K-derived planetary geomagnetic indices provide characterization of the overall energy status of the magnetosphere. They are in particular used in modeling the response of the magnetosphere/thermosphere/ionosphere system to the solar wind/magnetosphere coupling.

K-indices are proxies of the energy related to the geomagnetic activity. They are directly related to the range during 3-hour intervals of the irregular variations in the horizontal components of the magnetic field. There are accordingly 8 K-derived planetary indices per day, corresponding to UT intervals 00-03, 03-06 up to 21-24.

The 3-hour resolution is a strong limitation for precise modeling of the magnetosphere/thermosphere/ionosphere system. We therefore introduce new indices based on another proxy of the magnetic energy, namely the root mean square (rms) of the irregular variations in the magnetic horizontal components. Using such proxy does not put constraints on the length of the time interval over which the indices are derived.

At each observatory, the irregular variations are processed using the FMI algorithm. From the computed K indices, rms indices are calculated. Planetary magnetic indices are then derived following algorithms similar to those applied for am and aa planetary geomagnetic indices. rms-derived planetary geomagnetic indices based on different time intervals are presented, and their statistical relation with K-derived planetary indices is discussed. Such indices are computed over time intervals significantly shorter than 3 hours (typically few tens of minutes). They should provide a better description of the magnetic activity contribution to the Earth' thermosphere behavior.