Medium Solar Activity Research Articles

Forecasting of ionospheric vertical TEC 1-h ahead using a genetic algorithm and neural network

A hybrid back propagation artificial neural network (ANN) with a genetic algorithm (GA) is built to predict 1-h ahead vertical total electron content (TEC) of single station in China. An ionospheric TEC forecast model was developed based on TEC data from four dual-frequency GPS stations of BJFS (39.61°N, 115.89°E), XIAN (34.18°N, 108.99°E), WUHN (30.53°N, 114.36°E), and KUNM (25.03°N, 102.80°E) in both 2007 and 2011. The results show the mean relative errors of the model are smaller than 10% and the root mean square (RMS) error is less than 1 TECU at mid-high-latitudes during the period of low solar activity in 2007. Some large RMS errors with more than 5 TECU can be observed at low latitude during the medium solar activity period of 2011. Compared to the traditional BP algorithm, the new algorithm is a promising and reliable alternative forecast technology for ionospheric TEC.

The occurrence of equatorial spread-F at conjugate stations in Southeast Asia

In this study, the probability of equatorial spread-F (ESF) occurrence at the conjugate stations in Southeast Asia: Chiangmai station (CMU), Thailand, and Kototabang station (KTB), Indonesia, and near the magnetic equator, Chumphon station (CPN), Thailand, is presented. We analyze the ionogram data recorded by the Frequency Modulated Continuous Wave (FM/CW) ionosondes for the periods of minimum solar activity from September 2008 to April 2009 and in the equinoctial months (March and April) from 2006 to 2013. The spread-F signatures are manually categorized into three types: the frequency spread-F (FSF), the range spread-F (RSF) and the mixed spread-F (MSF) and the monthly average percentage of the occurrence of each ESF type is presented. The results show that the percentage of RSF occurrence at CPN, which is located around the magnetic equator, is higher than at other stations and the RSF mostly occurs during the equinoctial months. On the other hand, the FSF occurrence at CMU and KTB, that are located in the northern and southern hemispheres, respectively, are higher than at CPN. The RSF occurrence typically has the peaks before midnight, while the maximum occurrence rate of FSF is after midnight. Furthermore, the RSF onsets normally precede the FSF onsets by about 1–2h. As the solar activity levels go up, the percentages of RSF occurrence increase, but the percentages of FSF tends to decrease. In addition, we compare the statistics of observed RSF occurrence with the prediction of the IRI-2012 model. The results show that the IRI model overestimates the observed RSF occurrence at all stations during most of the solar activity levels and seasons, except in June 2008 (21:00–03:00LT), March 2011 (23:30–01:00LT) and March 2013 (01:00–02:30LT) when the IRI model underestimates our observations. However, the IRI model gives closer probability of RSF occurrence to our observed values at CPN, especially in equinoctial months and during the periods of medium solar activity. This work is important for an improvement of the IRI model in the prediction of the spread F occurrence probability in the low-latitude region.

Solar rotation effects on the Martian ionosphere

AbstractWe present a detailed investigation of the solar rotation effects on the Martian high‐latitude (~63°N–81°N) ionosphere using the electron density (Ne) data measured by Mars Global Surveyor and solar XUV and EUV fluxes measured by SOHO under high (2000–2001), medium (2003), and low (2005) solar activity conditions. A fast Fourier transform spectral analysis method is used to estimate the amplitude of the rotation period in these parameters. This method clearly reveals the presence of solar rotation effects in the Martian ionospheric Ne at all altitudes (90–220 km), peak electron density (NmM2), and total electron content under the three solar activity conditions. These effects are in phase with the solar UV fluxes (corrected for the Martian orbit). The period of rotation effect (~26 days) is the same at all altitudes, though its amplitude is strongest at the ionospheric M2 peak (~135–140 km, ~3.5–6% of the mean values) and has a secondary enhancement at the M1 peak (~110–115 km). The effect of solar rotation on the M2 peak is larger during medium solar activity (2003) than during high solar activity (2000–2001). The effect, however, is absent in the ionospheric peak height (hmM2). The rotation effects on Mars are also compared with those on the Earth. Unlike at Mars, the Earth's high‐latitude ionosphere shows no clear solar rotation effect, though the effect is observed clearly at lower latitudes.

