Recovery Phase Of Storm Research Articles

Corotation of ring current auroral spots at sub-auroral latitudes

We report observations of auroral spots s at sub-auroral latitudes. The auroral spots occurred during storm-recovery phases and corotated with the Earth at a speed either higher (super-rotation) or lower (sub-rotation) than the Earth's rotation rate. In the dawn side, the spots have a slightly higher probability of super-rotation than that of the duskside auroral spots. The super- and sub-rotation is likely due to dynamics of the plasmasphere that is controlled by both drag (sub-rotation) and solar wind driven plasma convection.

Correlation of Disturbed Dynamo Electric Field and Thermospheric Plasma Transport with Latitudinally Diverse Total Electron Content During Recovery Phase of a Geomagnetic Storm

The present paper establishes positive correlation between the latitudinal extents of Disturbed Dynamo electric Field (DDEF) with the intensity of geomagnetic storm during October 2003 using Total Electron Content (TEC) receivers located at diverse latitudes in Asia-Pacific longitudes. The thermospheric plasma transport process also affects the TEC near equatorial region.

Generation of Regional Ionospheric TEC Maps With EIA Nowcasting/Forecasting Capability During Geomagnetic Storm Conditions

In this paper, ground based Global Positioning System (GPS) Total Electron Content (TEC) observations collected from the GPS Aided GEO Augmented Navigation (GAGAN) network over low latitude Indian subcontinent are assimilated into the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM). Gauss-Markov Kalman filter methodology is utilized and the background model error covariance (BMEC) matrix is framed using solar, geomagnetic, cross tail potential and hemispheric power indices using multivariate principal component analysis (MPCA) method. The model variations through different high latitude electric field models (Weimer and Heelis) are utilized in the data assimilation analysis. The proper attempt is modeled for providing TEC forecasts during geomagnetic storm conditions from 15th to 20th March 2015 days over Indian region. The more concentration is given in understanding the equatorial ionization anomaly (EIA) characteristics during the initial, main and recovery phase of St. Patrick’s Day March 2015 geomagnetic storm. The proposed model forecast outperforms the persistence forecast with maximum forecast score (1.6) and forecast skill (2.2) during recovery phase of storm. TEC forecasts are validated with current time step GPS observations and 93 % correlation is observed on quiet day (10th March 2015) and 82 % correlation is noticed on main phase of storm (17th March 2015). Also proposed TEC model analysis and forecast results are compared with International Global Navigation Satellite Service (IGS) TEC stations datasets. A clear negative storm effect (EIA inhibition) has been forecasted well with the proposed Kalman filter and MPCA methodology aspects.

Evolution of Pitch Angle‐Distributed Megaelectron Volt Electrons During Each Phase of the Geomagnetic Storm

AbstractUsing Relativistic Electron Proton Telescope measurements onboard Van Allen Probes, the evolution of electron pitch angle distributions (PADs) during the different phases of magnetic storms is studied. Electron fluxes are sorted in terms of storm phase, value, energy, and magnetic local time (MLT) sectors for 55 magnetic storms from October 2012 through May 2017. To understand the potential mechanisms for the evolution of electron PADs, we fit PADs to a sinusoidal function , where is the equatorial pitch angle and n is a real number. The major inferences from our study are (i) at L 5, the prestorm electron PADs are nearly isotropic (n 0), which evolves differently in different MLT sectors during the main phase subsequently recovering back to nearly isotropic distribution type during the storm recovery phase; (ii) for 3.4 MeV, the main phase electron PADs become more pancake like on the dayside with high n values (>3), while it becomes more flattop to butterfly like on the nightside, (iii) at L = 5, magnetic field strength during the storm main phase enhances during the daytime and decreases during the nighttime. (iv) Conversely, at L 3, the electron PADs neither respond significantly to the different phase of the magnetic storm nor reflect any MLT dependence. (v) Main phase, electron fluxes with <4.2 MeV shows a persistent 90° maximum PAD with n ranging between 0 and 2, while for 4.2 MeV the distribution appears flattop and butterfly like. Our study shows that the relativistic electron PADs depend upon the geomagnetic storm phase and possible underlying mechanisms are discussed in this paper.

