and a possible cause.pdfVIP

Annales Geophysicae, 23, 1917–1930, 2005 SRef-ID: 1432-0576/ag/2005-23-1917 ? European Geosciences Union 2005 Annales Geophysicae Transpolar aurora: time evolution, associated convection patterns, and a possible cause L. G. Blomberg 1 , J. A. Cumnock 1,2 , I. I. Alexeev 3 , E. S. Belenkaya 3 , S. Yu. Bobrovnikov 3 , and V. V. Kalegaev 3 1 Alfve?n Laboratory, Royal Institute of Technology, Stockholm, Sweden 2 Center for Space Sciences, University of Texas at Dallas, USA 3 Skobeltsyn Institute of Nuclear Physics, Moscow State University, Russia Received: 22 April 2004 – Revised: 11 May 2005 – Accepted: 17 May 2005 – Published: 28 July 2005 Abstract. We present two event studies illustrating the de- tailed relationships between plasma convection, field-aligned currents, and polar auroral emissions, as well as illustrat- ing the influence of the Interplanetary Magnetic Field’s y- component on theta aurora development. The transpolar arc of the theta aurorae moves across the entire polar region and becomes part of the opposite side of the auroral oval. Elec- tric and magnetic field and precipitating particle data are pro- vided by DMSP, while the POLAR UVI instrument provides measurements of auroral emissions. Ionospheric electrostatic potential patterns are calculated at different times during the evolution of the theta aurora using the KTH model. These model patterns are compared to the convection predicted by mapping the magnetopause electric field to the ionosphere using the Paraboloid Model of the magnetosphere. The model predicts that parallel electric fields are set up along the magnetic field lines projecting to the transpolar aurora. Their possible role in the acceleration of the auroral electrons is discussed. Keywords. Ionosphere (Plasma convection; Polar iono- sphere) – Magnetospheric physics (Magnetosphere- ionosphere interactions) 1 Introduction The global distribution of the aurora has a qualitative as well as a quantitative dependence on the interplanetar