The LOFAR radio telescope consists of a large network of stations distributed across Europe, with a dense core in the east of the Netherlands. Each station consists of multiple antenna fields operating at frequencies between 20 and 80MHz and 110 and 240MHz. At these frequencies the ionosphere has a major impact on the astronomical observations, that needs to be corrected for.  This ionospheric calibration, at first order mainly a phase effect, provides valuable information about the ionospheric density variations above the telescope. We report on the use of the calibration solutions to extract the ionospheric information on structure, dominant direction and variability. In particular, we investigated the data recorded with the Dutch array, consisting of a core of 48 stations all within a 3 km diameter circle and another 14 remote stations with baselines up to 100 km, operating between 110 and 170 MHz.  The different baselines give access to different scales in the ionosphere. Furthermore, we present, for the same data, an imaging technique that allows direct imaging of larger scale gradients in the ionosphere.

How to cite: Mevius, M. and Beser, K.: Small scale ionospheric disturbances as seen by the LOFAR, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7259, https://doi.org/10.5194/egusphere-egu23-7259, 2023.

The storm-time mid-latitude ionosphere is an important interface in the global geospace dynamic system, which is characterized by energy and momentum ingests at the auroral/polar latitudes. This interface is affected by these high-latitude processes while being adjacent to expanded low-latitude electrodynamic/dynamic disturbances.  In particular, the mid-latitude and subauroral ionosphere can exhibit far more complicated multi-scale density/flow structures and disturbances than might otherwise be expected during geospace storms, such as large-scale and medium-scale traveling ionospheric disturbances (TIDs), storm-enhanced density (SED) plume, and subauroral polarization stream (SAPS). This presentation will describe some recent storm-time observations of these multi-scale ionospheric structures as well as discuss the underlying magnetosphere-ionosphere-thermosphere drivers. These observations provide some new scenarios to advance the current understanding of mid-latitude and subauroral dynamic processes at both large-scale and meso-scale levels.

How to cite: Aa, E., Zhang, S.-R., Erickson, P., Coster, A., and Goncharenko, L.: Understanding storm-time multi-scale ionospheric structures at mid-latitudes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2899, https://doi.org/10.5194/egusphere-egu23-2899, 2023.

Plasma escape from the high-latitude ionosphere (ion outflow) serves as a significant source of heavy plasma to magnetospheric plasma sheet and ring current regions. Outflows alter mass density and reconnection rates, hence global responses of the magnetosphere. The VISIONS-1 (VISualizing Ion Outflow via Neutral atom imaging during a Substorm) sounding rocket was launched on Feb. 7, 2013 at 8:21 UTC from Poker Flat, Alaska, into an auroral substorm with the objective of identifying the drivers and dynamics of nightside ion outflow at altitudes where it is initiated, below 1000 km. Energetic ion data from the VISIONS-1 polar cap boundary crossing show evidence of an ion "pressure cooker'' effect whereby ions energized via transverse heating in the topside ionosphere travel upward and are impeded by a parallel potential structure at higher altitudes.

A new fully kinetic model is constructed from first principles which traces large numbers of individual O+ ion macro-particles along curved magnetic field lines, using a guiding-center approximation, in order to facilitate calculation of ion distribution functions and moments. Particle forces in a three-dimensional global Cartesian coordinate system include mirror and parallel electric field forces, a self-consistent ambipolar electric field, and a parameterized source of ion cyclotron resonance (ICR) wave heating, thought to be central to the transverse energization of ions. The model is initiated with a steady-state ion density altitude profile and Maxwellian velocity distribution and multiple particle trajectories are advanced via a direct simulation Monte Carlo (DSMC) scheme. This document outlines the design and implementation of the kinetic outflow model and shows applications of simulated outflows representative of conditions observed during the VISIONS-1 campaign. This project provides quantitative means to interpret VISIONS-1 data and related remote sensing approaches to studying ion outflows and serves to advance our understanding of the drivers and particle dynamics in the auroral ionosphere and to improve data analysis for future sounding rocket and satellite missions.

How to cite: Albarran, R. and Zettergren, M.: Kinetic Modeling of Ion Outflows with Observations from the VISIONS-1 Sounding Rocket, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1919, https://doi.org/10.5194/egusphere-egu23-1919, 2023.

