Nighttime thermospheric meridional neutral winds inferred from ionospheric h′F and hpF2 data

Nighttime thermospheric meridional winds aligned to the magnetic meridian have been inferred using h′F and hpF2 ionosonde data taken from two equatorial stations, Manaus (2.9°S, 60.0°W, dip latitude 6.0°N) and Palmas (10.17°S, 48.2°W, dip latitude 6.2°S), and one low-latitude station, Sao Jose dos Campos (23.21°S, 45.86°W, dip latitude 17.26°S), during geomagnetic quiet days of August and September, 2002. Using an extension of the ionospheric servo model and a simple formulation of the diffusive vertical drift velocity, the magnetic meridional component of the thermospheric neutral winds is inferred, respectively, at the peak (hpF2) and at the base (h′F) heights of the F region over Sao Jose dos Campos. An approach has been included in the models to derive the effects of the electrodynamic drift over Sao Jose dos Campos from the time derivative of hpF2 and h′F observed at the equatorial stations. The magnetic meridional winds inferred from the two methods, for the months of August and September, are compared with winds calculated using the HWM-90 model and with measurements from Fabry–Perot technique. The results show varying agreements and disagreements. Meridional winds calculated from hpF2 ionospheric data (servo model) may produce errors of about 59 m/s, whereas the method calculated from the F-region base height (h′F) ionospheric data gives errors of about 69 m/s during the occurrence of equatorial spread-F.     

Equatorial vertical E × B drift velocities inferred from ionosonde measurements over Ouagadougou and the IRI-2007 vertical ion drift model

F-region vertical plasma drift velocities were deduced from the hourly hmF2 values acquired from ionogram data over a near dip equatorial station Ouagadougou (12.4°N, 358.5°E, dip angle 5.9°N) in Africa. Our results are compared against the global empirical model of Scherliess and Fejer (1999) incorporated in the IRI model (IRI-2007) for 1600 to 0800 LT from 1 year of data during sunspot maximum year of 1989 (yearly average solar flux intensity, F10.7 = 192) corresponding to the peak phase of solar cycle 22, under magnetically quiet conditions. The drifts are entirely downward between 2000 and 0500 LT bin for both techniques and the root mean square error (RMSE) between the modeled and the ionosonde vertical plasma drifts during these periods is 3.80, 4.37, and 4.74 m/s for June solstice, December solstice and equinox, respectively. Ouagadougou average vertical drifts show evening prereversal enhancement (PRE) velocity peaks (V_ZP) of about 16, 14, and 17 m/s in June solstice, December solstice, and equinox, respectively, at 1900–2000 LT; whereas global empirical model average drifts indicate V_ZP of approximately 33 m/s (June solstice), 29 m/s (December solstice), and 50 m/s (equinox) at 1800 LT. We find very weak and positive correlation (+0.10376) between modeled V_ZP versus F10.7, while ionosonde V_ZP against F10.7 gives worst and opposite correlation (−0.05799). The results also show that modeled V_ZP–Ap indicates good and positive correlation (+0.64289), but ionosonde V_ZP–Ap exhibits poor and negative correlation (−0.22477).     

Numerical simulation of equatorial plasma bubbles over Cachimbo: COPEX campaign

The problem of day-to-day variability in onset of equatorial spread F (ESF) is addressed using data from the 2002 COPEX observational campaign in Brazil and numerical modeling. The observational results show that for values of virtual height of the F layer base less than 355 km at around 18:35 LT, and for the prereversal peak enhancement of the vertical plasma drift (Vp) less than 30 m/s, the spread-F (ESF) was absent on four nights over Cachimbo (9.5°S, 54.8°W, dip latitude = −2.1°). In this work we analyze the geophysical conditions for the generation of the irregularities by comparing the nights with and without the ESF. In the comparison a numerical code is used to simulate plasma irregularity development in an extended altitude range from the bottom of the equatorial F   layer. The code uses the flux corrected transport method with Boris–Book’s flux limiter for the spatial integration and a predictor–corrector method for the direct time integration of the continuity equation for O⁺${\mathrm{O}}^{+}$ and the SOR (Successive-Over-Relaxation) method for electric potential equation. The code is tested with different evening eastward electric fields (or vertical drifts Vp < 30 m/s and Vp > 30 m/s) in order to study the influence of the prereversal enhancement in the zonal electric field on plasma bubble formation and development. The code also takes into account the zonal wind, the vertical electric field and the collision frequency of ions with neutrals and the amplitude of initial perturbation. The simulation shows a good agreement with the observational results of the ESF. The results of the code suggest that the instability can grow at the F layer bottomside by the Rayleigh–Taylor mechanism only when the Vp > 30 m/s. In the analyzed cases we have considered the competition of other geophysical parameters in the generation of plasma structures.     

