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

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

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

Formation of 30 KeV Proton Isotropic Boundaries During Geomagnetic Storms

We study the origin of the 30 keV proton isotropic boundary (IB) in the nightside auroral zone during geomagnetic storms, particularly, to address the recent results that the adiabaticity parameter K (ratio of the magnetic field line curvature radius to the particle gyroradius at the equator) on the IB field line can be much larger comparing to its theoretical estimate K ∼ 8 for the field line curvature (FLC) scattering mechanism. During nine storms in 2011–2013, we investigate ∼2,000 IBs observed by low‐altitude Polar Operational Environmental Satellites (POES) satellites and apply the TS05 magnetospheric model to estimate the K value in the equatorial part of the IB field line. The statistical distribution of the estimated K parameter, while being rather broad, is centered on K = 9–13. For smaller subset of ∼250 IBs, the concurrent magnetic field measurements on board Time History of Events and Macroscale Interaction During Substorms probes in the equatorial magnetotail were used to correct the estimated K‐values accounting for the TS05 deviations from the real magnetic configuration. After correction, the K distribution becomes narrower, being still centered on K = 9–12. Different estimates give percentages of events with K < 13, which can be attributed to IBs formed by FLC scattering, between 60% and 80%. Finally, we have not found any dependence of the K distribution on magnetic local time and IB latitude, except for events with IB located at extremely low latitudes (<59°). These findings imply that the FLC scattering is a dominant mechanism of IB formation operating in a variety of magnetospheric conditions.Key PointsConditions at equatorial part of proton Isotropic Boundary field lines are analyzed using TS05 magnetospheric model and THEMIS observationsAdiabaticity parameter values expected for isotropic boundary formation by scattering on curved field lines were found for 60–80% of eventsIsotropic boundaries which do not fit this scenario reveal higher occurrence during the main phase or/and at latitudes lower than 59 degreesPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/144595/1/jgra54191.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/144595/2/jgra54191_am.pd