Equatorial Location Research Articles

Ionospheric signatures from 2 years continuous monitoring of the equatorial ionosphere over Nigeria with HF Doppler sounder

A receiver that measures and logs Doppler shifts of high frequency (HF) radio signals reflected from the ionosphere was installed in Lagos (geographic: 6.48°N, 3.27°E; dip latitude −4.66°), Nigeria in March 2011. However, continuous monitoring of the ionosphere was facilitated by the installation of a transmitter in Abuja (geographic: 8.99°N, 7.39°E; dip latitude 1.01°), Nigeria in July 2019, dedicated to transmitting HF signals for this remote sensing system. This provided the opportunity to study ionospheric signatures in HF Doppler data obtained from an equatorial location. This paper presents a summary of key findings from analysis of data from the instrument during the first 28 months of operation from July 2019 to November 2021. In this work, a statistical analysis of two main daytime features in the Doppler data is presented. The first feature is irregularities that appear as spreading of the Doppler trace, while the second feature is wave structures consistent with travelling ionospheric disturbances (TIDs). In order to highlight trends in the data, the events were separated into morning (occurring from sunrise to 1159 LT) and afternoon (occurring from 1200 LT to sunset) events. The results showed that occurrences of either type of features were more frequent during the afternoon compared with morning hours. The occurrences of irregularities that appeared as a spread in the Doppler trace peaked in the month of July in the morning, while, in the afternoon these occurrences peaked in the month of March. The duration of most of these irregularities was ≥60 min. A peak in occurrences of TIDs was observed in the morning and afternoon epochs during the March equinox. It was also observed that over 80 % of occurrences of spreading in the Doppler trace during the equinoxes were associated with the occurrences of TIDs. In the month of July, despite a paucity of TIDs, there was a peak in occurrences of spreading in the Doppler trace. Overall, the lowest number of occurrences of both types of features was recorded in the month of August. Detailed analysis of selected events showed that the morning occurrences of spreading in the Doppler trace were mostly remnants of post-midnight spread F, while the afternoon occurrences were due to either TIDs or severe E-layer irregularities. The results from this study show the potential of the low-cost HF Doppler instrument as a real-time monitor of space weather activity at equatorial latitudes. However, further work will be required to establish what percentage of daytime spreading in the F-layer is caused by the remnants of nocturnal plasma bubbles, TIDs, or irregularities in the E-layer.

Water vapor condensation in optical instruments on Mars

Modern high-sensitivity spectrometers rely on photons reflecting thousands of times between extremely reflective mirrors to generate absorption pathlengths that are kilometers long. The absorption spectrum of trace gas species is enhanced when cooling the gas sample, however, should any atmospheric volatiles condense within the gas cell, the highly-reflective mirrors may become marred, drastically cutting down the effective optical path length. In the Martian atmosphere, the first volatile to condense is typically water vapor, thus understanding the variability of the water frost point is essential for determining the performance limit of any optical instrument. We will examine these performance limits and map the maximum temperatures at which water vapor will condense on the Martian surface with respect to a model instrument being prepared for flight. The variability of the frost point with time and solar longitude (Ls) therefore reveals areas of the Martian surface at which the precision of a high-sensitivity spectrometer is optimized. We find that the optimal performance is achieved during northern fall and winter (Ls = 180°–360°) at polar and mid-latitude locations in the northern hemisphere, and during northern spring (Ls = 0°–90°) at equatorial and mid-latitude locations in the southern hemisphere when the frost point reaches the lowest maximums.

Too close to the sun: solar farms’ impact on housing prices at subtropical latitudes

ABSTRACT While the transition from fossil fuels to renewable energy will benefit many constituencies, recent work suggests that newly activated solar panels may negatively impact nearby housing prices. Although a single mechanism driving these effects has not been causally identified, alternative explanations posit that homes near solar farms lose value either due to glare or the loss of open space amenities and associated rural character. We supplement this literature with an analysis distinguished by a unique sample with the most equatorial location to date and the largest average solar farm (26 MW), allowing for a careful investigation of the role of size and glare in the capitalization of solar farm proximity. Using hedonic analysis, manually traced solar farm footprints, and difference-in-differences identification, we find a 6.86% negative capitalization of solar farm proximity that does not appear to be attributable to glare and is driven by the impacts of very large solar farms. The results are robust to concerns of negative weights associated with bad controls. To limit economic losses associated with the renewable energy transition, solar farms should be strategically located to minimize the number of nearby homes regardless of whether glare is likely to be a concern.

