Geomagnetic Latitude Research Articles

Empirical Model of SSUSI‐Derived Auroral Ionization Rates

AbstractWe present an empirical model for auroral (90–150 km) electron–ion pair production rates, ionization rates for short, derived from Special Sensor Ultraviolet Spectrographic Imager electron energy and flux data. Using the Fang et al. (2010, https://doi.org/10.1029/2010gl045406) parametrization for mono‐energetic electrons, and the NRLMSISE‐00 neutral atmosphere model (Picone et al., 2002, https://doi.org/10.1029/2002ja009430), the calculated ionization rate profiles are binned in 2‐hr magnetic local time and 3.6°geomagnetic latitude to yield time series of ionization rates at 5‐km altitude steps. We fit each of these time series to the geomagnetic indices Kp, PC, and Ap, the 81‐day averaged solar radio flux index, and a constant term. The resulting empirical model can easily be incorporated into coupled chemistry–climate models to include particle precipitation effects.

Global Ionospheric Response During Extreme Geomagnetic Storm in May 2024

The main idea of the present study is to investigate in detail the time evolution of the spatial inhomogeneities connected with the ionospheric response to the geomagnetic storm registered in the period of 10–11 May 2024. The obtained ionospheric anomalies represented by the relative deviations of the global Total Electron Content (TEC) data have been utilized in the analysis. The used global TEC data have been converted to a coordinate system with a modip latitude and geographical longitude. In addition to the maps illustrating the global spatial distribution of the geomagnetically forced ionospheric anomalies, a presentation of the observed longitudinal structures by sinusoidal approximation has also been used. The resulting positive and negative responses have been studied depending on the magnetic latitude, local times and the behavior of the geomagnetic activity parameters during the considered event. The interpretation takes into account the known mechanisms for the effect of the geomagnetic storm on the electron density. A special attention is focused on the differences in the two hemispheres at high and mid latitudes, where a simultaneous direct impact of the particle precipitation and the change in the temperature regime of the neutral atmosphere has been assumed. The low-latitude response as a result of the Equatorial Ionization Anomaly (EIA) associated with Disturbed Dynamo Electric Fields (DDEFs) and its relationship with local time has also been considered.

Midlatitude Plasma Blob‐like Structures Along With Super Equatorial Plasma Bubbles During the May 2024 Great Geomagnetic Storm

AbstractPlasma blob is generally a low‐latitude phenomenon occurring at the poleward edge of equatorial plasma bubble (EPB) during post‐sunset periods. Here we report a case of midlatitude ionospheric plasma blob‐like structures occurring along with super EPBs over East Asia around sunrise during the May 2024 great geomagnetic storm. Interestingly, the blob‐like structures appeared at both the poleward and westward edges of EPBs, reached up to 40°N magnetic latitudes, and migrated westward several thousand kilometers together with the bubble. The total electron content (TEC) inside the blob‐like structures was enhanced by ∼50 TEC units relative to the ambient ionosphere. The blob‐like structure at the EPB poleward edge could be partly linked with field‐aligned plasma accumulation due to poleward development of bubble. For the blob‐like structure at the EPB west side, one possible mechanism is that it was formed and enhanced accompanying the bubble evolution and westward drift.

Detection of Extensive Equatorial Plasma Depletions After the 2022 Tongan Volcanic Eruption From Multiple Geodetic Satellite Ranging Systems

AbstractWe present a number of unique observations of ionospheric anomalies following the Hunga‐Tonga Hunga‐Ha'apai (HTHH) volcanic eruption on 15 January 2022. All are based on non‐dedicated geodetic satellite systems: Global Positioning System tracking of Low Earth Orbit (LEO) CubeSats, intersatellite tracking between two GRACE Follow‐On satellites, satellite radar altimeters to the ocean surface, and Doppler radio beacons from ground stations to LEO geodetic satellites. Their observations revealed the development of anomalously large trough‐like plasma depletions, along with plasma bubbles, in the equatorial regions of the Pacific and East Asian sectors. Trough‐like plasma depletions appeared to be confined within approximately ±20° magnetic latitude, accompanied by density enhancements just outside this latitude range. These plasma depletions and enhancements were aligned with the magnetic equator and occurred across broad longitudes. They were detected in regions where atmospheric waves from the HTHH eruption passed through around the time of the sunset terminator. We interpret these phenomena in terms of the E dynamo electric fields driven by atmospheric waves from the eruption. The uplift of the ionosphere beyond satellite altitudes, followed by subsequent plasma diffusion to higher latitudes along magnetic field lines, results in the formation of trough‐like plasma depletions around the magnetic equator and density enhancement at higher latitudes. The detection of plasma bubbles in the Asian sector during the non‐bubble season (January) is likely associated with the uplift of the ionosphere at the sunset terminator.

