Solar Activity Conditions Research Articles

Conjugacy of two types of phenotypic variability of small-leaved linden

The properties of five bilaterally symmetrical features of the leaf blades of the small-leaved linden (Tilia cordata Mill.) in four populations of the Moscow Region in 2014–2017 were studied. The angle trait was excluded, because it possessed the property of directional asymmetry. Instead, a new linear trait was used: the distance between the base of the second vein of the first order and the base of the first vein of the second order on the first vein of the first order. The population difference in fluctuating asymmetry (FA) was found only in the first two traits (leaf width and distance between the bases of the first vein of the first order and the second vein of the second order). The largest value of FA was in the urban environment, the smallest was in the rural areas. A weak negative correlation was obtained between the magnitude of linear characteristics and the value of FA, as well as a weak positive correlation relationship between the values of FA in five traits. The first trait had the highest fluctuation variability, and the second one had the highest plastic variability. The regression dependence of the fluctuation variability on the plastic variability (b1 = 0.25, p <0.05) and the dependence of these two types of variability on the interaction of the factors “year” and “site of sampling” were revealed. Thus, the conclusion was made about the conjugacy of two types of variability: fluctuation and plastic. According to the authors, asynchronous growth, competition for light in conditions of high solar activity in 2014–2016 compared to the abnormal wet summer of 2017 led to an increase in FA due to destabilization of mechanisms of growth and regulation of gene expression, which contributed to a decrease in the stability of development. The increase in FA and the decrease in the developmental stability in urban ambient in 2016 could be due to: a)an intensive flow of vehicles in spring and summer, b) a high level of groundwater in this part of the city and c) increased hydrolytic acidity of the soil.

Electron density in the F1 layer over Norilsk in 2007–2014

We report the results of the analysis of annual variations in daily electron density (N) for various solar activity conditions — minimum, rise, and maximum (2007–2014) — obtained from digisonde measurements at the ionospheric station Norilsk (69.4° N, 88.1° E). New coefficients of the known semi-empirical model (SEM) describing the connection between N and thermosphere characteristics are calculated to identify regularities of these variations exactly at Norilsk station. The height changes of annual variations in the noon electron density N are obtained in the F1 region (120–200 km). The experimental data approximation describes N quite satisfactorily at these heights in the daytime of different seasons under different solar activity conditions. It is shown that in the years of solar minimum at all heights of the F1 layer the tendency remains for maximum N in summer and for minimum N in winter. In later years and in the year of maximum solar activity, a characteristic feature of the behavior of N is the change in the phase of the annual variation by 180° in the range of heights from 170 to180 km: maximum N is observed in winter; and minimum, in summer.

Электронная концентрация на высотах ионосферного слоя F1 в период 2007–2014 гг. над Норильском

We report the results of the analysis of annual variations in daily electron density (N) for various solar activity conditions — minimum, rise, and maximum (2007–2014) — obtained from digisonde measurements at the ionospheric station Norilsk (69.4° N, 88.1° E). New coefficients of the known semi-empirical model (SEM) describing the connection between N and thermosphere characteristics are calculated to identify regularities of these variations exactly at Norilsk station. The height changes of annual variations in the noon electron density N are obtained in the F1 region (120–200 km). The experimental data approximation describes N quite satisfactorily at these heights in the daytime of different seasons under different solar activity conditions. It is shown that in the years of solar minimum at all heights of the F1 layer the tendency remains for maximum N in summer and for minimum N in winter. In later years and in the year of maximum solar activity, a characteristic feature of the behavior of N is the change in the phase of the annual variation by 180° in the range of heights from 170 to180 km: maximum N is observed in winter; and minimum, in summer.