Performance analysis of NeQuick2 and IRI-Plas models during quiet geomagnetic and low solar activity conditions at Thanjavur equatorial location: Preliminary results

Performance analysis of NeQuick2 and IRI-Plas models during quiet geomagnetic and low solar activity conditions at Thanjavur equatorial location: Preliminary results

Performance of Regional Climate Model Precipitation Simulations Over the Terrain‐Complex Andes‐Amazon Transition Region

AbstractRegional climate models (RCMs) are widely used to assess future impacts associated with climate change at regional and local scales. RCMs must represent relevant climate variables in the present‐day climate to be considered fit‐for‐purpose for impact assessment. This condition is particularly difficult to meet over complex regions such as the Andes‐Amazon transition region, where the Andean topography and abundance of tropical rainfall regimes remain a challenge for numerical climate models. In this study, we evaluate the ability of 30 regional climate simulations (6 RCMs driven by 10 global climate models) to reproduce historical (1981–2005) rainfall climatology and temporal variability over the Andes‐Amazon transition region. We assess spatio‐temporal features such as spatial distribution of rainfall, focusing on the orographic effects over the Andes‐Amazon “rainfall hotspots” region, and seasonal and interannual precipitation variability. The Eta RCM exhibits the highest spatial correlation (up to 0.6) and accurately reproduces mean annual precipitation and orographic precipitation patterns across the region, while some other RCMs have good performances at specific locations. Most RCMs simulate a wet bias over the highlands, particularly at the eastern Andean summits, as evidenced by the 100%–2,500% overestimations of precipitation in these regions. Annual cycles are well represented by most RCMs, but peak seasons are exaggerated, especially at equatorial locations. No RCM is particularly skillful in reproducing the interannual variability patterns. Results highlight skills and weaknesses of the different regional climate simulations, and can assist in the selection of regional climate simulations for impact studies in the Andes‐Amazon transition zone.

Performance evaluation of ionospheric models over equatorial Indian region

An extensive year-long evaluation of Total Electron Content (TEC) obtained from NCAR Thermosphere-Ionosphere Electrodynamics General Circulation Model (TIE-GCM) simulations along with TEC obtained from International Reference Ionosphere (IRI-2020) is carried out with respect to observations made by a GPS TEC receiver over the dip equatorial location of Thiruvananthapuram (8.5° N, 77° E, 0.5° magnetic), in the Indian region during solar minimum period of 2005–2006. The TIE-GCM model and IRI model were run for the period of 2005 (November December) and till October 2006 for each day, and the hourly values of TEC were compared to GPS TEC observations. Overall the temporal and seasonal characteristics of TEC over Thiruvananthapuram were simulated reasonably well by the TIE-GCM model and IRI model. The skill scores of normalized Root Mean Square Error (nRMSE), Prediction Efficiency (P.E), and Ratio between maximum and minimum values were estimated for both models to evaluate their performance. The mean percentage difference between the measured and the simulated TEC was found to be around −25% for IRI, indicating underestimation of the observations, and between −40% and −50% for TIE-GCM again indicating underestimation. A comprehensive analysis revealed that there is good conformity between the modeled and measured values for the whole observation period, with a correlation coefficient R-value of 0.8 and 0.9 for the TIE-GCM and IRI models respectively. This study brings out the competence of the two models in simulating the temporal and seasonal pattern of variability of ionospheric TEC over the equatorial Indian region.

