Apex Altitude Research Articles

GOLD Observations of Equatorial Plasma Bubbles Reaching Mid‐Latitudes During the 23 April 2023 Geomagnetic Storm

AbstractA coronal mass ejection erupted from the Sun on 21 April 2023 and created a G4 geomagnetic storm on 23 April. NASA's global‐scale observations of the limb and disk (GOLD) imager observed bright equatorial ionization anomaly (EIA) crests at ∼25° Mlat, ∼11° poleward from their average locations, computed by averaging the EIA crests during the previous geomagnetic quiet days (18–22 April) between ∼15°W and 5°W Glon. Reversed C‐shape equatorial plasma bubbles (EPBs) were observed reaching ∼±36° Mlat (∼40°N and ∼30°S Glat) with apex altitudes ∼4,000 km and large westward tilts of ∼52°. Using GOLD's observations EPBs zonal motions are derived. It is observed that the EPBs zonal velocities are eastward near the equator and westward at mid‐latitudes. Model‐predicted prompt penetration electric fields indicate that they may have affected the postsunset pre‐reversal enhancement at equatorial latitudes. Zonal ion drifts from a defense meteorological satellite program satellite suggest that westward neutral winds and perturbed westward ion drifts over mid‐latitudes contributed to the observed latitudinal shear in zonal drifts.

First Observations of Severe Scintillation Over Low‐to‐Mid Latitudes Driven by Quiet‐Time Extreme Equatorial Plasma Bubbles: Conjugate Measurements Enabled by Citizen Science Initiatives

AbstractLow‐cost instrumentation combined with volunteering and citizen science educational initiatives allowed the deployment of L‐band scintillation monitors to remote sense areas that are geomagnetically conjugated and located at low‐to‐mid latitudes in the American sector (Quebradillas in Puerto Rico and Santa Maria in Brazil). On 10 and 11 October, 2023, both monitors detected severe scintillations, some reaching dip latitudes beyond 26°N. The observations show conjugacy in the spatio‐temporal evolution of the scintillation‐causing irregularities. With the aid of collocated all‐sky airglow imager observations, it was shown that the observed scintillation event was caused by extreme equatorial plasma bubbles (EPBs) reaching geomagnetic apex altitudes exceeding 2,200 km. The observations suggest that geomagnetic conjugate large‐scale structures produced conditions for the development of intermediate scale (few 100 s of meters) in both hemispheres, leading to scintillation at conjugate locations. Finally, unlike previous reports, it is shown that the extreme EPBs‐driven scintillation reported here developed under geomagnetically quiet conditions.

Global Maps of Equatorial Plasma Bubbles Depletions Based on FORMOSAT‐7/COSMIC‐2 Ion Velocity Meter Plasma Density Observations

AbstractFORMOSAT‐7/COSMIC‐2 is the largest equatorial multi‐satellite constellation of six full‐size satellites to study the equatorial ionosphere. Each satellite is equipped by an ion velocity meter (IVM) instrument to provide high rate in situ plasma density observations along the low‐inclined satellite orbits at ∼530–550 km altitude. Six satellites provide an unprecedented dense coverage of the entire equatorial region around the globe and allow reliable detection of equatorial plasma bubbles (EPBs) and plasma density irregularities at different local times/longitudinal sectors simultaneously. We present a method for detection of EPBs in FORMOSAT‐7/COSMIC‐2 in situ plasma density data and construction of the global maps of EPB geolocations. The results in the form of time series and IVM‐based global Bubble Maps have a great potential for both near real‐time monitoring of space weather conditions and long‐term statistical analysis of EPB occurrence in regional or global scales. We present first FORMOSAT‐7/COSMIC‐2 derived climatological characteristics of the post‐sunset and post‐midnight EPBs occurrence probability and their apex altitudes during a period of low solar activity. Also, we demonstrate the good performance of the FORMOSAT‐7/COSMIC‐2 IVM‐based Bubble Maps when compared to optical images and ground‐based ionosonde observations.

