On the prediction of the auroral westward electrojet index

An ARMAX based model, to forecast the evolution of the of AL index, is developed. The model has been trained and validated using neural networks with the half wave rectifier (VBs) as input. It is shown that the model posses a good, reliable forecasting ability, including periods of intense geomagnetic activity. Prediction efficiency of the model is discussed in the context of 1 min resolution output smoothed over 7 min

Can ring current stabilize magnetotail during steady magnetospheric convection?

The present study investigates the role of the ring current in stabilizing the magnetotail during steady magnetospheric convection (SMC) events. We develop a method for estimation of the symmetric ring current intensity from the single spacecraft magnetic field observations. The method is applied to a large number of SMC events identified using three different automatic procedures adopted from the literature. It is found that the symmetric ring current can be weak or strong depending on a particular event. We find a significant fraction of events that have a rather weak symmetric ring current in spite of the strong solar wind driving during the event. These findings imply that the symmetric ring current plays no role in the magnetotail stabilization.Key PointsAnalysis of AE‐based criteria for SMC selectionNew method for ring current intensity estimationRing current plays no role in magnetotail stabilizationPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134802/1/jgra52295_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134802/2/jgra52295.pd

Solar wind‐driven variations of electron plasma sheet densities and temperatures beyond geostationary orbit during storm times

The empirical models of the plasma sheet electron temperature and density on the nightside at distances between 6 and 11 RE are constructed based on Time History of Events and Macroscale Interactions During Substorms (THEMIS) particle measurements. The data set comprises ∼400 h of observations in the plasma sheet during geomagnetic storm periods. The equatorial distribution of the electron density reveals a strong earthward gradient and a moderate variation with magnetic local time symmetric with respect to the midnight meridian. The electron density dependence on the external driving is parameterized by the solar wind proton density averaged over 4 h and the southward component of interplanetary magnetic field (IMF BS) averaged over 6 h. The interval of the IMF integration is much longer than a typical substorm growth phase, and it rather corresponds to the geomagnetic storm main phase duration. The solar wind proton density is the main controlling parameter, but the IMF BS becomes of almost the same importance in the near‐Earth region. The root‐mean‐square deviation between the observed and predicted plasma sheet density values is 0.23 cm−3, and the correlation coefficient is 0.82. The equatorial distribution of the electron temperature has a maximum in the postmidnight to morning MLT sector, and it is highly asymmetric with respect to the local midnight. The electron temperature model is parameterized by solar wind velocity (averaged over 4 h), IMF BS (averaged over 45 min), and IMF BN (northward component of IMF, averaged over 2 h). The solar wind velocity is a major controlling parameter, and IMF BS and BN are comparable in importance. In contrast to the density model, the electron temperature shows higher correlation with the IMF BS averaged over ∼45 min (substorm growth phase time scale). The effect of BN manifests mostly in the outer part of the modeled region (r > 8RE). The influence of the IMF BS is maximal in the midnight to postmidnight MLT sector. The correlation coefficient between the observed and predicted plasma sheet electron temperature values is 0.76, and the root‐mean‐square deviation is 2.6 keV. Both models reveal better performance in the dawn MLT sector.Key PointsEmpirical models of electron density and temperature at r = 6–11 Re on the nightside are constructedThe model performance has been essentially improved by using lagged and time‐averaged solar wind parameters as a model inputElectron temperature and density correllate best with IMF Bs averaged over substorm growth phase and storm main phase periods, respectivelyPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134493/1/jgra52881.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134493/2/jgra52881_am.pd

Storm-time ring current: model-dependent results

The main point of the paper is to investigate how much the modeled ring current depends on the representations of magnetic and electric fields and boundary conditions used in simulations. Two storm events, one moderate (SymH minimum of −120 nT) on 6–7 November 1997 and one intense (SymH minimum of −230 nT) on 21–22 October 1999, are modeled. A rather simple ring current model is employed, namely, the Inner Magnetosphere Particle Transport and Acceleration model (IMPTAM), in order to make the results most evident. Four different magnetic field and two electric field representations and four boundary conditions are used. We find that different combinations of the magnetic and electric field configurations and boundary conditions result in very different modeled ring current, and, therefore, the physical conclusions based on simulation results can differ significantly. A time-dependent boundary outside of 6.6 RE gives a possibility to take into account the particles in the transition region (between dipole and stretched field lines) forming partial ring current and near-Earth tail current in that region. Calculating the model SymH* by Biot-Savart's law instead of the widely used Dessler-Parker-Sckopke (DPS) relation gives larger and more realistic values, since the currents are calculated in the regions with nondipolar magnetic field. Therefore, the boundary location and the method of SymH* calculation are of key importance for ring current data-model comparisons to be correctly interpreted.Peer reviewe

