Quiet Geomagnetic Conditions Research Articles

Empirical models of Total Electron Content based on functional fitting over Taiwan during geomagnetic quiet condition

Abstract. Empirical models of Total Electron Content (TEC) based on functional fitting over Taiwan (120° E, 24° N) have been constructed using data of the Global Positioning System (GPS) from 1998 to 2007 during geomagnetically quiet condition (Dst>−30 nT). The models provide TEC as functions of local time (LT), day of year (DOY) and the solar activity (F), which are represented by 1–162 days mean of F10.7 and EUV. Other models based on median values have been also constructed and compared with the models based on the functional fitting. Under same values of F parameter, the models based on the functional fitting show better accuracy than those based on the median values in all cases. The functional fitting model using daily EUV is the most accurate with 9.2 TECu of root mean square error (RMS) than the 15-days running median with 10.4 TECu RMS and the model of International Reference Ionosphere 2007 (IRI2007) with 14.7 TECu RMS. IRI2007 overestimates TEC when the solar activity is low, and underestimates TEC when the solar activity is high. Though average of 81 days centered running mean of F10.7 and daily F10.7 is often used as indicator of EUV, our result suggests that average of F10.7 mean from 1 to 54 day prior and current day is better than the average of 81 days centered running mean for reproduction of TEC. This paper is for the first time comparing the median based model with the functional fitting model. Results indicate the functional fitting model yielding a better performance than the median based one. Meanwhile we find that the EUV radiation is essential to derive an optimal TEC.

West African equatorial ionospheric parameters climatology based on Ouagadougou ionosonde station data from June 1966 to February 1998

Abstract. This study is the first which gives the climatology of West African equatorial ionosphere by using Ouagadougou station through three solar cycles. It has permitted to show the complete morphology of ionosphere parameters by analyzing yearly variation, solar cycle and geomagnetic activity, seasonal evolution and diurnal development. This work shows that almost all ionospheric parameters have 11-year solar cycle evolution. Seasonal variation shows that only foF2 exhibits annual, winter and semiannual anomaly. foF2 seasonal variation has permitted us to identify and characterize solar events effects on F2 layer in this area. In fact (1) during quiet geomagnetic condition foF2 presents winter and semiannual anomalies asymmetric peaks in March/April and October. (2) The absence of winter anomaly and the presence of equinoctial peaks are the most visible effects of fluctuating activity in foF2 seasonal time profiles. (3) Solar wind shock activity does not modify the profile of foF2 but increases ionization. (4) The absence of asymmetry peaks, the location of the peaks in March and October and the increase of ionization characterize recurrent storm activity. F1 layers shows increasing trend from cycle 20 to cycle 21. Moreover, E layer parameters seasonal variations exhibit complex structure. It seems impossible to detect fluctuating activity effect in E layer parameters seasonal variations but shock activity and wind stream activity act to decrease E layer ionization. It can be seen from Es layer parameters seasonal variations that wind stream activity effect is fairly independent of solar cycle. E and Es layers critical frequencies and virtual heights diurnal variations let us see the effects of the greenhouse gases in these layers.

Solar flare effect on the geomagnetic field and ionosphere

This paper studies the ionospheric and geomagnetic response to an X6.2 solar flare recorded at 14:30 UT on December 13, 2001, in quiet geomagnetic conditions which allow the variations in the geomagnetic field and ionosphere measurements to be easily related to the solar flare radiation. By using measurements from the global positioning system (GPS) and geomagnetic observatories, the temporal evolution of ionospheric total electron content variation, vTEC V , and geomagnetic field variations, δB, as well as their rates of variation, were obtained around the subsolar point at different solar zenith angles. The enhancement of both parameters was recorded one to three minutes later than the Geostationary Operational Environmental Satellite (GOES) programme recording; such delay tends to depend on the latitude, longitude, and solar zenith angle of the observatory's observations. The vTEC V is related to the local time and the δB to the intensity and position of the ionospheric currents. The vTEC V ′s maximum value is always recorded later than the maximum values reached by δB and the X-ray intensity. The maximum δB is larger in the local morning than in the afternoon. The rates of vTEC V and δB have two maximum values at the same time as the maximum values recorded by Hα (for each ribbon). This work shows the quantitative and qualitative relations between a solar flare and the ionospheric and geomagnetic variations that it produces.

