Southern high-latitude Digisonde observations of ionosphere E-region Bragg scatter during intense lacuna conditions
International audience During summer months at solar cycle minimum, F-region lacuna and slant-Es conditions (SEC) are common features of daytime ionograms recorded around local magnetic noon at Casey, Antarctica. Digisonde measurements of drift velocity height profiles show that the occurrence of la...
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ftccsdartic:oai:HAL:hal-00317576v1 2023-11-12T04:04:58+01:00 Southern high-latitude Digisonde observations of ionosphere E-region Bragg scatter during intense lacuna conditions Monselesan, D. P. Morris, R. J. Dyson, P. L. Hyde, M. R. Australian Antarctic Division (AAD) Australian Government, Department of the Environment and Energy IPS Radio and Space Services Department of Physics La Trobe University Melbourne 2004-09-07 https://hal.science/hal-00317576 https://hal.science/hal-00317576/document https://hal.science/hal-00317576/file/angeo-22-2819-2004.pdf en eng HAL CCSD European Geosciences Union hal-00317576 https://hal.science/hal-00317576 https://hal.science/hal-00317576/document https://hal.science/hal-00317576/file/angeo-22-2819-2004.pdf info:eu-repo/semantics/OpenAccess ISSN: 0992-7689 EISSN: 1432-0576 Annales Geophysicae https://hal.science/hal-00317576 Annales Geophysicae, 2004, 22 (8), pp.2819-2835 [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 2004 ftccsdartic 2023-10-21T23:07:19Z International audience During summer months at solar cycle minimum, F-region lacuna and slant-Es conditions (SEC) are common features of daytime ionograms recorded around local magnetic noon at Casey, Antarctica. Digisonde measurements of drift velocity height profiles show that the occurrence of lacuna prevents the determination of F-region drift velocities and also affects E-region drift velocity measurements. Unique E-region spectral features revealed as intervals of Bragg scatter superimposed on typical background E-region reflection were observed in Digisonde Doppler spectra during intense lacuna conditions. Daytime E-region Doppler spectra recorded at carrier frequencies from 1.5 to 2.7MHz, below the E-region critical frequency f o E, have two side-peaks corresponding to Bragg scatter at approximately ±1-2Hz symmetrically located on each side of a central-peak corresponding to near-zenith total reflections. Angle-of-arrival information and ray-tracing simulations show that echo returns are coming from oblique directions most likely resulting from direct backscatter from just below the total reflection height for each sounding frequency. The Bragg backscatter events are shown to manifest during polar lacuna conditions, and to affect the determination of E-region background drift velocities, and as such must be considered when using standard Doppler-sorted interferometry (DSI) techniques to estimate ionospheric drift velocities. Given the Doppler and spatial separation of the echoes determined from high-resolution Doppler measurements, we are able to estimate the Bragg scatter phase velocity independently from the bulk E-region motion. The phase velocity coincides with the E x B direction derived from in situ fluxgate magnetometer records. When ionospheric refraction is considered, the phase velocity amplitudes deduced from DSI are comparable to the ion-acoustic speed expected in the E-region. We briefly consider the plausibility that these previously unreported polar cap E-region Bragg scatter Doppler ... Article in Journal/Newspaper Antarc* Antarctica Archive ouverte HAL (Hyper Article en Ligne, CCSD - Centre pour la Communication Scientifique Directe) |
institution |
Open Polar |
collection |
Archive ouverte HAL (Hyper Article en Ligne, CCSD - Centre pour la Communication Scientifique Directe) |
op_collection_id |
ftccsdartic |
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 Monselesan, D. P. Morris, R. J. Dyson, P. L. Hyde, M. R. Southern high-latitude Digisonde observations of ionosphere E-region Bragg scatter during intense lacuna conditions |
topic_facet |
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean Atmosphere [SDU.STU]Sciences of the Universe [physics]/Earth Sciences |
description |
International audience During summer months at solar cycle minimum, F-region lacuna and slant-Es conditions (SEC) are common features of daytime ionograms recorded around local magnetic noon at Casey, Antarctica. Digisonde measurements of drift velocity height profiles show that the occurrence of lacuna prevents the determination of F-region drift velocities and also affects E-region drift velocity measurements. Unique E-region spectral features revealed as intervals of Bragg scatter superimposed on typical background E-region reflection were observed in Digisonde Doppler spectra during intense lacuna conditions. Daytime E-region Doppler spectra recorded at carrier frequencies from 1.5 to 2.7MHz, below the E-region critical frequency f o E, have two side-peaks corresponding to Bragg scatter at approximately ±1-2Hz symmetrically located on each side of a central-peak corresponding to near-zenith total reflections. Angle-of-arrival information and ray-tracing simulations show that echo returns are coming from oblique directions most likely resulting from direct backscatter from just below the total reflection height for each sounding frequency. The Bragg backscatter events are shown to manifest during polar lacuna conditions, and to affect the determination of E-region background drift velocities, and as such must be considered when using standard Doppler-sorted interferometry (DSI) techniques to estimate ionospheric drift velocities. Given the Doppler and spatial separation of the echoes determined from high-resolution Doppler measurements, we are able to estimate the Bragg scatter phase velocity independently from the bulk E-region motion. The phase velocity coincides with the E x B direction derived from in situ fluxgate magnetometer records. When ionospheric refraction is considered, the phase velocity amplitudes deduced from DSI are comparable to the ion-acoustic speed expected in the E-region. We briefly consider the plausibility that these previously unreported polar cap E-region Bragg scatter Doppler ... |
author2 |
Australian Antarctic Division (AAD) Australian Government, Department of the Environment and Energy IPS Radio and Space Services Department of Physics La Trobe University Melbourne |
format |
Article in Journal/Newspaper |
author |
Monselesan, D. P. Morris, R. J. Dyson, P. L. Hyde, M. R. |
author_facet |
Monselesan, D. P. Morris, R. J. Dyson, P. L. Hyde, M. R. |
author_sort |
Monselesan, D. P. |
title |
Southern high-latitude Digisonde observations of ionosphere E-region Bragg scatter during intense lacuna conditions |
title_short |
Southern high-latitude Digisonde observations of ionosphere E-region Bragg scatter during intense lacuna conditions |
title_full |
Southern high-latitude Digisonde observations of ionosphere E-region Bragg scatter during intense lacuna conditions |
title_fullStr |
Southern high-latitude Digisonde observations of ionosphere E-region Bragg scatter during intense lacuna conditions |
title_full_unstemmed |
Southern high-latitude Digisonde observations of ionosphere E-region Bragg scatter during intense lacuna conditions |
title_sort |
southern high-latitude digisonde observations of ionosphere e-region bragg scatter during intense lacuna conditions |
publisher |
HAL CCSD |
publishDate |
2004 |
url |
https://hal.science/hal-00317576 https://hal.science/hal-00317576/document https://hal.science/hal-00317576/file/angeo-22-2819-2004.pdf |
genre |
Antarc* Antarctica |
genre_facet |
Antarc* Antarctica |
op_source |
ISSN: 0992-7689 EISSN: 1432-0576 Annales Geophysicae https://hal.science/hal-00317576 Annales Geophysicae, 2004, 22 (8), pp.2819-2835 |
op_relation |
hal-00317576 https://hal.science/hal-00317576 https://hal.science/hal-00317576/document https://hal.science/hal-00317576/file/angeo-22-2819-2004.pdf |
op_rights |
info:eu-repo/semantics/OpenAccess |
_version_ |
1782341823518212096 |