Sudden solar wind dynamic pressure enhancements and dayside detached auroras: IMAGE and DMSP observations

<p>Dayside detached auroras (DDA) refer to auroras observed separate from the equatorward edge of the main oval on the dayside. They are studied here using IMAGE FUV and DMSP particle data. Occurrence of these DDA appears to be correlated with sudden solar wind dynamic pressure enhancements and northward interplanetary magnetic field, as monitored by the Wind satellite. They are usually very dynamic and short-lived with a lifetime of the order of 10 minutes. Out of the three FUV instrument channels on IMAGE, DDA are best detected by the IMAGE FUV SI-12 instrument, which measures intensities of the Doppler red-shifted Hydrogen Lyman Alpha line. This indicates that energetic proton precipitation is the major component. Simultaneous DMSP particle observations confirm that energetic protons (\&gt;10 keV) in the dayside inner magnetosphere are the primary source of those DDA detected by the SI-12 instrument. DMSP also detected significant electron fluxes associated with the DDA, but the electron precipitations have little or no contribution to the DDA intensities detected by the SI-12 instrument. Precipitations of energetic protons (electrons) which caused DDA could be explained by enhanced cyclotron instability which arose from adiabatic compression following sudden solar wind dynamic pressure enhancements.</p>