A different method to update monthly median hmF2 values

The height, h_mF2, and the electron density, N_mF2, of the F2 peak are key model parameters to characterize the actual state of the ionosphere. These parameters, or alternatively the propagation factor, M3000F2, and the critical frequency, f_oF2, of the F2 peak, which are related to h_mF2 and N_mF2, are used to anchor the electron density vertical profile computed with different models such as the International Reference Ionosphere ( Bilitza, 2002), as well as for radio propagation forecast purposes. Long time series of these parameters only exist in an inhomogeneous distribution of points over the surface of Earth, where dedicated instruments (typically ionosondes) have been working for many years. A commonly used procedure for representing median values of the aforementioned parameters all over the globe is the one recommended by the ITU-R ( ITU-R, 1997). This procedure, known as the Jones and Gallet mapping technique, was based on ionosondes measurements gathered from 1954 to 1958 by a global network of around 150 ionospheric stations (  and ). Even though several decades have passed since the development of that innovative work, only few efforts have been dedicated to establish a new mapping technique for computing h_mF2 and N_mF2 median values at global scale or to improve the old method using the increased observational database. Therefore, in this work three different procedures to describe the daily and global behavior of the height of the F2 peak are presented. All of them represent a different and simplified method to estimate h_mF2 and are based on different mathematical expressions. The advantages and disadvantages of these three techniques are analyzed, leading to the conclusion that the recommended procedure to represent h_mF2 is best characterized by a Spherical Harmonics expansion of degree and order equal to 15, since the differences between the h_mF2 values obtained with the Jones and Gallet technique and those obtained using the abovementioned procedure are of only 1%.     

Comparison of observed hmF2 and IRI 2007 model with M(3000)F2 estimation of hmF2 at low solar activity for an equatorial station

This is to investigate ways of improving the Equatorial F2-layer peak heights estimated from M(3000)F2 ionosonde data measured using the Ionospheric Prediction Service (IPS-42) sounder at Ouagadougou, Burkina Faso (Latitude +12.4°N, Longitude +1.5°W, Dip latitude +5.9°N) during a low solar activity year (1995). For this purpose, we have compared the observed h_mF2 (h_mF2_obs) deduced using an algorithm from scaled virtual heights of quiet day ionograms and the predicted h_mF2 values which is given by the IRI 2007 model (h_mF2_{IRI 2007}) with the ionosonde measured M(3000)F2 estimation of the h_mF2 values (h_mF2_est) respectively. The correlation coefficients R² for all the seasons were found to range from 0.259 to 0.692 for h_mF2_obs values, while it ranges from 0.551 to 0.875 for the h_mF2_{IRI 2007} values. During the nighttime, estimated h_mF2 (h_mF2_est) was found to be positively correlated with the h_mF2_obs values by the post-sunset peak representation which is also represented by the h_mF2_{IRI 2007} values. We also investigated the validity of the h_mF2_est values by finding the percentage deviations when compared with the h_mF2_obs and h_mF2_{IRI 2007}.     

Longitudinal differences in the equatorial spread F characteristics between Vietnam and Brazil

We present the results of a comparative study of the equatorial spread F (ESF) and the F layer critical parameter, the base height of the F layer bottomside (h′F) over the two equatorial sites, Ho Chi Minh City – HCM (dip latitude: 2.9°N) in Vietnam and Sao Luis – SL (dip latitude: ∼2°S) in Brazil. The study utilizes simultaneous data collected by a CADI at HCM and a digisonde at SL during the year 2002 with the monthly mean solar 10.7 cm flux (F10.7) varying from ∼120 to ∼185. This study focuses on the quiet time seasonal behavior of the F layer parameters in the two widely separated longitude sectors, and addresses the question as to what can we learn from such comparative studies with respect to the ambient ionospheric and thermospheric parameters that are believed to control the ESF generation and hence its longitudinal occurrence pattern. The observed differences/similarities in the diurnal and seasonal patterns of the F Layer height vis-à-vis the ESF occurrences are evaluated in terms of the known longitudinal differences in the F layer heights, thermospheric meridional winds and the geomagnetic peculiarities of the two sites.     

