Space Weather

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Table of Contents for Space Weather. List of articles from both the latest and EarlyView issues.
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MHD Modeling of the Background Solar Wind in the Inner Heliosphere From 0.1 to 5.5 AU: Comparison With In Situ Observations

Fri, 06/05/2020 - 09:20
Abstract

The accurate prediction of solar wind conditions in the interplanetary space is crucial in the context of both scientific research and technical applications. In this study, we simulate the solar wind throughout the heliosphere from 0.1 to 5.5 astronomical units (AU) with our improved heliospheric magnetohydrodynamics (MHD) model during the time period from 2007 to 2017. The model uses synoptic magnetogram maps as input to derive the inner boundary conditions based on a series of empirical relations such as the Wang‐Sheeley‐Arge (WSA) relation. To test the performance of this model, we compare the simulation results with in situ measurements from multiple spacecraft including ACE/WIND, Solar TErrestrial Relations Observatory, Ulysses, Juno, and MErcury Surface, Space ENvironment, GEochemistry, and Ranging at different latitudes and heliocentric distances. There is an overall agreement between the model results and solar wind observations at different latitudes and heliocentric distances. Statistical analysis for Year 2007 reveals that our model can predict most of the corotation interaction regions, high‐speed streams, and magnetic sector boundaries at 1 AU. In addition, the bimodal structure of the solar wind for different latitudes is well reproduced by the model which is consistent with Ulysses data. This study demonstrates the capabilities of our heliosphere model in the prediction of the large‐scale structures of the solar wind in the inner heliosphere, and the model can be used to predict the ambient solar wind at locations of planets in the solar system such as Earth and Jupiter.

Future Interplanetary Space Weather Assets

Wed, 06/03/2020 - 11:40
Abstract

Late 2019 and early 2020 have witnessed numerous developments regarding future interplanetary space weather missions in Europe and in the United States. In parallel, space weather‐related legislation is being considered in the United States. A summary of these developments is presented, and two related topical issues of Space Weather are introduced.

Two‐Dimensional Reconstruction of Ionospheric Plasma Density Variations Using Swarm

Wed, 06/03/2020 - 11:32
Abstract

Space weather phenomena such as scintillations of Global Navigation Satellite Systems (GNSS) signals are of increasing importance for aviation, the maritime, and civil engineering industries. The ionospheric plasma irregularities causing scintillations are associated with strong gradients in ionospheric plasma density. To provide nowcasts and forecasts of space weather effects, it is vital to monitor the ionosphere and detect strong density variations. To reconstruct plasma density variations in the polar cap ionosphere, we use total electron content (TEC) estimates from the Swarm satellites' GPS receivers. By considering events where the Swarm satellites are in close proximity, we obtain plasma density variations by inverting TEC measurements on a two‐dimensional grid. We first demonstrate the method using synthetic test data, before applying it to real data. The method is validated using in situ Langmuir probe measurements and ground‐based TEC observations. We find that the new method can reproduce density variations, although it is sensitive to the geometry of the Swarm satellite constellation and to the calculated plasma temperature. Our proposed method opens new possibilities for ionospheric plasma monitoring that uses GPS receivers aboard low Earth orbit (LEO) satellites.

Issue Information

Wed, 05/27/2020 - 13:52

No abstract is available for this article

Anomalous propagation of radio waves from distant ILS localizers due to ionospheric sporadic‐E

Tue, 05/26/2020 - 09:44
Abstract

The ionospheric sporadic‐E (Es) layer occasionally causes anomalous propagation (AP) of VHF radio waves to distant locations. This effect, EsAP, may cause interference to VHF radio operation above 100 MHz. Recent study showed that VHF air‐navigation signals from distant stations are frequently observed when Es occurs. The observed frequencies includes channels of VHF omnidirectional radio range (VOR) and instrument landing system localizer (ILS LOC). The study showed that EsAP signals can be very strong and frequently exceedes the allowable interference limit of navigation receivers. In this paper we focus on EsAP on ILS LOC channels using the data obtained in the previous study. A series of extremely strong signals was observed on an ILS LOC frequency at Kure, Japan, on 15 May 2014 when an ionosphere sounder observed high‐density Es. The source of the signal was identified as an ILS LOC‐type direction aid (LDA) at Hualien, Taiwan. During the same period, several EsAP signals were observed on other ILS LOC channels, but their strengths were less significant. Analysis showed the causes of the strong signal from Hualien LDA: (1) the center of the narrow radio beam passed through the region very close to thr receiver site; (2) the elevation angle of the propagation path was very close to that of the actual beam center. Statistics showed that there were several outstanding EsAP events of which source was Hualien LDA. This study suggests that if similar conditions exist, radio interference to ILS LOC receiver can happen on any ILS LOC channels.

