Polar Tongue Of Ionization Research Articles

Impacts of Subauroral Polarization Streams on Storm‐Enhanced Density Plume and Consequently on Polar Tongue of Ionization

AbstractThe influences of subauroral polarization streams (SAPS) on storm‐enhanced density (SED) plume and consequently on polar tongue of ionization (TOI), an important topic in the field of magnetosphere‐ionosphere‐thermosphere coupling, however, remain undetermined. The Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIEGCM) with/without an empirical SAPS model has been used to investigate the impacts of SAPS on local ionosphere‐thermosphere system, which in turn affect the SED plume and consequently the TOI. The modeled total electron content and ion drift velocities agree reasonably well with the observations of Global Navigation Satellite System and Defense Meteorological Satellite Program satellites on 17 March 2013. The TIEGCM simulations show that SAPS can significantly affect the electron density of SED plume and consequently of TOI. The ionospheric‐thermospheric effect of SAPS can reduce the electron density of the SED plume in the afternoon sector and enhance the SED plume in the noon sector, which moves the SED plume dawnward. SAPS‐induced electron depletions in the throat region undergo anti‐sunward convection into the polar cap to weaken the TOI. A term‐by‐term analysis of the O+ ion continuity equation in the F‐region shows that the electron density depletions on the duskward edge of the SED plume are mainly due to the increased local plasma loss rates because of SAPS elevated plasma‐neutral temperatures and O/N2 reduction because of thermosphere upwelling. The electron density enhancements on the edge of the SED plume near noon are mainly due to the SAPS‐induced westward plasma E × B transports and the O/N2 increment because of thermospheric downwelling.

Relative importance of horizontal and vertical transports to the formation of ionospheric storm‐enhanced density and polar tongue of ionization

AbstractThere are still uncertainties regarding the formation mechanisms for storm‐enhanced density (SED) in the high and subauroral latitude ionosphere. In this work, we deploy the Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM) and GPS total electron content (TEC) observations to identify the principle mechanisms for SED and the tongue of ionization (TOI) through term‐by‐term analysis of the ion continuity equation and also identify the advantages and deficiencies of the TIEGCM in capturing high‐latitude and subauroral latitude ionospheric fine structures for the two geomagnetic storm events occurring on 17 March 2013 and 2015. Our results show that in the topside ionosphere, upward E × B ion drifts are most important in SED formation and are offset by antisunward neutral winds and downward ambipolar diffusion effects. In the bottomside F region ionosphere, neutral winds play a major role in generating SEDs. SED signature in TEC is mainly caused by upward E × B ion drifts that lift the ionosphere to higher altitudes where chemical recombination is slower. Horizontal E × B ion drifts play an essential role in transporting plasma from the dayside convection throat region to the polar cap to form TOIs. Inconsistencies between model results and GPS TEC data were found: (1) GPS relative TEC difference between storm time and quiet time has “holes” in the dayside ion convection entrance region, which do not appear in the model results. (2) The model tends to overestimate electron density enhancements in the polar region. Possible causes for these inconsistencies are discussed in this article.

Polar tongue of ionization (TOI) and associated Joule heating intensification investigated during the magnetically disturbed period of 1–2 October 2001

AbstractWe investigate storm‐enhanced density (SED) and polar tongue of ionization (TOI) over North America under southward Interplanetary Magnetic Field conditions. We focus on the 30 September to 1 October 2001 medium magnetic storm's recovery phase (Period 1) and on the last substorm (Period 2) of the following 2 October substorm series. We aim to study the SED‐TOI structure in the time frame of solar wind energy input to the magnetosphere‐ionosphere system and in terms of Joule heating. We utilize GPS total electron content maps tracking SED plume and polar TOI, and spectrogram images detecting polar rain and precipitation void and thus evidencing dayside merging. The variations of merging electric (E) field (EM) and its mapped‐down polar equivalent (EP), energy input efficiency (EIeff), and modeled Joule heating rate (QJoule) are monitored. Results show multiple Joule heating intensification points implying multiple energy deposition points at high latitudes where the magnetic pole was one of the preferred locations. During the higher EIeff (~1.5%) Period 2, the polar TOI was associated with a well‐defined strong QJoule intensification and with polar rain (or void) on the dayside (or nightside). During the lower EIeff (~0.5%) Period 1, only weak QJoule intensification occurred in the absence of both polar TOI and polar rain. We highlight the polar TOI's potential impact on the thermosphere. We conclude that (i) strong (EM ≈ 5 mV/m during Period 2) or weak (EM ≈ 0.5–2 mV/m during Period 1) EM facilitated energy deposition close to the magnetic pole and (ii) EIeff could be used as a diagnostic of the polar TOI's intensity.

