Polar tongue of ionisation during geomagnetic superstorm

Abstract

Abstract. During the main phase of geomagnetic storms, large positive ionospheric plasma density anomalies arise at middle and polar latitudes. A prominent example is the tongue of ionisation (TOI), which extends poleward from the dayside storm-enhanced density (SED) anomaly, often crossing the polar cap and streaming with the plasma convection flow into the nightside ionosphere. A fragmentation of the TOI anomaly contributes to the formation of polar plasma patches partially responsible for the scintillations of satellite positioning signals at high latitudes. To investigate this intense plasma anomaly, numerical simulations of plasma and neutral dynamics during the geomagnetic superstorm of 20 November 2003 are performed using the Thermosphere Ionosphere Electrodynamics Global Circulation Model (TIE-GCM) coupled with the statistical parameterisation of high-latitude plasma convection. The simulation results reproduce the TOI features consistently with observations of total electron content and with the results of ionospheric tomography, published previously by the authors. It is demonstrated that the fast plasma uplift, due to the electric plasma convection expanded to subauroral mid-latitudes, serves as a primary feeding mechanism for the TOI anomaly, while a complex interplay between electrodynamic and neutral wind transports is shown to contribute to the formation of a mid-latitude SED anomaly. This contrasts with published simulations of relatively smaller geomagnetic storms, where the impact of neutral dynamics on the TOI formation appears more pronounced. It is suggested that better representation of the high-latitude plasma convection during superstorms is needed. The results are discussed in the context of space weather modelling.

Satellite In Situ Electron Density Observations of the Midlatitude Storm Enhanced Density on the Noon Meridional Plane in the F Region During the 20 November 2003 Magnetic Storm

“…These characteristics deduced from Figure 11 are consistent with the SED dusk plume seen in the vertical TEC map over North America (Skone et al, 2004). Pokhotelov et al (2021Pokhotelov et al ( , 2008 examined TEC maps in the polar cap. They showed that TOI appeared after 17 hr UT.…”

“…High latitude Joule heating in the auroral zone generally produces meridional winds and generates storm wind cells during storms. Pokhotelov et al (2021) had examined meridional neutral winds (VN) at pressure levels corresponding to ∼120 and ∼400 km geopotential heights, E×B convection flow, and the Joule heating per unit mass (QJOULE). They noted that the high-latitude plasma convection pattern greatly expands equatorward and develops the characteristic two-cell pattern through the storm's main phase.…”

“…They also studied middle-low latitude thermospheric composition and neutral temperature responses (Yu, Wang, Ren, Cai, et al, 2021). Finally, Pokhotelov et al (2021) conducted TIEGCM simulations to investigate the polar cap TOI features observed during the storm. They showed that a complex interplay between electrodynamic and neutral wind transports contributes to forming a midlatitude SED anomaly.…”

High Latitude Ionospheric Gradient Observation Results from a Multi-Scale Network

“…Multiple publications are available addressing the specific aspects of the ionospheric phenomena typical for high latitude/auroral regions such as the storm-enhanced density (SED)/tongue of ionization (TOI) creation mechanisms [ 7 , 8 , 9 ], processes behind formation and perturbations of the polar cap patches [ 10 , 11 , 12 , 13 ] and auroral blobs [ 14 , 15 , 16 ], as well as the general cusp dynamics associated with polar patch production [ 17 ]. Created in the dayside cusp region, the high plasma densities of the polar cap patches (polar cap patches are defined as 100–1000 km scale regions with plasma densities 2–10 times higher than that of the surrounding plasma [ 11 , 12 ]) move with the local magnetospheric-driven convection, typically drifting across the polar cap and becoming increasingly structured due to plasma instabilities [ 7 , 8 , 18 ]. Some of the polar cap patches exit the polar cap and enter the nightside auroral latitudes becoming boundary/auroral blobs [ 11 , 12 , 18 ] leading to strong plasma irregularities when combined with nightside aurora [ 13 ].…”

Dynasonde Observations of Ionospheric Polar Holes Under Quiet Geomagnetic Conditions at Jang Bogo Station, Antarctica

“…During geomagnetic storms, the polar tongue of ionization (TOI) is observed to be a continuous density enhancement along the convecting plasma from dayside to nightside. TOI extends poleward from the dayside storm‐enhanced density anomaly, crossing the polar cap and entrained in the global convection pattern into the nightside ionosphere (e.g., Foster et al., 2005; Pokhotelov et al., 2021). Since polar cap patches and TOI are initiated in a dayside region equatorward of the cusp, both high‐density structures do not originate inside the polar cap.…”