Journal of Atmospheric and Solar-Terrestrial Physics 69 (2007) 1851–1863 Energy balance during intense and super-intense magnetic storms using an Akasofu e parameter corrected by the solar wind dynamic pressure A. de Lucas a,b, , W.D. Gonzalez a , E. Echer a , F.L. Guarnieri c , A. Dal Lago a , M.R. da Silva a , L.E.A. Vieira b , N.J. Schuch d a Instituto Nacional de Pesquisas Espaciais, Sa˜o Jose´dos Campos, Sa˜o Paulo, Brazil b Max-Planck-Institut fu¨ r Sonnensystemforschung, Katlenburg-Lindau, Germany c Universidade do Vale do Paraı´ba, Sa˜o Jose dos Campos, Sa˜o Paulo, Brazil d Centro Regional Sul de Pesquisas Espaciais, Santa Maria, Rio Grande do Sul, Brazil Received 9 September 2006; received in revised form 31 July 2007; accepted 2 September 2007 Available online 7 September 2007 Abstract Geomagnetic storms are large disturbances in the Earth’s magnetosphere caused by enhanced solar wind–magneto- sphere energy transfer. One of the main manifestations of a geomagnetic storm is the ring current enhancement. It is responsible for the decrease in the geomagnetic field observed at ground stations. In this work, we study the ring current dynamics during two different levels of magnetic storms. Thirty-three events are selected during the period 1981–2004. Eighteen out of 33 events are very intense (or super-intense) magnetic storms (Dst p250 nT) and the remaining are intense magnetic storms (250oDst p100 nT). Interplanetary data from spacecraft in the solar wind near Earth’s orbit (ACE, IMP-8, ISEE-3) and geomagnetic indices (Dst and Sym-H) are analyzed. Our aim is to evaluate the interplanetary characteristics (interplanetary dawn–dusk electric field, interplanetary magnetic field component B S ), the e parameter, and the total energy input into the magnetosphere (We) for these two classes of magnetic storms. Two corrections on the e energy coupling function are made: the first one is an already known correction in the magnetopause radius to take into account the variation in the solar wind pressure. The second correction on the Akasofu parameter, first proposed in this work, accounts for the reconnection efficiency as a function of the solar wind ram pressure. Geomagnetic data/indices are also employed to study the ring current dynamics and to search for the differences in the storm evolution during these events. Our corrected e parameter is shown to be more adequate to explain storm energy balance because the energy input and the energy dissipated in the ring current are in better agreement with modern estimates as compared with previous works. For super-intense storms, the correction of the Akasofu e is on average a scaling factor of 3.7, whilst for intense events, this scaling factor is on average 3.4. The injected energy during the main phase using corrected e can be considered a criterion to separate intense from very intense storms. Other possibilities of cutoff values based on the energy input are also ARTICLE IN PRESS www.elsevier.com/locate/jastp 1364-6826/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jastp.2007.09.001 Corresponding author. Instituto Nacional de Pesquisas Espaciais, Sa˜o Jose´ dos Campos, SP, Brazil. Tel.: +551239456838; fax: +55 1239456810. E-mail address: delucas@dge.inpe.br (A. de Lucas).