Changes in Extreme Rainfall in New Capital of Indonesia (IKN) Based on 20 Years of GPM-IMERG Data

The Indonesian government has decided to relocate the nation’s capital city from Jakarta on Java to the Nusantara Capital (IKN) on Kalimantan for political, socioeconomic, and infrastructure reasons, among others, including the threat of flood, earthquake, and land subsidence in Jakarta. However, IKN remains susceptible to hydro-meteorological disasters due to its equatorial location and high yearly rainfall amounts. In this article, we investigated changes in extreme rainfall in the IKN area over the last 20 years (2001- 2020) based on Integrated Multi-Satellite Retrievals for GPM (IMERG) version 6 data. Overall, extreme rain in the IKN area, especially in the Sepaku and Semboja sub-districts, has slightly declined in the last 2 decades, as shown by negative and positive Sen’s slopes of precipitation amount-based indices and the consecutive dry days (CDD), respectively. A decrease was also observed in RX1 day (annual maximum 1-day precipitation) and SDII (annual total rainfall divided by the number of wet days in the year) indices. This indicates that the IKN area is getting drier and could impact the availability of clean water in the future by increasing the intensity and duration of the drought. While the total amount of precipitation has decreased over the past 2 decades, there has been an increase in the intensity of more extreme precipitation events. This is evident from the rise in precipitation frequency-based indices (annual count of days with rainfall exceeding certain thresholds), such as R20mm and R50mm. The RX5day index (maximum 5-day precipitation) has also shown an increase. These changes increase the risk of flooding, so it is crucial to implement appropriate measures to mitigate the risk of floods in the IKN area. HIGHLIGHTS Extreme rain in the IKN area, especially in Sepaku and Semboja sub-districts, has slightly declined in the last 20 years. Increases were observed in the consecutive dry days (CDD) and some precipitation frequency-based indices. It is important to take appropriate measures to reduce the risk of floods and drought in the IKN areas. GRAPHICAL ABSTRACT

Ionospheric scintillation characteristics over Indian region from latitudinally-aligned geodetic GPS observations

Ionospheric scintillations pose one of the biggest threats to Satellite-Earth communication links in the communication and navigation systems services whose occurrence characteristics could be explained through the strength of fading (amplitude scintillation index; S4) and the rapidity of the fades (decorrelation time; \U0001d70f0). In the present work, we analyzed the S4 index from a latitudinal array of three geodetic global positioning system (GPS) stations along the Indian longitude sector during the descending phase of the 24th solar cycle. The results show predominant occurrences of scintillations during the post-sunset and nighttime periods indicating the level of scintillations close to equatorial, beyond anomaly crest, and near mid-latitude locations. The strong amplitude scintillations during 2014 and 2015 and their lowest magnitudes during 2016 and 2017 reflect the solar activity dependence of the scintillation occurrences. The directional distribution and 2-dimensional surface sky plots of the S4 index substantiate the occurrence of intense scintillation being more prevalent towards the equatorial location, whereas the weak and moderate scintillations are perceived towards the higher low latitude stations. The occurrences of intense scintillations are confirmed in high solar active years and equinox season at all stations, while the equatorial station presents relatively higher occurrences in winter followed by summer. The summer season witnessed intense occurrences even under moderate to low solar activity years (2016–2017), reflecting the post-midnight occurrences due to meridional thermospheric winds. Moreover, maximum percentage occurrences of weak scintillations in all seasons are evident towards the poleward side, far away from the anomaly crest. The amplitude scintillation frequency during the period is further compared with the solar and geomagnetic indices to substantiate the analysis drawn from the variations. The correlation coefficients between the scintillation index occurrence rate with the solar and geomagnetic in-dices at three GNSS stations provide valuable insights into the relationship between solar activity and scintillation. The results show that the strength and direction of the correlation can vary significantly depending on the specific solar index and location. Thus, emphasize further studies on scintillation occurrences for developing effective forecasting and mitigation models over the Indian low-latitude region.

