In this study, we report a special event of nighttime southwestward propagating medium scale traveling ionospheric disturbances (MSTIDs) observed in O(¹D) 630.0 nm airglow images from an all-sky imager at Hanle (32.7°N, 78.9°E; Mlat. ~24.1°N), Ladakh, India on a geomagnetically quiet (Ap = 7) night of 15 September 2018. The time sequence of airglow images unveiled two dynamic interactions between multiple dark bands of MSTID. Following the first interaction, one of the interacting bands decayed possibly due to the entrance of plasma from the ambient higher plasma density region. Shortly after this interaction, the other interacting dark band was involved in the second interaction with a third dark band which resulted in the co-alignment of the two interacting bands. Following this co-alignment, one of the bands started rotating prominently that led to further separation of these two co-aligned bands. These changes in the MSTID phase fronts (bands) are explained based on the development of the polarization electric fields arising out of the interactions. This investigation combines the all-sky 630.0 nm airglow imaging observations with TEC maps constructed, for the first time over the Indian sector, from 67 Global Navigation Satellite System (GNSS) measurements to capture the MSTID over this region. The investigation reveals a few important features of self-interactions of MSTID bands over the geomagnetic low-mid latitude transition region which is important to assess their impact over low latitudes. The highlights of these results will be discussed in the meeting.

How to cite: Sarkhel, S., Patgiri, D., Rathi, R., Yadav, V., Chakrabarty, D., Mondal, S., Sunil Krishna, M. V., K. Upadhayaya, A., G. Vivek, C., Kannaujiya, S., and Sunda, S.: A case study on multiple self-interactions of MSTID bands: New insights, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3051, https://doi.org/10.5194/egusphere-egu23-3051, 2023.

In the last decade, several instruments have been developped to measure the auroral light polarisation. However, its study has faced the issue of anthropic light pollution and scattering in the lower atmosphere (Bosse et al., 2020). To overcome this challenge, several methods were used, and until now, the most succesfull was the use of a polarised radiative transfer model (Bosse et al., 2022) to identify the light pollution contribution. However during the past year a new look at the data revealed that pulsating aurorae are polarised, and that this polarisation carries a lot of information. The main advantage of using pulsating aurorae is that the variations in the light polarisation are very fast, of the order of a few seconds. This allows us to dismiss any potential source of polarisation that are not synched with the pulsation of the aurora.

These polarisation patterns are seen in the green atomic oxygen line at 557.7 nm, the 1st N2+ negative band at 391.4 nm (purple) and 427.8 nm (blue).

There are no clear explanations on the origin of this auroral polarisation, or its relation to the local state of the upper atmosphere. An hypothesis is that this polarisation can be either created directly at the radiative de-excitation or may occur when the non-polarised emission crosses the ionospheric currents.

We will present how these new findings confirm the ionospheric origin of the polarisation observed from the ground, as well as some of the potentialities these observations and models offer in the frame of space weather, aerosol and light pollution study.

How to cite: Bosse, L., Cessateur, G., Lamy, H., Lilensten, J., Gillet, N., Brogniez, C., Pujol, O., Rochat, S., Curaba, S., Delboulbé, A., and Johnsen, M. G.: First evidence of polarized emissions in pulsating aurorae, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15004, https://doi.org/10.5194/egusphere-egu23-15004, 2023.

Studying the auroral emission is of strong importance since they are created in an atmospheric layer (80-300 km) where in situ measurements are complicated. They represent a good proxy of the particle precipitations into atmosphere.

The spectrum of the aurora is complex made of both atomic and molecular lines. The intensities of these emissions vary with the activity, especially the particle precipitations.

Transsolo is the kinetic code which solve the transport equation of the electrons along a vertical or a magnetic field line. It allows to obtain the particles fluxes at different energies, angles and altitudes. From this, the code is able to calculate the related emissions.

The emission modules have recently been updated by including the vibrational structures of the molecular bands. Several atomic lines have also been added. We can consider that we include more than 95% of the full emission spectra. From this, it is now possible to obtain some almost complete synthetic spectra of the aurora parametrized by the mean energy of the particle fluxes at the top of the atmosphere and the total precipitated energy.

Recently Robert et al. show that it is possible to reconstruct the energetic precipitation from the N₂⁺ 427 nm line. However, it remains clear that multiplying the number of considered lines, will allow to get more accurate measurements of these particle fluxes. Moreover, a large number of auroral monitoring instruments are done with filters with variable widths. Such synthetic spectra can help to identify the possible perturbation of the measurements due to wavelength coincidences. For example, the green line at 557 nm is in coincidence with several O₂⁺ and N₂ bands in a +/- 5 nm range. Calculating the relative ratio of these lines in different conditions is then crucial.