Climatological study of ionospheric irregularities over the European mid-latitude sector with GPS

High-frequency variability of the ionosphere, or irregularities, constitutes the main threat for real-time precise positioning techniques based on Global Navigation Satellite Systems (GNSS) measurements. Indeed, during periods of enhanced ionospheric variability, GNSS users in the field—who cannot verify the integrity of their measurements—will experience positioning errors that can reach several decimeters, while the nominal accuracy of the technique is cm-level. In the frame of this paper, a climatological analysis of irregularities over the European mid-latitude region is presented. Based on a 10 years GPS dataset over Belgium, the work analyzes the occurrence rate (as a function of the solar cycle, season and local time) as well as the amplitude of ionospheric irregularities observed at a single GPS station. The study covers irregularities either due to space weather events (solar origin) or of terrestrial origin. If space weather irregularities are responsible for the largest effects in terms of ionospheric error, their occurrence rate highly depends on solar activity. Indeed, the occurrence rate of ionospheric irregularities is about 9 % during solar maximum, whereas it drops to about 0 % during medium or low solar activity periods. Medium-scale ionospheric disturbances (MSTIDs) occurring during daytime in autumn/winter are the most recurrent pattern of the time series, with yearly proportions slightly varying with the solar cycle and an amplitude of about 10 % of the TEC background. Another recurrent irregularity type, though less frequent than MSTIDs, is the noise-like variability in TEC observed during summer nighttime, under quiet geomagnetic conditions. These summer nighttime irregularities exhibit amplitudes ranging between 8 and 15 % of the TEC background.

Validation of the NeQuick 2 and IRI-2007 models in East-African equatorial region

This paper examines the performances of NeQuick 2 and IRI-2007 ionospheric empirical models in describing the monthly median characteristics of the equatorial region ionosphere. This is carried out by comparing the vertical total electron content (vTEC) obtained from ground Global Positioning System (GPS) receivers and NmF2 obtained from digisonde with the corresponding values computed using these models. Four years worth of data have been considered in this study. We have shown that the performances of both models are better during the medium solar activity period than low solar activity period. The present investigation has depicted that both models overestimate the observed vTEC during low solar activity period. The modeled and experimental NmF2 has shown good agreement; but the modeled and experimental vTEC has shown significant discrepancy. This discrepancy is shown mainly due to inadequately computed ionospheric slab thicknesses using IRI-2007 and NeQuick 2. However, the chi-square test showed that both models are describing the observed vTEC with 99.9% of confidence level except in the time intervals when the double peaks of modeled vTEC are obtained. In addition, we have shown that both models have a relatively minimal mismodeling during the December solstices.

F3 layer feature under low and medium solar activity observed at a Chinese low latitude station Fuke

Ionogram observations from the ionosonde at Fuke (9.5°N geomagnetic latitude), a Chinese low latitude station, in 2010–2012 are analyzed to present the features of F3 layer under low and moderate solar activity conditions. Structure of the ionogram, displaying the F3 layer, was more distinct and clear during MSA than LSA periods especially during spring to summer. Start time of occurrence of the F3 layer is about at 0830–0900LT and is approximately the same for LSA and MSA conditions. The average duration time of the F3 layer occurrence was 181min per day under F10.7=75 condition, 263min in F10.7=99 and 358min in F10.7=125, respectively. The differences of h′F2 and h′F3 exhibited obvious semiannual variation observed at Fuke from March 2010 to June 2012 and increased with increasing solar activity. The difference of foF2 and foF3 in the months February, March, September, October and November is less evident in the middle solar activity period 2011–2012 than the low solar activity 2010 and in the other period it shows a slight increase (0.5MHz) or keeps constant. The results show that the solar activity dependence of the F3 layer occurrence at low latitude away from the magnetic equator is different from that at near the magnetic equator.

Dependence of the F-region peak electron density (foF2) on solar activity observed in the equatorial ionospheric anomaly region in the Brazilian sector

The long-term (solar cycle) changes in the Sun and how it affects the ionospheric F-region observed at São José dos Campos (23.2° S, 45.9° W), Brazil, a location under the southern crest of the equatorial ionospheric anomaly, have been investigated in this paper. The dependence of the F-region peak electron density (foF2) on solar activity during the descending phase of the 23rd solar cycle for the periods of high, medium, and low solar activity has been studied. The ionospheric F-region peak electron densities observed during high and medium solar activity show seasonal variations with maxima close to the equinox periods, whereas during the low solar activity the maxima during the equinox periods is absent. However, during the low solar activity only change observed is a large decrease from summer to winter months. We have further investigated changes in the different ionospheric F-region parameters (minimum virtual height of the F-region (h′F), virtual height at 0.834foF2 (hpF2), and foF2) during summer to winter months in low solar activity periods, 2006–2007 and 2007–2008. Large changes in the two ionospheric parameters (hpF2 and foF2) are observed during summer to winter months in the two low solar activity periods investigated.