Characterizing extreme geomagnetic storms using Extreme Value Analysis: a discussion on the representativeness of short datasets

Sat, 05/23/2020 - 13:38
Abstract

One of the main goals when studying Space Weather is to characterize extreme events occurrences and related characteristics. To do so, dedicated statistical methods from the so‐called Extreme Value Analysis (EVA) field have been developed. In this study we used Ca index, derived from aa, in order to characterize geoeffectiveness from the radiation belts point of view with a 150‐year long dataset. The analysis performed in this study thus focuses on this newsworthy index to provide clues on the reliability of EVA methods. The first main result we present here is that the 1‐in‐10, 1‐in‐50 and 1‐in‐100 year events respectively match Ca values of 100.39, 131.39 and 142.84 nT. Consequently the only 1‐in‐100 event observed during the Space Era would be the “Halloween Storm” in 2003 that reached a Ca value of 147.6 nT. The second main result highlighted in this work is that performing the same analysis with shorter subsets (20‐year long) can give significantly different results for two reasons. The first reason is that some short time periods do not display the same distribution of events as the full period. The second reason is that the choice of the correct threshold (when using a Peaks Over Threshold approach) is made difficult with a short dataset and leads to inaccurate results. This is a strong result as for accurate estimation of the induced effects of extreme events in radiation belts, we may only rely on short flux datasets from one or another mission (mostly shorter than 20 years).

Two dimensional reconstruction of ionospheric plasma density variations using Swarm

Tue, 05/19/2020 - 15:45
Abstract

Space weather phenomena such as scintillations of Global Navigation Satellite Systems (GNSS) signals are of increasing importance for aviation, the maritime, and civil engineering industries. The ionospheric plasma irregularities causing scintillations are associated with strong gradients in ionospheric plasma density. To provide now‐ and forecasts of space weather effects, it is vital to monitor the ionosphere and detect strong density variations. To reconstruct plasma density variations in the polar cap ionosphere, we use Total Electron Content (TEC) estimates from the Swarm satellites' GPS receivers. By considering events where the Swarm satellites are in close proximity, we obtain plasma density variations by inverting TEC measurements on a two dimensional grid. We first demonstrate the method using synthetic test data, before applying it to real data. The method is validated using in situ Langmuir probe measurements and ground‐based TEC observations. We find that the new method can reproduce density variations, although it is sensitive to the geometry of the Swarm satellite constellation and to the calculated plasma temperature. Our proposed method opens new possibilities for ionospheric plasma monitoring that uses GPS receivers aboard Low Earth Orbit (LEO) satellites.

Spatial and temporal evolution of different‐scale ionospheric irregularities in Central and East Siberia during the 27‐28 May 2017 geomagnetic storm

Tue, 05/19/2020 - 13:13
Abstract

We present a multi‐instrumental study of ionospheric irregularities of different scales (from tens of centimeters to few kilometers) observed over the Central and East Siberia, Russia, during a moderate‐to‐strong geomagnetic storm on 27‐28 May 2017. From high‐frequency (HF) and ultrahigh‐frequency (UHF) radar data, we observed an intense auroral backscatter developed right after the initial phase of the geomagnetic storm. Additionally, we examined variations of GPS‐based ROT (Rate of TEC changes, where TEC is Total Electron Content) for available GPS receivers in the region. Ionosondes, HF, and UHF radar data exhibited a presence of intense multi‐scale ionospheric irregularities. We revealed a correlation between different‐scale Auroral/Farley‐Buneman ionospheric irregularities of the E layer during the geomagnetic storm. The combined analysis showed that an area of intense irregularities are well connected and located slightly equatorward to Field‐Aligned Currents (FACs) and auroral oval at different stages of the geomagnetic storm. An increase and equatorward displacement of Region 1 (R1)/Region 2 (R2) FACs leads to appearance and equatorward expansion of ionospheric irregularities. During downward (upward) R1 FAC and upward (downward) R2 FAC, the eastward and upward (westward and downward) E × B drift of ionospheric irregularities occurred. Simultaneous disappearance of UHF/HF auroral backscatter and GPS ROT decrease occurred during a prolonged near noon reversal of R1 and R2 FAC directions that accompanied by R1/R2 FAC degradation and disappearance of high‐energy auroral precipitation.

