Towards better understanding of the ionospheric plasma irregularities and scintillations
Plasma density irregularities can occur at all latitudes in the Earth’s ionosphere. However, the onset and evolution of these irregularities as well as their influence on the radio wave signals continue to be unsolved scientific questions. The various proposed generation mechanisms, including instability growth rates and seeding processes, are strongly coupled to the neutral atmosphere and magnetospheric dynamics, making the forecasting of ionospheric irregularities much more challenging. Recent observations from ground- and space-based measurements, as well as new innovative data analysis and modeling techniques, e.g., data assimilation and machine learning, have the potential to advance our understanding of the ionospheric irregularities. Studies that focus on the observation, modeling and prediction of plasma irregularities of different scales are welcome at this session. The mitigation of negative effects and recent developments to forecast scintillation effects on Global Navigation Satellite or other communication systems are also of high interest.
The ionosphere is a dynamical system exhibiting nonlinear couplings with the other “spheres” characterizing the geospace environment. Such nonlinearity manifests also through the non-trivial, largely varying range of spatial and temporal scales. We investigate how the different scales of the in situ plasma density as provided by different data products measured by Swarm satellites relate to the same range of scales of the field-aligned currents from Swarm FAC dataset and how their intensifications reflect the various conditions of the geospace.
The present study compares the spatio-temporal variability in the topside ionosphere by leveraging on the Fast Iterative Filtering (FIF) technique. FIF is able to reveal the hidden features of a time series, as it decomposes any nonstationary, nonlinear signals, like those provided by Langmuir probes onboard Swarm, into oscillating modes, called intrinsic mode components or functions (IMCs or IMFs), characterized by their specific frequencies.
The instantaneous time-frequency representation of the IMFs is provided through the so-called “IMFogram” which illustrates the time development of the multi-scale processes. The IMFogram has the potentiality to show the finer details of the scale sizes which intensify during the various phases of geomagnetic storms.
This work is performed in the framework of the Swarm Variability of Ionospheric Plasma (Swarm-VIP) project, funded by ESA in the “Swarm+4D-Ionosphere” framework (ESA Contract No. 4000130562/20/I-DT).
How to cite:
Urbar, J., Spogli, L., Cicone, A., Clausen, L., Jin, Y., Wood, A., Alfonsi, L., Cesaroni, C., Rawlings, J., Kotova, D., Høeg, P., and Miloch, W.: Sources of variability in the ionospheric spatio/temporal scales measured by Swarm instrument suite, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8191, https://doi.org/10.5194/egusphere-egu22-8191, 2022.
Plasma density irregularities disturbing signals from Global Navigation Satellite Systems (GNSS) are known to be regular features of the high-latitude ionosphere, especially around the cusp and auroral regions. Despite their relevance for society, irregularity formation and evolution are still relatively poorly understood, and observations revealing the spatio-temporal characteristics of ionospheric structuring at different scales are needed to assess the exact mechanism(s) responsible for them.
In this study, we focus on data from the European Incoherent Scatter Scientific Association (EISCAT) Svalbard Radars (ESR) operating in fast scanning mode. We use ESR experiments in which the antenna was swept in elevation, and create consecutive two-dimensional images showing how electron density, ion velocity, electron temperature, and ion temperatures change with latitude and time at different altitudes.
We present selected events in which the ESR scans are combined with all-sky images and in-situ data from the Swarm satellites to provide multi-scale observations of cusp phenomena comprising polar cap patches, flow channels, particle precipitation, and ion heating. We compare the observations with the presence of GNSS scintillations, allowing to monitor the onset and development of irregularities causing scintillations, and to inspect their connection with the phenomena above-mentioned. We then extend the analysis by performing a statistical study using all ESR fast scans identified between January 2001 and December 2015. We investigate the statistical characteristics of the measured parameters at different altitudes and under different geomagnetic conditions. Overall, this study will provide further insights onto the spatio-temporal evolution of ionospheric cusp dynamics, and on the possible physical sources causing ionospheric irregularities with Space weather impacts.
How to cite:
Spicher, A., Vierinen, J., Oksavik, K., and Jin, Y.: Statistical characteristics of ionospheric irregularities in the cusp ionosphere based on multi-instrument techniques, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8293, https://doi.org/10.5194/egusphere-egu22-8293, 2022.
The formation of a sporadic-E (Es) layer at mid and low latitudes is generally attributed to the vertical wind shear, which is predicted to cause vertical ion convergence. According to wind shear theory, a negative shear of the eastward wind is effective in converging metallic ions into a thin layer to produce Es. However, the direct comparison of Es with the local wind shear has been limited due to the lack of neutral wind measurements. This study examines the role of the vertical wind shear for Es, using signal-to-noise ratio profiles from COSMIC-2 radio occultation measurements and concurrent measurements of neutral wind profiles from the Ionospheric Connection Explorer (ICON). We find that the Es occurrence rate is correlated with the negative vertical shear of the eastward wind, providing observational support for the wind shear theory.