Impact Pattern of Energetic Particle Precipitation on Polar Mesospheric Ozone

AbstractThe upper atmosphere of polar regions exhibits two distinct patterns of energetic particle precipitation that can lead to ozone destruction by ionizing the atmosphere: one is the energetic proton precipitation in the polar cap region during solar proton events (SPEs), and the other is the energetic electron precipitations (EEPs) in the auroral oval region from the radiation belt. In this study, we conduct case studies and statistical analyses of ozone observations from the Aura satellite to present the quantitative difference in the impact patterns of SPEs and EEPs on polar mesospheric ozone. According to our statistical analysis of 13 SPEs and 19 EEPs during the MLS time frame, the magnitude of ozone depletion during SPEs is greater than during EEPs. The ozone depletion during SPEs is more pronounced at higher geomagnetic latitudes and negatively correlates with the proton flux, while during EEPs the ozone depletion is more in favor of the geomagnetic latitude band of 60–70° but independent of the electron count rates. In addition, hydroxyl enhancement also exhibits different patterns during SPEs and EEPs, similar to that of ozone depletion. This study further validates the physical link between the magnetosphere and atmosphere and promotes our understanding of the solar influence on Earth's climate.

Location of Geomagnetic Disturbances in Relation to the Field Aligned Current Boundary

AbstractGeomagnetic disturbances (GMDs) are rapid fluctuations in the strength and direction of the magnetic field near the surface of the Earth which can cause electric currents to be induced in the ground. The geomagnetically induced currents (GICs) can cause damage to pipelines and power grids. A detection algorithm has been developed to identify rapid changes in 10 s averaged magnetometer data. This higher resolution data is important in capturing the most rapid changes associated with extreme GIC events. The algorithm has been used on an array of ground‐based magnetometers from SuperMAG data from 2010 to 2022, creating a new list of global GMDs. Data from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) is used to place the observed GMDs in the context of the global pattern of magnetosphere‐ionosphere field‐aligned currents (FACs). A dawn sector population of GMDs is found to lie near the boundary between the region 1 and region 2 FACs, while a pre‐midnight sector population is found to occur poleward of the FAC boundary on region 1 upward FACs. It is also shown that the latitude of the GMDs expands with the FAC boundary and their occurrence peaks around 77° magnetic latitude.

Rapid Geomagnetic Variations During High‐Speed Stream, Sheath and Magnetic Cloud‐Driven Geomagnetic Storms From 1996 to 2023

AbstractThe most detrimental geomagnetically induced currents (GICs) documented to date have all taken place during geomagnetic storms. Yet, the probability of GICs throughout geomagnetic storms driven by different solar wind transients, such as high‐speed streams/stream interaction regions (HSS/SIR) or interplanetary coronal mass ejection (ICME) sheaths and magnetic clouds (MC), is poorly understood. We present an algorithm to detect geomagnetic storms and storm phases, resulting in a catalog of 755 geomagnetic storms from January 1996 to June 2023 with the solar wind drivers. Using these storms and the IMAGE magnetometer network, we study the temporal and spatial evolution of spikes in the time derivative of the horizontal component of the external magnetic field, , greater than 0.5 nT/s during geomagnetic storms driven by HSS/SIR, sheaths and MCs. Spikes occur more often toward the end of the storm main phase for HSS/SIR and MC‐driven storms, while sheaths have spikes throughout the entire main phase. During the main phase most spikes occur in the morning sector around 05 magnetic local time (MLT) and the extent in MLT is narrowest for MCs and widest for sheaths. However, spikes in the pre‐midnight sector during the main and recovery phases are most prominent for HSS/SIR‐driven storms. During the storm sudden commencement (SSC), three MLT hotspots exist, the post‐midnight at 04 MLT, pre‐noon at 09 MLT and afternoon at 15 MLT. The pre‐noon hotspot has the highest probability of spikes and the widest extent in magnetic latitude.