Spatial and temporal evolution of different‐scale ionospheric irregularities in Central and East Siberia during the 27‐28 May 2017 geomagnetic storm

Tue, 05/19/2020 - 13:13
Abstract

We present a multi‐instrumental study of ionospheric irregularities of different scales (from tens of centimeters to few kilometers) observed over the Central and East Siberia, Russia, during a moderate‐to‐strong geomagnetic storm on 27‐28 May 2017. From high‐frequency (HF) and ultrahigh‐frequency (UHF) radar data, we observed an intense auroral backscatter developed right after the initial phase of the geomagnetic storm. Additionally, we examined variations of GPS‐based ROT (Rate of TEC changes, where TEC is Total Electron Content) for available GPS receivers in the region. Ionosondes, HF, and UHF radar data exhibited a presence of intense multi‐scale ionospheric irregularities. We revealed a correlation between different‐scale Auroral/Farley‐Buneman ionospheric irregularities of the E layer during the geomagnetic storm. The combined analysis showed that an area of intense irregularities are well connected and located slightly equatorward to Field‐Aligned Currents (FACs) and auroral oval at different stages of the geomagnetic storm. An increase and equatorward displacement of Region 1 (R1)/Region 2 (R2) FACs leads to appearance and equatorward expansion of ionospheric irregularities. During downward (upward) R1 FAC and upward (downward) R2 FAC, the eastward and upward (westward and downward) E × B drift of ionospheric irregularities occurred. Simultaneous disappearance of UHF/HF auroral backscatter and GPS ROT decrease occurred during a prolonged near noon reversal of R1 and R2 FAC directions that accompanied by R1/R2 FAC degradation and disappearance of high‐energy auroral precipitation.

Space Ionizing Radiation Environment and Effects (SIRE2) Toolkit

Sun, 05/17/2020 - 13:49
Abstract

The Space Ionizing Radiation Environment and Effects (SIRE2) toolkit has been developed to update and extend to the tools used by the space and radiation effects community. It includes new environment models, the capability to examine how the environment changes along satellite and other trajectories and batch processing capabilities for both environments and radiation effects on electronics. An overview of the capabilities in the SIRE2 Toolkit is provided and examples of applying SIRE2 to satellite orbits and arbitrary trajectories are given.

Space Ionizing Radiation Environment and Effects (SIRE2) Toolkit

Sun, 05/17/2020 - 13:49
Abstract

The Space Ionizing Radiation Environment and Effects (SIRE2) toolkit has been developed to update and extend to the tools used by the space and radiation effects community. It includes new environment models, the capability to examine how the environment changes along satellite and other trajectories and batch processing capabilities for both environments and radiation effects on electronics. An overview of the capabilities in the SIRE2 Toolkit is provided and examples of applying SIRE2 to satellite orbits and arbitrary trajectories are given.

The Day‐night Difference and Geomagnetic Activity Variation of Energetic Electron Fluxes in Region of South Atlantic Anomaly

Sat, 05/16/2020 - 09:59
Abstract

Utilizing the DEMETER observations at 670km, we examined the day‐night difference of energetic electrons (100 – 800keV) in the South Atlantic Anomaly (SAA) region and their dependence on geomagnetic activities in different seasons. Under geomagnetically quiet conditions, the fluxes of higher‐energy electrons (> 200keV) in the dusk and midnight (MLT ~ 19 – 24hr) are usually larger than those in the morning (MLT ~ 8 – 12hr) in the core region of the SAA (−50 ≤ λ ≤  − 20deg) during the northern and southern summers (21/03/2007 – 23/09/2007 and 23/09/2007 – 21/03/2008). The day‐night difference of energetic electrons in SAA region depends not only on the electron energy but also on the geomagnetic activity levels. Enhanced geomagnetic activities increase the energetic electrons in morning and hence weaken their day‐night difference in the SAA region.

The Day‐night Difference and Geomagnetic Activity Variation of Energetic Electron Fluxes in Region of South Atlantic Anomaly

Sat, 05/16/2020 - 09:59
Abstract

Utilizing the DEMETER observations at 670km, we examined the day‐night difference of energetic electrons (100 – 800keV) in the South Atlantic Anomaly (SAA) region and their dependence on geomagnetic activities in different seasons. Under geomagnetically quiet conditions, the fluxes of higher‐energy electrons (> 200keV) in the dusk and midnight (MLT ~ 19 – 24hr) are usually larger than those in the morning (MLT ~ 8 – 12hr) in the core region of the SAA (−50 ≤ λ ≤  − 20deg) during the northern and southern summers (21/03/2007 – 23/09/2007 and 23/09/2007 – 21/03/2008). The day‐night difference of energetic electrons in SAA region depends not only on the electron energy but also on the geomagnetic activity levels. Enhanced geomagnetic activities increase the energetic electrons in morning and hence weaken their day‐night difference in the SAA region.

