Dynamics of the earth radiation belts during strong magnetic storms based on <Emphasis Type="Italic">CORONAS-F</Emphasis> data

The results of an experimental study of the variations in the intensity of the fluxes of the Earth radiation belt (ERB) particles in 0.3–6 and 1–50 MeV energy intervals for electrons and protons, respectively, are reported. ERBs were studied during strong magnetic storms from August 2001 through November 2003. The results of the CORONAS-F mission obtained during the magnetic storms of November 6 (D _st = ?257 nT) and November 24, 2001 (D _st = ?221 nT), October 29–30 (D _st = ?400 nT) and November 20, 2003 (D _st = ?465 nT) are analyzed. The electron flux is found to decrease abruptly in the outer radiation belt during the main phase of the magnetic storms under consideration. During the recovery phase, the outer radiation belt is found to recover much closer to Earth, near the boundary of the penetration of solar electrons during the main phase of the magnetic storm. We associate the decrease in the electron flux with the abrupt decrease of the size of the magnetosphere during the main phase of the storm. Note that, in all cases studied, the Earth radiation belts exhibited rather long (several days) variations. In those cases where solar cosmic-ray fluxes were observed during the storm, protons with energies 1–5 MeV could be trapped to form an additional maximum of protons with such energies at L >2.     

Effect of low energy electron injection on storm-time evolution of radiation belt energetic electrons: three-dimensional modeling

Using the STEERB (storm-time evolution of electron radiation belt) code, we simulate the evolution of radiation belt energetic electrons during geomagnetic storms in the case of low energy electron injection. The STEERB code is used to solve the three-dimensional Fokker–Planck diffusion equation which incorporates wave-particle interaction, Coulomb collisions and radial diffusion. Numerical simulations show that under the short time (～1 h) injection of low energy (0.1 MeV≤E _k ≤0.2 MeV) fluxes of radiation belt energetic electrons can increase during the entire storm period. During the main and recovery phases, such injection efficiently enhances chorus-driven acceleration of radiation belt energetic electrons, allowing fluxes of energetic electrons by a factor of 1–2 orders higher than those in the absence of injection. The current results indicate that substorm-induced electron injection must be incorporated to investigate the evolution of radiation belt energetic electrons.     

The behaviour of outer radiation belt electrons (> 1·5 MeV) during a geomagnetically disturbed time on 8 March 1970 and its relationship to magnetospheric processes

Omnidirectional intensities of electrons with energies E_e > 1·5 MeV detected by a low orbiting polar satellite (GRS-A/AZUR) in the outer radiation belt are examined during disturbed times including the main phase of a very strong geomagnetic storm on 8 March 1970. The particle intensity features are discussed in relationship with proposed magnetospheric processes. It is found that a superposition of the two following effects can explain the particle behavior in the trapping region:(A) Radial diffusion. After the southward turning of the interplanetary field an inward motion of both the energetic electron belt and the plasmapause took place. This effect was observed at L > 3 R_E and we attribute it to enhanced magnetospheric electric field fluctuations. Later, a strong interplanetary shock impinged upon the magnetosphere which was related to the triggering of intense magnetospheric substorms; a further inward diffusion occurred at L ? 3 R_E, accompanied by an inward movement of the electron slot. A rough estimation of the diffusion coefficient leads to a power spectrum of the electric field fluctuations which seems to be consistent with experimentally determined power spectra (Mozer, 1971).(B) Adiabatic response to ring current changes. Large energetic electron intensity decreases within the outer radiation belt are shown to be adiabatic changes due to ring current variations. The influence of the inflation of the magnetosphere due to the developing ring current is simultaneously observed by the decrease of the solar proton outoff (1·7-2·5 MeV).     