Comparing IRI and a regional model with ionosonde measurements in Pakistan

We have used the technique of expansion in Empirical Orthogonal Functions (EOFs) to develop regional models of the critical frequencies of E and F₂ layers (f_oE, f_oF₂), peak height (h_mF₂), and semi-thickness of F₂ layer (Y_mF₂) over Pakistan. In the present study levels of solar activity specified by Smoothed Sunspot Number (R) from 10 to 200 are taken into account. The magnetic dip angle for the model ranges from 30° to 60°. We have compared the regional model and the International Reference Ionosphere (IRI) with measurements of three ionosondes in Pakistan. The model parameters f_oE and f_oF₂ are found overall comparable to the observed hourly median values during daytime at Karachi (geographic latitude = 24.95°N, longitude = 67.13°E, magnetic inclination = 37°), Multan (30.18°N, 71.48°E, 45°) and Islamabad (33.75°N, 73.13°E, 51.5°) during the years 1988, 1996 and 2000. For h_mF₂ the computed values by regional and IRI model for the year 1995 are found close to each other. However, for Y_mF₂the results are better during daytime as compared to nighttime.     

Variation in the ionospheric propagating factor M(3000)F2 at Ouagadougou,Burkina Faso

We use hourly monthly median values of propagation factor M(3000)F2 data observed at Ouagadougou Ionospheric Observatory (geographic12.4°N, 1.5°W; 5.9^o dip), Burkina Faso (West Africa) during the years Januar1987–December1988 (average F10.7 < 130 × 10⁻²² W/m²/Hz, representative of low solar flux conditions) and for January 1989–December1990 (average F10.7 ? 130 × 10⁻²² W/m²/Hz, representative of high solar epoch) for magnetically quiet conditions to describe local time, seasonal and solar cycle variations of equatorial ionospheric propagation factor M(3000)F2 in the African region. We show that that seasonal trend between solar maximum and solar minimum curves display simple patterns for all seasons and exhibits reasonable disparity with root mean square error (RMSE) of about 0.31, 0.29 and 0.26 for December solstice, June solstice and equinox, respectively. Variability Σ defined by the percentage ratio of the absolute standard deviation to the mean indicates significant dissimilarity for the two solar flux levels. Solar maximum day (10–14 LT) and night (22–02 LT) values show considerable variations than the solar minimum day and night values. We compare our observations with those of the IRI 2007 to validate the prediction capacity of the empirical model. We find that the IRI model tends to underestimate and overestimate the observed values of M(3000)F2, in particular, during June solstice season. There are large discrepancies, mainly during high solar flux equinox and December solstice between dawn and local midnight. On the other hand, IRI provides a slightly better predictions for M(3000)F2 between 0900 and 1500 LT during equinox low and high solar activity and equinox high sunspot number. Our data are of great importance in the area of short-wave telecommunication and ionospheric modeling.     

Study of maximum electron density NmF2 at Karachi and Islamabad during solar minimum (1996) and solar maximum (2000) and its comparison with IRI

The monthly hourly medians of maximum electron density, N_mF₂, at two Pakistani ionospheric stations, Karachi and Islamabad, have been determined for solar minimum (1996) and solar maximum (2000) and compared with IRI predictions using the URSI coefficients. At night and pre-noon period the N_mF₂ values at both stations are almost equal during the 2 years. However, at post-noon the values at Karachi are considerably larger than those at Islamabad due to the equatorial or geomagnetic anomaly. Karachi (geomag. coord. 16.44°N, 139.08°E) lies near the region of the equatorial anomaly (+20 and −20 geomagnetic latitude), so most of the N_mF₂ values at Karachi are larger than those at Islamabad (geomag. coord. 24.46°N, 145.67°E). The maximum monthly values of N_mF₂ show a semi-annual variation at Karachi and Islamabad both during 1996 and 2000 as predicted by IRI.     