The Equatorward Boundary of the Auroral Current System During Magnetic Storms

AbstractOur current knowledge of the geomagnetic poleward and equatorward boundary dynamics is limited, particularly, how deep those two latitudinal boundaries can extend into lower geomagnetic latitudes during magnetic storms. We want to understand the motion of the boundary because it is important in terms of the location and magnitude of the effects of geomagnetic disturbances associated with storms on the ground. In this study we derive spherical elementary ionospheric currents from ground magnetometer arrays covering North America and Greenland during six magnetic storms in 2015 and 2018. With two dimensional maps of the auroral region current, we select the equatorward boundary of the region 2 currents by‐eye and fit the boundary with an ellipse to derive the location of the equatorward boundary at magnetic midnight. We have obtained over 500 boundaries and find that the midnight boundary location varies between 45° and 66° magnetic latitude. We examine the influence of the interplanetary magnetic field (IMF), solar wind plasma, and geomagnetic indices on the location of the magnetic midnight equatorial boundary and find that the equatorial boundary location is best correlated with the IMF Bz, VBz, and the Sym‐H index. We demonstrate that as the Bz component becomes more negative, the magnitude of VBz increases, and the magnitude of the Sym‐H index increases, the magnetic midnight equatorial boundary shifts equatorward during periods of moderate to high geomagnetic activity.

Sensitivity of the Southern Hemisphere Wintertime Teleconnection to the Location of ENSO Heating

Abstract The Southern Hemisphere extratropical atmospheric circulation response to anomalous convection in the tropical western and eastern Pacific Ocean is distinctly different. The response to westward-located heating has a meridional dipole in the South Pacific with large zonal scale and appears unable to be interpreted simply as a stationary Rossby wave train that disperses poleward and eastward from a tropical source like the meridionally arched response to eastward-located heating. This study investigates the cause of this asymmetry by examining the daily evolution of the response to suddenly switching on steady diabatic heating over a western and central/eastern equatorial Pacific location using large-ensemble integrations from the Community Atmosphere Model version 5. We focus on the austral winter months when the subtropical jet supports the development of an effective Rossby wave source in the subtropical westerlies and acts as a waveguide. We show that the subtropical jet strongly influences the height response to the western tropical Pacific heating, promoting prominent zonal circumglobal propagation. Development of a transient eddy feedback in the extratropical storm track after approximately 10 days appears to play a primary role in establishing the time-mean response, which we test through comparison with similar experiments conducted using a simplified linear model. Conversely, the height anomalies for eastern tropical Pacific heating, farther away from the subtropical jet core, have larger meridional propagation, dispersing in a typical Hoskins–Karoly manner into the Southern Hemisphere extratropics, while the transient eddy feedback plays a secondary role for the establishment of the steady response.

Calibration of NASA’s Neutron Spectrometer System (NSS) for landed measurements of hydrogen content of the lunar subsurface

NASA Ames Research Center and the Lockheed Martin Advanced Technologies Center have developed a rugged, low-resource neutron spectrometer instrument to characterize the near-surface hydrogen content of the lunar surface. This Neutron Spectrometer System (NSS) monitors local thermal and epithermal neutron rates to provide information about the depth-dependent distribution of hydrogen to depths of a few tens of cm. As of mid-2022, NSS is currently slated to fly on two NASA Commercial Lunar Payload Services (CLPS) missions; the Astrobotic Peregrine-1 lander to a near-side equatorial location, and the VIPER lunar rover to explore the polar terrain around Nobile crater. We report the results of a science calibration campaign that characterized the performance of the NSS sensors. These measurements were used to benchmark the accuracy of Geant4 radiation transport simulations that provide the energy- and angle-dependent neutron sensitivity of the NSS sensors. This information is a necessary input for converting NSS measurements of the thermal and epithermal neutron leakage flux to constraints on local hydrogen content in regions with otherwise known geochemical composition.