Electrodynamical control of the ambient ionization near the equatorial anomaly crest in the Indian zone during counter electrojet days

The variability of ambient ionization near the crest of the equatorial anomaly on the days of counter electrojet (CEJ) is studied using a long‐term (1980–1990) database of total electron content (TEC) obtained from Calcutta (geographic: longitude, 88.38°E; latitude, 22.58°N; dip: 32°N), situated virtually below the northern crest of the equatorial anomaly, in conjunction with the equatorial electrojet (EEJ) data of the Indian subcontinent and foF2 data from the equatorial stations. On the days of CEJ events the diurnal variations of TEC exhibit deviations (decreases) from monthly mean values, but the feature is not regular throughout the observing period. A larger percentage of CEJ days show decreases in the descending phase (1980–1985) of solar cycle compared to the ascending one (1986–1990). During low to moderate solar activity years the ionosphere near the anomaly crest is found to be more susceptible to CEJ related equatorial electrodynamics than in the high solar activity periods. On the seasonal basis, though the solstitial months of ascending phase exhibit higher percentage occurrence of decreases, the feature is not so prominent in the descending epoch. An attempt is made to relate the decreases in TEC with the prevailing electrodynamics at the magnetic equator for which EEJ, under quiet geomagnetic conditions, may be treated as a proxy index. A statistical analysis reveals positive correlations of TEC decreases with strength and duration of CEJ but anticorrelations with rising slope, strength, and time‐integrated value of EEJ as well as initiation time of CEJ. To represent better correspondence of the TEC variability with the equatorial electrodynamics a function combining various EEJ parameters has been generated, which seems to exhibit significant association with TEC decreases on the days of CEJ events.

Thermospheric winds and temperatures above Mawson, Antarctica, observed with an all-sky imaging, Fabry-Perot spectrometer

Abstract. A new all-sky imaging Fabry-Perot spectrometer has been installed at Mawson station (67°36' S, 62°52' E), Antarctica. This instrument is capable of recording independent spectra from many tens of locations across the sky simultaneously. Useful operation began in March 2007, with spectra recorded on a total of 186 nights. Initial analysis has focused on the large-scale daily and average behavior of winds and temperatures derived from observations of the 630.0 nm airglow line of atomic oxygen, originating from a broad layer centered around 240 km altitude, in the ionospheric F-region. The 1993 Horizontal Wind Model (HWM93), NRLMSISE-00 atmospheric model, and the Coupled Thermosphere/Ionosphere Plasmasphere (CTIP) model were used for comparison. During the geomagnetically quiet period studied, observed winds and temperatures were generally well modelled, although temperatures were consistently higher than NRLMSISE-00 predicted, by up to 100 K. CTIP temperatures better matched our data, particularly later in the night, but predicted zonal winds which were offset from those observed by 70–180 ms−1 westward. During periods of increased activity both winds and temperatures showed much greater variability over time-scales of less than an hour. For the active night presented here, a period of 45 min saw wind speeds decrease by around 180 ms−1, and temperatures increase by approximately 100 K. Active-period winds were poorly modelled by HWM93 and CTIP, although observed median temperatures were in better agreement with NRLMSISE-00 during such periods. Average behavior was found to be generally consistent with previous studies of thermospheric winds above Mawson. The collected data set was representative of quiet geomagnetic and solar conditions. Geographic eastward winds in the afternoon/evening generally continued until around local midnight, when winds turned equatorward. Geographic meridional and zonal winds in the afternoon were approximately 50 ms−1 weaker than expected from HWM93, as was the transition to equatorward flow around midnight. There was also a negligible geographic zonal component to the post-midnight wind where HWM93 predicted strong westward flow. Average temperatures between 19:00 and 04:00 local solar time were around 60 K higher than predicted by NRLMSISE-00.

