scispace - formally typeset
Search or ask a question
Journal ArticleDOI

On the collocation of the cusp aurora and the GPS phase scintillation: A statistical study

01 Oct 2015-Journal of Geophysical Research (John Wiley & Sons, Ltd)-Vol. 120, Iss: 10, pp 9176-9191
TL;DR: In this paper, the authors investigated the role of the cusp auroral processes in the production of irregularities, and found that the occurrence rate of the GPS phase scintillation is highest inside the auroral cusp, regardless of the scintillillation strength and the interplanetary magnetic field (IMF).
Abstract: The climatology map of the GPS phase scintillation identifies two regions of high scintillation occurrences: around magnetic noon and around magnetic midnight. The scintillation occurrence rate is higher around noon, while the scintillation level is stronger around magnetic midnight. This paper focuses on the dayside scintillation region. In order to resolve the role of the cusp auroral processes in the production of irregularities, we put the GPS phase scintillation in the context of the observed auroral morphology. Results show that the occurrence rate of the GPS phase scintillation is highest inside the auroral cusp, regardless of the scintillation strength and the interplanetary magnetic field (IMF). On average, the scintillation occurrence rate in the cusp region is about 5 times as high as in the region immediately poleward of it. The scintillation occurrence rate is higher when the IMF Bz is negative. When partitioning the scintillation data by the IMF By, the distribution of the scintillation occurrence rate around magnetic noon is similar to that of the poleward moving auroral form (PMAF): there is a higher occurrence rate at earlier (later) magnetic local time when the IMF By is positive (negative). This indicates that the irregularities which give rise to scintillations follow the IMF By-controlled east-west motion of the aurora and plasma. Furthermore, the scintillation occurrence rate is higher when IMF By is positive when the cusp is shifted toward the post noon sector where it may get easier access to the higher density plasma. This suggests that the combined auroral activities (e.g., PMAF) and the density of the intake solar EUV ionized plasma are crucial for the production of scintillations.
Citations
More filters
Journal ArticleDOI
TL;DR: The 2015 St. Patrick's day storm was the first storm of solar cycle 24 to reach a level of "Severe" on the NOAA geomagnetic storm scale as discussed by the authors.
Abstract: The 2015 St. Patrick’s day storm was the first storm of solar cycle 24 to reach a level of “Severe” on the NOAA geomagnetic storm scale. The Norwegian Mapping Authority is operating a national real-time kinematic (RTK) positioning network and has in recent years developed software and services and deployed instrumentation to monitor space weather disturbances. Here, we report on our observations during this event. Strong GNSS (Global Navigation Satellite System) disturbances, measured by the rate-of-TEC index (ROTI), were observed at all latitudes in Norway on March 17th and early on March 18th. Late on the 18th, strong disturbances were only observed in northern parts of Norway. We study the ionospheric disturbances in relation to the auroral electrojet currents, showing that the most intense disturbances of GNSS signals occur on the poleward side of poleward-moving current regions. This indicates a possible connection to ionospheric polar cap plasma patches and/or particle precipitation caused by magnetic reconnection in the magnetosphere tail. We also study the impact of the disturbances on the network RTK and Precise Point Positioning (PPP) techniques. The vertical position errors increase rapidly with increasing ROTI for both techniques, but PPP is more precise than RTK at all disturbance levels.