F-region ionospheric parameters observed in the equatorial and low latitude regions during medium solar activity in the Brazilian sector and comparison with the IRI-2007 model results

The ionospheric sounding observations using the Canadian Advanced Digital Ionosondes (CADIs) operational at Palmas (PAL; 10.2°S, 48.2°W; dip latitude 6.6°S; a near-equatorial station), and São José dos Campos (SJC, 23.2°S, 45.9°W; dip latitude 17.6°S; a low-latitude station located under the southern crest of the equatorial ionospheric anomaly), Brazil, are analyzed during the different seasons viz., winter (June and July 2003), spring (September and October 2003), summer (December 2003 and January 2004), and fall (March and April 2004). The period used has medium solar activity (sunspot number between 77.4 and 39.3). The seasonal mean variations (using only geomagnetically quiet days) of the ionospheric parameters foF2 (critical frequency of the F-region), hpF2 (virtual height at 0.834 foF2; considered to be close to hmF2 (peak height of the F-region)), and h’F (minimum virtual height of the F-region) are calculated and compared between PAL and SJC. The prominent differences between PAL and SJC are as follows: h’F variations show strong post-sunset enhancement at PAL during the seasons of spring, summer, and fall; hpF2 variations show pre-sunrise uplifting of the F-layer at both stations during all the seasons and the hpF2 values during the daytime are lower at SJC compared with PAL during all the seasons; the foF2 variations show mid-day bite-out at PAL during all the seasons and SJC shows strong equatorial ionospheric anomaly during summer and fall seasons. Also, the seasonal variations of the ionospheric parameters foF2 and hpF2 (with ±1 standard deviation) observed at PAL and SJC are compared with the IRI-2007 model results of foF2 and hmF2. In addition, variations of the foF2 and hpF2 observed at SJC are compared with the IRI-2001 model results of foF2 and hmF2. It should be pointed out that the ionospheric parameter hpF2 is much easier to obtain using computer program developed at UNIVAP compared with hmF2 (using POLAN program). During the daytime due to underlying ionization hpF2 estimated is higher (approximately 50 km) than the true peak height hmF2. During the nighttime hpF2 is fairly close to hmF2. The comparison between the foF2 variations observed at PAL and SJC with the IRI-2007 model results shows a fairly good agreement during all the seasons. However, the comparison between the hpF2 variations observed at PAL and SJC with the hmF2 variations with the IRI-2007 model results shows: (1) a fairly good agreement during the nighttime in all the seasons; (2) the model results do not show the pre-sunrise uplifting of the F-layer at PAL and SJC in any season; (3) the model results do not show the post-sunset uplifting of the F-layer at PAL; (4) considering that, in general, hpF2 is higher than hmF2 during the daytime by about 50 km, the model results are in good agreement at PAL and SJC during all the seasons except summer at SJC, when large discrepancies in the observed hpF2 and modeled hmF2 are observed. Also, it has been observed that, in general, hmF2 values for SJC calculated using IRI-2001 are higher than IRI-2007 during the daytime in winter, summer, and fall. However, hmF2 values for SJC calculated using IRI-2001, are lower than IRI-2007 during the nighttime in spring.

Neutral wind and plasma drift effects on low and middle latitude total electron content

A physics‐based numerical ionosphere/plasmasphere model (IPM) was used to study the effects of daytime neutral wind and electric field perturbations on the subsequent evolution of the afternoon and postsunset total electron content (TEC) during vernal equinox conditions. The model solves the transport equations for six ions on convecting flux tubes that realistically follow the geomagnetic field. The IPM covers geomagnetic latitudes from about 60°N to 60°S and equatorial crossing altitudes from 90 to 30,000 km. Two of the input parameters required by the IPM are the thermospheric neutral wind and the low‐latitude electric field, which can be provided by existing empirical models or externally specified. To study effects of the neutral winds and the electric fields on TEC, these two model inputs were externally modified, and the resulting TEC variations were compared. Neutral wind and electric field modifications were introduced at three different local times in order to investigate the effect of different perturbation times on the evolution of TEC. Three longitudes (78°E, 273°E, and 318°E) were considered, and the results correspond to conditions of medium solar activity and low geomagnetic activity. The largest TEC changes were found predominantly in the equatorial anomaly, and a significant longitudinal dependence was observed. The simulation results indicate that TEC variations at 2100 LT vary nonlinearly at low latitudes and linearly at middle latitudes with the elapsed time after the imposed perturbations. An important outcome of this study is that daytime neutral wind and/or electric field modifications can lead to essentially identical TEC changes at 2100 LT.

