Ground-Based GNSS and Satellite Observations of Auroral Ionospheric Irregularities during Geomagnetic Disturbances in August 2018.

Irina Zakharenkova,Andrzej Krankowski,Iurii Cherniak

doi:10.3390/s21227749

Abstract

The 25–26 August 2018 space weather event occurred during the solar minimum period and surprisingly became the third largest geomagnetic storm of the entire 24th solar cycle. We analyzed the ionospheric response at high latitudes of both hemispheres using multi-site ground-based GNSS observations and measurements onboard Swarm and DMSP satellites. With the storm development, the zones of intense ionospheric irregularities of auroral origin largely expanded in size and moved equatorward towards midlatitudes as far as ~55–60° magnetic latitude (MLAT) in the American, European, and Australian longitudinal sectors. The main ionospheric trough, associated with the equatorward side of the auroral oval, shifted as far equatorward as 45–50° MLAT at both hemispheres. The interhemispheric comparison revealed a high degree of similarity in a large expansion of the auroral irregularities oval towards midlatitudes, in addition to asymmetrical differences in terms of larger intensity of plasma density gradients and structures over the Southern auroral and polar cap regions. Evolution of the intense ionospheric irregularities and equatorward expansion of the auroral irregularities oval were well correlated with increases of geomagnetic activity and peaks of the auroral electrojet index.

Highlights

Formation and evolution of plasma density irregularities in the Earth’s ionosphere in response to space weather phenomena represent one of the fundamental problems of near-Earth plasma physics and a challenging task for operational models and space weather prediction
One of the most important phenomena of a geomagnetic storm is a magnetospheric substorm, in which a significant amount of energy derived from the solar wind–magnetosphere interaction is deposited into the auroral ionosphere and magnetosphere [8,9]
The energy input coming from the magnetosphere–ionosphere interaction in the form of enhanced electric fields, currents, and energetic particle precipitation perturbs the ionosphere through high-latitude ionization, Joule and particle heating, ion-drag forcing, and disturbed electric fields, producing ionospheric plasma irregularities and gradients enhancements [10,11,12]

Summary

Introduction

Formation and evolution of plasma density irregularities in the Earth’s ionosphere in response to space weather phenomena represent one of the fundamental problems of near-Earth plasma physics and a challenging task for operational models and space weather prediction. The most severe ionospheric irregularities occur primarily in the equatorial region, within a band of 20◦ S–20◦ N of magnetic latitudes (MLAT), and at the high-latitude region, above ~65◦ MLAT, which includes auroral and polar cap regions These boundaries vary with time of day, season, sunspot number, and geomagnetic activity level. At the growth phase of a substorm, dayside magnetic field reconnection between the southwardly directed IMF and the geomagnetic field increases the number of open field lines—as a result, the polar cap expands due to the added open flux, and the auroral oval migrates equatorward to lower latitudes. Auroral particle precipitation creates highly structured enhancements and gradients of the ionospheric plasma density Such ionospheric irregularities occurring during intense geomagnetic storms can cause rapid phase fluctuations in Global

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