TY - JOUR

T1 - Magnetic signatures of the distant polar cusps

T2 - Observations by Polar and quantitative modeling

AU - Tsyganenko, NA

AU - Russell, CT

PY - 1999/11/1

Y1 - 1999/11/1

N2 - Polar cusps are an essential element of the magnetospheric topology. In the outermost regions of the cusp the magnetosheath plasma becomes entrained on magnetospheric field lines and penetrates to low altitudes along held lines on the dayside, causing a significant local depression of B, clearly visible in magnetometer data taken at high latitudes. This study addresses the spatial distribution of the magnetic depression associated with the polar cusp, as derived from a large set of Polar magnetometer data taken in 1996-1998. The depression Delta B was derived as the difference between the total. magnitude of the observed field and the one calculated from the International Geomagnetic Reference Field model of the internal held, combined with an external field model. In the noon sector the cusp depression is clearly visible in plots of Delta B versus solar magnetic latitude as a relatively narrow region of large negative Delta B (down to similar to -80 nT), extending from R similar to 8 - 9 R-E (Polar apogee) to R similar to 5 - 6 R-E. At closer geocentric distances the cusp depression fades out because of a rapid increase of the geomagnetic field toward Earth. The cusp depression also shallows as one moves away from the noon meridian and completely disappears at solar magnetic longitudes +/-40 - 60 degrees. The second part of the paper deals with a mathematical representation of the observed polar cusp depression in quantitative models of the geomagnetic field. A method is suggested on the basis of the field deformation technique, making it possible to incorporate a realistic structure of the polar cusps in global models of the magnetosphere.

AB - Polar cusps are an essential element of the magnetospheric topology. In the outermost regions of the cusp the magnetosheath plasma becomes entrained on magnetospheric field lines and penetrates to low altitudes along held lines on the dayside, causing a significant local depression of B, clearly visible in magnetometer data taken at high latitudes. This study addresses the spatial distribution of the magnetic depression associated with the polar cusp, as derived from a large set of Polar magnetometer data taken in 1996-1998. The depression Delta B was derived as the difference between the total. magnitude of the observed field and the one calculated from the International Geomagnetic Reference Field model of the internal held, combined with an external field model. In the noon sector the cusp depression is clearly visible in plots of Delta B versus solar magnetic latitude as a relatively narrow region of large negative Delta B (down to similar to -80 nT), extending from R similar to 8 - 9 R-E (Polar apogee) to R similar to 5 - 6 R-E. At closer geocentric distances the cusp depression fades out because of a rapid increase of the geomagnetic field toward Earth. The cusp depression also shallows as one moves away from the noon meridian and completely disappears at solar magnetic longitudes +/-40 - 60 degrees. The second part of the paper deals with a mathematical representation of the observed polar cusp depression in quantitative models of the geomagnetic field. A method is suggested on the basis of the field deformation technique, making it possible to incorporate a realistic structure of the polar cusps in global models of the magnetosphere.

KW - DIPOLE TILT ANGLE

KW - BOUNDARY-LAYER

KW - FIELD

KW - CLEFT

KW - PRECIPITATION

KW - MAGNETOSPHERE

KW - MAGNETOMETER

KW - WIND

U2 - 10.1029/1999JA900279

DO - 10.1029/1999JA900279

M3 - Article

VL - 104

SP - 24939

EP - 24955

JO - Journal of Geophysical Research: Biogeosciences

JF - Journal of Geophysical Research: Biogeosciences

SN - 0148-0227

IS - A11

ER -