In parallel, we are developing a series of calibrated high sensitivity spectrometers to validate the data and enhance the quality of particle precipitation reconstructions.

In this presentation, we will detail the links between these instruments and these synthetic spectra.

How to cite: Barthelemy, M., Robert, E., and Sequies, T.: Quasi exhaustive synthetic spectra of the aurora and spectrometers measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13647, https://doi.org/10.5194/egusphere-egu23-13647, 2023.

The impact of individual meteors on the lower ionosphere (90-150 km height) has been investigated during wintertime meteor showers using measurements of two DPS-4D Digisondes installed at Sopron (47.63°, 16.72°) and at Pruhonice (50°, 14.5°). The optical measurements of meteors have been performed by a zenith camera installed next to the digisonde at Sopron. It provided the opportunity to compare high cadence ionograms measured during meteor showers parallel with the optical data to determine the plasma trails of individual meteors. Campaign measurements with two ionograms/minute have been performed at Sopron station during the Leonid (16-18 November) and Geminid (10-15 December) meteor showers in 2019. Furthermore, skymaps (1/min) detected by the Digisonde at Sopron during the campaign were also investigated.

In the 20-25% of the observed meteors faint, short-lived (20-120 sec) Es layers were detected on the ionograms during and after (< 2 min) the optical record, which are typical signal of individual meteor trails on the ionogram based on previous studies. There was no observed Es activity at the same height on the ionograms detected before and after these events. Furthermore, the direction of the echo can be also defined on the ionograms of the DPS-4D Digisonde thanks to the multi-beam observation technique. The direction of the detected Es layers agreed well with the optical observations in most of the cases. The maximum frequency of the observed faint layers (foEs) varied between 1,6 and 4,5 MHz, while their height was between 85 and 136 km. Points on the skymaps were also detected at the time of the faint Es layers in 40 % of the cases. The height and direction of the observed points agreed with these parameters of the plasma traces on the ionograms.

Comparing the ionograms with the closest ionosonde observation at Pruhonice station at the same time, we could conclude that the detected faint Es layers were local plasma irregularities, no Es activity at the same height was observed there. This strengthens the hypothesis that the observed trails on the ionograms represents the echo of the optically recorded meteors.

How to cite: Barta, V., Szárnya, C., Kouba, D., Koucka Knizova, P., Podolska, K., Igaz, A., and Mosna, Z.: Impact of individual meteors on the midlatitude ionosphere during the Leonids and Geminids meteor showers, 2019, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6622, https://doi.org/10.5194/egusphere-egu23-6622, 2023.

ICEBEAR (Ionospheric Continuous-wave E-region Bistatic Experimental Auroral Radar) employs advanced software defined radio (SDR) and aperture synthesis radar imaging to produce unambiguous high resolution (1--2~km) 3-dimensional (range, azimuth, elevation) coherent E-region observations.  ICEBEAR-3D operates in the VHF at 49.5~MHz observing the auroral zone of the ionosphere from western Canada (58N, 106W geographic).  The receiver antenna array was re-configuration in 2019 to a non-uniform co-planar T-shaped double interferometer layout to complete the ICEBEAR design and allow for unambiguous, highly detailed, high-resolution coherent radar E-region observations.  We present the antenna array re-configuration; the novel and advanced synthesis aperture radar imaging technique; a low elevation angle accuracy and reliability solution; validations and calibrations of ICEBEAR-3D using celestial radio sources (Cygnus A) and interferometer closure angles; as well as some initial E-region and meteor trail observations and analysis.

How to cite: Hussey, G., Lozinsky, A., Pitzel, B., Ivarsen, M., Galsechuk, D., Huyghebaert, D., McWilliams, K., and St. Maurice, J.-P.: The highly advanced ICEBEAR-3D E-region coherent imaging radar, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10103, https://doi.org/10.5194/egusphere-egu23-10103, 2023.

