Recovery Phase Of Storm Research Articles

Field‐Aligned Electron Density Distribution of the Inner Magnetosphere Inferred From Coordinated Observations of Arase and Van Allen Probes

AbstractThe Radiation Belt Storm Probes (RBSP) and the Arase satellites have different inclinations and sometimes they fly both near the equator and off the equator on the same magnetic field line simultaneously. Such conjunction events give us opportunities to compare the electron density at different latitudes. In this study, we analyzed the plasma waves observed by Arase and RBSP during the three conjunction events during and after the September 7, 2017 storm. The electron number density at the satellite positions was estimated from frequencies of the Upper Hybrid Resonance emissions obtained by the High Frequency Analyzer of the Plasma Wave Experiment onboard the Arase and the Waves instrument onboard the RBSP, respectively. During the three conjunction events, the satellites passed through the plume, inner trough (the narrow region with low electron density between the main body of the plasmasphere and the plume), plasmatrough with variable electron density, and partially refilled plasmasphere. The power‐law index m for the inner trough and plume was inferred to be 4–7 and ∼0, respectively. This is interpreted to mean that the trough was close to collisionless and the plume was relatively near diffusive equilibrium. In the plasmatrough with the varying density, both the high‐density and low‐density regions had m ∼ 0. The low‐density portion of this region may have a different origin from the inner trough, because of the different m indices. For the partially refilled plasmasphere in the storm recovery phase, the power‐law index m showed negative values, meaning that the density in the equatorial plane was higher than at higher latitudes.

Statistical Analysis of Ring Ionospheric Trough Characteristics

AbstractIn this study, the statistical characteristics of the ring ionospheric trough (RIT) are determined. The RIT is formed by the decay processes of the magnetospheric ring current; therefore, it is most clearly distinguished from the main ionospheric trough (MIT) during the recovery phase of a geomagnetic storm. The dynamics of both the troughs is considered in the case of geomagnetic disturbances with Kp indices from 4 to 9 during 2000–2003. In total, 830 RIT occurrences were identified in the CHAMP satellite data. The RIT is most often formed in the post‐midnight period, less often in the evening, and never in the daytime between 10 and 14 LT. In the post‐midnight period, the RIT is observed in the belt of 39°–62° geomagnetic latitude (in both hemispheres), with an occurrence maximum at 55° (L‐shell, L = 3). This finding is in good agreement with the observations of stable auroral red (SAR) arcs and a residual magnetospheric ring current. When a storm exhibits a long recovery phase, during which the geomagnetic activity periodically resumes, the RIT can exist for more than two days. The RIT is most often formed at the longitudes of South America, where the geomagnetic field is the weakest. In contrast to the MIT position, the averaged RIT position is not so strongly dependent on the longitude and Kp index. At low Kp values, the plasmapause position is close to the MIT position, while at high Kp values, the plasmapause approaches the RIT position.

Properties of the Recovery Phase of Extreme Storms

AbstractA geomagnetic storm is a phenomenon of weakening of Earth's magnetic field from a few hours to several days, which directly or indirectly affects navigation, transportation, communication, power grids, satellite electronics, etc. In general, the duration of the recovery phase is larger. Thus, its cumulative effect is greater than the main phase. Therefore, it is important to understand the physical processes involved during the recovery phase. In this paper, we have studied the recovery phase of 31 extreme geomagnetic storms that occurred from 1990 to 2020. Each storm demonstrates two distinct features of the recovery phase that is, initial fast and later slow recovery phase. During the fast recovery phase, the rate of recovery either linearly or non‐linearly depends on , which has been characterized by an exponential or hyperbolic decay function in various reported studies. In our study, we have noted that the hyperbolic function explains the complete recovery phase of only 11 extreme events. Furthermore, both decay functions fail to explain the late recovery phase of storms. Interestingly, we have found that the rate of recovery during the slow phase shows steady variation (independent to ), that is, . Our analysis suggests that the magnitude of the recovery rate during the late phase is proportional to the magnitude of the storm.

