Scintillation Observations Research Articles

Scintillation Arcs in Pulsar B0450–18

Abstract We report on Green Bank Telescope observations of interstellar scintillation from the pulsar B0450−18 at 340 and 825 MHz, revealing prominent arcs in the secondary spectra at both frequencies. The arcs are successfully modeled by one-dimensional angular brightness distributions, estimated by two independent techniques. The distributions do not follow the expected shape for a Kolmogorov plasma density spectrum, and their overall angular widths follow a scaling law, versus frequency, that is slightly slower than the inverse square law expected from plasma dispersion. They also exhibit discrete peaks that are the cause of the occasional reverse sub-arcs. Over a narrow (5%) frequency range these peaks do not participate in the overall spreading, having angular positions that are fixed on the sky. However, the peaks do evolve over a wider range of frequencies and cannot be traced from 825 to 340 MHz. Our conclusions add further evidence for a widespread distribution of highly localized regions of interstellar plasma with small-scale structure that is either elongated or flattened.

The nature and likely redshift of GLEAM J0917–0012

AbstractWe previously reported a putative detection of a radio galaxy at$z=10.15$, selected from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey. The redshift of this source, GLEAM J0917–0012, was based on three weakly detected molecular emission lines observed with the Atacama Large Millimetre Array (ALMA). In order to confirm this result, we conducted deep spectroscopic follow-up observations with ALMA and the Karl Jansky Very Large Array (VLA). The ALMA observations targeted the same CO lines previously reported in Band 3 (84–115 GHz) and the VLA targeted the CO(4-3) and [CI(1-0)] lines for an independent confirmation inQ-band (41 and 44 GHz). Neither observation detected any emission lines, removing support for our original interpretation. Adding publicly available optical data from the Hyper Suprime-Cam survey, Widefield Infrared Survey Explorer (WISE), andHerschel Space Observatoryin the infrared, as well as$<$10 GHz polarisation and 162 MHz inter-planetary scintillation observations, we model the physical and observational characteristics of GLEAM J0917–0012 as a function of redshift. Comparing these predictions and observational relations to the data, we are able to constrain its nature and distance. We argue that if GLEAM J0917–0012 is at$z<3,$then it has an extremely unusual nature, and that the more likely solution is that the source lies above$z=7$.

Impact of Inner Heliospheric Boundary Conditions on Solar Wind Predictions at Earth

AbstractPredictions of the physical parameters of the solar wind at Earth are at the core of operational space weather forecasts. Such predictions typically use line‐of‐sight observations of the photospheric magnetic field to drive a heliospheric model. The models Wang‐Sheeley‐Arge (WSA) and ENLIL for the transport in the heliosphere are commonly used for these respective tasks. Here we analyze the impact of replacing the potential field coronal boundary conditions from WSA with two alternative approaches. The first approach uses a more realistic nonpotential rather than potential approach, based on the Durham Magneto Frictional Code (DUMFRIC) model. In the second approach the ENLIL inner boundary conditions are based on Inter Planetary Scintillation observations (IPS). We compare predicted solar wind speed, plasma density, and magnetic field magnitude with observations from the WIND spacecraft for two 6‐month intervals in 2014 and 2016. Results show that all models tested produce fairly similar output when compared to the observed time series. This is not only reflected in fairly low correlation coefficients (<0.3) but also large biases. For example, for solar wind speed some models have average biases of more than 150 km/s. On a positive note, the choice of coronal magnetic field model has a clear influence on the model results when compared to the other models in this study. Simulations driven by IPS data have a high success rate with regard to detection of the high speed solar wind. Our results also indicate that model forecasts do not degrade for longer forecast times.