Low altitude observations of the energetic electrons in the outer radiation belt during isolated substorms

The low energy (1–20 keV) detector registering particles onboard the polar-orbiting low altitude (~ 850 km) DMSP-F2 and -F3 satellites also records high energy electrons penetrating the detector walls. Thus we can study the dynamics of this electron population at L = 3.5, during isolated periods of magnetospheric substorms identified by the indices of auroral electrojet (AE), geomagnetic (K_p) and ring current (D_st). Temporal changes in the electron flux during the substorms are observed to be an additional contribution riding over the top of the pre-storm (or geomagnetically quiet-time) electron population ; the duration of the interval of intensity variation is observed to be about the same as that of the enhancement of the AE index. This indicates the temporal response of the outer radiation belt to the substorm activity, since the observation was made in the “horns” of the outer radiation belt. The observed enhanced radiation at low altitude may associate with the instantaneous increase and/or dumping of the outer radiation belt energetic electrons during each isolated substorm activity.     

Development of four magnetic storms in February 1972

Four magnetic storms were observed in February 1972, with instruments on the Explorer 45 satellite in the evening quadrant of the inner magnetosphere. The magnitude of the storms ranged from small, D_st ? ?40 γ, to moderate, D_st ? ?80 γ. During the development of the storms several substorms occurred. At the beginning of the substorms there was evidence of a partial ring current above L = 5. After the expansion phase of several substorms there was evidence of enhancement of a partial ring below L = 5. Distortions of the field in the east-west direction were observed, in conjunction with substorm expansions, that can be interpreted as due to field aligned currents flowing from the ionosphere. A substantial symmetric ring current, at L～4, developed during the largest storm. Very little additional ring current was contributed by the smallest storm. Relations between the magnetosphere inflation and ring current protons, plasmaspheric hiss, and ULF waves also measured on Explorer 45 were noted.     

Millstone Hill Thomson scatter results for 1966 and 1967

Thomson (incoherent) scatter radar measurements of F-region electron densities and temperatures were made approximately twice per month throughout 1966 and 1967 at Millstone Hill for periods of 24 hr. Owing to the increase in sunspot activity the results display a rich variety of different types of behaviour. Geomagnetically quiet days tended to follow patterns observed near sunspot minimum. Thus in winter there is typically a marked diurnal variation in electron density with a peak near noon and often a smaller secondary maximum between 02 and 04 EST. In summer there is less day-to-night variation and the peak density is encountered near ground sunset. Usually h_maxF2 is higher in summer than winter and the layer thickness is larger also.Some magnetically disturbed days follow a distinct pattern in which N_max and h_max are normal during the first day of the storm until afternoon when they both increase to very high values. There is then a corresponding decrease in electron temperature. During the night the electron temperature often reaches abnormally high values, providing evidence of nocturnal heating. On the following day N_max and h_max are abnormally low.During 1967 instances in which the trough of low electron density moved south to occupy a position over Millstone became frequent. The electron temperature rose to particularly high values on these occasions. These morphological features are discussed in terms of current theoretical ideas. The results are also employed to derive seasonal variations of electron temperature and protonospheric heat flux. It is shown that since 1964 the protonospheric heat flux has been larger in winter than summer and displays a clear sunspot cycle variation.     

SAR arcs and 6300 Å emission by dissociative recombination of O2+ observed from Africa during severe magnetic storms

SAR arcs were observed from Southern Africa on 17/18 December 1971, 4/5 August 1972 and 1/2 April 1973 with the equatorwards edge at L = 1.8. Simultaneous with the latter event the intertropical arc was observed at an equatorial station. There was no apparent relationship. Calculations show that while the entire observed inter-tropical emission results from dissociative recombination of O₂⁺ this process may, in some cases, account for only a fraction of a percent of the observed SAR arc emission. More than five years of geomagnetic storm data shows that Southern African SAR arcs are unlikely unless disturbances exceed 150 γ. For very severe 300 γ disturbances main phase SAR arcs may be observed. Estimates of the fraction of storm energy used in production of the present arcs indicate they are inefficient sinks for magnetic storms.     

