| About the short-duration heavy precipitation is always a hot spot issue, but its weather forecast is a important and difficult problem. Firstly, We do some research on the characteristics and genesis of the8August2010masssive; By using precipitation, radar and sounding data in the Southeast Gansu from2009-2010, the character of the short-duration precipitation in the Southeast Gansu were analyzed, we also analysis the radar echo and precipitation retrieved if occur short-duration heavy rainfall, It’s Application Of Areal Rainfall Estimation In The Northeastern Edge Of Tibetan Plateau also was researched; the distribution of physical quantities by compare heavy precipitation with no-rainfall have been researched, in addition, calculating the hit rate, false alarm rate and so on, when in different number of stable and unstable state physical quantities; At last, The character of boundary layer and land surface process on severe convection weather were analyzed. The main conclusions were as follows:(1) By using of meteorological and geological data of Zhouqu, analysis the Characteristics and Genesis of Masssive Mudslide in Zhouqu of the8August2010. On the background of Zhouqu special geological features and geographical environment,because of the pre-drought, heavy rainfall occurs suddenly resulted in a large geological disasters. Collapse, landslide, earthquake and human factors, especially the Wenchuan earthquake of the12May2008, a great extent destroyed the Zhouqu geology, and provided a lot of material source for debris flows; in certain extent, pre-drought aggravation the disaster; heavy precipitation which over the history extreme is the direct factor of trigger the debris flow. By research the Zhouqu climate found that rainfall intensity on July and August, particularly in early August is the highest frequency of heavy rain, should close concern of geological disasters;we studied the massive mudslide on the8August2010from the synoptic cause.Ths results demonstrated that on the background of pre-drought and low soil moisture,the heavy precipitation caused the heaviest masssive mudslide. The reasons are why the heavy precipitation occured were that invasion of cold advection combined with the shear line on700hPa and that weak cold air diffused triggered of releasing convection unsteady energy.A series of y meso-scale vortex which were formed by terrain and so on caused extremely non-uniform precipitation;The heavy precipitation paralleled with brightness temperature, but it was not the unique factors led to heavy precipitation;For y mesoscale vortex,radial velocity was a good indicator since rotation speed can indicate the vortex intensity;There was a good positive correlation between precipitation and scale; Attention to strengthening the protection of geological features, research the character of debris flow occurrence of climate impact and determination precipation threshold for forecasting debris flow is great significant.(2)The character of the short-duration precipitation in the Southeast Gansu were analyzed using hourly precipitation data which including2009and2010, and daily precipitation during1971-2000in Gansu province. The results show that main rainfall time section concentrate from April to September and all the proportions of precipitation account for more than80%. Rainfall rapidly increases from Northwest to Southeast, but on the other hand, the high and low centers more than other district on the nearer plateau, probably caused by plateau terrain and monsoon; The short-duration rainfall have their maximum around late-afternoon, but with the rainfall duration increase, the maximum gradually move to early morning and the amplitude decrease; Short-duration rainfall accounts for the max proportion not only frequency but also contribution to total precipitation; There are40.3%belong to short-duration precipitation and over30%of the stations account more than50%from April to September of precipitation, even part of stations more than90%.In a word, the short-duration precipitation is an important rainfall form. The composition of precipitation have19.4%caused by heavy precipitation, also proved that short-duration heavy precipitation is an important part of short-duration rainfall; Analysis the diurnal variation of short-duration rainfall events, frequency reaches the maximum at midnight and the second highest value at wee hours; In addition, research the distribution of heave precipitation-concentration degree (PCD) and heavy precipitation-concentration period (PCP),we find that the PCD is quite large, basically above the0.6,PCP mostly located in July and August, further study and prove that the main flood season at "late July and beginning of August".(3) Radar quantitative measurement of precipitation has more advantage in time and space, but the relationship with the change of terrain and precipitation type has great rate. Studying on the radar quantitative measurement of precipitation is one of the main development ways to improve the radar applied ability utilize radar volume scan data. The reflectivity difference of Tianshui, Qingyang and Lanzhou weather radars on the equidistant line are contrasted when they simultaneously observe and we also analysis the radar echo and precipitation retrieved if occur short-duration heavy rainfall, by using radar volume scan data in this paper. The research shows that there has no obvious difference when echo more than lOdBz; from compare the region station with automatic station of precipitation, we find that the weather scale is less caused by short-duration heavy precipitation than other rainfall type, on the other hand, this conclusion also proved by statistic of radar echo. There are the scale about which75%of the heavy precipitation are less than20km;we demonstrated that the original station can’t perfectly characterize the local precipitation; Studying on the estimated quantitative precipitation through packet of estimation, holistic and categorical Z-I relations, we knew that categorical Z-I relation is better than others on describe precipitation type in the Northeast edge of Tibetan Plateau, thus better solving the problem of underestimated light rain and overestimated heavy rain, and when rainfall belongs to15-20mm/h is best; At last we applied retrieve precipitation by using multi factors, this idea also has much effort to do.