Multi-Instrumental Observations of Early Morning Equatorial Plasma Depletions During the 2017 Memorial Weekend Storm

We investigate an equatorial plasma depletion (EPD) event in Japan near the early morning sector (04:30–7:30 LT) during the recovery phase of a geomagnetic storm occurred on Memorial weekend (May 28) 2017 by using multi-instrumental measurements, including ground-based Global Navigation Satellite Systems (GNSS) network, ionosonde stations, and space-based Swarm and Defense Meteorological Satellite Program (DMSP) missions. The detailed 2-D evolution of the early morning EPD is well observed using GNSS ROTI maps with high temporal-spatial resolution. Moreover, ROTI data from BeiDou Geostationary Earth Orbit satellites are used to detect the EPD signature for the first time. The dawn EPD signature was also observed at the topside ionosphere by in situ electron density (Ne) measurements and ROTI results by space-borne Swarm Alpha (A), Charlie (C), and DMSP F17 satellites, indicating that the equatorial depletions arose to higher altitudes. We suggest that both the eastward disturbance dynamo electric field and overshielding electric field near the early morning sector created a favorable condition for the growth of the Rayleigh–Taylor (R-T) instability, and thus result in the generation of the dawn EPD.

Observations of ULF Waves at the Late Recovery Phase of Magnetic Storm

利用Radiation Belt Storm Probes（RBSP）和Magnetospheric Multiscale（MMS）的联合观测研究了2016年1月25日和2月22日的两个超低频（ULF）波动事件.这两个事件均发生在磁暴的恢复相后期，波动分布在晨侧与正午之间的区域.RBSP观测到的两次波动都发生在低<i>L</i>-shell（4.7～5.8），MMS观测到的两次波动都发生在高<i>L</i>-shell（8.0～14.2）.在高<i>L</i>-shell，超低频波偏振以环向波为主，沿磁力线方向为基频谐波.在低<i>L</i>-shell，超低频波偏振以径向波为主，沿磁力线方向为二次谐波.对内磁层（<i>L</i><6）中的ULF波，通过比较<i>&#8706;f</i>/<i>&#8706;w</i>|<i>μ,L</i>和（d<i>L</i>）/（d<i>W</i>）（<i>&#8706;f</i>）/（<i>&#8706;L</i>）|<i>μ,W</i>的绝对值可知，bump-on-tail的离子分布和向地的离子相空间密度梯度通过<i>N</i>=1的弹跳共振，共同为波动的产生提供自由能.多重事例分析表明，在磁暴恢复相后期，约10keV的离子伴随着波动的存在而存在，并且为波动的产生提供自由能.

Characteristics of GNSS Total Electron Content Enhancements Over the Midlatitudes During a Geomagnetic Storm on 7 and 8 November 2004

AbstractThe characteristics of global electron density variations in the ionosphere during a geomagnetic storm on 7 and 8 November 2004 were investigated using total electron content (TEC) obtained from the global navigation satellite system (GNSS). The regions of enhanced TEC over North America, Europe, and Japan first appeared in the middle‐latitude regions. The TEC enhancements over North America showed a rapid longitudinal expansion and reached a wide longitudinal extent during the initial and main phases of the geomagnetic storm. TEC enhancements were simultaneously observed in both North America and Japan at 05:00 UT on 8 November. Observation data from the Defense Meteorological Satellite Program showed a slight enhancement of electron density at 850 km below the equatorward boundary of the middle‐latitude trough (45–48°N in geomagnetic latitude) over the Pacific Ocean. This electron density variation may correspond to the TEC enhancements observed in both Japan and North America. These results imply that an enhanced TEC region existed between North America and Japan. The TEC enhancement in Japan appeared with a magnetic conjugacy in the Southern Hemisphere, indicating one of the characteristics of storm‐enhanced density (SED). Moreover, TEC enhancements simultaneously appeared from Japan to central Asia at 11:00 UT on 8 November, corresponding to the early recovery phase of the geomagnetic storm. From the above results, it is suggested that SED phenomena can be simultaneously generated over a wide longitudinal width (~100°). The longitudinal extent of this SED event is 2.5–5.0 times longer than those reported by previous studies.