Precipitation of auroral particles in the central polar cap during a sudden commencement magnetic storm

All-sky camera observations from two stations in the inner (northern) polar cap and an auroral zone station are combined with photometer records from the polar cap station Nord in a study of the brilliant auroral display following the ssc of the storm of 7 November 1970. This display is the large, poleward expanding bulge of a substorm triggered by the ssc. It is composed of brilliant discrete forms embedded in low-intensity diffuse electron and proton aurora. The poleward edge of the diffuse electron aurora is 5° north of the discrete auroras and 3° north of the proton aurora. The intensity of the discrete aurora varies as the strength of the auroral electrojet as shown by magnetograms from auroral zone stations. Succeeding the retreating display a subvisible low-energy electron precipitation, which may be identified as the polar squall (Winningham and Heikkila, 1974) is observed over the polar cap during the main phase of the storm.In the early morning sector already existing diffuse auroras broaden towards the equator from the time of the ssc and at least during the following half hour.Ssc-triggered displays have been found (Feldstein, 1959) to withdraw from the inner polar cap as the initial (positive H) phase of the storm ends. A comparison of the records from seven low-latitude stations shows that during this particular storm the positive phase appears to be composed by two overlapping disturbances, i.e. the proper initial phase, which is generally thought to be due to compression of the inner magnetosphere and a series of positive bays accompanying the negative bays in auroral latitudes. These positive bays are observable over a great range of longitudes with a maximum of amplitude near midnight. As judged from the dayside magnetograms the initial (compression) phase ends at an early stage of the substorm. The observed coincidence between the withdrawal of the display and the cessation of the positive H phase of the storm is a consequence of the fact that the second component—the positive bays—and the auroral display over the polar cap are both signatures of the substorm activity.     

Temporal variations in the dawn and dusk midlatitude trough and plasmapause position

The temporal development of the latitudinal position of a 600 km midlatitude electron density trough at dawn and dusk during the period 25–27 May 1967, which encompassed a large magnetic storm, was measured by the RF capacitive probe on the polar orbiting Ariel 3 satellite. The substorm-related changes in the L coordinate of the trough minimum and the point of most rapid change of density gradient on the low latitude side of the trough are similar. Oscillations of the trough position at dusk are in phase with substorm activity whereas movement of the trough at dawn is only apparent with the onset of the large storm. Detailed model calculations of the plasmasphere dynamics assuming a spatially invariant equatorial convection E-field which varies in step with the K_p index produces a plasmapause motion which parallels the observed trough behaviour, particularly at dusk, and shows that the outer plasmasphere and possibly the trough region are characterized by complex fine structured variations due to the past history of the magnetosphere convection.     

Simultaneous storm-time increases of the ionospheric total electron content and the geomagnetic field in the dusk sector

Using the Faraday rotation technique with the ATS-3 satellite, it has been possible to monitor changes in the total electron content (N_T) of the mid-latitude ionosphere during the first day of 20 geomagnetic storms. Our analysis has shown that during the positive phase (ΔN_T > 0) of ionospheric storms the absolute magnitude of the increase in N_T exhibits a very pronounced maximum near sunset. The mean value of ΔN_T at 17:00 LT is more than five times the average ΔN_T value at local noon. This effect is basically independent of the storm commencement time and is usually associated with substantial local enhancements of the total geomagnetic field. The N_T enhancements are discussed in terms of a contraction and draining of the plasmasphere. A model is presented in which the dawn-dusk electric field responsible for the magnetospheric convection slows down the corotational motion of the plasmaspheric ionization in the dusk sector. This braking action causes a ‘pile up’ of the plasma and the magnetic field along the entire dusk sector.     

Secular spin dynamics of inner main-belt asteroids

Understanding the evolution of asteroid spin states is challenging work, in part because asteroids have a variety of orbits, shapes, spin states, and collisional histories but also because they are strongly influenced by gravitational and non-gravitational (YORP) torques. Using efficient numerical models designed to investigate asteroid orbit and spin dynamics, we study here how several individual asteroids have had their spin states modified over time in response to these torques (i.e., 951 Gaspra, 60 Echo, 32 Pomona, 230 Athamantis, 105 Artemis). These test cases which sample semimajor axis and inclination space in the inner main belt, were chosen as probes into the large parameter space described above. The ultimate goal is to use these data to statistically characterize how all asteroids in the main belt population have reached their present-day spin states. We found that the spin dynamics of prograde-rotating asteroids in the inner main belt is generally less regular than that of the retrograde-rotating ones because of numerous overlapping secular spin-orbit resonances. These resonances strongly affect the spin histories of all bodies, while those of small asteroids (?40 km) are additionally influenced by YORP torques. In most cases, gravitational and non-gravitational torques cause asteroid spin axis orientations to vary widely over short (?1 My) timescales. Our results show that (951) Gaspra has a highly chaotic rotation state induced by an overlap of the s and s₆ spin-orbit resonances. This hinders our ability to investigate its past evolution and infer whether thermal torques have acted on Gaspra's spin axis since its origin.     