Deriving Large Coronal Magnetic Loop Parameters Using LOFAR J Burst Observations

Large coronal loops around one solar radius in altitude are an important connection between the solar wind and the low solar corona. However, their plasma properties are ill-defined, as standard X-ray and UV techniques are not suited to these low-density environments. Diagnostics from type J solar radio bursts at frequencies above 10 MHz are ideally suited to understand these coronal loops. Despite this, J-bursts are less frequently studied than their type III cousins, in part because the curvature of the coronal loop makes them unsuited for using standard coronal density models. We used LOw-Frequency-ARray (LOFAR) and Parker Solar Probe (PSP) solar radio dynamic spectrum to identify 27 type III bursts and 27 J-bursts during a solar radio noise storm observed on 10 April 2019. We found that their exciter velocities were similar, implying a common acceleration region that injects electrons along open and closed magnetic structures. We describe a novel technique to estimate the density model in coronal loops from J-burst dynamic spectra, finding typical loop apex altitudes around 1.3 solar radius. At this altitude, the average scale heights were 0.36 solar radius, the average temperature was around 1 MK, the average pressure was 0.7~text{mdyn},text{cm}^{-2}, and the average minimum magnetic field strength was 0.13 G. We discuss how these parameters compare with much smaller coronal loops.

Merging of Storm Time Midlatitude Traveling Ionospheric Disturbances and Equatorial Plasma Bubbles

AbstractPostsunset midlatitude traveling ionospheric disturbances (TIDs) and equatorial plasma bubbles (EPBs) were simultaneously observed over American sector during the geomagnetic storm on 8 September 2017. The characteristics of TIDs are analyzed by using a combination of the Millstone Hill incoherent scatter radar data and 2‐D detrended total electron content (TEC) from ground‐based Global Navigation Satellite System receivers. The main results associated with EPBs are as follows: (1) stream‐like structures of TEC depletion occurred simultaneously at geomagnetically conjugate points, (2) poleward extension of the TEC irregularities/depletions along the magnetic field lines, (3) severe equatorial and midlatitude electron density (Ne) bite outs observed by Defense Meteorological Satellite Program and Swarm satellites, and (4) enhancements of ionosphere F layer virtual height and vertical drifts observed by equatorial ionosondes near the EPBs initiation region. The stream‐like TEC depletions reached 46° magnetic latitudes that map to an apex altitude of 6,800 km over the magnetic equator using International Geomagnetic Reference Field. The formation of this extended density depletion structure is suggested to be due to the merging between the altitudinal/latitudinal extension of EPBs driven by strong prompt penetration electric field and midlatitude TIDs. Moreover, the poleward portion of the depletion/irregularity drifted westward and reached the equatorward boundary of the ionospheric main trough. This westward drift occurred at the same time as the sudden expansion of the convection pattern and could be attributed to the strong returning westward flow near the subauroral polarization stream region. Other possible mechanisms for the westward tilt are also discussed.

Low and Midlatitude Ionospheric Plasma Density Irregularities and Their Effects on Geomagnetic Field