Multireceiver and multifrequency radar imaging techniques, implemented in the 46.5 MHz MU radar in Japan (34.85°N and 136.10°E), were employed to investigate the aspect sensitivity of field-aligned plasma irregularities (FAIs) in the mid-latitude ionospheric E region. Aspect sensitivity of refractive irregularities in the atmosphere describes the radar echo intensity varying with the radar beam direction. For the FAIs in the ionosphere, the radar echoes are generally strongest at the beam direction perpendicular to the geomagnetic field line, and decay rapidly with off-perpendicular angle along the geomagnetic field line. This feature relates partly with the values of electron-neutral collision frequency (ν_e), electron gyrofrequency (Ω_e), ion-neutral collision frequency (ν_i), ion gyrofrequency (Ω_i), the ratio ν_e/Ω_e, among others, and moreover, is also subjected to nonlinear coupling process of unstable waves in the plasma irregularities. In practical observation, the radar beam of the MU radar was directed to geographic north and at 51° zenith angle, which was normal to the geomagnetic field line around 100-110 km height (range: ~160-175 km along the beam direction). Five carrier frequencies and nineteen receivers were operated for radar imaging to retrieve the power distribution in the radar volume, and then the angular power distribution was used to estimate the aspect angle along the geomagnetic field line. Retrieval algorithms such as Fourier, Capon, and norm-constrained Capon (NC-Capon) were utilized, in which the NC-Capon was applied to FAIs for the first time and found to be more suitable for the present study. The aspect angles estimated by the NC-Capon algorithm ranged between 0.1° and 0.4° mostly, which are close to the previous measurements with the radar interferometry (RI) made for the lower mid-latitude sporadic E region and the equatorial electrojet irregularities.

How to cite: Chen, J.-S., Wang, C.-Y., and Chu, Y.-H.: Aspect Angle of Plasma Irregularities in the Ionosphere Measured by Using the Radar Imaging of VHF Arrayed Radar, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1198, https://doi.org/10.5194/egusphere-egu23-1198, 2023.

Precipitations of auroral electrons characterize the relationship of the magnetosphere and the upper atmosphere, therefore state of near-Earth space depending on their localization and their intensity. One of the main gaps in both data and modelling is the monitoring of the precipitation of low-energy (0.02 – 35 keV) particles in the ionosphere. These particles are responsible of the surface charging on satellites, which lead to trigger electrostatic discharge (ESD) on components. This impact is the most recurrent in space and need to better understand. The method present here, allows an alternative to particle detectors that do not have access to this area.

From optical data, it can be very interesting to reconstruct low energy electron flux in the aurora region. Therefore, the interpretation of the auroral intensities is made using the Transsolo code, a kinetic code which use as input the electron flux and the solar EUV flux on the dayside. It calculates the transport of the suprathermal electrons along a line of sight or a vertical and the subsequent auroral emissions. A optimization method is worked to trying to retrieve electron flux from optical measurements.

The study present here is based on ALIS network data which provides very useful data (Brandstorm, 2003). Tomographic data of the volume emission rate are built from ALIS measurements (Gustavsson, 2000). From tomographic data and transsolo simulations, we adapt the optimization method to reconstruct energetic particles flux. We focus on measurements of the event of 05 March 2008 at 18:41:30 UT and 18:42:40 UT acquired by 5 stations and centred above Skibotn city. Results are presented in the form of maps of mean energy and total energy (corresponding to the energy flux) depending on geographic coordinates. 

How to cite: Robert, E., Barthelemy, M., Cessateur, G., Woelffle, A., Lamy, H., Bouriat, S., Johnsen, M. G., Brändstörm, U., and Biree, L.: Reconstruction of precipitated electron fluxes using auroral data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5387, https://doi.org/10.5194/egusphere-egu23-5387, 2023.

Solar wind interactions with the Earth’s magnetosphere cause geomagnetic storms and thereby induce ionospheric storms. This study investigates the spatio-temporal evolution of the ionospheric Total Electron Content (TEC) during a moderate but long duration storm driven by solar wind high-speed streams (HSSs) and associated co-rotating interaction region (CIR) during 14-21 March 2016. The storm starts with a strong storm sudden commencement (SSC) with a peak close to 19 UT on 14 March 2016. The GNSS/TEC maps are obtained from the Madrigal database. The associated field-aligned currents (FACs) from AMPERE, ionospheric convection maps from SuperDARN, and the O/N2 ratio from TIMED/GUVI are also studied for understanding the physics behind the different features observed in TEC during the storm.

