Recovery Phase Of Geomagnetic Storm Research Articles

Refilling of the slot region between the inner and outer electron radiation belts during geomagnetic storms

Energetic electrons (≥50 keV) are injected into the slot region (2 < L < 4) between the inner and outer radiation belts during the early recovery phase of geomagnetic storms. Enhanced convection from the plasma sheet can account for the storm‐time injection at lower energies but does not explain the rapid appearance of higher‐energy electrons (≥150 keV). The effectiveness of either radial diffusion (driven by enhanced ULF waves) or local acceleration (during interactions with enhanced whistler mode chorus emissions), as a potential source for refilling the slot at higher energies, is analyzed for observed conditions during the early recovery phase of the 10 October 1990 storm. We demonstrate that local acceleration, driven by observed chorus emissions, can account for the rapid enhancement in 200–700 keV electrons in the outer slot region near L = 3.3. Radial diffusion is much less effective but may partially contribute to the flux enhancement at lower L. Subsequent outward expansion of the plasmapause during the storm recovery phase effectively terminates local wave acceleration in the slot and prevents acceleration to energies higher than ∼700 keV. A statistical analysis of energetic electron flux enhancements and wave and plasma properties over the entire CRRES mission supports the concept of local wave acceleration as a dominant process for refilling the slot during the main and early recovery phase of storms. For moderate storms, the injection process naturally becomes less effective at energies ≥1 MeV, due to the longer wave acceleration times and additional precipitation loss from scattering by electromagnetic ion cyclotron waves. However, during extreme events when the plasmapause remains compressed for several days, conditions may occur to allow wave acceleration to multi‐MeV energies at locations normally associated with the slot.

Role of geomagnetic disturbance on whistler occurrence at a low latitude station

In this paper, we report the results derived from a statistical analysis of whistlers recorded at Varanasi during the period January 1990–December 1999. The monthly occurrence rate shows a maximum during January to March. In order to study the role of geomagnetic disturbance on the whistler occurrence rate, we have used the K P index and its variation. It is found that the occurrence probability monotonically increases with ∑ K P (daily sum) values. It is found that, when ∑ K P>20, the occurrence rate is greater than the average value, in good agreement with results reported by other workers. In addition, we also present the probability of the observation of whistlers during weak/intense geomagnetic storms and also during the main phase and recovery phase of geomagnetic storms.

Parametric study of the resonant scattering process by narrow band whistler mode waves driven by temperature anisotropy

We study a combined effect of wave trapping due to oppositely propagating narrow band whistler mode waves and discuss its dependence on the background plasma density. In the case where forward and backward traveling whistler mode waves coexist, rapid scattering of resonant electrons occurs owing to the overlapping of diffusion curves of both waves. Simulation results show that the low-density plasma condition, where the electron plasma frequency is close to the electron gyrofrequency, is favorable for the significant resonant scattering of high energetic electrons. The results of the present study suggest that the combined effect plays an important role in energizing relativistic electrons in the equatorial region of the Earth's inner magnetosphere during the recovery phase of geomagnetic storms.

Intermittency analysis of geomagnetic storm time-series observed in Brazil

In this paper, we present and discuss the results of the statistical analysis applied to the geomagnetic field H-component (temporal resolution 1 min) observed at Vassouras (22.4°S, 43.6°W; dip lat. 18.5°S), Brazil, during the months of July 2000, March 2001, April 2001, April 2002 and May 2002. Each month studied had intense or very intense geomagnetic storm. For |Dst| max between 100 and 200 nT, the geomagnetic storms have been considered as intense, whereas for |Dst| max>200 nT, the geomagnetic storms have been considered very intense. The statistical parameter kurtosis (a measure of intermittency) shows that, the higher values in kurtosis cause the probability density function (PDF) more spiky. Furthermore, the higher values in kurtosis are possibly more efficient for the disturbed geomagnetic system to return to the steady-state conditions. In order to evaluate the importance of this feature in detail, we used the approach of the Hölder exponent applied to one of the periods studied, July 2000, representing respectively the interval of the quiet and post geomagnetically disturbed conditions. The results indicated that the part after the recovery phase had higher Hölder exponent than during quiet conditions. Thus, indicating that the intermittency introduced by disturbance acts more efficiently for return to the steady-state conditions. Analysis performed with Morlet wavelet transform and study of anisotropy in geomagnetic storm time-series show that the disturbances are important source of intermittency having small scales (with periods ≪1 day) and are much more dominant compared with the diurnal variations in geomagnetic field H-component. The present work indicates the importance of the intermittency in the recovery phase of geomagnetic storms.