Positive and negative ionospheric storms occurring during the 15 May 2005 geomagnetic superstorm

AbstractThis study focuses on the 15 May 2005 geomagnetic superstorm and aims to investigate the global variation of positive and negative storm phases and their development. Observations are provided by a series of global total electron content maps and multi‐instrument line plots. Coupled Thermosphere‐Ionosphere‐Plasmasphere electrodynamics (CTIPe) simulations are also employed. Results reveal some sunward streaming plumes of storm‐enhanced density (SED) over Asia and a well‐developed midlatitude trough over North America forming isolated positive and negative storms, respectively. The simultaneous development of positive and negative storms over North America is also shown. Then, some enhanced auroral ionizations maintained by strong equatorward neutral winds appeared in the depleted nighttime ionosphere. Meanwhile, the northern nighttime polar region became significantly depleted as the SED plume plasma could not progress further than the dayside cusp. Oppositely, a polar tongue of ionization (TOI) developed in the daytime southern polar region. According to CTIP simulations, solar heating locally maximized (minimized) over the southern (northern) magnetic pole. Furthermore, strong upward surges of molecular‐rich air created O/N2 decreases both in the auroral zone and in the trough region, while some SED‐related downward surges produced O/N2 increases. From these results we conclude for the time period studied that (1) composition changes contributed to the formation of positive and negative storms, (2) strengthening polar convection and increasing solar heating of the polar cap supported polar TOI development, and (3) a weaker polar convection and minimized solar heating of the polar cap aided the depletion of polar plasma.

Storm‐enhanced plasma density and polar tongue of ionization development during the 15 May 2005 superstorm

AbstractWe investigate the ionosphere's global response to the 15 May 2005 superstorm in terms of storm evolution and ionospheric electrodynamics. Our aim is to study the global distribution of plasma and the resultant large‐scale ionospheric features including the equatorial ionization anomaly (EIA), storm‐enhanced density (SED), and polar tongue of ionization (TOI). We have combined multi‐instrument ionospheric data, solar and terrestrial magnetic data, and polar convection maps. Results reveal the prompt penetration of the interplanetary electric field to the polar region and then to the equator with a dusk‐to‐dawn polarity during the initial phase and with a dawn‐to‐dusk polarity during the main phase. This drove during the initial phase a weak eastward equatorial electrojet (EEJ) in the American sector at nighttime and a weak westward EEJ in the Indian‐Australian sector at daytime. During the main phase, these EEJs intensified and changed polarities. SED and polar TOI development was observed prior to and during the initial phase at evening‐premidnight hours over North America and during the main phase in the south at afternoon‐evening hours in the Australian sector. During the main phase and early in the recovery phase, the EIA‐SED structure was well formed in the Asian longitude sector. Then, polar TOI development was absent in the north because of the long distance from the magnetic pole but was supported in the south because of the closeness of daytime cusp and magnetic pole. Thus, the EIA‐SED‐TOI structure developed twice but each time in a different longitude sector and with different characteristics.