Leveraging Geodetic GPS Receivers for Ionospheric Scintillation Science

AbstractWe demonstrate scintillation analysis from a network of geodetic Global Positioning System (GPS) receivers which provide data at 1‐second resolution. We introduce proxy phase (σTEC) and amplitude (SNR4) scintillation indices and validate them against the rate of change of TEC index (ROTI) and S4. Additionally, we validate scintillation observations against a Connected Autonomous Space Environment Sensor scintillation receiver. We develop receiver‐dependent scintillation event thresholding using hardware‐dependent noise variance. We analyze 6 days adjacent to the 7–8 September 2017 geomagnetic storm, using 169 receivers covering magnetic latitudes between 15° and 65° in the American longitude sector. We leverage the available spatial sampling coverage to construct 2‐D maps of scintillation and present episodic evolution of scintillation intensifications during the storm. We show that low‐latitude and high‐latitude scintillation morphology match well‐established scintillation climatology patterns. At midlatitudes, spatiotemporal evolution of scintillation partially agrees with known scintillation patterns. Additionally, the results reveal previously undocumented midlatitude scintillation‐producing structures. The results provide an unprecedented view into the spatiotemporal development of scintillation‐producing plasma irregularities and provide a resource to further exploit scintillation evolution at large spatial scales.

On the Assessment of Daily Equatorial Plasma Bubble Occurrence Modeling and Forecasting

AbstractPredicting the daily variability of Equatorial Plasma Bubbles (EPBs) is an ongoing scientific challenge. Various methods for predicting EPBs have been developed, however, the research community is yet to scrutinize the methods for evaluating and comparing these prediction models/techniques. In this study, 12 months of co‐located GPS and UHF scintillation observations spanning South America, Atlantic/Western Africa, Southeast Asia, and Pacific sectors are used to evaluate the Generalized Rayleigh‐Taylor (R‐T) growth rates calculated from the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM). Various assessment metrics are explored, including the use of significance testing on skill scores for threshold selection. The sensitivity of these skill scores to data set type (i.e., GPS versus UHF) and data set size (30, 50, 60, and 90 days/events) is also investigated. It is shown that between 50 and 90 days is required to achieve a statistically significant skill score. Methods for conducting model‐model comparisons are also explored, including the use of model “sufficiency.” However, it is shown that the results of model‐model comparisons must be carefully interpreted and can be heavily dependent on the data set used. It is also demonstrated that the observation data set must exhibit an appropriate level of daily EPB variability in order to assess the true strength of a given model/technique. Other limitations and considerations on assessment metrics and future challenges for EPB prediction studies are also discussed.

Active (Evolving) Phase of Equatorial Plasma Bubbles Observed Over Tirunelveli

AbstractUsual post‐sunset generation of equatorial spread F (ESF) irregularities on quiet days (Q‐days) and midnight or post‐midnight generation of ESF on magnetically disturbed days (D‐days) is widely known. However, the duration of evolving or active phase of these freshly generated ESF (FESF) irregularities is not clearly understood. Here, the active phase duration refers to the time period during which the perturbation electric field associated with equatorial plasma bubbles drifting over Tirunelveli is alive. Recently, Gurram et al. (2018) quantified the active phase duration of FESF for both Q‐days and D‐days. It was the first exercise to obtain the average active phase duration of FESF from observations. In view of this, we carried out detailed analysis to examine their dependence on solar flux and geomagnetic activity using long‐term amplitude scintillation observations on 251‐MHz signal. It is found that percentage of days with longer active phase (td≥ 50 min) is higher on D‐days, and it is consistent for all levels of solar flux. Average duration of the active phase of FESF, ⟨td⟩, is 57.9 ± 52.3 min on D‐days and 33.8 ± 23.4 min on Q‐days. The active phase of FESF has tendency to sustain for longer time during low solar flux, which is attributed to presence of weaker ambient ionospheric electric field during that period. It is noted that FESF generated on days with stronger geomagnetic activity tend to have longer active phase. Also, days with FESF cause more moderate–strong scintillations as compared to days with drifted‐in ESF.

Observation of primary scintillations in the visible range in liquid argon doped with methane

Neutron veto detector based on liquid scintillator containing hydrogen atoms is an integral part of any underground experiment for dark matter search. So far, a flammable mixture of liquid hydrocarbons was used as a liquid scintillator in such detectors. A safe alternative might be a liquid scintillator based on liquid argon doped with methane. In this work, we have studied the primary scintillations in pure liquid argon and its mixtures with methane, the CH4 content varying from 100 ppm to 5%. The primary scintillations have for the first time been observed in liquid argon doped with methane, in the visible and near infrared range, and their relative light yields have been measured as a function of the CH4 content.

