Convective Vorticity Vector Research Articles

The dynamic forecast method of convective vorticity vector

In this paper we introduce the convective vorticity vector and its application in the forecast and diagnosis of rainstorm. Convective vorticity vector is a parameter of vector field, different from scalar field, it contains more important information of physical quantities, so it could not be replaced. Considering the irresistible importance of vector field we will introduce the theory of vector field and its dynamic forecast method. With the convective vorticity vector and its vertical component's tendency equation, diagnostic analysis on the heavy-rainfall event caused by landfall typhoon “Morakot” in the year 2009 is conducted. The result shows that, the abnormal values of convective vorticity vector always changes with the development of the observed precipitation region, and their horizontal distribution is quite similar. Analysis reveals a certain correspondence between the convective vorticity vector and the observed 6-h accumulated surface rainfall, they are significantly related. The convective vorticity vector is capable of describing the typical vertical structure of dynamical and thermodynamic fields of precipitation system, so it is closely related to the occurrence and development of precipitation system and could have certain relation with the surface rainfall regions.

Evaluation of the Use of Moist Potential Vorticity and Moist Potential Vorticity Vector in Describing Annual Cycles of Rainfall over Different Regions in Tanzania

The economy of Tanzania heavily depends on agriculture sector which is primarily rain-fed. In this paper, we compute the moist potential vorticity (MPV) and evaluate its usefulness to describe annual cycles of rainfall. We also modify the convective vorticity vector ((CVV) ) which was defined as the cross product of absolute vorticity and the gradient of equivalent potential temperature to moist potential vorticity vector ((MPVV) ). This vector is calculated as a cross product of absolute vorticity and the gradient of moist air entropic potential temperature. The performance of (MPVV) to describe the annual cycles of rainfall over different regions in Tanzania is analyzed. Twenty six (26) years (1976-2001) daily data of air temperature, specific humidity, zonal and meridional components of the wind at 850 and 600hPa from numerical output generated by the Rossby Center regional climate model version four (RCA4) are used for computation of MPV and (MPVV) at 700hPa. The statistical relationship between (MPVV) and MPV against observed rainfall data from 22 synoptic meteorological stations using Pearson correlation coefficient indicate that (MPVV) bears strong and statistically significant correlation coefficient to rainfall than MPV suggesting its potential use as predictor of annual cycles of rainfall over different regions in Tanzania.

Moist Potential Vorticity Vector for Diagnosis of Heavy Rainfall Events in Tanzania

In this paper, we modify the convective vorticity vector (CVV) defined as a cross product of absolute vorticity and gradient of equivalent potential temperature to moist potential vorticity vector (MPVV) defined as a cross product of absolute vorticity () and the gradient of the moist-air entropy potential temperature (). The patterns of (MPVV) are compared with the patterns of heavy rainfall events that occurred over different regions in Tanzania on 20th to 22nd December, 2011 and on 5th to 8th May, 2015. Moreover, the article aimed at assessing the relative contributions of the magnitude, horizontal and vertical components of (MPVV) detecting on the observed patterns of rainfall events. Dynamic and thermodynamic variables: wind speed, temperature, atmospheric pressure and relative humidity from numerical output generated by the Weather Research and Forecasting (WRF) model running at Tanzania Meteorological Agency (TMA) were used to compute MPVV. It is found that MPVV provide accurate tracking of locations received heavy rainfall, suggesting its potential use as a dynamic tracer for heavy rainfall events in Tanzania. Finally it is found that the first and second components of MPVV contribute almost equally in tracing locations received heavy rainfall events. The magnitude of MPVV described the locations received heavy rainfall events better than the components.

