Magnetic Storm Of May Research Articles

Relative Contribution of ULF Waves and Whistler‐Mode Chorus to the Radiation Belt Variation During the May 2017 Storm

AbstractWe investigate the time and location where ULF waves and whistler‐mode chorus contributed to the net flux enhancement of relativistic electrons during the magnetic storm of May 2017. During the early recovery phase, both ULF and chorus waves contribute to the enhancement of relativistic electron fluxes, but ULF waves play roles of the inward diffusion. During the late recovery phase, both Van Allen Probe‐B and Arase show that whistler‐mode chorus contributes to the flux enhancement confined in the L‐value. The CRCM coupled with BATS‐R‐US simulation qualitatively reproduces the global evolution of ULF waves. Although the electron flux is underestimated by the simulation, this study reveals a large anisotropy of hot electrons in the region where whistler‐mode chorus waves were actually observed by satellites. In addition, the estimated magnetic field curvature on the dayside is small during the recovery phase. Furthermore, we investigate the control of wave evolution. Both observations and the simulation suggest that the observed ULF waves in the frequency range of ∼2–5 mHz are excited by the enhancement of the solar wind dynamic pressure. Observations also indicate that whistler‐mode chorus on the nightside is predominantly excited by hot electrons with temperature anisotropy, whereas the dayside chorus is enhanced by the change of the magnetic field line configuration. The estimated spatial distributions of electron anisotropy and magnetic field curvature provide an explanation for the presence of enhanced whistler‐mode chorus in the dusk sector, which is far from the usual location of wave generation.

Plasma Pressure Profiles in the Dark Sector of the Earth’s Magnetosphere during the Magnetic Storm of May 29, 2010

Variations in the radial profile of the pressure and distortions of the magnetic field of the magnetosphere in the dark sector near the equatorial plane during the storm of May 29, 2010, are analyzed based on THEMIS data. The position of the pressure maximum during the main phase of the storm is determined. The time dynamics of the pressure maximum is traced during the recovery phase. The time of pressure relaxation to initial values (before the main phase) during the recovery phase are assessed. The coincidence of the positions of the pressure peak maximum and of maximal deviation of the magnetic field from the dipole one is ascertained.

Applying the new method of time-frequency transforms to the analysis of the characteristics of geomagnetic Рс5 pulsations

This study considers the possibility of using the new methods of time-frequency transforms, such as chirplet and warblet transforms, to analyze the digital observational data of geomagnetic pulsations of Pc5 type. For this purpose, necessary algorithms of calculation and appropriate software were developed. The chirplet transform method (CT) is used to analyze signals with a linear frequency modulation. A chirplet variation, the so-called warblet transform, is used to analyze signals with a nonlinear frequency modulation. Since, in studying geomagnetic pulsations, it is difficult to make assumptions on the character of the behavior of the instantaneous frequency of the signal, the special generalized warblet transform (GWT) was used for the analysis. The GWT has a high spatiotemporal resolution and was developed to analyze oscillations both with a periodic and nonperiodic change of the instantaneous frequency. The software developed for GWT calculation was used to study daytime geomagnetic Pc5 pulsations with durations of several hours that were detected via the network of ground-based magnetometers of the Scandinavian IMAGE profile during the magnetic storm of May 29–30, 2003. For the first time, temporal variations of the instantaneous frequency of geomagnetic pulsations are determined and their possible use in studying the fine spatial structure of Pc5 waves is shown.

10.1007/s11478-008-2007-2

The negative and positive fronts of the IMF B z component arrived at intervals of 3 h during a strong magnetic storm of May 15, 2005. The occurrence of Pc5 pulsations at these three characteristic instants has been considered based on the WIND satellite magnetic data. Pulsations originated not only during sudden compression SC of the magnetosphere but also during the B z sign reversal from positive to negative. The IMF B z sign reversal from negative to positive did not affect the development of pulsations. It is assumed that Pc5 pulsations observed after the negative IMF B z front are related to the development of surface waves at the magnetopause as a result of impulsive reconnection of field lines.

Generation of Pc5 pulsations during the sign reversal of the IMF B z component

The negative and positive fronts of the IMF B z component arrived at intervals of 3 h during a strong magnetic storm of May 15, 2005. The occurrence of Pc5 pulsations at these three characteristic instants has been considered based on the WIND satellite magnetic data. Pulsations originated not only during sudden compression SC of the magnetosphere but also during the B z sign reversal from positive to negative. The IMF B z sign reversal from negative to positive did not affect the development of pulsations. It is assumed that Pc5 pulsations observed after the negative IMF B z front are related to the development of surface waves at the magnetopause as a result of impulsive reconnection of field lines.

