Region Neutral Wind Research Articles

F Region Neutral Wind and Electric Field Measured by SYISR and Evaluation

AbstractUsing experiments by Sanya (18.3°N, 109.6°E) Incoherent Scatter Radar (SYISR) during 22 days, we first obtained the line‐of‐sight ion velocity in multiple directions, further calculated three‐dimensional vector velocity through least squares fitting, and subsequently derived northward neutral wind and electric fields from 150 to 500 km based on the momentum equation. In order to verify the reliability of the derived northward neutral wind and electric field, we used NCAR‐TIEGCM and HWM for comparative analysis. They had a good consistency in terms of diurnal variation and direction. The SYISR vertical ExB velocity during the daytime is larger than that of TIEGCM, and the direction reverses occur after 20:00 for both TIEGCM and SYISR. We further compared our wind data with that of ICON satellite. They showed a positive correlation of ∼0.62. We also used the ∆H method to verify our eastward electric field. They showed a roughly linear dependency, although the correlation coefficient is not very high.

Comparison of ICON/MIGHTI and TIMED/TIDI Neutral Wind Measurements in the Lower Thermosphere.

This study cross-compares ICON/MIGHTI and Thermosphere, Ionosphere, Mesosphere Energetics & Dynamics (TIMED)/TIMED Doppler Interferometer (TIDI) MLT region neutral winds from middle Northern Hemisphere to low Southern Hemisphere latitudes. We utilized MIGHTI level-2.2 (v4) and TIDI level-3 (v11) neutral winds from January 2020 to November 2020 and found their conjunctions using a space-time window of LST ± 15 min, latitude ± 4°, and longitude ± 4° around each TIDI wind measurement. Due to the nature of their orbital geometry, frequent conjunctions occurred between MIGHTI and TIDI. These conjunctions are spread in longitudes and they occur at approximately fixed LSTs and latitudes, which allows us to compare their observed diurnal variability. MIGHTI and TIDI wind observations agree well (except on the TIDI coldside during forward flight) and show similar large amplitude longitudinal variations that can reach more than 100 m/s. MIGHTI and TIDI zonal and meridional winds show moderate correlations of 0.60 and 0.55, respectively. The slopes of regression fits for zonal and meridional winds are 0.92 and 0.91, respectively. The root mean square differences in zonal and meridional winds are 56 and 66 m/s, respectively. We found that TIDI coldside measurements in forward flight show a systematic bias and this behavior is repetitive as the instrument pointing direction is changed by the periodic TIMED yaw maneuver. The nature of this systematic bias suggests that the TIDI zero-wind references (at least for the coldside telescopes) need revision. This investigation can provide guidance toward improving the TIDI data analysis. In addition, the results of this study act as a validation of MIGHTI MLT winds.

Global distribution of the He+ column density observed by Extreme Ultra Violet Imager on the International Space Station

AbstractThe global distribution of He+ in the topside ionosphere was investigated using data of the He+ resonant scattering emission at 30.4 nm obtained by the Extreme Ultra Violet Imager (EUVI) onboard the International Space Station. The optical observation by EUVI from the low‐Earth orbit provides He+ column density data above the altitude of 400 km, presenting a unique opportunity to study the He+ distribution with a different perspective from that of past studies using data from in situ measurements. We analyzed data taken in 2013 and elucidated, for the first time, the seasonal, longitudinal, and latitudinal variations of the He+ column density in the dusk sector. It was found that the He+ column density in the winter hemisphere was about twice that in the summer hemisphere. In the December solstice season, the magnitude of this hemispheric asymmetry was large (small) in the longitudinal sector where the geomagnetic declination is eastward (westward). In the June solstice season, this relationship between the He+ distribution and the geomagnetic declination is reversed. In the equinox seasons, the He+ column densities in the two hemispheres are comparable at most longitudes. The seasonal and longitudinal dependence of the hemispheric asymmetry of the He+ distribution was attributed to the geomagnetic meridional neutral wind in the F region ionosphere. The neutral wind effect on the He+ distribution was examined with an empirical neutral wind model, and it was confirmed that the transport of ions in the topside ionosphere is predominantly affected by the F region neutral wind and the geomagnetic configuration.