Earth’s magnetic field results from various internal and external sources. The electric currents in the ionosphere are major external sources of the magnetic field in the daytime. High-resolution magnetometers onboard low-Earth-orbit satellites such as CHAMP and Swarm can detect small-scale currents in the nighttime ionosphere, where plasma density gradients often become unstable and form irregular density structures. The magnetic field variations caused by the ionospheric irregularities are comparable to that of the lithospheric contribution. Two phenomena in the nighttime ionosphere that contribute to the magnetic field variation are presented: equatorial plasma bubble (EPB) and medium-scale traveling ionospheric disturbance (MSTID). EPB is formed by the generalized Rayleigh–Taylor instability over the dip equator and grows nonlinearly to as high as 2000 km apex altitude. It is characterized by deep plasma density depletions along magnetic flux tubes, where the diamagnetic effect produced by a pressure-gradient-driven current enhances the main field intensity. MSTID is a few hundred kilometer-scale disturbance in the midlatitude ionosphere generated by the coupled electrodynamics between the ionospheric $E$ and $F$ regions. The field-aligned currents associated with EPBs and MSTIDs also have significant signatures in the magnetic field perpendicular to the main field direction. The empirical discovery of the variations in the magnetic field due to plasma irregularities has motivated the inclusion of electrodynamics in the physical modeling of these irregularities. Through an effective comparison between the model results and observations, the physical process involved has been largely understood. The prediction of magnetic signatures due to plasma irregularities has been advanced by modeling studies, and will be helpful in interpreting magnetic field observations from satellites.

Shrinking equatorial plasma bubbles

AbstractThe formation of equatorial plasma bubbles (EPBs) associated with spread F irregularities are fairly common phenomenon in the postsunset equatorial ionosphere. These bubbles grow as a result of eastward polarization electric field resulting in upward E × B drift over the dip equator. As they grow they are also mapped to low latitudes along magnetic field lines. The EPBs are often observed as airglow depletions in the images of OI 630 nm emission. On occasions the growth of the features over the dip equator is observed as poleward extensions of the depletions in all‐sky images obtained from low latitudes. Herein, we present interesting observations of decrease in the latitudinal extent of the EPBs corresponding to a reduction in their apex altitudes over the dip equator. Such observations indicate that these bubbles not only grow but also shrink on occasions. These are the first observations of shrinking EPBs. The observations discussed in this work are based on all‐sky airglow imaging observations of OI 630.0 nm emission made from Panhala (11.1°N dip latitude). In addition, ionosonde observations made from dip equatorial site Tirunelveli (1.1°N dip latitude) are used to understand the phenomenon better. The analysis indicates that the speed of shrinking occurring in the topside is different from the bottomside vertical drifts. When the EPBs shrink, they might decay before sunrise hours.

Shear in the zonal drifts of 3 m irregularities inside spread F plumes observed over Sanya

AbstractIncoherent scatter radars near magnetic equator regularly measured a vertical shear in zonal drifts of the evening background plasma, with westward drifts below the equatorial F region peak and eastward drifts above. We report here observations of a clear shear structure in the zonal drifts of 3 m irregularities inside spread F (SF) backscatter plumes measured with a 47.5 MHz coherent scatter radar operated at a low‐latitude site Sanya (18.4°N, 109.6°E; dip latitude 12.8°N). The radar interferometry analysis on the zonal drifts of the 3 m irregularities yields results consistent with that estimated from the irregularity echo Doppler velocity measurements with multiple beams. It is shown that the SF 3 m irregularities move westward at the lowest altitudes, while at higher altitudes in the same SF plume structure, the 3 m irregularities drift eastward. One interesting point is that the vertical shear of zonal drifts was centered at ~300 km altitude over Sanya, which maps to an apex altitude of ~650 km at magnetic equator and is thus apparently higher than the apex altitudes 250–450 km where the zonal velocity shear has usually been observed. Analysis of the observations suggests that while the possibility of local generation of the shear flow of the irregularities can exist, the possibility of a plasma vortex appearing at relative high altitudes causing the zonal drift shear of F region 3 m irregularities measured over Sanya cannot be totally ruled out.

