Shandong Province Hail Cloud Doppler Weather Radar Observations And Three-dimensional Structure Analysis

Two severe hailstorms, which occurred in Shandong in 2002 and 2003, were analyzed in this paper. The synoptic method was used with the surface observing data, Rawinsonde observation data and the grid-point data from NCEP. The meteorological satellite images were used to analyze the synoptic situation, energy field , water vapor content field , divergence field and upper wind field before hailfall . The analyzing method using Doppler weather radar observing data was used to analyze the reflectivity change from the development to dissipating process of hailfall, and to study the evolvement, macroscopical characters of the cloud system and the forming mechanism of the hailfall processing, with the observing data from the Doppler weather radar in Jinan and Binzhou, Shandong province.The outcome of synoptic situation analysis showed that Mongolia cold vortex or tough was the main large scale system effecting two hailstorms occurred in Shandong. The upper cold air came down due to the southward moving of large scale synoptic system and a deep southwest airflow was transported into hail-forming area. As a result, large-scale unstable layer in lower troposphere came into being. The coupling of the meso-scale low pressure and divergence zone of upper jet caused strong upward motion. Definite energy sustainability was needed for the development of hailstorm. In the dissipating process of the hailstorm , there was a high energy tongue at the low level under the west of the hailfall area and a center of low energy at the mid-and upper-lever while a center of negative energy advection over its west. There were upper jet near the west of hailfall area and the strongest wind shear in upper air which was propitious to the developing of the hailstorm. The water vaper transportation lied between 850 hPa to 925 hPa in low level.Doppler Radar data analysis result showed that the reflectivity of supercell hailstorm was elliptical shaped in horizontal, and hook shaped in the middle and low levels, the weak echo area was also the area with the main updraft, strong echo located in the top left of the hook shaped echo region. On the cross section along the direction of airflow and cross the center of strong echo area, there were significant vault and overhang echo, which was the position of main updraft. The echo feature of supercell hailstorm was that it had a strong echo wall—BWER(vault)—overhang echo structure. The stream fields inside supercell hailstorm had a circular structure, a large area of lean updraft with cyclonic convergence existed in the cloud base of hailstorm, and corresponding divergence existed in cloud top. The updraft reached its peak at the middle of troposphere, and decrease with height from that point. At high levels wind flowed out along the direction of storm moving. Upper cloud pulled out enormous anvil cloud with aloft. In the mature stage, storm was dominated by updraft, during the development of storm there was heavy down draft behind the main updraft, the strong down draft divergent at cloud base which caused severe wind at ground. Usually, the strong wind at ground occurred before hailfall.On the basis of the analyzing results above and the research the others had made before, a conceptual mode of supercell hailstorm was improved. For supercell hailstorm, there were overfull high supercooled water above the head water area, the gelation of high supercooled water was always the main source of hail embryo. The original hail embryos ascended to a certain height along with the leading updraft, and formed the source area of hail embryo over it, then they were thrown away along bothsides with the upper divergent airflows. Smaller the particles, further the distance of they were thrown. Meanwhile, the particles increasing by the coagulation of high supercooled water in the circular stream field, when descending to the lower air, they entered the rising airflow again. Some of these particles, which entered the strong rising airflow, were thrown away from the rising flows and came into falling ones;while the other effused from the right side with upper divergent airflows, and then came into rising flows again after their falling. The particle in strong upward current, some going on the cycle and some were thrown to the downward current. If the particles were thrown close to the upward current, it was very easy to collect by the strong upward air stream. With the growing up of the particle, there would be an accumulation zone of moderate hail right to the upward stream at about 6km, and this might results in the strong echo in the upward stream. The large water content was in the same place ( right to the upward stream RTRS),and that was the reason for the hail's growing up right in that place. After the particle grew up to big hail, they would transport to surface by down stream, and there was a strong radar echo center on the down stream, this might form large hailstone. Some small particles came into upstream and grew up again. So the hail embryo grew up on the recycle air stream.