A case study of isolated auroral spots based on DMSP data

This study employed ultraviolet images and particle data to investigate isolated auroral spots away from the Earth's auroral oval. Data from SSUSI (Special Sensor Ultraviolet Spectrographic Imager) and SSJ (Special Sensor J) mounted on the DMSP (Defence Meteorological Satellite Program) spacecraft were examined. The isolated auroral spots were observed by DMSP F16/SSUSI and F17/SSUSI on 29 May 2010 during the recovery phase of a moderate geomagnetic storm with a minimum SYM-H index of −70 nT. The auroral spots were observed between 18:00–21:00 MLT and corotated with the Earth, but stayed almost at the same magnetic latitude (MLAT) of −60°. It is found that the isolated auroral spots were produced mainly by energetic ring current ions at energies above ~10 keV. The enhancement in the electron flux with energy below ~200 eV was also observed for the isolated auroral spots. The MLAT of the electron flux was nearly 2°higher than that for the precipitating ions.

Features of Nightside ULF Wave Activity in the Ionosphere

AbstractWe investigate the features of nightside ultralow frequency (ULF) waves in the ionosphere using electric field data in the DC/ULF range observed by the Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite over a ~5.5‐year period from May 2005 to November 2010. The ULF wave events are recognized by an automatic detection algorithm, and a superposed epoch analysis is performed to study the characteristics of ULF waves during geomagnetic storms. The results show that (1) ULF waves of both nonmagnetospheric and magnetospheric origins occur in the ionosphere; (2) nonmagnetospheric ULF waves present seasonal variations but have no clear response to storms; (3) magnetospheric ULF waves show clear association with the recovery phase of storms but have no obvious seasonal variations; and (4) an interhemispheric asymmetry with higher magnetospheric ULF wave occurrence rate in the Southern Hemisphere particularly around storms can be partly explained by the fact that more of selected isolated storms occurred during summer in the Northern Hemisphere (NH), hence higher conductivity in the NH. However, an analysis of few storms during equinoxes also shows a minor asymmetry. These results still indicate that the ionospheric conductivity in the Southern Hemisphere would be lower than in the NH at nighttime.

Satellite Orbital Drag During Magnetic Storms

AbstractWe investigate satellite orbital drag effects at low‐Earth orbit associated with thermosphere heating during magnetic storms caused by coronal mass ejections. CHAllenge Mini‐satellite Payload (CHAMP) and Gravity Recovery And Climate Experiment (GRACE) neutral density data are used to compute orbital drag. Storm‐to‐quiet density comparisons are performed with background densities obtained by the Jacchia‐Bowman 2008 (JB2008) empirical model. Our storms are grouped in different categories regarding their intensities as indicated by minimum values of the SYM‐H index. We then perform superposed epoch analyses with storm main phase onset as zero epoch time. In general, we find that orbital drag effects are larger for CHAMP (lower altitudes) in comparison to GRACE (higher altitudes). Results show that storm time drag effects manifest first at high latitudes, but for extreme storms, particularly observed by GRACE, stronger orbital drag effects occur during early main phase at low/equatorial latitudes, probably due to heating propagation from high latitudes. We find that storm time orbital decay along the satellites' path generally increases with storm intensity, being stronger and faster for the most extreme events. For these events, orbital drag effects decrease faster probably due to elevated cooling effects caused by nitric oxide, which introduce modeled density uncertainties during storm recovery phase. Errors associated with total orbit decay introduced by JB2008 are generally the largest for the strongest storms and increase during storm times, particular during recovery phases. We discuss the implication of these uncertainties for the prediction of collision between space objects at low‐Earth orbit during magnetic storms.