Solar Flare Intensity Prediction with Machine Learning Models

Fri, 05/15/2020 - 17:18
Abstract

We develop a mixed Long Short Term Memory (LSTM) regression model to predict the maximum solar flare intensity within a 24‐hour time window 0~24, 6~30, 12~36 and 24~48 hours ahead of time using 6, 12, 24 and 48 hours of data (predictors) for each Helioseismic and Magnetic Imager (HMI) Active Region Patch (HARP). The model makes use of (1) the Space‐weather HMI Active Region Patch (SHARP) parameters as predictors and (2) the exact flare intensities instead of class labels recorded in the Geostationary Operational Environmental Satellites (GOES) data set, which serves as the source of the response variables. Compared to solar flare classification, the model offers us more detailed information about the exact maximum flux level, i.e. intensity, for each occurrence of a flare. We also consider classification models built on top of the regression model and obtain better results in solar flare classifications as compared to Chen et al. (2019). Our results suggest that the most efficient time period for predicting the solar activity is within 24 hours before the prediction time using the SHARP parameters and the LSTM model.

Solar Flare Intensity Prediction with Machine Learning Models

Fri, 05/15/2020 - 17:18
Abstract

We develop a mixed Long Short Term Memory (LSTM) regression model to predict the maximum solar flare intensity within a 24‐hour time window 0~24, 6~30, 12~36 and 24~48 hours ahead of time using 6, 12, 24 and 48 hours of data (predictors) for each Helioseismic and Magnetic Imager (HMI) Active Region Patch (HARP). The model makes use of (1) the Space‐weather HMI Active Region Patch (SHARP) parameters as predictors and (2) the exact flare intensities instead of class labels recorded in the Geostationary Operational Environmental Satellites (GOES) data set, which serves as the source of the response variables. Compared to solar flare classification, the model offers us more detailed information about the exact maximum flux level, i.e. intensity, for each occurrence of a flare. We also consider classification models built on top of the regression model and obtain better results in solar flare classifications as compared to Chen et al. (2019). Our results suggest that the most efficient time period for predicting the solar activity is within 24 hours before the prediction time using the SHARP parameters and the LSTM model.

Assimilation of GNSS Measurements for Estimation of High‐Latitude Convection Processes

Fri, 05/15/2020 - 17:14
Abstract

Geomagnetic storms produce significant electrodynamics at mid‐latitudes. Strong ion convection can affect thermospheric neutral wind motion. The converse is also true, such that both fields and winds can drive ionospheric plasma movement. This work adjusts a background modeled high‐latitude electrostatic potential to estimate the storm‐time electric field based on data‐derived plasma densities and measurements of neutral wind. Electron densities are derived from global navigation satellite system (GNSS) total electron content measurements using Ionospheric Data Assimilation Four‐Dimensional. These are input to Estimating Model Parameters from Ionospheric Reverse Engineering (EMPIRE) to estimate electric potential corrections to the background Weimer 2000 potential model. The EMPIRE basis functions for electric potential are spherical harmonics in dipole magnetic colatitude and longitude, enforced to be constant along a magnetic field line. For the 17 March 2015 storm, EMPIRE electric potential produces westward zonal ion drifts that more closely agree with incoherent scatter radar (ISR) measurements made at Millstone Hill than the background Weimer 2000 model alone, when electric potential and meridional neutral winds are both corrected. Additionally ingesting northward line‐of‐sight neutral wind measurements from a Fabry‐Perot interferometer at Millstone Hill makes little difference in the agreement between zonal ion drift predictions and measurements. Estimation of only electric potential reduces the agreement between the assimilated prediction of the field‐perpendicular zonal drifts and ISR measurements significantly.

