Whistler mode wave generation at the edges of a magnetic dip

On 18 May 2011, the Time History of Events and Macroscale Interactions during Substorms satellite observed whistler mode waves associated with a magnetic dip behind a dipolarization front structure in the bursty bulk flow braking region. For the first time, we find that whistler mode waves are generated at the edges of magnetic dip rather than at the center (also known as "minimum-B-pocket"). Detailed wave analysis indicates that the waves are likely lower and upper band whistler mode chorus. We examine electron pitch angle distributions at the edges of dip and compare them with those at the center and far outside the magnetic dip. Results confirm that the positive temperature anisotropy and pancake distributions at the edges of magnetic dip provide free energy source for growth of the whistler mode waves. We also interpret the whole physical process of how whistler mode waves generate in this event.