The relationship of thermospheric density anomaly with electron temperature, small-scale FAC, and ion up-flow in the cusp region, as observed by CHAMP and DMSP satellites

G N Kervalishvili,H Lühr

doi:10.5194/angeo-31-541-2013

Abstract

Abstract. We present in a statistical study a comparison of thermospheric mass density enhancements (ρrel) with electron temperature (Te), small-scale field-aligned currents (SSFACs), and vertical ion velocity (Vz) at high latitudes around noon magnetic local time (MLT). Satellite data from CHAMP (CHAllenging Minisatellite Payload) and DMSP (Defense Meteorological Satellite Program) sampling the Northern Hemisphere during the years 2002–2005 are used. In a first step we investigate the distribution of the measured quantities in a magnetic latitude (MLat) versus MLT frame. All considered variables exhibit prominent peak amplitudes in the cusp region. A superposed epoch analysis was performed to examine causal relationship between the quantities. The occurrence of a thermospheric relative mass density anomaly, ρrel >1.2, in the cusp region is defining an event. The location of the density peak is taken as a reference latitude (Δ MLat = 0°). Interestingly, all the considered quantities, SSFACs, Te, and Vz are co-located with the density anomaly. The amplitudes of the peaks exhibit different characters of seasonal variation. The average relative density enhancement of the more prominent density peaks considered in this study amounts to 1.33 during all seasons. As expected, SSFACs are largest in summer with average amplitudes equal to 2.56 μA m−2, decaying to 2.00 μA m−2 in winter. The event related enhancements of Te and Vz are both largest in winter (Δ Te =730 K, Vz =136 m s−1) and smallest in summer (Δ Te = 377 K, Vz = 57 m s−1. Based on the similarity of the seasonal behaviour we suggest a close relationship between these two quantities. A correlation analysis supports a linear relation with a high coefficient greater than or equal to 0.93, irrespective of season. Our preferred explanation is that dayside reconnection fuels Joule heating of the thermosphere causing air upwelling and at the same time heating of the electron gas that pulls up ions along affected flux tubes.

Highlights

All considered variables exhibit prominent peak amplitudes in the cusp region. formed to examineA superposed epoch analysis was per- The thermosphere causal relationship betwEeean rththe qSuaynsti-temcated in the altitude irsanpgaertboetfwteheenuapbEpoeuart r9att0mhkomSspayhnedsre1te0a0mn0dklmo-. ties. sityThe occurrence anomaly, ρrel >of a 1.2, itnhetrhme ocsupshperriecgrioelnatiisvedmeDfianysisnngdaeanmn- icsWtheernmootespthheartitchedyenxaombaisces is is located near affected by50D0 kymnaaltmituidces
This paper provides the first detailed comparison of CHAllenging Minisatellite Payload (CHAMP) and Defense Meteorological Satellite Program (DMSP) satellite observations, which have been made during 4 yr of continuous measurements, 2002 to 2006
The main purpose of this paper is to present the relationship of the thermospheric density anomaly with small-scale field-aligned currents (FACs), electron temperature, and ion vertical velocity using 4 yr of observations from CHAMP and DMSP in the Northern Hemisphere

Summary

Introduction

All considered variables exhibit prominent peak amplitudes in the cusp region. formed to examineA superposed epoch analysis was per- The thermosphere causal relationship betwEeean rththe qSuaynsti-temcated in the altitude irsanpgaertboetfwteheenuapbEpoeuart r9att0mhkomSspayhnedsre1te0a0mn0dklmo-. ties. sityThe occurrence anomaly, ρrel >of a 1.2, itnhetrhme ocsupshperriecgrioelnatiisvedmeDfianysisnngdaeanmn- icsWtheernmootespthheartitchedyenxaombaisces is is located near affected by50D0 kymnaaltmituidces. All considered variables exhibit prominent peak amplitudes in the cusp region. The location of the density peak is taken as a refer- plex processes and has a large variability in temperature and ence latitude ( MLat = 0◦). All the considered density depending upon solar extreme ultraviolet (EUV) raquantities, SSFACs, Te, and Vz are co-located wGitehothsecdieenn- tificdiation and geomagnetic disturbances.GItsedoysncamieicnstiafnicd resity anomaly. Expected, SSFACs are largest in summer with average am- ergy on the upper atmosphere was outlined inDaisccoumsspiorenhsenpwleasliritngtuitenedsret.ssiTunmehqwemuieanevlrteetn(rot(r2Te.el5Ta6=eteμ=d3A7e7n7m3hK0−aK2,n,cV,edzVme=zMcea=n5yot7is1nd3mog6festTmo−le1s2Da.G−.n0B1ed0)eaVvμsaoezAneddsamlroocse−mnipbe2aotmhlntilhne-teifnictsadainievrdnecstoirhtemyevpipdeoeewsrpitteubinroybdnaePtwnriooceelnrsessoiwn(n2vet0hre1eMes1tpil)geor.aveIdtseneeldenpo.tlafePrdDgtrGi.oeclAoeusemlslvaso(aroe2,gs0ptnlho1ceeDe1rtipiti)escmucmirnanoubcsdrateptsitiiciihfvoonaioinncttlsteysodgooyaff similarity of the seasonal behaviour we suggest a close rela- strong correlation of density perturbations on the AE A correlation analysis ral electrojet) index and weaker on the Dst (disturbance storm supports a linear relation with a high coefficHieyntdgrroealtoergthyanandtime) index and the interplanetaryHelyecdtrricofiloeldgyat haignhdlatior equal to planation is t0h.9at3,dairyrseisdpeerceticvoennoefcstieoansofnu.elOs uJEor uaplrerethfheerarteSidnygesxo-ftemtudUens.derstanding the variability of tEheanretuhtraSl myasstsedmensity

Objectives

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Discussion

Conclusion