Peculiarities of the outer radiation belt dynamics during the strong magnetic storm of May 15, 2005

The dynamics of energetic electrons (E e =0.17–8 MeV) and protons (E p =1 MeV) of the outer radiation belt during the magnetic storm of May 15, 2005, at high (GOES-10 and LANL-84 geosynchronous satellites) and low (Meteor-3M polar satellite) altitudes is analyzed. The data have been compared to the density, plasma velocity, solar wind, and magnetic field measurements on the ACE satellite and geomagnetic disturbances. During the magnetic storm main phase, the nighttime boundary of the region of trapped radiation and the center of westward electrojet shifted to L ∼ 3. Enhancements of only low-energy electrons were observed on May 15, 2005. The belt of relativistic electrons with a maximum at L ∼ 4 was formed during the substorm, the amplitude of which reached its maximum at ∼0630 UT on May 16. The results are in good agreement with the regularity relating the position of a maximum of the new relativistic electron belt, boundaries of the trapped radiation region, and extreme low-latitude position of westward electrojet center to the Dst variation amplitude.

Daytime quasiperiodic geomagnetic pulsations during the recovery phase of the strong magnetic storm of May 15, 2005

Intense quasimonchromatic geomagnetic pulsations with a period of ∼15 min, observed on the Earth’s surface in the near-noon sector at the beginning of the recovery phase of a very strong (Dstmin = −260 nT) magnetic storm of May 15, 2005, are analyzed. The variations were registered at auroral latitudes only in the X field component, and wave activity shifted into the postnoon sector of the polar cap an hour later; in this case pulsations were observed in the X and Y field components. Within the magnetosphere the source of magnetic pulsations could be the surface waves on the magnetopause caused by the pulse of the solar wind magnetic pressure. Geomagnetic pulsations in the polar cap, observed in phase at different latitudes, could apparently reflect quasiperiodic variations in the NBZ system of field-aligned currents. Such variations can originate due to the series of pulsed reconnections in the postnoon outer cusp at large (∼20 nT) positive Bz values and large (about −40 nT) negative values of IMF Bx.

Geomagnetic pulsations and magnetic disturbances during the initial phase of a strong magnetic storm of May 15, 2005

A very strong magnetic storm of May 15, 2005, was caused by an interplanetary magnetic cloud that approached the Earths’ orbit. The sheath region of this cloud was characterized by a high solar wind density (∼25–30 cm−3) and velocity (∼850 km/s) and strong variations (to ∼20 nT) in the interplanetary magnetic field (IMF). It has been indicated that an atypical bay-like geomagnetic disturbance was observed during the initial phase of this storm in a large longitudinal region at high latitudes: from the morning to evening sectors of the geomagnetic local time. Increasing in amplitude, the magnetic bay rapidly propagated to the polar cap latitudes up to the geomagnetic pole. An analysis of the global space-temporal dynamics of geomagnetic pulsations in the frequency band 1–6 mHz indicated that most intense oscillations were observed in the morning sector in the region of the equivalent ionospheric current at latitudes of about 72°–76°. The wavelet structure of magnetic pulsations in the polar cap and fluctuations in IMF was generally similar to the maximum at frequencies lower than 4 mHz. This can indicate that waves directly penetrated into the polar cap from the solar wind.

Self‐consistent magnetosphere‐ionosphere coupling: Theoretical studies

A theoretical examination of the electrodynamical interaction between the ionosphere and the inner magnetosphere is presented. A self‐consistent ring current (RC) model has been developed that couples the electron and ion magnetospheric dynamics with the calculation of the electric field. Two new features were taken into account in order to close the self‐consistent magnetosphere‐ionosphere coupling loop. First, in addition to the RC ions, we have solved an electron kinetic equation in our model. Second, using the relation of Galand and Richmond [2001], we have calculated the height integrated ionospheric conductances as a function of the precipitated high energy magnetospheric electrons and ions that are produced by our model. To validate the results of our model we simulate the magnetic storm of May 2, 1986, a storm that has been comprehensively studied by Fok et al. [2001], and have compared our results with different theoretical approaches. The self‐consistent inclusion of the hot electrons and their effect on the conductance results in deeper penetration of the magnetospheric electric field. In addition, a slight westward rotation of the potential pattern (compared to previous self‐consistent results) is evident in the inner magnetosphere. These effects change the hot plasma distribution, especially by allowing increased access of plasma sheet ions and electrons to low L shells. These results are consistent with recent observations from the IMAGE satellite.