Frequency‐Dependent Modulation of Whistler‐Mode Waves by Density Irregularities During the Recovery Phase of a Geomagnetic Storm

AbstractDensity irregularities near the plasmapause are commonly observed and play an important role in whistler‐mode wave excitation and propagation. In this study, we report a frequency‐dependent modulation event of whistler‐mode waves by background density irregularities during a geomagnetic storm. Higher‐frequency whistler waves (near , where is the equatorial electron cyclotron frequency) are trapped in the density trough regions due to the small refractive index near the parallel direction, while lower‐frequency whistler waves (below ) are trapped in the density crest regions due to the refractive index maximum along the parallel direction. In addition to the modulation, we also find that, quantitatively, the wave amplitude of the higher‐ (lower‐) frequency whistler‐mode waves is anti‐correlated (correlated) with the relative plasma density variation. Our study suggests the importance of density irregularity dynamics in controlling whistler‐mode wave intensity, and thus radiation belt dynamics.

Inhibition of F3 Layer at Low Latitude Station Sanya during Recovery Phase of Geomagnetic Storms

Inhibition of F3 Layer at Low Latitude Station Sanya during Recovery Phase of Geomagnetic Storms

Middle‐Low Latitude Neutral Composition and Temperature Responses to the 20 and 21 November 2003 Superstorm From GUVI Dayside Limb Measurements

AbstractTIMED/Global Ultraviolet Imager (GUVI) limb measurements of far‐ultraviolet airglow emission have been used to investigate middle‐low latitude thermospheric composition and neutral temperature responses to the 20 and 21 November 2003 (day of year [DOY] 324 and 325) superstorm. Altitude profiles of O, N2 number densities and temperature, as well as O/N2 column density ratio (∑O/N2), on the storm days along the GUVI limb tracks are compared with those on DOY 323 (quiet time). The storm‐time composition and temperature responses were global and evolved continuously as the storm progressed. Specially, N2 and temperature increased almost globally at all altitudes during the storm and their perturbation structures were similar. The magnitudes of their enhancements both increased with altitude and latitude. The storm‐induced O perturbations decreased in the lower thermosphere but increased in the upper thermosphere. Transition heights of O perturbations from decrease to increase changed with latitude and time. During the storm main and recovery phases, the storm‐induced ∑O/N2 decreases were mostly related to the O depletion in the low‐middle thermosphere, whereas ∑O/N2 increases during the storm were primarily caused by N2 depletion. There was a remarkable hemispheric asymmetry in composition responses as they have different morphologies and lifetime, especially during the storm recovery phase.

Alfvénicity-related Long Recovery Phases of Geomagnetic Storms: A Space Weather Perspective

Abstract This paper reports, for the first time on a statistical basis, on the key role played by the Alfvénic fluctuations in modulating the recovery phase of the geomagnetic storms, slowing down the restoration of the magnetosphere toward its pre-storm equilibrium state. Using interplanetary and geomagnetic measurements collected over more than one solar cycle, a high correlation between the durations of Alfvénic streams and concurrent recovery phases is found, pointing to a clear coupling between Alfvénic turbulence and magnetospheric ring current dynamics. By exploiting current solar wind models, these observations also provide space weather opportunities of predicting the total duration of any geomagnetic storm induced by any solar driver provided that it is followed by an Alfvénic stream, a crucial piece of information for ground technologies and infrastructures that are affected by time-integrated effects throughout the duration of the storm.

Characterization of High‐m ULF Wave Signatures in GPS TEC Data

AbstractGPS total electron content (TEC) measurements were used to investigate high‐m ultralow frequency (ULF) waves during the recovery phase of a geomagnetic storm. ULF wave signals in TEC data show high coherence and significant common power in the wavelet coherence and cross wavelet transform analyses with magnetic field radial component data from GOES‐15. They did not cause significant ionospheric scintillation or ground magnetic signatures due to ionospheric screening effects. An automatic identification procedure is developed to identify ULF wave signature in TEC data from 10 GPS receivers on January 25, 2016. The waves were mainly distributed on the dayside and post dusk sector from ∼64° to ∼71° magnetic latitude. This is the first time that the large‐scale 2D spatial structure and temporal evolution of high‐m ULF waves are revealed, which demonstrates TEC measurements as an effective high‐m ULF wave remote sensing tool.