Investigating storm‐enhanced density and polar tongue of ionization development during the 22 October 1999 great storm

AbstractWe investigate large‐scale plasma density increases occurring during the 22 October 1999 great storm and focus on storm‐enhanced density (SED) and polar tongue of ionization (TOI) development. Observations include two‐hourly Global Ionosphere Map series coupled with multi‐instrument in situ, space‐based, and ground‐based data plots, with Super Dual Auroral Radar Network two‐cell convection maps and with model‐generated neutral wind vector maps. Results demonstrate the equatorial electrojet events occurring in the Australian and American sectors, the high‐density plasma features, and their underlying plasma transportation processes. During the main phase, a series of four prompt penetration electric field (PPEF) events occurred with subauroral polarization stream E field development forming a plasmaspheric drainage plume. These E field events caused the repeated development of equatorial ionization anomaly (EIA), SED bulge, and SED plume during the local dusk‐midnight hours in those sectors that covered these local times. Showing a westward movement in accordance with their local time dependence, the EIA‐SED structure developed first in the American sector, later on over the Pacific, and finally in the Australian sector. The SED plume plasma found its way into the polar cap through the dayside cusp region, created in the north some large polar cap enhancements reaching up to seven times of the quiet time levels, and evolved in each hemisphere into a polar TOI. We speculate that the enhanced growth of EIA, transporting high‐density solar‐produced plasma to the SED bulge via strong net eastward E field effects, and the mechanical effects of equatorward neutral winds contributed to the polar TOI's increasingly better development.

Storm time observations of plasmasphere erosion flux in the magnetosphere and ionosphere

AbstractPlasmasphere erosion carries cold dense plasma of ionospheric origin in a storm‐enhanced density plume extending from dusk toward and through the noontime cusp and dayside magnetopause and back across polar latitudes in a polar tongue of ionization. We examine dusk sector (20 MLT) plasmasphere erosion during the 17 March 2013 storm (Dst ~ −130 nT) using simultaneous, magnetically aligned direct sunward ion flux observations at high altitude by Van Allen Probes RBSP‐A (at ~3.0 Re) and at ionospheric heights (~840 km) by DMSP F‐18. Plasma erosion occurs at both high and low altitudes where the subauroral polarization stream flow overlaps the outer plasmasphere. At ~20 UT, RBSP‐A observed ~1.2E12 m−2 s−1 erosion flux, while DMSP F‐18 observed ~2E13 m−2 s−1 sunward flux. We find close similarities at high and low altitudes between the erosion plume in both invariant latitude spatial extent and plasma characteristics.

Localized electron density enhancements in the high-altitude polar ionosphere and their relationships with storm-enhanced density (SED) plumes and polar tongues of ionization (TOI)

Abstract. Events of localized electron density increase in the high-altitude (>3000 km) polar ionosphere are occasionally identified by the thermal plasma instruments on the Akebono satellite. In this paper, we investigate the vertical density structure in one of such events in detail using simultaneous observations by the Akebono and DMSP F15 satellites, the SuperDARN radars, and a network of ground Global Positioning System (GPS) receivers, and the statistical characteristics of a large number (>10 000) of such events using Akebono data over half of an 11-year solar cycle. At Akebono altitude, the parallel drift velocity is remarkably low and the O+ ion composition ratio remarkably high, inside the high plasma-density regions at high altitude. Detailed comparisons between Akebono, DMSP ion velocity and density, and GPS total electron content (TEC) data suggest that the localized plasma density increase observed at high altitude on Akebono was likely connected with the polar tongue of ionization (TOI) and/or storm enhanced density (SED) plume observed in the F-region ionosphere. Together with the SuperDARN plasma convection map these data suggest that the TOI/SED plume penetrated into the polar cap due to anti-sunward convection and the plume existed in the same convection channel as the dense plasma at high altitude; in other words, the two were probably connected to each other by the convecting magnetic field lines. The observed features are consistent with the observed high-density plasma being transported from the mid-latitude ionosphere or plasmasphere and unlikely a part of the polar wind population.

Multiradar observations of the polar tongue of ionization

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−3) 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−2 s−1) were observed in the topside ionosphere from the SED/TOI plume within the cusp.