  Zebra pattern structure (ZP) is the most intriguing fine structure on the
dynamic spectrograph of solar microwave burst. On 15 February 2011, there
erupts an X2.2 flare event on the solar disk, it is the first X-class flare
since the solar Schwabe cycle 24. It is interesting that there are several
microwave ZPs observed by the Chinese Solar Broadband Radiospectrometer
(SBRS/Huairou) at frequency of 6.40 ~ 7.00 GHz (ZP1), 2.60 ~ 2.75 GHz (ZP2),
and the Yunnan Solar Broadband Radio Spectrometer (SBRS/Yunnan) at frequency of
1.04 ~ 1.13 GHz (ZP3). The most important phenomena is the unusual
high-frequency ZP structure (ZP1, up to 7.00 GHz) occurred in the early rising
phase of the flare, and there are two ZP structure (ZP2, ZP3) with relative low
frequencies occurred in the decay phase of the flare. By scrutinizing the
current prevalent theoretical models of ZP structure generations, and comparing
their estimated magnetic field strengths in the corresponding source regions,
we suggest that the double plasma resonance model should be the most possible
one for explaining the formation of microwave ZPs, which may derive the
magnetic field strengths as about 230 - 345 G, 126 - 147 G, and 23 - 26 G in
the source regions of ZP1, ZP2, and ZP3, respectively.

Solar and Stellar Astrophysics