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C D Odom - One of the best experts on this subject based on the ideXlab platform.
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obsErvations of altitudinal and latitudinal E rEgion nEutral wind gradiEnts nEar sunsEt at thE magnEtic Equator
Geophysical Research Letters, 1997Co-Authors: M F Larsen, C D OdomAbstract:Sounding rockEt chEmical rElEasE mEasurEmEnts of thE E-rEgion nEutral wind profilEs wErE carriEd out at thE magnEtic Equator at dusk on two consEcutivE days in SEptEmbEr 1994 whEn a strong prErEvErsal EnhancEmEnt of thE F-rEgion vErtical plasma drift was prEsEnt. Wind profilEs wErE obtainEd at thE Equator and ∼450–480 km furthEr north. ThE profilEs show wind spEEds of 80–100 m s−1 in thE lowEr E-rEgion and rEvErsals of thE wind dirEction ovEr vErtical scalEs of 10–15 km. On both days, thE wind dirEction in thE lowEr E rEgion changEd consistEntly bEtwEEn thE northErn and Equatorial rElEasEs, with a strong southward wind EvidEnt at thE northErn position and a strongEr Eastward wind at thE Equator.
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ObsErvations of altitudinal and latitudinal E‐rEgion nEutral wind gradiEnts nEar sunsEt at thE magnEtic Equator
Geophysical Research Letters, 1997Co-Authors: M F Larsen, C D OdomAbstract:Sounding rockEt chEmical rElEasE mEasurEmEnts of thE E-rEgion nEutral wind profilEs wErE carriEd out at thE magnEtic Equator at dusk on two consEcutivE days in SEptEmbEr 1994 whEn a strong prErEvErsal EnhancEmEnt of thE F-rEgion vErtical plasma drift was prEsEnt. Wind profilEs wErE obtainEd at thE Equator and ∼450–480 km furthEr north. ThE profilEs show wind spEEds of 80–100 m s−1 in thE lowEr E-rEgion and rEvErsals of thE wind dirEction ovEr vErtical scalEs of 10–15 km. On both days, thE wind dirEction in thE lowEr E rEgion changEd consistEntly bEtwEEn thE northErn and Equatorial rElEasEs, with a strong southward wind EvidEnt at thE northErn position and a strongEr Eastward wind at thE Equator.
M F Larsen - One of the best experts on this subject based on the ideXlab platform.
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obsErvations of altitudinal and latitudinal E rEgion nEutral wind gradiEnts nEar sunsEt at thE magnEtic Equator
Geophysical Research Letters, 1997Co-Authors: M F Larsen, C D OdomAbstract:Sounding rockEt chEmical rElEasE mEasurEmEnts of thE E-rEgion nEutral wind profilEs wErE carriEd out at thE magnEtic Equator at dusk on two consEcutivE days in SEptEmbEr 1994 whEn a strong prErEvErsal EnhancEmEnt of thE F-rEgion vErtical plasma drift was prEsEnt. Wind profilEs wErE obtainEd at thE Equator and ∼450–480 km furthEr north. ThE profilEs show wind spEEds of 80–100 m s−1 in thE lowEr E-rEgion and rEvErsals of thE wind dirEction ovEr vErtical scalEs of 10–15 km. On both days, thE wind dirEction in thE lowEr E rEgion changEd consistEntly bEtwEEn thE northErn and Equatorial rElEasEs, with a strong southward wind EvidEnt at thE northErn position and a strongEr Eastward wind at thE Equator.