Ionospheric reflection of the magnetic activity described by the index η

Differences in the external part of the vertical geomagnetic component point to the existence of local inhomogeneities in the magnetosphere or the ionosphere. Usually used magnetic indices are not sufficient to express the state of ionosphere, the common used global Kp index derived in the three-hour interval does not indicate much more rapidly changes appearing in ionosphere. Magnetic index η reflects ionospheric disturbances when other indices show very quiet conditions. Data of ionospheric characteristics (foE, foEs, h’E, h’F2) during 28-day long quiet day conditions (Kp = 0–2) in 2004 were analyzed. The correlations between strong local disturbances in ionosphere during very quiet days and high values of magnetic index η were found. The most sensitive to magnetic influence – ionospheric E layer data (foE characteristic) – reaches median deviations up to (+0.8 MHz and −0.8 MHz) during very low magnetic activity (Kp = 0–1). The high peaks (2–2.7) of the magnetic index η correlate in time with large local median deviations of foE. Such local deviations can suggest local inhomogeneities (vertical drifts) in the ionosphere. The correlation in space is not trivial. The strong peak of η is situated between the positive and negative deviations of foE. Additional observation is connected with correlation in time of the high η value with the negative median deviations of h’F2 (in some cases up to −90 km). The analysis was based on one-minute data recorded at each of 20 European Magnetic Observatories working in the INTERMAGNET network and from 19 ionosondes for 2004. Ionospheric data are sparse in time and in space in opposite to the magnetic data. The map of the magnetic indices can suggest the behavior of ionospheric characteristics in the areas where we have no data.     

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.     

Low latitude nighttime ionospheric vertical E × B drifts at African region

The nighttime vertical E × B drifts velocities of the F2-region were inferred from the hourly hmF2 values obtained from ionosonde data over an African equatorial station, Ilorin (8.50^oN, 4.68^oE; dip lat. 2.95^o) during period of low solar activity. For each season, the plasma drift Vz is characterized by an evening upward enhancement, then by a downward reversal at 1900 LT till around 0000 LT, except for June solstice. This was explained using the Rayleigh–Taylor (R-T) instability mechanism. The occasional drift differences in Vz obtained by inferred and direct measurement over Ilorin and Jicamarca, respectively are reflective of the importance of chemistry and divergent transport system due to both the E region electric and magnetic fields instead of simple motions. The pre-reversal enhancement (PRE) magnitude is higher during the equinoctial months than the solsticial months over Jicamarca, highest during December solstice and the equinoctial months over Ilorin, suggesting the dominance of higher E × B fountain during equinoxes at both stations. The lowest PRE magnitude was in June solstice. The appearance of post-noon peak in NmF2 around 1700 LT is highest during the equinoctial months and lowest during the solsticial period. A general sharp drop in NmF2 around 1800 LT is distinct immediately after sunset, lowest during June solstice and highest in March equinox. Our result suggests that between 0930 and 2100 LT, the general theory that vertical drifts obtained by digisonde measurements only match the E × B drift if the F layer is higher than 300 km is reliable, but does not hold for the nighttime period of 2200–0600 LT under condition of solar minima. Hence, the condition may not be sufficient for the representation of vertical plasma drift at nighttime during solar minima. This assertion may still be tentative, as more equatorial stations needed to be studied for better confirmation.     

Planetary wave coupling of the atmosphere–ionosphere system during the Northern winter of 2008/2009

This paper presents the global spatial (latitude and altitude) structure and temporal variability of the ∼23-day ionospheric zonally symmetric (s = 0) planetary wave (PW) seen in the Northern winter of 2008/2009 (October 2008–March 2009). It is shown that these ∼23-day ionospheric oscillations are forced from PWs propagating from below. The COSMIC ionospheric parameters f_oF2 and h_mF2 and electron density at fixed altitudes and the SABER temperatures were utilized in order to define the waves which are present simultaneously in the atmosphere and ionosphere. The long-period PWs from the two data sets have been extracted through the same data analysis method. The similarity between the lower thermospheric ∼23-day (s = 0) temperature PW and its ionospheric electron density response provides valuable and strong experimental evidence for confirming the paradigm of atmosphere–ionosphere coupling.     