Numerical simulation of the 6 day wave effects on the ionosphere: Dynamo modulation

AbstractThe Thermosphere‐Ionosphere‐Mesosphere Electrodynamics General Circulation Model (TIME‐GCM) is used to theoretically study the 6 day wave effects on the ionosphere. By introducing a 6 day perturbation with zonal wave number 1 at the model lower boundary, the TIME‐GCM reasonably reproduces the 6 day wave in temperature and horizontal winds in the mesosphere and lower thermosphere region during the vernal equinox. The E region wind dynamo exhibits a prominent 6 day oscillation that is directly modulated by the 6 day wave. Meanwhile, significant local time variability (diurnal and semidiurnal) is also seen in wind dynamo as a result of altered tides due to the nonlinear interaction between the 6 day wave and migrating tides. More importantly, the perturbations in the E region neutral winds (both the 6 day oscillation and tidal‐induced short‐term variability) modulate the polarization electric fields, thus leading to the perturbations in vertical ion drifts and ionospheric F2 region peak electron density (NmF2). Our modeling work shows that the 6 day wave couples with the ionosphere via both the direct neutral wind modulation and the interaction with atmospheric tides.

Equatorial F region neutral winds and shears near sunset measured with chemical release techniques

AbstractThe period near sunset is a dynamic and critical time for the daily development of the equatorial nighttime ionosphere and the instabilities that occur there. It is during these hours that the preconditions necessary for the later development of Equatorial Spread F (ESF) plasma instabilities occur. The neutral dynamics of the sunset ionosphere are also of critical importance to the generation of currents and electric fields; however, the behavior of the neutrals is experimentally understood primarily through very limited single‐altitude measurements or measurements that provide weighted altitude means of the winds as a function of time. To date, there have been very few vertically resolved neutral wind measurements in the F region at sunset. We present two sets of sounding rocket chemical release measurements, one from a launch in the Marshall Islands on Kwajalein atoll and one from Alcantara, Brazil. Analysis of the release motions has yielded vertically resolved neutral wind profiles that show both the mean horizontal winds and the vertical shears in the winds. In both experiments, we observe significant vertical gradients in the zonal wind that are unexpected by classical assumptions about the behavior of the neutral wind at these altitudes at sunset near the geomagnetic equator.

Comparison of the neutral wind seasonal variation from midlatitude conjugate observations

The seasonal variation of F region neutral wind from the midlatitude conjugate Fabry‐Perot interferometer observations has been studied. The meridional wind at Palmer station (64°S,64°W) has a significant local time dependence with strong equatorward wind at midnight and polarward wind at dawn and dusk. The zonal wind switches from eastward to westward in the early morning section. From the June solstice (austral winter) to equinox, the maximum meridional wind increases from 90 m/s to 130 m/s, and the zonal wind switches direction at an earlier local time. The neutral winds from Palmer have been compared with those from the geomagnetic conjugate location, Millstone Hill (MH). At equinox, the local time variation of neutral wind shows a very good conjugacy between these two locations. But at June solstice, the similarity in the zonal wind becomes less clear. This seasonal dependence can be attributed to the seasonal variation of solar and geomagnetic forcings. The annual variation of daily average neutral wind from Palmer and MH has also been compared. The meridional wind shows a clear offset of season, and the magnitude at Palmer is averagely 40 m/s more equatorward than that at MH. The zonal wind is dominantly westward at Palmer and eastward at MH. The annual variation of neutral wind, especially the zonal component, is much less symmetric between the two sites than the local time variation. The empirical horizontal wind model shows a good agreement with the observations in both local time and annual variations.

Latitude and local time variations of topside magnetic field-aligned ion drifts at solar minimum

[1] The movement of ions along terrestrial magnetic field lines frequently causes the redistribution of ionization between northern and southern hemispheres. This behavior is known as interhemispheric transport and is an important source of coupling between the ion and neutral gases in the upper atmosphere. The Communications/Navigation Outage Forecast System (C/NOFS) satellite and the Coupled Ion Neutral Dynamics Investigation (CINDI) provide an opportunity to directly measure ion velocities and ion densities in the topside ionosphere, facilitating the study of the field-aligned ion motions near the equator. Using data from 2008 and 2009, the field-aligned ion velocities shows the presence of and variations in the interhemispheric transport during this extreme solar minimum. Solar local time and corrected magnetic latitude variations in field-aligned plasma transport at equinox and solstice are examined for a fixed longitude region and the consistency or the observed trends are compared to the expected behavior of F region neutral winds.