SOLAR MICRO-TYPE III BURST STORMS AND LONG DIPOLAR MAGNETIC FIELD IN THE OUTER CORONA

Solar micro-type III radio bursts are elements of the so-called type III storms and are characterized by short-lived, continuous, and weak emissions. Their frequency of occurrence with respect to radiation power is quite different from that of ordinary type III bursts, suggesting that the generation process is not flare-related, but due to some recurrent acceleration processes around the active region. We examine the relationship of micro-type III radio bursts with coronal streamers. We also explore the propagation channel of bursts in the outer corona, the acceleration process, and the escape route of electron beams. It is observationally confirmed that micro-type III bursts occur near the edge of coronal streamers. The magnetic field line of the escaping electron beams is tracked on the basis of the frequency drift rate of micro-type III bursts and the electron density distribution model. The results demonstrate that electron beams are trapped along closed dipolar field lines in the outer coronal region, which arise from the interface region between the active region and the coronal hole. A 22 year statistical study reveals that the apex altitude of the magnetic loop ranges from 15 to 50 RS. The distribution of the apex altitude has a sharp upper limit around 50 RS suggesting that an unknown but universal condition regulates the upper boundary of the streamer dipolar field.

Heat-activated Parachute Release System

Release of a parachute at the apex of a rocket flight is a problem for every amateur rocket enthusiast. Existing commercially available methods all require the use of gunpowder, which can have licensing and safety complications depending upon the local laws. Axiomatic design analysis has shown that there is also high information content in this method. Users must precisely calculate the amount of black gunpowder to be used based upon altitude and rocket geometry. At the highest altitudes, gunpowder combustion gases are insufficient due to the low ambient pressure, so CO2 expansion actuation is used instead. These solutions using CO2 have lower information content, but are still activated using gunpowder and dependent upon altitude. Our analysis has led to the technique of using heat-activated materials as a CO2 valve release, a solution with lower information content. This design works with all sizes of amateur rockets up to Tripoli Rocketry Association Class 3 without knowledge of rocket apex altitude.

Gravity wave effects on postsunset equatorial F region stability

AbstractThe influence of gravity waves on the stability of the postsunset equatorial F region ionosphere is investigated numerically. For this investigation, we use the output of a direct numerical simulation of waves and turbulence in the mesosphere and lower thermosphere to force a simulation of ionospheric dynamics. Both simulations are cast in three dimensions. The effectiveness of the neutral‐plasma coupling involved is generally thought to depend on the dynamo efficiency and spatial resonance of the forcing, which we evaluate. In our simulations, the postsunset equatorial ionosphere could be deformed by neutral waves after 5–15 min most severely when the wavefronts were aligned approximately with the magnetic meridian, despite the fact that the dynamo efficiency is modest even in that case. However, poor spatial resonance limits the subsequent growth of the deformations in our simulations, and the seeding of interchange instabilities does not occur. The coupled simulations predict the formation of intermediate layers in the equatorial valley region (150–250 km apex altitude) under some circumstances that could serve as telltales in nature of the presence of the kind of neutral forcing we simulate.

Topside equatorial zonal ion velocities measured by C/NOFS during rising solar activity

Abstract. The Ion Velocity Meter (IVM), a part of the Coupled Ion Neutral Dynamic Investigation (CINDI) instrument package on the Communication/Navigation Outage Forecast System (C/NOFS) spacecraft, has made over 5 yr of in situ measurements of plasma temperatures, composition, densities, and velocities in the 400–850 km altitude range of the equatorial ionosphere. These measured ion velocities are then transformed into a coordinate system with components parallel and perpendicular to the geomagnetic field allowing us to examine the zonal (horizontal and perpendicular to the geomagnetic field) component of plasma motion over the 2009–2012 interval. The general pattern of local time variation of the equatorial zonal ion velocity is well established as westward during the day and eastward during the night, with the larger nighttime velocities leading to a net ionospheric superrotation. Since the C/NOFS launch in April 2008, F10.7 cm radio fluxes have gradually increased from around 70 sfu to levels in the 130–150 sfu range. The comprehensive coverage of C/NOFS over the low-latitude ionosphere allows us to examine variations of the topside zonal ion velocity over a wide level of solar activity as well as the dependence of the zonal velocity on apex altitude (magnetic latitude), longitude, and solar local time. It was found that the zonal ion drifts show longitude dependence with the largest net eastward values in the American sector. The pre-midnight zonal drifts show definite solar activity (F10.7) dependence. The daytime drifts have a lower dependence on F10.7. The apex altitude (magnetic latitude) variations indicate a more westerly flow at higher altitudes. There is often a net topside subrotation at low F10.7 levels, perhaps indicative of a suppressed F region dynamo due to low field line-integrated conductivity and a low F region altitude at solar minimum.