Different Origin Field‐Aligned Currents and Their Relationship With Auroral Intensity

AbstractThe ionospheric field‐aligned current (FAC) consists of three components related to ionospheric vortices and gradients of Pedersen and Hall conductances, with the first term being of magnetospheric origin and the latter two being of ionospheric origin (Eq. 1). We calculate each of them between 2010 and 2016 using line‐of‐sight velocity data from the Super Dual Auroral Radar Network radar and auroral electron precipitation data from the Defense Meteorological Satellite Program. Then, we investigate the contribution of each FAC component, as well as the relationship between each FAC component and auroral activity. Our result shows that ionospheric‐origin FACs contribute up to 54% (dawn) and 42% (dusk) within the auroral oval. Both magnetospheric‐origin FACs and ionospheric‐origin FACs initially increase and then stabilize as the SuperMAG electrojet (SME) index increases. After stabilization, these two currents have almost equally important roles, with an average contribution rate of 56% and 44%, respectively. Additionally, the ionospheric‐origin FACs are found to have a higher dependency on auroral intensity. We also find that magnetospheric‐origin FACs exhibit distribution patterns similar to the R1/R2 FAC systems because their directions are determined by vorticities. When the SME index exceeds 200 nT, the contribution from the Pedersen conductance gradient consistently exhibits downward currents near 70° magnetic latitude in the dusk and predawn sectors due to the combined effects of velocities and Pedersen conductance gradients. However, the distribution pattern from the Hall conductance gradient is not so clear due to the uncertainty in the angle between velocity and Hall conductance gradient.

Interplanetary Causes and Impacts of the 2024 May Superstorm on the Geosphere: An Overview

The recent superstorm of 2024 May 10–11 is the second largest geomagnetic storm in the space age and the only one that has simultaneous interplanetary data (there were no interplanetary data for the 1989 March storm). The May superstorm was characterized by a sudden impulse (SI+) amplitude of +88 nT, followed by a three-step storm main-phase development, which had a total duration of ∼9 hr. The cause of the first storm main phase with a peak SYM-H intensity of −183 nT was a fast-forward interplanetary shock (magnetosonic Mach number M ms ∼ 7.2) and an interplanetary sheath with a southward interplanetary magnetic field component B s of ∼40 nT. The cause of the second storm's main phase with an SYM-H intensity of −354 nT was a deepening of the sheath B s to ∼43 nT. A magnetosonic wave (M ms ∼ 0.6) compressed the sheath to a high magnetic field strength of ∼71 nT. Intensified B s of ∼48 nT were the cause of the third and most intense storm main phase, with an SYM-H intensity of −518 nT. Three magnetic cloud events with B s fields of ∼25–40 nT occurred in the storm recovery phase, lengthening the recovery to ∼2.8 days. At geosynchronous orbit, ∼76 keV to ∼1.5 MeV electrons exhibited ∼1–3 orders of magnitude flux decreases following the shock/sheath impingement onto the magnetosphere. The cosmic-ray decreases at Dome C, Antarctica (effective vertical cutoff rigidity <0.01 GV) and Oulu, Finland (rigidity ∼0.8 GV) were ∼17% and ∼11%, respectively, relative to quiet-time values. Strong ionospheric current flows resulted in extreme geomagnetically induced currents of ∼30–40 A in the subauroral region. The storm period is characterized by strong polar-region field-aligned currents, with ∼10 times intensification during the main phase and equatorward expansion down to ∼50° geomagnetic (altitude-adjusted) latitude.

Rapid Transport of Energetic Electrons to Low L $L$‐Shells: The Key Role of Electric Fields

AbstractThe dynamics of the outer radiation belt are traditionally associated with wave‐particle resonant interactions, which provide local electron acceleration and losses through very low‐frequency waves, and electron radial transport by ultra‐low frequency waves. However, these processes cannot explain observations of rapid radial transport of energetic electrons (on a time‐scale of a couple of hours), deep into the inner magnetosphere (down to , mapping to magnetic latitude in the ionosphere). This transport is likely associated with strong convection electric fields forming around the plasmapause. To investigate these rapid, low‐latitude electron transport, we combine low‐altitude observations of energetic electron fluxes by the ELFIN CubeSats and DMSP satellites, SuperDARN measurements of ionospheric plasma flows (electric fields), and equatorial measurements of energetic electrons and electric fields by THEMIS. Our findings demonstrate that the rapid filling of the slot region by keV electrons is directly associated with electric field penetration to low latitudes (down to ). The proposed electron transport scenario, the direct penetration of energetic electrons by strong, localized electric fields, underscores the importance of ionosphere‐magnetosphere coupling in radiation belt dynamics.

