ST3.1 | Ionosphere – upper atmosphere physics with ground-based instrumentation
EDI
Ionosphere – upper atmosphere physics with ground-based instrumentation
Convener: Veronika Haberle | Co-conveners: Andrew J. Kavanagh, Neethal Thomas, Sophie Maguire, Jade Reidy, Steve Milan, Jia Jia
Orals
| Fri, 19 Apr, 14:00–15:45 (CEST), 16:15–18:00 (CEST)
 
Room 1.34
Posters on site
| Attendance Thu, 18 Apr, 16:15–18:00 (CEST) | Display Thu, 18 Apr, 14:00–18:00
 
Hall X3
Orals |
Fri, 14:00
Thu, 16:15
The Earth’s upper atmosphere and ionosphere are subject to significant variability associated with solar forcing. While in situ observations of the ionosphere-upper atmosphere are only possible with spacecraft and sounding rockets, a wealth of information is obtained thanks to remote sensing techniques using ground-based instruments.
For instance, ground-based magnetometers, used in dense networks, routinely enable the derivation of ionospheric currents and geomagnetic indices. Optical instruments not only provide measurements of auroral and airglow emissions, but are also used to observe upper atmospheric winds and temperatures, e.g. in the thermosphere and mesosphere. Such parameters can also be measured with radars, spanning a wide range of active (ionosondes, meteor radars, coherent and incoherent scatter radars, VLF transmitters, Lidars) and passive (riometers, VLF receivers) systems.
Combining ground-based observations from various instruments enables the development of novel data analysis methodologies which in turn enhance our understanding of the underlying physics of space weather and ionosphere-upper atmosphere processes. This includes the study of densities, temperatures and composition of the ionosphere–upper atmosphere, monitoring of its dynamics and chemistry, and measuring of fluxes from precipitating particles and current systems.
In this session, we invite contributions featuring the use of ground-based instruments in studies of the ionosphere–upper atmosphere system across all latitudes and of space weather and ionospheric–atmospheric physics processes of various time and spatial scales.

Orals: Fri, 19 Apr | Room 1.34

Chairpersons: Veronika Haberle, Neethal Thomas, Jia Jia
14:00–14:05
14:05–14:35
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EGU24-10388
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ECS
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solicited
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On-site presentation
Rowan Dayton-Oxland and Daniel Whiter

Energetic proton precipitation causes proton aurora over Svalbard, but its effects on the chemistry and heat economy of the atmosphere are not well observed. Temperature and intensity changes in the OH layer have been observed during auroral electron precipitation (Suzuki et al., 2018), but no studies have yet investigated the effect of auroral proton precipitation. This study will use observations made by the HiTIES (High-Throughput Imaging Echelle Spectrograph) instrument located at the Kjell Henriksen Observatory near Longyearbyen, Svalbard. This spectrograph observes proton precipitation in the H-alpha wavelength as well as the OH*(8-3), (9-4), (5-1) airglow vibrotational bands. These OH bands are temperature and species density dependent which can be compared to the H-alpha profile and luminosity as a measure of proton aurora energy and flux. In addition, the vibrotational states above and below v'=6 result from different production processes which can be studied. Prelimiary results will be presented. 

How to cite: Dayton-Oxland, R. and Whiter, D.: Does auroral proton precipitation affect the temperature and chemistry of excited OH in the Svalbard mesopause?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10388, https://doi.org/10.5194/egusphere-egu24-10388, 2024.

14:35–14:45
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EGU24-14785
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On-site presentation
Andreas Stokholm, Njål Gulbrandsen, Nicolas Pedersen, Andrzej Kucik, Daniel Olesen, Anna Naemi Willer, Sine Munk Hivdegaard, and Olivier Chanrion

Auroras are a faint space weather light phenomenon caused by the interaction between the solar wind and the Earth’s magnetic field. This interaction can lead to processes that increase the energy of charged particles in the magnetosphere, enabling the particles to enter the ionosphere and cause diffuse or discrete auroras. Often, the images of auroras are captured using exposure times of 1-2 seconds to collect sufficient light. However, prolonged exposure times also intensify other light sources, such as urban- or moonlight, thus, dark night conditions are preferred. Long exposure times are also incapable of capturing fast dynamics, though some studies have carried out high-speed imaging with up to 160 frames per second (160Hz). 

Instead of traditional cameras, we propose to utilise the emerging optical technology, Dynamic Vision Sensors (DVS), that possess high dynamic ranges (110 - 120 dB) and sampling rates. DVS is a biologically-inspired silicon retina that detects negative or positive brightness change on a logarithmic scale similar to human eyes. In addition, pixels can independently adjust to lighting scenarios with an adaptable brightness threshold and without a static upper limit or constant frame rate. If no change occurs, no information is registered, providing a variable data rate and low power consumption.

Here, we present the first DVS observations of auroras in 5kHz, captured in March 2023 in Tromsø, Norway. We extract and interpret information based on reconstructed brightness and event frames. Further, we derive the incoming photon flux by mimicking a photometer. In all, we show that DVS is capable of observing auroras in challenging urban- and moonlight conditions while preserving the high temporal resolution that could enable a paradigm shift for aurora monitoring.

How to cite: Stokholm, A., Gulbrandsen, N., Pedersen, N., Kucik, A., Olesen, D., Willer, A. N., Hivdegaard, S. M., and Chanrion, O.: Observing auroras with dynamic vision sensors, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14785, https://doi.org/10.5194/egusphere-egu24-14785, 2024.

14:45–14:55
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EGU24-19091
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On-site presentation
Gaël Cessateur, Léo Bosse, Hervé Lamy, Jean Lilensten, Mathieu Barthelemy, and Magnar G. Johnsen

We review the last advances in the study of upper atmospheric emissions polarisation. Since 2008, observations and modeling initiatives aimed at detecting and understanding the auroral emission polarisation. In recent years, this field saw major advances, which confirm the ionospheric origin of the polarisation. Polarisation has been observed in all four main auroral visible emissions lines (the red (630 nm), green (557.7 nm), blue (427.8) and purple (391.4 nm)), in several geomagnetic and auroral activity levels and has been confirmed for the N2+ lines through laboratory experiments. However, the origin of this polarisation is still debated. Several points show that it cannot be due to atmospheric scattering, and must originate from ionosphere. The link between the polarisation state of the emission and the local ionospheric conditions is still uncertain and raises a number of questions, such as: Can ground based measurements of the polarisation with light instruments track ionospheric currents? What is the origin of the green line polarisation?