Validation of a method for ionospheric electron density reconstruction by means of vertical incidence data during quiet and storm periods

A preliminary validation of the technique developed using the NeQuick ionospheric model and the «effective ionization parameter» Az, based on vertical total electron content data ingestion, was carried out in a previous study. The current study was performed to extend the analyzed conditions and confirm the results. The method to validate this technique is based on a comparison between hourly F2 peak values measured with Vertical Incidence (VI) soundings and those calculated with the new technique. Data corresponding to different hours and seasons (equinox, summer solstice, and winter solstice) during the period 2000-2003 (high and medium solar activity conditions) were compared for all available ionosonde stations. The results show a good agreement between foF2 and hmF2 values obtained with the new technique and measurements from vertical incidence soundings during quiet and storms conditions.

Solar activity variations of nighttime ionospheric peak electron density

Monthly median NmF2 (maximum electron density of the F2‐layer) data at Okinawa, Yamagawa, Kokubunji, and Wakkanai have been collected to investigate the solar activity dependence of the nighttime ionosphere. The result shows that there are seasonal and latitudinal differences of the solar activity variation of nighttime NmF2. The main seasonal effects are as follows: nighttime NmF2 increases with F107 linearly in equinoctial months (March and September), and it tends to saturate with F107 increasing in summer solstice month (June). What is peculiar is that there is an amplification trend of nighttime NmF2 with F107 in winter solstice month (December). The latitudinal difference is mainly displayed by the evolvement course of the variation trend between NmF2 and F107. Using hmF2 (peak height of the F2‐layer) data and the NRLMSISE00 model, we estimated the recombination loss around the F2‐peak at different solar activity levels. We found that the solar activity variation of the recombination processes around the F2‐peak also shows seasonal dependence, which can explain the variation trends of nighttime NmF2 with F107 qualitatively, and field‐aligned plasma influx plays an important role in the equatorial ionization anomaly (EIA) crest region. During the first several hours following sunset in December, there are faster recombination processes around the F2‐peak at medium solar activity level in mid‐latitude regions. This feature is suggested to be responsible for inducing the amplification trend in winter. In virtue of the calculation of neutral parameters at 300‐km altitude and hmF2 data, the variation trend of the recombination processes around the F2‐peak with F107 can be explained. It shows that both the solar activity variations of hmF2 and neutral parameters (neutral temperature, density, and vibrational excited N2) are important for the variation trend of nighttime NmF2 with F107. Furthermore, the obvious uplift of hmF2 at low solar activity level following sunset in December is important for the amplification trend.

Evidence of baroclinic waves in the upper atmosphere of Mars using the Mars Global Surveyor accelerometer data

Here we use accelerometer data of 115 orbits (#P0670–P0789) from 1–30 November 1998, between latitude ranges (50–70°N), and of 57 orbits (#P0588–P0648) from 30 September 1998 to 24 October 1998, between latitude ranges (50–70°N), both under spring equinox and medium solar activity conditions. The neutral densities of different gases are derived from their mixing ratio. From these neutral densities, the longitudinal distribution of total peak ionization rates of CO2+, N2+, O2+, O+, and CO+ are obtained for solar zenith angle 78° because of solar EUV and soft X‐ray (1–102.57 nm) radiation using Analytical Yield Spectrum approach. These calculations are made at different altitudes and longitudes starting from 115 to 220 km and from 0 to 360°E using intervals of 0.1 km and 5°, respectively. These conditions are appropriate for Mars Global Surveyor Phase 2 aerobraking period from which the accelerometer data is used. The Fourier analysis is carried out on the calculated total peak ionization rates for different gases both at midlatitude (17–42°N) and high‐latitude (50–70°N) range in the upper atmosphere of Mars. This analysis at high latitude indicates the presence of two dominant harmonic regions, in which the first is a class of long planetary‐scale waves, associated with the fixed topography of Martian surface, while the second is a class of rapidly moving transient disturbances associated with baroclinic instability processes. The similar analysis carried out at midlatitude (17–42°N) region indicates the absence of second peak at higher wave number, confirming that the baroclinic instability is almost absent at this latitude region.