Geomagnetic disturbances at F1-layer heights under different solar activity conditions over Norilsk

We analyze the influence of geomagnetic disturbances on the electron density Ne at Norilsk ionospheric station (69° N; 88° E) at F1-layer heights (120–200 km). For the analysis, we have selected 25 moderate and weak geomagnetic disturbances for two seasons — spring and fall — of 2003–2014. Using the Ne values obtained from measurements made with the Norilsk digisonde during this period, we analyze Ne variations during geomagnetic disturbances in spring and fall for a long period of time. We determine the effect of spring-fall asymmetry occurring in all solar activity phases and manifesting itself in a significant decrease in the electron density during the main phase of fall storms at all heights in comparison with quiet days: up to 2.6 times at a height of 200 km and slightly less at lower heights. This phenomenon is not observed during spring disturbances: Ne variations are much weaker.

Whole Atmosphere Climate Change: Dependence on Solar Activity

AbstractWe conducted global simulations of temperature change due to anthropogenic trace gas emissions, which extended from the surface, through the thermosphere and ionosphere, to the exobase. These simulations were done under solar maximum conditions, in order to compare the effect of the solar cycle on global change to previous work using solar minimum conditions. The Whole Atmosphere Community Climate Model‐eXtended was employed in this study. As in previous work, lower atmosphere warming, due to increasing anthropogenic gases, is accompanied by upper atmosphere cooling, starting in the lower stratosphere, and becoming dramatic, almost 2 K per decade for the global mean annual mean, in the thermosphere. This thermospheric cooling, and consequent reduction in density, is less than the almost 3 K per decade for solar minimum conditions calculated in previous simulations. This dependence of global change on solar activity conditions is due to solar‐driven increases in radiationally active gases other than carbon dioxide, such as nitric oxide. An ancillary result of these and previous simulations is an estimate of the solar cycle effect on temperatures as a function of altitude. These simulations used modest, five‐member, ensembles, and measured sea surface temperatures rather than a fully coupled ocean model, so any solar cycle effects were not statistically significant in the lower troposphere. Temperature change from solar minimum to maximum increased from near zero at the tropopause to about 1 K at the stratopause, to approximately 500 K in the upper thermosphere, commensurate with the empirical evidence, and previous numerical models.

Empirical Orthogonal Function Analysis and Modeling of the Topside Ionospheric and Plasmaspheric TECs

AbstractThe topside total electron contents (TECs) observed by the MetOp‐A (above 832 km) and TerraSAR‐X (above 520 km) satellites for multiple local times during 2008–2018 have been used to develop global topside ionospheric and plasmaspheric TEC models, based on empirical orthogonal function (EOF) analysis. Gridded TEC maps are first obtained from the original quiet time TECs, and then, they are decomposed into EOF basis modes and associated amplitude coefficients. The EOF analysis well captures the latitudinal, longitudinal, and seasonal variations of the topside ionosphere and plasmasphere, and the associated dependence on solar EUV forcing. The first five EOFs, which can account for more than 98.8% of the total variance, are applied in model construction. The comparison with two empirical models indicates that the EOF TEC models can reproduce the observations well, including TEC magnitudes and longitudinal variations. Moreover, the annual anomaly is obviously seen in the topside TECs. The global averaged TECs are greatest in December and smallest in June. With increasing solar EUV forcing, the global averaged TECs always increase, but the winter hemisphere TECs do not change much and even decrease, especially at night and in the Southern Hemisphere. The overall increasing rate with solar EUV forcing is larger under higher solar activity conditions. The direct plasma diffusion through ionosphere‐plasmasphere coupling may not be able to explain some of the features seen in the topside TECs.

