Radar observations in the vicinity of pre-noon auroral arcs
International audience A combination of EISCAT incoherent scatter radar measurements, optical and magnetometer data is used to study the plasma in and around pre-noon structured precipitation and auroral arcs. Particular attention is paid to regions of comparatively low E-region density observed adj...
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ftinsu:oai:HAL:hal-00317828v1 2023-11-12T04:16:35+01:00 Radar observations in the vicinity of pre-noon auroral arcs Nilsson, Hans Kozlovsky, A. Sergienko, T. Kotikov, A. Swedish Institute of Space Physics Kiruna (IRF) University of Oulu Sodankylä Geophysical Observatory St Petersburg State University (SPbU) 2005-07-28 https://hal.science/hal-00317828 https://hal.science/hal-00317828/document https://hal.science/hal-00317828/file/angeo-23-1785-2005.pdf en eng HAL CCSD European Geosciences Union hal-00317828 https://hal.science/hal-00317828 https://hal.science/hal-00317828/document https://hal.science/hal-00317828/file/angeo-23-1785-2005.pdf info:eu-repo/semantics/OpenAccess ISSN: 0992-7689 EISSN: 1432-0576 Annales Geophysicae https://hal.science/hal-00317828 Annales Geophysicae, 2005, 23 (5), pp.1785-1796 [SDU.OCEAN]Sciences of the Universe [physics]/Ocean Atmosphere [SDU.STU]Sciences of the Universe [physics]/Earth Sciences info:eu-repo/semantics/article Journal articles 2005 ftinsu 2023-10-25T16:25:11Z International audience A combination of EISCAT incoherent scatter radar measurements, optical and magnetometer data is used to study the plasma in and around pre-noon structured precipitation and auroral arcs. Particular attention is paid to regions of comparatively low E-region density observed adjacent to arcs or structured precipitation in the EISCAT Svalbard radar field-aligned measurements. Comparison between luminosity and incoherent scatter electron density measurements shows that the low-density regions occur primarily due to the absence of diffuse precipitation rather than to a cavity formation process. Two cases of arcs and low density/luminosity regions are identified. The first is related to a strong Pc5 pulsation event, and the absence of diffuse precipitation is due to a large-scale modulation of the diffuse precipitation. In the second case the equatormost arc is on a shielding boundary and the low-density region coincides with a strong flow region just poleward of this arc. Regions of high electric field and low luminosity and conductance are observed prior to intensification of the structured precipitation in both cases. The ionospheric current is enhanced in the low conductance region, indicating that the strong electric fields do not result solely from ionospheric polarization electric fields, and thus are mainly driven by magnetospheric processes. The average energy of the precipitating electrons in the arcs and structured precipitation is, according to EISCAT measurements, 500eV and the energy spectra are similar for the pulsation and shielding cases. The average energy is thus significantly less than in the diffuse precipitation region which shows central CPS-like energy spectra. We suggest that the low ionospheric conductance of 0.7S in the low density regions is favorable for the arc formation process. This is in quantitative agreement with recent simulations of the ionospheric feedback instability. Keywords. Magnetospheric physics (Auroral phenomena; Magnetosphere-ionosphere ... Article in Journal/Newspaper EISCAT Svalbard Institut national des sciences de l'Univers: HAL-INSU Svalbard |
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Open Polar |
collection |
Institut national des sciences de l'Univers: HAL-INSU |
op_collection_id |
ftinsu |
language |
English |
topic |
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean Atmosphere [SDU.STU]Sciences of the Universe [physics]/Earth Sciences |
spellingShingle |
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean Atmosphere [SDU.STU]Sciences of the Universe [physics]/Earth Sciences Nilsson, Hans Kozlovsky, A. Sergienko, T. Kotikov, A. Radar observations in the vicinity of pre-noon auroral arcs |
topic_facet |
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean Atmosphere [SDU.STU]Sciences of the Universe [physics]/Earth Sciences |
description |
International audience A combination of EISCAT incoherent scatter radar measurements, optical and magnetometer data is used to study the plasma in and around pre-noon structured precipitation and auroral arcs. Particular attention is paid to regions of comparatively low E-region density observed adjacent to arcs or structured precipitation in the EISCAT Svalbard radar field-aligned measurements. Comparison between luminosity and incoherent scatter electron density measurements shows that the low-density regions occur primarily due to the absence of diffuse precipitation rather than to a cavity formation process. Two cases of arcs and low density/luminosity regions are identified. The first is related to a strong Pc5 pulsation event, and the absence of diffuse precipitation is due to a large-scale modulation of the diffuse precipitation. In the second case the equatormost arc is on a shielding boundary and the low-density region coincides with a strong flow region just poleward of this arc. Regions of high electric field and low luminosity and conductance are observed prior to intensification of the structured precipitation in both cases. The ionospheric current is enhanced in the low conductance region, indicating that the strong electric fields do not result solely from ionospheric polarization electric fields, and thus are mainly driven by magnetospheric processes. The average energy of the precipitating electrons in the arcs and structured precipitation is, according to EISCAT measurements, 500eV and the energy spectra are similar for the pulsation and shielding cases. The average energy is thus significantly less than in the diffuse precipitation region which shows central CPS-like energy spectra. We suggest that the low ionospheric conductance of 0.7S in the low density regions is favorable for the arc formation process. This is in quantitative agreement with recent simulations of the ionospheric feedback instability. Keywords. Magnetospheric physics (Auroral phenomena; Magnetosphere-ionosphere ... |
author2 |
Swedish Institute of Space Physics Kiruna (IRF) University of Oulu Sodankylä Geophysical Observatory St Petersburg State University (SPbU) |
format |
Article in Journal/Newspaper |
author |
Nilsson, Hans Kozlovsky, A. Sergienko, T. Kotikov, A. |
author_facet |
Nilsson, Hans Kozlovsky, A. Sergienko, T. Kotikov, A. |
author_sort |
Nilsson, Hans |
title |
Radar observations in the vicinity of pre-noon auroral arcs |
title_short |
Radar observations in the vicinity of pre-noon auroral arcs |
title_full |
Radar observations in the vicinity of pre-noon auroral arcs |
title_fullStr |
Radar observations in the vicinity of pre-noon auroral arcs |
title_full_unstemmed |
Radar observations in the vicinity of pre-noon auroral arcs |
title_sort |
radar observations in the vicinity of pre-noon auroral arcs |
publisher |
HAL CCSD |
publishDate |
2005 |
url |
https://hal.science/hal-00317828 https://hal.science/hal-00317828/document https://hal.science/hal-00317828/file/angeo-23-1785-2005.pdf |
geographic |
Svalbard |
geographic_facet |
Svalbard |
genre |
EISCAT Svalbard |
genre_facet |
EISCAT Svalbard |
op_source |
ISSN: 0992-7689 EISSN: 1432-0576 Annales Geophysicae https://hal.science/hal-00317828 Annales Geophysicae, 2005, 23 (5), pp.1785-1796 |
op_relation |
hal-00317828 https://hal.science/hal-00317828 https://hal.science/hal-00317828/document https://hal.science/hal-00317828/file/angeo-23-1785-2005.pdf |
op_rights |
info:eu-repo/semantics/OpenAccess |
_version_ |
1782333647769042944 |