Global Pc5 Pulsations From the Polar Cap to the Equator: Wave Characteristics, Phase Variations, Disturbance Current System, and Signal Transmission

AbstractWe present observations of global Pc5 pulsations by ∼180 ground magnetometers during the recovery phase of an intense geomagnetic storm. Measurements of magnetic fields along four latitudinal magnetometer chains and one longitudinal magnetometer chain are used to determine the wave characteristics of Pc5 pulsations. Many new features of Pc5 pulsations are identified from a single event for the first time. The Pc5 pulsations occur simultaneously at all latitudes and longitudes/local times, and the period of the Pc5 pulsations is about 10 min and does not depend on latitude and longitude. The latitudinal distributions of the northward (H) component and magnetic pressure of Pc5 perturbations are derived. The phase of the H component reverses across 50–70° magnetic latitude (MLat) but is nearly the same at middle and low latitudes. The phase of the H component at low latitudes does not vary much with longitude/local time. The phase of the D component magnetic field reverses near the equator in the latitudinal direction and also reverses around dawn, noon, dusk, and midnights in the longitudinal direction. The distribution and evolution of global ionospheric equivalent disturbance currents during Pc5 pulsations are derived. A coupled magnetospheric‐ionospheric current system is proposed to explain the observed characteristics of global Pc5 pulsations. It is suggested that the variations of the phase of Pc5 pulsations with latitude and local time are determined by the global distribution of the coupled magnetospheric‐ionospheric current system but not caused by propagation delay of the signals.

High-Latitude Geomagnetic Disturbances and Field Aligned Currents in the Recovery Phase of the Large Magnetic Storm on June 21–26, 2015

High-Latitude Geomagnetic Disturbances and Field Aligned Currents in the Recovery Phase of the Large Magnetic Storm on June 21–26, 2015

Discovery of a low-latitude ionospheric trough associated with the inner radiation belt

The dynamics of ionospheric troughs that developed during a great geomagnetic storm on 11–13 April 2001 are studied using measurements of electron density obtained by the CHAMP satellite at an altitude of 410–465 km. Subauroral, mid-latitude and low-latitude troughs were observed at nighttime, sometimes simultaneously. The subauroral trough is usually defined as the main ionospheric trough, whereas the mid-latitude trough is associated with the magnetospheric ring current. It appeared at the beginning of the storm recovery phase around latitudes of 40°–45° GMLat (L = 1.7–2.0) and existed for a long period of time throughout the late recovery phase of the residual ring current at latitudes of 50°–55° GMLat (L ~ 2.4–3.0). For the first time, a low-latitude trough was revealed. It developed at latitudes of 34°–45° GMLat (L = 1.45–2.00) in association with the precipitation of energetic particles from the inner radiation belt.

Comments on “Poststorm Thermospheric NO Overcooling?” by Mikhailov and Perrone (2020)

AbstractRecently Mikhailov and Perrone (2020, https://doi.org/10.1029/2019ja027122) proposed the mechanism of neutral atomic oxygen reduction, which is associated with the upper atmospheric circulation, to explain the reduction of total thermospheric mass density during the storm recovery phase. The authors further concluded arbitrarily that there is no need to introduce the storm‐time overcooling concept. However, their methodology is fundamentally flawed and their results and conclusions are incorrect. Instead, the overcooling scenario remains a viable concept in understanding thermospheric variations in the storm recovery phase.

Hemispheric Asymmetries in the Mid‐latitude Ionosphere During the September 7–8, 2017 Storm: Multi‐instrument Observations

AbstractHemispheric asymmetries of the Vertical Total Electron Content (VTEC) were observed during the first recovery phase of the geomagnetic storm on September 7–8, 2017. These asymmetries occurred at the mid latitudes at two different local times simultaneously: In the European‐African sector (early morning), the storm time VTEC in the southern/northern hemisphere was higher/lower than the quiet time value, suggesting the southern/northern hemisphere entered the positive/negative phase (N−S+). In the East Asian‐Australian sector (afternoon), the storm time VTEC change was positive in the northern hemisphere, but negative in the southern hemisphere (N+S−). The electron density profiles from digisondes demonstrated that the asymmetries appeared in the F region density as well. The plasma drifts data from digisondes, the column‐integrated [O]/[N2] ratio from GUVI onboard the TIMED satellite, and the detrended VTEC were utilized to study the drivers of the asymmetries. Traveling Ionospheric Disturbance (TID) signatures were identified in the digisonde drift and detrended VTEC data before the appearance of the asymmetry. The magnitude of TIDs was larger in the hemisphere where the negative phase occurred later. The storm time [O]/[N2] ratio change was positive in Africa (S+) and negative in Europe (N−). However, the [O]/[N2] measurements were not available in the East Asian‐Australian sector during the focused period. The hemispheric differences in the vertical drifts were also observed in both sectors. Therefore, the observed hemispheric asymmetries in both sectors are suggested to be due to the hemispheric asymmetries in the thermospheric composition change, vertical drift, and TID activity.