Observations concerning the relationship between the quiet-time ring current and electron temperatures at trough latitudes

The relationship between the simultaneously observed positions of the maximum omnidirectional flux of the quiet-time ring current positive ions (Λ_φ) and the maximum electron temperature Λ_T in the trough is studied in the midnight sector of the topside ionosphere. Λ_φ maps to the inner edge of the plasma sheet where ring current fluxes change from nearly isotropic to trapped. At altitudes near 2500 km, the electron temperature at trough latitudes were always sharply peaked. Although Λ_φ varied with the level of geomagnetic activity, (Λ_φ ? Λ_T) did not. These observations support the hypothesis that the quiet-time ring current is the source of elevated electron temperatures found near the plasmapause. Below 1300 km, peaked electron temperature distributions in the trough were not consistent features of the data. It is shown that (Λ_φ ? Λ_T) increased with decreasing altitude. The possible influences of a westward component to the convective electric field and ionospheric refraction of ion cyclotron waves are discussed.     

Thermal infrared opacity of the Mars atmosphere

A refined technique is presented for deriving 9-μm extinction opacities of the Mars atmosphere from brightness temperature measurements made by the Viking Infrared Thermal Mapper. Improvements include modeling of the vertical temperature profile, a surface-atmosphere temperature discontinuity, and the effects of surface emissitivity and particle scattering. The routine is applied to the Mars Average Data Set to yield zonal mean opacities for more than one Mars year. The mean 9-μm opacity for one year is 0.5, yet the mode value is only 0.056, due to the very skewed distribution. Time histories of opacity at the Viking Lander 1 and 2 sites are generated and compared to in situ data. Opacity maps are presented for the period L_s 168–270 covering the 1977a dust storm; these show the genesis and spread of the storm with 10° L_s resolution.     

HEOS-2 observations of the boundary layer from the magnetopause to the ionosphere

HEOS-2 low energy electron data (10 eV–3.7 keV) from the LPS Frascati plasma experiment have been used to identify three different magnetospheric electron populations. Magnetosheathlike electron energy spectra (35–50 eV) are characteristic of the plasma mantle, entry layer and cusps from the magnetopause down to 2–3 R_E Plasma sheet electrons (energy > 1 keV) are found at all local times, with strong intensities in the early morning quadrant and weaker intensities in the afternoon quadrant. The plasma sheet shows a well defined inner edge at all local times and latitudes, the inner edge coinciding probably with the plasmapause. The plasma sheet does not reach the magnetopause, but it is separated from it by a boundary layer electron population that is very distinct from the other two electron populations, most electrons having energies 100–300 eV.We map these three electron populations from the magnetopause down to the high latitude near earth regions, by making use of the HEOS-2 low latitude inbound passes and the high latitude outbound passes (in Solar Magnetic (SM) coordinates). The boundary layer extends along the magnetopause up to 5–7 R_E above the equator; at higher latitudes it follows the magnetic lines of force and it is found closer and closer to the earth, so that it has the same invariant latitudes of the system 1 currents observed by Iijima and Potemra (1976) in their region 1. The plasma sheet can be mapped into their region 2 and the cusp-entry layer-plasma mantle can be mapped into their cusp currents region. The boundary layer is observed for any Interplanetary Magnetic Field (IMF) direction. We speculate that magnetosheath particles penetrate into the magnetosphere everywhere along the magnetopause. The electron energization, however, is observed only in the boundary layer, on both dawn and dusk side and could be due to the polarization electric field at magnetopause generated by the magnetosheath plasma bulk motion in the region where such motion is roughly perpendicular to the magnetospheric magnetic field. The electron energization is absent in the regions (entry layer and plasma mantle) where the sheath plasma motion is roughly parallel or antiparallel to the magnetospheric magnetic field.     

