Vertical Helicity Analysis of First Rainstorm at the Beginning of Meiyu in Hubei in 2009

By using the data in Hubei automatic rainfall station and NCEP 1°×1° global reanalysis data,the vertical helicity analysis on the rainstorm weather process which happened in Hubei Province during June 28-30 in 2009 was done.The results showed that the spatial and temporal evolution characteristic of vertical helicity could reflect well the occurrence time and the falling zone of strong precipitation in the situation that the strong vertical ascent movement in the whole layer stably maintained.The distribution of 700 hPa vertical helicity gradient big value area which was 6 h interval and the ∑θse(500+700+850) horizontal energy frontal zone superposition area both had the good directive significance for the falling zone of 6 h heavy precipitation.The zone where the heavy precipitation appeared had the configuration of positive vertical helicity in the low layer and the negative vertical helicity in the high layer.When the positive vertical helicity in the low layer was slightly higher than the negative vertical helicity in the high layer,it favored the generation of heavy rainstorm center.

On the physical significance and use of a set of horizontal and vertical helicity budget equations

For better understanding the variation of helicity and its governing mechanisms,based on the primary momentum equation under the local Cartesian coordinate,a set of horizontal and vertical helicity equations are derived in this study.On this basis,a storm-relative helicity budget equation is derived,the main factors that govern the variation of helicity are discussed,and the key mechanisms underlying the helicity variation are illustrated by using schematic images.Both scale analysis and real case diagnosis are used to compare the relative importance of di erent factors on the variation of helicity.For a meso-α system,it is found that:(i)horizontal helicity is much larger than vertical helicity,and they show signi cantly di erent variation mechanisms;(ii)for the vertical helicity,the vertical perturbation pressure gradient force,buoyancy,the diver-gence-related e ect,and the conversion between vertical and horizontal helicity govern its variation(whereas,the conversion is negligible for the evolution of horizontal helicity);and(iii)baroclinity is crucial for the variation of horizontal helicity,but it is only of secondary importance for the vertical helicity variation.

Analysis on the TBB Bright Temperature and Vertical Helicity in a Heavy Rain at Anqiu in 2010

In order to get insight into the mechanism of summer rainstorm occurred in central Shandong Province and further improve the prediction accuracy,the FY-2E satellite TBB data and 6 h of NCEP/NCAR 1°×1° reanalysis data were used to carry out the weather dynamics diagnosis and TBB cloud image analysis of a heavy rain happened in Anqiu City on July 18,2010.The results showed that the Anqiu torrential rain was caused by common effects of the subtropical high and upper trough and ground cyclone system;TBB strong low clouds moved with cloud band along the low level jet direction,and closely associated with water vapor and energy belt,while the heavy rain occurred in the north of TBB light in low temperature zone,making the unstable energy release above the Anqiu area;the changes of the vertical spiral degrees at center could well guide the movement of the ground cyclonic center.

Study of Helicity in Typhoon Rainfall Regions——A Case Study of Typhoon "Muifa"

Using the center of figure method and center of mass method, precipitation and heavy precipitation processes caused by No. 9 typhoon ＂ Muifa＂ in 2011 were analyzed based on helicity, and the mechanism of typhoon rainfall was interpreted from the relation between helicity and ener- gy. The results showed that horizontal helicity checked the diffusion of nonlinear energy and maintained the development of the system. Precipitati- on mainly appeared on the southeast of vertical helicity, while heavy precipitation mainly occurred on its southwest. Compared with the center of fig- ure method, the center of mass method had good results, especially for heavy precipitation. Vertical helicity at 700 hPa reflected system deviation in rainfall regions well and had the best correction effect on rainfall intensity and regions