Response of the ionospheric F-region in the Brazilian sector during the super geomagnetic storm in April 2000 observed by GPS

The response of the ionospheric F-region in the equatorial and low latitude regions in the Brazilian sector during the super geomagnetic storm on 06–07 April 2000 has been studied in the present investigation. The geomagnetic storm reached a minimum D_st of −288 nT at 0100 UT on 07 April. In this paper, we present vertical total electron content (VTEC) and phase fluctuations (in TECU/min) from GPS observations obtained at Imperatriz (5.5°S, 47.5°W; IMPZ), Brasília (15.9°S, 47.9°W; BRAZ), Presidente Prudente (22.12°S, 51.4°W; UEPP), and Porto Alegre (30.1°S, 51.1°W; POAL) during the period 05–08 April. Also, several GPS-based TEC maps are presented from the global GPS network, showing widespread and drastic TEC changes during the different phases of the geomagnetic storm. In addition, ion density measurements on-board the satellite Defense Meteorological Satellite Program (DMSP) F15 orbiting at an altitude of 840 km and the first Republic of China satellite (ROCSAT-1) orbiting at an altitude of 600 km are presented. The observations indicate that one of the orbits of the DMSP satellite is fairly close to the 4 GPS stations and both the DMSP F15 ion-density plots and the phase fluctuations from GPS observations show no ionospheric irregularities in the Brazilian sector before 2358 UT on the night of 06–07 April 2000. During the fast decrease of D_st on 06 April, there is a prompt penetration of electric field of magnetospheric origin resulting in decrease of VTEC at IMPZ, an equatorial station and large increase in VTEC at POAL, a low latitude station. This resulted in strong phase fluctuations on the night of 06–07 April, up to POAL. During the daytime on 07 April during the recovery phase, the VTEC observations show positive ionospheric storm at all the GPS stations, from IMPZ to POAL, and the effect increasing from IMPZ to POAL. This is possibly linked to the equatorward directed meridional wind. During the daytime on 08 April (the recovery phase continues), the VTEC observations show very small negative ionospheric storm at IMPZ but the positive ionospheric storm effect is observed from BRAZ to POAL possibly linked to enhancement of the equatorial ionospheric anomaly.     

Equatorial M(3000)F2 estimation of F2-layer models peak heights during low solar activity

M(3000)F2 estimation of h_mF2 based on four different formulated models viz: (1) Shimazaki (1955) (2) Bradley and Dudeney (1973), (3) Dudeney (1974) and (4) Bilitza et al. (1979) at an equatorial station in West Africa during low solar activity period (1995) are used to validate its conformity with observed and International Reference Ionosphere (IRI) model. Local time analyses of data from fifteen (15) selected days during the January and July solstices and April and October equinoxes are used. The results obtained show that the M(3000)F2 estimation of h_mF2 from the ionosonde-measured values using the Ionospheric Prediction Service (IPS-42) sounder compared to the observed values which were deduced using an algorithm from scaled virtual heights of quiet day ionograms are highly correlated with Bilitza model. International Reference Ionosphere (IRI 2007) model for the equatorial region also agrees with the formulation developed by Bilitza et al. (1979) for the four different seasons of the year. h_mF2 is highest (425 km) in summer (June solstice) season and lowest (386 km) in autumn (September equinox) season with daytimes peaks occurring at 1100–1200 LT during the solstices and at 1000 LT during the equinoxes respectively. Also, the post-sunset peaks are highest (362 km) at the spring (March equinox) and lowest (308 km) at the summer (June solstice) both occurring between 1800 and 2000 LT.     

Dynamics of the convection in the inner magnetosphere by observations of the diffuse aurora,SAR arc and ionospheric drift

The first results of the comparison of subauroral luminosity dynamics in 557,7 and 630,0 nm emission with simultaneous measurements of the ionospheric drift in the F2 region with a digisonde DPS-4 at the Yakutsk meridian (CGMC: 55–60N, 200°E) at Kp = 2–6 are presented. It is shown from the analysis of individual events that during the magnetospheric convection intensification after the turn of the IMF B_z – component to the south the equatorward extension of diffuse aurora takes place. At the same time the westward ionospheric drift velocity increases both in the diffuse aurora region and much equatorward of it due to the occurrence of the northward polarization electric field. We suppose that the generation of polarization field can be associated with the development of the region 2 FAC during the intensification of magnetospheric convection. The comparison of ground-based observations with measurements of the plasma drift aboard the DMSP-F15 satellite has been carried out.     