Statistical analysis of the occurrence of medium‐scale traveling ionospheric disturbances over Brazilian low latitudes using OI 630.0 nm emission all‐sky images

In this work we report a statistical analysis of the occurrence frequency of medium‐scale traveling ionospheric disturbances (MSTIDs) observed over Cachoeira Paulista (22.7°S, 45.0°W, −13.2° mag lat), Brazil. The optical signatures of the low‐latitude MSTIDs in the southern hemisphere observed in the OI 630.0 nm emission images can be a single dark band structure or alternating dark/light bands aligned in the northeast‐southwest direction and propagating towards northwest. Because this feature these events were also referred as thermospheric dark band structures. The statistical study is based on 28 events of MSTIDs observed during seven years of optical data, obtained during low, medium, and high solar activities, for geomagnetically quiet nights. We find that the occurrence frequency of the MSTIDs presents a maximum during low solar activity, decreasing during medium solar activity with no occurrences during high solar activity. Also, the occurrence rates are greater near the June‐solstice months.

Global validation of IRI TEC for high and medium solar activity conditions

The IRI model offers a choice of options for the computation of the electron density profile and electron content (TEC). Recently new options for the topside electron density profile have been developed, which have a strong impact on TEC. Therefore it is important to test massively the IRI and the new options with experimental data. A large number of permanent stations record dual frequency GPS data from which it is possible to obtain TEC values. Thirty-one worldwide distributed stations have been selected to investigate the capabilities of the IRI to reproduce experimental TEC. Data for years 2000 (high solar activity) and 2004 (medium solar activity) have been analyzed computing modeled values with the IRI-2001 and the IRI-2007-NeQuick topside options. It is found that IRI-2007-NeQuick option generally improves the estimate of the slant TEC, especially in the case of high latitudes stations during high solar activity.

Longitudinal distribution of thermospheric densities and ionization rates in the upper atmosphere of Mars at mid-latitude using MGS ACC data

The Accelerometer Experiment (ACC) onboard Mars Global Surveyor (MGS) measured 1600 density profiles in the upper atmosphere of Mars during aerobraking. These measurements reveal large-scale and small-scale structure in the thermosphere of Mars. Here, the measurements of mass density for 115 orbits (#P0670–P0789) from November 1 to 30, 1998, under spring equinox and medium solar activity conditions (average F 10.7 ∼ 137) during phase 2 of the aerobraking in the thermosphere of Mars at different altitudes and longitudes are presented for northern mid-latitude (17–42°N) in the dayside atmosphere using ACC onboard MGS. From these mass densities, the neutral densities of different gases are derived from their mixing ratios. Using these neutral densities, the longitudinal distribution of photoionization rates and photoelectron impact ionization rates are calculated at wavelength range 1–102.57 nm due to EUV and soft X-ray radiation under photochemical controlled region using Analytical Yield Spectrum approach (AYS). These conditions are appropriate for MGS Phase 2 aerobraking period from which the accelerometer data is used. Under the photochemical equilibrium condition, the electron density near the peak varies as the square root of the total peak ionization rate. Using this fact, an attempt is being made to estimate the mean primary and secondary peak electron density by averaging the longitudinal variations of total peak ionization rates in the northern mid-latitude (17–42°N) ionosphere of Mars, as there is no radio science measurement at this latitude region by MGS.

Validation of the STORM model used in IRI with ionosonde data

The empirical ionospheric storm correction model STORM included in the new version of the IRI model is driven by the previous time-history of the ap index and is designed to be dependent on latitude and season. The behavior of this correction model has been analyzed comparing foF2 values obtained by the IRI model with or without storm correction and those measured by ionosondes distributed around the world. A statistical analysis was done using two geomagnetic storms during 2003 (medium solar activity).

