K. Aarsnes

Storm time equatorial belt – an “image” of RC behavior

[1] During geomagnetic storms a well defined belt of trapped protons and ENAs (energetic neutral atoms) is observed around geomagnetic equator at low L-values. Their source is RC (ring current) protons existing at larger L-values. Through charge exchange with the geocorona RC protons become ENAs and if subjected to a new charge exchange become trapped protons. From low latitude particle observations at four different local times we follow; the RC injection region, the drift of RC-particles through the evening/afternoon into the morning sector, the RC-asymmetry and convection loss to the dayside during the storm initial and main phase, and its development into a symmetric RC in the recovery phase of the storm. INDEX TERMS: 2778 Magnetospheric Physics: Ring current; 2720 Magnetospheric Physics: Energetic particles, trapped; 2730 Magnetospheric Physics:Magnetosphere— inner; 2788 Magnetospheric Physics: Storms and substorms. Citation: Soraas, F., K. Oksavik, K. Aarsnes, D. S. Evans, and M. S. Greer, Storm time equatorial belt – an ‘‘image’’ of RC behavior, Geophys. Res. Lett., 30(2), 1052, doi:10.1029/ 2002GL015636, 2003.

Enhanced Pitch Angle Scattering of Protons at Mid-Latitudes During Geomagnetic Storms

Abstract During geomagnetic storms highly localised regions of enhanced proton (ion) precipitation in the tens to several hundred keV energy range can appear at mid-latitudes. The particle pitch angle distribution in these enhanced regions is anisotropic with maximum intensity perpendicular to the magnetic field. In a few cases, however, the distribution can approach isotropy. These regions typically have widths of a few degrees invariant latitude, but can be as narrow as 0.25°. The intensity peak is most often concentrated in a specific particle energy range, although in many cases the intensity peak at a given location is distributed over a broader energy range. During the main phase of the storms the ion enhancement is mostly observed in the highest energy protons and only in the midnight/evening MLT sector. Coincident with the ion enhancement there was often an enhancement in electrons with energies > 300 keV. In the recovery phase of the storms the ion enhancement can be observed at all local times covered by our observations and there was not any coincident enhancement in the high energy electrons. Overall the observations seem to support a picture where scattering of protons into the loss cone by cyclotron resonant wave-particle interaction occurs, while high energy electrons are parasitically scattered into the loss cone by the same ion cyclotron waves. Throughout the storm the L-dependence of the enhancements in proton fluxes is similar to the K p dependence of the location of the plasmapause. Whenever a direct comparison could be made, the SAR arc and the ion enhancement overlap. Thus the ion enhancement and SAR arc are associated, but not necessarily on a cause-effect basis.

Particle and auroral observations from the ESRO I/AURORAE satellite

Abstract The polar-orbiting satellite ESRO I/AURORAE (1968-084A) was designed to investigate auroral particles, luminosity, and associated ionospheric effects. Three groups of three consecutive passes over the auroral zone at three levels of magnetic activity were chosen for a special study. The passes occurred between midnight and 0100 hr geomagnetic time near the Scandinavian meridian. The latitude profile of the electron density at altitudes 300–400 km shows the ionospheric electron density trough (associated with the plasmapause) just equatorward of the main precipitation zone. The poleward wall of the trough is associated with a maximum in electron temperature. A broad maximum in electron density lies both poleward and equatorward of the high, structured gradients associated with the main precipitated zone. Finally, a depression in electron density approaching the pole is associated with an increase in electron temperature and a disappearance of O+. The effect of increased magnetic activity is to steepen the gradients and to extend the precipitation zone both poleward and equatorward. The latitudinal profile of 4278 A N2+ and 4861 A Hβ emissions can, in all cases, be characterized as a single, broad maximum on the equatorward side inside the trapping boundary and one or more sharp maxima usually on the poleward side of the trapping boundary. The colatitude of both regions and their separation vary directly as the magnetic activity as does the particle flux associated with them. Comparison of the auroral emissions and the electron flux equatorward of the trapping boundary gives a conversion factor of 270 Rayleighs of 4278 N2+ emission per erg net downward flux. Wide variations in the production efficiency for electrons on the poleward factor. The observed intensities referring to observations equatorward of the trapping boundary are then in fair agreement with calculations.

Substorm morphology of > 100 keV protons

Abstract The latitudinal morphology of > 100 keV protons at different local times has been studied as a function of substorm activity. A characteristic pattern is found: during quiet-times there is an isotropic zone centred around 67° near midnight, but located on higher latitudes towards dusk and dawn. This zone moves slightly equatorward during the substorm growth phase. During the expansive phase the precipitation spreads poleward apparently to ~ 71° near midnight. The protons are precipitated over a large local time interval on the nightside, but the most intense fluxes are found in the pre-midnight sector. A further poleward expansion, to more than 75° near midnight, seems to take place late in the substorm. Away from midnight, the expansion reaches even higher latitudes. During the recovery phase the intensity of the expanded region decreases gradually; the poleward boundary is almost stationary if the interplanetary magnetic field (IMF) has a northward component and no further substorm activity takes place. Mainly protons with energy below ~ 500 keV are precipitated in the expanded region. On the dayside no increase in the precipitation rates is found during substorm expansion, but late in the substorm an enhanced precipitation is found, covering several degrees in latitude. The low-latitude anisotropic precipitation zone is remarkably stable during substorms. A schematic model is presented and discussed in relation to earlier results.

VARIATIONS IN THE HIGH-LATITUDE PROTON TRAPPING BOUNDARY ASSOCIATED WITH POLAR MAGNETIC SUBSTORMS.