Latitudinal Mapping of Chorus Waves Growth Rates Based on Multi‐Spacecraft Wave and Plasma Measurements

AbstractWhistler mode chorus waves are one of the most intense and important electromagnetic emissions in the Earth's radiation belt, where these waves are responsible for electron acceleration to relativistic energies and for energetic electron precipitation into the Earth's atmosphere. This study reports a unique multi‐spacecraft observation event that allowed for the first time to verify theoretical models of chorus wave generation. The growth rates derived from the multi‐spacecraft observations of chorus waves Cluster WBD electric field waveforms collected during the crossing of the equatorial source region were compared to the theoretical linear and nonlinear growth rates calculated using simultaneous PEACE electron measurements. We have revealed that the growth rate estimated from wave measurements is substantially higher than the estimated linear growth rate but is quite close to the estimated nonlinear growth rate. A notable wave amplification is found up to 5 degrees of magnetic latitude and higher.

Comparison of modeling of the polar cap absorption effect with observations at the AARI ground-based network

An elliptical model of cutoff for solar cosmic rays (SCR) at high latitudes has been calculated for SCR events and geomagnetic storms that occurred in February, March, and September 2014, June 2015, and September 2017 in order to predict the polar cap absorption (PCA) effect. The prediction is compared with observations of the PCA effect at the AARI network of six ionosondes, located in the north of Russia in a wide range of longitudes from 30 to 170 and magnetic latitudes from 56 to 64. We examine the dependence of the cutoff latitude on the magnetic storm strength, as well as the effect of additional ionization of the dayside and nightside ionosphere by SCR protons and electrons. The model demonstrates a satisfactory statistical accuracy up to 0.83 for the PCA prediction. We discuss prospects for further improvement of the elliptical model, such as consideration of the impact of SCRs of higher energies and inclusion of the PC index of energy flux into the polar cap.

Сравнение моделирования эффекта поглощения в полярной шапке с наблюдениями на сети станций ААНИИ

An elliptical model of cutoff for solar cosmic rays (SCR) at high latitudes has been calculated for SCR events and geomagnetic storms that occurred in February, March, and September 2014, June 2015, and September 2017 in order to predict the polar cap absorption (PCA) effect. The prediction is compared with observations of the PCA effect at the AARI network of six ionosondes, located in the north of Russia in a wide range of longitudes from 30 to 170 and magnetic latitudes from 56 to 64. We examine the dependence of the cutoff latitude on the magnetic storm strength, as well as the effect of additional ionization of the dayside and nightside ionosphere by SCR protons and electrons. The model demonstrates a satisfactory statistical accuracy up to 0.83 for the PCA prediction. We discuss prospects for further improvement of the elliptical model, such as consideration of the impact of SCRs of higher energies and inclusion of the PC index of energy flux into the polar cap.

Investigating azimuthal propagation of Pc5 geomagnetic pulsations and their equivalent current vortices from ground-based and satellite data

Using phase delays at spaced stations and satellite observations in the magnetosphere during two events, we have studied azimuthal propagation of resonant bursts of geomagnetic pulsations in the Pc5 range. We have also examined propagation of equivalent current vortices during these events. It has been found that the pulsations, observed in the magnetosphere and ionosphere, and the equivalent current vortices in the ionosphere propagate in the azimuthal direction from the dayside to the nightside. Propagation velocities according to ground-based observations are 5–25 km/s; according to satellite observations, 114–236 km/s. Propagation velocities according to satellite observations do not exceed the Alfvén velocity in the magnetosphere, which is 620–1006 km/s. According to data from various instruments, there are signatures of fast magnetosonic and Alfvén waves at a time in one of the events on the satellite. This clearly reflects the transformation of these waves. The geomagnetic latitude of registration of vortex centers coincides with the latitude of the maximum amplitude of geomagnetic pulsations (field line resonances) and decreases by ~15° toward the early hours of MLT. The observed dynamics of Pc5 pulsations and vortices is assumed to reflect MHD wave propagation in the magnetosphere.