Global changes in the state of the ionosphere-thermosphere system depend to a large extent on the energy input from the solar wind and magnetosphere, which occurs in the high-latitude regions. On the one hand energy is deposited in the form of Joule heating causing changes in the thermosphere composition and circulation. On the other hand, imposed electric fields change plasma transport. Joule heating is closely related to changes in the solar wind dynamic pressure, because it can cause a compression of the magnetosphere driving currents in the magnetosphere, and the currents transfer electromagnetic energy into the ionosphere. The enhancement of plasma convection in the polar ionosphere is related to the intensification of the convection electric field, which is driven by the solar wind sweeping across the open magnetic field lines of the polar magnetosphere. These changes are most significant during storm conditions, caused e.g. by coronal mass ejections and corotating interaction regions. The storm related energy release in the high-latitude ionosphere is impacting the thermosphere-ionosphere system on a global scale.

However, the solar wind impact causes a regular every day variability of the polar ionosphere, too. We are investigating how the solar wind variability in time scales of days and weeks is reflected in the ionosphere variability at Tromso, which is located in Scandinavia at 70°N, 19°E. We use cross correlation analysis of total electron content with solar wind merging electric field and dynamic pressure data. It can be shown that in timescales of days and weeks, the magnitude of correlation between TEC and solar wind reaches similar values to the correlation of TEC and F10.7. However, the results show that the correlation between TEC and solar wind parameters depends strongly on local time, season and solar cycle. There is a clear annual cycle in the variability of the correlation coefficient, with higher correlation values in winter than in summer. The positive correlation in winter close to local midnight hours is related to precipitation effects increasing the electron densities. During summer in solar maximum condition, clear negative correlation values are retrieved. These are considered to be caused by increased convection.

How to cite: Borries, C., Davies, F., Iochem, P., Tasnim, S., and Vogt, J.: The regular solar wind impact on the high-latitude electron density in time scales of days and weeks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11628, https://doi.org/10.5194/egusphere-egu23-11628, 2023.

Solar EUV radiation is the dominant driver for upper atmosphere ionization. Ionospheric variations that affect radio signal propagation and thus affect technical systems such as satellite-based positioning systems. One significant time scale for the solar variability is the solar 27-day rotation period that causes a corresponding response in ionospheric observables like the height-dependent electron density (Ne) or the integrated total electron content (TEC). To enhance our understanding of the processes within the ionosphere we investigate a combination of observations and physical models, namely the Coupled Thermosphere Ionosphere Plasmasphere electrodynamics (CTIPe) model and the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIE-GCM), are analyzed to identify differences in Ne, TEC data and ionized oxygen (O⁺ and O₂⁺). Furthermore, the model results are compared to ground-based ionosonde Ne measurements with regard to the spatial and temporal response of the ionosphere to the 27-day solar rotation period. Modeled Ne correlates strongly with the observed Ne at mid-latitudes, but at low-latitudes the modeled TEC distribution follows the geomagnetic coordinates more strictly when compared to the observational data. Local TEC and F2 layer peak Ne are well represented by CTIPe, whereas TIE-GCM represents the global TEC and F2 layer peak height well.

How to cite: Dühnen, H., Vaishnav, R., Schmölter, E., and Jacobi, C.: Reaction of the Upper Atmosphere to the 27-d Solar Cycle - Comparison of CTIPe and TIE-GCM Simulations to Observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4832, https://doi.org/10.5194/egusphere-egu23-4832, 2023.

The ESA Swarm satellites have since year 2014 provided measurements of electron density at a frequency of 2 Hz and at times also 16 Hz corresponding to about 500 m along the satellite paths. Spectral indices, structure functions and scaling exponents of these 16 Hz density estimates were analyzed to study the F-region ionospheric irregularities at altitudes between about 425 and 510 km. The data were obtained during the period from October 2014 to October 2022.The Power Spectral Densities (PSDs) observed followed to a very good approximation a power law. The values of spectral indices p obtained showed a peak centered at around -2.5, located at the Equatorial Ionization Anomaly (EIA) belts. The largest contribution to the spectra came from in the South American-Antlantic-African longitudes and it was generally low in the Asian-Pacific region. The angle between the Swarm satellite orbital path and the magnetic field (∠(B, v)) was examined. The highest percentage of occurrence of ionospheric irregularities and the peak in spectral index was obtained for ∠(B, v) between 0° and about 40°. Over this range of angles PSD spectra steepened with increasing ∠(B, v) (p becomes increasingly negative), consistent with local anisotropic turbulence at scales of a few km. The probability distributions of density differences (structure functions) are non-Gaussian at all orders, similar to many other observations in space plasma. The scaling exponent function is non-linearly concave, which is usually taken as a sign of intermittency.