Equatorial F-region vertical ion drifts during quiet solar maximum

Median values of ionosonde h′ F data acquired at Ibadan (Geographic:7.4°N, 3.9°E, Magnetic: dip 6°S, and magnetic declination, 3°W), Nigeria, West Africa, have been used to determine vertical ion drift (electric field) characteristics in the postsunset ionosphere in the African region during a time of high solar activity (average F 10.7 −208). The database spans from January and December 1958 during the era of International Geophysical Year (IGY) for geomagnetic quiet conditions. Bimonthly averaged diurnal variations patterns are very similar, but differ significantly in magnitude and in the evening reversal times. Also, monthly variations of F-region vertical ion drift reversal times inferred from the time of h′ F maximum indicates early reversal during equinoxes and December solstice months except for the month of April. Late reversal is observed during the June solstice months. The equatorial evening prereversal enhancement in vertical ion drift ( V zp ) occurs largely near 1900 LT with typical values ∼20–45 m/s. Comparison of Ibadan ionosonde V zp with the values of prereversal peak velocity reported for Jicamarca (South America), Kodaikanal (India), and Scherliess and Fejer global model show considerable disparity. The changes of postsunset peak in virtual height of F-layer ( h′ F P ) with prereversal velocity peak V zp are anti-correlated. Investigation of solar effects on monthly values of V zp and h′ F P revealed that these parameters are independent of monthly averaged solar flux intensity during quiet-time sunspot maximum conditions.

Outflowing protons and heavy ions as a source for the sub-keV ring current

Abstract. Data from the Cluster CIS instrument have been used for studying proton and heavy ion (O+ and He+) characteristics of the sub-keV ring current. Thirteen events with dispersed heavy ions (O+ and He+) were identified out of two years (2001 and 2002) of Cluster data. All events took place during rather geomagnetically quiet periods. Three of those events have been investigated in detail: 21 August 2001, 26 November 2001 and 20 February 2002. These events were chosen from varying magnetic local times (MLT), and they showed different characteristics. In this article, we discuss the potential source for sub-keV ring current ions. We show that: (1) outflows of terrestrial sub-keV ions are supplied to the ring current also during quiet geomagnetic conditions; (2) the composition of the outflow implies an origin that covers an altitude interval from the low-altitude ionosphere to the plasmasphere, and (3) terrestrial ions are moving upward along magnetic field lines, at times forming narrow collimated beams, but frequently also as broad beams. Over time, the ion beams are expected to gradually become isotropised as a result of wave-particle interaction, eventually taking the form of isotropic drifting sub-keV ion signatures. We argue that the sub-keV energy-time dispersed signatures originate from field-aligned terrestrial ion energising and outflow, which may occur at all local times and persist also during quiet times.

Global comparison of the model results of GSM TIP with IRI for summer conditions

This paper presents the results of the numerical calculations thermosphere/ionosphere parameters which were executed with using of the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP)and comparison of these results with empirically-based model IRI-2001. Model GSM TIP was developed in West Department of IZMIRAN and solves self-consistently the time-dependent, 3-D coupled equations of the momentum, energy and continuity for neutral particles (O 2, N 2, O), ions (O +, H +), molecular ions (M +) and electrons and largescale eletric field of the dynamo and magnetospheric origin in the range of height from 80 km to 15 Earth’s radii. The empirically derived IRI model describes the E and F regions of the ionosphere in terms of location, time, solar activity and season. Its output provides a global specification not only of N e but also on the ion and electron temperatures and the ion composition. These two models represent a unique set of capabilities that reflect major differences in along with a substantial approaches of the first-principles model and global database model for the mapping ionosphere parameters. We focus on global distribution of the N e, T i, T e and TEC for the one moment UT and fixed altitudes: 110 km, h mF2, 300 km and 1000 km. The calculations were executed with using of GSM TIP and IRI models for August 1999, moderate solar activity and quiet geomagnetic conditions. Results present as the global differences between the IRI and GSM TIP models predictions. The discrepancies between model results are discussed.

