S9

The thermosphere and ionosphere (TI) system, which represent neutral and charged particles respectively in the upper atmosphere in more than 80 km altitude, is characterized by highly variable electrodynamic processes. Changes in the thermosphere find their response in the ionosphere and vice versa. The TI system is driven to a large extend by forcing from the Sun causing a typical daily, seasonal, 11-year and other regional variability. Solar forcing also includes storm conditions, when suddenly large amounts of solar wind energy is transferred into the TI system, resulting in significant changes in thermosphere and ionosphere conditions. Although the solar forcing dominates the TI variability, the dynamics and chemistry from the atmosphere below do not have a neglectable influence, too.

In this presentation, I will show campaign studies with the EISCAT instrumentation in North-Norway, which reveal solar and atmosphere TI-coupling processes on different temporal and spatial scales. The observations are combined with modelling results from numerical models of the TI system.

How to cite: Borries, C., Sato, H., Günzkofer, F., Yaroshenko, V., and Pokhotelov, D.: Campaign studies for investigating the coupling processes in the thermosphere and ionosphere, 2nd Symposium of IAG Commission 4 “Positioning and Applications”, Potsdam, Germany, 5–8 Sep 2022, iag-comm4-2022-40, https://doi.org/10.5194/iag-comm4-2022-40, 2022.

The negative impacts of space weather conditions on human activity have become a vital concern over the last decades, as humans increasingly use satellite communications, Positioning-Navigation-Timing (PNT) with Global Navigation Satellite Systems (GNSS), Earth’s observation and forecasting with in-situ and remote sensing satellites, and countless other applications. This situation underscores the necessity to better understand and predict the effects of Magnetosphere-Ionosphere-Thermosphere (MIT) processes and coupling in the near-Earth environment and to prevent potential detrimental influences on orbiting, aerial, and ground-based technologies (e.g., the radio signal propagation delay in the ionosphere affecting GNSS and communications, the drag force disturbances on Low Earth Orbit satellites, the power and internet outages due to intense electric currents induced during geomagnetic storms, etc.). For instance, the variability of the ozone layer has strong dependence on space weather, and it connects with the troposphere and the surface temperature variability. The ozone is a strong absorber of Solar ultraviolet (UV) and Earth’s long-wave radiations, playing thus a key role in global warming and climate change, which is affected by natural and human contributions such as solar activity and powerful ground-based radio transmitters. In the intricate MIT coupling, the UV and extreme UV (EUV) radiation are mostly absorbed by the thermosphere to create the ionosphere through ionization/dissociation of neutrals, and the thermosphere and ionosphere are strongly influenced by wave motions from the lower atmosphere, and also by energetic particle precipitation and field‐aligned currents through the magnetosphere and solar wind. Addressing the challenge of completely understanding the coupled MIT processes requires significant advances in geodetic observations of plasma and neutral density, “compositions”, and “velocities”, observations of energetic particles and “magnetic field perturbations” both in space and on the ground, as well as advanced theoretic and numerical modelling capabilities. The Joint Study Group 1 ‘Coupling processes between Magnetosphere, Ionosphere, and Thermosphere and (MIT)’ is implemented at the International Association of Geodesy (IAG) Inter-Commission Committee on Theory (ICCT), joint with the IAG Global Geodetic Observing System (GGOS), Focus Area on Geodetic Space Weather Research (FA-GSWR), the IAG Commission 4 ‘Positioning & Applications’, and the IAG Sub-Commission 4.3 ‘Atmosphere Remote Sensing’. The JSG1 aims to better understand Space Weather phenomena within the coupled MIT system, and formulate predictive models of the near-Earth space environment. We provide an introduction of the coupled MIT system and recent updates and results achieved by the group.

How to cite: Calabia, A., Olabode, A., Amory-Mazaudier, C., Maute, A., Yasyukevich, Y., Lu, G., Bolaji, O., Ariyibi, E., Anoruo, C., Jimoh, O., Shah, M., Adhikari, B., Mehta, P., Yuan, L., Maruyama, N., Ayorinde, T., and Owolabi, C.: The Joint Study Group 1 (JSG T.27): Coupling processes between Magnetosphere, Ionosphere, and Thermosphere, 2nd Symposium of IAG Commission 4 “Positioning and Applications”, Potsdam, Germany, 5–8 Sep 2022, iag-comm4-2022-48, https://doi.org/10.5194/iag-comm4-2022-48, 2022.

