A study on the multiscale characteristics of the rainstorm occurred in north of Guangzhou on 23 May 2014

By using the NCEP FNL 6 h interval reanalysis data with 1°×1° resolution, the windprofiler data and other general observation data, the characteristics of circulation environment, the synoptic and mesoscale systems of the rainstorm occurred in Guangzhou on May 23, 2014 are studied. The results are as follows. (1) This storm is caused by the interaction of multiscale systems occurred in the "two troughs and one ridge" circulation environment. South China was continuously affected by shortwave trough. The low-level jet from Bay of Bengal and the South China Sea provides adequate moisture conditions, the divergent circulation at high-level over the South Asia makes the pumping action more evident. (2) Before the heavy precipitation happens, the strong wind field and the momentum continuously go downstream, making the low-level positive vorticity increase, and water vapor condition is favorable. The pulsation of low-level jet index is closely related to the occurrence of heavy precipitation. The low-level jet index increases rapidly 1-2 hours before the heavy precipitation, and then decreased rapidly after heavy precipitation. (3) The increase of low-level vertical wind shear has a good time correspondence with the strong wind going downstream, indicating that the vertical shear of the wind field is enhanced due to the decrease of the height of the strong wind. The corresponding changes of low-level jet, low-level jet index and vertical wind shear before the occurrence of heavy precipitation have a certain significance for the prediction of short-term heavy precipitation.