The structure and formation mechanism of a supercell-like storm in a moist environment below a melting layer were investigated using dual-Doppler radar analysis and a cloud-resolving storm simulator (CReSS). The supercell-like storm developed over the Kanto Plain, Japan, on 24 May 2000. The environment of the supercell-like storm possessed large convective available potential energy (1000 J kg Ϫ1 ), strong vertical wind shear (4.2 ϫ 10 Ϫ3 s Ϫ1 between the surface and 5 km above sea level), and a moist layer (the relative humidity was 60%-90% below a melting layer at 3 km in height). The dual-Doppler radar analysis with a variational method revealed that the supercell-like storm had similar structures to those of a typical supercell in a dry environment below a melting layer, such as that in the Great Plains in the United States. The structures included a hook echo, an overhanging echo structure, and a strong updraft with strong vertical vorticity. However, some of the characteristics of the supercell-like storm differed from those of a typical supercell. For example, a weak downdraft, a weak outflow, a weak inflow, and a short time maintenance of a single cyclonically rotating updraft (about 30 min) were noted. Dual-Doppler radar analysis revealed that the convergence between the weak outflow and the weak inflow kept its location just under the updraft for about 30 min; in other words, the strength of the outflow balanced the strength of the inflow. The observed features were simulated well using CReSS, and the thermodynamical features of the formation mechanism were revealed. The weak downdraft with a small evaporative cooling rate was simulated in a moist layer below the melting layer at 3 km in height. The small evaporation cooling was a major cause of the weak downdraft and the weak outflow. Because the outflow was weak and did not cut off the initial updraft, the weak inflow was able to keep supplying warm air to the initial updraft for about 30 min. Therefore, the present supercell-like storm could form as a result of the balance of the strengths of the weak inflow and the weak outflow in a moist environment.
In order to investigate microphysical processes in the stratiform precipitations including melting layers, size distributions of the precipitation particles were measured by "filterpapers method" at three observational stations with different altitude on Mt. Fuji.The following conclusions on the microphysical processes in the stratiform precipitations were obtained inspecting the time variations of the size distribution at each station i) In the upper part of the melting layer, small sized snowflakes (melted diameter <0.1cm)were predominant in volume and number. ii) In the middle part of the melting layer, melting and growth due to coalescence of the melting snowflakes seem to have occurred simultaneously, and the large sized particles (>0.2cm) were found frequently. iii) In the lower part and just below the melting layer, precipitation particles had finished melting. The large sized particles decreased in volume and number perhaps due to breakup and therefore the medium sized particles (0.1*0.2cm) were predominant. iv) The vertical change of the size distribution of raindrops was insignificant far below the melting layer.
Real-time monitoring of quantitative precipitation distribution is essential to prevent natural disasters caused by heavy rainfall. Precipitation distribution by rain gauge network or combined with radar/satellite data is operationally used in Viet Nam. Previously, meteorological radar data was simply converted to precipitation amount by using simple Z-R relationship. In order to get the accurate quantitative precipitation estimation (QPE) data, converted precipitation amount from radar should be corrected by rain gauge data. In the ongoing JICA technical cooperation project, preliminary development of the QPE product has been conducted by utilizing the data from the automatic rain gauge network and meteorological radar network in Viet Nam. The fundamental part of this QPE algorithm has been used and updated in Japan Meteorological Agency (JMA) for more than 25 years. This is the first attempt to get quantitative precipitation distribution with precise resolution by combining radar and rain gauge data in Viet Nam. This paper describes each process to introduce this QPE method to Viet Nam and indicates some preliminary results. Several issues to improve its accuracy is also proposed.
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