The study predominantly focuses on the changes of TEC at high and middle latitudes. The storm induced changes in the TEC were extracted by removing the quiet time background (mean of five quietest days of the month) from the TEC maps. During the initial phase, TEC enhancements and depletions are found mainly at high latitudes within the auroral oval and close to the cusp, plausibly associated with auroral precipitation and variations in the upward and downward field-aligned currents (FACs). After the onset of the main phase, the TEC is enhanced at mid-latitudes and auroral ovals with a maximum of ~10 TECU. Meanwhile, a significant decrease in TEC is observed in the polar cap region. During the main phase, we observe the evolution of a storm-enhanced-density (SED) plume and a transient enhancement of TEC in the polar cap. Later during the storm, a strong TEC depletion at high and middle latitudes is found on the dayside and in the evening sector. The depletion of O/N2 ratio, triggered by Joule heating and atmospheric upwelling, could be a plausible reason for the TEC depletion. The possible physical mechanisms associated with the observed TEC variations will be discussed. 

How to cite: Prasannakumara Pillai Geethakumari, G., Aikio, A., Cai, L., Vanhamaki, H., Pedersen, M., J. Coster, A., Marchaudon, A., Blelly, P.-L., Haberele, V., Maute, A., Ellahouny, N., Virtanen, I., Norberg, J., Oyama, S., Kozlovsky, A., and Grandin, M.: HSS/CIR driven storm effects on the ionosphere-thermosphere system, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9293, https://doi.org/10.5194/egusphere-egu23-9293, 2023.

The forcing component of energetic particle precipitation (EPP) is recently added into the IPCC's official Coupled Model Intercomparison Project (CMIP) climate modelling. According to these simulations, the impact of inclusion of the medium energy electrons to the ozone variability was estimated to be 12-24% in the mesosphere and 5-7% in the stratosphere.
However, to obtain a continuous particle forcing required for these multi-decadal simulations, the precipitating particle flux spectrum was parameterised by the magnetic Ap index to match statistically to the POES satellite's MEPED particle detector data. This rather simple approach has several uncertainties, but the most critical one is that the existing satellite-borne particle detectors, including the MEPED instrument, struggle to separate the loss cone populations from trapped particles, leading to biases in EPP forcing especially in the relativistic energies.
In this presentation, we evaluate various EPP forcing models proposed for the future CMIP climate models against the EISCAT VHF data. This can be regarded as a ground-thruth approach for the mesospheric ionisation essential for the atmospheric consequences of the EPP.

How to cite: Kero, A., Thomas, N., Virtanen, I., Verronen, P., van de Kamp, M., and Nesse, H.: Ground truth validation of the CMIP energetic particle precipitation forcing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17159, https://doi.org/10.5194/egusphere-egu23-17159, 2023.

On 4 November 2021 it was detected the most intense geomagnetic storm that occurred so far during the rising phase of solar cycle 25 (Kp=8-). This work summarizes the state of the solar wind before and during the geomagnetic storm, the response of the plasmasphere-ionosphere-thermosphere system in the European sector and, for a comparison, the ionosphere-thermosphere response of the American sector. The plasmasphere dynamics was investigated through field line resonances detected at the European quasi-Meridional Magnetometer Array. The ionosphere was investigated through the combined use of ionospheric parameters (foF2, hmF2) from ionosondes and Total Electron Content (TEC) obtained from Global Navigation Satellite System receivers at four locations in the European sector and three locations in the American sectors. Aeronomic parameters were retrieved by using an original method based on the observed electron concentration in the ionospheric F region. The behavior of foF2 and TEC data is also discussed, speculating about the possible interconnection between the topside ionosphere and the plasmasphere at the investigated European sites. Experimental results can be summarized as it follows: a) The plasmasphere, originally in a state of saturation, was eroded up to two Earth’s radii, and only partially recovered after the main phase of the storm, and a possible formation of a drainage plume is also observed; b) The ionospheric parameters showed phases characterized by negative and positive variations, with longitudinal and latitudinal dependence of storm features in the European sector; c) Negative storm signature in electron concentration at the F2 region is also observed in the American sector. This result is mainly attributable to the neutral composition and temperature variations.

How to cite: Regi, M., Perrone, L., Del Corpo, A., Spogli, L., Sabbagh, D., Cesaroni, C., Alfonsi, L., Bagiacchi, P., Cafarella, L., Carnevale, G., De Lauretis, M., Di Mauro, D., Di Pietro, P., Francia, P., Heilig, B., Lepidi, S., Marcocci, C., Masci, F., Nardi, A., and Piscini, A. and the Mauro Regi: Space Weather Effects On Plasmasphere, Ionosphere and Thermosphere Systems during November 2021 Geomagnetic Storm, as probed in the Northern Hemisphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16488, https://doi.org/10.5194/egusphere-egu23-16488, 2023.