Response of data-driven artificial neural network-based TEC models to neutral wind for different locations, seasons, and solar activity levels from the Indian longitude sector
TL;DR: In this article, a set of observations carried out in the Indian longitude sector have been reported in order to find the amount of improvement in performance accuracy of an ANN-based Vertical Total Electron Content (VTEC) model after incorporation of neutral wind as model input.
Abstract: The perturbations imposed on transionospheric signals by the ionosphere are a major concern for navigation. The dynamic nature of the ionosphere in the low latitude equatorial region and the Indian longitude sector has some specific characteristics such as sharp temporal and latitudinal variation of Total Electron Content (TEC). TEC in the Indian longitude sector also undergoes seasonal variations. The large magnitude and sharp variation of TEC causes large and variable range errors for satellite based navigation system such as Global Positioning System (GPS) throughout the day. For accurate navigation using Satellite Based Augmentation Systems (SBAS), proper prediction of TEC under certain geophysical conditions is necessary in the equatorial region. It has been reported in the literature that prediction accuracy of TEC has been improved using measured data driven Artificial Neural Network (ANN) based VTEC models, compared to standard ionospheric models. A set of observations carried out in the Indian longitude sector have been reported in this paper in order to find the amount of improvement in performance accuracy of an ANN-based Vertical TEC (VTEC) model after incorporation of neutral wind as model input. The variations of this improvement in prediction accuracy with respect to latitude, longitude, season and solar activity have also been reported in this paper.
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TL;DR: In this article , a commentary about the state of Integrated, Coordinated, Open, and Networked (ICON) principles in Space Physics and Aeronomy and a discussion on several scopes and limitations to implementing them are discussed.
Abstract: This article is a commentary about the state of Integrated, Coordinated, Open, and Networked (ICON) principles (Goldman et al., 2021) in Space Physics and Aeronomy and a discussion on several scopes and limitations to implementing them. The commentary focuses on the basic introduction and brief literature survey (Section 1); possibilities of implementation of ICON in Space Physics and Aeronomy (Section 2) and limitations or challenges in this field with possible solutions using ICON principles (Section 3). The Space Physics and Aeronomy section of the American Geophysical Union (AGU) comprises the interactions between solar wind, Interplanetary Magnetic Field (IMF) and different planetary magnetospheres and ionospheres. The section also deals with solar physics, mechanisms behind existence of solar magnetic fields, and evaluations of high and low speed solar winds. This field is a collection of different interdisciplinary subtopics, making this an excellent example of integrated research. Similar and transparent methodologies are adopted to solve problems all over the world which shows a coordinated approach of research. Freely available data from different space agencies and universities are also great assets for this domain which supports open research. The scopes of possible networked research with mutual benefits are also highlighted. Examples of ICON-based international collaborations and support mechanisms towards young scientists are elaborated which are helpful to mitigate limitations in this domain. Space Physics and Aeronomy Perspectives on Integrated, Coordinated, Open, Networked (ICON) Science
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TL;DR: In this paper, the authors used total electron content (TEC) measurements made by a network of dense GPS receivers over the continental US to investigate ionospheric longitudinal differences and found that the evening TEC is substantially higher on the US east coast than on the west, and vice versa for the morning TEC; the longitudinal difference displays a clear diurnal variation.
Abstract: [1] Total electron content (TEC) measurements made by a network of dense GPS receivers over the continental US are used to investigate ionospheric longitudinal differences. We find that the evening TEC is substantially higher on the US east coast than on the west, and vice versa for the morning TEC; the longitudinal difference displays a clear diurnal variation. Through an analysis of morning-evening variability in the east-west TEC difference, minimum variability is found to coincide with the longitudes of zero magnetic declination over the continental US. We suggest that these new findings of longitudinal differences in ionospheric TEC at midlatitudes are caused by the longitudinal difference in magnetic declination combined with the effects of thermospheric zonal winds which are subject to directional reversal over the course of a day. This study indicates that longitudinal variations in TEC measurements contain critical information on thermospheric zonal winds. The proposed declination-zonal wind mechanism may also provide a new insight into longitude/UT changes at midlatitudes on a global scale, as well as into some geospace disturbances.
71 citations
TL;DR: In this article, the Hinotori satellite has been used to determine the yearly variations of the electron density and electron temperature in the low-latitude ionosphere, revealing the existence of an equinoctial asymmetry in the topside electron density at low latitudes.