Anomalous enhancement of ionospheric electron content in the Asian‐Australian region during a geomagnetically quiet day

We investigate an event of anomalous enhancement in ionospheric electron content on 28 June 2002 from a network of 70 GPS receivers and a chain of ionosondes distributed around the Asian‐Australian sector. After local sunset, the low‐latitude peak electron density of the F2 layer (NmF2) was observed to increase by 200% compared to the 27‐day median value. Geomagnetic environment was quiet during 27–28 June as the SYM‐H index was larger than −20 nT and AE was less than 200 nT under conditions of a constant northward interplanetary magnetic field Bz. A continuously enhanced eastward electric field has been identified as the main cause of this effect, though it is not fully consistent with the prediction of Scherliess and Fejer (1997) for wind disturbance dynamo model. Our observations show that the ionosphere was very disturbed in the Northern Hemisphere during summer even under low geomagnetic activity. The large ionospheric disturbance may be caused by the combination of the effects due to auroral activity and tides, a combination that still needs further investigation. This work suggests that studying very large day‐to‐day variability under quiet geomagnetic conditions could reveal more about the coupling processes between the ionosphere and lower atmosphere.

Study of plasma pressure distribution in the inner magnetosphere using the low altitude satellite data and its relevance for magnetospheric dynamics

Plasma pressure distribution in the inner magnetosphere is one of the key parameters for understanding the main magnetospheric processes including geomagnetic storms and substorms. However, the pressure profiles obtained from in-situ particle measurements by the high-altitude satellites inside the plasma sheet do not allow tracking the pressure variations related to the magnetospheric dynamics, because time interval needed to do this generally exceeds the characteristic times of the main magnetospheric processes. On the contrary, fast movement of low-altitude satellites makes it possible to restore quasi-instantaneous profiles of plasma pressure along the satellite trajectory, using the precipitating particle flux data in the regions of isotropic plasma pressure. It was found that during quiet geomagnetic conditions profiles obtained from low-altitude and high-altitude satellites coincide. Nevertheless, the plasma pressure profiles change significantly during the development of storms and substorms, that indicates possibility of the interchange (storm) or modified interchange (substorm) instability development.

Periodic traveling compression regions during quiet geomagnetic conditions and their association with ground Pi2

Abstract. Recently, Keiling et al. (2006) showed that periodic (~90 s) traveling compression regions (TCRs) during a substorm had properties of Pi2 pulsations, prompting them to call this type of periodic TCRs "lobe Pi2". It was further shown that time-delayed ground Pi2 had the same period as the lobe Pi2 located at 16 RE, and it was concluded that both were remotely driven by periodic, pulsed reconnection in the magnetotail. In the study reported here, we give further evidence for this association by reporting additional periodic TCR events (lobe Pi2s) at 18 RE all of which occurred in succession during a geomagnetically very quiet, non-substorm period. Each quiet-time periodic TCR event occurred during an interval of small H-bay-like ground disturbance (<40 nT). Such disturbances have previously been identified as poleward boundary intensifications (PBIs). The small H bays were superposed by Pi2s. These ground Pi2s are compared to the TCRs in the tail lobe (Cluster) and both magnetic pulsations and flow variations at 9 RE inside the plasma sheet (Geotail). The main results of this study are: (1) Further evidence is given that periodic TCRs in the tail lobe at distances of 18 RE and ground Pi2 are related phenomena. In particular, it is shown that both had the same periodicity and occurred simultaneously (allowing for propagation time delays) strongly suggesting that both had the same periodic source. Since the TCRs were propagating Earthward, this source was located in the outer magnetosphere beyond 18 RE. (2) The connection of periodic TCRs and ground Pi2 also exists during very quiet geomagnetic conditions with PBIs present in addition to the previous result (Keiling et al., 2006) which showed this connection during substorms. (3) Combining (1) and (2), we conclude that the frequency of PBI-associated Pi2 is controlled in the outer magnetosphere as opposed to the inner magnetosphere. We propose that this mechanism is pulsed reconnection based on previous results which combined modeled results and observations of substorm-related periodic TCRs and ground Pi2. (4) We show that TCRs with small compression ratios (ΔB/B<1%) can be useful in the study of magnetotail dynamics and we argue that other compressional fluctuations with ΔB/B<1% (without having all of the characteristic signatures of TCRs) seen in the tail lobe could possibly be related to the same mechanism that generates TCR with ΔB/B>1% (which are more commonly studied). (5) Finally, it is noted that both quiet time and substorm-related periodic TCRs had remarkably similar periods in spite of the drastically different geomagnetic conditions prevailing during the events which poses the important question of what causes this periodicity under these different conditions.