Isolated Auroral Spots Observed by DMSP/SSUSI

AbstractThis work reports auroral spots event observed by the SSUSI instruments on board the DMSP spacecraft between 22 and 23 July 2009 during the recovery phase of a moderate magnetic storm. The spots were observed between 18:00 and 02:00 magnetic local time and stayed at ~60° magnetic latitude. They lasted for ~10 hr and corotated with ~64% of the Earth's rotational speed. In situ observations indicate that the isolated auroral spots were produced by energetic ions at energies between 10 and 240 keV, with significantly anisotropic electron (30–300 keV) precipitations. It is expected that the energetic ions originate from the ring current and can be scattered by the EMIC waves through cyclotron resonance. The energetic electrons can be precipitated by the nonresonant interaction between the electrons and EMIC waves, which is suggested by previous works.

Oxygen Ion Dynamics in the Earth's Ring Current: Van Allen Probes Observations

AbstractOxygen (O+) enhancements in the inner magnetosphere are often observed during geomagnetically active times, such as geomagnetic storms. In this study, we quantitatively examine the difference in ring current dynamics with and without a substantial O+ ion population based on almost 6 years of Van Allen Probes observations. Our results have not only confirmed previous finding of the role of O+ ions to the ring current but also found that abundant O+ ions are always present during large storms when sym‐H &lt; −60 nT without exception, while having the pressure ratio (ℛ) between O+ and proton (H+) larger than 0.8 and occasionally even larger than 1 when L &lt; 3. Simultaneously, the pressure anisotropy decreases with decreasing sym‐H and increasing L shell. The pressure anisotropy decrease during the storm main phase is likely related to the pitch angle isotropization processes. In addition, we find that ℛ increases during the storm main phase and then decreases during the storm recovery phase, suggesting faster buildup and decay of O+ pressure compared to H+ ions, which are probably associated with some species dependent source and/or energization as well as loss processes in the inner magnetosphere.

Nighttime Magnetic Perturbation Events Observed in Arctic Canada: 2. Multiple‐Instrument Observations

AbstractThe rapid changes of magnetic fields associated with nighttime magnetic perturbations with amplitudes |ΔB| of hundreds of nanoteslas and 5‐ to 10‐min periods can induce bursts of geomagnetically induced currents that can harm technological systems. This paper presents three cases of intervals of intense and complex nighttime magnetic perturbations in eastern Arctic Canada in 2015, augmented by observations from auroral imagers and high‐altitude spacecraft in the nightside magnetosphere. Each case occurred within 1 hr after substorm onsets. None occurred during the main phase of a geomagnetic storm, and only the first during the early recovery phase (of a moderate storm). The cases were similar in that two or three intervals occurred in this region over a span of ~1 hr; these showed a spatial progression, in that successive intervals occurred later at more western and northern stations. During several intervals, individual peak Bx impulses occurred nearly simultaneously (within 1–2 min) at several stations, while during others the impulses occurred later at more western and northern stations, and during one interval they occurred later at southern stations. During both of the cases for which auroral images were available, a westward traveling surge and a poleward auroral expansion and/or poleward boundary intensification occurred, and during two events auroral streamers coincided in time and location with magnetic perturbations. These observations appear to be consistent with several earlier studies connecting nighttime magnetic perturbation events to localized auroral structures and to dipolarizing flux bundles and bursty bulk flows in the magnetotail.

The effect of different phases of severe geomagnetic storms on the low latitude ionospheric critical frequencies

In this paper, the effect of different phases of severe geomagnetic storms on low latitude ionospheric critical frequencies (foF2) is investigated. For this purpose, hourly ionospheric critical frequency (foF2) data measured at the low latitude ionosonde station Manila during 1981 and 1991 is examined. The investigation is carried out using superposed epoch analysis method considering the disturbance storm time index Dst ≤ −100 nT hours as event times. To examine depending on local time the effect of the phases of geomagnetic storms on foF2, this analysis was conducted for separately for the day hours, night hours, and all hours during both the main and the recovery phases of the severe geomagnetic storms and the results were compared with each other. It is observed that for both 1981 and 1991, the highest change (increase or decrease) in foF2 values occurs at the event times for all hours of day during both the main and the recovery phase of severe geomagnetic storms. Also, during the main phases of severe geomagnetic storms, the foF2 values increase at day hours, while the foF2 values decrease at night hours. However, during the recovery phases of severe geomagnetic storms, the foF2 values decrease at day hours, while the foF2 values increase at night hours. For both the day and night hours, the changes in the foF2 values during the recovery phase of severe geomagnetic storms are greater than the changes in the foF2 values during the main phase of severe geomagnetic storms.

