Solar Wind Density Research Articles

Data‐Driven Forecasting of Low‐Latitude Ionospheric Total Electron Content Using the Random Forest and LSTM Machine Learning Methods

AbstractIn this research, we present data‐driven forecasting of ionospheric total electron content (TEC) using the Long‐Short Term Memory (LSTM) deep recurrent neural network method. The random forest machine learning method was used to perform a regression analysis and estimate the variable importance of the input parameters. The input data are obtained from satellite and ground based measurements characterizing the solar‐terrestrial environment. We estimate the relative importance of 34 different parameters, including the solar flux, solar wind density, and speed the three components of interplanetary magnetic field, Lyman‐alpha, the Kp, Dst, and Polar Cap (PC) indices. The TEC measurements are taken with 15‐s cadence from an equatorial GPS station located at Bogota, Columbia (4.7110° N, 74.0721° W). The 2008–2017 data set, including the top five parameters estimated using the random forest, is used for training the machine learning models, and the 2018 data set is used for independent testing of the LSTM forecasting. The LSTM method as applied to forecast the TEC up to 5 h ahead, with 30‐min cadence. The results indicate that very good forecasts with low root mean square (RMS) error (high correlation) can be made in the near future and the RMS errors increase as we forecast further into the future. The data sources are satellite and ground based measurements characterizing the solar‐terrestrial environment.

Geosynchronous Magnetopause Crossings and Their Relationships With Magnetic Storms and Substorms

AbstractThe paper investigates the strengthening of magnetospheric activity related to geosynchronous magnetopause crossings (GMCs). We make a list of GMC events using the empirical magnetopause model (Lin et al., 2010, https://doi.org/10.1029/2009ja014235) and hourly averaged OMNI data and find which solar wind and magnetospheric conditions accompany and follow the GMCs. The GMCs are mostly caused by the impact of interplanetary coronal mass ejections (ICMEs) and/or interplanetary shocks often with a strong increase in the density and a moderate increase in velocity. The average solar wind density during the first GMC hour is higher than 20 cm−3 in 70% cases, while the velocity is higher than 500 km/s in 56% cases. The hourly interplanetary magnetic field (IMF) BZ is negative in 87% cases. The average over all events SMU (SML), Kp, and PC indices reach maxima (minima) in 1 h after the GMC beginning, while the delay of the minimum of the Dst index is usually 3–8 h. These average time delays do not depend on the strength of the storms and substorms. The SML (Dst) minimum is less than −500 nT (−30 nT) in the next 24 h in 95% (99%) cases, that is, the GMC events are mostly followed by magnetic storms and substorms. We compare solar wind and magnetospheric conditions for GMCs connected with ICMEs and stream interaction regions (SIRs). Our study confirms that the ICME‐related events are characterized by stronger ring current and auroral activity than the SIR‐related events. The difference might be explained by the different behavior of the solar wind velocity.

Correlation analyses between solar activity parameters and cosmic ray muons between 2002 and 2012 at high cutoff rigidity