Solar Rotational Periodicities and the Semiannual Variation in the Solar Wind, Radiation Belt, and Aurora

The behavior of a number of solar wind, radiation belt, auroral and geomagnetic parameters is examined during the recent extended solar minimum and previous solar cycles, covering the period from January 1972 to July 2010. This period includes most of the solar minimum between Cycles 23 and 24, which was more extended than recent solar minima, with historically low values of most of these parameters in 2009. Solar rotational periodicities from 5 to 27 days were found from daily averages over 81 days for the parameters. There were very strong 9-day periodicities in many variables in 2005?–?2008, triggered by recurring corotating high-speed streams (HSS). All rotational amplitudes were relatively large in the descending and early minimum phases of the solar cycle, when HSS are the predominant solar wind structures. There were minima in the amplitudes of all solar rotational periodicities near the end of each solar minimum, as well as at the start of the reversal of the solar magnetic field polarity at solar maximum (～?1980, ～?1990, and ～?2001) when the occurrence frequency of HSS is relatively low. Semiannual equinoctial periodicities, which were relatively strong in the 1995?–?1997 solar minimum, were found to be primarily the result of the changing amplitudes of the 13.5- and 27-day periodicities, where 13.5-day amplitudes were better correlated with heliospheric daily observations and 27-day amplitudes correlated better with Earth-based daily observations. The equinoctial rotational amplitudes of the Earth-based parameters were probably enhanced by a combination of the Russell-McPherron effect and a reduction in the solar wind-magnetosphere coupling efficiency during solstices. The rotational amplitudes were cross-correlated with each other, where the 27-day amplitudes showed some of the weakest cross-correlations. The rotational amplitudes of the >?2 MeV radiation belt electron number fluxes were progressively weaker from 27- to 5-day periods, showing that processes in the magnetosphere act as a low-pass filter between the solar wind and the radiation belt. The A _p/K _p magnetic currents observed at subauroral latitudes are sensitive to proton auroral precipitation, especially for 9-day and shorter periods, while the A _p/K _p currents are governed by electron auroral precipitation for 13.5- and 27-day periodicities.     

Latitudinal and Solar-Cycle Variations of the White-Light Corona from SOHO/LASCO Observations

SOHO/LASCO data were used to obtain the latitudinal and radial distributions of the brightness of the K- and F-corona in the period of 1996 – 2007, and their solar-cycle variations were studied. Then an inversion method was employed to obtain the radial distributions of the electron density N _e(R,θ) for various latitude values on the coronal images. Our values of N _e(R,θ) are in good agreement with the findings of other authors. We found that in an edge-on streamer belt the electron density, like the K-corona brightness, varies with distance more slowly in the near-equatorial rays than in near-polar regions. We have developed a method for assessing the maximum values of the electron density at the center of the face-on streamer belt in its bright rays and depressions between them. Not all bright rays observed in the face-on streamer belt are found to be associated with an increased electron density in them. Mechanisms for forming such rays have been suggested.     