The relationship between the recovery phase of geomagnetic storms and the magnetic clouds

Starting with our elliptical cross-section model for the study of the magnetic topology of magnetic clouds (MCs) in the interplanetary medium, we develop an analytical approach to the behavior of the D st index at the recovery phase of a geomagnetic storm. Assuming an axially symmetric ring current, we estimate its physical parameters during that recovery phase of the storm-time. We compare the theoretical and measured D st indexes in two intense geomagnetic storms ( D st <–100 nT), both associated with MCs.

Mid-Latitude Pc1, 2 Pulsations Induced by Magnetospheric Compression in the Maximum and Early Recovery Phase of Geomagnetic Storms

We investigate the properties of interplanetary inhomogeneities generating long-lasting mid-latitude Pc1, 2 geomagnetic pulsations. The data from the Wind and IMP 8 spacecrafts, and from the Mondy and Borok midlatitude magnetic observatories are used in this study. The pulsations under investigation develop in the maximum and early recovery phase of magnetic storms. The pulsations have amplitudes from a few tens to several hundred pT andlast more than seven hours. A close association of the increase (decrease) in solar wind dynamic pressure (Psw) with the onset or enhancement (attenuation or decay) of these pulsations has been established. Contrary to high-latitude phenomena, there is a distinctive feature of the interplanetary inhomogeneities that are responsible for generation of long-lasting mid-latitude Pc1, 2. It is essential that the effect of the quasi-stationary negative Bz-component of the interplanetary magnetic field on the magnetosphere extends over 4 hours. Only then are the Psw pulses able to excite the above-mentioned type of mid-latitude geomagnetic pulsations. Model calculations show that in the cases under study the plasmapause can form in the vicinity of the magnetic observatory. This implies that the existence of an intense ring current resulting from the enhanced magnetospheric convection is necessary for the Pc1, 2 excitation. Further, the existence of the plasmapause above the observation point (as a waveguide) is necessary for long-lasting Pc1 waves to arrive at the ground.

An Approach to the Relationship Between Magnetic Clouds and the Recovery Phase of Geomagnetic Storms

Using an elliptical cross-section model for the study of the magnetic topology of magnetic clouds (MCs) in the interplanetary medium, we develop an analytical approach to their relationship with geomagnetic storms. Assuming an axially symmetric ring current and once we have obtained the disturbances produced in its current density due to the passage of a MC through it (whose axis has a latitude θ, a longitude φ, and its cross-section has an orientation ζ), then we determine the decrease in the value of the geomagnetic field at the Earth's equator, i.e., the Dst index. The Dst model presented allows us to estimate the physical parameters which characterize the symmetric ring current during the recovery phase of the storm time. The theoretical and experimental Dst indexes are compared for four intense geomagnetic storms (Dst<−100 nT), all of them associated with MCs. As seen in the figures presented, the fits are good for every storm. In view of these results we conclude that the effects of a MC over the symmetric ring current can explain the main profile of the recovery phase of a geomagnetic storm.

Neural network prediction of relativistic electrons at geosynchronous orbit during the storm recovery phase: effects of recurring substorms

Abstract. During the recovery phase of geomagnetic storms, the flux of relativistic (&gt;2 MeV) electrons at geosynchronous orbits is enhanced. This enhancement reaches a level that can cause devastating damage to instruments on satellites. To predict these temporal variations, we have developed neural network models that predict the flux for the period 1–12 h ahead. The electron-flux data obtained during storms, from the Space Environment Monitor on board a Geostationary Meteorological Satellite, were used to construct the model. Various combinations of the input parameters AL, SAL, Dst and SDst were tested (where S denotes the summation from the time of the minimum Dst). It was found that the model, including SAL as one of the input parameters, can provide some measure of relativistic electron-flux prediction at geosynchronous orbit during the recovery phase. We suggest from this result that the relativistic electron-flux enhancement during the recovery phase is associated with recurring substorms after Dst minimum and their accumulation effect.Key words. Magnetospheric physics (energetic particles, trapped; magnetospheric configuration and dynamics; storms and substorms)

Relativistic electron microbursts during the GEM storms

Observations of relativistic (&gt;1 MeV) electron microbursts by the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) satellite are frequently associated with geomagnetic storms. We examine the characteristics of these microbursts during 1997 and 1998, paying particular attention to the three storms selected by the Geospace Environment Modeling (GEM) community for special study: May 15, 1997, September 25, 1998, and October 19, 1998. The relativistic electron microbursts strongly correlate with both the Dst and Kp indices and generally increase in intensity and move to lower L shells during the recovery phases of geomagnetic storms. During the recovery phases of the September and October 1998 storms, the numbers of &gt;1 MeV electrons lost from the radiation belts to the microburst precipitation are estimated to be 2.5 × 1025 and 3.3 × 1024, respectively. In both cases, the microburst loss is a significant fraction of the total radiation belt population.

