Lukianova, R.1, Kozlovsky, A.2 and Turunen, T.3
1 Arctic and Antarctic Research Institute, St. Petersburg, Russia
2 Sodankylš Geophysical Observatory, Oulu unit, Oulu, Finland
3 Sodankylš Geophysical Observatory, Sodankylš, Finland
We use the ionospheric velocity measurements obtained by the European incoherent scatter (EISCAT) Svalbard radar (ESR) for comparison with the electric field distribution predicted by new ionospheric convection model based on realistic maps of field-aligned currents [Lukianova and Christiansen, 2006].
The velocity vector at high latitudes (>75 deg. MLAT) can be obtained only in the cases when the antenna is pointed northward and swings between two directions. Altogether, 110 hours of such observation during 2000-2002 have been selected from the MADRIGAL database. In 2004, two campaigns have been performed to observe the azimuthal plasma flow. During these campaigns the ESR steerable antenna was directed to the east or west along the corrected geomagnetic latitude at an elevation angle of 45. The measurements were made in the dayside during 60 hours, altogether. These data which include only the east-west flow component are also used in the present study.
Thus, the comparative analysis of modelí output and observations is based on the data contained both the north-south and east-west components of the ionospheric electric field. First, a comparison provides an independent check of the model. It is shown that the model represents accurately the large-scale features of statistical electric field inferred from the ion velocity measured by the ESR. Also, from observations and modeling we quantitatively determine the dependence of the ionospheric electric field strength on the IMF conditions and how this varies with MLT. Such dependence are clearly seen by contrasting the results for two magnitudes of the IMF strength (BT=1 and 5 nT), for two opposite directions of the IMF BZ, and for BY+, BY-. For specification of the dependence we derive average convection patterns for sorting by the magnitude and direction of the IMF. The magnitude of the IMF has the main impact on the average flows under BZ- conditions. We calculated coefficients characterizing a linear increase of the electric field strength with BT and obtained a good consistency between simulation and observations with regard of this parameter. The sign of IMF BY is the most important factor influenced the convection system under BZ+ conditions. For BY- the northward component of the electric field is negative during ¾ part of the day indicating clockwise plasma flow around the pole. For BY+, the electric field is directed poleward and the plasma rotate anticlockwise. These are confirmed nicely by the ESR observations.
This work was supported by the Academy of Finland (project 214621), RFBR grant 06-05-64311 and INTAS grant 06-1000013-8823.