105 citations

Journal ArticleDOI
TL;DR: In this paper, the in situ electron density obtained with the Langmuir probe and the total electron content from onboard global positioning system receiver are used to detect ionospheric plasma irregularities, and the irregularity parameters from the electron density in terms of the rate of change of density index and electron density gradients.
Abstract: The polar ionosphere is often characterized by irregularities and fluctuations in the plasma density. We present a statistical study of ionospheric plasma irregularities based on the observations from the European Space Agency's Swarmmission. The in situ electron density obtained with the Langmuir probe and the total electron content from the onboard global positioning system receiver are used to detect ionospheric plasma irregularities.We derive the irregularity parameters from the electron density in terms of the rate of change of density index and electron density gradients. We also use the rate of change of total electron content index as the irregularity parameter based on the global positioning system data. The background electron density and plasma irregularities are closely controlled by the Earth's magnetic field, with averaged enhancements close to the magnetic poles. The climatological maps in magnetic latitude/magnetic local time coordinates show predominant plasma irregularities near the dayside cusp, polar cap, and nightside auroral oval. These irregularities may be associated with large‐scale plasma structures such as polar cap patches, auroral blobs, auroral particle precipitation, and the equatorward wall of the ionospheric trough. The spatial distributions of irregularities depend on the interplanetary magnetic field (IMF). By filtering the irregularity parameters according to IMF By, we find a clear asymmetry of the spatial distribution in the cusp and polar cap between the Northern (NH) and Southern Hemispheres (SH). For negative IMF By, irregularities are stronger in the dusk (dawn) sector in the NH (SH) and vice versa. This feature is in agreement with the high‐latitude ionospheric convection pattern that is regulated by the IMF By component. The plasma irregularities are also controlled by the solar activity within the current declining solar cycle. The irregularities in the SH polar cap show a seasonal variation with higher values from September to April, while the seasonal variation in the NH is only obvious around solar maximum during 2014–2015.

66 citations

Journal ArticleDOI
TL;DR: In this paper, the spatial and seasonal distributions of the patches identified separately by Swarm A and Swarm B between December 2013 and August 2016 were computed for both hemispheres, and it was shown that in the NH the number of patches is higher in the postnoon and prenoon sectors for interplanetary magnetic field (IMF) By 0, and that this trend is mirrored in the SH, consistent with the ionospheric flow convection.
Abstract: The Swarm satellites offer an unprecedented opportunity for improving our knowledge about polar cap patches, which are regarded as the main space weather issue in the polar caps. We present a new robust algorithm that automatically detects polar cap patches using in situ plasma density data from Swarm. For both hemispheres, we compute the spatial and seasonal distributions of the patches identified separately by Swarm A and Swarm B between December 2013 and August 2016. We show a clear seasonal dependency of patch occurrence. In the Northern Hemisphere (NH), patches are essentially a winter phenomenon, as their occurrence rate is enhanced during local winter and very low during local summer. Although not as pronounced as in the NH, the same pattern is seen for the Southern Hemisphere (SH). Furthermore, the rate of polar cap patch detection is generally higher in the SH than in the NH, especially on the dayside at about 77° magnetic latitude. Additionally, we show that in the NH the number of patches is higher in the postnoon and prenoon sectors for interplanetary magnetic field (IMF) By 0, respectively, and that this trend is mirrored in the SH, consistent with the ionospheric flow convection. Overall, our results confirm previous studies in the NH, shed more light regarding the SH, and provide further insight into polar cap patch climatology. Along with this algorithm, we provide a large data set of patches automatically detected with in situ measurements, which opens new horizons in studies of polar cap phenomena.

61 citations

Journal ArticleDOI
TL;DR: In this paper, the authors studied how GPS, GLONASS, and Galileo navigation signals are compromised by strong irregularities causing severe phase scintillation (σϕ>1) in the nightside high-latitude ionosphere during a substorm on 3 November 2013.
Abstract: In this paper we study how GPS, GLONASS, and Galileo navigation signals are compromised by strong irregularities causing severe phase scintillation (σϕ>1) in the nightside high-latitude ionosphere during a substorm on 3 November 2013. Substorm onset and a later intensification coincided with polar cap patches entering the auroral oval to become auroral blobs. Using Global Navigation Satellite Systems (GNSS) receivers and optical data, we show severe scintillation driven by intense auroral emissions in the line of sight between the receiver and the satellites. During substorm expansion, the area of scintillation followed the intense poleward edge of the auroral oval. The intense auroral emissions were colocated with polar cap patches (blobs). The patches did not contain strong irregularities, neither before entering the auroral oval nor after the aurora had faded. Signals from all three GNSS constellations were similarly affected by the irregularities. Furthermore, two receivers spaced around 120km apart reported highly different scintillation impacts, with strong scintillation on half of the satellites in one receiver and no scintillation in the other. This shows that areas of severe irregularities in the nightside ionosphere can be highly localized. Amplitude scintillations were low throughout the entire interval.