• The impacts of seven solar, interplanetary, and geophysical parameters on CR data have been investigated. • CR data for the period 2002–2012 from KACST muon detector located at high cutoff rigidity have been used. • CR data from Oulu neutron monitor for the same period have been used for comparisons. • Multivariable models were developed to predict CR variability at KACST and Ouu. Solar activity modulates cosmic ray (CR) flux with different magnitudes on different time scales. Several investigations from locations with different, mainly low, cutoff rigidity utilizing different solar activity parameters have been carried out to characterize their influence on the observed CR flux. In this study, the effect of seven solar, interplanetary, and geophysical parameters on the secondary CR muons has been investigated and established using correlation analyses. Daily mean values of the CR data for the period between 2002 and 2012 were obtained from the King Abdulaziz City for Science and Technology (KACST) muon detector, Riyadh, central Saudi Arabia (Rc = 14.4 GV). Considered parameters are sunspot number, radial component of the interplanetary magnetic field, Kp index, solar radio emission flux at 10.7 cm, Dst index, solar wind speed, and solar wind density. Same analyses have been carried out using data from the Oulu neutron monitor (Rc = 0.8 GV) for comparison purposes. Obtained results showed that the intensities of the secondary CRs from both stations are significantly correlated with the Dst index and plasma density, and anti-correlated with the rest of the variables. These results are in agreement with those obtained by several investigators. Magnitude and strength of the correlations between the considered variables and CRs were higher and stronger for the CR neutrons than the CR muons. These findings may be due to the greater influence of seasonal variations on the CR muons than on the CR neutrons. Additionally, the muon detector is sensitive (due to its high cutoff rigidity) to higher-energy CR particles, which are less affected by solar disturbances. Time-lag cross-correlation analyses between the monthly mean CR values from both stations and the monthly mean values of the considered variables were conducted. Comparable results with the previous investigations were found. Multivariable models using the seven parameters were developed to predict the CR variations for both sites. For the data from the KACST detector, the model was able to predict the measured data with a correlation coefficient of 0.48 and a standard deviation of 0.60%. On the other hand, the developed model for the Oulu neutron monitor has a correlations coefficient of 0.77 and a standard deviation of 3.7%.

An approximate analytic solution to the coupled problems of coronal heating and solar-wind acceleration

Between the base of the solar corona at $r=r_\textrm {b}$ and the Alfvén critical point at $r=r_\textrm {A}$ , where $r$ is heliocentric distance, the solar-wind density decreases by a factor $ \mathop > \limits_\sim 10^5$ , but the plasma temperature varies by a factor of only a few. In this paper, I show that such quasi-isothermal evolution out to $r=r_\textrm {A}$ is a generic property of outflows powered by reflection-driven Alfvén-wave (AW) turbulence, in which outward-propagating AWs partially reflect, and counter-propagating AWs interact to produce a cascade of fluctuation energy to small scales, which leads to turbulent heating. Approximating the sub-Alfvénic region as isothermal, I first present a brief, simplified calculation showing that in a solar or stellar wind powered by AW turbulence with minimal conductive losses, $\dot {M} \simeq P_\textrm {AW}(r_\textrm {b})/v_\textrm {esc}^2$ , $U_{\infty } \simeq v_\textrm {esc}$ , and $T\simeq m_\textrm {p} v_\textrm {esc}^2/[8 k_\textrm {B} \ln (v_\textrm {esc}/\delta v_\textrm {b})]$ , where $\dot {M}$ is the mass outflow rate, $U_{\infty }$ is the asymptotic wind speed, $T$ is the coronal temperature, $v_\textrm {esc}$ is the escape velocity of the Sun, $\delta v_\textrm {b}$ is the fluctuating velocity at $r_\textrm {b}$ , $P_\textrm {AW}$ is the power carried by outward-propagating AWs, $k_\textrm {B}$ is the Boltzmann constant, and $m_\textrm {p}$ is the proton mass. I then develop a more detailed model of the transition region, corona, and solar wind that accounts for the heat flux $q_\textrm {b}$ from the coronal base into the transition region and momentum deposition by AWs. I solve analytically for $q_\textrm {b}$ by balancing conductive heating against internal-energy losses from radiation, $p\,\textrm {d} V$ work, and advection within the transition region. The density at $r_\textrm {b}$ is determined by balancing turbulent heating and radiative cooling at $r_\textrm {b}$ . I solve the equations of the model analytically in two different parameter regimes. In one of these regimes, the leading-order analytic solution reproduces the results of the aforementioned simplified calculation of $\dot {M}$ , $U_\infty$ , and $T$ . Analytic and numerical solutions to the model equations match a number of observations.