Numerical modeling of the light ion trough and heat balance of the topside ionosphere in quiet geomagnetic conditions

The results from the numerical calculations of the global distribution of topside ionospheric parameters such as H + ions and ion and electron temperatures up to 1500 km height are presented for equinoctial conditions at solar minimum. Calculations are carried out using the Global Self-consistent Model of Thermosphere, Ionosphere and Protonosphere (GSM TIP) developed in WD IZMIRAN, and using a new calculation block for electric fields due to dynamo and of magnetospheric origin. A comparison of two sets of calculations of magnetospheric convection electric field for a given potential difference is carried out, one through polar caps and other through field aligned currents of first zone. It is shown that the distribution of the electric potential obtained through field aligned currents of first zone is more self-consistent than that through polar caps. The light ion trough in H + ions is deeper and occupies larger region for the potential difference through polar cap. For a given potential difference through field aligned current, at 1500 km, the maximum ion temperature is 150 K higher, minimum ion temperature is 200 K lower and maximum electron temperature is 100 K higher than those obtained for the same potential difference through polar caps. It is concluded that for modeling the electric field of magnetospheric origin, it is necessary to use the potential difference through field aligned current of first zone instead of through polar caps.

Daily variation at three Antarctic geomagnetic observatories within the polar cap

Abstract. In this work we present a statistical analysis of the diurnal variation as observed at three Antarctic observatories located at different positions within the polar cap during the year 2006. Data used for the analysis are from the Italian geomagnetic observatory at Mario Zucchelli Station (formerly Terra Nova Bay, geographic latitude 74.7° S, corrected geomagnetic latitude 80.0° S), from the French-Italian observatory at Concordia Station (75.1° S, 88.9° S) and from the French observatory at Dumont D'Urville (66.7° S, 80.4° S), which are located in pairs at the same geographic and corrected geomagnetic latitude; such a position allows to distinguish whether the geographic or the geomagnetic reference system is better suitable to describe the observed phenomena at so high latitudes. The peculiarities of the daily variation as observed during this year and its relation with the observatory location and magnetospheric and interplanetary conditions were analysed. Data were also studied taking into account different Lloyd seasons. The results indicate that the 24-h variation is quite persistent, but its amplitude strongly depends on season and global geomagnetic activity: indeed, it almost vanishes during local winter for quiet geomagnetic conditions; this reduction is more evident at the stations closer to the geographic pole, where the solar radiation reduction during winter is more dramatic. The Interplanetary Magnetic Field orientation has been found to be important in that the north-south and the east-west components control the amplitude and the diurnal pattern of the variation, respectively.

Multipoint observations of magnetospheric compression‐related EMIC Pc1 waves by THEMIS and CARISMA

Following a long interval (many days) of sustained very quiet geomagnetic conditions, electromagnetic ion cyclotron (EMIC) wave activity was seen by the CARISMA array (www.carisma.ca) on the ground for several hours simultaneously with enhanced solar wind density and related magnetic compression seen at GOES 12 on 29th June 2007. The THEMIS C, D, and E satellites were outbound in a “string‐of‐pearls” configuration and each observed EMIC waves on L‐shells ranging from 5 to 6.5. THEMIS resolved some of the spatial‐temporal ambiguity and defined the radial extent of EMIC activity to be ∼1.3 Re. The band‐limited EMIC waves were seen slightly further out in radial distance by each subsequent THEMIS satellite, but in each case were bounded at high‐L by a decrease in density as monitored by spacecraft potential. The EMIC wave activity appears to be confined to a region of higher plasma density in the vicinity of the plasmapause, as verified by ground‐based cross‐phase analysis. The structured EMIC waves seen at THEMIS E and on the ground have the same repetition period, in contradiction to expectations from the bouncing wave packet hypothesis. Compression‐related EMIC waves are usually thought to be preferentially confined to higher L's than observed here. Our observations suggest solar wind density enhancements may also play a role in the excitation of radially localised EMIC waves near the plasmapause.