Local Time and Seasonal Variations in the Electron Density at the Ionospheric F2-Layer Maximum with Wave Disturbances under Low Solar Activity Conditions

Regular and quasi-periodic local time and seasonal variations in the electron density in the maximum of the ionospheric F2 layer during low solar activity in 2016 are analyzed. System spectral analysis of temporal variations in the electron density in the range of 30–180 min is based on windowed Fourier transform, adaptive Fourier transform, and wavelet transform. In all seasons, the ionospheric F2 layer is dominated by oscillation with a period of 70–120 min, an amplitude of ΔNa ≈ (2–10) × 1010 m–3, and a relative amplitude of $${{\Delta {{N}_{a}}} \mathord{\left/ {\vphantom {{\Delta {{N}_{a}}} {\bar {N}}}} \right. \kern-0em} {\bar {N}}}$$ ≈ 0.20–0.70. The duration of this oscillation varied from 6 to 17 h depending on the season. The amplitude of oscillations with other periods is significantly smaller. It has been confirmed that the regular local time and seasonal variations in the electron density in the F2-layer maximum are fully consistent with the existing views on physicochemical processes in the ionosphere. The main regularities in the behavior of quasi-periodic variations in the electron density have been revealed.

Investigation of exceptional solar activity in September 2017: GLE 72 and unusual Forbush decrease in GCR

The exceptional solar activity in early September 2017 at minimum of solar cycle 24 is analyzed. Intensive solar-terrestrial disturbances was caused by Active Region AR2673, which produced four powerful eruptions class X, including the strongest flare X9.3 of Solar Cycle 24 on September 6, 2017, after which began G4 – Severe geomagnetic storm on 07-08.09.2017 with Ap = 96, and also the second strongest flare X8.2 of Solar Cycle 24 on September 10, 2017, which generated Ground Level Enhancement (GLE) of cosmic rays. This was GLE72 with increase of solar cosmic ray flux 6% in Oulu Station (Finland) (effective vertical geomagnetic cutoff rigidity: 0.8 GV), and increase 9% in DOMC Antartica and 14% in DOMB Antartica (in the latter case - lead free neutron monitors with effective vertical cutoff rigidity <0.01 GV). The GLE72 develops under the conditions of a deep Forbush decrease (around 15%) in South Pole cusp caused by September 7th Coronal Mass Ejection. The Forbush effect ends on September 11th (http://cosmicrays.oulu.fi). But cosmic ray measurements by flying balloons to the stratosphere over California show that after solar eruptions in September 2017 the radiation levels in stratosphere took more than two months to fully rebound to the conditions of minimal solar activity. This is interesting fact which deserves to be explored in detail. It is precisely the study and interpretation of this process that is concerned with this work.

Variability of the Critical Frequency foF2 for Equatorial Regions during Solar Cycle’s Minima and Maxima at Ouagadougou and Manila Stations

In this paper we report on the foF2 variabilities for two equatorial regions (Ouagadougou: Lat. 12.4°N; Long. 358.5°E, Dip. 1.43°S; and Manila: Lat. 14°36'15.12''N; Long. 120°58'55.92''E; Dip. 0.6°S) during solar cycles 20 and 21 minima and maxima phases. Many previous works have argued on the diurnal and seasonal variation of foF2 for different solar events conditions for latitudinal position. But there are few investigations for Africa equatorial region longitudinal variation. The present paper’s goal is to outline possible similarity in foF2 behavior between variations for better understanding of physical process lead to some observed phenomenon in Asia-Africa equatorial sector. The F-layer critical frequency (foF2) data observed from the two equatorial ionosonde stations have been used for the present comparative study. The results show significant similarity between the critical frequency (foF2) seasonal variations over the time intervals 1976-1996. During day-time measured data from Manila station are higher than those from Ouagadougou station. That may lie in that Manila is closer to equatorial ionization crest region. During solar minimum phase, the longitudinal variation of foF2 shows two crossing points (11:00 UT and 22:00 UT) between the foF2 profiles form the two stations for all seasons regardless of the solar cycle. However during intense solar activity condition, the number of crossing-point between measured data from Manila and Ouagadougou stations varies by seasons and solar cycle. This phenomenon may be due to the compilations of severe activities (storms, coronal mass ejection, heliosheet fluctuations) during the solar maximum phases.

