52 research outputs found
A technique for volumetric incoherent scatter radar analysis
Volumetric measurements of the ionosphere are important for investigating spatial variations of ionospheric features, like auroral arcs and energy deposition in the ionosphere. In addition, such measurements make it possible to distinguish between variations in space and time. While spatial variations in scalar quantities such as electron density or temperature have been investigated with incoherent scatter radar (ISR) before, spatial variation in the ion velocity, which is a vector quantity, has been hard to measure. The upcoming EISCAT3D radar will be able to do volumetric measurements of ion velocity regularly for the first time. In this paper, we present a technique for relating volumetric measurements of ion velocity to neutral wind and electric field. To regularize the estimates, we use Maxwell's equations and fluid-dynamic constraints. The study shows that accurate volumetric estimates of electric field can be achieved. Electric fields can be resolved at altitudes above 120 km, which is the altitude range where auroral current closure occurs. Neutral wind can be resolved at altitudes below 120 km.</p
GPS scintillations associated with cusp dynamics and polar cap patches
This paper investigates the relative scintillation level associated with cusp
dynamics (including precipitation, flow shears, etc.) with and without the
formation of polar cap patches around the cusp inflow region by the EISCAT
Svalbard radar (ESR) and two GPS scintillation receivers. A series of polar cap
patches were observed by the ESR between 8:40 and 10:20 UT on December 3, 2011.
The polar cap patches combined with the auroral dynamics were associated with a
significantly higher GPS phase scintillation level (up to 0.6 rad) than those
observed for the other two alternatives, i.e., cusp dynamics without polar cap
patches, and polar cap patches without cusp aurora. The cusp auroral dynamics
without plasma patches were indeed related to GPS phase scintillations at a
moderate level (up to 0.3 rad). The polar cap patches away from the active cusp
were associated with sporadic and moderate GPS phase scintillations (up to 0.2
rad). The main conclusion is that the worst global navigation satellite system
space weather events on the dayside occur when polar cap patches enter the
polar cap and are subject to particle precipitation and flow shears, which is
analogous to the nightside when polar cap patches exit the polar cap and enter
the auroral oval
Ionospheric Flow Vortex Induced by the Sudden Decrease in the Solar Wind Dynamic Pressure
Abrupt changes in the solar wind dynamic pressure can greatly affect the Earth's magnetosphere-ionosphere system. We present an ionospheric flow vortex in the morning sector during the sudden decrease in the solar wind dynamic pressure. The flow vortex was clearly observed by both the Hankasalmi radar and the azimuthal scan mode of the European Incoherent Scatter (EISCAT) Svalbard Radar (ESR). The flow vortex was first seen in the eastern field of view (FOV) of the Hankasalmi radar, and then propagated poleward and westward into the FOV of the ESR. During the passage of the flow vortex, a gradual decrease of electron density was observed by the field-aligned ESR 42 m antenna. When the equatorward directed ionospheric flow reached the ESR site, weak and visible increases in the electron density and electron temperature were observed. This impact was likely caused by soft electron precipitation associated with the clockwise flow vortex and upward field-aligned current. The azimuthal scan mode of the ESR 32 m radar at low elevation angle (30°) allowed us to measure key ionospheric parameters over a larger area (6° in latitude and 120° in azimuthal angle). The latitudinal scan of the electron temperature was used to proxy the equatorward auroral boundary, which shows that the flow vortex was located in the subauroral region. We further demonstrated that it is possible to study the weak increase of electron density by using GPS total electron content (TEC) data. A minor TEC increase was observed near the center of the flow vortex
GNSS Scintillations in the Cusp, and the Role of Precipitating Particle Energy Fluxes
Using a large data set of ground-based GNSS scintillation observations coupled with in situ particle detector data, we perform a statistical analysis of both the input energy flux from precipitating particles, and the observed occurrence of density irregularities in the northern hemisphere cusp. By examining trends in the two data sets relating to geomagnetic activity, we conclude that observations of irregularities in the cusp grows increasingly likely during storm-time, whereas the precipitating particle energy flux does not. We thus find a weak or nonexistent statistical link between geomagnetic activity and precipitating particle energy flux in the cusp. This is a result of a previously documented tendency for the cusp energy flux to maximize during northward IMF, when density irregularities tend not to be widespread, as we demonstrate. At any rate, even though