  A GOES M1.9 flare took place in active region AR 11153 on February 9,2011.
With the resolution of 200 kHz and a time cadence of 80 ms, the
reverse-drifting (RS) type III bursts, intermittent sequence of type U bursts,
drifting pulsation structure (DPS), and fine structures were observed by the
Yunnan Observatories Solar Radio Spectrometer(YNSRS). Combined information
revealed by the multi-wavelength data indicated that after the DPS which
observed by YNSRS, the generation rate of type U bursts suddenly increased 5
times than before. In this event, the generation rate of type U bursts may
depend on the magnetic reconnection rate. Our observations are consistent with
previous numerical simulations results. After the first plasmoid produced
(plasma instability occurred), the magnetic reconnection rate increased
suddenly 5-8 times than before. Furthermore, after the DPS, the frequency range
of turnover frequency of type U bursts is obviously broadened 3 times than
before, which indicates the fluctuation amplitude of the density in the
loop-top. Our observations also support the numerical simulations during the
flare impulsive phase. The turbulence occurs at the top of the flare loop, the
plasmoids can trap the non-thermal particles and cause the density fluctuation
at the loop-top. The observations are generally consistent with the results of
numerical simulations, helping us to better understand the characteristics of
the whole physical process of eruption.