Our international collaboration gathers several instruments dedicated to the observations of the auroral emission polarisation, mainly located at the Skibotn observatory in Norway. The CRU series instruments, which are spectro-photo polarimeters able to measure faint polarized signals in a 2° FOV, are coupled with PLIP, for Polar Lights Imaging Polarimeter, able to measure polarization of the three main auroral emissions on a large FOV (~44° × 30°) on the sky. Some results will be presented from our last observation campaigns in Skibotn, Norway. Combining the CRU instruments with the PLIP imager opens a new chapter of investigation.

How to cite: Cessateur, G., Bosse, L., Lamy, H., Lilensten, J., Barthelemy, M., and Johnsen, M. G.: Latest news about the auroral emission polarisation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19091, https://doi.org/10.5194/egusphere-egu24-19091, 2024.

14:55–15:05
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EGU24-3725
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On-site presentation
Qian Wu, Dong Lin, Wenbin Wang, Liying Qian, Geohwa Jee, Changsup Lee, and Jeong-han Kim

Using the HIWIND balloon and Antarctic Jang Bogo station high latitude conjugate observations of the thermospheric winds we investigate the seasonal and hemispheric differences between the northern and southern hemispheres in June 2018.   We found that the summer (northern) hemisphere dayside meridional winds have a double hump feature, whereas in the winter (southern) hemisphere the dayside meridional winds have a single hump feature.   We attribute that to stronger summer, perhaps, northern hemisphere cusp heating.   We also compared the observation with NCAR TIEGCM (Thermosphere Ionosphere Electrodynamics General Circulation Model) and GTR (GAMERA TIEGCM RCM) models. The TIEGCM reproduced the double hump feature because of added cusp heating.    The summer hemisphere has stronger anti-sunward winds.  This is the first time we have very high latitude conjugate thermospheric wind observations.   

How to cite: Wu, Q., Lin, D., Wang, W., Qian, L., Jee, G., Lee, C., and Kim, J.: HIWIND Balloon and Antarctica Jang Bogo FPI High Latitude Conjugate Thermospheric Wind Observations and Simulations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3725, https://doi.org/10.5194/egusphere-egu24-3725, 2024.

15:05–15:15
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EGU24-14342
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On-site presentation
Space Weather Ionospheric Network Canada (SWINCan)
(withdrawn)
Christopher Watson, Thayyil Jayachandran, and Anton Kascheyev
15:15–15:25
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EGU24-1554
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ECS
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On-site presentation
Changzhi Zhai, Tong Dang, Yibin Yao, and Jian Kong

The three‐dimensional computerized ionospheric tomography (3DCIT) technique has been used to reconstruct the ionospheric response to the 21 June 2020 annular solar eclipse and the results are evaluated by constellation observing system for meteorology, ionosphere, and climate (COSMIC) observations. The 3DCIT-derived electron density (Ne) difference between the eclipse and quiet days showed that the Ne depletion was between 200-550 km and the maximum magnitude was about -3.0×1011 el/m3 which was at 280 km in altitude. The contributions from below 250 and 350 km altitudes to VTEC (Vertical Total Electron Content) depletion were ~30% and ~60%, respectively. Significant asymmetry of Ne depletion with respect to the eclipse path was captured in 3DCIT results, and the deviation conditions between the Ne depletion central line and eclipse path varied at different altitudes. Simulations with the thermosphere‐ionosphere‐electrodynamics general circulation model (TIEGCM) generally showed consistent ionospheric variations with GNSS (Global Navigation Satellite System) VTEC and 3DCIT electron density. Furthermore, term analysis on the ion continuity equation indicates that the asymmetry of Ne depletion was mainly induced by the neutral wind disturbance which converged toward the eclipse region and caused opposite transport effects on both sides of the eclipse path. The thermospheric composition was also changed by disturbed neutral wind and impacted plasma production and loss rates, contributing to the Ne depletion asymmetry.

How to cite: Zhai, C., Dang, T., Yao, Y., and Kong, J.: Three-Dimensional Ionospheric Evolution and Asymmetry of the Electron Density Depletion Generated by the 21 June 2020 Annular Solar Eclipse, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1554, https://doi.org/10.5194/egusphere-egu24-1554, 2024.

15:25–15:35
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EGU24-4444
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On-site presentation
Gareth Perry, Katarzyna Beser, and Angeline Burrell

Ionization patches are a common feature of the polar-cap, F-region ionosphere. Patches can be detected using a variety of remote sensing instruments including optical imagers and incoherent scatter radars. Due to their pronounced plasma density gradients, patches are believed to be a strong source of decameter-scale field-aligned-irregularities which are responsible for ionospheric backscatter observed by High Frequency (HF; 3 – 30 MHz) over-the-horizon (OTH) radar systems. Indeed, Super Dual Auroral Radar Network (SuperDARN) systems at high latitudes have been used for investigating polar-cap patches for decades. Current techniques for identifying patches in SuperDARN ionospheric backscatter data are rudimentary and labor intensive as they require human intervention—an automated detection algorithm does not yet exist. This presentation will detail progress on the development of an automated algorithm for detecting patches in SuperDARN ionospheric backscatter data. The end-goal of the development effort is to transition the algorithm into a near real-time patch detection capability for SuperDARN and other OTHR systems. Patches are an important signature of magnetosphere-ionosphere-thermosphere (M-I-T) coupling in the polar regions; they are also an agent of space weather as they are a source of HF scintillation there. An automated algorithm for detecting patches will allow for their potentially hazardous influence on HF radio wave propagation conditions to be identified and mitigated.

How to cite: Perry, G., Beser, K., and Burrell, A.: F-region ionization patches in High Frequency over-the-horizon radar data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4444, https://doi.org/10.5194/egusphere-egu24-4444, 2024.

15:35–15:45
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EGU24-13945
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On-site presentation
Nozomu Nishitani and Tomoaki Hori

During periods of severe geomagnetic activity, auroras can be observed at much lower geomagnetic latitudes than the average auroral oval, e.g., lower than 40 degrees. Although several papers discussed the possible generation mechanisms for these auroras, their relationship with the ionospheric plasma convection pattern or the electric field distribution is not well understood, mainly because there are few observation data available.

