility of using magnetic proxy of injection amplitude to infer the substorm response of auroral absorption and to reconstruct its azimuthal dynamics was recently investigated by Sergeev et al. (2020), hereafter referred to as Paper 1. They used the MPB injection proxy and applied the linear prediction filter (LPF) method which allows to account for different intensities and multiplicity of substorm injections.…”

Occurrence rate and duration of space weather impacts on high-frequency radio communication used by aviation

“…Auroral absorption is typically observed during periods of enhanced geomagnetic activity (e.g., Hargreaves, 1969) and can be characterized using various geomagnetic activity indices such as the PC index (Frank-Kamenetsky & Troshichev, 2012), the mid-latitude positive bay index (Sergeev et al, 2020), the hourly range of the magnetic field (Fiori et al, 2020), and more commonly the Kp or Ap index (e.g., Holt et al, 1961;Hargreaves, 1966;Hargreaves & Cowley, 1967;Foppiano & Bradley, 1983, 1984Kavanagh et al, 2004).…”