Temporal and spatial characteristics of Pc1 waves observed by ST5

We present the results of a study of Pc1 waves (0.2–5 Hz) recorded by the three spacecraft of NASA's Space Technology 5 (ST5) mission, which operated in a dawn‐dusk, 300 × 4500 km Sun‐synchronous orbit in a “string‐of‐pearls” configuration from 26 March through 23 June 2006. Regions with Pc1 wave activity are not only localized to rather narrow L shells but can appear and disappear on the time scales of ∼10 s to 10 min as examined by ST5. Only half of the 48 identified events were observed by all three spacecraft, and five events were observed by only one spacecraft. Only seven events were observed below L = 4, and only one was observed below L = 3.6, consistent with the relatively quiet geomagnetic conditions during this interval. The temporal occurrence distribution of Pc1 events was similar to that recorded at Halley, Antarctica (L = 4.56), during this same interval in that the number and intensity of events increased during magnetospheric compressions and during the recovery phase of magnetic storms, but they were reduced or absent during main phase and early recovery phase. This agreement suggests that if Pc1 events occur during main phase, their nearly universal absence in ground records cannot be ascribed to ionospheric screening effects or obscuration by irregular ULF noise generated in the ionosphere. These findings also suggest that although electromagnetic ion cyclotron waves might theoretically cause rapid depletion of radiation belt electrons during the main phase of storms, such waves cannot be assumed to occur during the main phase of all storms.

Anomalous variations in the ionospheric F 2-layer structure at geomagnetic midlatitudes of the Southern and Northern hemispheres at the transition from summer to winter conditions under low solar activity

The structure and dynamics of the ionosphere and plasmasphere at low solar activity under quiet geomagnetic conditions on January 15–17, 1985, and July 10–13, 1986, over Millstone Hill station and Argentine Islands ionosonde, the locations of which are approximately magnetically conjugate, have been theoretically calculated. The detected correction of the model input parameters makes it possible to coordinate the measured and calculated anomalous variations in the electron density NmF2 at the height hmF2 of the ionospheric F2 layer over Argentine Islands ionosonde as well as the calculated and measured values of NmF2 and electron temperature at the hmF2 height over Millstone Hill station. It has been shown that vibrationally excited N2 and O2 molecules almost do not influence the formation of the winter anomaly under the conditions of low solar activity. A difference between the influence of electronically excited O+ on N e ions under winter and summer conditions forms not more than 11% of the N e winter anomaly event in the F 2 layer and topside ionosphere. The model without electronically excited O+ ions reduces the duration of the N e winter anomaly event. It has been shown that the seasonal variations in the composition of the neutral atmosphere form mainly the NmF2 winter anomaly event over the Millstone Hill radar at low solar activity.

The F-Region Equatorial Ionospheric Electrodynamics Drifts

The ionospheric plasma drift is one of the most essential parameters for understanding the dynamics of ionospheric F-region. F-region electromagnetic drifts are calculated for three seasonal conditions from ionosonde observations acquired during quiet period of a typical year of high and low solar activity at Ibadan (7.4oN, 3.9oE, dip 6oS), Nigeria. The vertical plasma drifts derived from h' (f) ionosonde data are compared with vertical drifts obtained by incoherent scatter radar and AE-E satellite measurements during nighttime periods under similar solar and geomagnetic conditions. We find comparable variability among the ionosonde drifts at Ibadan, Jicamarca VHF radar drifts, and AE-E satellite drifts during high solar flux and geomagnetic quiet conditions at equinox and solstices periods. The equinoctial average evening upward drifts enhancements by the three methods are roughly similar and occur at the same local time (19 LT) for all the seasons. Additionally, the evening reversal time from upward daytime to downward nighttime does not vary much except during the winter months; and occurs earliest in summer and equinox, but least during winter period. Also the data indicate asymmetry of evening reversal times about the dip-equator between the Peruvian, Indian, and the African equatorial regions. Our observations are in conformity with some results obtained at other equatorial ionospheric stations Journal of the Nigerian Association of Mathematical Physics Vol. 10 2006: pp. 27-34