The SuperDARN (SD) Hokkaido East and West radars, located at the lowest geomagnetic latitude among the SD radars at present, have been operating since 2006 and 2014, respectively, and observed ionospheric plasma convection patterns for three storm events in March 2015, November 2023, and December 2023, when low-latitude aurora was observed in Rikubetsu, Hokkaido, Japan (geomagnetic latitude: 37 degrees). Generally, the low-latitude auroral precipitation regions are accompanied by a shear of east-west ionospheric flows, although the detailed flow structure differs for each event. Some discussions and interpretations of these plasma flow patterns associated with the low-latitude auroras will be presented.

How to cite: Nishitani, N. and Hori, T.: SuperDARN observation of ionospheric plasma flows associated with low-latitude auroras in Hokkaido, Japan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13945, https://doi.org/10.5194/egusphere-egu24-13945, 2024.

Coffee break
Chairpersons: Sophie Maguire, Jade Reidy, Andrew J. Kavanagh
16:15–16:45
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EGU24-9787
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solicited
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Highlight
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Virtual presentation
Thomas Ulich, Ingemar Häggström, Axel Steuwer, Anders Tjulin, Carl-Fredrik Enell, and Maria Mihalikova and the EISCAT Staff

The EISCAT Scientific Association is currently building the most advanced 3-dimensional imaging radar for atmospheric, ionospheric and near-Earth space investigations. The fully steerable, tri-static, phased-array incoherent scatter radar is located in Skibotn (inland from Tromsø, Norway), Karesuvanto (Finland, north of Kiruna), and Kaiseniemi (Sweden, west of Kiruna). The transmit-receive array at Skibotn consists of about 10,000 aerials and ten 91-aerial outrigger receivers in the immediate vicinity. The receive-only arrays of Kaiseniemi and Karesuvanto consist of about 5,000 aerials each. Construction of the facility began after the project kick-off in September 2017. During 2024, EISCAT_3D will gradually begin operations, starting with a seven-element test system and expanding from that. EISCAT_3D will replace the EISCAT mainland radars, i.e. the mono-static, 930-MHz UHF radar at Tromsø and the tri-static, 224-MHz radar at Tromsø with additional receivers at Sodankylä (Finland) and Kiruna (Sweden). The EISCAT Svalbard Radar (ESR) and the Ionospheric Heating facility at Tromsø will not be affected by EISCAT_3D becoming operational. Here we give an status update of the new facility. EISCAT_3D is a European Strategy Forum for Research Infrastructures (ESFRI) Landmark in the Environment domain.

How to cite: Ulich, T., Häggström, I., Steuwer, A., Tjulin, A., Enell, C.-F., and Mihalikova, M. and the EISCAT Staff: EISCAT_3D – Volumetric Phased-Array Incoherent Scatter Radar in the European Arctic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9787, https://doi.org/10.5194/egusphere-egu24-9787, 2024.

16:45–16:55
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EGU24-3847
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Virtual presentation
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Spencer Mark Hatch, Ilkka Virtanen, and International Space Science Institute Team 506

The EISCAT_3D incoherent scatter radar presents a groundbreaking opportunity for studying a wide variety of phenomena. One of the challenges presented by such an advanced facility is its tremendous flexibility: Given a science question and an estimate of the the associated ionospheric conditions, how does one begin to design an EISCAT_3D experiment? Here we present a set of open-source tools written primarily in R and Python for estimating uncertainties of EISCAT_3D measurements of three scalar quantities (plasma density, electron and ion temperature) and one vector quantity (ion drift) for arbitrary radar configurations and different combinations of beams. Using these tools one can assess whether a candidate EISCAT_3D experiment is likely to achieve the temporal and spatial resolution needed to study a particular phenomenon, and vary parameters such as beam width, bit length, and duty cycle to understand their effect on experimental uncertainties. As a demonstration we use these tools to assess the uncertainty of maps of F-region ionospheric convection reconstructed from EISCAT_3D ion drift measurements.

How to cite: Hatch, S. M., Virtanen, I., and Team 506, I. S. S. I.: e3doubt: An open-source toolkit for E3D experiment planning and uncertainty estimation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3847, https://doi.org/10.5194/egusphere-egu24-3847, 2024.

16:55–17:05
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EGU24-8301
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ECS
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On-site presentation
Juan Araujo, Stefan Johansson, Assar Westman, and Madelen Bodin

Incoherent scatter radar (ISR) techniques provide reliable measurements for the analysis of ionospheric plasma. Measurements of electron and ion densities, temperatures, and line-of-sight velocities are derived by employing antennas that transmit and receive radio waves. Recent developments in ISR technologies are capable of generating high-resolution volumetric data from multiple beam measurements. Examples of such technologies employ the so-called phased array antennas like the AMISR in North America or the upcoming EISCAT_3D in the northern Fennoscandia region. Traditional visualization methods, for example, 2D projections, applied to volumetric images render a reduced set of the available data and important aspects of the data may be lost to the analyst.
     
We present an interactive approach for the exploration and visualization of spatio-temporal and volumetric ionospheric data. The strategy is targeted at offering the analyst a wider range of alternatives in order to interpret ISR data. The proposed novel strategy allows for the reconstruction of ionospheric volume images by means of a novel sparse interpolation algorithm tailored for the particular features of ISR data. The interpolation offers estimation of gradients and processing of the challenging case of missing data. The reconstructed image is output by using volume rendering combined with customizable transfer functions. We propose to utilize reconstructed volumetric images for the estimation of ionospheric conductivities and volumetric currents, which in turn can be used for studying the evolution of storms and substorms in the ionosphere.

How to cite: Araujo, J., Johansson, S., Westman, A., and Bodin, M.: Post-processing and visualization of ISR data , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8301, https://doi.org/10.5194/egusphere-egu24-8301, 2024.

17:05–17:15
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EGU24-7173
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ECS
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On-site presentation
Taishi Hashimoto

EISCAT_3D is an international research infrastructure consisting of multiple phased-array incoherent-scatter radars in the northmost areas of Norway, Finland, and Sweden. Since EISCAT_3D is capable of rapid and flexible beam steering with a high transmission power, it is considered to be potentially dual-use, as it could be used to track any objects in orbit, including military satellites. Hence, the radar system has a software component that automatically filters out the echoes from hard targets in real-time, called Hard Target Echo Removal (HTER). There are many satellites and space debris in orbit nowadays, and a large amount of data would be discarded if the HTER procedure was too simple just to throw data packets with hard target echoes.
Meanwhile, each antenna array of EISCAT_3D is composed of multiple receivers, enabling adaptive array signal processing. The direction of arrivals for the incoherent scatter and interference from hard targets would be different, as the former comes from the main lobe while the latter from the sidelobe; hence, the interference would be efficiently suppressed with the directionally-constrained minimization of power (DCMP) approach with a constraint to the loss of the signal-to-noise ratio for the incoherent scattering signal.
In this presentation, the effectiveness of the adaptive array signal processing is demonstrated on a simulation with realistic settings of the standard experiment of the EISCAT_3D to mitigate the number of discarded data with the HTER processing.