Forest loss analysis and calculation with geospatial artificial intelligence: A case study of papua province

The combination of its equatorial location and number of islands of Indonesia provides numbers of biomass storage capability, bioenergy resources and abundant natural wealth of forest, while known as home to the world's third largest tropical forest. Forest loss can cause many adverse impacts on ecosystem balance and biodiversity by changing the configuration and structure of the forest landscape. Over the last twenty years, the deforestation in Indonesia keeps increasing with uneven distribution between the western and eastern part of the country. Consistent and efficient observation of forest loss using remote sensing data provides important information for understanding the role of forest in the role of forest conversion in the global carbon cycle, biodiversity analysis, and selecting potential strategies on reducing deforestation. In this study, a Global Forest Change Datasets were utilized to analyze, calculate, and map forest loss in Papua, Indonesia from 2001 to 2021. Cloud data processing is carried out using the google earth engine to obtain the total forest loss data in district scale of Papua Province. Three indicators used in this method, the tree cover in the year of 2000 as the forest baseline, yearly forest gain (2000 - 2012), and yearly forest loss (2001 - 2021). The results of the study show that in the last two decades, Papua Province has lost 2,806% or 9.062 km2 of its forest cover area, while the semi-urban and urban areas are 2-20 times more prone to deforestation compared to the dense forest area. Although increasing each year, Papua Province has a very low threat of deforestation compared to other provinces in Indonesia. However, the anthropogenic conversion to the productive plantation site might become a significant hazard in the upcoming years, not only in urban and semi-urban area, but also in remote and dense forest areas.

Investigation on the Anomalous Weakening of Diurnal Tides in the Mesosphere‐Lower Thermosphere

AbstractVariations in tidal characteristics assume importance as far as the atmosphere‐ionosphere coupling is concerned. The present study examines short‐term variabilities in diurnal tidal characteristics, using one decade (2006–2015) of wind measurements in the mesosphere‐lower thermosphere (MLT) region over a near equatorial location, Thumba (8.5°N, 77°E). The study presents two distinct events of anomalous tidal weakening, with decrease in monthly mean tidal amplitude by −38 ms−1 (−26 ms−1) in February 2010 and −17 ms−1 (−8 ms−1) in January 2012 at 98 km (91 km). These events are observed to be coinciding with the occurrence of strong quasi‐two‐day wave (QTDW). Compared to pre‐event conditions, decrease (increase) in tidal (QTDW) amplitudes at 91 km is −13.03 ms−1 (34.97 ms−1) and −15.65 ms−1 (52.81 ms−1) during the first and second event, respectively. However, causative mechanisms are found to be different for both the events. While the former event is primarily due to parametric excitation of phase locked 2‐day waves by diurnal tide, the latter one is mainly due to non‐linear interaction between tide and QTDW and subsequent generation of secondary waves. While QTDW phase is relatively stable during the former event, it shows steep temporal variations during the latter one. Changes in background wind conditions are also found to be more conducive for weakening of diurnal tide during the former event. These anomalous changes in tidal characteristics would have significant impacts on ionospheric processes. The significance of this study lies in providing observational evidence for the existence of different pathways through which QTDW affects tidal amplitudes over the low‐latitude MLT region.

Wind Characteristics and Potentials of Two-Parameter Weibull Distribution and Maximum Entropy-Based Distribution Functions at an Equatorial Location

Thorough knowledge of the wind characteristics and variations are of great importance in the development of wind energy resource in any location. This study examines the wind characteristics and assess the potential of two distribution functions in a low wind equatorial region of West Africa. High resolution wind speed and direction data were obtained from a site in Nsukka, a location chosen in the region of study. Diurnal, seasonal and annual variations of both the wind speed and directions were examined. The potentials of two-parameter Weibull distribution and another distribution function based on Maximum Entropy principle (MEP) were assessed using R2 and root mean squared error (RMSE). The results indicated that day-time is windier than night-time. The transitions months of February, March and April have the highest wind speed. The dry season has greater energy potential than rainy season. The predominant wind direction lay within the sectors: South-South-West and East. The predominant wind sector for February, March and April is South-East. The R2for daily, sub-seasonal day-time and night-time, monthly, and annual ranged between 0.90 and 0.99 for both MEP-based and Weibull distributions. The daily, sub-seasonal day-time and night-time, monthly, and annual RMSE also ranged between 0.011 to 0.075 for MEP-based and Weibull distribution respectively. Thus, both MEP-based and Weibull two-parameter distribution functions can be used to model wind data at the location of study.