First assimilations of COSMIC radio occultation data into the Electron Density Assimilative Model (EDAM)

Abstract. Ground based measurements of slant total electron content (TEC) can be assimilated into ionospheric models to produce 3-D representations of ionospheric electron density. The Electron Density Assimilative Model (EDAM) has been developed for this purpose. Previous tests using EDAM and ground based data have demonstrated that the information on the vertical structure of the ionosphere is limited in this type of data. The launch of the COSMIC satellite constellation provides the opportunity to use radio occultation data which has more vertical information. EDAM assimilations have been run for three time periods representing quiet, moderate and disturbed geomagnetic conditions. For each run, three data sets have been ingested – only ground based data, only COSMIC data and both ground based and COSMIC data. The results from this preliminary study show that both ground and space based data are capable of improving the representation of the vertical structure of the ionosphere. However, the analysis is limited by the incomplete deployment of the COSMIC constellation and the use of auto-scaled ionosonde data. The first of these can be addressed by repeating this type of study once full deployment has been achieved. The latter requires the manual scaling of ionosonde data; ideally an agreed data set would be scaled and made available to the community to facilitate comparative testing of assimilative models.

Mechanism of formation of Q-disturbances in the F 2 region of the equatorial ionosphere

Using model simulations, the morphological picture (revealed earlier) of the disturbances in the F2 region of the equatorial ionosphere under quiet geomagnetic conditions (Q-disturbances) is interpreted. It is shown that the observed variations in the velocity of the vertical E × B plasma drift, related to the zonal Ey component of the electric field, are responsible for the formation of Q-disturbances. The plasma recombination at altitudes of the lower part of the F2 region and the dependence of the rate of this process on heliogeophysical conditions compose the mechanism of Q-disturbance formation at night. The daytime positive Q-disturbances are caused exclusively by a decrease in the upward E × B drift, and this type of disturbances could be related to the known phenomenon of counter electrojet. Possible causes of formation of the daytime negative Q-disturbances are discussed.

Anomalous variations in the structure of the ionospheric F 2 region at geomagnetic midlatitudes of the Southern and Northern hemispheres in going from summer to winter conditions at high solar activity

The structure and dynamics of the ionosphere and plasmasphere at high solar activity under quiet geomagnetic conditions of June 2–3, 1979, and January 5–6, 1980, over Millstone Hill station and Argentine Islands ionosonde, the locations of which are approximately magnetically conjugate, have been theoretically calculated. The plasma drift velocity, determined by comparing the calculated and measured heights of the F2 layer maximum (hmF2), and the correction of [N2] and [O2], found in the NRLMSISE-00 model, make it possible to coordinate the electron densities (NmF2) calculated at the hmF2 height and the measured anomalous variations in NmF2 over the Argentine Islands ionosonde as well as the calculated and measured NmF2 and electron temperature at the hmF2 height over Millstone Hill station. It has been shown that, if the interference of the diffusion velocities of O+(4S) and H+ ions is taken into account, the additional heating of plasmaspheric electrons leads to an increase in the flux of O+(4S) ions from the topside ionosphere to lower F2 layer altitudes, as a result of which an anomalous nighttime increase in NmF2 6, observed on January 6, 1980, over Millstone Hill station, is mainly produced. The second component of the formation of anomalous night-time NmF2 is the plasma drift along the magnetic field caused by the neutral wind, which shifts O+(4S) ions to higher altitudes where the recombination rate of O+(4S) with N2 and O2 is lower and slows down a decrease in NmF2 in the course of time. It has been shown that the influence of electronically excited O+ ions and vibrationally excited N2 and O2 molecules on electron density (Ne) considerably differs under winter and summer conditions. This difference forms significant part of the winter anomaly in Ne at heights of the F2 region and topside ionosphere over Millstone Hill station.