The effect of solar activity on ill and healthy people under conditions of nervous (correction of neurous) and emotional stresses.

It is commonly agreed that solar activity has adverse effects first of all on enfeebled and ill organisms. In our study we have traced that under conditions of neurvous and emotional stresses (at work, in the street, and in cars) the effect may be larger (~ 30%) for healthy people. Our calculations have been carried out applying the epoch-superposition method, spectrum and correlation analyses to daily data over a 1992 to 1994 period from three independent databases (Kharkiv City) on patients (adults and children) suffering from mental diseases and physical traumas. The effect is most marked during the recovery phase of geomagnetic storms and accompanied by the inhibition in the central nervous system.

Space environment effects on geostationary spacecraft: Analysis and prediction

We investigate how the two geostationary spacecraft, Meteosat-3 and Tele-X, are affected by the space environment, as characterized by Dst, Kp, and energetic electron flux (> 2 MeV, EEF). Neural network models are developed to predict spacecraft anomalies 1 day ahead. It is found from superposed epoch analysis that the spacecraft anomalies frequently occurred during the recovery phase of geomagnetic storms and that the space environment during the last 4–6 days preceding an anomaly contributes statistically the most to the anomaly occurrence. We find from network prediction (1) that when training is only on Meteosat-3, Kp, Dst, and the EEF, respectively, give the total prediction rate of 79%, 73%, and 62% for Meteosat-3 (both anomalies and non-anomalies) and the total prediction rate of 64%, 66%, and 67% for Tele-X; (2) that when training is only on Tele-X, Kp, Dst, and the EEF, respectively, give the total prediction rate of 57%, 58%, and 51% for Meteosat-3 and the total prediction rate of 70%, 71%, and 74% for Tele-X; (3) that Kp is the optimal environment parameter to correlate with the anomalies on both Meteosat-3 and Tele-X. It is revealed from the anomaly local time distribution, superposed epoch analysis, and network prediction that Meteosat-3 was more subject to surface charging than to internal dielectric charging, and that Tele-X was more subject to internal dielectric charging than to surface charging. The developed neural network models can be used to predict times with higher risks for anomalies in real-time from ACE data.

Correlations between SAR arc intensity and solar and geomagnetic activity

Abstract. We present a study of statistical relationships between SAR arc intensities acquired by the Pacific Northwest Laboratory Photometer Network during 1978-1988 and solar and geomagnetic activity indices Dst, F10.7, and Kp by use of the method of multiple regression analysis. We found significant correlations between intensity and all of the indices involved. In the present work we show for the first time that the partial correlation coefficients depend on the time offset, t, between the time of SAR arc intensity observations and the onset of the geomagnetic storm recovery phase, with the largest correlations being observed when 8 h &lt; t &lt; 16 h. It is also shown that there are significant differences between partial correlation coefficients calculated for SAR arcs associated with strong (Dstmin&lt; -100 nT) and weak (Dstmin&gt;-100 nT) geomagnetic storms. We observe also that the multiple correlation coefficients for strong storms are much larger than for weak ones. We found that the variations in the electron temperature, Te, in the SAR arc region are not mainly produced by variations in the electron density of the ionosphere but are strongly driven by the additional heating of the electron gas due to an interaction of the ring current ions and the plasmaspheric electrons. As a result, variations of Te in the SAR arc region with characteristic time scales from several minutes to several hours are stipulated by time variations of ring current parameters.Key words. Atmospheric composition and structure (airglow and aurora) · Ionosphere (ionosphere · atmosphere interactions; ionosphere · magnetosphere interactions)