Model of photoelectron impact ionization within the high latitude ionosphere at Mars: Comparison of calculated and measured electron density

The production rate, ion density and electron density are calculated between longitudes 0° and 360° E due to incident radiation of wavelength range 1–102.57 nm in the dayside atmosphere of Mars. These calculations are made by using global analytical yield spectrum (AYS) model at solar zenith angle 80° between latitudes 50° and 70° N for spring equinox and medium solar activity condition. These conditions are appropriate for Mars Global Surveyor (MGS) Phase 2 aerobraking period during which both the accelerometer and the radio occultation data are used. The calculated results are compared with MGS radio occultation measurements carried out at different latitudes (64.7°–67.3° N) and longitudes (0°–360° E) in December 1998 between solar zenith angle 78° and 81°. This measurement shows primary and secondary ionization peaks, which are varying with longitudes. Our calculation suggests that first peak is produced by photoionization and photoelectron impact ionization processes due to absorption of solar EUV radiation (9–102.57 nm). The second peak is produced by photoelectron impact ionization of soft X-ray photon (1–9 nm). There is a good agreement between our calculation and measurement as far as the maximum and the minimum values of primary peak altitude/peak density of electrons are concerned. However, the calculated values of secondary peak density and peak altitude are higher than the measured values by a factor of 1.5–2.0 and 1.1, respectively. The secondary peak is brought into agreement with the measurement using low X-ray flux by a factor of 2 to 3 below 9 nm. The longitudinal distribution of calculated and measured peak density and peak altitude are fitted by least-square method with 0.95 confidence limits.

Zonal variations of peak ionization rates in upper atmosphere of Mars at high latitude using Mars Global Surveyor accelerometer data

The Accelerometer Experiment onboard Mars Global Surveyor (MGS) measured many density profiles in the upper atmosphere of Mars during aerobraking at many latitudes, longitudes, altitudes, local solar time (LST), and seasons. Here, in this paper, we use the accelerometer data of 57 orbits (P0588–P0648) from 30 September 1998 to 24 October 1998 between latitude ranges (50°–70°N) at LST 1600 hours, under spring equinox and medium solar activity conditions (average F10.7 ∼ 120). Using these densities, the neutral densities of different gases are derived from their mixing ratio. From these neutral densities the longitudinal distribution of peak photoionization rates, peak photoelectron impact ionization rates, and the total peak ionization rates of CO2+, N2+ and O+ are obtained for solar zenith angle 78° at wavelength range 10–1025.7 Å due to solar EUV radiation using analytical yield spectrum approach (AYS). These calculations are made at different altitudes and longitudes starting from 115 to 220 km and 0° to 360°E using intervals of 0.1 km and 5°, respectively. These conditions are appropriate for MGS phase 2 aerobraking period from which the accelerometer data are used. The Fourier analysis of the various peak ionization rates of CO2+, N2+, and O+ indicates the presence of two dominant harmonic regions at high latitude in the upper atmosphere of Mars. The first is a class of long planetary‐scale waves that may be associated with the fixed topography of Martian surface. The second is a class of rapidly moving transient disturbances that may be associated with baroclinic instability processes.

An empirical topside electron density model for calculation of absolute ion densities in IRI

An empirical model of the electron density in the topside ionosphere for solar maximum and minimum is introduced. This model is intended for use in combination with the relative ion composition (TTS) model that will be included in the forthcoming version of the IRI code to calculate the absolute ion composition in the topside ionosphere. The validation of the model using satellite data from five different satellites for different altitudes and high and medium solar activity is presented. The proposed model is based on the Langmuir Probe measurements onboard the Atmosphere Explorer satellites for low solar activity and Retarding Potential Analyzer measurements onboard the Intercosmos satellites for high solar activity. Examples of vertical profiles of the absolute density of the most important ions following from the mentioned models are shown.

Manifestation of solar activity in the global topside ion composition − a study based on satellite data

Abstract. The solar cycle variation of the most important parameters characterizing the ion composition in the topside ionosphere is studied. For this purpose data from the ACTIVE mission (the IK-24 satellite) for the maximum of solar cycle 22 (aver F10.7~200), complemented by data available from the Atmosphere Explorer (AE) satellites, for the minimum of solar cycle 21 (average F10.7~85), were processed. OGO-6 data from the low maximum of solar cycle 20 (average F10.7~150) were used for medium solar activity conditions. The results for the equinox from the recently developed empirical model of ion composition are analyzed and presented, and typical vertical profiles from solar maxima and minima are shown. It was found that the logarithm of the O+, H+, He+, and N+ densities in the topside ionosphere at a fixed altitude, latitude, and local time is, in the first approximation, a linear function of solar activity characterized by the daily F10.7. On the other hand, the upper transition height is generally a non linear function of the daily F10.7, the deviation from linear dependence increases with latitude. Keywords. Ionosphere (Plasma temperature and density; Ion chemistry and composition; Modeling and forecasting)