FAST interstellar scintillation observation of PSR B1929+10 and PSR B1842+14

In this paper, we present the Five-hundred-meter Aperture Spherical radio Telescope (FAST) observations of PSRs B1929+10 and B1842+14. Through analysis of the pulsars’ scintillation pattern, we detected the known scintillation arc from PSR B1929+10 and two previously undetected scintillation arcs from B1842+14. We find that the B1929+10 arc’s curvature scales with observing frequency as η− ∝ ν−2.1±0.1 and η+ ∝ ν−1.8±0.2, consistent with Arecibo results and the theoretical expectations of η ∝ ν−2. From the arc curvature, we infer the scattering screen to be located at 0.20±0.02 kpc from the Earth, close to what was measured by RadioAstron at 324 MHz. From B1842+14, we find two scintillation arcs for the first time. The arcs’ curvatures imply that they are caused by two scattering screens located at a distance of 0.3±0.2 kpc and 1.6±0.6 kpc from the Earth, respectively. The screen distance uncertainties mainly come from the uncertainty in pulsar’s dispersion measure (DM)-derived distance. We present these FAST scintillation observations and discuss the future prospect of FAST pulsar scintillation study.

Development of Forecast Algorithm for Coronal Mass Ejection Speed and Arrival Time Based on Propagation Tracking by Interplanetary Scintillation g-Value

We have developed an algorithm for tracking coronal mass ejection (CME) propagation that allows us to estimate CME speed and its arrival time at Earth. The algorithm may be used either to forecast the CME’s arrival on the day of the forecast or to update the CME tracking information for the next day’s forecast. In our case study, we successfully tracked CME propagation using the algorithm based on g-values of interplanetary scintillation (IPS) observation provided by the Institute for Space- Earth Environmental Research (ISEE). We were able to forecast the arrival time (Δt = 0.30 h) and speed (Δv = 20 km/s) of a CME event on October 2, 2000. From the CME-interplanetary CME (ICME) pairs provided by Cane & Richardson (2003), we selected 50 events to evaluate the algorithm’s forecast capability. Average errors for arrival time and speed were 11.14 h and 310 km/s, respectively. Results demonstrated that g-values obtained continuously from any single station observation were able to be used as a proxy for CME speed. Therefore, our algorithm may give stable daily forecasts of CME position and speed during propagation in the region of 0.2–1 AU using the IPS g-values, even if IPS velocity observations are insufficient. We expect that this algorithm may be widely accepted for use in space weather forecasting in the near future.

Open-field Coronal Structures Neighbouring the Sunspot of AR 8535

We make use of the Potential Field Source Surface (PFSS) model and reveal new details in the strong fields of the dominant sunspot of the active region (AR) 8535. Due to its importance in determining the field line connectivity and topology with resulting consequences for both plasma confinement and dynamics we construct the global magnetic fields with the PFSS model. The coronal emission – observed in the soft X-ray images taken with the Yohkoh Soft X-ray Telescope and 284 A images taken with the Extreme-ultraviolet Imaging Telescope aboard the Solar and HeliosphericObservatory (SOHO/EIT) – is largely asymmetric owing to two dark coronal lanes, which are traceable across the sunspot. The modelled open-field structures overlap with the observed coronal dark lanes and include two narrow coronal corridors that persist for days in the large sunspot. Since the open-field structures overlap also with the plasma upflow observed in the sunspot as Doppler blue-shifts in a set of EUV emission lines (SOHO/Coronal Diagnostic Spectrometer) on 9 May and 13 May 1999, we examine the plasma outflow from the AR 8535. From near-Earth measurements aboard the Advanced Composition Explorer (ACE) spacecraft we estimate the solar-wind speed $V _{\mathrm{p}} \approx 400~\mbox{km}\,\mbox{s}^{-1}$ and the charge state ratio $\mbox{O}^{7+}/\mbox{O}^{6+} = 0.4$ (corresponding to coronal “freezing-in temperature” $T _{\mathrm{e}} = 1.7 \times 10^{6}~\mbox{K}$). However, the abnormally low proton temperature of solar wind, $T _{\mathrm{p}} = 3 \times 10^{4}~\mbox{K}$, implies some impact of the interplanetary coronal mass ejection (ICME) on the plasma flow. The evidence in favour of the outflow from AR 8535 is given by the semi-empirical Wang–Sheeley–Arge model, as it predicts the ACE measurements of solar wind and the relevant features in the tomographic velocity map resulted from the Solar-Terrestrial Environment Laboratory observations of the interplanetary scintillations. Finally, we propose constructing a model atmosphere of the sunspot with the narrow coronal corridors included in order to further elaborate the magnetic-field structure through its effect on the observed microwave radiation.