Preliminary Investigation of the Potentialities of a Mesoscale Meteorological Model to Reproduce Experimental Statistics of Rain Attenuation on Earth-Space Links

Current spatial resolutions achieved by mesoscale weather forecast models allow them to be used to generate the state of the lowest layers of the atmosphere over areas as small as a few square kilometers which corresponds to the typical size of the tropospheric area crossed by Earth-space links. Furthermore, they allow the evolution of the troposphere to be predicted with a time stamp of five minutes instead of every hour with large-scale weather forecast models which makes them attractive for radio propagation predictions for satellite communication applications. This paper aims at studying the capability of the Weather Research and Forecast (WRF) model coupled with an electromagnetic physical model to reproduce rain attenuation statistics for Earth-space paths at Ka-band. To this purpose, one year of propagation measurements collected at 20 GHz in different places at midlatitudes in Toulouse and Salon de Provence (France), Spino d’Adda (Italy), Aveiro (Portugal), and Madrid (Spain), at high latitudes in Svalbard (Norway) and at low latitudes in Kourou are used to make comparisons between simulations and measurements. Comparisons between the simulated and the experimental annual statistics considered in this paper provide encouraging results, with a similar accuracy as Recommendation ITU-R P.618–13 for midlatitude European locations and with better accuracy for a high latitude area in Svalbard and for an equatorial location in French Guiana.

A Review on Rain Signal Attenuation Modeling, Analysis and Validation Techniques: Advances, Challenges and Future Direction

Radio waves are attenuated by atmospheric phenomena such as snow, rain, dust, clouds, and ice, which absorb radio signals. Signal attenuation becomes more severe at extremely high frequencies, usually above 10 GHz. In typical equatorial and tropical locations, rain attenuation is more prevalent. Some established research works have attempted to provide state-of-the-art reviews on modeling and analysis of rain attenuation in the context of extremely high frequencies. However, the existing review works conducted over three decades (1990 to 2022), have not adequately provided comprehensive taxonomies for each method of rain attenuation modeling to expose the trends and possible future research directions. Also, taxonomies of the methods of model validation and regional developmental efforts on rain attenuation modeling have not been explicitly highlighted in the literature. To address these gaps, this paper conducted an extensive literature survey on rain attenuation modeling, methods of analyses, and model validation techniques, leveraging the ITU-R regional categorizations. Specifically, taxonomies in different rain attenuation modeling and analysis areas are extensively discussed. Key findings from the detailed survey have shown that many open research questions, challenges, and applications could open up new research frontiers, leading to novel findings in rain attenuation. Finally, this study is expected to be reference material for the design and analysis of rain attenuation.

Conclusion

Conclusion

On the significant impact of the 17 March 2015 St. Patrick’s Day geomagnetic storm on the ionosphere over Indian region

The response of the ionosphere in the Indian region to the extreme space weather events of 17–19 March 2015 is studied using Global Positioning System (GPS) Total electron Content (TEC) measurements, Thermosphere Ionosphere Electrodynamics-General Circulation Model (TIE-GCM) simulations and High Frequency (HF) Radar observations. The data from Thiruvananthapuram (8.5° N, 77° E geographic, 0.3° N magnetic latitude) and northern hemispheric midlatitude station Hanle (32.80° N, 79° E geographic, 23.9° N magnetic latitude) have been analyzed for the above event. The TEC over Thiruvananthapuram, a dip equatorial location exhibits a decrease during the post sunset hours on 17 March 2015 and is followed by the generation of F region irregularities at an altitude of 600 km, as observed by HF radar as well as TEC scintillations. The TEC over the mid latitude station of Hanle decreased during the storm recovery phase on 18March 2015 in response to negative storm effects. The extent of decrease in TEC as observed during the recovery phase could not be simulated by TIE-GCM over Hanle. This difference is attributed to the enhanced Joule heating taking place in the polar region during St. Patrick’s Day storm and the associated composition changes. An anomalous heating scenario was introduced and the simulated TIE-GCM results were found to match the observations. The present study clearly brings out the impact of 17 March 2015, St. Patrick’s Day geomagnetic storm on the ionization distribution over equatorial as well as mid latitude stations over the Indian region using observations as well as TIE-GCM simulations and the evolutionary features of ionospheric irregularities over equatorial location using TEC and HF radar observations. The role played by thermosphere ionosphere coupling in modulating the ionization variability over equatorial as well as mid latitude region during periods of extreme geomagnetic forcing is highlighted.

