Ionosphere Monitoring with Remote Sensing

This book focuses on the characterization of the physical properties of the Earth’s ionosphere, contributing to unveiling the nature of several processes responsible for a plethora of space weather-related phenomena taking place in a wide range of spatial and temporal scales. This is made possible by the exploitation of a huge amount of high-quality data derived from both remote sensing and in situ facilities such as ionosondes, radars, satellites and Global Navigation Satellite Systems receivers

GPS Scintillations and Total Electron Content Climatology in the Southern American Sector

The radio communication and navigation systems can be strongly affected by the ionospheric conditions, which are controlled by solar phenomena associated with radiation variations and solar wind disturbances. These phenomena can generate ionospheric large-scale plasma redistribution and irregularities with scale sizes varying from centimeters to hundred kilometers. These ionospheric irregularities can produce rapid fluctuations in the amplitude and phase of global navigation satellite system (GNSS) signals, degrading the accuracy of GNSS measurements. Here we give a short review of the ionospheric variations associated with solar phenomena, and the actual state of art in the investigations of long-term (seasonal and solar cycle scales) TEC variations and climatology of scintillations, with focus on the southern American sector. It also presented a new TEC calibration procedure when applied to single-frequency PPP

Review of Environmental Monitoring by Means of Radio Waves in the Polar Regions: From Atmosphere to Geospace

The Antarctic and Arctic regions are Earth's open windows to outer space. They provide unique opportunities for investigating the troposphere–thermosphere–ionosphere–plasmasphere system at high latitudes, which is not as well understood as the mid- and low-latitude regions mainly due to the paucity of experimental observations. In addition, different neutral and ionised atmospheric layers at high latitudes are much more variable compared to lower latitudes, and their variability is due to mechanisms not yet fully understood. Fortunately, in this new millennium the observing infrastructure in Antarctica and the Arctic has been growing, thus providing scientists with new opportunities to advance our knowledge on the polar atmosphere and geospace. This review shows that it is of paramount importance to perform integrated, multi-disciplinary research, making use of long-term multi-instrument observations combined with ad hoc measurement campaigns to improve our capability of investigating atmospheric dynamics in the polar regions from the troposphere up to the plasmasphere, as well as the coupling between atmospheric layers. Starting from the state of the art of understanding the polar atmosphere, our survey outlines the roadmap for enhancing scientific investigation of its physical mechanisms and dynamics through the full exploitation of the available infrastructures for radio-based environmental monitoring

AATR an ionospheric activity indicator specifically based on GNSS measurements

This work reviews an ionospheric activity indicator useful for identifying disturbed periods affecting the performance of Global Navigation Satellite System (GNSS). This index is based in the Along Arc TEC Rate (AATR) and can be easily computed from dual-frequency GNSS measurements. The AATR indicator has been assessed over more than one Solar Cycle (2002–2017) involving about 140 receivers distributed world-wide. Results show that it is well correlated with the ionospheric activity and, unlike other global indicators linked to the geomagnetic activity (i.e. DST or Ap), it is sensitive to the regional behaviour of the ionosphere and identifies specific effects on GNSS users. Moreover, from a devoted analysis of different Satellite Based Augmentation System (SBAS) performances in different ionospheric conditions, it follows that the AATR indicator is a very suitable mean to reveal whether SBAS service availability anomalies are linked to the ionosphere. On this account, the AATR indicator has been selected as the metric to characterise the ionosphere operational conditions in the frame of the European Space Agency activities on the European Geostationary Navigation Overlay System (EGNOS). The AATR index has been adopted as a standard tool by the International Civil Aviation Organization (ICAO) for joint ionospheric studies in SBAS. In this work we explain how the AATR is computed, paying special attention to the cycle-slip detection, which is one of the key issues in the AATR computation, not fully addressed in other indicators such as the Rate Of change of the TEC Index (ROTI). After this explanation we present some of the main conclusions about the ionospheric activity that can extracted from the AATR values during the above mentioned long-term study. These conclusions are: (a) the different spatial correlation related with the MOdified DIP (MODIP) which allows to clearly separate high, mid and low latitude regions, (b) the large spatial correlation in mid latitude regions which allows to define a planetary index, similar to the geomagnetic ones, (c) the seasonal dependency which is related with the longitude and (d) the variation of the AATR value at different time scales (hourly, daily, seasonal, among others) which confirms most of the well-known time dependences of the ionospheric events, and finally, (e) the relationship with the space weather events.Postprint (published version