Climatology of the Quasi‐6‐Day Wave in the Mesopause Region and Its Modulations on Total Electron Content During 2003–2017

AbstractThe westward quasi‐6‐day planetary wave (Q6DW) with zonal wave number 1 is a prominent oscillation in the mesosphere and lower thermosphere region, which causes significant variabilities in the ionosphere through E region wind dynamo. In this paper, the neutral wind observations from the Thermosphere Ionosphere and Mesosphere Electric Dynamics Doppler Imager experiment, the kinetic temperature observations from the Sounding of the Atmosphere using Broadband Emission Radiometry instrument, and the total electron content (TEC) maps from globally distributed Global Positioning System (GPS) receivers during 2003–2017 are utilized to statistically study the Q6DW in both the neutral atmosphere and the ionosphere. Our statistical results show that (1) the Q6DW is most likely to occur during May and September, exhibiting a quasi‐semiannual oscillation. (2) The periods of the Q6DW show two statistical crests at ~6 and ~7 days separately. (3) The ionospheric oscillations due to the Q6DW are positively related to both the 10.7‐cm solar flux index and the neutral wave amplitudes in the mesosphere and lower thermosphere region. The stronger oscillations in TEC under higher solar activity conditions are due to the larger ionization rate and thus larger background TEC. A stronger Q6DW results in stronger wind dynamos in the E region, which leads to stronger F region responses indirectly. (4) The interhemispheric asymmetries of the ionospheric responses to Q6DW show weak negative correlations with both solar activities and neutral wave perturbations, the mechanism of which needs our further investigation.

Variability of the Martian ionosphere from the MAVEN Radio Occultation Science Experiment

The Martian ionosphere is produced by a number of controlling processes, including solar extreme ultraviolet radiation (EUV) and X-ray ionization, impact ionization by precipitating electrons, and day-to-night transport. This study investigates the structural variability of the Martian ionosphere with the aid of the radio occultation (RO) experiments made on board the recent Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft. On the dayside, the RO electron density profiles are described by the superposition of two Chapman models, representing the contributions from both the primary layer and the low-altitude secondary layer. The inferred subsolar peak electron densities and altitudes are 1.24×105 cm–3 and 127 km for the former, and 4.28×104 cm–3 and 97 km for the latter, respectively, in general agreement with previous results appropriate for the low solar activity conditions. Our results strengthen the role of solar EUV and X-ray ionization as the driving source of plasma on the dayside of Mars. Beyond the terminator, a systematic decline in ionospheric total electron content is revealed by the MAVEN RO measurements made from the terminator crossing up to a solar zenith angle of 120°. Such a trend is indicative of day-to-night plasma transport as an important source for the nightside Martian ionosphere.

Photochemical escape of atomic C and N on Mars: clues from a multi-instrument MAVEN dataset

Context. Photochemical escape of hot atoms is crucial to the long-term evolution of the Martian climate. For atomic C and N, photochemical escape is primarily driven by photodissociation (PD) of CO and N2. Aims. Combining the Mars Atmosphere and Volatile Evolution (MAVEN) measurements of atmospheric neutral densities and solar EUV/X-ray irradiance, we perform a state-of-the-art analysis of atomic C and N escape on Mars. Methods. For each MAVEN orbit, we calculated the hot C and N production rates in the dayside Martian upper atmosphere via PD, from which the escape rates are estimated using a simplified technique to parameterize the respective escape probabilities taking into account multiple collisions with ambient neutrals. Results. The mean C and N escape rates are 1 × 1024 s−1 and 9 × 1024 s−1, appropriate for low to moderate solar activity conditions, and thermospheric PD makes a larger contribution to the total N escape than to the total C escape. The above differences highlight the importance of nascent energy, with more energetic nascent escaping atoms able to survive collisions with ambient neutrals more easily, thus extending down to deeper regions of the atmosphere. Solar cycle variation in C and N escape is revealed by our analysis, whereas solar zenith angle variation is absent for both species. These results could be explained by the fact that the production of nascent escaping atoms responds to varying solar illumination angle at low altitudes where the escape probability is negligible, but responds to varying level of solar EUV/X-ray irradiance at high altitudes where the atmosphere is essentially collisionless.