(4) The use of radar-rain gauge to estimate areal rainfall was one of the major directions to improve the application of radar, which had great advantages on both the wide coverage of radar scanning and high single-point precision of rain-gauge. Based on the correlation with radar echo and rainfall in northeastern edge of Tibetan Plateau, a regional heavy rain case on May10,2012was compared and spatial calibrated by using average calibration, optimal interpolation and variational-Kalman filter. The results demonstrated that the Z-I relationship was very different with the terrain changing. Compared with the precipitation observation,the local Z-I relationship by method of optimization was better than the others in diverseband or district, which effectively changed the situation of estimating lowly. In the mean time, the variational-Kalman filter method with the advantage of radar areal scan, which nicely reflected the spatial distribution of rainfall, calibrated best. In addition, it could be more effective in spatial precipitation estimation by taking correct mathematical measures through the equations with multi-elevation angles and multi variate.(5) Sounding data play an important role in analysis of heavy precipitation, in general, strong weather inevitable associate with mesoscale physical quantities. In this paper, the distribution of physical quantities by compare heavy precipitation with no-rainfall have been researched, in addition, calculating the hit rate, false alarm rate and so on, when in different number of stable and unstable state physical quantities by using precipitation and sounding data. The results show that physical quantities about thermal stability have positive correlation. In another word, the short-duration precipitation has been decided by thermal factors. We also find that the revision of convective available potential energy (CAPE) can well represent the heavy precipitation, because over500J/Kg account for65%, and demonstrated that there were no heavy precipitation when the convective inhibition(CIN) more than500J/Kg, most concentrated below in300J/Kg. At last, the probability of forecasting the heavy precipitation when those parameters are colligated is analyzed. Then, some diagnosis indexes for heavy precipitation are given. With increase the unstable physical quantities the precipitation probability rapid increase and false alarm rate gradually decreased, this results show that using combined parameters is a effective way of improve rainfall forecasting. In addition, it is found that with increase the number of unstable physical quantities will have more chance and precipitation. These results can provide the reference for short-duration precipitation inspection and forecasting in the northeast edge of Tibetan plateau.(6) Land surface process and atmospheric boundary layer processes was the important link in Exchange and transmission for Earth-atmosphere system, such as Energy, momentum, and water vapor and so on, which has been inherent connection with surprised severe weather disaster. The character of boundary layer and land surface process on severe convection weather were analyzed by using precipitation, sounding data and land surface data. We found that the maximum atmospheric mixed layer depth (hereafter ML depth) present a continuous and gradually basically thickening phenomenon before the convection weather, at last reaches a maximum in front of the rainfall in1day, but the ML depth had some differences in the next day of rainfall, through researched the ML depth continuous changes from3days before to the next day of convection weather. All of this demonstrated that the thermal convection environment of boundary layer maybe was the important energy source for the convection weather development. We also found the obviously difference through statistical land surface heat fluxes by divide3periods according to occurrence time of convective precipitation, the cumulative value of sensible heat flux was maximum at nightfall convection period and the latent heat flux was minimum at afternoon convection period; About wee hours convection period, the latent heat flux close to nightfall, but sensible heat flux approached afternoon period; By comparing classification of rainfall, there had a significant positive correlation between sensible heat flux and precipitation, especially in the period of17-25mm, the sensible heat flux reaches2141Wm-2, but they had complex correlation from among latent heat flux and precipitation, the results demonstrated that land-surface thermal effects had important function on formation of convection weather, however, local evaporation to local water cycle take shape has no substantial contribution to convection precipitation formation. |
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