An Opposite Response of the Low‐Latitude Ionosphere at Asian and American Sectors During Storm Recovery Phases: Drivers From Below or Above

AbstractIn this study, we focus on the recovery phase of a geomagnetic storm that happened on 6–11 September 2017. The ground‐based total electron content data, as well as the F region in situ electron density, measured by the Swarm satellites show an interesting feature, revealing at low and equatorial latitudes on the dayside ionosphere prominent positive and negative responses at the Asian and American longitudinal sectors, respectively. The global distribution of thermospheric O/N2 ratio measured by global ultraviolet imager on board the Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics satellite cannot well explain such longitudinally opposite response of the ionosphere. Comparison between the equatorial electrojet variations from stations at Huancayo in Peru and Davao in the Philippines suggests that the longitudinally opposite ionospheric response should be closely associated with the interplay of E region electrodynamics. By further applying nonmigrating tidal analysis to the ground‐based total electron content data, we find that the diurnal tidal components, D0 and DW2, as well as the semidiurnal component SW1, are clearly enhanced over prestorm days and persist into the early recovery phase, indicating the possibility of lower atmospheric forcing contributing to the longitudinally opposite response of the ionosphere on 9–11 September 2017.

Hertz Range Pulsations during Recovery Phase of the Magnetic Storm on September 7–8, 2017, and Relation between their Dynamics and Changes in the Parameters of the Interplanetary Medium

The shape and dynamics of an unusual disturbance in the Pc1 geomagnetic pulsation range recorded by ground-based induction magnetometers during the morning hours (03–06 MLT) on September 11, 2017, in the late recovery phase of a strong magnetic storm were analyzed in the context of changes in the parameters of the interplanetary medium. Pulsations were observed in the auroral and subauroral zones, as well as at midlatitudes, and had a complex structure in the form of multiplet “pearls” (1–1.5 Hz range) and two series of narrow-band bursts (2–3 Hz range) with a repetition period of ~5 and ~20 min. Pulsations in the form of a series of bursts are a rare event and are recorded mainly during the daytime hours. Comparison of the dynamics of Pc1 pulsations with the parameters of the interplanetary medium was carried out with data from the DSCOVR and THEMIS satellites. A change in the carrier frequency and intensity of multiplet pearls was a response to a jump in the plasma density of the solar wind. A series of bursts with a period of ~5 min could be initiated by a simultaneous increase in the solar-wind velocity and the By-component of the interplanetary magnetic field, which was observed ~40 min after the density jump. We associate bursts with a period of ~20 min either with the response of the magnetosphere to the short-term excursion of the daytime magnetopause to the Earth or with oscillations of a close period in the transition region ahead of the front of the density perturbation. The frequency, period, and amplitude of the pulsations are estimated.

Leveraging Commercial Cubesat Constellations for Auroral Science: A Case Study

AbstractMagnetometers deployed on the largest satellite constellation to date are leveraged as a space‐based sensor network to study space‐time variability in auroral field‐aligned currents (FACs). The cubesat constellation of Planet Labs Inc. consists of nearly 200 satellites in two polar Sun‐synchronous orbits, with median spacecraft separations on the order of 375 km, and some occasions of opportunity providing much closer spacing. Each spacecraft contains a magnetoinductive magnetometer, able to sample the ambient magnetic field at 0.1 to 10 Hz with &lt;200‐nT sensitivity. In this study, seven satellites from the Planet constellation were used to investigate space‐time variations in FACs over an active auroral display during a 10‐min interval. The aurora occurred during the early recovery phase of a geomagnetic storm and was characterized by large‐scale vortical motions and embedded rayed structure. Clear signatures of the large‐scale auroral current system were detected by the orbital magnetometers. Estimation of FAC patterns was carried out using three different methods. The results suggest a high degree of spatial and temporal variability during the 10‐min interval. The location of upward and downward current channels relative to the aurora was consistent with theoretical expectations, but current densities were not well correlated with visible features in the available imagery, suggesting unresolved small‐scale structure not captured by the collaborative observations. Advantages, limitations, and caveats in using opportunistic networks of low‐quality space‐based magnetometers to study dynamic auroral phenomena are discussed.

