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GNSS radio occultation measurements are used to observe the occurrence and the intensity of sporadic E layers on a global scale. We analysed data acquired by several satellite missions. Our data set currently comprises more than 17.7 million of globally distributed radio occultation profiles. For our study, we use ionosonde data at midlatitude and low latitude stations as well as Signal-to-Noise Ratio (SNR) GNSSS L1 radio occultation profiles. The SNR is sensitive to vertical changes in the electron density which is reflected in large fluctuations in the according altitude range of the profile. Therefore, vertically thin ionospheric phenomena like sporadic E layers (Es) can easily be identified using numerical filtering techniques.In this study, we are focusing on sporadic E layers that appear in the northern polar region (60°N – 90°N). We will present a climatology of the polar Es events and will discuss their temporal and spatial occurrence. Generally, polar Es layers show a different local time distribution compared to midlatitude sporadic E events which might be caused by electric fields influencing the sporadic E formation process., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Thin layers of enhanced electron density, detected at the altitude range of 90 to 120km, are referred to as Sporadic E and abbreviated as Es. Wind shear theory is the most commonly accepted physical mechanism for mid-latitude Es layer formation. According to wind shear theory Es layers form by the convergence of metallic ions in the ionosphere dynamo region due to vertical shears of the neutral wind mainly caused by tides in the lower thermosphere. Apart from atmospheric tides, planetary waves can also contribute to wind shear formation in the lower thermosphere. Previous studies based on ground-based measurements suggested that planetary waves with periods of several days play a role in the day-to-day variation of Es intensity.The purpose of this study is to determine the role of planetary waves in the day to day variation of Es layer. For this investigation, radio occultation data of FORMASAT-3/COSMIC2 and Spire have been used. The use of the global data based on satellite measurements makes it possible to investigate the zonal structure of planetary wave signatures in Es. The results will be compared to planetary waves in the dynamo-region winds as simulated by the GAIA (Ground-to-topside model of Atmosphere and Ionosphere for Aeronomy) model., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Two main methods used in the study of the Es layer are ground-based measurements and satellite observations. In this study, we compare mid- and low-latitude Es layer observations of FORMOSAT-3/COSMIC radio occultation with those recorded in ground-based digisonde stations. For this purpose, we have used a 2° latitude x 5° longitude grid around ionosonde sites, and compared ionosonde Es recording with GNSS radio occultation measurements of the Es layer within that grid.Es layer measurements of a multi-year radio occultation data set has been compared with conjunction Es recordings from six ionosonde stations in mid and low latitudes. It has been found that in more than 20% of cases Es layers detected by those two methods do not agree. The spatial and temporal dependence of their agreement has been discussed. This study suggests that Es layer recordings using ground-based ionosonde observations has the best agreement with the Es layers measured by radio occultation data during daytime and local summers., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

The dynamics of the electron population in the Earth’s radiation belts affect the upper atmosphere’s ionization level through the low-energy Electron Precipitation (EP). The impact of low-energy EP on the high-latitude ionosphere has been well explained since the 1960’s decade. Conversely, it is still not well understood for the region of the South American Magnetic Anomaly (SAMA). In this study, we present the results of analysis of the strong geomagnetic storm associated with the Interplanetary Coronal Mass Ejection (May 27-28, 2017). The atypical auroral sporadic E layers (Esa) over SAMA are observed in concomitance with the hiss and magnetosonic wave activities in the inner radiation belt. The wave-particle interaction effects have been estimated, and the dynamic mechanisms that caused the low-energy EP over SAMA were investigated. We suggested that the enhancement in pitch angle scattering driven by hiss waves result in the low-energy EP (≥10 keV) into the atmosphere over SAMA. The impact of these precipitations on the ionization rate at the altitude range from 100 to 120 km can generate the Esa layer in this peculiar region. In contrast, we suggested that the low-energy EP (≤1 keV) causes the maximum ionization rate close to 150 km altitude, contributing to the Esa layer occurrence in these altitudes.