Modelling of thermospheric composition changes caused by a severe magnetic storm

The UCL 3-dimensional time-dependent thermospheric model, with atomic and molecular components, is used to study composition changes in the neutral gas at F-layer heights produced by a severe magnetic storm. The computations give the mean molecular weight (MW), temperature and winds as functions of latitude, longitude, height and time for a period of 30 h.Starting from quiet-day conditions, the simulation starts with a 6-h “substorm” period in which strong electric fields are imposed in the auroral ovals, accompanied by particle input. Weaker electric fields are imposed for the remaining 24 h of the simulation. The energy input causes upwelling of air in the northern and southern auroral ovals, accompanied by localized composition changes (increases of MW), which spread no more than a few hundred kilometres from the energy sources. There is a corresponding downward settling of air at winter midlatitudes and low latitudes, producing widespread decreases of MW at a fixed pressure-level. These storm effects are superimposed on the quiet-day summer-to-winter circulation, in which upwelling occurs in the summer hemisphere and down welling in the winter hemisphere. The composition changes seen at a fixed height differ somewhat from those at a fixed pressure-level, because of the expansion resulting from the storm heating.The results can be related to the well-known prevalence of “negative” F-layer storms (with decreases of F2-layer electron density) in summer, and “positive” F-layer storms in winter and at low latitudes. However, the modelled composition changes are not propagated far enough to account for the observed occurrence of negative storms at some distance from the auroral ovals. This difficulty might be overcome if particle heating occurs well equatorward of the auroral ovals during magnetic storms, producing composition changes and negative storm effects at midlatitudes. Winds do not seem a likely cause of negative storm effects, but other factors (such as increases of vibrationally-excited N₂) are possibly important.     

Evolution of the Solar Flare Energetic Electrons in the Inhomogeneous Inner Heliosphere

Solar flare accelerated electrons escaping into the interplanetary space and seen as type III solar radio bursts are often detected near the Earth. Using numerical simulations we consider the evolution of energetic electron spectrum in the inner heliosphere and near the Earth. The role of Langmuir wave generation, heliospheric plasma density fluctuations, and expansion of magnetic field lines on the electron peak flux and fluence spectra is studied to predict the electron properties as could be observed by Solar Orbiter and Solar Probe Plus. Considering various energy loss mechanisms we show that the substantial part of the initial energetic electron energy is lost via wave–plasma processes due to plasma inhomogeneity. For the parameters adopted, the results show that the electron spectrum changes mostly at the distances before ～?20 R _⊙. Further into the heliosphere, the electron flux spectrum of electrons forms a broken power law relatively similar to what is observed at 1 AU.     

High albedos of low inclination Classical Kuiper belt objects

We present observations of thermal emission from fifteen transneptunian objects (TNOs) made using the Spitzer Space Telescope. Thirteen of the targets are members of the Classical population: six dynamically hot Classicals, five dynamically cold Classicals, and two dynamically cold inner Classical Kuiper belt objects (KBOs). We fit our observations using thermal models to determine the sizes and albedos of our targets finding that the cold Classical KBOs have distinctly higher visual albedos than the hot Classicals and other TNO dynamical classes. The cold Classicals are known to be distinct from other TNOs in terms of their color distribution, size distribution, and binarity fraction. The Classical objects in our sample all have red colors yet they show a diversity of albedos which suggests that there is not a simple relationship between albedo and color. As a consequence of high albedos, the mass estimate of the cold Classical Kuiper belt is reduced from approximately 0.01 M_⊕ to approximately 0.001 M_⊕. Our results also increase significantly the sample of small Classical KBOs with known albedos and sizes from 21 to 32 such objects.     

A study of the relationship between geo-magnetic storms and ionospheric disturbances at mid-latitudes

The problem of the ionospheric disturbances associated with geomagnetic storms is examined with the goal of searching for a relationship between the time-developments of the two phenomena. Faraday rotation measurements of total electron content (N_T) are used to monitor the ionospheric F-region at a mid-latitude site, while a variety of geomagnetic parameters are examined as possible ways of following the geomagnetic variations. The ionospheric and geomagnetic data taken during 28 individual storms from 1967 to 1969 are used to search for a predictive scheme which can be tested using data from 17 storms in 1970. The specific aim is to find the geomagnetic parameter whose time-development can best forecast whether or not the ionospheric response will include an initial positive phase prior to the normally extended period of F-region depletions. Correlations between N_T and the geomagnetic indices K_p, and equatorial Dst(H) prove to be wholly inadequate. The local times of main-phase-onset (MPO) determined from the equatorial Dst(H) indices as well as from local horizontal component data, also prove to be unsatisfactory. The best correlations are obtained using local measurements of the total geomagnetic field (F). These results show that a storm commencement (SC) will produce an enhancement in n_t during the afternoon period following the SC unless there is an intervening post-midnight period with a strong depression of the geomagnetic field. Operationally this is taken to be a depression in F of at least 100γ near 03:00 LT