A LOFAR observation of ionospheric scintillation from two simultaneous travelling ionospheric disturbances

This paper presents the results from one of the first observations of ionospheric scintillation taken using the Low-Frequency Array (LOFAR). The observation was of the strong natural radio source Cassiopeia A, taken overnight on 18–19 August 2013, and exhibited moderately strong scattering effects in dynamic spectra of intensity received across an observing bandwidth of 10–80 MHz. Delay-Doppler spectra (the 2-D FFT of the dynamic spectrum) from the first hour of observation showed two discrete parabolic arcs, one with a steep curvature and the other shallow, which can be used to provide estimates of the distance to, and velocity of, the scattering plasma. A cross-correlation analysis of data received by the dense array of stations in the LOFAR “core” reveals two different velocities in the scintillation pattern: a primary velocity of ~20–40 ms−1 with a north-west to south-east direction, associated with the steep parabolic arc and a scattering altitude in the F-region or higher, and a secondary velocity of ~110 ms−1 with a north-east to south-west direction, associated with the shallow arc and a scattering altitude in the D-region. Geomagnetic activity was low in the mid-latitudes at the time, but a weak sub-storm at high latitudes reached its peak at the start of the observation. An analysis of Global Navigation Satellite Systems (GNSS) and ionosonde data from the time reveals a larger-scale travelling ionospheric disturbance (TID), possibly the result of the high-latitude activity, travelling in the north-west to south-east direction, and, simultaneously, a smaller-scale TID travelling in a north-east to south-west direction, which could be associated with atmospheric gravity wave activity. The LOFAR observation shows scattering from both TIDs, at different altitudes and propagating in different directions. To the best of our knowledge this is the first time that such a phenomenon has been reported.

Automated power spectrum analysis of low-latitude ionospheric scintillations recorded using software GNSS receiver

The impact of equatorial plasma bubbles (EPBs) on signals from navigation satellites has remained unpredictable. EPBs could be tracked to some extent with prior knowledge of zonal drift and other important parameters associated with scintillations for a given local time. Aiming for this, we analyze high-rate carrier-to-noise (C/N0) GPS L1 signals recorded using a software GNSS receiver during February–April 2015. In the absence of an automated algorithm in this domain, a new algorithm is developed for estimation of power spectra, Fresnel frequency, noise floor, spectral slope, and ionospheric zonal irregularity drift using per minute scintillation patches. Importantly, since multipath and scintillation can co-occur at lower elevation angles, a new criterion for multipath identification and separation from scintillation and fading is defined as part of the automated algorithm. The C/N0 data above the threshold value of 0.17 of the scintillation index (S4) are only considered by this algorithm. Details of the approach and method are presented with example sets. Results for the estimated zonal drifts, spectral index, and decorrelation length of the post-sunset irregularities are illustrated. Variations in these parameters are presented along with local time, latitude, and longitude of the ionospheric pierce points. The drastic variations that a GPS user and a forecaster would encounter in equatorial latitudes are explained in terms of the challenge they pose. This study is probably the first in terms of automation of the process that shall be highly useful for single-station scintillation observations.

