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Basin Vortex is a type of Southwest Vortex， which refers to the vortex generated in the Sichuan Basin on the 700 hPa isobaric surface， with two consecutive low pressures with closed Contour line or cyclonic circulation in the wind direction of three stations.It is the main system that causes precipitation in the Sichuan Basin， and the "southwest type" Basin Vortex is the most frequent and strong type of Basin Vortex.This article utilizes ERA5 （0.25°×0.25°） hourly reanalysis data， GPM satellite precipitation data， and the Southwest Low Eddy Yearbook explored the characteristics and development mechanism of a typical “southwest type” Basin Vortex that occurred in the Sichuan Basin from June 26 to 28， 2020.The results indicate that the Basin Vortex was generated in the southwestern part of the Sichuan Basin， then moved towards the northeast direction， reached the northeastern part of Sichuan， turned eastward， and disappeared after entering Chongqing， with a total life history of 48 hours.The formation and development of the Basin Vortex are closely related to its divergence zone located on the northeast side of the 200 hPa South Asian High and on the right side of the entrance area of the high-altitude jet stream， as well as the low-level decompression caused by the positive vorticity advection in front of the 500 hPa short wave trough.The southwest part of the Sichuan Basin at 700 hPa is located to the left front of the low-level jet stream， which is conducive to the development of convergent upward motion and the formation of low eddies.The high value area of frontogenesis in the northeast direction of the 700 hPa Basin Vortex， the strengthening of the low-level jet and the guidance of the southwest airflow in front of the 500 hPa high altitude trough are the main factors for the movement of the Basin Vortex towards the northeast direction.As the center of the 200 hPa South Asian High moves eastward over the Yangtze-Huaihe River and the upper level jet weakens， the 500 hPa shortwave trough moves eastward， and the Basin Vortex is located in the negative vorticity advection zone behind the trough.The vertical direction turns into a sinking motion， with surface pressure increasing and the low vortex gradually weakening and disappearing.Analysis of the vorticity budget equation reveals that low-level convergence is the main contributor to the increase in the Basin Vortex intensity， and the increase in positive vorticity of the Basin Vortex caused by low-level convergence almost runs through the entire life cycle of the vortex.In addition， the existence of high-altitude orthonormal vortices and the release of condensation latent heat from the Basin Vortex precipitation also play an important role in the development and movement of the Basin Vortex.

Many new-generation Doppler weather radars in China are located in mountainous areas with complex topography， and the problem of low elevation angle terrain occlusion is prominent.When estimating precipitation by radar in the occluded area， observations with higher elevation angles need to be used， and due to the micro-physical changes and horizontal motion of precipitation particles during their descent， the reflectivity factor at high locations of the same site is often very different from that near the surface， which will increase the estimation error when used directly for estimating surface precipitation.In this paper， we propose a method for the vertical revision of reflectivity factor.First， we establish the vertical reflectivity factor profiles （VPR） of different precipitation types in the unobstructed observation area， and then revise the observations above the height to be revised to the target height by determining the height threshold to be revised and the near-surface target height based on the vertical variation characteristics of the profiles.The comparison test results show that： the revised target reflectivity factor data are less different from the actual observed data values， and the consistency is improved； moreover， the data at low VPR are more accurate by considering the occlusion factor； since the VPR of different precipitation types are significantly different， the differentiation of precipitation types can avoid mis-correction.The proposed revision method is not only applicable to the beam blocking area， but also generally applicable to the revision of the observed data at high beam height at long distances.

Using observed hourly precipitation data and disaster records of flooding in Qinghai， we adopt the ratio weight method to construct the disaster index of flood disaster events based on the direct economic loss， disaster-affected population， collapsed houses， agricultural economic loss and agricultural disaster area.According to the percentile method， flood disasters are graded into general， heavy， severe， and extra heavy.The disaster distribution characteristics and differences of the four ranks are analyzed and compared with the precipitation characteristics in Qinghai.Principal component analysis， box-whisker plot and correlation analysis are employed to investigate the main factors that lead to flood disasters in Qinghai and the differences among regions.Results show that flood disasters occur frequently， and losses caused by floods increase.The frequency of severe and extra heavy disasters increases significantly after 2016， and the periods of July and August are the most frequent periods of flood disasters in Qinghai every year.The eastern part of Qinghai is an area of frequent floods and the most serious disasters.The Hainan Prefecture has the most flooding frequency and the Haidong City suffers the most serious disaster losses.The flooding disasters in Qinghai are mainly induced by rainfall processes that are more serious than heavy rainfall.The process of flood-causing precipitation in Qinghai can divide into two categories， one is short-lived but has a high rainfall intensity， which has a rainfall duration of 12 h and can cause high accumulated precipitation.The other can also induce high accumulated precipitation， and its rainfall duration is generally longer than 12 h.The flood disasters occurring in eastern cities like Hainan， Huangnan， Haibei， Xining and Haidong are mainly induced by the first category of precipitation process mentioned above.The second category of rainfall process is mainly found in Haixi and Yushu Prefecture， and Huangnan， Haibei， Xining and Haidong are also affected by this precipitation process.The accumulated precipitation and 24 h precipitation are closely associated with flood disaster losses， and longer precipitation duration can further aggravate flood disaster losses.

Using ERA5 （0.25°×0.25°） hourly reanalysis data， TRMM satellite precipitation data and FY-2E satellite black-body temperature （TBB） data， the circulation background and movement characteristics of the formation and development of a Qinghai-Xizang Plateau vortex （QXPV） moving out of the Tibetan Plateau from July 7 to July 9， 2017， as well as the dynamical and thermal mechanism of the heavy precipitation in the Yangtze-Huaihe River Basin were discussed， and the HYSPLIT4 model was used to track the water vapor source of the heavy precipitation in the Yangtze-Huaihe River Basin.The results show as follow： The QXPV was generated in the central part of the Tibetan Plateau， first moved to the southeast and then to the northeast after reaching the central part of Sichuan， with the life history of 39 h.At 200 hPa， the South Asian High and the upper-level jet stream were strong， and the vortex was located in the divergence region on the right side of the upper-level jet inlet area， which promoted the formation and development of the QXPV.The negative height center in the front of the vortex and the southwest airflow at the edge of the West Pacific Subtropical High lead the eastward movement and turn of the QXPV at 500 hPa.After the QXPV moved out of the Qinghai-Xizang Plateau， it was in the decompression area caused by positive vorticity advection in front of the high trough.In addition， the leeward slope of the large terrain was conducive to the enhancement of cyclonic vorticity， so the QXPV developed.The QXPV moved along the Yangtze-Huaihe shear line after it moved out of the Tibetan Plateau， and the cold air behind the trough merged with the southerly airflow carrying water vapor from the Bay of Bengal and the South China Sea.Under the action of frontogenesis， the QXPV developed into a Yangtze-Huaihe cyclone， and the rainfall rapidly increased to the standard of heavy rain.The coupling of upper-level jet and low-level jet， and the development of low-level convective instability strengthened the dynamic uplift， which was conducive to the formation of heavy precipitation over the Yangtze-Huaihe River Basin.The water vapor source of heavy precipitation was mainly the South China Sea and the Bay of Bengal.The convergence upward movement was the strongest during the period of the strongest precipitation， and the convective clouds developed vigorously to maintain the precipitation.