Interstellar Pickup Ion Observations Halfway to the Termination Shock

Abstract In this study, we extend the prior interstellar pickup ion (PUI) observations from the Solar Wind Around Pluto (SWAP) instrument on New Horizons out to nearly 47 au—essentially halfway to the termination shock in the upwind direction. We also provide significantly improved analyses of these and prior observations, including incorporating a cooling index, α, to characterize the nonadiabatic heating of PUI distributions. We find that the vast majority (93.6%) of all distributions show additional heating above adiabatic cooling. Speed jumps indicate compressional waves and shocks with associated enhancements in core solar wind and PUI densities and temperatures. Interestingly, additional heating of the PUIs as indicated by a peak in the cooling index follows the jumps by about a week. We characterize nearly continuous solar wind and H+ PUI data over ∼22–47 au, producing radial gradients, “fiducial” values at 45 au—halfway to the nominal upstream termination shock—for direct comparison to models, and extrapolated values at the shock. These termination shock values are n PUI = (4.1 ± 0.6) × 10−4 cm−3, T PUI = (5.0 ± 0.4) × 106 K, P PUI = 30 ± 4 fPa, α = 2.9 ± 0.2, n PUI/n Total = 0.24 ± 0.02, T PUI/T SW = 716 ± 124, P PUI/P SW = 173 ± 32, P PUI/P SW − Dyn = 0.14 ± 0.01. The PUI thermal pressure exceeds by more than an order of magnitude the thermal solar wind and magnetic pressures in the outer heliosphere. SWAP provides the first and only direct observations of interstellar PUIs in the outer heliosphere, which are critical for both inferring the plasma conditions at the termination shock and understanding PUI-mediated shocks in general. This study examines these observations and serves as the citable reference for these critical data.

Spatial structures in solar wind superthermal electrons and polar rain aurora

We report a special polar rain aurora case around 11:24 UT on October 27, 2003, where intense polar rain electrons produced observable polar rain auroral emission with the shape of a roughly dawn-dusk aligned bar. Associated solar wind speed and density observations during the event were around 450 km/s and 2.5 cm−3 respectively. The interplanetary magnetic field (IMF) components Bx, By, and Bz were ~5, −3, and 5 nT respectively. The negative By condition likely caused the dawnside shift and slight tilt of the polar rain aurora bar. Furthermore, although Kelvin-Helmholtz waves on the high latitude magnetopause have been previously reported to induce dawn-dusk aligned auroral bars (Zhang et al., 2007), the solar wind and IMF conditions of the event are not favorable for generating them (Zhang et al., 2013) and are therefore not a likely cause. Instead, coincident observations by the Geotail satellite show enhanced anti-sunward flux in the solar wind superthermal electrons (7 eV–42 keV) around the time of the auroral bar. The solar wind superthermal electron spatial size, when mapped into the polar ionosphere, is consistent with the width of the auroral bar, confirming a connection between the two.

Dynamics of Cosmic-Ray Cutoff Rigidity and Magnetospheric Parameters during Different Phases of the Storm of November 20, 2003

The correlations between variations in the geomagnetic cutoff rigidity of cosmic rays and the Dst and Kp geomagnetic indices and solar-wind and IMF parameters are calculated for the three phases of the magnetic storm of November 20–21, 2003: before the storm and during its main and recovery phases. The correlations are the strongest between variations in the cutoff rigidity and the Dst index during all stages. A significant correlation was recorded with the By component of IMF and the field magnitude B; the correlation with By dominated during the main phase, and the correlation with B was dominant during the recovery phase. There is also a high correlation with the dynamic parameters of solar activity during the main phase, especially with the solar-wind speed. As far as we know, hysteresis phenomena have been discovered for the first time in the relationship between the cosmic-ray cutoff rigidities and the parameters of the helio- and magnetosphere on the scale of the magnetic storm (with Moscow station as an example). Loop-like patterns formed, because the trajectories of variations in the cutoff rigidities versus the studied parameters during storm intensification (development of current systems) did not coincide with the trajectories during the recovery phase (decay of current systems). The correlations of the cutoff rigidities with Dst and Kp indices were characterized by a narrow hysteresis loop, and their correlations with the IMF parameters were characterized by a wide hysteresis loop. The hysteresis loops for the relationship between the cutoff rigidities and solar-wind density and pressure were disordered.