GNSS remote sensing of space weather at mid-latitudes: ionospheric irregularities and source analysis

The Earth's Ionosphere frequently disrupts Space to Earth communication such as Global Navigation Satellite Systems (GNSS) and international telecommunications critical to a modern technological world. As human society has become heavily dependent on GNSS services, timely and accurate space weather characterization and forecasts are needed. This is particularly true at mid-latitudes, such as the contiguous United States (US), where population density is greatest, hence technological interruptions most impactful. As a conducting layer, the ionosphere delays radio signals by refraction, and in some circumstances causes wave interference due to diffraction off density irregularities. Ionospheric refraction can be used to estimate the path-integrated plasma density, referred to as the Total Electron Content (TEC). Maps of TEC constructed from ground-based receiver networks provide a global and time-dependent image of ionospheric dynamics. While refraction scales with radio-frequency and dual-frequency GNSS receivers routinely compensate for this effect. Radio receivers, including GNSS monitors, are being used to monitor and quantify these effects, producing climatological maps of ionospheric irregularities. However, efforts have focused on low- and high-latitude regions as they are continuously perturbed by geophysical processes related to the orientation of the Earth’s magnetic field. The region in-between has a much more nuanced space-time connection to geomagnetic disturbances. As a consequence, no dedicated observatories are operating today at mid-latitudes. This dissertation provides a fundamental analysis of this underexplored territory in the burgeoning field of space weather. In this dissertation, we develop signal processing techniques to leverage data from geodetic GNSS receivers to study ionospheric irregularities and scintillation, and their connection to spatiotemporal variations in TEC. Newly introduced data source covers areas of Central America and the Caribbean, contiguous US, and Alaska. We applied these techniques initially to study the ionospheric effects of the 2017 solar eclipse and terrestrial weather patterns. We then focused our effort on a long term study of geomagnetic storm effects at mid-latitudes. Eight years of data have been processed in the last solar cycle (2012-2019), and nine profound space weather events were identified. The newly constructed maps were used in conjunction with TEC maps to provide a critical spatial context for understanding the origin of the irregularities. The observations revealed several types of space weather events that affected the area, including a poleward expansion of equatorial plasma bubbles near local midnight, a single plasma bubble expanding poleward while trailing the terminator, and a newly observed mid-latitude phenomena we termed mid-latitude density striations. We also discovered evidence for expansion into and coupling with processes in the near Earth magnetosphere. All events occurred during geomagnetic storms, with an average strength of Dst=-125 nT, and Kp=6+. The events were recorded at all seasons. One event showing mid-latitude density striations was analyzed in greater detail using both GNSS-derived products, and in-situ measurements of plasma parameters in the ionosphere and conjugate magnetosphere. While the large scale TEC projection closely resembles the expected characteristics of an equatorial plasma bubble, we observed that the electric field peaked at the density gradients instead of in the trough, and the density irregularities lagged the trough formation by about one hour. Morphology of TEC irregularities measured by a ground-based GNSS receiver was compared to the first GNSS scintillation observations at mid-latitudes from 2001. We found the large scale density structures, as well as the respective location of scintillation, closely resemble the mid-latitude density striations. We suggest the narrow density, and electric field perturbations were likely caused by the penetration of a substorm-induced electric field to lower latitudes. We conclude the dissertation by discussing the implication of such space weather events on modern technology