Correlations between SAR arc intensity and solar and geomagnetic activity

We present a study of statistical relationships between SAR arc intensities acquired by the Pacific Northwest Laboratory Photometer Network during 1978-1988 and solar and geomagnetic activity indices Dst, F10.7, and Kp by use of the method of multiple regression analysis. We found significant correlations between intensity and all of the indices involved. In the present work we show for the first time that the partial correlation coefficients depend on the time offset, t, between the time of SAR arc intensity observations and the onset of the geomagnetic storm recovery phase, with the largest correlations being observed when 8 h < t < 16 h. It is also shown that there are significant differences between partial correlation coefficients calculated for SAR arcs associated with strong (Dstmin< -100 nT) and weak (Dstmin>-100 nT) geomagnetic storms. We observe also that the multiple correlation coefficients for strong storms are much larger than for weak ones. We found that the variations in the electron temperature, Te, in the SAR arc region are not mainly produced by variations in the electron density of the ionosphere but are strongly driven by the additional heating of the electron gas due to an interaction of the ring current ions and the plasmaspheric electrons. As a result, variations of Te in the SAR arc region with characteristic time scales from several minutes to several hours are stipulated by time variations of ring current parameters.Key words. Atmospheric composition and structure (airglow and aurora) · Ionosphere (ionosphere · atmosphere interactions; ionosphere · magnetosphere interactions)

Relativistic theory of wave‐particle resonant diffusion with application to electron acceleration in the magnetosphere

Resonant diffusion curves for electron cyclotron resonance with field‐aligned electromagnetic R mode and L mode electromagnetic ion cyclotron (EMIC) waves are constructed using a fully relativistic treatment. Analytical solutions are derived for the case of a single‐ion plasma, and a numerical scheme is developed for the more realistic case of a multi‐ion plasma. Diffusion curves are presented, for plasma parameters representative of the Earth's magnetosphere at locations both inside and outside the plasmapause. The results obtained indicate minimal electron energy change along the diffusion curves for resonant interaction with L mode waves. Intense storm time EMIC waves are therefore ineffective for electron stochastic acceleration, although these waves could induce rapid pitch angle scattering for ≳ 1 MeV electrons near the duskside plasmapause. In contrast, significant energy change can occur along the diffusion curves for interaction between resonant electrons and whistler (R mode) waves. The energy change is most pronounced in regions of low plasma density. This suggests that whistler mode waves could provide a viable mechanism for electron acceleration from energies near 100 keV to above 1 MeV in the region outside the plasmapause during the recovery phase of geomagnetic storms. A model is proposed to account for the observed variations in the flux and pitch angle distribution of relativistic electrons during geomagnetic storms by combining pitch angle scattering by intense EMIC waves and energy diffusion during cyclotron resonant interaction with whistler mode chorus outside the plasmasphere.

Theoretical interpretation of thermal O ++ ions density enhancement in the midlatitude outer ionosphere

Ion composition measurements made on board the near polar orbiting satellites INTERCOSMOS 24 and INTERCOSMOS 25 revealed a middle latitude O ++ density enhancement, which is ∼10x larger than seen at lower and higher latitudes. Previous analysis showed that an O ++ density enhancement occurred in the equatorial edge of the light ion trough at the altitude range ∼750–3000 km especially during recovery phases of geomagnetic storms. A time dependent model that includes two main ions and one minor ion has been constructed to study the responsible mechanisms. Results of calculations for a given geomagnetic field line for the first days of the recovery phase when H + ions fluxes are upwards confirm the decisive influence of H + ion fluxes.

Characteristics of VLF emissions observed by DE-1 in the equatorial magnetosphere

Whistler-triggered hiss, banded hiss, ELF hiss, impulsive VLF waves and magnetospheric chorus are analysed by using analog data of wideband electric fields (650 Hz – 40 kHz) from DE-1 satellite received at Kashima, Japan in the NASA DE guest investigator program. The whistler-triggered hiss was observed after a whistler trace at frequencies below about 15 kHz in low-latitude plasmasphere, and its generation models are discussed. Wave modes of banded hiss, impulsive VLF waves and ELF hiss successively observed for about one minute are discussed in terms of the spin modulated effect of whistler-mode ELF hiss. Magnetospheric chorus with a frequency gap around 5.8 kHz was observed in the geomagnetic storm recovery phase. This indicates a field decrease by about one fifth of the quiet-time geomagnetic field produced by a storm-time equatorial ring current.

Global structures of Alfvén‐ballooning modes in magnetospheric plasmas

We show that a steep plasma pressure gradient can lead to radially localized Alfvén modes, which are damped through coupling to field line resonances. These have been called drift Alfvén ballooning modes (DABM) by [Chen and Hasegawa, 1991] and are the prime candidates to explain Pc4–Pc5 geomagnetic pulsations observed during the recovery phase of geomagnetic storms. A strong dependence of the damping rate on the azimuthal wave number m is established, as well as on the equilibrium profile. A minimum azimuthal mode number can be found for the DABM to be radially trapped. We find that higher m DABMs are better localized, which is consistent with high‐m observations.