ionization and subsequent density gradients directly caused by soft electron precipitation in the cusp are not to be ignored for the trigger of irregularities, our results point to the need to scrutinize additional physical processes for the creation of irregularities causing scintillations in and around the cusp. While numerous phenomena known to cause density irregularities have been identified and described, there is a need for a systematic evaluation of the conditions under which the various destabilizing mechanisms become important and how they sculpt the observed ionospheric “irregularity landscape.” As such, we call for a quantitative assessment of the role of particle precipitation in the cusp, given that other factors contribute to the production of irregularities in a major way
Investigating Spatial and Temporal Structuring of E-Region Coherent Scattering Regions Over Northern Norway
Recently, it has been shown that the Spread Spectrum Interferometric Multistatic meteor radar
Observing Network radar system located in northern Norway is capable of measuring ionospheric E-region
coherent scatter with spatial and temporal resolutions on the order of 1.5 km and 2 s, respectively. Four
different events from June and July of 2022 are examined in the present study, where the coherent scatter
measurements are used as a tracer for large-scale ionospheric phenomena such as plasma density enhancements
and ionospheric electric fields. By applying a two-dimensional Fourier analysis to range-time-intensity data,
we perform a multi-scale spatial and temporal investigation to determine the change in range over time of
large-scale ionospheric structures (>3 km) which are compared with line-of-sight velocities of the small scale
structures (∼5 m) determined from the Doppler shift of the coherent scatter. The spectral characteristics of
the large-scale structures are also investigated and logarithmic spectral slopes for scale sizes of 100–10 km
were found to be between −3.0 and −1.5. This agrees with much of the previous work on the spatial spectra
scaling for ionospheric electric fields. This analysis aids in characterizing the source of the plasma turbulence
and provides crucial information about how energy is redistributed from large to small scales in the E-region
ionosphere
2022 Tonga Volcanic Eruption Induced Global Propagation of Ionospheric Disturbances via Lamb Waves
The Tonga volcano eruption at 04:14:45 UT on 2022-01-15 released enormous amounts of energy into the atmosphere, triggering very significant geophysical variations not only in the immediate proximity of the epicenter but also globally across the whole atmosphere. This study provides a global picture of ionospheric disturbances over an extended period for at least 4 days. We find traveling ionospheric disturbances (TIDs) radially outbound and inbound along entire Great-Circle loci at primary speeds of ∼300–350 m/s (depending on the propagation direction) and 500–1,000 km horizontal wavelength for front shocks, going around the globe for three times, passing six times over the continental US in 100 h since the eruption. TIDs following the shock fronts developed for ∼8 h with 10–30 min predominant periods in near- and far- fields. TID global propagation is consistent with the effect of Lamb waves which travel at the speed of sound. Although these oscillations are often confined to the troposphere, Lamb wave energy is known to leak into the thermosphere through channels such as atmospheric resonance at acoustic and gravity wave frequencies, carrying substantial wave amplitudes at high altitudes. Prevailing Lamb waves have been reported in the literature as atmospheric responses to the gigantic Krakatoa eruption in 1883 and other geohazards. This study provides substantial first evidence of their long-duration imprints up in the global ionosphere. This study was enabled by ionospheric measurements from 5,000+ world-wide Global Navigation Satellite System (GNSS) ground receivers, demonstrating the broad implication of the ionosphere measurement as a sensitive detector for atmospheric waves and geophysical disturbances
The role of particle precipitation on plasma structuring at different altitudes by in-situ measurements
The plasma in the cusp ionosphere is subject to particle precipitation, which is important for the
development of large-scale irregularities in the plasma density. These irregularities can be broken down
into smaller scales which have been linked to strong scintillations in the Global Navigation Satellite System
(GNSS) signals. We present power spectra for the plasma density irregularities in the cusp ionosphere for
regions with and without auroral particle precipitation based on in-situ measurements from the Twin
Rockets to Investigate Cusp Electrodynamics-2 (TRICE-2) mission, consisting of two sounding rockets
flying simultaneously at different altitudes. The electron density measurements taken from the multi-needle
Langmuir probe system (m-NLP) were analyzed for the whole flight duration for both rockets. Due to their
