Whistler mode waves atmagnetotail dipolarization fronts

We report the statistics of whistler mode waves observed in relation to dipolarization fronts (DFs) in Earth's magnetotail using data from the four Cluster spacecraft spanning a period of 9 years, 2001-2009. We show that whistler mode waves are common in a vicinity of DFs: between 30 and 60% of all DFs are associated with whistlers. Whistlers are about 7 times more likely to be observed near a DF than at any random location in the magnetotail. Therefore, whistlers are a characteristic signature of DFs. We find that whistlers are most often detected in the flux pileup region (FPR) following the DF, close to the center of the current sheet (B-x approximate to 0) and in association with anisotropic electron distributions (T>T-vertical bar). This suggests that we typically observe emissions in the source region where they are generated by the anisotropic electrons produced by the betatron process inside the FPR.