How to cite: Hashimoto, T.: Adaptive sidelobe suppression to mitigate interference from hard targets in EISCAT_3D, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7173, https://doi.org/10.5194/egusphere-egu24-7173, 2024.

17:15–17:25
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EGU24-19112
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On-site presentation
Estimating ionospheric currents using one plasma line and NHDS dispersion relation solver 
(withdrawn)
Patrick Guio and Mini Gupta
17:25–17:35
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EGU24-20593
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On-site presentation
Feng Ding, Xinan Yue, Yihui Cai, Junyi Wang, and Linxuan Zhao

Previous observations shows that during rocket launches, the water in the plume released by rockets usually caused a wide range of ionosphere electron density depletion. While a number of publications devoted to the horizontal variations of such ionosphere holes, observation of the vertical features of ionosphere holes has seldom been reported. In this paper, we used the Sanya Incoherent Scattering Radar (SYISR) to observe the vertical variations of the ionosphere hole during two rocket launch events in year 2022. Both the rockets passed through the topside ionosphere over the China South Sea, with an estimated minimum distance of ~100-300 km from SYISR. About ~15 min after the rocket launch, we observed the ionosphere hole with an altitude range of ~200-800 km. The maximum electron density depletion of -20% occurred at ~420 km, with a duration of 2.2 hours. Based on the observations, we discussed the diffusion of water molecules and its influences on altitude distribution of the ionosphere holes during the rocket launches.

How to cite: Ding, F., Yue, X., Cai, Y., Wang, J., and Zhao, L.: Vertical features of the ionospheric holes during rocket launches observed by the Sanya Incoherent Scattering Radar, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20593, https://doi.org/10.5194/egusphere-egu24-20593, 2024.

17:35–17:45
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EGU24-9902
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ECS
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On-site presentation
Gopika Prasannakumara Pillai Geethakumari, Anita Aikio, Lei Cai, Heikki Vanhamäki, Ilkka Virtanen, Anthea J. Coster, Aurellie Marchaudon, Pierre-Louis Blelly, Astrid Maute, Nada Ellahouny, Johannes Norberg, Shin Oyama, and Maxime Grandin

During the declining phase of the solar cycle, geomagnetic storms, primarily driven by high-speed solar wind streams (HSSs) and associated co-rotation interaction regions (CIRs), become prominent. One of the major effects of these storms are the F region electron density perturbations, usually referred to as ionospheric storms. This study focuses on a positive ionospheric storm, characterized by an increase in electron density at mid-latitudes (40°- 60° MLAT) and observed during a moderate yet prolonged HSS/CIR-driven geomagnetic storm with a SYM-H minimum of -65 nT. The storm commenced on 14 March 2016 at 17:20 UT with a strong storm sudden commencement (SSC) and lasted until 21 March. This study uses global navigation satellite system (GNSS) total electron content (TEC) data for a global perspective of electron density variations and Millstone Hill incoherent scatter radar (52° MLAT, MLT=UT-4.6) data to provide local measurements of plasma parameters during the positive storm.

In the global analysis of the TEC variations during the storm, a 6-h long strong positive ionospheric storm (TEC increase up to 50 %) at the mid-latitudes was observed in the day and dusk sectors, whereas a depletion in TEC (negative storm) prevailed at the high latitudes. The positive ionospheric storm initiated during the SSC and subsequently intensified with the onset of the main phase. The local electron density data from the Millstone Hill incoherent scatter radar showed an enhancement throughout the local evening MLTs. An uplift in the peak height together with an increased line-of-sight upward ion velocity was observed simultaneously as the traveling ionospheric disturbances (TIDs) reached Millstone Hill from the north-east direction with a phase velocity of 760 m/s. When the plasma is uplifted to greater altitudes in the F region, the recombination rate becomes slower and electron density may be enhanced. The TIDs were plausibly triggered by the Joule heating at high latitudes during the main phase of the geomagnetic storm. After the initial uplift, the peak height of electron density at Millstone Hill descended but electron densities were further enhanced. We will discuss the possible mechanisms including transportation of oxygen-rich air from high to mid latitudes when interpreting the measurements.

How to cite: Prasannakumara Pillai Geethakumari, G., Aikio, A., Cai, L., Vanhamäki, H., Virtanen, I., Coster, A. J., Marchaudon, A., Blelly, P.-L., Maute, A., Ellahouny, N., Norberg, J., Oyama, S., and Grandin, M.: HSS/CIR Driven Positive Ionospheric Storm at Mid-latitudes: Insights from Millstone Hill Radar and GNSS TEC measurements, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9902, https://doi.org/10.5194/egusphere-egu24-9902, 2024.

17:45–17:55
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EGU24-16550
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Virtual presentation
Leslie J. Lamarche, Asti Bhatt, and Roger Varney

The Advanced Modular Incoherent Scatter Radars (AMISR) are monostatic phased-array incoherent scatter radars.  A technique for estimating the 3D plasma drift velocity vectors from line-of-sight velocity measurements across the radar field-of-view was originally published in Heinselman and Nicolls [2008].  We discuss recent improvements to this algorithm, including better error filtering and more rigorous treatment of magnetic coordinate systems, as well as a re-examination of the underlying assumptions.  These improvements result in better fidelity of the resolved vector velocities data product, which generally now cover a larger geographic area with smaller errors. Initial results are discussed, as well as next steps for the resolved vector velocities data product.

 

How to cite: Lamarche, L. J., Bhatt, A., and Varney, R.: Improvements to the AMISR Resolved Vector Velocities Data Product, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16550, https://doi.org/10.5194/egusphere-egu24-16550, 2024.