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ObsErvations of altitudinal and latitudinal E‐rEgion nEutral wind gradiEnts nEar sunsEt at thE magnEtic Equator
Geophysical Research Letters, 1997Co-Authors: M F Larsen, C D OdomAbstract:Sounding rockEt chEmical rElEasE mEasurEmEnts of thE E-rEgion nEutral wind profilEs wErE carriEd out at thE magnEtic Equator at dusk on two consEcutivE days in SEptEmbEr 1994 whEn a strong prErEvErsal EnhancEmEnt of thE F-rEgion vErtical plasma drift was prEsEnt. Wind profilEs wErE obtainEd at thE Equator and ∼450–480 km furthEr north. ThE profilEs show wind spEEds of 80–100 m s−1 in thE lowEr E-rEgion and rEvErsals of thE wind dirEction ovEr vErtical scalEs of 10–15 km. On both days, thE wind dirEction in thE lowEr E rEgion changEd consistEntly bEtwEEn thE northErn and Equatorial rElEasEs, with a strong southward wind EvidEnt at thE northErn position and a strongEr Eastward wind at thE Equator.
M R Hyde - One of the best experts on this subject based on the ideXlab platform.
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E-rEgion Bragg scattEr during intEnsE lacuna conditions
2016Co-Authors: Didier Monselesan, P L Dyson, R. J. Morris, M R HydeAbstract:Abstract. During summEr months at solar cyclE minimum, F-rEgion lacuna and slant-Es conditions (SEC) arE com-mon fEaturEs of daytimE ionograms rEcordEd around local magnEtic noon at CasEy, Antarctica. DigisondE mEasurE-mEnts of drift vElocity hEight profilEs show that thE occur-rEncE of lacuna prEvEnts thE dEtErmination of F-rEgion drift vElocitiEs and also affEcts E-rEgion drift vElocity mEasurE-mEnts. UniquE E-rEgion spEctral fEaturEs rEvEalEd as intEr-vals of Bragg scattEr supErimposEd on typical background E-rEgion rEflEction wErE obsErvEd in DigisondE DopplEr spEc-tra during intEnsE lacuna conditions. DaytimE E-rEgion DopplEr spEctra rEcordEd at carriEr frEquEnciEs from 1.5 to 2.7 MHz, bElow thE E-rEgion critical frEquEncy foE, havE two sidE-pEaks corrEsponding to Bragg scattEr at approximatEly ±1–2 Hz symmEtrically locatEd on Each sidE of a cEntral
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southErn high latitudE digisondE obsErvations of ionosphErE E rEgion bragg scattEr during intEnsE lacuna conditions
Annales Geophysicae, 2004Co-Authors: Didier Monselesan, P L Dyson, R. J. Morris, M R HydeAbstract:Abstract. 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 spEctral signaturEs, obsErvEd at CasEy in DEcEmbEr 1996 during SEC/lacuna conditions may bE linkEd to ionosphErE irrEgularitiEs. ThEsE irrEgularitiEs may possibly bE gEnEratEd by primary plasma wavEs triggErEd by currEnt-drivEn instabilitiEs, that is to say, a hybrid of thE "modifiEd two-strEam" and "gradiEnt drift" instability mEchanisms.
Asgeir Brekke - One of the best experts on this subject based on the ideXlab platform.
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SamplEs of Auroral E-REgion ParamEtErs DErivEd from EISCAT ExpErimEnts
Journal of geomagnetism and geoelectricity, 1995Co-Authors: Asgeir Brekke, Satonori Nozawa, Mariko SatoAbstract:In this work wE havE madE a comparison bEtwEEn quiEt and disturbEd timE valuEs of thE auroral zonE E-fiEld ionosphEric conductancEs and E-rEgion nEutral winds as dErivEd from EISCAT-UHF mEasurEmEnts. ThE avEragE diurnal mEan valuEs of thE E-fiEld arE rathEr unchangEd bEtwEEn quiEt and disturbEd days whilE thE amplitudE of thE 24-hour diurnal oscillation is EnhancEd by a factor of 3 from avEragEd quiEt to disturbEd days. ThE E-rEgion nEutral wind has an Eastward componEnt bEtwEEn 90 and 110 km which is sEasonal dEpEndEnt, showing highEst valuEs in summEr and lowEst in wintEr with spring and fall valuEs in bEtwEEn. ThE most outstanding diffErEncE bEtwEEn quiEt and disturbEd timE E-rEgion nEutral winds is an incrEasE in thE Eastward diurnal fidE of a factor of 3-4 abovE 100 km. ThE mEan wind as wEll as thE highEr ordEr tidal modEs (12-, 8- and 6-hour modEs) display rathEr minor diffErEncEs.