Исследование особенностей азимутального распространения геомагнитных Pс5-пульсаций и их эквивалентных токовых вихрей по данным наземных и спутниковых наблюдений

Using phase delays at spaced stations and satellite observations in the magnetosphere during two events, we have studied azimuthal propagation of resonant bursts of geomagnetic pulsations in the Pc5 range. We have also examined propagation of equivalent current vortices during these events. It has been found that the pulsations, observed in the magnetosphere and ionosphere, and the equivalent current vortices in the ionosphere propagate in the azimuthal direction from the dayside to the nightside. Propagation velocities according to ground-based observations are 5–25 km/s; according to satellite observations, 114–236 km/s. Propagation velocities according to satellite observations do not exceed the Alfvén velocity in the magnetosphere, which is 620–1006 km/s. According to data from various instruments, there are signatures of fast magnetosonic and Alfvén waves at a time in one of the events on the satellite. This clearly reflects the transformation of these waves. The geomagnetic latitude of registration of vortex centers coincides with the latitude of the maximum amplitude of geomagnetic pulsations (field line resonances) and decreases by ~15° toward the early hours of MLT. The observed dynamics of Pc5 pulsations and vortices is assumed to reflect MHD wave propagation in the magnetosphere.

Dayside Magnetic Depression Following Interplanetary Shock Arrivals During the February 1958 and July 1959 Superstorms

AbstractThe present study investigates mid‐ and low‐latitude ground magnetic disturbances observed following the arrival of three interplanetary (IP) shocks during the super‐geomagnetic storms of February 1958 and July 1959. One may expect that after IP shocks, the H (northward) magnetic component increases globally but especially on the dayside. However, in each event, the H component was depressed sharply for 1–2 hr in the dawn‐to‐noon sector, whereas it increased in other local time (LT) sectors. Observed magnetic deflections suggest that there existed field‐aligned currents (FACs) flowing into and out of the auroral zone around the western and eastern edges of the LT sector of the dayside H depression. These features strongly suggests that the observed H depression was a remote effect of a R1‐sense FAC system. It was previously reported that similar ground magnetic disturbances were observed after the SSC of the 2003 Halloween storm, which reveals striking similarities to the well‐known H depression observed at Colaba during the 1859 Carrington storm. It is therefore suggested that the external driving behind IP shocks, especially those associated with major storms, is most optimum for the sharp reduction of the dayside H component through the formation and intensification of the dayside FAC system. Associated magnetic disturbances are considered to be larger in magnitude with increasing magnetic latitude, and oriented azimuthally as well as meridionally. Such magnetic disturbances in dayside midlatitudes may not be discussed very often as a target of space weather, but their potential impacts on ground infrastructures probably require closer attention.

Pitch-Angle Diffusion of Radiation Belt Electrons and Precipitating Particle Fluxes: Dependence on VLF Wavefield Parameters

The dependence of the pitch-angle diffusion efficiency of energetic electrons in the Earth’s magnetosphere on the distribution of the whistler wave field along the geomagnetic flux tube is quantitatively studied for parameters corresponding to the location of the Sura and HAARP HF heating facilities. The expansion of the precipitation energy range with the increase of the region of geomagnetic latitudes occupied by the waves is shown. Using the calculated pitch-angle diffusion coefficient for a given spectrum of waves and their distribution along the flux tube, the ratio of the fluxes of precipitating and trapped particles at low altitude is determined. It is shown that at typical wave intensities corresponding to chorus VLF waves and plasmaspheric hiss, the fluxes of precipitating and trapped electrons can be comparable to each other. At the same time, for the wave amplitudes observed as a result of the action of heating facilities, the flux of precipitating electrons is negligible.

