Energy balance during intense and super-intense magnetic storms using an Akasofu ε parameter corrected by the solar wind dynamic pressure |
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| Institution: | 1. Instituto Nacional de Pesquisas Espaciais, São José dos Campos, São Paulo, Brazil;2. Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany;3. Universidade do Vale do Paraíba, São Jose dos Campos, São Paulo, Brazil;4. Centro Regional Sul de Pesquisas Espaciais, Santa Maria, Rio Grande do Sul, Brazil;1. Department of Geosciences, Tel Aviv University, Tel Aviv, Israel;2. Department of Meteorology and Atmospheric Science, Pennsylvania State University, University Park, PA, USA;3. German Remote Sensing Data Center – German Aerospace Center (DLR), Oberpfaffenhofen, Germany;4. Institute of Physics, University of Augsburg, Germany;5. National Institute of Geophysics and Volcanology (I.N.G.V.), Osservatorio Etneo, Section of Catania, Catania, Italy;1. Federal Institute for Geosciences and Natural Resources (BGR), 30655 Hannover, Germany;2. Augsburg University (UNA), 86135 Augsburg, Germany;3. German Aerospace Center (DLR), 82 234 Oberpfaffenhofen, Germany;1. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States;2. Center for Space and Aeronomy Research, UAH, Huntsville, AL, United States;3. NASA Langley Research Center, Hampton, VA, United States;4. Sciences Systems and Applications, Inc., Hampton, VA, United States;5. Johns Hopkins University Applied Physics Laboratory, Laurel, MD, United States;1. National Atmospheric Research Laboratory, Gadanki 517112, India;2. Government College (Autonomous), Rajahmundry 533105, India;3. Department of Physics, Andhra University, Visakhapatnam 530003, India |
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| Abstract: | Geomagnetic storms are large disturbances in the Earth's magnetosphere caused by enhanced solar wind–magnetosphere 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 ??250 nT) and the remaining are intense magnetic storms (?250<Dst ??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 BS), the ε parameter, and the total energy input into the magnetosphere (Wε) for these two classes of magnetic storms. Two corrections on the ε 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 ε 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 ε 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 ε can be considered a criterion to separate intense from very intense storms. Other possibilities of cutoff values based on the energy input are also investigated. A threshold value for the input energy is much more clear when a new classification on Dst=?165 nT is considered. It was found that the energy input during storms with Dst<?165 nT is double of the energy for storms with Dst>?165 nT. |
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