Validation of the Alfvén Wave Solar Atmosphere Model (AWSoM) with Observations from the Low Corona to 1 au

Abstract We perform a validation study of the latest version of the Alfvén Wave Solar atmosphere Model (AWSoM) within the Space Weather Modeling Framework. To do so, we compare the simulation results of the model with a comprehensive suite of observations for Carrington rotations representative of the solar minimum conditions extending from the solar corona to the heliosphere up to the Earth. In the low corona (r < 1.25 ), we compare with EUV images from both Solar-Terrestrial Relations Observatory-A/EUVI and Solar Dynamics Observatory/Atmospheric Imaging Assembly and to three-dimensional (3D) tomographic reconstructions of the electron temperature and density based on these same data. We also compare the model to tomographic reconstructions of the electron density from Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph observations (2.55 < r < 6.0 ). In the heliosphere, we compare model predictions of solar wind speed with velocity reconstructions from InterPlanetary Scintillation observations. For comparison with observations near the Earth, we use OMNI data. Our results show that the improved AWSoM model performs well in quantitative agreement with the observations between the inner corona and 1 au. The model now reproduces the fast solar wind speed in the polar regions. Near the Earth, our model shows good agreement with observations of solar wind velocity, proton temperature, and density. AWSoM offers an extensive application to study the solar corona and larger heliosphere in concert with current and future solar missions as well as being well suited for space weather predictions.

Challenges of predicting low-latitude ionospheric scintillations

Two regions of the globe that are most affected by ionospheric scintillations are the auroral region and the low-latitude region encompassing the dip equator. Our present-day dependence on satellite-based communication and navigation has led to a resurgence of interest in the prediction of ionospheric scintillations, which degrade the performance of such systems. In the low-latitude ionosphere, the genesis of intermediate-scale (∼100 m to a few km) irregularities, which cause the most severe scintillations on VHF to L-band trans-ionospheric radio signals, is in the growth of the Rayleigh-Taylor (R-T) plasma instability on the bottom-side of the post-sunset equatorial F layer. Theoretical developments and observations by various ground-based instruments, as well as in-situ measurements by instruments onboard rockets and satellites, have identified several parameters of the ambient ionosphere that play key roles in the occurrence of these irregularities over the dip equator. However, the presence of basic conditions for the linear growth of the Rayleigh-Taylor instability fails to explain the large day-to-day variability in the characteristics of these irregularities, which determines the latitudinal distribution and strength of scintillations, and is a result of the nonlinear evolution of the Rayleigh-Taylor instability. In this paper, the present status of the efforts at prediction of low-latitude scintillations on the basis of a multitude of observations and numerical simulation of the development of the Rayleigh-Taylor instability in the equatorial ionosphere are reviewed. In particular, this review describes how observations of ionospheric scintillations may be used to obtain information about the nonlinear evolution of the Rayleigh-Taylor instability under different ambient conditions, which is yet to be explored through numerical simulation of the phenomenon. Such studies have pointed out important gaps in our knowledge about the evolution of equatorial ionospheric irregularities that are responsible for producing scintillations on L-band signals recorded in the equatorial and low-latitude regions around the globe.

Comparison of Ground‐Based Ionospheric Scintillation Observations With In Situ Electron Density Variations as Measured by the Swarm Satellites

AbstractIonospheric scintillation is known to be associated with irregularities in electron density, which manifests as rapid fluctuations in the amplitude and phase of radio signals traversing the ionosphere. The scintillations caused by irregularity structures in the ionosphere can be directly measured using ground‐based GPS scintillation measurement receivers. In this work we have used in situ measurements of electron density by means of the Langmuir probe on the Swarm satellites to derive an index called the rate of density index (RODI). Using a ground‐based International Global Navigation Satellite Systems Service receivers and one dedicated scintillation measurement receiver, we have examined if we can identify ionospheric scintillation events that are correlated with space‐based electron density variations characterized by the RODI for cases when the Swarm satellites orbital tracks traverse coincidental locations to the ground‐based station. The selected Swarm B passes over Africa have been limited to the longitudes within ±7° of longitude relative to the position of a dedicated scintillation receiver located at Pwani, Kenya (Geo. Lon: 39.78°E, Geo. Lat: 3.24°S). Our results show that RODI could be a useful index for detecting irregularities associated with scintillation events that can also be observed from the ground. There is a similarity in RODI fluctuations and ground‐based irregularity measures based on rate of total electron content index with an asymmetry in irregularity activity across African region. There is stronger irregularity activity and high background nighttimes electron density on the western side of Africa than on the eastern side. This work shows the potential of using space‐based in situ measurement for scintillation detection and mitigation for operational purposes particularly for regions where terrestrial scintillation measurement are not possible like over oceans and deserts.