A Comparative Study of Magnetic Storm Effects on the Ionosphere in Polar Cap and Auroal Oval —F‐Region Negative Storm

AbstractWith coordinated EISCAT and ESR radar data, ionospheric storm in both the dayside polar cap and the auroral oval during the major magnetic storm of May 15, 1997 is studied, focusing on the F‐region negative storm. It is found that in both the polar cap and the auroral zone a F1‐like peak of ionization appeared at 190km height during the main and recovery phase of the storm, while the normal F2 peak disappeared and great depletions of electron density occurred. In contrast, variations of ion temperature are very different in the two regions, with little change in polar cap while strong enhancement in auroral oval, implying a difference in key mechanisms for the negative storms in the two regions. The increased O+ ion loss rate through chemical reaction due to Joule heating and ion temperature enhancement, which are resulted from strong electric field, played a crucial role in the auroral zone. The plasma transport process, however, especially the long‐lasting large ion upflow, is of great importance in the polar cap. In addition, large F‐region electron density depletion associated with null Joule heating and ion temperature enhancement is observed by EISCAT radar in the transient region of the two cells of plasma convection, which is caused by strong field‐aligned O+ ion outflow when the radar passing through probably under the polar cleft ion fountain region.

Variations of Inner Magnetospheric Currents During the Magnetic Storm of May 1998

AbstractTransient variations of the geomagnetic field at low latitudes are mainly caused by the following current systems: the ionospheric dynamo current (IDC), the symmetrical ring current (SRC), and the 3D partial ring current system (PRFI). Meanwhile, the region I ield aligned current‐ionospheric current system (FACI) annot be ignored. In this paper, the ariations of these current systems during the large storm on May 1‐6, 1998 are discussed. The disturbances of the storm contains two events. One is during May 1‐3 and the other is during May 4‐5. The Sq‐field caused by IDC is calculated by using several station pairs. Then, the fields of other sources are separated by fitting data to their field models. Results show that: (1) PRFI and FACI do not develop significantly in the first event, while they develop strongly with substorms in the second event. (2) The variations of SRC‐field are similar to Dst index in the first event and delayed to Dst in the second event. (3) In the second event, PRFI develops before SRC, and SRC depresses associated with the recovery of PRFI and FACI. These results provide a clue to understand the formation of the ring current and field‐aligned currents and their relationship.

Comprehensive computational model of Earth's ring current

A comprehensive ring current model (CRCM) has been developed that couples the Rice Convection Model (RCM) and the kinetic model of Fok and coworkers. The coupled model is able to simulate, for the first time using a self‐consistently calculated electric field, the evolution of an inner magnetosphere plasma distribution that conserves the first two adiabatic invariants. The traditional RCM calculates the ionospheric electric fields and currents consistent with a magnetospheric ion distribution that is assumed to be isotropic in pitch angle. The Fok model calculates the plasma distribution by solving the Boltzmann equation with specified electric and magnetic fields. To combine the RCM and the Fok model, the RCM Birkeland current algorithm has been generalized to arbitrary pitch angle distributions. Given a specification of height‐integrated ionospheric conductance, the RCM component of the CRCM computes the ionospheric electric field and currents. The Fok model then advances the ring current plasma distribution using the electric field computed by the RCM and at the same time calculates losses along particle drift paths. We present the logic of CRCM and the first validation results following the H+ distribution during the previously studied magnetic storm of May 2, 1986. The H+ fluxes calculated by the coupled model agree very well with observations by AMPTE/CCE. In particular, the coupled model is able to reproduce the high H+ flux seen on the dayside at L ∼ 2.3 that the previous simulation, which employed a Stern‐Volland convection model with shielding factor 2, failed to produce. Though the Stern‐Volland and CRCM electric fields differ in several respects, the most notable difference is that the CRCM predicts strong electric fields near Earth in the storm main phase, particularly in the dusk‐midnight quadrant. Thus the CRCM injects particles more deeply and more quickly.

Satellite and ground observations of magnetospheric VLF hiss associated with the severe magnetic storm on May 25-27, 1967

The purpose of this paper is to make clear the characteristics of magnetospheric VLF hiss during storm times. The study is based on the VLF observations on board the Ariel 3 satellite as well as on the ground during the severe magnetic storm of May 25–27, 1967. Soon after the onset of the main phase there appeared the VLF hiss in the morning sector of the magnetosphere (‘morning hiss’) on the satellite as well as ground records, but the hiss is not observed in the evening sector. It was not until during the recovery phase that we could recognize the stationary occurrence of strong VLF hiss in the evening side of the magnetosphere (‘evening hiss’). The important features of the morning and evening hiss are described, and some discussions concerning their generation mechanism by the ring current particles are given.