How to cite:
Yamazaki, Y., Arras, C., Andoh, S., Miyoshi, Y., Shinagawa, H., Harding, B. J., Englert, C. R., Immel, T. J., Sobhkhiz-Miandehi, S., and Stolle, C.: Direct comparison of sporadic E from COSMIC-2 radio occultation and vertical wind shears from ICON/MIGHTI, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8954, https://doi.org/10.5194/egusphere-egu22-8954, 2022.
The global total electron content (TEC) map in 2013, retrieved from the International Global Navigation Satellite Systems (GNSS) Service (IGS), and the International Reference Ionosphere (IRI-2016) model are used to monitor the diurnal evolution of the equatorial ionization anomaly (EIA). The statistics are conducted during geomagnetic quiet periods in the Peruvian and Indian sectors, where the equatorial electrojet (EEJ) data and reliable TEC are available. The EEJ is used as a proxy to determine whether the EIA structure is fully developed. Most of the previous studies focused on the period in which the EIA is well developed, while the period before EIA emergence is usually neglected. To characterize dynamics accounting for the full development of EIA, we defined and statistically analyzed the onset, first emergence, and the peaks of the northern crest and southern crest based on the proposed crest-to-trough difference (CTD) profiles. These time points extracted from IGS TEC show typical annual cycles in the Indian sector which can be summarized as winter hemispheric priority, i.e., the development of EIA in the winter hemisphere is ahead of that in the summer hemisphere. However, these same time points show abnormal semiannual cycles in the Peruvian sector, that is, EIA develops earlier during two equinoxes/solstices in the northern/southern hemisphere. We suggest that the onset of EIA is a consequence of the equilibrium between sunlight ionization and ambipolar diffusion. However, the latter term is not considered in modeling the topside ionosphere in IRI-2016, which results in a poor capacity in IRI to describe the diurnal evolution of EIA. Meridional neutral wind’s modulation on the ambipolar diffusion can explain the annual cycle observed in the Indian sector, while the semiannual variation seen in the Peruvian sector might be due to additional competing effects induced by the F region height changes
How to cite:
Wan, X., Zhong, J., Xiong, C., and Liu, Y.: Seasonal and Interhemispheric Effects on the Diurnal Evolution of EIA: Assessed by IGS TEC and IRI-2016 over Peruvian and Indian sectors, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9000, https://doi.org/10.5194/egusphere-egu22-9000, 2022.
The polar ionosphere is often highly irregular and turbulent with significant plasma structures. As a result, the satellite-based navigation and communication systems that rely on trans-ionospheric radio signals can be severely disrupted. In this study, we take advantage of the high-resolution (1 kHz) electron density observations of a polar orbiting satellite (NorSat-1) to address plasma structures at several 10s of meters that are responsible for scattering of High Frequency (HF) radar signals. The in-situ electron density data are taken from the winter season of 2017-2018. Though the solar activity is very low, NorSat-1 frequently observes significant plasma irregularities from several 10s km down to several decameter. These are often observed near the dayside cusp and dawnside auroral zone. The decameter-scale irregularities are positively correlated with intermediate-scale (10 km) density gradients, for both negative and positive gradients encountered by the satellite. The spatial distribution of electron density over two winter months in the Northern hemisphere along NorSat-1 orbits is constructed, which shows significant density increases in the cusp ionosphere (75º-80º MLAT) and in regions near the dawnside auroral oval. Intermediate scale density gradients and small-scale irregularities are clearly collocated with these density enhancements. These density enhancements and irregularities are likely induced by auroral particle precipitation/plasma dynamics. The power of decameter scale irregularities is also directly compared with the backscatter echo of HF radars.
How to cite:
Jin, Y., Clausen, L., Spicher, A., Ivarsen, M., Zhang, Y., Miloch, W., and Moen, J.: Statistical Study of Decameter Scale Plasma Irregularities in the Polar Ionosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9366, https://doi.org/10.5194/egusphere-egu22-9366, 2022.
In the framework of space weather, the understanding of the physical mechanisms responsible for the generation of ionospheric irregularities is particularly relevant for their effects on global positioning and communication systems. Ionospheric equatorial plasma bubbles are one of the possible irregularities. Using data from the ESA’s Swarm mission, we investigate the scaling features of electron density fluctuations characterizing equatorial plasma bubbles. Results strongly support the turbulent character of these structures and suggest the existence of a clear link between the observed scaling properties and the value of the Rate Of change of electron Density Index (RODI).