high sampling rates, the probes allow for a study of plasma irregularities down to kinetic scales. A steepening of the slope in the power spectra may indicate two regimes, a frequency interval with a shallow slope,
where fluid-like processes are dominating, and an interval with a steeper slope which can be addressed with
kinetic theory. The steepening occurs at frequencies between 20 Hz and 100 Hz with a median similar to
the oxygen gyrofrequency. Additionally, the occurrence of double slopes increases where precipitation
starts and throughout the rest of the flight. In addition, strong electron density fluctuations were found
in regions poleward of the cusp, thus in regions immediately after precipitation. Furthermore, by investigating the integrated power of the fluctuations within different frequency ranges, we show that at low
frequencies (10–100 Hz), the power is pronounced more evenly while the rocket encounters particle precipitation, while at high frequencies (100–1000 Hz) fluctuations essentially coincide with the passing
through a flow channel
Steepening Plasma Density Spectra in the Ionosphere: The Crucial Role Played by a Strong E-Region
Based on the Swarm 16 Hz Advanced Plasma Density data set, and using the Swarm A satellite, we apply automatic detection of spectral breaks in seven million sampled plasma density power spectra in the high-latitude F-region ionosphere. This way, we survey the presence of plasma irregularity dissipation due to an enhanced E-region conductance, caused both by solar photoionization and particle precipitation. We introduce a new quantity named the steepening slope index (SSI) which we use to estimate the occurrence rate of break-points in sampled plasma densities. We provide an interpretation of SSI in the context of solar photoionization-induced conductance enhancements of the E-region. We present a comprehensive climatology of the SSI occurrence rate, along with statistics documenting characteristic high-latitude plasma density spectra. In the absence of steepening, the typical spectral index is 2.1. When density spectra steepen, the index is typically 1.6 at large scales, and 2.7 at small scales. We discuss the impact of high-energy deeply penetrating electron precipitation in the diffuse aurora, and precipitating electrons in the aurora at large. Here, a key finding is that near the cusp, where the F-region conductance is enhanced, spectra tend not to steepen. We find that both the diffuse and discrete aurora are modulating F-region plasma irregularity dissipation through an enhancement of E-region conductance, highlighting the role played by factors other than solar zenith angle in high-latitude plasma dynamics. The influence of E-region conductance on spectral shapes indicates the need for a new discussion of how particle precipitation can structure the local winter high-latitude F-region ionosphere
Simultaneous Global Ionospheric Disturbances Associated With Penetration Electric Fields During Intense and Minor Solar and Geomagnetic Disturbances
A new observational phenomenon, named Simultaneous Global Ionospheric Density Disturbance
(SGD), is identified in GNSS total electron content (TEC) data during periods of three typical geospace
disturbances: a Coronal Mass Ejection-driven severe disturbance event, a high-speed stream event, and a minor
disturbance day with a maximum Kp of 4. SGDs occur frequently on dayside and dawn sectors, with a ∼1%
TEC increase. Notably, SGDs can occur under minor solar-geomagnetic disturbances. SGDs are likely caused
by penetration electric fields (PEFs) of solar-geomagnetic origin, as they are associated with Bz southward,
increased auroral AL/AU, and solar wind pressure enhancements. These findings offer new insights into
the nature of PEFs and their ionospheric impact while confirming some key earlier results obtained through
alternative methods. Importantly, the accessibility of extensive GNSS networks, with at least 6,000 globally
distributed receivers for ionospheric research, means that rich PEF information can be acquired, offering
researchers numerous opportunities to investigate geospace electrodynamics
Interferometric Study of Ionospheric Plasma Irregularities in Regions of Phase Scintillations and HF Backscatter
We investigate the nature of small-scale irregularities observed in the cusp by the Twin Rockets to Investigate Cusp Electrodynamics-2 (TRICE-2) in regions of enhanced phase scintillations and high-frequency coherent radar backscatter. We take advantage of the fact that the irregularities were detected by spatially separated probes, and present an interferometric analysis of both the observed electron density and electric field fluctuations. We provide evidence that fluctuations spanning a few decameters to about a meter have low phase velocity in the plasma reference frame and are nondispersive, confirming that decameter-scale irregularities follow the E × B velocity. Furthermore, we show that these “spatial” structures are intermittent and prominent outside of regions with strongest precipitation. The observations are then discussed in the context of possible mechanisms for irregularity creation.publishedVersio
- …