Solar Cycle Variations in the Response of the Magnetosphere to the Solar Wind

Understanding how mass, momentum and energy are coupled between the solar wind and magnetosphere is crucial in studies of magnetospheric physics. For many years, substorms were thought to be the only mechanism responsible for reconnecting and returning the open field lines. However, we have now observed several additional modes of energy release and flux return. These include pseudo breakups, steady magnetospheric convection (SMC), poleward boundary intensifications, and sawtooth injection events. It has been suggested that the properties of these different forms of geomagnetic activity may be modulated by the solar cycle. Currently there are only a few large statistical studies that have investigated this issue. Most of these either use local geomagnetic indices or space observations for substorm identification which restricts the scope of studies. In our work we apply a procedure utilizing the global AL index and Pi 2 pulsations from multiple stations to construct a substorm list from solar cycle # 20 to cycle 24 (1969 to 2012). Our preliminary list of substorms for cycle 21~23 is complete and has more than 40,000 AL onset events. A more refined substorm list based on Pi 2 timing of the AL onsets is under development. The preliminary AL onset list enables us to examine several important phenomena such as the occurrence frequency of intense substorms, duration of substorm phases, changes in tail lobe field strength during substorms, and solar wind condition during different phases of the solar cycle. These characteristics of substorm will be compared with those of SMC and sawtooth events in different phases of the solar cycle. Several recent satellites (Cluster, Geotail and Themis) observations will be used to examine the magnetospheric condition during different modes of magnetosheric response.