Comparison of zonal neutral winds with equatorial plasma bubble and plasma drift velocities

A one‐year dataset spanning March 2011 to March 2012 of coincident observations of nighttime thermospheric zonal neutral winds, equatorial plasma bubble (EPB) velocities, and zonal plasma drifts is used to examine the relationship between the thermosphere and the ionosphere near the geomagnetic equator over Peru. Thermospheric neutral winds are determined by using a bistatic Fabry‐Perot interferometer (FPI) experiment located at Merihill and Nazca in Peru. The ambient plasma drift velocities were obtained using the incoherent scatter radar at the Jicamarca Radio Observatory in Peru. The EPB zonal velocities were estimated utilizing images of the OI 630.0 nm emission recorded by a narrow‐field optical imaging system at the Cerro Tololo Inter‐American Observatory in Chile. The joint analysis of these datasets illustrates that the nighttime and night‐to‐night variations in the zonal neutral winds, EPB velocities, and plasma drifts are well correlated. This consistent result of the local time variations of the neutral winds with that of EPB and plasma drifts illustrates that the F‐region dynamo is, in general, fully activated. However, at times, the magnitude of the EPB velocities and the plasma drifts are different from the neutral winds. It is plausible that such a difference is due either to the effect of polarization electric fields developed inside the EPB or due to the latitudinal gradient of the neutral winds and EPB velocity measurements since the EPB velocities are estimated at a higher latitude, corresponding to an apex altitude of ~400 km, than the wind estimates, which derive from an apex altitude of ~250 km.

Correlation of in situ measurements of plasma irregularities with ground‐based scintillation observations

We present here the first comparison of in situ ion density fluctuations measured by the Planar Langmuir Probe on Communication\Navigation Outage Forecasting System (C/NOFS) with coincident ground‐based measurements of scintillation from the Scintillation Decision Aid (SCINDA) network and coherent scatter radar located on Christmas Island (3°N, 157°W) over a 15 month period from May 2008 through June 2009. The Planar Langmuir Probe on C/NOFS measures absolute ion densities from 10 to 108 cm−3 at a rate up to 1024 Hz. The instrument is conceptually similar to ion traps and retarding potential analyzers that have flown on many past satellite and rocket missions. However, the present design includes advances in electronic capability compared with past designs. Initial results from this study show that in situ density fluctuations observed on magnetic flux tubes that pass over Christmas Island can be used as an indicator of ionospheric radio wave scintillation at that site. This is true even when the measurements are made at horizontal ranges of over 1000 km away from the ground site as long as the field line apex altitudes are less than ∼600 km.

Simultaneous ground- and satellite-based airglow observations of geomagnetic conjugate plasma bubbles in the equatorial anomaly

Abstract We compare, for the first time, geomagnetically-conjugate plasma bubbles observed by ground-based OI 630.0-nm all-sky imagers at Shigaraki, Japan (34.8°N, 136.1°E; magnetic latitude 25.4°N) and Darwin, Australia (12.4°S, 131.0°E; magnetic latitude 22.0°S), with global-scale plasma structures (≈10,000 km in longitude) in the equatorial anomaly simultaneously detected with an OI 135.6-nm imager on the IMAGE satellite at ≈7 earth radii. As found previously, global-scale plasma structures in both hemisphere imaged by IMAGE consist of an array of geomagnetically-conjugate small- to medium-scale (a few hundreds to 1000 km in longitude) wavy structures that move to the east at ≈100 ms−1. We find the following: 1) plasma bubbles detected with the allsky imagers reach an apex altitude of ≈1800 km over the geomagnetic equator while moving to the east at ≈100 m s−1 with spacings of 200–250 km. 2) Bubbles observed with the all-sky imagers and IMAGE are embedded within the small- to medium-scale wavy structures, and some of them are located near the crest of an enhanced electron density region associated with the wavy structures. 3) The bubbles and wavy structures that are generated near sunset slant to the west with increasing latitude in both hemispheres, and tilts do not change with longitude (i.e., local time). The results suggest that the generation and evolution of plasma bubbles are closely related to those of the small- to medium-scale plasma structures.