Mesoscale ionospheric plasma irregularities and scintillation over Svalbard

This thesis investigates how navigation signals are compromised by ionospheric plasma irregularities in the auroral and polar ionosphere over Svalbard. In 2013, four multiconstellation global navigation satellite system (GNSS) receivers were installed in NyÅlesund, Longyearbyen, Hopen, and Bjørnøya. These receivers provide unprecedented coverage of scintillation and plasma density (total electron content) in the region. The four research papers in this thesis are detailed case studies investigating mesoscale irregularities and scintillation.We use data from these GNSS receivers, all-sky imagers, coherent and incoherent scatter radars, ionosondes, and in-situ satellite measurements. Paper I [van der Meeren et al., 2014] investigates scintillation and irregularities on the front of a tongue of ionization (TOI) in the polar cap. Moderate scintillation and structuring is observed on the leading edge of the TOI. We employ a novel method where we use spectrograms of the phase of raw GNSS signals to show that the structuring is real and not due to erroneous data detrending of the σφ phase scintillation index. Paper II [Oksavik et al., 2015] investigates irregularities in the dayside auroral region, specifically in relation to poleward-moving auroral forms (PMAFs). Scintillation is strongly localized to these intense and transient features, even in the presence of polar cap patches. Paper III [van der Meeren et al., 2015] investigates scintillation from substorm auroral emissions as polar cap patches enter the nightside auroral oval. The most severe scintillation is found when the auroral precipitation coincides with polar cap patches. The scintillation is strongly localized to signals intersecting intense auroral emissions. Paper IV [van der Meeren et al., 2016] investigates irregularities during quiet geomagnetic conditions. We find weak irregularities in relation to a stable and intense transpolar arc, but no scintillation is seen. The main results in this thesis are: Scintillation-producing irregularities can exist on the leading edge of TOIs, in PMAFs, and in substorm auroral precipitation when patches enter the nightside auroral oval. Of these, auroral precipitation on top of pre-existing plasma patches seems to produce the strongest scintillation. The scintillation generally shows a high degree of localization, varying significantly over distances of ∼ 100km. This clearly indicates the need for a dense network of scintillation receivers in the polar ionosphere to fully resolve this spatial variation. It also shows that detailed case studies are important to complement the averaged, static, large-scale picture common in statistical studies. We have developed a novel method of using spectrograms of the phase of raw GNSS signals to get a more complete view of irregularities than aggregate scintillation indices like σφ . Furthermore, our method does not require data detrending, and it is therefore more robust than traditional scintillation indices that are frequently used by the community. The observed irregularities cover a wide range of spatial scale sizes, from decameters to several kilometers. Irregularities at these spatial scale sizes can affect radio wave propagation from HF to GNSS frequencies. </ul

Multitechnique studies of ionospheric phenomena

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Geomagnetic Activity Control of Irregularities Occurrences Over the Crests of the African EIA

Abstract This paper investigated the behavior of ionospheric irregularities over the African equatorial ionization anomaly (EIA) crests during intense geomagnetic storms that occurred from 2012 to 2015. Irregularities were monitored using the rate of change of TEC index along with variations of the horizontal component of the Earth's magnetic field (H) and ionospheric electric current disturbance (Diono). The predictive capability of the Prompt Penetration Equatorial Electric Field Model (PPEFM) was assessed by comparing prompt penetration electric field (PPEF) inferred from interplanetary electric field and Diono with PPEF derived from the PPEFM, with emphasis on how well the model reproduced enhancement/reduction in the prereversal enhancement (PRE). Eastward PPEF triggered short duration irregularities on 23 April 2012, 17 March 2013, and 20 February 2014 while westward electric field reduced them thereafter. The PPEFM rightly predicted enhancement (reduction) in PRE on 17 March 2013 (19 February 2014) when irregularities were triggered (inhibited). It, however, showed no change in the PRE on 23 April 2012 and 20 February 2014. During the storms recoveries, irregularities were always inhibited/reduced over the trough by westward disturbance dynamo and the inhibition lasted longer during the superstorm of March 2015. Also, there was a hemispheric asymmetry in irregularities over the African EIA crests. On 16–17 July 2012, 15 November 2012, and 19 March 2013, there were differences in irregularities behavior. On these days, the asymmetry of the postsunset crests was pronounced in both hemispheres