Nowcast model for low‐energy electrons in the inner magnetosphere

We present the nowcast model for low‐energy (<200 keV) electrons in the inner magnetosphere, which is the version of the Inner Magnetosphere Particle Transport and Acceleration Model (IMPTAM) for electrons. Low‐energy electron fluxes are very important to specify when hazardous satellite surface‐charging phenomena are considered. The presented model provides the low‐energy electron flux at all L shells and at all satellite orbits, when necessary. The model is driven by the real‐time solar wind and interplanetary magnetic field (IMF) parameters with 1 h time shift for propagation to the Earth's magnetopause and by the real time Dst index. Real‐time geostationary GOES 13 or GOES 15 (whenever each is available) data on electron fluxes in three energies, such as 40 keV, 75 keV, and 150 keV, are used for comparison and validation of IMPTAM running online. On average, the model provides quite reasonable agreement with the data; the basic level of the observed fluxes is reproduced. The best agreement between the modeled and the observed fluxes are found for <100 keV electrons. At the same time, not all the peaks and dropouts in the observed electron fluxes are reproduced. For 150 keV electrons, the modeled fluxes are often smaller than the observed ones by an order of magnitude. The normalized root‐mean‐square deviation is found to range from 0.015 to 0.0324. Though these metrics are buoyed by large standard deviations, owing to the dynamic nature of the fluxes, they demonstrate that IMPTAM, on average, predicts the observed fluxes satisfactorily. The computed binary event tables for predicting high flux values within each 1 h window reveal reasonable hit rates being 0.660–0.318 for flux thresholds of 5 ·104–2 ·105 cm−2 s−1 sr−1 keV−1 for 40 keV electrons, 0.739–0.367 for flux thresholds of 3 ·104–1 ·105 cm−2 s−1 sr−1 keV−1 for 75 keV electrons, and 0.485–0.438 for flux thresholds of 3 ·103–3.5 ·103 cm−2 s−1 sr−1 keV−1 for 150 keV electrons but rather small Heidke Skill Scores (0.17 and below). This is the first attempt to model low‐energy electrons in real time at 10 min resolution. The output of this model can serve as an input of electron seed population for real‐time higher‐energy radiation belt modeling.Key PointsNowcast model for low‐energy electronsOnline near‐real‐time comparison to GOES MAGED dataFirst successful model for low‐energy electrons in real timePeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/110719/1/swe20196.pd

Locations of boundaries of outer and inner radiation belts as observed by Cluster and Double Star

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95464/1/jgra21211.pd

Inner magnetosphere currents during the CIR/HSS storm on July 21–23, 2009

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94920/1/jgra21817.pd

Electron Fluxes at Geostationary Orbit From GOES MAGED Data

Electron behavior in energies below 200 keV at geostationary orbit has significance for satellite operations due to charging effects on spacecraft. Five years of keV energy electron measurements by the geostationary GOES‐13 satellite’s MAGnetospheric Electron Detector (MAGED) instrument has been analyzed. A method for determining flight direction integrated fluxes is presented. The electron fluxes at the geostationary orbit are shown to have significant dependence on solar wind speed and interplanetary magnetic field (IMF) BZ: increased solar wind speed correlates with higher electron fluxes with all magnetic local times while negative IMF BZ increases electron fluxes in the 0 to 12 magnetic local time sector. A predictive empirical model for electron fluxes in the geostationary orbit for energies 40, 75, and 150 keV was constructed and is presented here. The empirical model is dependent on three parameters: magnetic local time, solar wind speed, and IMF BZ.Plain Language SummaryLow‐energy electrons in near‐Earth space can be hazardous to satellites due to charging effects they may cause. Five years of low‐energy electron data from the geostationary orbit of Earth by GOES‐13 satellite was analyzed. The statistical analysis showed that low‐energy electron fluxes were elevated by increased solar wind velocity for any position on the geostationary orbit. In addition, when the magnetic field carried by the solar wind was southward, the electron fluxes were elevated in about half the orbit, while on the other half the fluxes were not affected. A predictive model of low‐energy electrons at geostationary orbit was built based on this data. A new empirical model was constructed to predict electron fluxes in energies between 30 and 200 keV at the different positions at the geostationary orbit. The model uses solar wind speed and magnetic field values to calculate the predicted electron fluxes.Key PointsAn empirical, predictive model function is presented for electron fluxes for energies of 40, 75, and 150 keV at geostationary orbitHigher solar wind speed in general results in electron flux enhancements in energies 30–200 keV at geostationary orbitNegative IMF BZ at midnight to noon results in electron flux enhancements in energies 30–200 keV at geostationary orbitPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141709/1/swe20538.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/141709/2/swe20538_am.pd