17:55–18:00

Posters on site: Thu, 18 Apr, 16:15–18:00 | Hall X3

Display time: Thu, 18 Apr, 14:00–Thu, 18 Apr, 18:00
Chairpersons: Jade Reidy, Sophie Maguire, Neethal Thomas
X3.1
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EGU24-7480
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ECS
Mizuki Fukizawa, Yasunobu Ogawa, Koji Nishimura, Genta Ueno, Takanori Nishiyama, Taishi Hashimoto, and Takuo Tsuda

We conducted a feasibility study to estimate the horizontal ion velocity field in the ionospheric F region from ion velocities observed by the EISCAT_3D radar. We assumed a 27-beam configuration with a minimum elevation angle of 30 degrees. The ion velocity observation data from 200 km to 500 km altitude were projected to 200 km altitude, assuming ions above 200 km altitude follow the E x B drift. Then, we reconstructed ion velocity vectors for ±250 km in the east-west direction and ±500 km in the north-south direction at 200 km altitude. The resolution in north-south and east-west directions was 25 km. The reconstruction was conducted by maximizing a posterior probability based on Bayes’ theorem. The constraints were set to minimize the L2 norms of the following four vectors in the horizontal plane: (1) the first and (2) the second derivative of three components of the ion velocity vector, (3) the divergence of the ion velocity perpendicular to the magnetic field lines, and (4) the ion velocity parallel to the magnetic field lines. We investigated which combination of the four constraints would reconstruct the shear flow field most correctly and found that the best combination was (2), (3), and (4).

How to cite: Fukizawa, M., Ogawa, Y., Nishimura, K., Ueno, G., Nishiyama, T., Hashimoto, T., and Tsuda, T.: Feasibility study to estimate the ion velocity field in the F region from EISCAT_3D radar observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7480, https://doi.org/10.5194/egusphere-egu24-7480, 2024.

X3.2
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EGU24-17198
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ECS
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Mahith Madhanakumar, Andres Spicher, Juha Vierinen, and Kjellmar Oksavik

Scintillation causing irregularities can occur in the E region or the F region ionosphere or even in both. This is due to the stochastic nature of the ionosphere that varies with the time of day, latitudes, seasons, solar and geomagnetic effects, etc. The relative importance of the different regions in hosting irregularities that can cause scintillation at GNSS frequencies in the dayside high latitude ionosphere is yet to be established. This study makes use of the 32-m European Incoherent SCATer (EISCAT) radar on Svalbard (ESR) to identify the ionospheric signatures during scintillation events. In particular, it takes advantage of the fast-scanning capability of ESR allowing it to image large areas of the ionosphere. This allows to capture ionospheric phenomena over a wide range of geographic latitudes in a short span of time. The scintillation measurements are obtained from the receiver installed at the nearby Kjell Henriksen Observatory (KHO) which can track signals from multiple GNSS constellations simultaneously. By combining the radar observations with scintillation measurements, the source regions responsible for GNSS scintillation at the dayside auroral/cusp regions are identified and characterized. The results are discussed in the context of nighttime statistics when patches and auroral dynamics are responsible for strong scintillation in GNSS signals. The results shown help better understand the impact of ionospheric irregularities on radio wave propagation in the high latitude ionosphere. Furthermore, the capability of extending the analysis to the upcoming EISCAT 3D using a simultaneous multi-beam multi-direction pattern is emphasized.

How to cite: Madhanakumar, M., Spicher, A., Vierinen, J., and Oksavik, K.: Source regions of irregularities causing GNSS radio scintillation: An investigation using EISCAT, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17198, https://doi.org/10.5194/egusphere-egu24-17198, 2024.

X3.3
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EGU24-17646
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ECS
Jade Reidy and Andrew Kavanagh

The mesosphere/lower-thermosphere/ionosphere (MLTI) region is a critical boundary in the coupling of the atmosphere, climate and space weather, however it is one of the least understood regions, making it hard to include in whole atmosphere models. The EISCAT radars at Tromsø (UHF and VHF) have been measuring ionospheric parameters, such as electron density, for almost 4 decades making them an excellent resource to study changes in the ionosphere over a long time period.  We have generated two data archives using 20 years of observations of EISCAT Tromsø from 2001 to 2021; the data have been re-analysed at 10-minutes and 1-hour integrations. These archives are used to study the different sources of variability in the MLTI from 50-200 km. This is the first time the mainland EISCAT data has been converted into a format that allows for long term statistical study. We have created electron density climatologies split by solar, geomagnetic and atmospheric indices to investigate the different drivers of variability in the MLTI region. We show seasonal averages of the electron density altitude profiles and compare our results to the Empirical Canadian High Arctic Ionospheric Model (E-CHAIM) and the Whole Atmosphere Community Climate Model.

How to cite: Reidy, J. and Kavanagh, A.: Investigating seasonal to decadal variability in the electron density of the mesosphere using historical EISCAT data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17646, https://doi.org/10.5194/egusphere-egu24-17646, 2024.

X3.4
|
EGU24-17680
Andrew J. Kavanagh, Adrian Grocott, Maria-Theresia Walach, Jade Reidy, and Mark Clilverd

The important question of how much of the variability in the high latitude ionosphere is driven by atmospheric processes as opposed to space weather impacts remains unanswered.  The EISCAT-3D radar provides a unique opportunity to probe this variability across multiple spatial and temporal scales. One of the key aims of the DRIIVE project (DRivers and Impacts of Ionospheric Variability with EISCAT-3D) is to determine the balance of energy input to the lower ionosphere and quantify the variability under different atmospheric and geomagnetic conditions.  Here we present a preliminary study of the variability using historic data from the EISCAT UHF radar taken over the course of several years in the winter months. We identify wave like signatures that occur simultaneously with Travelling Ionospheric Disturbances (TID) as seen in coherent radar data (SuperDARN), alongside enhancements due to energetic precipitation.  The magnitude of the variations are compared for different years and different driving conditions. This study will allow us to optimize the design of future experiments for EISCAT-3D to study the variability while developing effective analysis techniques to maximise utility of the new radar system.

How to cite: Kavanagh, A. J., Grocott, A., Walach, M.-T., Reidy, J., and Clilverd, M.: Identifying sources of Ionospheric Variability: planning for EISCAT-3D operations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17680, https://doi.org/10.5194/egusphere-egu24-17680, 2024.