Analysis of Equation for Convective Vorticity Vector during a Torrential Rainfall Process in Meiyu Season of 2011

Using NCEP FNL analysis data,black body temperature from FY-2E satellite,conventional and auto-metrological stations' observational precipitation data,and simulation output from high-resolution mesoscale model WRF V3. 3 to analyze a precipitation process in Jiang-Huai valley in June 2011. Analysis results show that the simulation results are in good agreement with the observations when comparing the precipitation betw een simulations and observations and reproduce the precipitation process well. This precipitation process was controlled and influenced by the surface low and Meiyu front systems. Period from 14 to 15 June is the mature phase of whole precipitation process,and the most significant character of this period is that many mesoscale convective systems move and develop along the Meiyu front. To investigate how MCS impacts on Meiyu front and torrential rainfall,convective vorticity vector and its vertical component tendency equation were employed to analyze. The result shows that local variation for the vertical component was influenced by the diabatic term,and the relationships among diabatic heating,secondary circulation and Meiyu frontogenesis imply a CISK-like response betw een MCS and Meiyu frontogenesis. So as a good atmospheric variable,the convective vorticity vector,especially,the vertical component can be used to diagnose and reveal the relationship betw een MCS associated with diabatic heating and Meiyu frontogenesis.

Mesoscale dynamics and its application in torrential rainfall systems in China

Progress over the past decade in understanding moisture-driven dynamics and torrential rain storms in China is reviewed in this paper. First, advances in incorporating moisture effects more realistically into theory are described, including the development of a new parameter, generalized moist potential vorticity (GMPV) and an improved moist ageostrophic Q vector (Qum). Advances in vorticity dynamics are also described, including the adoption of a “parcel dynamic” approach to investigate the development of the vertical vorticity of an air parcel; a novel theory of slantwise vorticity development, proposed because vorticity develops easily near steep isentropic surfaces; and the development of the convective vorticity vector (CVV) as an effective new tool. The significant progress in both frontal dynamics and wave dynamics is also summarized, including the geostrophic adjustment of initial unbalanced flow and the dual role of boundary layer friction in frontogenesis, as well as the interaction between topography and fronts, which indicate that topographic perturbations alter both frontogenesis and frontal structure. For atmospheric vortices, mixed wave/vortex dynamics has been extended to explain the propagation of spiral rainbands and the development of dynamical instability in tropical cyclones. Finally, we review wave and basic flow interaction in torrential rainfall, for which it was necessary to extend existing theory from large-scale flows to mesoscale fields, enriching our knowledge of mesoscale atmospheric dynamics.

Diagnosis and application of potential shear deformation wave-activity density in the torrential rain of Typhoon Morokat (2009)

Based on previous studies of the interaction between wave and flow, combining the vertical component of disturbance convective vorticity vector, the disturbance horizontal divergence and the vertical gradient of disturbance generalized potential temperature, We define a new disturbance thermodynamic shear advection parameter in this paper. This parameter means a typical wave action density, its equation of tendency is a typical wave action equation, which could describe the development or evolution of mesoscale disturbance. With the wave action density and the wave action equation, we have conducted a diagnostic analysis of the heavy-rainfall event caused by landfall typhoon "Morakot" in 2009. Results show that the abnormal values of the wave action density (namely the disturbance thermodynamic shear advection parameter) will always change with the development of the observed precipitation regions, both their horizontal distribution and their temporal evolution are quite similar. Statistical analysis reveals a certain correspondence between the wave action density and the observed 6-hour accumulated surface rainfall in the summer of 2009, and they are intimately related to each other. The wave action density may be used to describe the typical vertical structure of dynamic and thermodynamic fields of a precipitation system, so it is closely related to the occurrence and development of the precipitation system and may have certain relation with the surface rainfall regions. The calculation of the wave action flux divergence shows that at the time around the landing of typhoon "Morakot" in the southeastern China coastal region, the potential vorticity of disturbance ageostrophic wind is the main forcing term affecting the local variation of wave action density. The contribution of the coupled term between the first-order disturbance advection and disturbance shear to the local variation of wave action density is secondary. While the exchange of disturbance momentum and disturbance heat between the basic state and disturbance has relatively weak influence on the development and evolution of disturbance. After the landing of typhoon "Morakot" in the southeastern China coastal region, these forcing terms and the wave action itself are apparently weakened.