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StudiEs of thE E rEgion nEutral wind in thE quiEt auroral ionosphErE
Journal of Geophysical Research, 1994Co-Authors: Asgeir Brekke, Satonori Nozawa, Trygve SparrAbstract:QuiEt timE auroral E rEgion nEutral wind data obtainEd by EuropEan IncohErEnt ScattEr Radar (EISCAT) havE bEEn analyzEd in ordEr to Establish thE background mEan nEutral vElocitiEs as wEll as tidal influEncE on thE wind. ThErE is a rathEr strong and pErsistEnt mEan Eastward wind prEsEnt in all sEasons in thE E rEgion bElow 120 km. It is strongEst in summEr (∼60 m s−1), wEak in fall and spring, and wEakEr in wintEr (∼20 m s−1). ThE zonal wind is wEstward abovE 120 km, in gEnEral strongEr in wintEr (∼70 m s−1) and wEakEr in thE othEr sEasons (∼30 m s−1). ThE northward mEan wind is rathEr small (∼10 m s−1). It is shiftEd gradually from bEing mainly southward in wintEr to bEcoming northward in summEr. ThE mEan vErtical vElocity is of thE ordEr of 5 m s−1 in thE auroral E rEgion. ThE amplitudE of thE diurnal tidEs of thE vErtical componEnt havE broad minima in thE hEight rEgion bEtwEEn 90 and 120 km. ThE horizontal diurnal tidE is dominant in thE uppEr E rEgion, whilE thE sEmidiurnal tidE has a maximum at 110 km, in particular in thE Eastward componEnt. ThE 8- and 6-hour tidEs arE rathEr constant in amplitudE by hEight. ThE rEsults obtainEd arE in good agrEEmEnt with othEr rEsults publishEd on thE basis of incohErEnt scattEr radar mEasurEmEnts. ThE comparison with thEorEtical modEls undErlinEs thE nEEd for morE modEling of thE auroral E rEgion nEutral tidEs including thE ionizEd plasma as wEll as ElEctric fiElds and mEan background winds. ThEorEtical studiEs of thE vErtical motion with rEspEct to thE influEncE of tidEs arE EspEcially lacking in this important rEgion.
Satonori Nozawa - One of the best experts on this subject based on the ideXlab platform.
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VElocity of E-rEgion HF EchoEs undEr strongly-drivEn ElEctrojEt conditions
Annales Geophysicae, 2012Co-Authors: J. D. Gorin, Roman A. Makarevich, A. V. Koustov, J.-p. Maurice, Satonori NozawaAbstract:Abstract. Data collEctEd by thE StokksEyri SupErDARN HF radar simultanEously at short and far rangEs arE usEd to invEstigatE thE rElationship bEtwEEn thE vElocity of E-rEgion HF EchoEs, E×B ElEctron drift and thE isothErmal ion-acoustic spEEd CS. ThE work targEts largE E×B drifts of >1000 m s−1 and obsErvations prEdominantly along thE flow. By considEring thE EISCAT tEmpEraturE and ElEctric fiEld data, an Empirical rElationship bEtwEEn thE E×B drift vElocity and CS is EstablishEd for a numbEr of ionosphEric hEights. For thE StokksEyri HF radar bEams oriEntEd roughly along thE E×B dirEction, thE obsErvEd E-rEgion HF vElocitiEs arE consistEnt with thE CS valuEs at thE bottom of thE ElEctrojEt but not at its cEntEr. For a subsEt of thE data with smooth and consistEnt vElocity variation with thE bEam azimuth at both short and far radar rangEs thE vElocity variEs according to thE cosinE law. For thE E-rEgion EchoEs, thE proportionality coEfficiEnt in thE cosinE law is consistEnt with thE CS valuEs at thE bottom of thE ElEctrojEt. For thEsE EvEnts, thE E-rEgion vElocity maximum is shown to bE bEtwEEn thE E×B and ElEctric fiEld dirEctions. ThE statistically avEragE shift is ~20° and it incrEasEs slightly with thE E×B magnitudE.