Signal Frequency Dependence of Ionospheric Scintillations: An Indicator of Irregularity Spectrum Characteristics

AbstractMultifrequency scintillation observations show that strong amplitude scintillations on very high frequency (VHF) signals are accompanied by weak L‐band scintillations near the dip equator and strong L‐band scintillations in equatorial ionization anomaly (EIA) region. For several decades this has been attributed to higher ambient plasma density in the EIA region. Recent work suggests that occurrence of stronger L‐band scintillations in the EIA region requires that the intermediate‐scale (~100 m to few km) ionospheric irregularity spectrum in this region be significantly shallower than that in the equatorial region. However, this has not been established so far. Signal frequency dependence of amplitude scintillations is characterized by the frequency exponent that determines the dependence on signal frequency of the S4 index: the standard deviation of normalized intensity fluctuations. In this paper, theoretical calculations of the frequency exponent for VHF and L‐band signals are carried out using different irregularity spectra and compared with observations in order to characterize power‐law irregularity spectra in different latitude zones. Intermediate‐scale irregularities in the equatorial and low‐latitude region, which are aligned with the geomagnetic field, are described by a two‐dimensional model. Model simulations show that the frequency exponent derived from S4 indices for VHF and L‐band signals is determined only by the characteristics of the irregularity spectrum and hence can be utilized to identify the nature of the power‐law irregularity spectrum. Frequency exponents computed using VHF and L‐band observations near the dip equator and EIA regions show distinct patterns, which clearly indicate steep and shallow irregularity spectra, respectively, in these regions.

Effect of Anisotropy on Ionospheric Scintillations Observed by SAR

Studies pertaining to small scale structures producing scintillations using synthetic aperture radars (SARs) have predominantly been conducted at low-latitude regions. The high-latitude region (auroral belt and polar caps) is highly dynamic and varies in response to stimuli from solar winds and the magnetosphere in complex ways. In this paper, the authors have shown the capability of SAR for scintillation observation in the auroral region. An attempt has been made to fit an irregularity anisotropy model to SAR measurements for characterizing the ionospheric irregularities in the auroral regions. The dependency of anisotropy irregularity model on parameters, such as irregularity structure (axial ratio), their orientation with respect to magnetic field lines, and the ionospheric plasma drift, is closely studied using Advanced Land Observing Satellite (ALOS)-2 datasets acquired over Alaska. Geomagnetic indices and total electron content data are consistent with the occurrence of the scintillation event under study. Drift velocity measurements from high-frequency radars in the super dual array radar network (SuperDARN) showed that the anisotropy is independent of the magnitude and the azimuth angle of the plasma drift. The typical range of orientation angle suitable for the high latitude regions probed by ALOS-2 is demonstrated to be between 120°–135°. This paper explores the idea of inferring irregularity anisotropy by comparing the amplitude scintillation (S4) index measured in SAR data pairs using two well-established techniques. The image contrast technique heavily relies on the accurate modeling of anisotropy, whereas the radar cross-sectional enhancement method is independent of it. This feature has been exploited in the $S_{4}$ comparison to finally fit the choice of irregularity axial ratio and conclude that the sheet-like structures best describe the ionospheric irregularity structure in the region under observation.

Global Solar Magnetic Field and Interplanetary Scintillations During the Past Four Solar Cycles