On the relative roles of the neutral density and photo chemistry on the solar zenith angle variations in the V2 layer characteristics of the Venus ionosphere under different solar activity conditions

Using an in-house developed one dimensional photo-chemical model (1D-PCM), which considers production and loss of 11 ions namely, CO2+, CO+, C+, N2+, N+, He+, O+(2D), O+(2P), O+(4S), O2+ and NO+, characteristics of the V2 layer in the Venus ionosphere has been studied. It is noted that existing ionospheric model for the Venus ionosphere, such as the IonA (Ionization in Atmospheres) model, not only over/under estimate the peak electron density of V2 layer, it also has significant departures from the observations on the solar zenith angle and solar activity control. The IonA model uses VenusGRAM model (Venus Global Reference Atmosphere Model) as input for the neutral density and temperature and considers Venus atmosphere consisting of CO2, O, and N2 molecules only. Further, it oversimplifies the ion chemistry by assuming Venus ionosphere to have O2+ as the only dominant ion species. Using VTS3 model, an empirical model based on measurements from Orbiter Neutral Mass Spectrometer on Pioneer Venus Orbiter (PVO) which considers profiles of six neutrals (CO2, O, CO, He, N, and N2), we modified IonA model, named as IonA-VTS3, to find that it reproduced the altitude of V2 peak electron density (hmV2) quite well. However, the model still lacked in reproducing observed peak V2 electron density (NmV2). The in-house developed one dimensional photo-chemical model (1D-PCM) not only estimated NmV2 accurately, the hmV2 was also reproduced quite well. Comparison of Venera and PVO radio occultation measurements with 1D-PCM and IonA-VTS3 calculations reveals the role of complex chemical reactions in determining the features of peak altitude and density of V2 layer during different solar activity periods. We surmised that differences in the observed and IonA modeled peak V2 layer altitudes were due to the limitations associated with VenusGRAM neutral density model. It shows that variations in the neutral density controls the V2 layer peak density height. 1D-PCM calculations also showed that the complex chemistry including production and loss reactions of 11 ions could reproduce the variations in the peak density of Venusian ionosphere during different solar activity conditions. It suggests that the ion-chemistry has wider control over the peak plasma density in the Venus ionosphere.

A study on Nighttime Winter Anomaly (NWA) and other related Mid-latitude Summer Nighttime Anomaly (MSNA) in the light of International Reference Ionosphere (IRI) – Model

The ionospheric Nighttime Winter Anomaly (NWA) is a feature observed in the Northern Hemisphere at the American and in the Southern Hemisphere at the Asian longitude sector under low solar activity conditions. Jakowski et al. (2015) analyzed ground-based GPS derived TEC and peak electron density data from radio occultation measurements on Formosat-3/COSMIC satellites and confirmed the persistence of the phenomenon. Further, they assumed that Mid-latitude Summer Nighttime Anomaly (MSNA) and related special anomalies such as the Weddell Sea Anomaly (WSA) and the Okhotsk Sea Anomaly (OSA) are closely related to the NWA via enhanced wind-induced uplifting of the ionosphere. The aim of this paper is to study the factors causing these anomalies and also to investigate if these anomalies are re-produced by IRI. The results show that IRI model does include the NWA effect, though at a different longitude and could be improved for better predictions. The IRI-2016 model does show WSA in TEC but not in NmF2. Further, the IRI-2016 model could clearly predict the OSA both in NmF2 and TEC.