Multi‐Event Analysis of Plasma and Field Variations in Source of Stable Auroral Red (SAR) Arcs in Inner Magnetosphere During Non‐Storm‐Time Substorms

AbstractStable auroral red (SAR) arcs are optical events with dominant 630.0‐nm emission caused by low‐energy electron heat flux into the topside ionosphere from the inner magnetosphere. SAR arcs are observed at subauroral latitudes and often occur during the recovery phase of magnetic storms and substorms. Past studies concluded that these low‐energy electrons were generated in the spatial overlap region between the outer plasmasphere and ring‐current ions and suggested that Coulomb collisions between plasmaspheric electrons and ring‐current ions are more feasible for the SAR‐arc generation mechanism rather than Landau damping by electromagnetic ion cyclotron waves or kinetic Alfvén waves. This work studies three separate SAR‐arc events with conjunctions, using all‐sky imagers and inner magnetospheric satellites (Arase and Radiation Belt Storm Probes [RBSP]) during non‐storm‐time substorms on December 19, 2012 (event 1), January 17, 2015 (event 2), and November 4, 2019 (event 3). We evaluated for the first time the heat flux via Coulomb collision using full‐energy‐range ion data obtained by the satellites. The electron heat fluxes due to Coulomb collisions reached ∼109 eV/cm2/s for events 1 and 2, indicating that Coulomb collisions could have caused the SAR arcs. RBSP‐A also observed local enhancements of 7–20‐mHz electromagnetic wave power above the SAR arc in event 2. The heat flux for the freshly detached SAR arc in event 3 reached ∼108 eV/cm2/s, which is insufficient to have caused the SAR arc. In event 3, local flux enhancement of electrons (<200 eV) and various electromagnetic waves were observed, these are likely to have caused the freshly detached SAR arc.

Two Whistler-mode Waves Modulation By Background-level Density Irregularity During The Recovery Phase of A Geomagnetic Storm

Two Whistler-mode Waves Modulation By Background-level Density Irregularity During The Recovery Phase of A Geomagnetic Storm

Sub-Auroral, Mid-Latitude, and Low-Latitude Troughs during Severe Geomagnetic Storms

The dynamics of ionospheric troughs during intense geomagnetic storms is considered in this paper. The study is based on electron density measurements at CHAMP satellite altitudes of 405–465 km in the period from 2000 to 2002. A detailed analysis of four storms with Kp from 5+ to 9− is presented. Three troughs were identified: sub-auroral, mid-latitude, and low-latitude. The sub-auroral trough is usually defined as the main ionospheric trough (MIT). The mid-latitude trough is observed equatorward of the MIT and is associated with the magnetospheric ring current; therefore, it is named the ring ionospheric trough (RIT). The RIT appears at the beginning of the storm recovery phase at geomagnetic latitudes of 40–45° GMLat (L = 1.75–2.0) and exists, for a long time, at the late stage of the recovery phase at latitudes of the residual ring current 50–55° GMLat (L ~ 2.5–3.0). The low-latitude trough (LLT) is discovered for the first time. It forms only during great storms at the latitudes of the internal radiation belt (IRB), 34–45° GMLat (L = 1.45–2.0). The LLT’s lowest latitude of 34° GMLat was recorded in the night sector (2–3 LT). The occurrence probability and position of the RIT and LLT depend on the hemisphere and longitude.

A Possible Mechanism on the Detachment Between a Subauroral Proton Arc and the Auroral Oval

AbstractSubauroral proton arcs are a type of terrestrial auroral phenomena, which are often detached equatorially from the auroral oval. This work presents evolution of a subauroral proton arc using observations of the Special Sensor Ultraviolet Spectrographic Imager and Special Sensor J (SSJ) on board Defense Meteorological Satellite Program (DMSP) spacecraft. The arc was observed in the afternoon sector and was located within 60°–70° geomagnetic latitude during the recovery phase of a moderate magnetic storm with the minimum SYM‐H index of −55 nT. Particle measurements from DMSP F17/SSJ indicate that the arc was detached from the normal oval and produced by energetic ring current ions with energies above 10 keV. These energetic ions were likely scattered into the magnetic loss cone by electromagnetic ion cyclotron waves in the frequency range between 0.1 and 0.5 Hz, as confirmed by Pc1 waves derived from the observations of a ground station. Continuous auroral observations directly show that the subauroral proton arc was detached from the oval during evolution. Following a northward interplanetary magnetic field turning, the auroral oval moved toward higher latitudes. We propose that the equatorward edge of the auroral oval is less influenced by the convection electric field, and thus moves more slowly than the poleward edge. This mechanism is proposed for producing a separation between the equatorward and poleward parts of the auroral oval, with the former evolving into the subauroral proton arc.