Mesoscale observations of Joule heating near an auroral arc and ion-neutral collision frequency in the polar capEregion

[1] We report on the first mesoscale combined ionospheric and thermospheric observations, partly in the vicinity of an auroral arc, from Svalbard in the polar cap on 2 February 2010. The EISCAT Svalbard radar employed a novel scanning mode in order to obtain F and E region ion flows over an annular region centered on the radar. Simultaneously, a colocated Scanning Doppler Imager observed the E region neutral winds and temperatures around 110 km altitude using the 557.7 nm auroral optical emission. Combining the ion and neutral data permits the E region Joule heating to be estimated with an azimuthal spatial resolution of ∼64 km at a radius of ∼163 km from the radar. The spatial distribution of Joule heating shows significant mesoscale variation. The ion-neutral collision frequency is measured in the E region by combining all the data over the entire field of view with only weak aurora present. The estimated ion-neutral collision frequency at ∼113 km altitude is in good agreement with the MSIS atmospheric model.

First observations of simultaneous interhemispheric conjugate high‐latitude thermospheric winds

We report the first observations of simultaneous high‐latitude interhemispheric F region neutral wind fields by combining the 630 nm optical measurements from two scanning Doppler imagers (SDIs) and three Fabry‐Perot interferometers (FPIs) for a period exceeding 5 h. From the Southern Hemisphere, a SDI at Mawson and a FPI at Davis, both in Antarctica, are geomagnetically mapped onto the Northern Hemisphere. These data are combined in the Northern Hemisphere with a SDI at Longyearbyen, Svalbard, and two FPIs near Kiruna in Sweden and Sodankyla in Finland. Geomagnetic conditions were moderate (Kp = 3−−3+) and steady although the interplanetary magnetic field Bz component did change polarity several times. There is good agreement between the conjugate 630 nm optical intensities and wind vectors where the two SDIs' fields of view overlap. All wind field vectors are overlaid onto the northern Super Dual Auroral Radar Network ion convection contours. Qualitatively, the agreement between neutral and ion flow is remarkably good throughout the study interval, even down to mesoscale spatial size.

First E region observations of mesoscale neutral wind interaction with auroral arcs

We report the first observations of E region neutral wind fields and their interaction with auroral arcs at mesoscale spatial resolution during geomagnetically quiet conditions at Mawson, Antarctica. This was achieved by using a scanning Doppler imager, which can observe thermospheric neutral line‐of‐sight winds and temperatures simultaneously over a wide field of view. In two cases, the background E region wind field was perpendicular to an auroral arc, which when it appeared caused the wind direction within ∼50 km of the arc to rotate parallel along the arc, reverting to the background flow direction when the arc disappeared. This was observed under both westward and eastward plasma convection. The wind rotations occurred within 7–16 min. In one case, as an auroral arc propagated from the horizon toward the local zenith, the background E region wind field became significantly weaker but remained unaffected where the arc had not passed through. We demonstrate through modeling that these effects cannot be explained by height changes in the emission layer. The most likely explanation seems to be the greatly enhanced ion drag associated with the increased plasma density and localized ionospheric electric field associated with auroral arcs. In all cases, the F region neutral wind appeared less affected by the auroral arc, although its presence is clear in the data.

Correlations of mesospheric winds with subtle motion of the Arctic polar vortex

Abstract. This paper investigates the relationship between high latitude upper mesospheric winds and the state of the stratospheric polar vortex in the absence of major sudden stratospheric warmings. A ground based Michelson Interferometer stationed at Resolute Bay (74°43' N, 94°58' W) in the Canadian High Arctic is used to measure mesopause region neutral winds using the hydroxyl (OH) Meinel-band airglow emission (central altitude of ~85 km). These observed winds are compared to analysis winds in the upper stratosphere during November and December of 1995 and 1996; years characterized as cold, stable polar vortex periods. Correlation of mesopause wind speeds with those from the upper stratosphere is found to be significant for the 1996 season when the polar vortex is subtly displaced off its initial location by a strong Aleutian High. These mesopause winds are observed to lead stratospheric winds by approximately two days with increasing (decreasing) mesospheric winds predictive of decreasing (increasing) stratospheric winds. No statistically significant correlations are found for the 1995 season when there is no such displacement of the polar vortex.