Transition of Interhemispheric Asymmetry of Equatorial Ionization Anomaly During Solstices

AbstractThe magnitudes of the two crests of equatorial ionization anomaly (EIA) vary with local time. During the solstices, EIA crest in the winter hemisphere is larger than that in the summer hemisphere before noon/early afternoon. Whereafter, the crest in the summer hemisphere becomes intensified, and the stronger EIA crest transits to the summer hemisphere. Using Constellation Observing System for Meteorology, Ionosphere, and Climate ionospheric radio occultation data, we examine the longitudinal and altitudinal variations of this interhemispheric transition in four longitudinal sectors and at seven heights under low/high solar activity conditions. The results show that during the June solstice the transition of the stronger EIA peak from the winter to the summer hemisphere is earlier in the sectors where the geomagnetic equator is further away from the subsolar point and the geomagnetic field declination is larger, while during the December solstice the longitudinal variations generally show the opposite compared with that in the June solstice. The distance between the geomagnetic equator and subsolar point and the geomagnetic field configuration control the upward/downward plasma movements in the summer/winter hemisphere, leading to the different transition times in different longitudinal sectors. For both solstices, transition times emerge earlier as height increases, which is mainly caused by the larger effective scale height in the summer hemisphere than in the winter hemisphere, resulting in a smaller electron density difference at higher altitudes with a fast transition. Solar activity alters the transition time below 320 km, whereas it has no evident effect at higher altitudes.

Hemispheric Asymmetry of the Vertical Ion Drifts at Dawn Observed by DMSP

AbstractBased on the measurements from Defense Meteorological Satellite Program (DMSP) F12, F13, and F15 satellites in 1995–2014, we report significant hemispheric asymmetries in vertical ion drift velocity (Vz) at dawn (0500–0700 solar local time) in geomagnetic and geographic coordinates. Vz is distributed in 0300–0900 magnetic local time sector in both the northern (NH) and southern (SH) hemispheres. The north‐south asymmetries are persistent no matter under what kind of seasonal, solar activity, and IMF conditions. In the polar cap, downward Vz is stronger in the SH. Such difference shows clear IMF BY dependence and is more significant in the local winter and/or under low solar activity conditions. In the geomagnetic coordinates, the auroral zone is dominated by upward Vz in the NH but by downward Vz in the SH statistically. In the geographic coordinates, the geographic longitudinal variation of Vz is more pronounced in the SH. The seasonal variations of high‐latitude Vz are different in the NH and SH. The average asymmetric feature of Vz largely depends on the occurrence and magnitude of ion upflow/outflow, which are modulated by the combined effects of the asymmetric magnetic field configuration between the two hemispheres, and the dynamic processes in the tightly coupled ionosphere‐thermosphere system, and their (probably nonlinear) interactions with each other.

Daytime Ionospheric TEC Weather Study Over Latin America

AbstractThe present work is the first of a two‐part weather study of the ionospheric Total Electron Content (TEC), based on data collected by four ground‐based Global Navigation Satellite System networks that cover the whole Latin America from the Patagonia to the north of Mexico. From the best of our knowledge, the maps presented here are the first TEC maps obtained using ground‐based data that covers the entire Latin America region, which represent an advance to the space weather monitoring and forecasting of the ionosphere. This work provides a qualitative and quantitative daytime analysis of the ionospheric TEC variation, which encompasses: (a) the response of TEC to the solar flux at midday; (b) the seasonal variation of TEC in different latitudinal ranges; and (c) the North‐South asymmetry of TEC over Latin America. The response to the solar flux is based on day‐to‐day TEC variations during two periods of different solar activity conditions: 2011 (ascending phase) and 2014 (maximum). The approximations of meridional wind component derived from Horizontal Wind Model‐14 model and hmF2 obtained from International Reference Ionosphere model were used. Equinoctial asymmetries with an opposite configuration in high and moderate solar activity were identified in the TEC variation. For 2011, it was related to the solar flux change. However, in 2014, according to the hmF2 variation, the influence of neutral wind becomes dominant. Among the results, we highlight an absence of winter anomaly in the Northern Hemisphere in 2014 and a stronger annual anomaly for latitudes under −20∘.