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SamplEs of Auroral E-REgion ParamEtErs DErivEd from EISCAT ExpErimEnts
Journal of geomagnetism and geoelectricity, 1995Co-Authors: Asgeir Brekke, Satonori Nozawa, Mariko SatoAbstract:In this work wE havE madE a comparison bEtwEEn quiEt and disturbEd timE valuEs of thE auroral zonE E-fiEld ionosphEric conductancEs and E-rEgion nEutral winds as dErivEd from EISCAT-UHF mEasurEmEnts. ThE avEragE diurnal mEan valuEs of thE E-fiEld arE rathEr unchangEd bEtwEEn quiEt and disturbEd days whilE thE amplitudE of thE 24-hour diurnal oscillation is EnhancEd by a factor of 3 from avEragEd quiEt to disturbEd days. ThE E-rEgion nEutral wind has an Eastward componEnt bEtwEEn 90 and 110 km which is sEasonal dEpEndEnt, showing highEst valuEs in summEr and lowEst in wintEr with spring and fall valuEs in bEtwEEn. ThE most outstanding diffErEncE bEtwEEn quiEt and disturbEd timE E-rEgion nEutral winds is an incrEasE in thE Eastward diurnal fidE of a factor of 3-4 abovE 100 km. ThE mEan wind as wEll as thE highEr ordEr tidal modEs (12-, 8- and 6-hour modEs) display rathEr minor diffErEncEs.
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StudiEs of thE E rEgion nEutral wind in thE quiEt auroral ionosphErE
Journal of Geophysical Research, 1994Co-Authors: Asgeir Brekke, Satonori Nozawa, Trygve SparrAbstract:QuiEt timE auroral E rEgion nEutral wind data obtainEd by EuropEan IncohErEnt ScattEr Radar (EISCAT) havE bEEn analyzEd in ordEr to Establish thE background mEan nEutral vElocitiEs as wEll as tidal influEncE on thE wind. ThErE is a rathEr strong and pErsistEnt mEan Eastward wind prEsEnt in all sEasons in thE E rEgion bElow 120 km. It is strongEst in summEr (∼60 m s−1), wEak in fall and spring, and wEakEr in wintEr (∼20 m s−1). ThE zonal wind is wEstward abovE 120 km, in gEnEral strongEr in wintEr (∼70 m s−1) and wEakEr in thE othEr sEasons (∼30 m s−1). ThE northward mEan wind is rathEr small (∼10 m s−1). It is shiftEd gradually from bEing mainly southward in wintEr to bEcoming northward in summEr. ThE mEan vErtical vElocity is of thE ordEr of 5 m s−1 in thE auroral E rEgion. ThE amplitudE of thE diurnal tidEs of thE vErtical componEnt havE broad minima in thE hEight rEgion bEtwEEn 90 and 120 km. ThE horizontal diurnal tidE is dominant in thE uppEr E rEgion, whilE thE sEmidiurnal tidE has a maximum at 110 km, in particular in thE Eastward componEnt. ThE 8- and 6-hour tidEs arE rathEr constant in amplitudE by hEight. ThE rEsults obtainEd arE in good agrEEmEnt with othEr rEsults publishEd on thE basis of incohErEnt scattEr radar mEasurEmEnts. ThE comparison with thEorEtical modEls undErlinEs thE nEEd for morE modEling of thE auroral E rEgion nEutral tidEs including thE ionizEd plasma as wEll as ElEctric fiElds and mEan background winds. ThEorEtical studiEs of thE vErtical motion with rEspEct to thE influEncE of tidEs arE EspEcially lacking in this important rEgion.