Abstract: Observations made by the Hinotori satellite have been analysed to determine the yearly variations of the electron density and electron temperature in the low- latitude topside ionosphere. The observations reveal the existence of an equinoctial asymmetry in the topside electron density at low latitudes, i.e. the density is higher at one equinox than at the other. The asymmetry is hemisphere-dependent with the higher electron density occurring at the March equinox in the Northern Hemisphere and at the September equinox in the Southern Hemisphere. The asymmetry becomes stronger with increasing latitude in both hemispheres. The behaviour of the asymmetry has no significant longitu- dinal and magnetic activity variations. A mechanism for the equinoctial asymmetry has been investigated using CTIP (coupled thermosphere ionosphere plasmasphere model). The model results reproduce the observed equinoctial asymmetry and suggest that the asymmetry is caused by the north-south imbalance of the thermo- sphere and ionosphere at the equinoxes due to the slow response of the thermosphere arising from the eAects of the global thermospheric circulation. The observations also show that the relationship between the electron density and electron temperature is diAerent for daytime and nighttime. During daytime the yearly variation of the electron temperature has negative correlation with the electron density, except at magnetic latitudes lower than 10∞. At night, the correlation is positive.
71 citations
TL;DR: In this article, the authors examined the contribution of gravity and plasma pressure gradient driven current, the geomagnetic main field, and longitudinal variation in the conductivities to the vertical drift.
Abstract: [1] The complete mechanism of how upward propagating tropospheric tides connect to the upper atmosphere is not yet fully understood. One proposed mechanism is via ionospheric wind dynamo. However, other sources can potentially alter the vertical E × B drift: gravity and plasma pressure gradient driven current, the geomagnetic main field, and longitudinal variation in the conductivities. In this study we examine the contribution to the vertical drift from these sources, and compare them. We use March equinox results from the Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model. We found that the gravity and plasma pressure gradient driven current and the longitudinal variation of the conductivities excluding the variation due to the geomagnetic main field do not change the longitudinal variation of the vertical drift significantly. Modifying the geomagnetic main field will change the vertical drift at 5–6 LT, 18–19 LT and 23–24 LT at almost all longitudes. In general the influence of the geomagnetic main field on the vertical drift is larger, with respect to the maximum difference, at 18–19 LT and 23–24 LT, equal at 5–6 LT, and smaller at 14–15 LT than the influence due to nonmigrating tidal components in the neutral winds. Examination of the contribution from E- and F-region neutral winds to the vertical drift shows that their importance depends on the local time and the solar activity. This implies that the vertical drift has to be analyzed at specific local times to examine the relation between the wave number in the vertical drift and in the neutral winds.
71 citations
TL;DR: In this paper, the authors investigate the annual and local time variations of the wave-4 structures in the plasma density and vertical drift in the low-latitude F region by analyzing the measurements from the first Republic of China satellite (ROCSAT-1) and conducting simulations with the Global Ionosphere and Plasmasphere (GIP) model.
Abstract: [1] We investigate the annual and local time variations of the wave-4 structures in the plasma density and vertical drift in the low-latitude F region by analyzing the measurements from the first Republic of China satellite (ROCSAT-1) and conducting simulations with the Global Ionosphere and Plasmasphere (GIP) model. The GIP model uses apex magnetic coordinates with International Geomagnetic Reference Field (IGRF) for magnetic field, neutral wind from HWM-07, and thermospheric parameters from the NRLMSISE-00 model. In order to understand how the vertical drifts relate to the longitudinal structure of the topside ionosphere, we apply the equatorial vertical drifts observed from ROCSAT-1 to drive the GIP model. The model well reproduces the longitudinal structure in electron density, and the magnitudes of electron density are comparable with ROCSAT-1 measurement at 600 km. The ROCSAT-1 observations of the vertical drift and plasma density show maximum amplitudes of their wave-4 components in July–September and minimum amplitudes in December–February. An eastward shift of the wave-4 components with increasing local time is observed in both the density and the vertical drift. The GIP model density showed similar annual and local time variations of the wave-4 component. Since the model uses the observed equatorial vertical E × B drift as an input, the results indicate the vertical drifts are essential in the formation and evolution of the longitudinal wave-4 density structure. The amplitude of the eastward propagating diurnal tide (DE3) at 110 km shows similar annual and local time variations as the F region parameters, supporting the link between the DE3 tide, vertical E × B drift, and F region plasma density on a global scale.
69 citations
TL;DR: In this paper, it was shown that the ionospheric F region at low midlatitudes does not show a seasonal anomaly, and that its behavior versus the solar zenith angle is identical with that in the winter at higher iatitudes.
Abstract: It is shown that in the morning hours the ionospheric F region at low midlatitudes does not show a seasonal anomaly, and that its behavior versus the solar zenith angle is identical with that in the winter at higher iatitudes. A departure from this law develops progressively with increasing latitude in the summer season. Mechanisms are presented that could reduce the summer electron content whereas it is difficult to find a sensible process that could markedly enhance the winter values.
68 citations