POLAR-CAP CONVECTION PATTERNS INFERRED FROM EISCAT OBSERVATIONS

From data of the European incoherent scatter radar EISCAT, and mainly from its tristatic capabilities, statistical models of steady convecti on in the auroral ionosphere were achieved for various levels of magne tic activity. We propose here to consistently extend these models to t he polar cap, by avoiding the use of a predefined convection pattern. Basically, we solve the second-order differential equation governing t he polar cap convection potential with the boundary conditions provide d by these models. The results display the classical twin-vortex conve ction pattern, with the cell centres around 17 MLT for the evening cel l and largely shifted towards midnight (3-3.5 MLT) for the morning cel l, both slightly moving equatorward with activity. For moderate magnet ic activities, the convection flow appears approximately oriented alon g the meridian from 10:00 MLT to 22:00 MLT, while in more active situa tions, it enters the polar cap at prenoon times following the antisunw ard direction, and then turns to exit around 21:00 MLT. Finally, from these polar cap patterns combined with the auroral. statistical models , we build analytical models of the auroral and polar convection expec ted in steady magnetic conditions.