The wind shear theory is widely accepted as an explanation for the formation of a sporadic E (Es) layer, but the direct comparison of Es with the local wind shear has been limited due to the lack of neutral wind measurements. This study examines the role of the vertical wind shear for Es, using signal‐to‐noise ratio profiles from COSMIC‐2 radio occultation measurements and concurrent measurements of neutral wind profiles from the Ionospheric Connection Explorer. It is observed that the Es occurrence rate and average S4 index are correlated with the negative vertical shear of the eastward wind, providing observational support for the wind shear theory. Es can be observed even when the vertical wind shear is positive, which is interpreted as metallic ion layers generated at an earlier time., Plain Language Summary: Sporadic E (Es) is anomalous radio propagation resulting from intense clouds of ionization at heights of the E‐region ionosphere (90–120 km). The formation of an Es layer is generally attributed to the vertical wind shear, which can move metallic ions in the vertical direction by the Lorentz force. According to the wind shear theory, a negative shear of the eastward wind is effective in converging the metallic ions into a thin layer to produce Es. Although previous observations and modeling studies have supported the theory to various degrees, the direct comparison of Es with the vertical wind shear has been limited due to sparse observations of neutral winds at E‐region heights. Neutral wind profiles from the Ionospheric Connection Explorer mission, together with Es data from COSMIC‐2 radio occultation measurements, provide an opportunity to fill this knowledge gap. Direct comparisons of these measurements reveal that the Es occurrence rate is higher and lower for larger negative and positive wind shears, respectively, providing observational evidence for the wind shear theory., Key Points: Conjunction observations of sporadic E (Es) from COSMIC‐2 and neutral wind profiles from Ionospheric Connection Explorer/Michelson Interferometer for Global High‐Resolution Thermospheric Imaging are analyzed. Es occurrence rate correlates with the negative vertical shear of eastward wind, providing observational evidence for the wind shear theory. Es can be observed even when the vertical shear of the local eastward wind is positive., Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659, NASA, DFG Priority Program Dynamic Earth

Ponencia expuesta online en el 8th International Radio Occultation Working Group Meeting (2021) celebrado del 7 al 9 de abril, Ground and satellite based GNSS Remote Sensing (GNSS-RS) developed during the recent two decades into a very powerful and versatile tool for Earth System Research. A highlight of these developments is the operational use of spaceborne GNSS Radio Occultation (RO) data from several satellite missions to improve day-by-day global weather predictions. GNSS Remote Sensing is briefly introduced with selected applications. One prominent example is the improvement of regional and global weather forecasts. GNSS signals, reflected from water, ice and land surfaces (GNSS-Reflectometry, GNSS-R) can usefully complement the observation capabilities of GNSS-RO mission and enable versatile additional geophysical applications such as observation of wind speed and precipitation over oceans, which are illustrated. Finally, selected aspects for a comprehensive GNSS based Earth Observation with small satellite constellations are presented.

During the recent two decades ground- and satellite-based GNSS remote sensing (GNSS-RS) methods evolved into a ver-satile and powerful tool for Earth system research on dif-ferent spatio-temporal scales with operational applications. Large regional and global GNSS ground networks and numer-ous space-borne receivers provide unique neutral atmospher-ic/ionospheric data and observations of the Earth’s surface. One of the pioneering institutions for these developments is the German Research Centre for Geosciences GFZ at Potsdam. We briefly review recent GFZ developments in GNSS remote sensing.