Ionospheric irregularity behavior during the September 6\u201310, 2017 magnetic storm over Brazilian equatorial\u2013low latitudes

The September 6–10, 2017 two-step magnetic storm was caused by an X9 solar flare followed by a CME. The SSC that occurred at 23:43 UT on day 06 when Sym-H reached about 50 nT, was due to a sudden increase in solar wind. The first step of the storm was caused by a Bz southward incursion on day 07. The magnetic index Kp reached 08, and the Sym-H magnetic index reached a minimum value of − 146 nT on day 08 at 01:08 UT, ending the main phase. On day 07, the solar wind intensified once again and the auroral index AE reached 2500 nT. During the recovery phase of this first storm, there was another Bz southward incursion on day 08 at 13:56 UT when Sym-H reached − 115 nT, and Kp reached a value of 08.33, marking the second step of the storm. In this work, the ionospheric irregularity over São Luís (02.5°S, 44.3°W, dip lat − 04.67°) was studied using data from the VHF, Digisonde and GPS receivers. Electron density data from the satellite SWARM-A were also analyzed for those orbits close to São Luís, and they presented large fluctuations during the storm night of 07/08. To analyze the latitudinal effects of the storm on the plasma irregularities, GPS data from 6 Novatel receivers were used. The vertical plasma drifts during daytime hours were determined using magnetometer data and during the evening using ionogram data. Compared to the ‘quiet’ days of September 2017, the VHF and GPS S4 amplitude scintillation indices increased substantially during the night of 07/08 when there was a strong intensification in the vertical plasma drift due to a prompt penetration under shielding magnetospheric electric field of eastward polarity. On the other hand, on the night of 08/09 the ionospheric scintillation was completely inhibited due to the disturbance dynamo electric field of westward polarity associated with the first and second storms. The irregularity zonal drifts measured by a VHF receiver around 24 UT (21 LT) were eastward on the nights of 05/06 and 06/07; however, during the night of 07/08, it reversed to westward.

Understanding the Behaviors of Thermospheric Nitric Oxide Cooling During the 15 May 2005 Geomagnetic Storm

AbstractThe behaviors of thermospheric nitric oxide (NO) cooling during the 15 May 2005 intense geomagnetic storm are studied using measurements by the Sounding of the Atmosphere using Broadband Emission Radiometry instrument on board the Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics satellite and simulations by the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model. The geomagnetic storm was the most intense (Dst = −247 nT) of 2005 with a short and rapid main phase and long‐lasting recovery (more than 3 days). NO cooling responded globally to the geomagnetic storm within 2 hr after the onset of storm main phase. The most significant NO cooling increases occurred at middle and low latitudes in the Northern Hemisphere and at middle latitudes in the Southern Hemisphere. The model outputs agree with observations in general but overestimate the NO cooling at high latitudes and underestimate the NO cooling elsewhere. Furthermore, observations show a significant upward shifting of the NO cooling peak altitude in the storm main phase and a significant downward shifting of the NO cooling peak altitude during the storm recovery phase at low latitudes. An unusual double‐peak structure in the NO cooling rate appeared during storm main phase and recovery phase. By investigating the NO cooling vertical profiles, we suggest that the horizontal equatorward transport plays an important role in inducing these significant variations of the NO cooling peak altitude.

Supersubstorms and Conditions in the Solar Wind

This article examines the effect of various large-scale solar-wind structures and streams on the occurrence of a special type of substorms—the so-called supersubstorms (SSS), which are very intense substorms defined by the indices SML –50 nT, the events occur mostly right after the sudden onset (SC) of a storm (11%) and, very rarely, happen late in the storm recovery phase (1.2%). The space weather conditions associated with SSS events differ sharply from those associated with other types of high-latitude substorms, such as polar and expanded substorms.