Analysis of a Wenzhou-Hitting Exceptionally Strong Rainstorm Associated with a Typhoon Inverted Trough in September,1999

Using T106 numerical products, MM5 simulations in conjunction of Q-vector scheme-computed NCEP results, observations and satellite cloud images, study is undertaken for an exceptionally intense rainstorm event afflicting the Wenzhou region of Zhejiang province far away from the tropical storm center happening early on the morning of September 4, 1999 （TS9909 hereinafter）. Evidence suggests that, like previously-studied typhoons landing in autumn south of Xiamen to the eastern part of Guangdong, TS9909 has an inverted trough in the central south of the coastal belt of Zhejiang province that produces the rainstorm from the meso convective complex （MCC） on the warm, moist shear inside; the time and order of the magnitude of the rainfall are bound up with the development of the pattern of strong Q-vector divergence gradients during the event for the study area; the NE - SW coastline and the unique topography of the Yandang mountains inside the region are favorable for air lifting are the major contributors to the torrential rains.

Trigger mechanism of a snow burst event in Northeast China

A snow burst event characterized by brief heavy snowfall affected Northeast China and caused serious social impact on 26 January 2017,with the snowband generally aligned with a northeast–southwest-oriented cold front.ECMWF reanalysis data were used to diagnose the possible trigger mechanism.Results showed there were two stages:(a)an initial stage far away from the Changbai Mountains,and(b)an enhancement stage under the influence of high terrain.During the initial stage,the coupling of low-level frontogenesis and a favorable convergence pattern caused strong upward motion,contributing to the release of instability.When the snowband approached the high terrain during the enhancement stage,the various instabilities were triggered by the low-level frontogenesis,terrain circulation,and strong wind shear associated with the low-level jet.Further,a modified Q-vector divergence including generalized potential temperature was calculated to diagnose the vertical motion.It showed that the frontogenesis terms contributed greatly to the negative Q-vector divergence along the moist isentropes,while the pseudo-vorticity terms played a role in the regions with strong wind shear associated with the low-level jet in the warm section,suggesting both were important in stimulating the ascending motion.The regions with negative Q-vector divergence had a close relationship with the vertical structure of convection,indicating the potential to track the development of the snowband in the next few hours.

Deformation characteristics of the ‘7.20' heavy rainfall event in North China

A heavy-rainfall event that occurred in North China during 19–20 July 2016,resulting in severe flooding,was investigated in this study.In this event,high-value total deformation overlapped the precipitation region,implying a close relationship between them.By deriving the nongeostrophicωequation in a non-uniformly saturated moist atmosphere,the relation between vertical velocity and deformation was diagnosed.The Q-vector divergence on the right-hand side of the newωequation was divided into three compositions,associated with horizontal divergence,vertical vorticity,and horizontal-wind deformation,respectively.It was found that the deformation component of Q-vector divergence contributed most to the negative Q-vector divergence in the precipitation region,implying an important role of deformation forcing in facilitating the vertical motion.In order to track the precipitation on the basis of deformation,potential deformation was proposed by virtue of the generalized potential temperature.The high-value potential deformation and precipitation were always overlapping,and shared an analogous temporal trend.This means that potential deformation can reflect the variation of heavy precipitation to a certain extent,and can serve as a tracker of the precipitation region.

A NOVEL METHOD FOR CALCULATING VERTICAL VELOCITY:A RELATIONSHIP BETWEEN HORIZONTAL VORTICITY AND VERTICAL MOVEMENT

The present work provides a novel method for calculating vertical velocity based on continuity equations in a pressure coordinate system.The method overcomes the disadvantage of accumulation of calculating errors of horizontal divergence in current kinematics methods during the integration for calculating vertical velocity,and consequently avoids its subsequent correction.In addition,through modifications of the continuity equations,it shows that the vorticity of the vertical shear vector(VVSV) is proportional to-ω,the vertical velocity in p coordinates.Furthermore,if the change of ω in the horizontal direction is neglected,the vorticity of the horizontal vorticity vector is proportional to-ω.When ω is under a fluctuating state in the vertical direction,the updraft occurs when the vector of horizontal vorticity rotates counterclockwise;the downdraft occurs when rotating clockwise.The validation result indicates that the present method is generally better than the vertical velocity calculated by the ω equation using the wet Q-vector divergence as a forcing term,and the vertical velocity calculated by utilizing the kinematics method is followed by the O'Brien method for correction.The plus-minus sign of the vertical velocity obtained with this method is not correlated with the intensity of d BZ,but the absolute error increases when d BZ is >=40.This method demonstrates that it is a good reflection of the direction of the vertical velocity.

Diagnosis of deformation-derived ascending areas in a rainband

This paper demonstrates that,for a moist baroclinic frontal system,the large-value deformation belt in the low-level atmosphere overlaps with precipitation.To precisely describe the relationship between deformation and heavy precipitation,deformation is introduced into the nongeostrophic Q^#-vector.Q^#is then decomposed into three parts:the divergence-related term,the vorticity-related term,and the deformation-related term.By calculating the divergence of Q#and its components,it is found that in strong ascending areas within precipitation regions the nongeostrophic Q^#-vector divergence shows strong negative values.Its deformational component can contribute about 68%to these negative values.This verifies that strong deformation in a precipitating atmosphere is favorable for the development of convection and precipitation.In addition,by calculating the correlation coefficients between the Q^#-vector(including its components)divergence and vertical motions,it is also found that the Q^#-vector divergence shows higher correlation with vertical motion within the precipitation belt and lower correlation in the non-precipitation areas,which indicates a larger contribution of Q^#to vertical motion when precipitation occurs and implies an effect of Q^#to the precipitation distribution or spatial variability.Among the three components of the Q^#-vector,the correlation coefficients between the deformational component and vertical motion are the most similar in pattern to that of the correlation coefficients between the Q#-vector and vertical motion,which further reflects the important contribution of deformation to the large spatial variability of precipitation.

The Analysis of the Asymmetric Precipitation Caused by the No.10 Tropical Cyclone “Damrey” in 2012 Based on Observation and Numerical Simulation

The No.10 tropical cyclone “Damrey” in 2012 is the first landing typhoon on the north of the Yangtze River after 1949. After its landing, Damrey showed an obvious asymmetric structure and precipitation. Using the ERA-interim reanalysis data from the European Centre for Medium-Range Weather Forecasting (ECMWF), the study simulated the whole process of Damrey from pre-landing to extinct by using WRF model. Based on the model result and FY-2E satellite data and observation data, the study analysis the causes of the asymmetric structure of Damrey. It is found that the descending motion is strong on the west and south sides of the typhoon, they blocked the southwest water vapor transport. So the development of convective cloud system was hindered, and the wind shear on the west and south sides on the typhoon was stronger than on the east and north. It caused the result of the precipitation on the east and north sides of typhoon much more than on the west and south. Q-vector, upper level jets and other factors are also analyzed in this study.