Space weather means a very up-to-date and interdisciplinary field of research. It describes physical processes in space mainly caused by the Sun’s radiation of energy. The manifestations of space weather are multiple, for instance, the variations of the Earth’s magnetic field or the changing states of the upper atmosphere, in particular the ionosphere and the thermosphere.

The main objectives of the Focus Area on Geodetic Space Weather Research (FA GSWR) are (1) the development of improved ionosphere models, (2) the development of improved thermosphere models, (3) the study of the coupled processes between magnetosphere, ionosphere and thermosphere (MIT) and (4) the improved understanding of space weather events and their monitoring by space observations (geodetic and non-geodetic).

Objective (1) aims at the high-precision and the high-resolution (spatial and temporal) modelling of the electron density. This allows to compute a signal propagation delay, which will be used in many geodetic applications, in particular in positioning, navigation and timing (PNT). Moreover, it is also important for other techniques using electromagnetic waves, such as satellite- or radio-communications. Concerning objective (2), satellite geodesy will obviously benefit when working on Precise Orbit Determination (POD), but there are further technical matters like collision analysis or re-entry calculation, which will become more reliable when using high-precision and high-resolution thermospheric drag models. Objective (3) links the magnetosphere with the first two objectives by introducing physical laws and principles such as continuity, energy and momentum equations and solving partial differential equations. Objective (4) finally connects the improved understanding to the monitoring techniques and vice versa.      

To arrive at the above described objectives of the FA GSWR one Joint Study Group (JSG) and three Joint Working Groups (JWG) have been installed. In detail, these groups are titled as JSG 1: Coupling processes between magnetosphere, thermosphere and ionosphere, JWG 1: Electron density modelling, JWG 2: Improvement of thermosphere models, and JWG 3: Improved understanding of space weather events and their monitoring by satellite missions. Other implemented IAG Study and Working Groups within the IAG programme 2019 to 2023 will provide valuable input for the FA GSWR. In this presentation we provide an overview about the FA GSWR.

How to cite: Schmidt, M. and Forootan, E.: GGOS Focus Area on Geodetic Space Weather Research – objectives and structure, 2nd Symposium of IAG Commission 4 “Positioning and Applications”, Potsdam, Germany, 5–8 Sep 2022, iag-comm4-2022-46, https://doi.org/10.5194/iag-comm4-2022-46, 2022.

Space Weather refers to events on the Sun that have an impact on terrestrial technologies and man-made satellites. The Global Navigation Satellite System (GNSS) is extensively used for Geodesy and is subject to Space Weather impacts in several ways. These impacts all have the potential to reduce the accuracy of geodetic measurements utilizing GNSS.  The importance of Space Weather to the Geodesy community has been recognized by the establishment of the Focus Area on Geodetic Space Weather Research (FA-GSWR) (https://ggos.org/about/org/fa/geodetic-space-weather-research/)

The objectives of the FA-GSWR include the development of methodologies to deal with:

• The ionosphere, since the measurements of most of the space-geodetic observation techniques are depending on the properties of the ionosphere along the ray path of an electromagnetic wave between transmitters on satellites and receivers on the ground,
• The thermosphere, since the thermospheric drag is the most important deceleration effect on Low-Earth Orbiting (LEO) satellites that affects the lifetime of such satellites, which are often used for Earth observation.
• The history, experience and state of the art in developing and using sophisticated analysis techniques and modelling approaches for the estimation of the impacts of space weather on geodetic measurements.

This presentation will provide an overview of the nature and frequency of Space Weather events and how they impact technologies related to Geodesy. This will include the occurrence of ionospheric scintillation affecting signals from GNSS satellites to receivers on the ground, and the resulting loss-of-lock on GNSS satellites that compromises the accuracy of position estimates. Typical values of fluctuations in the position estimates derived from both single frequency geodetic GNSS receivers and dual frequency geodetic reference receivers during space weather events will be presented.

The space weather services provided by the South African National Space Agency (SANSA) and other Regional Space Weather Warning Centres associated with the International Space Environment Service (ISES) will be presented as well as the state of the art in the prediction of ionospheric total electron content and ionospheric scintillation.

How to cite: Cilliers, P. and Lotz, S.: Space weather impacts on Geodesy, 2nd Symposium of IAG Commission 4 “Positioning and Applications”, Potsdam, Germany, 5–8 Sep 2022, iag-comm4-2022-17, https://doi.org/10.5194/iag-comm4-2022-17, 2022.