The impact of solar wind variability on pulsar timing

Context. High-precision pulsar timing requires accurate corrections for dispersive delays of radio waves, parametrized by the dispersion measure (DM), particularly if these delays are variable in time. In a previous paper, we studied the solar wind (SW) models used in pulsar timing to mitigate the excess of DM that is annually induced by the SW and found these to be insufficient for high-precision pulsar timing. Here we analyze additional pulsar datasets to further investigate which aspects of the SW models currently used in pulsar timing can be readily improved, and at what levels of timing precision SW mitigation is possible. Aims. Our goals are to verify: (a) whether the data are better described by a spherical model of the SW with a time-variable amplitude, rather than a time-invariant one as suggested in literature, and (b) whether a temporal trend of such a model’s amplitudes can be detected. Methods. We use the pulsar timing technique on low-frequency pulsar observations to estimate the DM and quantify how this value changes as the Earth moves around the Sun. Specifically, we monitor the DM in weekly to monthly observations of 14 pulsars taken with parts of the LOw-Frequency ARray (LOFAR) across time spans of up to 6 years. We develop an informed algorithm to separate the interstellar variations in the DM from those caused by the SW and demonstrate the functionality of this algorithm with extensive simulations. Assuming a spherically symmetric model for the SW density, we derive the amplitude of this model for each year of observations. Results. We show that a spherical model with a time-variable amplitude models the observations better than a spherical model with a constant amplitude, but that both approaches leave significant SW-induced delays uncorrected in a number of pulsars in the sample. The amplitude of the spherical model is found to be variable in time, as opposed to what has been previously suggested.

A space hurricane over the Earth\u2019s polar ionosphere

In Earth’s low atmosphere, hurricanes are destructive due to their great size, strong spiral winds with shears, and intense rain/precipitation. However, disturbances resembling hurricanes have not been detected in Earth’s upper atmosphere. Here, we report a long-lasting space hurricane in the polar ionosphere and magnetosphere during low solar and otherwise low geomagnetic activity. This hurricane shows strong circular horizontal plasma flow with shears, a nearly zero-flow center, and a coincident cyclone-shaped aurora caused by strong electron precipitation associated with intense upward magnetic field-aligned currents. Near the center, precipitating electrons were substantially accelerated to ~10 keV. The hurricane imparted large energy and momentum deposition into the ionosphere despite otherwise extremely quiet conditions. The observations and simulations reveal that the space hurricane is generated by steady high-latitude lobe magnetic reconnection and current continuity during a several hour period of northward interplanetary magnetic field and very low solar wind density and speed.

Performance and simulated moment uncertainties of an ion spectrometer with asymmetric 2π field of view for ion measurements in space.

Space plasma instruments provide 3D particle velocity distribution functions. Because of telemetry limitations, these cannot be transmitted in high time resolution and the plasma needs to be characterized by moments of the velocity distribution function. These moment uncertainties have vital effects on the reliability and accuracy of onboard plasma moments. We assess the measurement accuracy for magnetosheath and solar wind ions using an ion spectrometer with an asymmetric field of view designed for the all-sky measurement of low-energy ions in the magnetosheath and solar wind. We focus on moment uncertainties for the ideal spectrometer, not considering the background counts, which may have considerable effects on the uncertainties in real life. To obtain number density, bulk velocity, and temperature, different orders of moments are integrated assuming a Maxwellian velocity distribution. Based on the design specifications, we use simulations to estimate systematic and random errors for typical plasma conditions. We find that the spectrometer resolution is adequate for determining the density of solar wind (∼7% error) and magnetosheath ions (∼4% error). The resolution is also adequate for determining the temperature of solar wind (∼10% error) and magnetosheath ions (∼2% error). For high speed flows with a bulk velocity of 750 km/s and a temperature of 20 eV, the maximum density and temperature errors become 9% and 7%, respectively. The bulk velocity errors are less than 2% for all cases. The contributions of heavy ions to the systematic errors are less than 5% for magnetosheath ions and less than 8% for solar wind ions.