Quasi‐6‐Day Wave Effects on the Equatorial Ionization Anomaly Over a Solar Cycle

AbstractThe quasi‐6‐day wave (Q6DW) has recently been recognized as an important source of ionospheric variability. This study shows how the response of the equatorial ionosphere to the Q6DW changes over a solar cycle. Global maps of total electron content (TEC) from Global Positioning System data are used to quantify Q6DW effects on the equatorial ionization anomaly during 2004–2017. The results are compared with the Q6DW amplitude in the lower thermosphere as derived from the geopotential height measurements by the Aura satellite. A nearly one‐to‐one correspondence is found between Q6DW activities in the ionosphere and lower thermosphere, indicating robust vertical coupling. The absolute amplitude of the Q6DW in low‐latitude TEC varies with the solar activity index F10.7 and can reach 8 TEC unit (=1016 el/m2) near the crests of the equatorial ionization anomaly during solar maximum. On the other hand, the relative amplitude is unaffected by solar activity, with its annual maximum value being ∼10% for both solar minimum and solar maximum. These results establish the persistent influence of the Q6DW on the equatorial ionosphere under different solar activity conditions.

Longitudinal variations of the ionospheric trough position

For the first time a comprehensive pattern of the longitudinal effect of the ionospheric trough position was obtained. We present new results with longitudinal variations of the winter trough position as a function of geomagnetic latitude for both hemispheres and conditions of high and low solar activity and all local time hours. We used a large observational data set obtained onboard the Kosmos-900, Interkosmos-19 and CHAMP satellites for quiet geomagnetic conditions. We found that a magnitude of the trough position longitudinal effect averaged for a fixed local time is greater in the daytime (6–8°) than in the nighttime (3–5°). The longitudinal effect magnitude reaches its maximum (16°) in the morning (at 08 LT) in the Southern hemisphere at high solar activity. But on certain days at any solar activity the longitudinal effect magnitude can reach 9–10° even at night. The shape of the longitudinal effect was found to differ significantly in two hemispheres. In the Northern hemisphere the trough is usually closest to the pole in the eastern (American) longitudinal sector, and in the Southern hemisphere the trough is closest in the western (Eurasian) longitudinal sector. The magnitude and shape of the longitudinal effect is also different during low and high solar activity. The Global Self-consistent Model of the Thermosphere, Ionosphere, and Protonosphere (GSM TIP) simulations demonstrate that during low solar activity, the longitudinal variations of the daytime trough position is mainly determined by longitudinal variations of the ionization function, formed due to the longitudinal variations in the solar zenith angle and the atomic oxygen density distribution. The longitudinal variations of the nighttime trough position is formed by the longitudinal variations in ionization of precipitating auroral particles, neutral atmosphere composition, and electric field.

Study on the plasmaspheric Weddell Sea Anomaly based on COSMIC onboard GPS measurements

This study investigated the morphology of the Plasmaspheric Weddell Sea Anomaly (PWSA). Measurements by GPS receivers onboard COSMIC satellites were used to determine the slant total electron content (STEC) along signal propagation paths during 2007–2017, which were converted to the zenith direction using a specific plasmaspheric projection function to obtain vertical total electron content (VTEC). The characteristics of seasonal variation of the PWSA between the four seasons were examined under conditions of high and low solar activity that corresponded to values of the F10.7 index of >120 and ≤ 120, respectively. To investigate seasonal variation of plasmaspheric VTEC, maps of geographic latitude versus geographic longitude were constructed by binning the data into 5° latitudinal grids and 15° longitudinal grids. The median value of VTEC in each grid was calculated for each season under low and high solar activity conditions. The results showed that the WSA phenomenon could also be observed in the plasmasphere (altitude ≥ 800 km) as well as in the ionosphere. The anomaly is most prominent in winter under conditions of high solar activity, and it also can be found in spring and autumn, although its amplitude is relatively small. The equatorward neutral wind is the critical driver for PWSA formation. In addition, during the polar summer, high geographic latitudes are sunlit during the entire day, leading to prolonged photoionization. This is the most essential process for the existence of the nighttime maximum in the VTEC diurnal variation at the geographic latitudes of the PWSA.