Regional Total Electron Content (TEC) Maps proffer better mitigation effects in ionospheric models which are needed to resolve ionospheric TEC gradient errors associated with space-based technologies such as Global Navigation Satellite Systems (GNSS) and Space-Based Augmentation Systems (SBAS). EGNOS (European Geostationary Navigation Overlay System) is a European SBAS system that provides integrity, accuracy, continuity and availability to critical GNSS applications like aviation and others over ECAC (European Civil Aviation Conference) area. The EGNOS Ionospheric model is built with the concept of the ordinary Planar fit technique. This paper focuses on modified Planar fit, ordinary Kriging and modified Kriging techniques to validate the EGNOS algorithm during different geophysical (geomagnetically quiet and disturbed) conditions. The structure of EGNOS was strictly adhered to during the study and only publicly available GNSS ground-based stations over the ECAC area are engaged in the study. The preliminary results obtained show that adapting modified Planar fit and Kriging techniques could improve the EGNOS services over the ECAC area, most especially the northern part near the high latitudes and the southern part near the low latitude regions.

How to cite: Olabode, A., Abe, O., Cesaroni, C., Brack, A., Oluwadare, T., Nguyen, C., and Schuh, H.: EGNOS Performance during Different Space Weather Conditions Over ECAC Region, 2nd Symposium of IAG Commission 4 “Positioning and Applications”, Potsdam, Germany, 5–8 Sep 2022, iag-comm4-2022-47, https://doi.org/10.5194/iag-comm4-2022-47, 2022.

The ionosphere is an ionized part of the upper atmosphere, where the number of electrons in is large enough to affect the propagation of electromagnetic signals, including those of the GNSS systems. Therefore, knowing electron density values in the ionosphere is crucial for both industrial and scientific applications. Here, we employ the radio occultation profiles collected by the CHAMP, GRACE, and COSMIC missions, to model the electron density in the topside ionosphere. We assume a linear decay of scale height with altitude and create a model of 4 parameters, namely the F2-peak density and height (NmF2 and hmF2) and the slope and gradient of scale height in the topside (H0 and dHs/dh). The resulting model (NET) is based on feedforward neural networks and takes as input the geographic and geomagnetic position, the solar flux and geomagnetic indices. The resulting density reconstructions are validated on more than a hundred million in-situ measurements from CHAMP, CNOFS and Swarm satellites, as well as on the GRACE/KBR data, and the developed model is compared to several topside options of the Internation Reference Ionosphere (IRI) model. The NET model yields highly accurate reconstructions of electron density in the topside ionosphere and gives unbiased predictions for all seasonal and solar activity conditions.

How to cite: Smirnov, A., Shprits, Y., Prol, F., Lühr, H., Berrendorf, M., Zhelavskaya, I., and Xiong, C.: Neural network model of Electron density in the Topside ionosphere (NET), 2nd Symposium of IAG Commission 4 “Positioning and Applications”, Potsdam, Germany, 5–8 Sep 2022, iag-comm4-2022-9, https://doi.org/10.5194/iag-comm4-2022-9, 2022.

The high-quality dual-frequency phase measurements from Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) system provide a valuable opportunity to examine the Earth’s ionosphere. In this paper, the ionospheric information retrieved from the DORIS system is used as an external and independent data source to validate the performance of GNSS-generated ionospheric models. The concept of DORIS differential Slant Total Electron Content (dSTEC) analysis is presented, to examine the feasibility of DORIS data in the quality assessment of GNSS derived ionosphere models. Thanks to the large relative frequency ratio between the two frequencies of DORIS, the theoretical precision of DORIS dSTEC is at the level of 0.028 TECu, which is about 10 times better than that of GNSS-derived dSTEC. Using 48 co-located DORIS beacon sites of the International DORIS Service (IDS) and GNSS stations of the International GNSS Service (IGS), the comparison between DORIS and GNSS dSTEC assessments of Real-Time Global Ionospheric Maps (RT-GIMs) from different analysis centers is performed in this paper. The analysis is performed during the first four months of 2022. Based on the analysis results of more than 18,000,000 Jason-3 DORIS ionospheric observables, no systematical deviation is found between DORIS and RT-GIM derived dSTECs, with a mean bias of 0.14 TECu. Compared to DORIS dSTEC, the root-mean-square (RMS) of those RT-GIMs reaches 4.5-5.4 TECu at low-latitudes, which is 2.2-3.6 TECu in mid- and high-latitude regions. The latitudinal variation of RT-GIM errors is clearly observed in DORIS dSTEC analysis. In addition, the correlation coefficient between Jason-3 DORIS dSTEC RMS and GPS-plus-GLONASS dSTEC RMS is 0.81, and no significant dependence on GPS-only or GLONASS-only data is found. It is suggested to perform the dSTEC analysis with higher satellite elevation cutoff angle, e.g., 45o, to ensure a better consistency between DORIS and GNSS dSTEC assessments. Overall, DORIS dSTEC assessment provides an independent reference for the validation of GNSS based ionosphere maps.