Some topside electron density measurements from Ariel III satellite during the geomagnetic storm of 25–27 May 1967

The Ariel III electron density data obtained during the magnetic storm of May 25–27 1967, have been studied and show that the storm day profile (electron density along the satellite orbit) was almost symmetric around the invariant magnetic equator. Since the satellite orbit was not perfectly circular, storm time electron densities encountered in the Southern Hemisphere were, on average, greater than the quiet day electron densities; whereas the opposite was the case in the north. Observations of visual aurora and the occurrence of the trough seem to be correlated on the storm day.

Radial diffusion observations in the Earth's outer radiation belt

We examined the intensities and differential energy spectra of electrons between 1 and 3.6 Mev obtained with an instrument flown on polar-orbiting AF Satellite OV1 9 during May and June 1967, which almost coincided with the time of maximum solar activity. We observed a severe depletion of the outer-belt electrons with Ee>0.94 Mev coincident with the onset of the magnetic storm of May 25, and the subsequent growth of the peak flux at L≃3.0 (pre-storm L≃3.8). Over the region 2.5≲L≲5, and on May 23, 24, and June 16, the e-folding energies (E0) versus L distributions were found to be characteristic of the bimodal diffusion process. After the May 25 storm, the E0 distributions were independent of L, and we observed a spectral hardening from 〈E0〉 = 482 ± 67 kev (May 27) to the pre-storm value of 〈E0〉 = 567 ± 57 kev (June 14). On June 5, a secondary electron maximum appeared at L=3.40, which then diffused outward across field lines, with a velocity ∝ L10.6±2.0.

Solar flares and magnetic storm of May 21 to 28, 1967

Solar flares and magnetic storm of May 21 to 28, 1967

A Man-made or Artifical Aurora

AT 1051 G.M.T. on August 1, 1958, Mr. J. G. Keys, observer-in-charge at Apia Observatory, latitude 13° 48′ S., longitude 171° 46′ W., witnessed at Apia a manifestation which was at first thought to be a display of the aurora australis but is now believed to be due to a nuclear bomb explosion in the upper atmosphere. The occurrence of an auroral display in the tropics is always of unusual interest to geophysicists because of its exceeding rarity. In particular, the Aurora Australis has been reported at Apia on one occasion only, and then only in association with the severe magnetic storm of May 13–16, 1921. This display was described in detail by Angenheister1 and Angenheister and Westland2.

Solar and magnetic data, April to June, 1946, Mount Wilson Observatory

The magnetic storm of April 22–24 began when an active bipolar sunspot‐group, Mount Wilson No. 8026, was 50° east of the central meridian, in latitude 33° north. Two solar flares were observed in this group on April 22, one 8 hours, the other 13 hours after the storm began.When the magnetic storm of May 5–7 began, groups 8033, 8038, and 8039 were west of the central meridian, having crossed it on May 4.3, 4.5, and 5.3, respectively. Solar flares were observed in No. 8038 on May 2, 3, and 7.

Solar and Magnetic Data, April to June, 1941, Mount Wilson Observatory

The magnetic storm of May 21, 1941, ended a sequence of four which began with the great storm of March 1. Each storm of this sequence was apparently associated with a different sunspot group: That of March 1 with Mount Wilson No. 7132, 24° west, 16° north at the beginning of the storm; March 28 with No. 7156, 13° east, 8° north; April 24 with No. 7172, 7° east, 6° south; May 21 with No. 7192, 0°, 16° south. These storms, however, may have been associated with other less active groups or with hypothetical activity in the region of No. 7132, although no spot or other activity was seen in that region after it passed from view at the west limb on March 4.Small magnetic disturbances beginning on June 9 and 13, were probably associated with group No. 7201, which crossed the central meridian on June 9.3, 12° north of the center of the disk.

Terrestrial Magnetic Disturbances and Sun-spots

MAY I add a few remarks on Mr. Evershed's interesting letter on this topic (NATURE, December 29, p. 566), and supplementary also to my former letter (NATURE, October 27, p. 272). The protracted magnetic storm of May 12–21, 1921, after a lull on May 18, resumed an active phase on May 19–21. In my former letter I traced a sequence of magnetic disturbances, in connection with that of May 21, which extended to October 5. I may now add that the sequence has persisted until December 24, that is for 217 days, embracing eight synodical rotations of the sun, with a mean period of 27.13 days. The corresponding mean sidereal period would be 25.25 days, or 14.26° per day. This is Carrington's rotation period for latitudes 10° to 15°, and agrees closely with the sidereal period found by Mr. Evershed for the main series of disturbances from March 22 to September 29, 1921.