Assimilation of GNSS Measurements for Estimation of High‐Latitude Convection Processes

Fri, 05/15/2020 - 17:14
Abstract

Geomagnetic storms produce significant electrodynamics at mid‐latitudes. Strong ion convection can affect thermospheric neutral wind motion. The converse is also true, such that both fields and winds can drive ionospheric plasma movement. This work adjusts a background modeled high‐latitude electrostatic potential to estimate the storm‐time electric field based on data‐derived plasma densities and measurements of neutral wind. Electron densities are derived from global navigation satellite system (GNSS) total electron content measurements using Ionospheric Data Assimilation Four‐Dimensional. These are input to Estimating Model Parameters from Ionospheric Reverse Engineering (EMPIRE) to estimate electric potential corrections to the background Weimer 2000 potential model. The EMPIRE basis functions for electric potential are spherical harmonics in dipole magnetic colatitude and longitude, enforced to be constant along a magnetic field line. For the 17 March 2015 storm, EMPIRE electric potential produces westward zonal ion drifts that more closely agree with incoherent scatter radar (ISR) measurements made at Millstone Hill than the background Weimer 2000 model alone, when electric potential and meridional neutral winds are both corrected. Additionally ingesting northward line‐of‐sight neutral wind measurements from a Fabry‐Perot interferometer at Millstone Hill makes little difference in the agreement between zonal ion drift predictions and measurements. Estimation of only electric potential reduces the agreement between the assimilated prediction of the field‐perpendicular zonal drifts and ISR measurements significantly.

Effect of additional magnetograph observations from different Lagrangian points in Sun‐Earth system on predicted properties of quasi‐steady solar wind at 1 AU

Fri, 05/15/2020 - 16:09
Abstract

Modeling the space weather conditions for a near‐Earth environment depends on a proper representation of magnetic fields on the Sun. There are discussions in the community with respect to the value of observations taken at several Lagrangian points (L1‐L5) in the Sun‐Earth system. Observations from a single (e.g., Earth/L1) vantage point are insufficient to characterize rapid changes in magnetic field on the far side of the Sun. Nor can they represent well the magnetic fields near the solar poles. However, if the changes in sunspot activity were moderate, how well would our predictions of the solar wind based on a single viewing point work? How much improvement could we see by adding magnetograph observations from L5, L4, and even L3? Here, we present the results of our recent modeling, which shows the level of improvement in forecasting the properties of the solar wind at Earth made possible by using additional observations from different vantage points during a period of moderate evolution of sunspot activity. As an example, we also show the improvements to the solar wind forecast from adding a single observation of the southern polar area from out‐of‐ecliptic spacecraft at ‐30° heliographic latitude vantage point.

Effect of additional magnetograph observations from different Lagrangian points in Sun‐Earth system on predicted properties of quasi‐steady solar wind at 1 AU

Fri, 05/15/2020 - 16:09
Abstract

Modeling the space weather conditions for a near‐Earth environment depends on a proper representation of magnetic fields on the Sun. There are discussions in the community with respect to the value of observations taken at several Lagrangian points (L1‐L5) in the Sun‐Earth system. Observations from a single (e.g., Earth/L1) vantage point are insufficient to characterize rapid changes in magnetic field on the far side of the Sun. Nor can they represent well the magnetic fields near the solar poles. However, if the changes in sunspot activity were moderate, how well would our predictions of the solar wind based on a single viewing point work? How much improvement could we see by adding magnetograph observations from L5, L4, and even L3? Here, we present the results of our recent modeling, which shows the level of improvement in forecasting the properties of the solar wind at Earth made possible by using additional observations from different vantage points during a period of moderate evolution of sunspot activity. As an example, we also show the improvements to the solar wind forecast from adding a single observation of the southern polar area from out‐of‐ecliptic spacecraft at ‐30° heliographic latitude vantage point.

Prediction of Dst During Solar Minimum Using In Situ Measurements at L5

Thu, 05/14/2020 - 19:00
Abstract

Geomagnetic storms resulting from high‐speed streams can have significant negative impacts on modern infrastructure due to complex interactions between the solar wind and geomagnetic field. One measure of the extent of this effect is the Kyoto D s t index. We present a method to predict D s t from data measured at the Lagrange 5 (L5) point, which allows for forecasts of solar wind development 4.5 days in advance of the stream reaching the Earth. Using the STEREO‐B satellite as a proxy, we map data measured near L5 to the near‐Earth environment and make a prediction of the D s t from this point using the Temerin‐Li D s t model enhanced from the original using a machine learning approach. We evaluate the method accuracy with both traditional point‐to‐point error measures and an event‐based validation approach. The results show that predictions using L5 data outperform a 27‐day solar wind persistence model in all validation measures but do not achieve a level similar to an L1 monitor. Offsets in timing and the rapidly changing development of B z in comparison to B x and B y reduce the accuracy. Predictions of D s t from L5 have a root‐mean‐square error of 9 nT, which is double the error of 4 nT using measurements conducted near the Earth. The most useful application of L5 measurements is shown to be in predicting the minimum D s t for the next 4 days. This method is being implemented in a real‐time forecast setting using STEREO‐A as an L5 proxy and has implications for the usefulness of future L5 missions.

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