Variation of ionospheric total electron content in Taiwan region of the equatorial anomaly from 1994 to 2003

The ionospheric total electron content (TEC) in the northern hemispheric equatorial ionospheric anomaly (EIA) region is studied by analyzing dual-frequency signals of the Global Position System (GPS) acquired from a chain of nine observational sites clustered around Taiwan (21.9–26.2°N, 118.4–112.6°E). In this study, we present results from a statistical study of seasonal and geomagnetic effects on the EIA during solar cycle 23: 1994–2003. It is found that TEC at equatorial anomaly crests yield their maximum values during the vernal and autumnal months and their minimum values during the summer (except 1998). Using monthly averaged I_c (magnitude of TEC at the northern anomaly crest), semi-annual variations is seen clearly with two maxima occurring in both spring and autumn. In addition, I_c is found to be greater in winter than in summer. Statistically monthly values of I_c were poorly correlated with the monthly Dst index (r = −0.22) but were well correlated with the solar emission F_10.7 index (r = 0.87) for the entire database for the period during 1994–2003. In contrast, monthly values of I_c were correlated better with Dst (r ? 0.72) than with F_10.7 (r ? 0.56) in every year during the low solar activity period (1994–1997). It suggests that the effect of solar activity on I_c is a longer term (years), whereas the effect of geomagnetic activity on I_c is a shorter term (months).     

Comparison of the CHAMP radio occultation data with the Canadian advanced digital ionosonde in the Polar Regions

In this paper we present the results of the comparison of the retrieved electron density profiles of the Ionospheric Radio Occultation (IRO) experiment on board CHAMP (CHAllenging Minisatellite Payload), with the ground ionosonde profiles for the Polar Regions. IRO retrieved electron density profiles from CHAMP are compared with Canadian Advanced Digital Ionosonde (CADI) measurements at two vertical sounding stations well within the Polar Cap, Eureka (geog. 80°13′ N; 86°11′ W) and Resolute Bay (geog. 74°41′ N; 94°54′ W). We compared the ionospheric parameters such as the peak electron density of the F-layer (NmF₂) and the peak height of the F-layer (h_mF₂) for a 3-year period, 2004–2006. CHAMP derived NmF₂ shows reasonable agreement with the ionosonde retrieved NmF₂ for both the stations (0.76 and 0.71 correlation coefficient, for Eureka and Resolute Bay, respectively) whereas the h_mF₂ agreement is not that acceptable (0.25 and 0.37 correlation coefficient, respectively). The h_mF₂ from vertical sounding showed less spread than the CHAMP h_mF₂.     

Longitudinal behaviors of the IRI-B parameters of the equatorial electron density profiles retrieved from FORMOSAT-3/COSMIC radio occultation measurements

The electron density profiles in the bottomside F₂-layer ionosphere are described by the thickness parameter B0 and the shape parameter B1 in the International Reference Ionosphere (IRI) model. We collected the ionospheric electron density (N_e) profiles from the FORMOSAT-3/COSMIC (F3/C) radio occultation measurements from DoY (day number of year) 194, 2006 to DoY 293, 2008 to investigate the daytime behaviors of IRI-B parameters (B0 and B1) in the equatorial regions. Our fittings confirm that the IRI bottomside profile function can well describe the averaged profiles in the bottomside ionosphere. Analysis of the equatorial electron density profile datasets provides unprecedented detail of the behaviors of B0 and B1 parameters in equatorial regions at low solar activity. The longitudinal averaged B1 has values comparable with IRI-2007 while it shows little seasonal variation. In contrast, the observed B0 presents semiannual variation with maxima in solstice months and minima in equinox months, which is not reproduced by IRI-2007. Moreover, there are complicated longitudinal variations of B0 with patterns varying with seasons. Peaks are distinct in the wave-like longitudinal structure of B0 in equinox months. An outstanding feature is that a stable peak appears around 100°E in four seasons. The significant longitudinal variation of B0 provides challenges for further improving the presentations of the bottomside ionosphere in IRI.     

The accuracy of data from ionosondes for the estimation of hmF2 and the identification of global change in the ionosphere

A long temporal series of simulated ionograms was generated with a superimposed secular variation of −14 km/century on the h_mF2 parameter. These ionograms were interpreted by the automatic scaling program Autoscala. By applying four different empirical formulas, four artificial series of h_mF2 were generated and then processed with the same methods used by other authors for real data sets. Data analysis of the simulated ionograms revealed the artificially imposed long-term trend. These results lead to the conclusion, that regardless of the empirical formula used, the accuracy of h_mF2 from ionosonde measurements would be adequate to observe a long-term trend of −14 km/century.