Comment on 'Wavelet-based ULF wave diagnosis of substorm expansion phase onset' by K. Murphy et al.

摘要

On the basis of a wavelet analysis of ULF Pit/2 onset time for five substorm events, Murphy et al. [2009] concluded that the ULF onset is observed several minutes prior to the auroral substorm onset when the magnetometer is located near the ground foot point of the auroral substorm onset. While the newly developed technique Automated Wavelet Estimation of Substorm Onset and Magnetic Events (AWESOME) demonstrates a potentially powerful tool for timing and locating substorm onset using magnetic field measurements from a dense array of ground magnetometer in the polar region, the conclusion of the study is, in our opinion, premature. Our concern is not about the wave analysis technique but about the auroral substorm onsets, which were determined with the global auroral images acquired' from the FUV instrument on board the IMAGE spacecraft (see Mende et al. [2000] for the instrument design).