Interaction of Space Weather Phenomena with Mars Plasma Environment During Solar Minimum 23/24

AbstractWe study the interaction of three solar wind (SW) structures, two stream interaction regions, and one interplanetary coronal mass ejection, with Mars’ plasma environment during November 20–27, 2007. This period corresponds to the solar minimum between the solar cycles 23 and 24 which was characterized by very low values of the SW density and dynamic pressure and low interplanetary magnetic field magnitude. During that time the Mars Express orbit was in the terminator plane, while the Earth, Sun, and Mars were almost aligned, so we use the Advance Composition Explorer and Solar Terrestrial Relations Observatory probes as SW monitors in order to identify and characterize the structures that later hit Mars. We find that the passage of these structures caused strong variations in the bow shock location (between 2.2 and 3.0 RM), compression of the magnetospheric cavity (up to 45%), and an increased transterminator flow below 2 RM (by a factor of ≤ 8). This study shows that during times of low solar activity, modest space weather phenomena may cause large variations of plasma flow at Mars.

Variability of Upstream Proton Cyclotron Wave Properties and Occurrence at Mars Observed by MAVEN

AbstractThe presence of plasma waves upstream from the Martian bow shock, with frequencies near the local proton cyclotron frequency in the spacecraft frame, constitutes, in principle, an indirect signature for the existence of planetary protons from the ionization of Martian exospheric hydrogen. In this study, we determine the "proton cyclotron wave” (PCW) occurrence rate between October 2014 and February 2020, based on Magnetometer and Solar Wind Ion Analyzer measurements from the Mars Atmosphere and Volatile EvolutioN mission. We characterize its dependence on several wave and solar wind (SW) properties, and solar longitude ranges. We confirm a previously reported long‐term trend with more PCWs near perihelion, likely associated with changes in exospheric hydrogen density. Furthermore, we report for the first time a decrease in median PCW amplitude for each consecutive Martian perihelion. Such variability cannot be attributed to differences in the distribution of SW conditions. This trend could be associated with changes in solar inputs, foreshock effects, and asymmetries due to the SW convective electric field influencing newborn protons. In addition, we observe PCWs more frequently for low to intermediate interplanetary magnetic field (IMF) cone angles, slower SW speeds, and higher SW proton densities. The IMF cone angle preference likely results from the trade‐off between associated linear wave growth rates, wave saturation energies, and pick‐up proton densities. Moreover, the dependencies on SW speed and density indicate the importance of the characteristic SW transit timescale and the charge exchange process coupling SW protons with the hydrogen exosphere.

Deriving CME Density From Remote Sensing Data and Comparison to In‐Situ Measurements

AbstractWe determine the three‐dimensional geometry and deprojected mass of 29 well‐observed coronal mass ejections (CMEs) and their interplanetary counterparts (ICMEs) using combined Solar Terrestrial Relations Observatory ‐ Solar and Heliospheric Observatory white‐light data. From the geometry parameters, we calculate the volume of the CME for the magnetic ejecta (flux‐rope type geometry) and sheath structure (shell‐like geometry resembling the (I)CME frontal rim). Working under the assumption that the CME mass is roughly equally distributed within a specific volume, we expand the CME self‐similarly and calculate the CME density for distances close to the Sun (15–30 Rs) and at 1 AU. Specific trends are derived comparing calculated and in‐situ measured proton densities at 1 AU, though large uncertainties are revealed due to the unknown mass and geometry evolution: (1) a moderate correlation for the magnetic structure having a mass that stays rather constant (cc ≈ 0.56 − 0.59), and (2) a weak correlation for the sheath density (cc ≈ 0.26) by assuming the sheath region is an extra mass—as expected for a mass pile‐up process—that is in its amount comparable to the initial CME deprojected mass. High correlations are derived between in‐situ measured sheath density and the solar wind density (cc ≈ −0.73) and solar wind speed (cc ≈ 0.56) as measured 24 h ahead of the arrival of the disturbance. This gives additional confirmation that the sheath‐plasma indeed stems from piled‐up solar wind material. While the CME interplanetary propagation speed is not related to the sheath density, the size of the CME may play some role in how much material could be piled up.