Neutral-ion interaction in the auroralEregion obtained from coordinated Fabry-Perot imager and VHF radar observations

[1] It is important to investigate the small-scale dynamics of thermospheric neutrals and ionospheric plasmas at high latitudes since there are local and temporal variations in energy input and transfer processes associated with auroral activities. To clarify these ionosphere-thermosphere interactions in the auroral E region, we examined neutral winds and plasma motions obtained by coordinated Fabry-Perot imager and VHF radar observations at Syowa Station, Antarctica. From case studies on 11 and 12 September 1996, we found a good correlation between temporal variation (period < 1 hr) of E region neutral winds measured by the Fabry-Perot imager and the Doppler velocities of plasmas obtained from the VHF radar echoes. On the other hand, the absolute mean values of the neutral winds were around zero whereas the plasma Doppler velocities were 350–400 m/s, showing a significant discrepancy. Considering that the neutral-ion and ion-neutral momentum transfer collision frequencies in the E region are ∼10−6 Hz and ∼102 Hz, respectively, these good correlations are probably due to ion motions driven by neutral drag force, suggesting a strong coupling between neutrals and ions in the E region. The observed correlation and discrepancy between the radar Doppler velocity and the neutral wind velocity are consistent with the linear theory of E region irregularities that shows the radar Doppler velocity is the sum of two components; one is the E × B drift speed, and another is proportional to the neutral wind velocity.

Role of the equatorial ionization anomaly in the development of the evening prereversal enhancement of the equatorial zonal electric field

During the evening prereversal enhancement of the zonal electric field (EPRE) that begins around 1700 LT when the F region neutral winds turn eastward, as assumed here, and continues till the postsunset zonal electric field reversal time, an overall positive feedback is shown to occur between the eastward electric field in the lower side of the flux tube integrated (LSFTI) F region and the increased flux tube integrated Pedersen conductivity (FTIC) of the tropical F region. The increase in this FTIC can take place because of the increase in electron density through the increase in solar flux and the intensification of the equatorial ionization anomaly (EIA). While the influence of EIA on EPRE is immediate, the growth time for EIA is 2 to 3 h. Therefore, for a strong EPRE to occur, a fairly strong EIA is required at 1700 LT which is then sustained by the electric field associated with EPRE during its growth period. This study suggests that the postsunset eastward electric field is due to the combined currents in the equatorial electrojet and the LSFTI F regions that get diverted from the daytime Sq current system and flow from the presunset region toward the postsunset zonal electric field reversal region. Thereafter these currents turn and flow poleward to meet the current continuity requirement of the F region dynamo followed by a westward turn to rejoin the daytime Sq current system in midlatitudes. Thus the currents responsible for EPRE are an extension of the daytime Sq current system.

A Bayesian approach to electric field and E‐region neutral wind estimation with the Poker Flat Advanced Modular Incoherent Scatter Radar

In this paper, we describe an approach for computing vector electric fields in the F region and neutral winds in the E region from incoherent scatter radar (ISR) measurements, applicable especially for Advanced Modular Incoherent Scatter Radar (AMISR) systems, namely, the Poker Flat Incoherent Scatter Radar (PFISR). PFISR is a 128‐panel (upgraded from 96 panels in September 2007) AMISR system installed at the Poker Flat Research Range near Fairbanks, Alaska. The pulse‐to‐pulse steering capabilities of AMISR support the measurement of line‐of‐sight velocities in multiple look directions essentially simultaneously. This capability in turn allows electric fields and neutral winds to be resolved with minimal assumptions regarding time stationarity of the medium. The multibeamforming capability also allows additional flexibility in the estimation of those parameters, for which experiment planning can become very important. The approach described herein is ideally suited for such planning, is appropriate for the overdetermined problem characteristic of AMISR measurements, and allows in a simple way for the inclusion of appropriate a priori information such as the assumption of negligible parallel electric fields and negligible vertical neutral winds. We present some case studies from the PFISR that demonstrate some of the new capabilities.

Ion and neutral motions observed in the winter polar upper atmosphere

Continuous samples of the ion drift are made near 800‐km altitude from the DMSP satellite and compared with remote measurements of the F region neutral winds made from the ground at Eureka in the northern polar cap. These measurements are compared with each other and with variations in the interplanetary magnetic field and solar wind. Over a 6‐day period, linear relationships between the north‐south component of the IMF and the noon‐midnight components of the ion and neutral drifts are used to determine the response times of the gas motions to changes in the solar wind driver. When the IMF is southward or weakly northward, the ion and neutral gas response begins almost immediately following a change in the solar wind driver. The time constant for the ion response is about 20 min, while for an F peak density of about 5 × 105 cm−3 the neutral time constant is 75 min. While significant variability exists, the 55‐min time difference between the response times is consistent with the neutral‐ion collision time prevailing in the F region at the time and location of the measurements. In the quasi‐equilibrium state, antisunward ion drifts in excess of 150 m s−1 drive the neutral gas antisunward with speeds about 60% of the ion drift.