Study of Spatiotemporal Development of Global Distribution of Magnetospheric ELF/VLF Waves Using Ground‐Based and Satellite Observations, and RAM‐SCB Simulations, for the March and November 2017 Storms

AbstractMagnetospheric Extremely Low‐Frequency/Very Low‐Frequency (ELF/VLF) waves have an important role in the acceleration and loss of energetic electrons in the magnetosphere through wave‐particle interaction. It is necessary to understand the spatiotemporal development of magnetospheric ELF/VLF waves to quantitatively estimate this effect of wave‐particle interaction, a global process not yet well understood. We investigated spatiotemporal development of magnetospheric ELF/VLF waves using 6 PWING ground‐based stations at subauroral latitudes, Exploration of energization and Radiation in Geospace and RBSP satellites, POES/MetOp satellites, and the RAM‐SCB model, focusing on the March and November 2017 storms driven by corotating interaction regions in the solar wind. Our results show that the ELF/VLF waves are enhanced over a longitudinal extent from midnight to morning and dayside associated with substorm electron injections. In the main to early storm recovery phase, we observe continuous ELF/VLF waves from ∼0 to ∼12 MLT in the dawn sector. This wide extent seems to be caused by frequent occurrence of substorms. The wave region expands eastward in association with the drift of source electrons injected by substorms from the nightside. We also observed dayside ELF/VLF wave enhancement, possibly driven by magnetospheric compression by solar wind, over an MLT extent of at least 5 h. Ground observations tend not to observe ELF/VLF waves in the post‐midnight sector, although other methods clearly show the existence of waves. This is possibly due to Landau damping of the waves, the absence of the plasma density duct structure, and/or enhanced auroral ionization of the ionosphere in the post‐midnight sector.

Local Time and Longitudinal Differences in the Occurrence Frequency of Ionospheric EMIC Waves During Magnetic Storm Periods

AbstractThe spatial and temporal distributions of ionospheric electromagnetic ion cyclotron (EMIC) waves during magnetic storms from 2014 to 2018 were studied using Swarm observations. Ionospheric EMIC waves preferably occurred during storms and their recovery phases at subauroral regions within an average magnetic latitude of 40–55°. There were more wave events during more intense and longer period storms. However, the correlation between event number and storm duration was not good. This might be due to the effect of heavy oxygen ions on EMIC wave generation and the loss of ring current high‐energy ions by the EMIC waves. There are obvious magnetic local time (MLT) differences in the peak occurrence frequency of EMIC waves during storm phases. The enhanced solar wind dynamic pressure was favorable for duskside EMIC waves. With an increased substorm activity, the wave occurrence rate peak shifted from the morning side to the dusk‐premidnight sector. During the recovery phase of a storm, EMIC waves in the 12–24 MLT sector appeared preferably in the earlier part than those in the 00–12 MLT sector. This shift in local time is related to the eastward rotation of the plasmaspheric plume toward morning during the late storm recovery phase and its overlap with the ring current. Highest occurrence frequency of the storm time EMIC waves could be found in the South Atlantic Anomaly region, which might be related to the drift shell splitting and the wave propagation effect in the weak magnetic field region.

Ring Current Decay During Geomagnetic Storm Recovery Phase: Comparison Between RBSP Observations and Theoretical Modeling

AbstractRing current decay during storm recovery phase may be affected by different loss processes. In this study, we have investigated the lifetimes of ring current ions (H+ and O+) of energies from 1 keV to several hundred keV at L shell from 3 to 6 during the storm recovery phase through a statistical survey. The observational data of 48 geomagnetic storms from March 2013 to May 2019 are collected based on Van Allen Probe observations. We find that (1) the observed lifetimes of H+ and O+ in general increase with L shell and (2) the lifetimes of H+ is short than that of O+ when E < ∼50 keV while the situation is reversed when E > ∼50 keV. In addition, we have made use of the charge exchange theory, combined with previous experimental results on the charge exchange cross section and two distribution models of neutral hydrogen atoms in the exosphere, so as to directly estimate the ring current ions decay caused by charge exchange mechanism only. Through the comparison between the model predictions of charge exchange lifetime and the observed lifetimes, we find that (3) the observed lifetimes are in general consistent with model results, which confirms that charge exchange is a dominant loss mechanism of ring current ions during storm recovery phase.