Total deformation and its role in heavy precipitation events associated with deformation-dominant flow patterns

et al. 2020

Self Cite

In this study, the physical meaning and generation mechanism of potential deformation (PD) are reinvestigated. A main trait of PD is that it contains deformation, which is an important factor to precipitation but not well applied in precipitation diagnosis. This paper shows PD shares similar features to deformation, but contains much more physical information than deformation. It can be understood as a type of deformation of a thermodynamic-coupled vector (u*, v*). For convenient application, squared PD (SPD) is used instead for analysis. By deriving the tendency equation of SPD, it is found that whether SPD is produced or reduced in the atmosphere is associated with the angle between the dilatation axes of PD and geostrophic PD. When the angle is less than π 2 , SPD is generated. The diagnostic results during a heavy rainfall event in North China on 20 July 2016 show that the process of rapid increase in precipitation can be well revealed by SPD. The distribution of SPD becomes more organized and concentrated with increasing precipitation intensity. A diagnostic analysis of the SPD tendency equation shows that concentrated SPD is associated with the generation of SPD in the boundary layer followed by upward transport of the SPD. The concentration of SPD indicates a confluence of precipitation-favorable factors-namely, vertical wind shear and moist baroclinity, which can enhance vertical motions and thus cause an increase in precipitation. These diagnostic results further verify PD as a useful physical parameter for heavy precipitation diagnosis.

Section: Introductionmentioning

confidence: 99%

Reinvestigation of potential deformation during a heavy rainfall event in North China

et al. 2020

Self Cite

“…As an important characteristic of the horizontal wind field, deformation is usually associated with heavy rainfall near fronts due to its important role in enhancing frontogenesis (Han et al 2005;Jiang et al 2011). Gao, Yang, and Xue (2008) derived the tendency equation for deformation and studied the role of deformation on redistributing the moisture. Li et al (2013) showed the deformation vector had a small angle with the isothermal line for the precipitation that occurred in Beijing on 21 July 2012, and the local frontogenesis process was strongly forced by the deformation field.…”

Section: Introductionmentioning

confidence: 99%

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

Jiao³

et al. 2018

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 nongeostrophic ω equation 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 new ω equation 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.

“…The second is by concentrating moisture. Through a simple numerical experiment, Gao et al (2008) showed the process of deformation redistributing water vapor. The third may come from an impact of deformation on mesoscale disturbances or vortex evolutions, which is the direct producer of precipitation (Jiang 2011).…”

Section: Introductionmentioning

confidence: 99%

Diagnosis of deformation-derived ascending areas in a rainband

Gao

2018

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.