다목적 실용위성 1호로 측정한 저위도 상부 이온층의 전자 온도와 전자 밀도의 경도 및 계절별 변화

다목적 실용위성 1호는 고도 685km, <TEX>$98^{\circ}$</TEX>의 궤도 경사각를 가지며, 탑재된 이온층 측정 센서(Ionospheric Measurement Sensor)로 전자 온도와 전자 밀도를 측정하였다. 이 관측 자료로부터 22:50LT인 밤 시간에 <TEX>$+60^{\circ}~-60^{\circ}$</TEX>의 저위도 지역에서 자기적으로 안정한 상태(Kp <4)의 계절별 전자 밀도와 전자 온도의 분포를 구하였다. 관측 결과, 전자 온도와 전자 밀도의 분포는 계절과 경도에 따라 변화를 나타냈다. 대체로 전자 밀도는 자기 적도 부근에서 높아지고, 전자 온도는 낮아지는 경향을 보였다. 봄, 가을에는 전자 밀도와 온도 모두 자기 적도를 중심으로 대칭적으로 분포하였다. 그러나 여름에는 전체적으로 북반구 쪽으로 이동하여 전자 밀도의 극대점과 전자 온도의 극소점이 자기 적도 북쪽에 위치하였고, 겨울에는 이와 반대의 변화를 나타냈다. 또한, 각 계절에서 경도에 따라서도 전자 온도와 밀도 분포의 차이를 보였다. 이러한 차이가 생기는 원인은 경도와 계절에 따라 달라지는 F층의 중성 바람이 이온층 플라즈마에 영향을 주는 것에 의해 설명될 수 있다. 이 관측에서 얻은 전자온도와 밀도의 분포는 IRI95모델을 이용해 구한 분포와 차이를 보였다. The electron density and temperature in the topside ionosphere are observed by the ionosphere Measurement Sensor (IMS) onboard the KOMPSAT-1, which has the sun-synchronous orbit of the altitude of 685 km and the orbital inclination of <TEX>$98^{\circ}$</TEX> with a descending node at 22:50LT. Observations have been analyzed to determine the seasonal variations of the electron density and temperature in the low-latitude region. Only the night-time (22:50LT) behavior on magnetically quiet days (Kp < 4) has been examined. Observations show a strong longitudinal and seasonal variation. Generally, in the dip equator the density increases and the temperature decreases. In equinox the latitudinal distributions of the electron density and temperature are quite symmetric about the dip equator. However, the local maximum of the density and the local minimum of the temperature shift toward the Northern hemisphere in summer solstice but the Southern hemisphere in winter solstice. Such variations are due to the influences of field-aligned plasma transport induced by F region neutral wind. Compared with the IRI95 model, the observed electron density and temperature show significant differences from those predicted by the IRI95 model.

Comparison of the auroral E region neutral winds derived with the European Incoherent Scatter radar and predicted by the National Center for Atmospheric Research Thermosphere‐ionosphere‐mesosphere‐electrodynamics general circulation model

A comparison study of the auroral E region neutral wind has been conducted using the European Incoherent Scatter (EISCAT) radar observations and Thermosphere‐Ionosphere‐Mesosphere‐Electro dynamics general circulation model (TIME GCM) predictions. The daily mean wind data as well as diurnal and semidiurnal tidal wind data, are compared for the three seasons summer, equinox, and winter between 95 and 119 km. Fairly good agreement is found in the altitude profile of the mean zonal wind between the EISCAT observation and the TIME GCM prediction for summer, indicating the parameterization of gravity waves employed in the TIME GCM is adequate for this feature. The meridional mean wind amplitude predicted by the TIME GCM is considerably smaller than that observed by EISCAT, and the predicted wind is slightly northward for all the seasons above 100 km. Generally good agreement is found for the amplitude of the diurnal tide, especially the summer prediction, while disagreements between the model and observational results are found for the corresponding phases. The semidiurnal amplitude predicted by the TIME GCM is much smaller than that observed by EISCAT, and relatively large differences of the semidiurnal phase between the observations and predictions are found for all seasons. These comparison results suggest that further advancements in the gravity wave parameterization, as well as the addition of planetary wave effects, are needed to predict more realistic lower thermospheric winds at high latitude.