The extended minimum of Solar Cycle 23, the extremely quiet solar-wind conditions prevailing, and the mini-maximum of Solar Cycle 24 drew global attention and many authors have since attempted to predict the amplitude of the upcoming Solar Cycle 25, which is predicted to be the third successive weak cycle; it is a unique opportunity to probe the Sun during such quiet periods. Earlier work has established a steady decline, over two decades, in solar photospheric fields at latitudes above $45^{\circ}$ and a similar decline in solar-wind micro-turbulence levels as measured by interplanetary scintillation (IPS) observations. However, the relation between the photospheric magnetic fields and those in the low corona/solar-wind are not straightforward. Therefore, in the present article, we have used potential-field source-surface (PFSS) extrapolations to deduce global magnetic-fields using synoptic magnetograms observed with National Solar Observatory (NSO), Kitt Peak, USA (NSO/KP) and Solar Optical Long-term Investigation of the Sun (NSO/SOLIS) instruments during 1975-2018. Furthermore, we have measured the normalized scintillation index [m] using the IPS observations carried out at the Institute of Space Earth Environment Research (ISEE), Japan during 1983-2017. From these observations, we have found that, since the mid-1990s, the magnetic-field over different latitudes at 2.5 $\rm R_{\odot}$ and 10 $\rm R_{\odot}$(extrapolated using PFSS method) has decreased by $\approx 11.3-22.2 \%$. In phase with the declining magnetic-fields, the quantity m also declined by $\approx 23.6 \%$. These observations emphasize the inter-relationship between the global magnetic-field and various turbulence parameters in the solar corona and solar wind.

Simultaneous Rocket and Scintillation Observations of Plasma Irregularities Associated With a Reversed Flow Event in the Cusp Ionosphere

AbstractWe present an overview of the ionospheric conditions during the launch of the Investigation of Cusp Irregularities 3 (ICI‐3) sounding rocket. ICI‐3 was launched from Ny‐Ålesund, Svalbard, at 7:21.31 UT on 3 December 2011. The objective of ICI‐3 was to intersect the reversed flow event (RFE), which is thought to be an important source for the rapid development of ionospheric irregularities in the cusp ionosphere. The interplanetary magnetic field was characterized by strongly negative Bz and weakly negative By. The EISCAT Svalbard radar (ESR) 32‐m beam was operating in a fast azimuth sweep mode between 180° (south) and 300° (northwest) at an elevation angle of 30°. The ESR observed a series of RFEs as westward flow channels that were opposed to the large‐scale eastward plasma flow in the prenoon sector. ICI‐3 intersected the first RFE in the ESR field of view and observed flow structures that were consistent with the ESR observations. Furthermore, ICI‐3 revealed finer‐scale flow structures inside the RFE. The high‐resolution electron density data show intense fluctuations at all scales throughout the RFE. The ionospheric pierce point of the GPS satellite PRN30, which was tracked at Hornsund, intersected the RFE at the same time. The GPS scintillation data show moderate phase scintillations and weak amplitude scintillations. A comparison of the power spectra reveals a good match between the ground‐based GPS carrier phase measurements and the spectral slope of the in situ electron density data in the lower frequency range. It demonstrates the possibility of modelling GPS scintillations from high‐resolution in situ electron density data.

Statistical features of TEC and ionospheric scintillation over the low latitude of China

In this paper, a new index is established which is defined by the standard deviation of total electron content (TEC) fluctuation and denoted by the symbol σtec. It is demonstrated that the index σtec is equivalent to the phase scintillation index and can serve as an indicator of the strength of the phase scintillation. The receiver transiently loses lock on the signal, leading to cycle slips and jumps in the TEC time series. In order to obtain continuous TEC data in the situation of the disturbed ionosphere, a batch processing method is developed to detect and correct cycle slip. Based on the methods mentioned above, we investigate the statistical features of the phase scintillations and cycle slips by means of the data from a scintillation observation network in the south-central region of China during 2012–2015. The results show that the variations of phase scintillation occurrences with local time and season display very similar features to those of the cycle slip occurrences, implying that cycle slips are closely related to phase scintillations. Phase scintillations occur mainly during the night, most frequently before midnight and seldom in the daytime. It is found that phase scintillations occur mainly in equinox months but seldom in solstice months in the crest of the ionization equatorial anomaly and its adjacent regions, and an equinoctial asymmetry that phase scintillations occur more frequently in Spring than in Autumn is also found. Besides, a comparison of the TEC fluctuation index (σtec) and amplitude scintillation index (S4) indicates that there is close relation between the σtec and S4, indicating the co-existence of large and small scale irregularities in equatorial irregularity structures.