In addition, considering that important features of plasma bubbles such as their dependence on latitude, longitude, solar and geomagnetic activities have been inferred indirectly using their magnetic signatures, we study also the scaling properties of the magnetic field inside them. We show that the spectral features of plasma irregularities cannot be directly inferred from their magnetic signatures. A relation more complex than the linear one is necessary to properly describe the role played by the evolution of plasma bubbles with local time and by the development of turbulent phenomena. A better comprehension of the plasma bubbles dynamics and of the turbulence processes that characterize their time evolution may benefit from the use of very high-resolution vector magnetic field and plasma density measurements such as those available from the future NanoMagSat mission.
How to cite:
De Michelis, P., Alberti, T., Coco, I., Consolini, G., Giannattasio, F., Pezzopane, M., Pignalberi, A., and Tozzi, R.: Ionospheric Turbulence and the Equatorial Plasma Density Irregularities: Scaling Features and RODI, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10099, https://doi.org/10.5194/egusphere-egu22-10099, 2022.
Variations in ionospheric electron density, so-called irregularities, produce rapid fluctuations on propagating communication and navigation signals, which can be severe near the magnetic equator and in the polar regions. This may result in positioning error. Due to sparse sampling, our knowledge of the vertical distribution of small-scale irregularities is limited. In this study, we examine the vertical distribution of multi-scale scintillation-inducing irregularities in the low-latitude ionosphere. In four sets of novel experiments, we sampled altitudes from 330-1280 km in the 18-24 MLT sector using the Swarm Echo GAP-O GPS receiver with its antenna oriented toward zenith. In order to identify multi-scale irregularities both above and at the satellite’s position, we utilize high-sample-rate GAP-O amplitude and phase measurements along with a measurement of net current onto the surface of the IRM sensor on board, which serves as a proxy for density variations. We find that amplitude scintillations on the GPS signal coincide with strong in-situ small-scale density irregularities in 74% of cases, and above 500 km of altitude in all but one instance. In addition, we show that large-scale ionospheric disturbances occur predominantly below 500 km, and down to the 330 km perigee of Swarm Echo in the 18-21 MLT sector. In contrast, small-scale variations on total electron content (TEC) are detected at all MLTs between 18 MLT and magnetic midnight and at all altitudes sampled in this experiment. However, they are more frequent in the 22-24 MLT range.
How to cite:
Mohandesi, A., Knudsen, D. J., Skone, S., Langley, R. B., and Yau, A. W.: Altitude distribution of large and small-scale equatorial ionospheric irregularities sampled by the Swarm Echo satellite, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10326, https://doi.org/10.5194/egusphere-egu22-10326, 2022.
The ionospheric plasma irregularities can cause severe scintillation of the trans-ionospheric radio waves, e.g., signals from the global navigation satellite system (GNSS). The phase scintillation of GNSS signal are usually caused by both refractive and diffractive variations, while the amplitude scintillation is mainly attributed to diffractive process. At high latitude, the GNSS signals usually exhibit strong phase scintillation, but the meanwhile amplitude scintillation is very low. Such a feature leads to the commonly known issue as “phase without amplitude scintillation at high latitude”. In this study, we focused on the geomagnetic storm happened on 7-8 September 2017. High-resolution data from four GNSS receivers at high latitudes were utilized. Quite intense phase and amplitude scintillations, represented by σ4 and S4, respectively, were observed during the storm mainly phase. By checking the ionosphere-free linear combination (IFLC) parameter, the intense phase and amplitude scintillations are found associated with diffractive effects. Simultaneous observations from the Swarm satellite have been further analyzed to resolve the possible reasons that cause the diffractive influence of scintillation.
How to cite:
Xiong, C., Zheng, Y., Jin, Y., Liu, D., Xu, C., Zhu, Y., and OKsavik, K.: Diagnose the diffractive contribution to GNSS scintillation at high latitude during the geomagnetic storm on 7-8 September 2017, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11014, https://doi.org/10.5194/egusphere-egu22-11014, 2022.
A large number of studies have confirmed the frequent occurrence of plasma irregularities in the mid-latitude ionospheric trough (MIT), but their distribution characteristics have not been fully understood. Based on the Swarm in situ plasma density measurements from 2014 to 2020, the diurnal, seasonal, solar activity and geomagnetic activity variations of the occurrence rate of MIT region irregularities are analyzed. The results show that for the irregularities with scale size of 7.5-75 km: (1) the geomagnetic activity has an obvious inhibitory effect on the formation of irregularities inside the MIT region, regardless of dayside or nightside. (2) The occurrence rate of irregularities inside MIT region during the day is significantly higher than that at night, and the difference between day and night is greater than the difference between the two walls at the same local time sector. (3) On the dayside, the highest and lowest occurrence rate appears in winter and summer, respectively; but on the nightside, the highest and lowest occurrence rate appears in equinoxes and winter, respectively. (4) On the nightside, it shows lower occurrence rate under high solar activity conditions, but no obvious solar activity effect is shown on the dayside occurrence rate. The above results of the seasonal dependence, geomagnetic activity inhibitory effect, and solar activity influnce are newly and important for understanding the behaviors of the plasma irregularities at MIT region.