X3.5
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EGU24-14792
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ECS
Mini Gupta and Patrick Guio

In the Incoherent Scatter Radar (ISR) spectrum, we observe a large amount of scattered power at frequencies corresponding to plasma electrostatic modes with wavenumber imposed by the radar. The commonly occurring resonant frequencies are ion and plasma lines. Ion lines are signatures of ion-acoustic waves travelling towards and away from the radar and are observable all the time. Plasma lines are signatures of high-frequency electrostatic waves and are observable when enhanced above the thermal level by a suprathermal electron population. In this work, we assume a Maxwellian thermal population together with a suprathermal population derived from the electron transport code Aeroplanets that calculates the angular electron flux. We provide the numerical electron velocity distribution function as an input to the Arbitrary Linear Plasma Solver (ALPS) to numerically solve the linear Vlasov-Maxwell dispersion relation and estimate the resonance frequency at angles to the magnetic field. The linear resonance frequency calculated from ALPS is then compared to the resonance frequency estimated from ISR plasma line measurements.  

How to cite: Gupta, M. and Guio, P.: Modelling ISR plasma line frequency using ALPS dispersion relation solver , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14792, https://doi.org/10.5194/egusphere-egu24-14792, 2024.

X3.6
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EGU24-15254
Mathieu Barthelemy and Elisa Robert

The auroral emissions are due to electron precipitations into the upper atmosphere in polar regions. These electrons populations, called suprathermal, due to their high energies (10 eV to 50/100 keV) generates some emissions mainly in the green (O I 557 nm), the red (O I 630-636 nm) and the purple (N2+ 427 nm). However the spectra contains much more lines especially molecular bands such as the 1st , 2nd postive bands and the Vegard Kaplan band of molecular nitrogen which produces structured vibrational emissons. It is then important to be able to get quasi exhaustive simulations of these emissions. Based on kinetic calculations from the Transsolo code, we implemented simulations of almost all the visible emissions lines of the auroras parametized by the particle precipitations. The code used MSIS 2.0 as atmospheric model, IRI  2020 for the ionosphere and a very large set of updated cross sections. We propose in this work to present the result of these simulatins in different conditions and to consider the potential uses of such calculations for different auroral physics applications.

How to cite: Barthelemy, M. and Robert, E.: Synthetic spectra of the auroras, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15254, https://doi.org/10.5194/egusphere-egu24-15254, 2024.

X3.7
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EGU24-6117
Hervé Lamy, Gaël Cessateur, Leo Bosse, David Bolsée, Mathieu Barthélemy, Thierry Sequies, and Magnar Gullikstad Johnsen

In October 2023, a spectrograph has been permanently installed at the Skibotn Observatory (Norway) in order to regularly monitor the auroral spectrum between ~ 400 and 700 nm with a time resolution of 30 seconds. Using a 300 lines/mm grating and a slit of 100 nm width, the wavelength resolution is approximately of 0.3 nm.  The instrument is pointing field-aligned.

The characteristics of the instrument will be provided as well as examples of spectra obtained during quiet, moderate and strong geomagnetic conditions.  A relative flux calibration is currently under way and will be discussed as well.  This will allow the computation of line ratios or a comparison with synthetic spectra obtained using kinetic transport codes such as e.g. Transsolo. Both approaches will provide an estimate of the precipitating fluxes (for electrons but also possibly for protons).

Later on we aim to provide a database of low resolution auroral spectra accessible to the community, which will nicely complement data obtained with the new EISCAT_3D radar located a few kilometers from the observatory and data from the other optical instruments located at the observatory itself.  We will also consider the possibility to obtain higher resolution spectra using a 1800 lines/mm grating during specific requested campaigns.

This project is a joint collaboration between BIRA-IASB (Belgium), IPAG (France) and UiT (Norway).

How to cite: Lamy, H., Cessateur, G., Bosse, L., Bolsée, D., Barthélemy, M., Sequies, T., and Johnsen, M. G.: Optical auroral spectra obtained at the Skibotn Observatory, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6117, https://doi.org/10.5194/egusphere-egu24-6117, 2024.

X3.8
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EGU24-19428
Daniel Whiter, Jonathan Rae, Srimoyee Samaddar, Patrik Krcelic, Betty Lanchester, Ishbel Carlyle, Nicholas Brindley, Kamalam Thillaimaharajan, and Robert Fear

We have constructed a new high-resolution auroral imager, called Embla, to simultaneously measure energy and flux of auroral precipitation, neutral temperature, and electric fields in fine scale aurora. Embla is designed primarily for studies of auroral electrodynamics, substorm onset, and neutral heating by aurora. The instrument has recently been installed at Skibotn, Norway, very close to the EISCAT_3D radar transmitter site, and we expect the combination of radar and optical observations to enable better measurements for our science than either instrument can provide alone.

Embla builds on work done using the Auroral Structure and Kinetics (ASK) instrument, which has been stationed at the EISCAT Svalbard Radar since 2007. Embla has a spatial resolution in the E-region of ~30 m and a planned temporal resolution of at least 32 frames per second, allowing us to resolve the fine-scale structure and rapid dynamics of auroral features. It consists of 4 co-aligned imagers with identical 9 degree fields of view centred on magnetic zenith. Each imager is equipped with a different narrow passband interference filter, targetting emissions in N2 1P (2 imagers), OI 777.4 nm, and O+ 2P. The combination of N2 1P and OI 777.4 nm observations allows us to image the characteristic energy and flux of auroral electron precipitation. The O+ 2P emission has a long lifetime of 5 s, providing a means to observe ion drift perpendicular to the magnetic field and therefore a way to determine ionospheric electric fields at very high cadence in localised regions around the aurora. Finally, by combining observations from two of the imagers in separate regions of the N2 1P band we can image the neutral temperature at the altitude of the auroral emission. The simultaneous measurement of these properties of the aurora and ionosphere will allow us to investigate auroral electrodynamics in detail.

How to cite: Whiter, D., Rae, J., Samaddar, S., Krcelic, P., Lanchester, B., Carlyle, I., Brindley, N., Thillaimaharajan, K., and Fear, R.: Embla: A new optical instrument to measure auroral precipitation, neutral temperature and electric fields at high resolution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19428, https://doi.org/10.5194/egusphere-egu24-19428, 2024.