Loss of ring current O+ ions due to interaction with Pc 5 waves

The behavior of ring current ions in low‐frequency geomagnetic pulsations is investigated analytically and numerically. We focus primarily on ring current O+ ions, whose flux increases dramatically during geomagnetic storms and decays at a rate which is not fully explained by collisional processes. This paper presents a new loss mechanism for the O+ ions due to the combined effects of convection and corotation electric fields and interaction with Pc 5 waves (wave period: 150–600 s) via a magnetic drift‐bounce resonance. A test particle code has been developed to calculate the motion of the ring current O+ ions in a time‐independent dipole magnetic field, and convection and corotation electric fields, plus Pc 5 wave fields, for which a simple analytical model has been formulated based on spacecraft observations. For given fields, whether a particle gains or loses energy depends on its initial kinetic energy, pitch angle at the equatorial plane, and the position of its guiding center with respect to the azimuthal phase of the wave. The ring current O+ ions show a dispersion in energies and L values with decreasing local time across the day side, and a bulk shift to lower energies and higher L values. The former is due to the wave‐particle interaction causing the ion to gain or lose energy, while the latter is due to the convection electric field. Our simulations show that, due to interaction with the Pc 5 waves, the particle's kinetic energy can drop below that required to overcome the convection potential and the particle will be lost to the dayside magnetopause by a sunward E × B drift. This may contribute to the loss of O+ ions at intermediate energies (tens of keV) observed during the recovery phase of geomagnetic storms.

Plasmaspheric hiss observed in the topside ionosphere at mid- and low-latitudes

Latitudinal characteristics of ELF hiss in mid- and low-latitudes have been statistically studied by using ELF/VLF electric field spectra (50 Hz-30 kHz) from ISIS-1 and -2 received at Kashima station, Japan from 1973 to 1977. Most ISIS ELF/VLF data observed in mid- and low-latitude include ELF hiss at frequencies below a few kHz. The ELF hiss has the strongest intensity among VLF phenomena observed by the ISIS electric dipole antenna in mid- and low-latitudes, but the ELF hiss has no rising structure like the chorus in the detailed frequency-time spectrum. The ELF hiss is classified into the steady ELF hiss whose upper frequency limit is approximately constant with latitude and the ELF hiss whose upper frequency limit increases with latitude. These two types of ELF hiss occur often in medium or quiet geomagnetic activities. Sometimes there occurs a partial or complete lack of ELF hiss along an ISIS pass. Spectral shape and bandwidth of ELF hiss in the topside ionosphere are very similar to those of plasmaspheric hiss and of inner zone hiss. The occurrence rate of steady ELF hiss is about 0.3 near the geomagnetic equator and decreases rapidly with latitude around L = 3. Hence it seems likely that ELF hiss is generated by cyclotron resonant instability with electrons of several tens of keV in the equatorial outer plasmasphere beyond L = 3. Thirty-seven per cent of ELF hiss events received at Kashima station occurred during storm times and 63% of them occurred in non-storm or quiet periods. Sixty-seven per cent of 82 ELF hiss events during storm times were observed in the recovery phase of geomagnetic storms. This agrees with the previous satellite observations of ELF hiss by search coil magnetometers. The electric field of ELF hiss becomes very weak every 10 s, which is the satellite spin period, in mid- and low-latitudes, but not near the geomagnetic equator. Ray tracing results suggest that waves of ELF hiss generated in the equatorial outer plasmasphere propagate down in the electrostatic whistler mode towards the equatorial ionosphere, bouncing between the LHR reflection points in both the plasmaspheric hemispheres.

A simplified D-region model and its application to magnetic storm after-effects

Energetic electron precipitation from the Earth's radiation belts can provide the dominant D-region ionization source at middle latitudes during the recovery phase of geomagnetic storms. To study the ionospheric response, a simplified D-region ionic model is developed with emphasis placed on obtaining a reasonably accurate evaluation of the free electron concentration. The precise distribution amongst the multiply hydrated water cluster ions and high affinity negative ions is not considered. Instead the complicated heavy ion chemistry is replaced by a scheme which simply applies an average rate of clustering and subsequent recombination. The model provides an adequate fit with observed quiet-time electron concentration in the D-region. It is shown that typical poststorm electron precipitation can increase mesospheric electron densities by a factor of three during the day and by more than an order of magnitude at night. Such enhancements are consistent with VLF and LF radio wave disturbances observed during the recovery phase of major geomagnetic storm. The disturbances are expected to exhibit considerable short term variability and should persist for over a week consistent with the observed decay rate for the enhanced geomagnetically trapped electron flux.