How to cite:
Liu, Y., Xie, W., Xiong, C., Ye, T., Wang, Y., Wan, X., and Cao, Y.: Climatological distributions of mid-latitude trough region irregularities based on Swarm in situ measurements, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11044, https://doi.org/10.5194/egusphere-egu22-11044, 2022.
Plasma anomalies appear at high latitudes, extending across the polar cap as a tongue of ionisation and/or polar patches. Physical mechanisms responsible for plasma uplifts and transport are investigated using global ionospheric circulation models driven by parameterised high-latitude plasma convection models. Various convection models will be considered, including the models based on satellite data, SuperDARN radar data, and data assimilation models. Relative contributions from electrodynamic plasma transport and neutral wind forcing are assessed. The simulations are compared with GNSS and radar observations. The results are discussed in the context of space weather modelling and scintillation environment modelling at high latitudes.
How to cite:
Pokhotelov, D., Fernadez-Gomez, I., and Borries, C.: Plasma transport across high latitudes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11426, https://doi.org/10.5194/egusphere-egu22-11426, 2022.
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. The spectral characteristics of these 16 Hz density estimates were analyzed to study the F-region ionospheric irregularities at altitudes between about 440 and 510 km. The data were obtained during the period from October 2014 to October 2018. The Power Spectral Densities (PSDs) observed followed to a very good approximation a power law. The values of spectral indices obtained showed a peak centered at around -2.5, located at the Equatorial Ionization Anomaly (EIA) belts. The spectral indices were found to be sensitive to the amplitudes of the irregular variations. Most spectra were obtained within the time sector 20:00 LT - 22:00 LT, and they became slightly shallower towards later local times. 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 20° and 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.
How to cite:
Buchert, S., Aol, S., Jurua, E., and Sorriso-Valvo, L.: Spectral Properties of Kilometer-scale Equatorial Irregularities as Seen by theSwarm Satellites, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11690, https://doi.org/10.5194/egusphere-egu22-11690, 2022.
To provide new insights into the relationship between geomagnetic conditions and plasma irregularity scale-sizes, high-latitude irregularity spectra are developed using a novel Incoherent Scatter Radar (ISR) technique. This new technique leverages: 1) the ability of phased array Advanced Modular ISR (AMISR) technology to collect volumetric measurements of plasma density, 2) the slow F-region cross-field plasma diffusion at scales greater than 10 km, and 3) that high-latitude geomagnetic field lines are nearly vertical. The resulting irregularity spectra are of a higher spatial-temporal resolution than has been previously possible with ISRs, capable of resolving approximately 20 km structures in less than two minutes (depending on the radar mode). By comparing irregularity spectra from high-latitude Resolute Bay ISR data to solar and magnetospheric conditions, we have found that although structures 100s of km wide can be prevalent for a variety of geomagnetic conditions, polar cap structures 10s of km will become more prevalent during quiet geomagnetic conditions. Furthermore, structures that are 10s of km wide will also become more dominant near midnight, reflecting the role of polar cap convection in breaking down structures as they travel from the dayside ionosphere to the nightside. This presentation will expand on these and other findings, as well as discuss the future goals of this work.
How to cite:
Goodwin, L. and Perry, G.: The Impact of Solar and Magnetospheric Conditions on High-Latitude Irregularity Spatial-Scales as Observed Using Advanced Radar Techniques, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11882, https://doi.org/10.5194/egusphere-egu22-11882, 2022.
Due to its small intensity, ionospheric scintillation at the mid-latitudes is difficult to observe. The measurements of signal amplitude scintillation from GNSS in this region are almost impossible to perform with sufficient quality. The European interferometer LOFAR observing in the frequency range 10-90 MHz, provides a good opportunity to carry out complex studies on the ionospheric scintillation in the mid-latitudes. In this work, we show statistical analysis of amplitude scintillation intensity described by the S4 index as well as spectral parameters given from specially designed pipelines dedicated to computing and analyzing spectra obtained with a single LOFAR station and ILT observation. We also show temporal and spatial statistics for spectral index, Fresnel frequency, and noise level of measurement.
How to cite:
Pożoga, M., Ciechowska, H., Matyjasiak, B., Grzesiak, M., Rothkaehl, H., Wronowski, R., Tomasik, Ł., and Beser, K.: LOFAR ionospheric scintillation spectral measurements in mid-latitude region, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12957, https://doi.org/10.5194/egusphere-egu22-12957, 2022.
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