48 citations

References
More filters
Journal ArticleDOI
TL;DR: In this paper, the authors analyzed hourly averaged interplanetary magnetic field (IMF) and plasma data from the Advanced Composition Explorer (ACE) and Wind spacecraft, generated from 1 to 4 min resolution data time-shifted to Earth.
Abstract: [1] Hourly averaged interplanetary magnetic field (IMF) and plasma data from the Advanced Composition Explorer (ACE) and Wind spacecraft, generated from 1 to 4 min resolution data time-shifted to Earth have been analyzed for systematic and random differences. ACE moments-based proton densities are larger than Wind/Solar Wind Experiment (SWE) fits-based densities by up to 18%, depending on solar wind speed. ACE temperatures are less than Wind/SWE temperatures by up to ∼25%. ACE densities and temperatures were normalized to equivalent Wind values in National Space Science Data Center's creation of the OMNI 2 data set that contains 1963–2004 solar wind field and plasma data and other data. For times of ACE-Wind transverse separations <60 RE, random differences between Wind values and normalized ACE values are ∼0.2 nT for ∣B∣, ∼0.45 nT for IMF Cartesian components, ∼5 km/s for flow speed, and ∼15 and ∼30% for proton densities and temperatures. These differences grow as a function of transverse separation more rapidly for IMF parameters than for plasma parameters. Autocorrelation analyses show that spatial scales become progressively shorter for the parameter sequence: flow speed, IMF magnitude, plasma density and temperature, IMF X and Y components, and IMF Z component. IMF variations have shorter scales at solar quiet times than at solar active times, while plasma variations show no equivalent solar cycle dependence.

1,062 citations

Journal ArticleDOI
01 Apr 1982
TL;DR: In this article, a review of scintillation of radio waves propagating through the ionosphere is presented, focusing on propagational aspects, including both theoretical and experimental results, with a discussion of the motivation for stochastic formulation of the problem.
Abstract: The phenomenon of scintillation of radio waves propagating through the ionosphere is reviewed in this paper. The emphasis is on propagational aspects, including both theoretical and experimental results. The review opens with a discussion of the motivation for stochastic formulation of the problem. Based on measurements from in-situ, radar, and propagation experiments, ionospheric irregularities ate found to be characterized, in general, by a power-law spectrum. While earlier measurements indicated a spectral index of about 4, there is recent evidence showing that the index may vary with the strength of the irregularity and possibly a two-component spectrum may exist with different spectral indices for large and small structures. Several scintillation theories including the Phase Screen, Rytov, and Parabolic Equation Method (PEM) are discussed next. Statistical parameters of the signal such as the average signal, scintillation index, rms phase fluctuations, correlation functions, power spectra, distributions, etc., are investigated. Effects of multiple scattering are discussed. Experimental results concerning irregularity structures and signal statics are presented. These results are compared with theoretical predictions. The agreements are shown to be satisfactory in a large measure. Next, the temporal behavior of a transionospheric radio signal is studied in terms of a two-frequency mutual coherence function and the temporal moments. Results including numerical simulations are discussed. Finally, some future efforts in ionospheric scintillation studies in the areas of transionospheric communication and space- and geophysics are recommended.