This study only uses co-located DORIS/GNSS stations in order to ensure a fair comparison between DORIS and GNSS dSTEC validation. However, for future validation activities, all DORIS beacons can and should be used. This will lead to a more homogeneous data distribution covering also more ocean areas. Moreover, the DORIS NRT measurements are fully independent of the data used for RT-GIM generation, and as such is a perfect source for validation. In addition to Jason-3 altimetry, more satellite missions providing NRT DORIS data are planned, which will indeed extend the coverage of DORIS ionospheric observables and benefit the ionospheric associated analysis. In the next step, we will continue the work on the analysis of dSTEC consistency between DORIS and those new GNSS constellations, e.g., BDS and Galileo. The feasibility of using DORIS data in the generation of real-time global ionospheric maps will also be analyzed.

How to cite: Wang, N., Liu, A., Dettmering, D., Li, Z., and Schmidt, M.: Using Near-Real-Time DORIS Data for Validating Real-Time GNSS Ionospheric Maps, 2nd Symposium of IAG Commission 4 “Positioning and Applications”, Potsdam, Germany, 5–8 Sep 2022, iag-comm4-2022-13, https://doi.org/10.5194/iag-comm4-2022-13, 2022.

High-resolution 3D ionosphere modelling is crucial to monitor and understand space weather. Prol et al. (2021) is one of the most recent developments in advanced global-scale tomography that can represent the ionospheric electron density in a relatively high spatial and temporal resolution. The study was applied to the March 17, 2015 geomagnetic storm, showing that global-scale tomography could be useful to reproduce the system dynamics during a severe geomagnetic storm. Our results show good agreement with several ground- and space-based measurements of the ionosphere. The dataset used as reference is based on electron density observations from worldwide ionosondes, Millstone Hill incoherent scatter radar and in-situ measurements from the DMSP, GRACE and SWARM missions. The obtained results presented more accurate electron density profiles when compared to the Neustrelitz Electron Density Model, which is the model used as background, and physics-based thermosphere-ionosphere-electrodynamics general circulation model (TIE-GCM). Here we will present the main results in Prol et al. (2021), as well as provide guidelines and recommendations for future improvements in the development of 3D ionospheric models.

Reference:

Prol, F. S., Kodikara, T., Hoque, M. M., & Borries, C. (2021). Global-scale ionospheric tomography during the March 17, 2015 geomagnetic storm. Space Weather, 19, e2021SW002889. https://doi.org/10.1029/2021SW002889

How to cite: Prol, F. S., Hoque, M. M., Kodikara, T., and Borries, C.: Imaging the 3D Ionosphere by Global-Scale Tomography, 2nd Symposium of IAG Commission 4 “Positioning and Applications”, Potsdam, Germany, 5–8 Sep 2022, iag-comm4-2022-3, https://doi.org/10.5194/iag-comm4-2022-3, 2022.

A major problem in the precise orbit determination of Low-Earth-Orbiting (LEO) satellites at altitudes below 1000 km is modeling the aerodynamic drag which mainly depends on the thermospheric density and causes the largest non-gravitational acceleration. Typically, empirical thermosphere models such as NRLMSISE-00, NRLMSIS 2.0, JB2008 or DTM2013 are used to calculate density values at satellite positions. However, since the current thermosphere models cannot provide the required accuracy, unaccounted variations in the thermospheric density may lead to significantly incorrect satellite positions.

In this presentation, we will report about the most important results from our recently published paper Zeitler et al. (2021). In this study we compared for the first time thermospheric density corrections for the NRLMSISE-00 model in terms of scale factors calculated from satellite laser ranging (SLR) measurements to various spherical LEO satellites (Starlette, Stella, Larets, etc.) with the corresponding values from accelerometer measurements on-board CHAMP and GRACE.