Ionospheric data assimilation: recovery of strong mid-latitudinal density gradients

The September 1999 Caribbean Ionospheric Campaign (CIC99), spanning the period 15–17 September 1999, was a period of repeated moderate geomagnetic storms. Both incoherent scatter radar (ISR) and digisonde F-layer measurements were made in the vicinity of Arecibo, Puerto Rico by the Arecibo ISR and Ramey Digisonde, which is one of the Digital Ionospheric Sounding System instruments. These data sets showed significant day-to-day F-layer variability, especially in the evening sectors. Local ionospheric data assimilation with the Assimilation Ionospheric Model (AIM1.06L) was able to reproduce this ionospheric day-to-day weather. However, during this time the Arecibo ISR was able to determine that strong latitude density gradients existed in the evening sector. These latitude gradients ranged from 5% to over 10% per degree of latitude, increasing equatorward. The climatological ionospheric forecast model (IFM) predicts gradients of the correct sign but significantly less than 5% per degree. Using the observed fact that the strong local vertical plasma drift was produced by an eastward electric field, an enhanced equatorial electric field model was created. This model was used to drive the IFM-E model. The effect of the enhanced electric field is to drive plasma flux tubes to higher latitudes and effectively move the poleward shoulder of the equatorial anomalies to higher latitudes. In this simulation, the simulated Arecibo density gradients range from 10% to 20% per degree. In addition, the local densities at Arecibo are now higher than the observed ones in the evening sector. The irony of this study is that the local AIM1.06L assimilation provides the correct local densities in the F region but is based upon the assumption of corotating field lines. When the plasma flux tubes are free to be E × B/B 2 convected, as in the IFM equator model simulations, the local densities are too high. However, gradients in latitude are more realistic although somewhat larger than observed. This latter simulation is based on “better” physics than the AIM1.06L, but because the latitude (apex altitude) distribution of the eastward electric field driver is uncertain, it produces poor assimilation results. This study points to the need for more extended latitude coverage in the CIC campaigns in order to address the issue of a minimum data requirement for the assimilation.

Geomagnetic conjugate observations of equatorial airglow depletions

We report for the first time large‐scale equatorial F‐region airglow depletions extending to low‐midlatitudes in both hemispheres. The observational sites were located at low‐midlatitude geomagnetic conjugate points. Clear depletions of 630.0‐nm airglow intensity due to equatorial plasma bubbles were simultaneously observed with two all‐sky imagers at Sata, Japan (magnetic latitude 24°N), and its geomagnetic conjugate point, Darwin, Australia (magnetic latitude 22°S), on the night of November 12, 2001. Airglow depletion regions with east‐west scale sizes of 40–100 km extend poleward. The maximum apex altitude of the plasma bubbles is about 1,700 km over the geomagnetic equator. The depletions move eastward at about 100 m/s, without changing their structures. The Darwin depletion structures mapped onto the northern hemisphere along the geomagnetic field coincide closely with structures in the Sata images, even for the 40‐km structure. These observations indicate that plasma depletions in the equatorial ionosphere elongate along the geomagnetic field lines.