726 citations

Journal ArticleDOI
TL;DR: In this article, the authors presented a variation on the corrected geomagnetic coordinate system that is well defined and smooth over the entire globe, and provided an analytic expression relating geographic coordinates, including altitude, to the magnetic coordinates.
Abstract: Studying magnetically conjugate phenomena at very high latitudes requires a magnetic coordinate system that is smooth and well defined at the geographic poles In addition, it should provide for accurate comparisons at different altitudes In this report the authors present a variation on the corrected geomagnetic coordinate system that is well defined and smooth over the entire globe It provides an analytic expression relating geographic coordinates, including altitude, to the magnetic coordinates The coordinate system is produced by tracing magnetic field lines using the IGRF85 reference magnetic field model with time derivatives updating the model to 1988 An expansion of the relationship in terms of spherical harmonics has been determined, which then provides the required well-defined and smooth relationship over the entire globe Independent expansions for different altitudes show a smooth functional relationship of the coefficients of the expansion with altitude, and therefore simple interpolation schemes can be used to provide an appropriate expansion at any altitude between 0 km and approximately 600 km By reversing the process, the inverse expansions relating the magnetic coordinates to geographic coordinates have also been determined The effects of the seasonal variation in the Sun's declination along with the variation in the Sun's declinationmore » along with the variation in the Sun's apparent position due to the eccentricity of the Earth's orbit result in a variation of nearly 1 hour of magnetic local time for a fixed UT over the course of a year In many applications this variation may be important and should be included when presenting data in terms of magnetic latitude and MLT« less

678 citations

Journal Article
TL;DR: In this paper, the authors considered the high-latitude ionospheric flows and their excitation and decay and proposed a flow-free equilibrium configuration for a magnetosphere which contains a given (arbitrary) amount of open flux.
Abstract: Basic concepts of the form of high-latitude ionospheric flows and their excitation and decay are discussed in the light of recent high time-resolution measurements made by ground-based radars. It is first pointed out that it is in principle impossible to adequately parameterize these flows by any single quantity derived from concurrent interplanetary conditions. Rather, even at its simplest, the flow must be considered to consist of two basic time-dependent components. The first is the flow driven by magnetopause coupling processes alone, principally by dayside reconnection. These flows may indeed be reasonably parameterized in terms of concurrent near-Earth interplanetary conditions, principally by the interplanetary magnetic field (IMF) vector. The second is the flow driven by tail reconnection alone. As a first approximation these flows may also be parameterized in terms of interplanetary conditions, principally the north-south component of the IMF, but with a delay in the flow response of around 30-60 min relative to the IMF. A delay in the tail response of this order must be present due to the finite speed of information propagation in the system, and we show how "growth" and "decay" of the field and flow configuration then follow as natural consequences. To discuss the excitation and decay of the two reconnection-driven components of the flow we introduce that concept of a flow-free equilibrium configuration for a magnetosphere which contains a given (arbitrary) amount of open flux. Reconnection events act either to create or destroy open flux, thus causing departures of the system from the equilibrium configuration. Flow is then excited which moves the system back towards equilibrium with the changed amount of open flux. We estimate that the overall time scale associated with the excitation and decay of the flow is about 15 min. The response of the system to both impulsive (flux transfer event) and continuous reconnection is discussed in these terms.

621 citations

Journal ArticleDOI
01 Feb 1971
TL;DR: In this article, a review of the available amplitude and phase scintillation data is presented, where the effect of magnetic activity, solar sunspot cycle, and time of day is shown for each three latitudinal sectors.
Abstract: Starting with post World War II studies of fading of radio star sources and continuing with fading of satellite signals of Sputnik, vast quantities of data have built up on the effect of ionospheric irregularities on signals from beyond the F layer. The review attempts to organize the available amplitude and phase scintillation data into equatorial, middle-, and high-latitude morphologies. The effect of magnetic activity, solar sunspot cycle, and time of day is shown for each of these three latitudinal sectors. The effect of the very high levels of solar flux during the past sunspot maximum of 1979-1981 is stressed. During these years unusually high levels of scintillation were noted near the peak of the Appleton equatorial anomaly (∼ ±15° away from the magnetic equator) as well as over polar latitudes. New data on phase fluctuations are summarized for the auroral zone with its sheet-like irregularity structure. One model is now available which will yield amplitude and phase predictions for varying sites and solar conditions. Other models, more limited in their output and use, are also available. The models are outlined with their limitations and data bases noted. New advances in morphology and in understanding the physics of irregularity development in the equatorial and auroral regions have taken place. Questions and unknowns in morphology and in the physics of irregularity development remain. These include the origin of the seeding sources of equatorial irregularities, the physics of development of auroral irregularity patches, and the morphology of F-layer irregularities at middle latitudes.

572 citations