Monitoring of Sudden Ionospheric Disturbance (SID) with 0–50 kHz Frequency Receiver over Aliero, Nigeria

Solar flares are known to produce fast Corona Mass Ejections (CMEs) that can lead to the occurrence of different classes of geomagnetic storms. Severe geomagnetic storms can generate disturbances in the magnetosphere and the ionosphere that can affect communication channels; by disrupting Satellite and navigation systems, such as GPS, Galileo, Compass and GLONASS. During intense Solar flares, enhancement in the ionospheric electron density usually occurs, leading to the absorption of the High Frequency (HF) signals by the ionosphere. Enhancement in the Very Low Frequency (VLF) radio waves (3 – 30 kHz) usually takes place during solar flares. This phenomenon is called Sudden Ionospheric Disturbance (SID). These SIDs serves as an opportunity for the tracking of solar flares using VLF. In this study, the diurnal variation of the VLF signals transmitted from six locations selected from USA, Australia and Japan were used to monitor SIDs. The signals were received using the 0-50 kHz frequency receiver (Super SID Monitor) installed at the Kebbi State University of Science and Technology (KSUST), Aliero, Nigeria (latitude: 12.31°N and Longitude: 4.50°E). The diurnal variation of the VLF signals alongside some magnetic indices (Dst, kp, and ap), solar wind speed and density as well as the solar flux index (f10.7) for the month of February, 2020 was investigated. Results from this study reveal that; the VLF amplitudes appeared to be stronger when the lowest level of the geomagnetic activity was recorded across all stations on the quietest day of the month. During this day, the intensity of the signals received vary across the stations, ranging from 2*10⁴ to 4*10⁷dB. During the disturbed period, decrease in the Disturbance Storm Time (Dst) index was observed to have two minimum excursion with values of -31 and -33 nT, thus indicating a weak geomagnetic storm (-30<Dst>-50) event. Consequently a gradual increase in the solar wind speed with a peak value of 520 km/s, significant decrease in the VLF amplitude ranging from 50 – 7*10⁵dB was observed during the weak geomagnetic storm, on 19 February, 2020. It is also evident from this study that the intensity/strength of the VLF signal and its pattern of propagation are greatly affected by the geomagnetic storm. In spite of the changes in the VLF amplitude observed, there was no trace of solar flares during the weak geomagnetic storm. This therefore suggests that not all classes of geomagnetic storms are connected to solar flares.

Non-storm erosion of MeV electron outer radiation belt down to &lt;em&gt;L&lt;/em&gt;* &amp;lt; 4.0 associated with successive enhancements of solar wind density

We report an unusual non-storm erosion event of outer zone MeV electron distribution during three successive solar wind number density enhancements (SWDEs) on November 27−30, 2015. Loss of MeV electrons and energy-dependent narrowing of electron pitch angle distributions (PAD) first developed at <italic>L</italic>* = 5.5 and then moved down to <italic>L</italic>* &lt; 4. According to the evolution of the electron phase space density (PSD) profile, losses of electrons with small pitch angles at <italic>L</italic>* &gt; 4 during SWDE1 are mainly due to outward radial diffusion. However during SWDE2&amp;3, scattering loss due to EMIC waves is dominant at 4 &lt; <italic>L</italic>* &lt; 5. As for electrons with large pitch angles, outward radial diffusion is the primary loss mechanism throughout all SWDEs which is consistent with the incursion of the Last Closed Drift Shell (LCDS). The inner edge of EMIC wave activity moved from <italic>L</italic>* ~5 to <italic>L</italic>* ~4 and from <italic>L</italic> ~6.4 to <italic>L</italic> ~4.2 from SWDE1 to SWDE2&amp;3, respectively, observed by Van Allen Probes and by ground stations. This is consistent with the inward penetration of anisotropic energetic protons from <italic>L</italic>* = 4.5 to <italic>L</italic>* = 3.5, suggesting that the inward extension of EMIC waves may be driven by the inward injection of anisotropic energetic protons from the dense plasma sheet.

