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Journal ArticleDOI

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

01 Jul 2017-Journal of Geophysical Research (John Wiley & Sons, Ltd)-Vol. 122, Iss: 7, pp 7713-7733
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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Journal ArticleDOI
Libo Liu1, Maosheng He1, Xinan Yue1, Baiqi Ning1, Weixing Wan1 
TL;DR: In this article, the authors utilized the data of ionospheric electron density profiles from COSMIC mission radio occultation measurements, total electron density (TEC) from TOPEX and Jason-1, and TEC from Global Positioning System (GPS) receivers as well as global ionosonde measurements of the F2 layer peak electron density to investigate the behaviors of the daytime ionosphere around equinoxes during low solar activity.
Abstract: [1] The seasonal behaviors of the ionosphere have been investigated for several decades, but the differences of the ionosphere between the March and September equinoxes are still an open question. In this analysis we utilize the data of ionospheric electron density (Ne) profiles from Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission radio occultation measurements, total electron density (TEC) from TOPEX and Jason-1, and TEC from Global Positioning System (GPS) receivers as well as global ionosonde measurements of the F2 layer peak electron density (NmF2) to investigate the behaviors of the daytime ionosphere around equinoxes during low solar activity (LSA). The analysis reveals that during LSA the equinoctial asymmetry in ionospheric plasma density is mainly a low-latitude phenomenon. The differences of equinoctial TEC and NmF2 have considerable amplitudes at low latitudes in both hemispheres and less significant at higher latitudes. With increasing altitude, the asymmetry in COSMIC Ne becomes weaker in the Southern Hemisphere, and the northern pronounced asymmetry regions move toward the magnetic equator. The ionospheric equinoctial asymmetry may be considered as a manifestation of the annual variation, whose annual phase significantly shifts away from the solstices. The F layer peak height (hmF2) extracted from COSMIC Ne profiles also shows an equinoctial asymmetry at low latitudes, indicating the existence of equinoctial differences in low-latitude neutral winds, specifically in the Northern Hemisphere. It reveals that, besides the important effect of the neutral wind, other processes should play roles in the forming of the observed equinoctial asymmetry in the ionosphere.

64 citations

Journal ArticleDOI
TL;DR: In this article, the authors analyzed the 10-year measurements of total ion density (Ni) from the Defense Meteorological Satellite Program (DMSP) spacecraft at 0930 and 2130 LT have been analyzed to investigate the yearly variations of global plasma densities in the topside ionosphere at magnetic latitudes from 60°S to 60°N.
Abstract: [1] In this paper, the 10-year (1996–2005) measurements of total ion density (Ni) from the Defense Meteorological Satellite Program (DMSP) spacecraft at 0930 and 2130 LT have been analyzed to investigate the yearly variations of global plasma densities in the topside ionosphere at magnetic latitudes from 60°S to 60°N. Results indicate that there are strong yearly variations in the DMSP Ni at 840 km. The annual components of longitude-averaged Ni dominate at most latitudes with maxima around the June solstices in the Northern Hemisphere and the December solstice in the Southern Hemisphere. In contrast, seasonal anomaly (maxima Ni around the December solstice) exists in the northern equatorial zone. Moreover, the differences in Ni at the two solstices are not symmetrical about the magnetic equator, being generally higher in the Southern Hemisphere than in the Northern Hemisphere. Conjugate-averaged Ni is substantially greater at the December solstice than at the June solstice. This annual asymmetry is modulated by solar activity effect and has latitudinal and longitudinal structures. The longitude effects of the annual asymmetry depend on local time, being stronger in the evening sector than in the morning sector. The solstice differences and annual asymmetry are more marked with increasing solar activity. The annual asymmetry appears not only in the rising phase of the solar cycle but also in the declining phase. Thus the solar condition differences between the two solstices do not account for the Ni asymmetry. The concentration of neutral oxygen [O], provided from the NRLMSIS model, shows a similar pattern of annual and hemispheric asymmetries. Moreover, effects of the HWM model neutral winds are also constituent with the change patterns of Ni. Therefore, considering the principal processes in the topside ionosphere, the changes of [O] and the rates of thermospheric winds should contribute to the annual asymmetry in Ni at 840-km altitude.

62 citations

Journal ArticleDOI
TL;DR: In this paper, GPS-TEC data were observed at the same local time at two equatorial stations on both longitudes: Lagos (6.52° N, 3.4° E, 4.25° N magnetic latitude), Nigeria; and Pucallpa (8.38° S, 74.57° W,4.04° S magnetic latitude) during the minimum (2009, 2010) and ascending (2011) phases of solar cycle 24.
Abstract: . GPS-TEC data were observed at the same local time at two equatorial stations on both longitudes: Lagos (6.52° N, 3.4° E, 3.04° S magnetic latitude), Nigeria; and Pucallpa (8.38° S, 74.57° W, 4.25° N magnetic latitude), Peru during the minimum (2009, 2010) and ascending (2011) phases of solar cycle 24. These data were grouped into daily, seasonal and solar activity sets. The day-to-day variations in vertical TEC (VTEC) recorded the maximum during 14:00–16:00 LT and minimum during 04:00–06:00 LT at both longitudes. Seasonally, during solar minimum, maximum VTEC values were observed during March equinox and minimum during solstices. However, during the ascending phase of the solar activity, the maximum values were recorded during the December solstice and minimum during the June solstice. VTEC also increased with solar activity at both longitudes. On longitude by longitude comparison, the African GPS station generally recorded higher VTEC values than the American GPS station. Furthermore, harmonic analysis technique was used to extract the annual and semi-annual components of the amplitudes of the TEC series at both stations. The semi-annual variations dominated the TEC series over the African equatorial station, while the annual variations dominated those over the American equatorial station. The GPS-TEC-derived averages for non-storm days were compared with the corresponding values derived by the IRI-2007 with the NeQuick topside option. The NeQuick option of IRI-2007 showed better performance at the American sector than the African sector, but generally underestimating TEC during the early morning hours at both longitudes.

60 citations

Journal ArticleDOI
TL;DR: More than 60 multiday incoherent scatter radar experiments conducted at Millstone Hill, Massachusetts, between 1984 and 1990 have been analyzed to determine neutral winds along the magnetic meridian as discussed by the authors.
Abstract: More than 60 multiday incoherent scatter radar experiments conducted at Millstone Hill, Massachusetts, between 1984 and 1990 have been analyzed to determine neutral winds along the magnetic meridian. The wind determinations from geomagnetically undisturbed periods have been sorted into seasonal, solar cycle, and local time bins, and climatological averages have been calculated and compared with complementary empirical wind model predictions. The climatological wind averages have also been harmonically decomposed. Strong seasonal and solar cycle dependences characterize both the mean winds and diurnal wind amplitudes. This analysis suggests that the aurorally driven high-latitude circulation cell is important to the interpretation of variability in thermospheric circulation over Millstone Hill even during geomagnetically undisturbed periods. 40 refs., 3 figs., 3 tabs.

60 citations

Journal ArticleDOI
TL;DR: A review of the annual variations of the ionosphere, which focuses on the physical mechanisms causing the well-known seasonal anomaly and equinoctial asymmetry, is presented in this paper.

58 citations