What is magnetically quiet time?

Abstract:

We present the new SuperMAG Disturbance Level indices SMDL_hi (> 55 deg MLat) and SMDL_lo (<55 deg MLat). These indices objectively quantify the external magnetic field perturbations with a 1 min temporal resolution appropriate for the magnetosphere-ionosphere (M-I) system (reconfiguration time ~10 min). The indices are derived from all the ground based magnetometer stations that are part of the SuperMAG collaboration and thus they have the sufficient spatial coverage. Historically the selection of the quietest days (Q-days) and most disturbed days (D-days) of each month is deduced from the Kp indices. Other techniques include the use of magnetic indices and solar wind conditions. Common for these techniques is the long list of assumptions on which they are based. For example: duration of quiet period (e.g. 1 hour or 24 hours), start of quiet periods (e.g. 0 UT), inferred response of the magnetosphere-ionosphere system to solar wind conditions, and the ability of the magnetic indices to quantify the external field contributions (e.g. using only north-south component). We show that previous published techniques include periods of intense substorms and magnetic storms while SMDL effectively excludes these disturbances. The SMDL indices provides more temporal coverage through better quantification of the external field component. We show events, statistics, and we show that the SMDL index provides a powerful tool to quantify the external field contribution.