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Relative outflow enhancements during major geomagnetic storms: Cluster observations
Instiutet for rymdfysik, Kiruna, Sweden.
Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Instiutet for rymdfysik, Kiruna, Sweden.
Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
Swedish Institute of Space Physics, Kiruna, Sweden.
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2017 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 5, no 6, p. 1341-1352Article in journal (Refereed) Published
Abstract [en]

The rate of ion outflow from the polar ionosphere is known to vary by orders of magnitude, depending on the geomagnetic activity. However, the upper limit of the outflow rate during the largest geomagnetic storms is not well constrained due to poor spatial coverage during storm events. In this paper, we analyse six major geomagnetic storms between 2001 and 2004 using Cluster data. The six major storms fulfil the criteria of Dst 100 nT or Kp 7C. Since the shape of the magnetospheric regions (plasma mantle, lobe and inner magnetosphere) are distorted during large magnetic storms, we use both plasma beta and ion characteristics to define a spatial box where the upward OC flux scaled to an ionospheric reference altitude for the extreme event is observed. The relative enhancement of the scaled outflow in the spatial boxes as compared to the data from the full year when the storm occurred is estimated. Only OC data were used because HC may have a solar wind origin. The storm time data for most cases showed up as a clearly distinguishable separate peak in the distribution toward the largest fluxes observed. The relative enhancement in the outflow region during storm time is 1 to 2 orders of magnitude higher compared to less disturbed time. The largest relative scaled outflow enhancement is 83 (7 November 2004) and the highest scaled OC outflow observed is 2 1014 m2 s1 (29 October 2003).

Place, publisher, year, edition, pages
Copernicus GmbH , 2017. Vol. 5, no 6, p. 1341-1352
National Category
Aerospace Engineering Fluid Mechanics and Acoustics
Research subject
Atmospheric science; Fluid Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-67138DOI: 10.5194/angeo-35-1341-2017ISI: 000418075000001Scopus ID: 2-s2.0-85038635321OAI: oai:DiVA.org:ltu-67138DiVA, id: diva2:1170152
Note

Validerad;2018;Nivå 2;2018-01-04 (svasva)

Available from: 2018-01-02 Created: 2018-01-02 Last updated: 2018-06-12Bibliographically approved
In thesis
1. O+ outflow during geomagnetic storms observed by Cluster satellites
Open this publication in new window or tab >>O+ outflow during geomagnetic storms observed by Cluster satellites
2018 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The region of space dominated by the Sun's magnetic field is called the heliosphere. It envelops the entire solar system including Earth. Therefore, a strong coupling exists between the Sun and our planet. The Sun continuously ejects particles, the solar wind, and when these high energy particles hit Earth, the magnetosphere (the region around the Earth governed by the geomagnetic field) is affected. When the solar wind is enhanced this disturbs the magnetosphere and perturbations can be seen also in ground-based observations.

The upper atmosphere is subjected to solar radiation that ionise the neutral atoms and molecules, this region is referred to as the ionosphere. In the ionosphere, some of the heavier ion populations, such as O+, are heated and accelerated through several processes and flow upward. In the polar regions these mechanisms are particularly efficient and when the ions have enough energy to escape the Earth's gravity, they move outward along open magnetic field lines and may be lost into interplanetary space. Ion outflow in general has already been well studied, however, ion outflow under extreme magnetospheric conditions has not been investigated in detail.

Disturbed magnetospheric conditions correlate with solar active periods, such as coronal holes or the development of solar active regions. From these regions, strong ejections called coronal mass ejections (CMEs) emerge. When these extreme events interact with Earth, they produce a compression of the magnetosphere as well as reconnection between the terrestrial magnetic field lines and the interplanetary magnetic field (IMF) lines, which most of the time leads to geomagnetic storms. The amounts of incoming solar particles and energy increase during geomagnetic storms and we also observe an increase in the O+ outflow.

Our observations are made with the Cluster mission, a constellation of 4 satellites flying around Earth in the key magnetospheric regions where ion outflow is usually observed. In this thesis, we estimate O+ outflow under disturbed magnetospheric conditions and for several extreme geomagnetic storms. We find that O+ outflow lost into the solar wind increases exponentially with enhanced geomagnetic activity (Kp index) and increases about 2 orders of magnitude during extreme geomagnetic storms.

Abstract [sv]

Den del av rymden som domineras av solens magnetfält kallas heliosfären. Helios-fären omfattar hela solsystemet inklusive jorden, vilket gör att det finns en starkkoppling mellan solen och jorden. Solen sänder oavbrutet ut laddade partiklar in denså kallade solvinden och när dessa energika partiklar träffar jorden påverkas mag-netosfären (det område kring jorden där det geomagnetiska fältet dominerar). Närsolvinden är starkare än vanligt uppstår störningar. I magnetosfären som ger effektersom kan uppmätas med markbaserade instrument.

Den övre atmosfären utsätts för strålning från solen som joniserar atomer ochmolekyler, och formar det område som kallas jonosfären. Några av de tyngre jonpop-ulationerna i jonosfären, som till exempel syrejoner, kan hettas upp och accelererasgenom flera olika möjliga processer. Detta gör att de flödar uppåt i atmosfären. Ipolarområdena är dessa mekanismer särskilt effektiva och om tillräckligt med energitillförs jonerna kan gravitationen övervinnas, vilket gör att jonerna flödar upp längsöppna magnetfältlinjer och kan gå förlorade ut i den interplanetära rymden. Generelltsett har jonutflöde redan studerats väl, men jonutflöde under extrema magnetosfäriskaförhållanden har inte undersökts i detalj.

Störda magnetosfäriska förhållanden korrelerar med då solen är aktiv, som tillexempel koronahål eller under utvecklingen av aktiva solområden. Från dessa områ-den härstammar koronamassautkastningar. När dessa extrema händelser når jordenkomprimeras magnetosfären och det geomagnetiska och interplanetära magnetiskafältet omkopplas, vilket ofta leder till geomagnetiska stormar. Under dessa införsstora mängder av partiklar i solvinden och energi till magnetosfären, och ett högresyrejonsutflöde är också observerat.

Data från Clustersatelliterna har använts; dessa utgörs av fyra satelliter i for-mation i omloppsbana kring jorden. Plasmaområdena där de befinner sig är därjonutflödet vanligtvis observeras. Denna avhandling behandlar syrejonsutflöde understörda magnetosfäriska förhållanden och flera extrema geomagnetiska stormar. Detvisas att syrejonsutflödet som förloras till solvinden ökar exponentiellt med geomag-netiskt aktivitet (Kp-index) och ökar med upp till 2 storleksordningar under extremageomagnetiska stormar.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2018
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
National Category
Fusion, Plasma and Space Physics Aerospace Engineering
Research subject
Atmospheric science
Identifiers
urn:nbn:se:ltu:diva-68586 (URN)978-91-7790-138-9 (ISBN)978-91-7790-139-6 (ISBN)
Presentation
2018-06-08, Kiruna-IRF, Rymdcampus, Luleå tekniska universitet, Kiruna, 09:00 (English)
Opponent
Supervisors
Available from: 2018-05-03 Created: 2018-05-02 Last updated: 2018-06-12Bibliographically approved

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