The GPS radio occultation technique is used to study sporadic E (Es) layer plasma irregularities of the Earth’s ionosphere on a global scale using COSMIC/FORMOSAT-3 satellite constellation GPS signal-to-noise ratio (SNR) profiles. The maximum deviation from the mean SNR is attributed to the height of the Es layer. Es are produced by ion convergence due to vertical wind shear in the presence of a horizontal component of the Earth magnetic field, while the wind shear is provided mainly by solar tides. Indeed, close correlation between Es and wind shear phases have already been found for the semidiurnal and terdiurnal tidal components. Here, we present the global distribution of quarterdiurnal (QDT) signatures in Es occurrence rates. We find that, in accordance with upward energy flux, negative vertical phase gradients of QDT Es signatures are observed. The maximum signal of QDT Es is found at altitudes above 100 km. In the southern hemisphere, maximum QDT Es occurrence rates are found in winter and during equinoxes. In the northern hemisphere, however, at altitudes above 100 km strong QDT activity is also visible. Die GPS-Radiookkultationstechnik wird verwendet, um ionosphärische Plasmairregularitäten in Verbindung mit sporadischen E- (Es) Schichten auf globaler Skala zu untersuchen. Verwendet werden Signal-Rauschverhältnis- (SNR-) Profile. Die maximale Abweichung vom mittleren SNR wird der Höhe der Es-Schicht zugeordnet. Es werden durch Ionenkonvergenz aufgrund von vertikaler Windscherung in Anwesenheit einer horizontalen Komponente des Erdmagnetfeldes hervorgerufen, wobei die Scherung hauptsächlich durch solare Gezeiten verursacht wird. Tatsächlich wurden schon früher deutliche Übereinstimmungen zwischen dem Auftreten von Es und den Phasen der halb- und dritteltägigen Gezeiten gefunden. Hier stellen wir die globale Verteilung der vierteltägigen (QDT) Signaturen in Es- Auftretensraten vor. Es zeigt sich dass, in Übereinstimmung mit einem aufwärts gerichteten Energietransport, negative vertikale Phasengradienten der QDT in Es auftreten. Die maximale Auftretenswahrscheinlichkeit liegt bei Höhen oberhalb von 100 km. Auf der Südhemisphäre fällt das Maximum der QDT in Es-Auftretensraten in den Winter, während auf der Nordhemisphäre oberhalb von 100 km auch im Sommer starke QDT-Aktivität zu verzeichnen ist.

Radio occultation measurements performed by the satellites CHAMP, GRACE and FORMOSAT-3/COSMIC provide a huge data set for atmospheric and ionospheric investigations on a global scale. The data sets are used to extract information on sporadic E layers appearing in the lower ionospheric E region. This is done by analyzing signal amplitude variations of the GPS L1 signal. Sporadic E altitudes in northern midlatitudes found from radio occultation measurements are compared with ground-based ionosonde soundings. A large correlation of sporadic E altitudes from these two techniques is found.

Global Positioning System radio occultation measurements by the FORMOsa SATellite mission-3/Constellation Observing System for Meteorology, Ionosphere and Climate satellites were used to analyse the behaviour of the signature of the terdiurnal tide in sporadic E (ES) layers at midlatitudes (43–63° N). According to theory, the occurrence of ES is expected when the vertical zonal wind shear, which is mainly owing to solar tides, is negative. 4 yr means, based on 3-monthly running mean zonal means from December 2006–November 2010, were constructed for the terdiurnal oscillation in the occurrence frequency of ES. Comparison of the results with VHF meteor radar observations of the terdiurnal tide and the 8 h oscillation in the vertical zonal wind shear at Collm, Germany (51.3° N, 13° E) shows a clear correspondence between the 8 h in ES and in wind shear signature.

Understanding and predicting of atmospheric temperature and water vapor variations is a key issue for characterizing global change. To precisely determine the current and future variations on a global scale, accurate atmospheric observations with satellites are indispensable. We introduce an innovative and very precise satellite based atmospheric observation technique, which became operational during the recent years, pioneered also by the work of GFZ technicians and scientists: GNSS (Global Navigation Satellite System) Radio Occultation (RO). The technique is based on the influence of the Earth’s atmosphere on the propagation of navigation signals (L-Band, 1.2 and 1.5 GHz). A key parameter for this influence is the bending angle of the signal path from the transmitting navigation to the receiving Low Earth Orbiting (LEO) satellite, which depends on atmospheric temperature and water vapor. The GNSS RO method is currently applied aboard several LEO satellites, as GRACE, TerraSAR-X, TanDEM-X, COSMIC and Metop. We also present recent scientific GFZ results related to the characterization of global atmospheric variations using the world-wide unique long-term GNSS RO data set from the GFZ geoscience satellite CHAMP (2000-2010). Hereby, tropopause temperature and altitude properties, precisely derived from the GNSS RO data, are also used to reveal even very small variations of the global atmosphere.