Causes of Large-scale Ionospheric Disturbances and Challenges in Predicting Them

Abstract:

Ionospheric disturbances, such as an increase or decrease of the peak electron density and variations of the total electron content (TEC), are known to have detrimental effects on the communication and navigation systems. Magnetospheric electric fields associated with a strongly southward interplanetary magnetic field are most effective in producing large geomagnetic storms. In addition to drive strong ion convection in the high-latitude polar regions, a fraction of magnetospheric electric fields can penetrate to middle and low latitudes, prompting nearly simultaneous ionospheric disturbances there. At high latitudes the fast-moving ions collide with neutrals to produce Joule heating. The excessive Joule heating launches large-scale gravity waves that propagate equatorward toward middle and low latitudes in the form of traveling ionospheric disturbances (TIDs). Besides the dynamical and electrodynamical processes, chemical reactions associated with composition changes also play an important role in regulating ionospheric disturbances. In a real storm event, several different processes often work in concert. Untangling the various physical processes is a great challenge to reliably predict ionospheric disturbances. This paper presents detailed model-data intercomparison to illustrate the current capabilities of the Thermosphere-Ionosphere Electrodynamics General Circulation Model (TIEGCM) in reproducing the observed large-scale TEC features during the 2015 St. Patrick’s storm, particularly features associated with penetration electric fields, neutral wind dynamics, and the subauroral polarization stream. The importance of accurately specifying the high-latitude forcing is also discussed as another great challenge to space weather prediction.