Multiradar observations of the polar tongue of ionization

Abstract

[1] We present a global view of large-scale ionospheric disturbances during the main phase of a major geomagnetic storm. We find that the low-latitude, auroral, and polar latitude regions are coupled by processes that redistribute thermal plasma throughout the system. For the large geomagnetic storm on 20 November 2003, we examine data from the high-latitude incoherent scatter radars at Millstone Hill, Sondrestrom, and EISCAT Tromso, with SuperDARN HF radar observations of the high-latitude convection pattern and DMSP observations of in situ plasma parameters in the topside ionosphere. We combine these with north polar maps of stormtime plumes of enhanced total electron content (TEC) derived from a network of GPS receivers. The polar tongue of ionization (TOI) is seen to be a continuous stream of dense cold plasma entrained in the global convection pattern. The dayside source of the TOI is the plume of storm enhanced density (SED) transported from low latitudes in the postnoon sector by the subauroral disturbance electric field. Convection carries this material through the dayside cusp and across the polar cap to the nightside where the auroral F region is significantly enhanced by the SED material. The three incoherent scatter radars provided full altitude profiles of plasma density, temperatures, and vertical velocity as the TOI plume crossed their different positions, under the cusp, in the center of the polar cap, and at the midnight oval/polar cap boundary. Greatly elevated F peak density (>1.5E12 m À3) and low electron and ion temperatures ($2500 K at the F peak altitude) characterize the SED/TOI plasma observed at all points along its high-latitude trajectory. For this event, SED/TOI F region TEC (150-1000 km) was $50 TECu both in the cusp and in the center of the polar cap. Large, upward directed fluxes of O+ (>1.E14 m À2 s À1 ) were observed in the topside ionosphere from the SED/TOI plume within the cusp.

Prompt energization of relativistic and highly relativistic electrons during a substorm interval: Van Allen Probes observations

“…Using a combination of Van Allen Probes data, ground-based radar, and DMSP observations, Foster et al (this issue) interrelate low-altitude and GPS TEC measurements with in situ plasmaspheric characteristics. They describe the redistribution fluxes of plasmasphere and ionosphere material from dusk sector field lines at the plasmapause (1) to the dayside cusp (3) via the storm enhanced density [Foster, 1993;/plasmasphere erosion plume (2), and back across polar latitudes to the midnight sector (4) in a polar tongue of ionization (TOI) [Foster et al, 2005]. Foster et al (this issue) report a pronounced increase in polar cap TEC magnitude beginning at the onset of the 17 March storm and continuing sporadically until~22 UT, at which time a sudden decrease in north polar TOI was observed.…”

Response of the equatorial ionosphere at dusk to penetration electric fields during intense magnetic storms

“…These studies established that at low latitudes, the dynamo effect of the perturbed wind causes the equatorial anomaly to be weaker on the dayside and enhanced on the nightside. The dynamic and electrodynamic responses at low latitudes have been investigated by Fuller-Rowell et al [2002] by using a coupled three-dimensional model of the thermosphere, ionosphere, plasmasphere, and electrodynamics. Modeling the disturbance dynamo phase is complicated because the disturbance dynamo electric fields have to operate on an ionosphere that has been modified by the initial prompt penetration electric fields [Maruyama et al, 2005].…”

First storm‐time plasma velocity estimates from high‐resolution ionospheric data assimilation

“…Since the electric field is perpendicular to isopotentials, and the drift is perpendicular to the field, the ExB velocity is generally parallel to the isopotential lines. In Figure 5 of [Foster et al, 2005], isopotentials centered around the "+" cell correspond to a counterclockwise flow. Just past noon, the Great Lakes can be seen at the lower latitudes.…”

“…In the paper by Foster et al [2005], the polar electric potentials two-cell patterns are plotted for these times. Since the electric field is perpendicular to isopotentials, and the drift is perpendicular to the field, the ExB velocity is generally parallel to the isopotential lines.…”

“…In some cases the SED has an associated plume of plasma that extends poleward. Studies by Foster et al [2005] show sunward convection toward the plasmasphere as well and refer to the cause of the plume phenomenon as a subauroral polarization stream. The plume and SED can have a clearly defined boundary relative to the background ionosphere.…”