Классификация магнитосферных откликов на взаимодействие с диамагнитными структурами медленного солнечного ветраОСФЕРНЫХ ОТКЛИКОВ НА ВЗАИМОДЕЙСТВИЕ С ДИАМАГНИТНЫМИ СТРУКТУРАМИ МЕДЛЕННОГО СОЛНЕЧНОГО ВЕТРА

We propose a possible classification of the responses of the magnetosphere to the interaction with diamagnetic structures (DS), which form the basis of the slow solar wind. The main determinants of the classification are the value and orientation of the vertical component Bz of the interplanetary magnetic field (IMF) and the solar wind density N. We have identified three types of magnetospheric responses. Type 1 has two subtypes whose main difference is the presence or absence of auroras on the day side of the magnetosphere. Within an hour before DS arrival, Bz has a positive value (up to 12 nT) or fluctuates about 0 in the range from –1 to +1 nT. For both subtypes, the duration of substorm disturbances approximately coincides with the duration of DS, and their intensity does not exceed AE~500 nT. Type 2 is characterized by the fact that before the contact with DS positive IMF Bz (0–10 nT) is recorded for an hour, and at the interface of DS a rapid (≤2 min) change in the orientation of the IMF vertical component from north to south occurs. For type 3, Bz within an hour before the contact with DS is negative (from –10 to 0 nT).&#x0D; We address the problem of DS energy transfer to the magnetosphere.

CLASSIFICATION OF MAGNETOSPHERIC RESPONSES TO INTERACTION WITH DIAMAGNETIC STRUCTURES OF SLOW SOLAR WIND

We propose a possible classification of the responses of the magnetosphere to the interaction with diamagnetic structures (DS), which form the basis of the slow solar wind. The main determinants of the classification are the value and orientation of the vertical component Bz of the interplanetary magnetic field (IMF) and the solar wind density N. We have identified three types of magnetospheric responses. Type 1 has two subtypes whose main difference is the presence or absence of auroras on the day side of the magnetosphere. Within an hour before DS arrival, Bz has a positive value (up to 12 nT) or fluctuates about 0 in the range from –1 to +1 nT. For both subtypes, the duration of substorm disturbances approximately coincides with the duration of DS, and their intensity does not exceed AE~500 nT. Type 2 is characterized by the fact that before the contact with DS positive IMF Bz (0–10 nT) is recorded for an hour, and at the interface of DS a rapid (≤2 min) change in the orientation of the IMF vertical component from north to south occurs. For type 3, Bz within an hour before the contact with DS is negative (from –10 to 0 nT).&#x0D; We address the problem of DS energy transfer to the magnetosphere.