Our results demonstrate that both measurement techniques can be used to derive comparable (with correlations of up to 80% and more depending on altitude) scale factors of the thermospheric density with a temporal resolution of 12 hours, which vary around the value 1. This indicates to which extent the NRLMSISE-00 model differs from the observed thermospheric density. On average, during high solar activity, the model underestimates the thermospheric density and should be scaled up using the estimated scale factors. We find a linear decrease of the estimated thermospheric density scale factors above 680 km of about −5% per decade due to climate change.

Furthermore, we validate the approach of deriving scale factors from SLR measurements by using two independent software packages.

Zeitler L., Corbin A., Vielberg K., Rudenko S., Löcher A., Bloßfeld M., Schmidt M., and Kusche J. (2021). Scale factors of the thermospheric density ‐ a comparison of SLR and accelerometer solutions. Journal of Geophysical Research: Space Physics, 126, e2021JA029708. doi: 10.1029/2021JA029708

How to cite: Schmidt, M., Zeitlhöfler, J., Corbin, A., Vielberg, K., Löcher, A., Rudenko, S., Bloßfeld, M., Zeitler, L., and Kusche, J.: A comparison of scale factors for the thermospheric density derived from Satellite Laser Ranging and Accelerometer Measurements to LEO satellites, 2nd Symposium of IAG Commission 4 “Positioning and Applications”, Potsdam, Germany, 5–8 Sep 2022, iag-comm4-2022-37, https://doi.org/10.5194/iag-comm4-2022-37, 2022.

An accurate estimation of the Thermospheric Neutral Density (TND) is important for predicting the orbit of satellites and objects, for example, those with the altitude of less than 1000 km. Models are often used to simulate TNDs but their accuracy is limited due to modelling restrictions and sensitivity to the calibration period. Satellite missions such as CHAMP, GRACE, GOCE, Swarm, and GRACE-FO are equipped with on-board accelerometer sensors to measure drag forces, which can be used to estimate along-track TNDs. However, spatial and temporal coverage of these space borne TNDs is restricted to the mission design. To make the best use of the modelling tools and measurements, we applied these along-track TND measurements within the sequential Calibration and Data Assimilation (C/DA) framework proposed by (Forootan et al., 2022, doi:10.1038/s41598-022-05952-y). The C/DA is used to re-calibrate the NRLMSISE00 model, which is called “C/DA-NRLMSISE00”, whose outputs fit well to the introduced space-borne TNDs. The C/DA-NRLMSISE00 is applicable for forecasting TNDs and individual neutral mass compositions at any predefined vertical level (between ~100 and ~600 km) with user-defined spatial-temporal sampling. Nine time periods (October 2003, July 2004, March 2008, April 2010, March 2015, September 2017, August 2018, September 2020 and October 2021) associated with space weather storms are selected for our investigations because most of the available models lack accuracy to provide reasonable TND simulations. Independent comparisons are performed with the space-borne TNDs that were not used within the C/DA framework, as well as with the outputs of other thermospheric models such as Jacchia-Bowman 2008 (JB2008) and the High Accuracy Satellite Drag Model (HASDM) database. The numerical results indicate improvements in the Root Mean Squared Errors (RMSE) of the C/DA-NRLMSISE00's TND forecasts compared to NRLMSISE-00, JB2008 and HASDM along-track of the LEO missions. The percentage reductions are found to be: 51%, 8% and 8 % along GRACE (2003, average altitude 490 km), 25%, 20% and 48% along GOCE (2010, average altitude 270 km), 46%, 37% and 35% along Swarm B (2015, average altitude 520 km), 54%, 12% and 5 % along Swarm B (2017, average altitude 514 km), and 41% and 64% along GRACE (FO) (2021, average altitude 504 km), respectively.

How to cite: Forootan, E., Kosary, M., Farzaneh, S., Borries, C., Kodikara, T., Doornbos, E., and Siemes, C.: How can space-borne along-track neutral density measurements be used to predict multi-level global thermospheric neutral density fields?, 2nd Symposium of IAG Commission 4 “Positioning and Applications”, Potsdam, Germany, 5–8 Sep 2022, iag-comm4-2022-44, https://doi.org/10.5194/iag-comm4-2022-44, 2022.