Origin and development of vertical propagating oscillations with periods of planetary waves in the ionospheric F region

Starting from previous results of vertical propagating 6.5-day oscillations observed in the F region of the ionosphere during 1998, we investigated their possible forcing from both the planetary wave activity of the neutral winds in the mesosphere/lower thermosphere and the geomagnetic activity. For this purpose we used the electron density profiles and geomagnetic field components obtained at Observatori de l'Ebre station (40.8°N, 0.5°E), the mesopause region neutral wind data obtained at Collm Observatory (52°N, 15°E) and the 3-hourly geomagnetic index Ap. From the four events of 6.5-day oscillations observed in the ionosphere, we found that two of them are contemporary with two events of 6.5-day period in the neutral winds and the coherency between the neutral winds and ionosphere variations at 6.5-day periods is very large. The other ionospheric events are contemporary with the existence of two geomagnetic storms and the coherency between the ionospheric and geomagnetic activity variations is very large at periods at 6.5 days. The potential mechanisms linking the geomagnetic activity variations and the planetary wave activity of the neutral winds in the mesosphere/lower thermosphere with the wave events observed in the ionosphere are discussed in order to explain the possible origin of the ionospheric waves.

A case study of the auroral E region neutral wind on a quiet summer day: Comparison of the European Incoherent Scatter UHF radar for deriving the E region wind

Comparison study of three methods of the European Incoherent Scatter (EISCAT) radar for furnishing E region neutral wind data is performed on the basis of observational data. A Special Program by using the EISCAT UHF radar located in northern Scandinavia was conducted for 24 hours starting at 1000 UT on July 14, 1997. Two modes of EISCAT Common Program 1 and 2 are combined in this Special Program, so that the capability of the tristatic method and monostatic (or beamswinging) methods are compared on the basis of observations at four heights between 99 and 108 km under geomagnetic quiet conditions. The meridional neutral wind is derived by the field‐aligned method as well. Derived wind velocities by the three methods are compared, and fairly good agreement is found in terms of a relatively longer temporal variation (∼2–3 hours). The comparison of the derived velocities shows that the tristatic method (i.e., Common Program 1) is superior to the monostatic method (i.e., Common Program 2) in terms of an instantaneous measurement, while the monostatic method has an advantage on a tidal study. Regarding the meridional wind component, the filed‐aligned method has significant advantages compared to the other methods concerning temporal data coverage, error, and height coverage. The derived neutral wind in this Special Program is compared with that from a statistical study by Nozawa and Brekke [1999a]. Generally good agreement for mean and semidiurnal winds is found with the statistical result, but relatively strong amplitude (∼35 m s−1) of 8‐hour meridional component is found in this case study. Comparison of the zonal mean wind and mean temperature is made with the CIRA (1986) model as well. Good agreement is obtained for the temperature, while poor agreement is found for the zonal mean wind.

On the usefulness of &amp;lt;i&amp;gt;E&amp;lt;/i&amp;gt; region electron temperatures and lower &amp;lt;i&amp;gt;F&amp;lt;/i&amp;gt; region ion temperatures for the extraction of thermospheric parameters: a case study

Abstract. Using EISCAT data, we have studied the behavior of the E region electron temperature and of the lower F region ion temperature during a period that was particularly active geomagnetically. We have found that the E region electron temperatures responded quite predictably to the effective electric field. For this reason, the E region electron temperature correlated well with the lower F region ion temperature. However, there were several instances during the period under study when the magnitude of the E region electron temperature response was much larger than expected from the ion temperature observations at higher altitudes. We discovered that these instances were related to very strong neutral winds in the 110-175 km altitude region. In one instance that was scrutinized in detail using E region ion drift measurement in conjunction with the temperature observations, we uncovered that, as suspected, the wind was moving in a direction closely matching that of the ions, strongly suggesting that ion drag was at work. In this particular instance the wind reached a magnitude of the order of 350 m/s at 115 km and of at least 750 m/s at 160 km altitude. Curiously enough, there was no indication of strong upper F region neutral winds at the time; this might have been because the event was uncovered around noon, at a time when, in the F region, the E×B drift was strongly westward but the pressure gradients strongly northward in the F region. Our study indicates that both the lower F region ion temperatures and the E region electron temperatures can be used to extract useful geophysical parameters such as the neutral density (through a determination of ion-neutral collision frequencies) and Joule heating rates (through the direct connection that we have confirmed exists between temperatures and the effective electric field).Key words. Ionosphere (auroral ionosphere; ionosphere atmosphere interactions; plasma temperature and density)