How to cite: Buchert, S. C., Aol, S., Sorriso-Valvo, L., and Jurua, E.: Turbulence Properties of Kilometer-scale Equatorial Irregularities as Deduced from Swarm Satellites LP Observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14686, https://doi.org/10.5194/egusphere-egu23-14686, 2023.

Ionospheric irregularities are structures or fluctuations of plasma density having different scale sizes. These irregularities can disrupt radio waves and produce errors in space-based or ground-based technologies, which depend on the GNSS/ GPS signals. Post-sunset ionospheric plasma irregularities are a common characteristic of the equatorial ionosphere. These irregularities, associated with plasma bubbles, are defined as strong density depletions relative to the background plasma as determined by in situ measurements. 
Finding a system parameter's probability distribution function (PDF) can lead us to understand the system's underlying physics. In this study, we investigate the probability distribution of the integrated power of post-sunset plasma density irregularities in the equatorial ionosphere measured with the Langmuir probes on Swarm C in four different frequency bands between 0-1 Hz for the entire Swarm mission. We find evidence of  "heavy tail" distribution in the PDFs, indicating the system's complexity and self-organized criticality. Moreover, we study the relation between Integrated power and different geomagnetic indices, e.g. F10.7 and sunspot number, to find the potential drivers of severe events. While we find no obvious driver of individual events, we find a strong solar cycle dependence in their occurrence.

How to cite: Ghadjari, H., Knudsen, D., and Skone, S.: Probability distribution of integrated power of equatorial ionosphere plasma density fluctuations measured by the Swarm Langmuir probes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8677, https://doi.org/10.5194/egusphere-egu23-8677, 2023.

The analysis of the structure function of a GNSS signal amplitude measured on the ground has revealed that ionospheric scintillation could be considered a proxy for ionospheric turbulence. More precisely, and in a recent report, the existence of a linear range with respect to the time lag in the structure function has been highlighted. In this context, the inertial-range analog has been determined from the analysis of a large set of scintillation events collected over several days from Pond Inlet located in the northern polar region and from Sao Paolo located at 23.2 degrees South of the Equator. At high latitude, we found that the mean value of the first-order scaling exponent is H = 0.55 ± 0.07, while a low altitude H is typically larger with H = 0.84 ±.11. This result clearly indicates that the long-time lag positive correlation remains persistent in the low latitude region. At high latitude however, both negative and positive long time lag correlation can occur. In addition, the obtained results clearly show that the inertial range analog is significantly smaller at high latitude, particularly the upper bound time lags at which the structure function deviates from linearity. This distinction may pinpoint to a difference in the ionospheric irregularity drift speed.   

How to cite: Meziane, K., Hamza, A. M., and Jayachandran, T. P.: Inferred Ionospheric irregularity scales from amplitude scintillation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10171, https://doi.org/10.5194/egusphere-egu23-10171, 2023.

Recently it has been shown that the SIMONe meteor radar network located in northern Norway is capable of measuring ionospheric E-region coherent scatter with spatial and temporal resolutions on the order of 1.5 km and 2 s (Huyghebaert et al, 2022).  These measurements are further studied, where the coherent scatter measurements are used as a tracer for large scale ionospheric phenomena, such as plasma density enhancements and ionospheric electric fields.  By applying 2D Fourier analysis to range-time-intensity data, we perform a multi-scale spatial and temporal investigation to determine the change in range over time of the large scale ionospheric structures (> 1 km) which are compared with the line-of-sight velocities of the small scale structures (< 10 m) determined from the Doppler shift of the coherent scatter.  The spectral characteristics of the structures are also investigated. This aids in characterizing the source of the structures and provides crucial information about how energy is redistributed from large to small scales in the E-region ionosphere.  Four different events are examined from June and July of 2022.

Huyghebaert D, Clahsen M, Chau JL, Renkwitz T, Latteck R, Johnsen MG and Vierinen J (2022) Multiple E-Region Radar Propagation Modes Measured by the VHF SIMONe Norway System During Active Ionospheric Conditions. Front. Astron. Space Sci. 9:886037. doi: 10.3389/fspas.2022.886037

How to cite: Huyghebaert, D., Chau, J. L., Spicher, A., Ivarsen, M. F., Clahsen, M., Latteck, R., and Vierinen, J.: Large Scale Temporal and Spatial Characteristics of E-region Plasma Irregularities Measured by SIMONe Norway, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12464, https://doi.org/10.5194/egusphere-egu23-12464, 2023.