Pattern of F2-layer peak electron density across African Ionosonde locations and response to solar activity

The diurnal, longitudinal, and latitudinal characteristics of the F2-layer peak electron density (NmF2) at six African stations comprising mid- and equatorial latitudes was investigated. The study covers years of low- (F10.7 = 82.2sfu) and high- (198.6sfu) solar activities. The results revealed that the NmF2 noontime-bite-out was prevalent only in the equatorial latitude. There is latitudinal (geographic) influence on the NmF2 pre-noon and post-noon peak magnitudes at the equatorial locations irrespective of solar activity. The pattern of the NmF2 amplitude during some selected specific time showed that the noontime-12LT, sunset-18LT and midnight-00LT observations are latitudinally inclined, whereas that of the sunrise-06LT is longitudinally-based for both conditions of solar events. Generally, there is a semi-annual asymmetry in the NmF2 monthly pattern with peaks in the equinoctial months. This asymmetry is significant at equatorial latitudes at daytime (06LT/12LT) and nighttime (18LT/00LT) but absent at nighttime of mid-latitudes. The asymmetry feature at the equatorial stations finds its explanation in the ionization anomaly being triggered by the fountain effect mechanism. The NmF2/F10.7 pair correlation (r) presents highest value at 06LT at all equatorial stations for both conditions of solar activity. Generally, r is higher during LSA than during HSA, and finds its explanation in the rate of ionized neutral species and ionospheric electrodynamics. The equatorial noontime bite-out amplitude (bite-outamp) is highest in equinoxes and is latitudinally inclined. We obtained a higher bite-out intensity at the equatorial stations during the HSA than the LSA period by a factor of ≈ 41 %. The importance of thermospheric neutral winds in the large-scale distribution of plasmas was emphasized.

Investigation of Kinetic Ballooning Instability in 2D Harris Sheet Equilibrium With Finite Normal B z Field

Substorm onset is believed to be a fundamental process for magnetic and plasma energy transport in both magnetosphere and ionosphere. In this regard, the ballooning instability is considered to be one of the key trigger mechanism for the substorm onset scenario in the near-Earth plasma sheet. Here, the kinetic ballooning instability (KBI) in the near-Earth magnetotail is analyzed using the two-dimensional (2D) generalized Harris sheet and Voigt equilibrium models. The corresponding kinetic ballooning mode is unstable in the intermediate range of perpendicular wave number (ky) and the equatorial beta (βeq). We further note that the growth rate of the ballooning mode reduces significantly with the increase in electron-to-ion temperatures ratio (Te/Ti) and wave number ky. The kinetic ballooning mode is found to be most unstable in a thin current sheet region at the equatorial location xe ∼ (8.5 − 10)RE, where the ballooning drive term (βeq/LpRc) is dominant on stiffening effect due to minimum in normal magnetic field. Because of the stabilizing effect as caused by the field line stiffening and the strong field line stabilization, the ballooning mode is stable (marginally unstable) close (away) from the Earth. The magnitude of the KBI growth rates as a function of the equatorial beta βeq and location xe for a wide and thin current sheets using the Voigt equilibrium model are smaller than the Harris sheet counterpart, which are used for modeling the near-Earth plasma sheet configuration for the slow and fast substorm growth phases, respectively. The results suggest that the excitation of KBI through the local current sheet thinning may also be an effective trigger mechanism for the substorm onset in the near-Earth magnetotail. This article is protected by copyright. All rights reserved.