TY - JOUR

T1 - Proton isotropy boundaries as measured on mid- and low-altitude satellites

AU - Ganushkina, Nataly Yu

AU - Pulkkinen, T. I.

AU - Kubyshkina, M. V.

AU - Sergeev, V. A.

AU - Lvova, E. A.

AU - Yahnina, T. A.

AU - Yahnin, A. G.

AU - Fritz, T.

PY - 2005

Y1 - 2005

N2 - Polar CAMMICE MICS proton pitch angle distributions with energies of 31-80keV were analyzed to determine the locations where anisotropic pitch angle distributions (perpendicular flux dominating) change to isotropic distributions. We compared the positions of these mid-altitude isotropic distribution boundaries (IDB) for different activity conditions with low-altitude isotropic boundaries (IB) observed by NOAA 12. Although the obtained statistical properties of IDBs were quite similar to those of IBs, a small difference in latitudes, most pronounced on the nightside and dayside, was found. We selected several events during which simultaneous observations in the same local time sector were available from Polar at mid-altitudes, and NOAA or DMSP at low-altitudes. Magnetic field mapping using the Tsyganenko T01 model with the observed solar wind input parameters showed that the low- and mid-altitude isotropization boundaries were closely located, which leads us to suggest that the Polar IDB and low-altitude IBs are related. Furthermore, we introduced a procedure to control the difference between the observed and model magnetic field to reduce the large scatter in the mapping. We showed that the isotropic distribution boundary (IDB) lies in the region where Rc/ρ∼6, that is at the boundary of the region where the non-adiabatic pitch angle scattering is strong enough. We therefore conclude that the scattering in the large field line curvature regions in the nightside current sheet is the main mechanism producing isotropization for the main portion of proton population in the tail current sheet. This mechanism controls the observed positions of both IB and IDB boundaries. Thus, this tail region can be probed, in its turn, with observations of these isotropy boundaries.

AB - Polar CAMMICE MICS proton pitch angle distributions with energies of 31-80keV were analyzed to determine the locations where anisotropic pitch angle distributions (perpendicular flux dominating) change to isotropic distributions. We compared the positions of these mid-altitude isotropic distribution boundaries (IDB) for different activity conditions with low-altitude isotropic boundaries (IB) observed by NOAA 12. Although the obtained statistical properties of IDBs were quite similar to those of IBs, a small difference in latitudes, most pronounced on the nightside and dayside, was found. We selected several events during which simultaneous observations in the same local time sector were available from Polar at mid-altitudes, and NOAA or DMSP at low-altitudes. Magnetic field mapping using the Tsyganenko T01 model with the observed solar wind input parameters showed that the low- and mid-altitude isotropization boundaries were closely located, which leads us to suggest that the Polar IDB and low-altitude IBs are related. Furthermore, we introduced a procedure to control the difference between the observed and model magnetic field to reduce the large scatter in the mapping. We showed that the isotropic distribution boundary (IDB) lies in the region where Rc/ρ∼6, that is at the boundary of the region where the non-adiabatic pitch angle scattering is strong enough. We therefore conclude that the scattering in the large field line curvature regions in the nightside current sheet is the main mechanism producing isotropization for the main portion of proton population in the tail current sheet. This mechanism controls the observed positions of both IB and IDB boundaries. Thus, this tail region can be probed, in its turn, with observations of these isotropy boundaries.

KW - Magnetospheric physics (Energetic particles, precipitating; magnetospheric configuration and dynamics; magnetotail)

UR - http://www.scopus.com/inward/record.url?scp=24044439493&partnerID=8YFLogxK

U2 - 10.5194/angeo-23-1839-2005

DO - 10.5194/angeo-23-1839-2005

M3 - Article

AN - SCOPUS:24044439493

VL - 23

SP - 1839

EP - 1847

JO - Annales Geophysicae

JF - Annales Geophysicae

SN - 0992-7689

IS - 5

ER -