Comparative Analysis of PCA and ANOVA for Assessing the Subset Feature Selection of the Geomagnetic Disturbance Storm Time

A Disturbance Storm Time (Dst) index represents the geomagnetic storm strength due to interaction of the Sun towards Earth in the space weather. Formation of the Dst contributed by the total of nine (9) input features namely interplanetary magnetic field (IMF), solar wind density (SWD), solar wind speed (SWS), solar wind input energy (SWIP) and also Earth’s magnetic field components comprise of the horizontal intensity component (H), declination component (D), north component (N), east component (E), and vertical intensity component (Z). Large datasets which comprise of 157896 number of data have existed for all features thus require pre-processing and subset feature selection for reducing data dimensionality in order to reduce the data processing time and enhance the performance of the learning algorithm. In this paper two methods of analyzing the features were compared: Principal Component Analysis (PCA) and one-way Analysis of Variance (ANOVA). The main aims for this works are to reduce a large set of input parameters from the Dst index and to compare the subset feature using the proposed methods for acquiring the reduced features. Prior to analyse the features, an independent-samples t-test is used to evaluate if there is a large difference between the mean of two groups that can be correlated with certain characteristics. The results for the features analyzed demonstrated that one-way ANOVA performed better in eliminating seven (7) components out of nine (9) components of features as compared to PCA. This finding was validated with a dendrogram to support that one-way ANOVA outperformed the PCA in reducing the subset features.

The Solar Wind Density Control on the Prompt Penetration Electric Field and Equatorial Electrojet

AbstractPrompt penetration of convection/overshielding electric fields to equatorial and low latitudes during the southward/northward turnings of interplanetary magnetic field (IMF Bz) have been widely studied in the literature. The other types of penetration electric fields due to sudden changes in the solar wind dynamic pressure, IMF By and during the onset of substorms have also been recently reported. In this paper, we present the exclusive role of solar wind density changes on the prompt equatorial electric field disturbances using the long‐term observations of equatorial electrojet (EEJ) from the Indian sector. In response to the sharp increases in the solar wind density, prompt increases/decreases in the EEJ indicating the eastward/westward prompt penetration electric field (PPEF) of ~20 min periods have been consistently observed on the dayside/nightside. The prompt equatorial electric field disturbances of the opposite polarity have also been observed when the density decreases sharply. Further, the polarity of these PPEF disturbances does not show any clear dependency on the direction of IMF Bz and By. This paper is the first report with a statistically significant number of observations on the characteristics of equatorial electric field disturbances in response to the sudden enhancements/decreases in the solar wind density alone on both dayside and nightside. The underlying physical mechanisms for the prompt equatorial electric field disturbances have been discussed in light of enhanced high‐latitude convection and additional field‐aligned currents due to sudden enhancement of solar wind density.

Dependence of Major Geomagnetic Storm Intensity ($\mathrm{Dst}\le -100$ nT) on Associated Solar Wind Parameters

A geomagnetic storm is the result of sustained interaction between solar wind with a southward magnetic field and the magnetosphere. To investigate the influence of various solar wind parameters on the intensity of major geomagnetic storm, 67 major geomagnetic storms that occurred between 1998 and 2006 were used to calculate the correlation coefficients (CCs) between the intensities of major geomagnetic storms and the time integrals of southward interplanetary magnetic field $B_s$, solar wind electric field ($E_y$) and injection function (Q) during the main phase of the associated geomagnetic storms. SYM-H$_{min}$ was used to indicate the intensity of the associated major geomagnetic storm, while I($B_z$), I($E_y$) and I(Q) were used to indicate the time integrals of $B_z$, $E_y$ and Q during the main phase of associated major geomagnetic storm respectively. The derived CC between I($B_z$) and SYM-H$_{min}$ is 0.33, while the CC between I($E_y$) and SYM-H$_{min}$ is 0.57 and the CC between I(Q) and SYM-H$_{min}$ is 0.86. The results provide statistical evidence that solar wind dynamic pressure or solar wind density plays a significant role in transferring solar wind energy into the magnetosphere, in addition to the southward magnetic field and solar wind speed. Solar wind that has a strong geoeffectiveness requires solar wind dynamic pressure $>$3 nPa or solar wind density $>3$ nPa$/V_{sw}^2$. Large and long duration $B_s$ alone cannot ensure a major geomagnetic storm, especially if the solar wind dynamic pressure is very low, as large and long duration Bs is not a full condition, only a necessary condition to trigger a major geomagnetic storm.