Plasmasphere electron temperature profiles and the effects of photoelectron trapping and an equatorial high‐altitude heat source

The electron temperature Te in the Earth's plasmasphere up to 10,000 km altitude, has been measured routinely by a thermal electron energy distribution instrument on board the EXOS D satellite. The measurements made during the years 1989–1995 have been analyzed to obtain altitude (1000–8000 km) profiles of Te for magnetic latitudes 0°–40°N at different times of the day. The profiles are compared with those computed by the Sheffield University plasmasphere‐ionosphere model, modified to include nonlocal heating due to trapped photoelectrons and an equatorial high‐altitude heat source. The photoelectrons are trapped at altitudes above 600 km, and the high‐altitude heat source is applied as energy input along the magnetic field lines with apex altitude greater than 600 km between ±10° magnetic latitude. The results for 8000 km altitude show that the modeled values of Te computed without photoelectron trapping and the high‐altitude heat source are much less than the mean measured values, 3700 K compared with 6500 K. Depending upon altitude and latitude, a photoelectron trapping of up to 100% is required to raise the modeled electron temperatures to the mean measured values. However, photoelectron trapping alone cannot account for the observed latitude variation of Te, which depends on altitude. Model calculations carried out with 50% photoelectron trapping and an altitude and local time‐dependent high‐altitude heat source reproduce the measurements, including the latitude variation; the heat source required for nighttime is about one fourth of that required for daytime. An equatorial high‐altitude heat source appears to be the only mechanism that can account for the measured values of Te; values in excess of 12,000 K have been measured. There are some quantitative differences between the measured and modeled temperatures at night in the lower plasmasphere (<2500 km), which could be caused, in whole or in part, by the inaccuracies of the nighttime measurements due to the low plasma densities.

Comparison of satellite electron density and temperature measurements at low latitudes with a plasmasphere‐ionosphere model

Observations made by the Hinotori satellite of the latitude and diurnal variations of electron density and temperature near 600 km altitude in the low‐latitude region are studied by comparison with values from the Sheffield University plasmasphere‐ionosphere model (SUPIM). The model results show that the observed features of higher electron density in the summer hemisphere and higher electron temperature in the winter hemisphere are caused principally by the difference in the summer and winter hemisphere values of the meridional neutral wind. Closer agreement between the modeled and observed values is obtained when the interhemisphere difference in the meridional wind, as given by the horizontal wind model (HWM) 90, is reduced and when the peak value of the daytime poleward wind is moved to the afternoon sector in the winter hemisphere and to the morning sector in the summer hemisphere. The model results also show that the altitude variation of the vertical E×B drift velocity plays an important role in the development of the ionospheric equatorial anomaly. The latitude and diurnal variations of the modeled electron density and temperature are in good agreement with the observations when the E×B drift velocity used by the model is in accord with the observations made by the AE‐E satellite for magnetic field lines with apex altitude less than 400 km and at Arecibo for magnetic field lines with apex altitude greater than 2000 km; linear interpolation of the observed values is used for the intermediate magnetic field lines.

Comparison of plasma drift modeling to DE 2 data

Nighttime zonal plasma drifts in the equatorial region are calculated from a simplified expression involving Pedersen conductivity, geomagnetic field strength, and zonal neutral wind, integrated along flux tubes between apex altitudes of 250–1500 km. The ambient conditions correspond to solar maximum at equinox over the American sector with vertical electron density profiles derived from average drift measured over Jicamarca. Plasma drift outputs from four neutral wind models are evaluated for overall consistency and compared to similar data from the DE 2 satellite collected during solar cycle 21 from 1.5 to 3 years after the solar maximum peak. Drift velocities are displayed to compare model output against the DE 2 measurements. Model inputs of solar maximum with vertical electron drift reduced to one‐half average strength and a heuristically derived wind are found to give very good agreement with the DE 2 results. The implicit conclusion is that this final model is most representative of actual thermospheric winds for the conditions of near‐solar maximum at equinox in the nighttime sector.