X3.9
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EGU24-18848
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ECS
Kamalam Thillaimaharajan, Daniel Whiter, Nicholas Brindley, and Patrik Krcelic

Ground based optical observations of aurora reveal fine scale structures with brightness width less than 10 kms in the direction perpendicular to B. These fine scale structures exhibit a phenomenon called arc splitting, also known as bifurcating elemental arcs or packets. One can witness the arc splitting in the auroral image when elemental arcs peel away from a central bright arc which is then followed by the generation of new arcs. Dispersive Alfvén waves have been suggested as a possible generation mechanism for this phenomenon. Semeter et al., JGR 2008 interpreted the observations of splitting elemental arcs with respect to inertial Alfvén waves. They suggested that the energy of the precipitating electrons should decrease as the arc packets move away from the central bright arc. We tested this theory by using the data from the multi spectral imager called ASK (Auroral Structure and Kinetics) stationed on Svalbard. The energy and flux of the precipitating electrons are calculated from the ASK data and Southampton ionospheric model. We used empirical number density and IGRF (International Geomagnetic Reference Field) model to calculate the properties of the inertial Alfvén waves. A comparison between the splitting elemental arcs and Alfvén waves indicates that the wave particle interaction between Alfvén waves and the precipitating electrons is a possible generation mechanism for the production of these splitting elemental arcs. From our data and calculations, we infer an acceleration height of precipitating electrons just under 3000 km.

 

References:

Semeter, J., M. Zettergren, M. Diaz, and S. Mende (2008), Wave dispersion and the discrete aurora:

New constraints derived from high-speed imagery, J. Geophys. Res., 113, A12208.

How to cite: Thillaimaharajan, K., Whiter, D., Brindley, N., and Krcelic, P.: Splitting elemental arcs of aurora and their association with inertial Alfvén waves, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18848, https://doi.org/10.5194/egusphere-egu24-18848, 2024.

X3.10
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EGU24-3145
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ECS
Penghao Tian

Ionospheric sporadic E layers (Es) are intense plasma irregularities between 80 and 130 km in altitude and are generally unpredictable. Reconstructing the morphology of sporadic E layers is not only essential for understanding the nature of ionospheric irregularities and many other atmospheric coupling systems, but is also useful for solving a broad range of demands for reliable radio communication of many sectors reliant on ionosphere-dependent decision-making. Despite the efforts of many empirical and theoretical models, a predictive algorithm with both high accuracy and high efficiency is still lacking. Here we introduce a new approach for Sporadic E Layer Forecast using Artificial Neural Networks (SELF-ANN). The prediction engine is trained by fusing observational data from multiple sources, including a high-resolution ERA5 reanalysis dataset, Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) radio occultation (RO) measurements, and integrated data from OMNIWeb. The results show that the model can effectively reconstruct the morphology of the ionospheric E layer with intraseasonal variability by learning complex patterns. The model obtains good performance and generalization capability by applying multiple evaluation criteria. The random forest algorithm used for preliminary processing shows that local time, altitude, longitude, and latitude are significantly essential for forecasting the E-layer region. Extensive evaluations based on ground-based observations demonstrate the superior utility of the model in dealing with unknown information. The presented framework will help us better understand the nature of the ionospheric irregularities, which is a fundamental challenge in upper-atmospheric and ionospheric physics. Moreover, the proposed SELF-ANN can make a significant contribution to the development of the prediction of ionospheric irregularities in the E layer, particularly when the formation mechanisms and evolution processes of the Es layer are not well understood.

How to cite: Tian, P.: Ionospheric irregularity reconstruction using multisource data fusion via deep learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3145, https://doi.org/10.5194/egusphere-egu24-3145, 2024.

X3.11
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EGU24-6197
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ECS
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solicited
|
|
Sophie Maguire, Alan Wood, and David Themens

The terrestrial ionosphere is a highly variable medium that affects the propagation of radio waves. Within the ionosphere, large-scale structures, such as polar cap patches, auroral forms, blobs, and polar holes, have been observed. Small-scale irregularities associated with these large-scale structures result from instability processes which can lead to scintillation of trans-ionospheric radio signals, such as those used for Global Navigation Satellite Systems (GNSS). To investigate plasma irregularities and scintillation in the high-latitude ionosphere, the Scales of Ionospheric Plasma Structuring (SIPS) experiment was conducted using a suite of ground-based instrumentation between the 3rd and 15th of January 2024.

The aim of the SIPS experiment was to observe the high-latitude ionosphere across several scale sizes, and this required a variety of ground-based instruments, in conjunction with the Swarm satellites. The European Incoherent SCATter (EISCAT) radars were used to measure the plasma parameters, such as density, giving indication to the presence of large-scale plasma structures that were several hundreds of km in size. Medium-scale plasma irregularities, with scale sizes of several km, were inferred from the ground by the LOw Frequency ARray (LOFAR) and the Kilpisjärvi Atmospheric Imaging Receiver Array (KAIRA). Smaller-scale irregularities less than 500m in scale size were inferred from the scintillation data from ground-based GNSS receivers giving an indication to the scintillation effects. To assist in the interpretation of the results, the Swarm Ionospheric Scintillation (SWIS) methodology was also used, which utilises data from the Swarm satellites to give a spectrum of irregularities to scale sizes down to 500m (Spogli et al., 2022). Using this array of observations, the relationship between irregularities of varying scale sizes could be explored, along with the formation and generation of small-scale irregularities due to instability mechanisms and the subsequent scintillation effects which can occur.

The combination of both ground-based and space-based instruments in this experiment, observing and modelling the ionospheric plasma, gives unprecedented coverage of varying scale sizes which is not possible with individual instrumentation alone. 72 hours of EISCAT observation time was awarded for this experiment which was carried out over 5 nights in January 2024 between 18:00 and 23:59 UT. These experiments yielded a wealth of new results, the most significant of which will be discussed in this presentation.

Spogli, L., Iman, R., Alfonsi, L., Cesaroni, C., Jin, Y., Clausen, L., Wood, A., & Miloch, W. J. (2022). Feasibility of a Swarm Ionospheric Scintillation (SWIS) proxy for L-band scintillation. AGU Fall Meeting 2022.

How to cite: Maguire, S., Wood, A., and Themens, D.: Observing plasma structures at multiple scale sizes in the high-latitude ionosphere with a suite of ground-based instrumentation. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6197, https://doi.org/10.5194/egusphere-egu24-6197, 2024.