Dependence of the main ionospheric trough position on local time, longitude and geomagnetic activity in the southern winter hemisphere

Based on the meticulous identification of ionization troughs, performed earlier from the CHAMP satellite data, twoadditional issueswereresolved: (1) the longitudinal effect characteristics in the position of the main ionospheric trough (MIT) were corrected, and (2) for the first time,the dependence of theMITposition on geomagnetic activity was determined foralllocaltime hours. A large dataset from the CHAMP satellite in the southern winter hemisphere under high solar activity was utilized. According to the refined data the amplitude of the longitudinal effect in the MITposition changes from ∼ 3° to ∼ 5° in the course of the day. The shape of the longitudinal effectvarieswith local time, however, the MIT in the eastern hemisphere isconsistentlylocated at higher latitudes than in the western hemisphere. The main reason for the longitudinal effect is the dependence of the equatorward boundary of auroral diffuse precipitation on the tilt angle of the Earth’s dipole. The dependence on geomagnetic activitywas determined as a linear regression ΛT = Λ0 − aKp, where Λ is the geomagnetic latitude, and the Kp indexisconsidered for the previous6 h. The latitude Λ0 and coefficient a exhibited pronounced dependence on local time, with Λ0 increasing and a decreasing when moving from night to day. Because the amplitude of the longitudinal effect decreases with increasing magnetic activity, the value of a alsodependson longitude. Consequently, coefficienta wasdetermined separatelyforthe eastern and western hemispheres. Theaveragevaluesof a vary from 1.3 − 1.4° during the day to 1.8 − 1.9° at night. Thedifference between theeastern and western hemispheres is ∼ 0.3°.

Time‐Lagged Effects of Ionospheric Response to Severe Geomagnetic Storms on GNSS Kinematic Precise Point Positioning

AbstractThis paper investigates time‐lag effects of ionospheric response to two severe geomagnetic storms (Kp = 8) on the degradation of kinematic precise point positioning (PPP) solutions, utilizing over 5500 Global Navigation Satellite Systems (GNSS) stations distributed worldwide. Focusing on these two severe geomagnetic storms that occurred during solar cycle 24, the study employs an open‐source positioning software package, namely RTKLIB, to derive the PPP solutions. The findings reveal significant variations in time lags across different magnetic latitudes. These variations are driven by ionospheric responses to a southward interplanetary magnetic field and subsequent decreases in the SMY‐H index during the 2015 St. Patrick's Day Storm and the 2017 September 7–8 Storm. Specifically, at high latitudes, PPP degradation primarily manifests during the main phase of the storm, resulting in delays spanning from several minutes to 1–2 hr after the sudden onset of the storm. In contrast, mid‐ and low latitudes exhibit a wider range of delays extending up to tens of hours. Notably, rapid positioning degradation is observed predominantly at the magnetic local time noon and midnight sectors. The study discusses these time lag effects concerning the intensity of various ionospheric disturbances triggered by the interactions among the solar wind, magnetosphere, and ionosphere during geomagnetic storms. The insights obtained from this research have the potential to be integrated into physics‐based and machine‐learning models to enhance forecasting capabilities of space weather impacts.

Field-Aligned Currents during the Strong December 2023 Storm: Local Time and Hemispheric Differences

This study investigates field-aligned currents (FACs) during strong magnetic storms in December 2023, analyzing variations in different local times and in the Northern (NH) and Southern Hemispheres (SH). Peak FAC densities were approximately 7.8 times higher than nominal values, with the most equatorward FACs reaching −52° magnetic latitude (MLat). In the summer hemisphere, the daytime FACs were stronger than the nighttime FACs, with the daytime westward Polar Electrojet (PEJ) surpassing nighttime levels. In the winter hemisphere, the nighttime FACs and westward PEJ were stronger than daytime. Generally, the FACs and westward PEJ were stronger in the SH than in the NH across most local time sectors, attributed to greater solar illumination. The NH pre-midnight currents were stronger than for the SH, indicating enhanced substorm currents during winter nights. The nighttime FACs occurred at lower MLat than daytime, with pre-noon FACs at a higher MLat than post-noon. The NH FACs were positioned more equatorward than their SH counterparts. In the NH, the mean FACs correlated most strongly with the merging electric field (Em) at pre-noon, post-noon, and post-midnight and with the SMU (SuperMAG Electrojet Upper Index) at pre-midnight. In the SH, the mean FACs correlated best with the SMU at pre-midnight/pre-noon, with the SML (SuperMAG Electrojet Lower Index) at post-midnight, and Em at post-noon. The mean MLat of the peak FACs show the strongest correlation with Em across most local times and hemispheres.