Low‐energy electrons (5–50 keV) in the inner magnetosphere

Transport and acceleration of the 5–50 keV electrons from the plasma sheet to geostationary orbit were investigated. These electrons constitute the low‐energy part of the seed population for the high‐energy MeV particles in the radiation belts and are responsible for surface charging. We modeled one nonstorm event on 24–30 November 2011, when the presence of isolated substorms was seen in the AE index. We used the Inner Magnetosphere Particle Transport and Acceleration Model (IMPTAM) with the boundary at 10 R E with moment values for the electrons in the plasma sheet. The output of the IMPTAM modeling was compared to the observed electron fluxes in 10 energy channels (from 5 to 50 keV) measured on board the AMC 12 geostationary spacecraft by the Compact Environmental Anomaly Sensor II with electrostatic analyzer instrument. The behavior of the fluxes depends on the electron energy. The IMPTAM model, driven by the observed parameters such as Interplanetary Magnetic Field (IMF) B y and B z , solar wind velocity, number density, dynamic pressure, and the Dst index, was not able to reproduce the observed peaks in the electron fluxes when no significant variations are present in those parameters. We launched several substorm‐associated electromagnetic pulses at the substorm onsets during the modeled period. The observed increases in the fluxes can be captured by IMPTAM when substorm‐associated electromagnetic fields are taken into account. Modifications of the pulse front velocity and arrival time are needed to exactly match the observed enhancements. Key Points Electron flux peaks due to substorm activity Solar wind driven inner magnetosphere model does not work for quiet times Substorm‐associated fields to explain electron flux peaksPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106068/1/jgra50735.pd

Testing the magnetotail configuration based on observations of low‐altitude isotropic boundaries during quiet times

We investigate the configuration of the geomagnetic field on the nightside magnetosphere during a quiet time interval based on National Oceanic and Atmospheric Administration Polar Orbiting Environment Satellites Medium Energy Proton and Electron Detector (NOAA/POES MEPED) measurements in combination with numerical simulations of the global terrestrial magnetosphere using the Space Weather Modeling Framework. Measurements from the NOAA/POES MEPED low‐altitude data sets provide the locations of isotropic boundaries; those are used to extract information regarding the field structure in the source regions in the magnetosphere. In order to evaluate adiabaticity and mapping accuracy, which is mainly controlled by the ratio between the radius of curvature and the particle’s Larmor radius, we tested the threshold condition for strong pitch angle scattering based on the MHD magnetic field solution. The magnetic field configuration is represented by the model with high accuracy, as suggested by the high correlation coefficients and very low normalized root‐mean‐square errors between the observed and the modeled magnetic field. The scattering criterion, based on the values of k=Rcρ ratio at the crossings of magnetic field lines, associated with isotropic boundaries, with the minimum B surface, predicts a critical value of kCR∼33. This means that, in the absence of other scattering mechanisms, the strong pitch angle scattering takes place whenever the Larmor radius is ∼33 times smaller than the radius of curvature of the magnetic field, as predicted by the Space Weather Modeling Framework.Key PointsWe tested the threshold condition for strong pitch angle scattering based on the MHD magnetic fieldSWMF model suggests a threshold condition for strong pitch angle scattering of k = 33For quiet time, the k parameter varies within 2 orders of magnitudePeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135070/1/jgra52310.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/135070/2/jgra52310_am.pd