Abstract Protons in the energy range (100–200) keV in the noon-midnight meridian plane are studied from data obtained by the ESRO IA satellite. From this study, it is observed that: (1) During quiet geomagnetic conditions there is a single zone of precipitating protons located at an invariant latitude of 67° on the nightside and two zones located at invariant latitudes of 70° and 77° on the dayside. (2) Closely correlated with the polar magnetic substorm, the proton trapping boundary moves poleward, the two zones of proton precipitation on the dayside merge into one zone, and the energy input into the atmosphere increases. (3) Preceding the poleward movement of the trapping boundary, there is an intensity increase in the already existing proton precipitation on the nightside.

In‐flight calibration of NOAA POES proton detectors—Derivation of the MEPED correction factors

The MEPED instruments on board the NOAA POES andMetOp satellites have been continuously measuring energetic particles in the magnetosphere since 1978. However, degradation of the proton detectors over time leads to an increase in the energy thresholds of the instrument and imposes great challenges to studies of long-term variability in the near-Earth space environment as well as a general quantification of the proton fluxes. By comparing monthly mean accumulated integral flux from a new and an old satellite at the same magnetic local time (MLT) and time period, we estimate the change in energy thresholds. The first 12 monthly energy spectra of the new satellite are used as a reference, and the derived monthly correction factors over a year for an old satellite show a small spread, indicating a robust calibration procedure. The method enables us to determine for the first time the correction factors also for the highest-energy channels of the proton detector. In addition, we make use of the newest satellite in orbit (MetOp-01) to find correction factors for 2013 for the NOAA 17 and MetOp-02 satellites. Without taking into account the level of degradation, the proton data from one satellite cannot be used quantitatively for more than 2 to 3 years after launch. As the electron detectors are vulnerable to contamination from energetic protons, the corrected proton measurements will be of value for electron flux measurements too. Thus, the correction factors ensure the correctness of both the proton and electron measurements.

Polar 5—an electron accelerator experiment within an aurora. 1. Instrumentation and geophysical conditions

Abstract A “mother-daughter” rocket was launched from Andoya, Norway, February 1 1976 over two auroral structures. The “daughter” payload carried a 10keV electron accelerator and the “mother” carried a series of diagnostic instruments for monitoring optical and wave effects generated through beam-atmospheric interactions and production of secondary electrons. The experimental details are presented in this paper together with a survey of some of the results. This paper is also intended as a reference for a series of accompanying papers.

Observations of ENA in and near a proton arc

A rocket equipped with solid state detectors sensitive to ions/protons and ENA with energies above 20 keV was launched into the poleward leap phase of the auroral substorm. The rocket reached an altitude of 454 km, that is into the region of intense charge exchange for precipitating ions. At low altitudes the pitch angle distribution of the precipitating particles was observed symmetric with respect to the magnetic field line. At higher altitudes this changed, the particle flux did not exhibit symmetry around the magnetic field as would be expected for a charged particle beam. This asymmetry and the fact that it only occurs at high altitudes is interpreted to indicate the detection of ENA, most likely hydrogen in our case. The ENA arrive from a specific azimuthal direction. The observations are consistent with calculations of the atmospheric spreading of the precipitating protons due to charge exchange. The importance of charge transfer collisions in the ion-outflow problem is considered.

Electron density and electron flux in a glow aurora

Abstract Electron densities and electron intensities were measured from a Nike-Apache rocket, Ferdinand 14, launched into a glow aurora at Andoya in Northern Norway on 3 March 1967. The measurements give effective recombination coefficientsαeff for the altitude range 90–120 km that are consistent with current models of the lower E-region and rate coefficients measured in the laboratory. The mean value of αeff is (3 ± 1.5) × 10−7 cm3 sec−1. The proportion of the incoming electron energy converted into light is found to be 6 × 10−3 ± 2 × 10−3 at OI (5577 A) and 1.1 × 10−3 ± 0.4 × 10−3 at N2+(4278 A).

Ring Current Behavior as Revealed by Energetic Proton Precipitation

The precipitation of energetic ions and electrons into the upper atmosphere is a direct manifestation of their acceleration and pitch angle scattering in the magnetosphere. Electric fields inject/convect the particles from the tail plasma sheet towards the earth, and when closer to the Earth they spread in local time due to magnetic field forces. The electrons drift towards the morning sector and the ions towards the evening sector thus creating the ring current. Certain aspects of the ring current behavior can be revealed by the precipitating energetic protons. From these particles a proxy for the energy injection rate into the ring current can be estimated, and a ring current index which correlates highly with the pressure corrected D st * can be calculated. The pitch angle distribution of the precipitating ring current protons is either isotropic with a filled loss cone, or anisotropic with an almost empty loss cone. In the isotropic zone the ring current protons are stable to wave growth. In the anisotropic zone, however, the protons are unstable to wave growth. Thus, there exists a fairly wide L-value interval equatorward of the isotropic zone with ample conditions for EMIC (electromagnetic ion-cyclotron) wave generation. In the anisotropic zone a number of wave-particle phenomena linked to the precipitating protons take place: enhanced proton pitch angle scattering manifested as intensity peaks at mid-latitudes, SAR arc formation, Pcl and IPDP wave generation, and increased loss of relativistic electrons. An important decay process for the ring current protons is through charge exchange. The ENAs (Energetic Neutral Atoms) from this process create a well defined belt or region of ENA and protons observed at low altitudes along the geomagnetic equator. This belt reveals important aspects of the ring current such as: the ring current injection region, the drift of ring current particles, and convection losses of the ring current particles to the dayside magnetopause, and its asymmetric and symmetric behavior.