X3.12
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EGU24-20754
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ECS
Diurnal and seasonal variation in the ion flux in relation to altitude
(withdrawn after no-show)
Chizurumoke Michael, Timothy David, Nurudeen Bakare, Abayomi Ajetunmobi, and Tunde Awoyinka
X3.13
|
EGU24-8057
Veronika Barta, Tamás Bozóki, Dávid Péter Süle, Daniel Kouba, Jens Mielich, Tero Raita, and Attila Buzás

The sudden increase of Solar X-ray and EUV emission following solar flares causes ionization and increased absorption of electromagnetic (EM) waves in the sunlit hemisphere of the Earth’s ionosphere. Solar flares are also accompanied by energetic particles which can lead to additional ionization and absorption especially at the higher latitudes (> 60 °). A novel method has been developed by Buzás et al. [1] based on the amplitude data of the EM waves measured by Digisondes to calculate and investigate the relative absorption changes (compared to quiet period) occurring during solar flares. The effect of 13 intense (>C4.8) solar flares that occurred between 06:00 and 16:30 (UT, daytime LT = UT+2 h) from 04 to 10 September 2017 have been studied using the so-called "amplitude method". Total and partial radio fade-outs, furthermore, +20%–1400% amplitude changes (measured at 2.5 and 4 MHz) were experienced at three Digisonde stations (Juliusruh (54.63° N, 13.37° E), Průhonice (49.98° N, 14.55° E) and San Vito (40.6° N, 17.8° E)) during and after the investigated flares.

In the present study we compare the results of the amplitude method with the absorption changes measured by the Finnish Riometer Chain and determined by the NOAA D-RAP model during the same solar flare events. The X-class flares caused 1.5–2.5 dB attenuation at 30–32.5 MHz based on riometer data, while the absorption changes were between 10 and 15 dB in the 2.5–4.5 MHz frequency range (thus 10 times higher) according to the amplitude data measured by the Digisondes. The impact caused by the energetic particles after the solar flares are clearly seen in the riometer data, while it can be observed only at Juliusruh (~55°) at some certain cases among the Digisonde stations. Therefore, the absorption changes as a result of the particle precipitation is significant at high latitudes, but decreases rapidly with decreasing latitude, and is no longer detectable below the sub-auroral region. The main conclusion from the comparison of the amplitude method with the D-RAP model is that the model underestimates the values obtained from the Digisonde's measurements at both 2.5 and 4 MHz in almost every case. The differences varied between 0.2 and 15 dB at 2.5 MHz and 2.9–10 dB at 4 MHz and they did not show any systematic trend with the intensity of the flare, or with the latitude of the station. 

[1] Buzás, A., Kouba, D., Mielich, J., Burešová, D., Mošna, Z., Koucká Knížová, P., & Barta, V. (2023). Investigating the effect of large solar flares on the ionosphere based on novel Digisonde data comparing three different methods. Frontiers in Astronomy and Space Sciences, 10.

How to cite: Barta, V., Bozóki, T., Süle, D. P., Kouba, D., Mielich, J., Raita, T., and Buzás, A.: Ionospheric absorption variation as measured by European Digisondes, riometers and determined by the NOAA D-RAP model during intense solar flares in September, 2017, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8057, https://doi.org/10.5194/egusphere-egu24-8057, 2024.

X3.14
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EGU24-8363
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ECS
Muyiwa Paul Ajakaiye, Ben Romano, and Yuval Reuveni

The idea of searching for the manifestations of solar and geomagnetic events on a very low frequency and low frequency (VLF/LF, 3-30/0.5-470 kHz) radio signals as a means of probing the ionospheric  D-region has drawn much attention in the last few decades. In this study, we present the impacts of the 22-26 March 2023 geomagnetic storm (GS) observed from the Atmospheric Weather Electromagnetic System for Observation Modeling and Education (AWESOME) VLF/LF radio waves receiver located in Ariel University, Israel.  The station collects narrowband (NB) and broadband (BB) data of electromagnetic waves originating from various global VLF transmitters, and also from natural sources such as lightning discharges around the globe to complement other available data sources from ground- and space- based observatories. Our careful analysis of the received LF signals amplitude and phase, under distinct GS phases (initial, main and recovery stages), revealed significant spatial and temporal variations along the different transmitters’ propagation path, both for the N/S and the E/W signal channels.  Such manifestations include both signal enhancement (up to several dB) and signal attenuation. Additionally, analysis between other available data sources from ground- and space- based observatories, such as high (SYM-H) and low (Dst) time resolution GS indices under the three GS regimes, was conducted via a wide range of correlation techniques.

How to cite: Ajakaiye, M. P., Romano, B., and Reuveni, Y.: Ionospheric D-region response to the 22-26 March 2023 Intense Geomagnetic Storm: a manifestation on Very Low Frequency (VLF) Radio Wave Signals received in the Eastern Mediterranean , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8363, https://doi.org/10.5194/egusphere-egu24-8363, 2024.

X3.15
|
EGU24-10825
|
ECS
Neethal Thomas, Antti Kero, Ilkka Virtanen, and Satonori Nozawa

We have analyzed all the existing European incoherent scatter (EISCAT) radar VHF measurements carried out together with the neutral temperature measurements from LIDAR collocated at Tromsø, Norway. Incoherent scatter radar (ISR) spectral parameters are estimated from the backscattered signal autocorrelation function by fitting the D-region lag profiles (pulse-to-pulse fitting). This study focuses on the ISR spectral width which is a function of the ion-to-neutral collision frequency, neutral temperature, and ion mass. Using the neutral temperatures obtained from LIDAR, we have measured for the first time the ion-to-neutral collision frequency in the mesosphere lower thermosphere (MLT) altitude range (80-100 km) by fitting the ISR spectral width. The model ion-to-neutral collision frequencies estimated using MSIS neutral densities are found to be underestimated on average by 1.5 in comparison to the measurements. Also, the ISR collision frequencies showed large temporal variations caused by neutral density fluctuations, which are absent in the model values. These large-scale neutral density fluctuations which are thought to be caused by atmospheric waves are found to have amplitudes as large as 50% of the background density. This indicates that the ISR spectral width is largely influenced by the neutral density fluctuations. In light of these observations, the inherent limitations of inferring the neutral temperatures from ISR spectral width are studied. This study showcases the challenges of estimating neutral temperatures from ISR spectral width in the MLT altitudes, which is significant in the context of the upcoming EISCAT_3D.

How to cite: Thomas, N., Kero, A., Virtanen, I., and Nozawa, S.: Incoherent scatter radar measurements of ion-to-neutral collision frequencies and neutral temperatures in the D-region ionosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10825, https://doi.org/10.5194/egusphere-egu24-10825, 2024.