Numerical simulation of a torrential rain event in the northeast of Huaihe Basin. Part II: Instability conditions and the mechanism of intensification and maintenance

Based on the simulation displayed in Part I of this study, the intensification and maintenance, the relationship between deep moist mesoscale convective system (DMMCS) and instability, convective vorticity vector (CVV) are analyzed in the present paper. Results show that: (1) middle-low level convective instability is the precondition of the occurrence of DMMCS. The convergence and merger enhancement of convection cells, as well as the convective instability energy transporting from the left-front of typhoon play an essential role in the re-establishment and enhancement of convective instability. (2) Baroclinic instability and conditional symmetric instability appear not only in the middle-low level, but also are distinct in the middle-upper level of DMMCS. (3) In DMMCS, there is an alternative distribution of inertial instability column and inertial stability column. In the west and south, there are negative CVV columns, which is favorable for the burst of deep moist convection. (4) The strong slantwise convection induced by inertial instability, baroclinic instability, and conditional symmetric instability enhance the upper-level southerly component. Due to the appearance of the compensated downdraft at the low level of south side of DMMCS, the low level southerly intensified, and the enhancement of upper- and low-level cores is in favor of the development of DMMCS, which will be beneficial to the reinforcement and maintenance of inertial instability, baroclinic instability, and conditional symmetric instability. It is a positive feedback process. (5) There is a downshear circulation to the east of rainfall cell. Shallow convections near this cell absorb the vapor and instability energy coming from the south. In the meanwhile, the mesoscale convergence line and meso-β-scale vortex organize and intensify convective cells. In DMMCS, there is an alternative distribution of convergence and divergence columns, and the couple between strong divergence and vorticity columns. They are both conducive to the development of DMMCS, and the instability will be intensified and maintained for its development in depth.

Analysis and forecasting of heavy-rainfall event by strong convection

For the case of severe convection occurring in the southern region of North China on July 8, 2009, the three dynamical factors, namely, vertical component of convective vorticity vector, moist thermodynamic advection parameter and wave-activity density are diagnosed. The result shows that the anomalous-value regions of dynamical factors are located mainly in middle and lower troposphere over the strong precipitation area. Since the dynamical factors can effectively describe the synthetical characteristics of strong convective system, such as vertical shear of horizontal wind, advection of potential temperature, vorticity perturbation and baroclinicity of moist atmosphere, they correspond to the observation of 6-h accumulative rainfall in horizontal distribution patterns. Using the 6-h, 12-h, 18-h and 24-h forecasting dataset of U.S. NCEP/NCAR 0.5-Degree GFS, the dynamical factors are calculated to analyze their indications of precipitation forecasting during a longer period. The results show that during June 2 – Oct 1, 2009, the 6-h, 12-h, 18-h and 24-h forecasted dynamical factors each have an indication of strong precipitation. The moist thermodynamic advection parameter suggests that the precipitation is best among the three dynamical factors.

Diagnosis of dynamic process over rainband of landfall typhoon

This paper introduces a new physical parameter — thermodynamic shear advection parameter combining the perturbation vertical component of convective vorticity vector with the coupling of horizontal divergence perturbation and vertical gradient of general potential temperature perturbation. For a heavy-rainfall event resulting from the landfall typhoon ‘Wipha’, the parameter is calculated by using National Centres for Enviromental Prediction/National Centre for Atmospheric Research global final analysis data. The results showed that the parameter corresponds to the observed 6 h accumulative rainband since it is capable of catching hold of the dynamic and thermodynamic disturbance in the lower troposphere over the observed rainband. Before the typhoon landed, the advection of the parameter by basic-state flow and the coupling of general potential temperature perturbation with curl of Coriolis force perturbation are the primary dynamic processes which are responsible for the local change of the parameter. After the typhoon landed, the disturbance is mainly driven by the combination of five primary dynamic processes. The advection of the parameter by basic-state flow was weakened after the typhoon landed.

Comparative Studies of Different Mesoscale Convection Parameterization Schemes in the Simulation of Mei-Yu Front Heavy Rain

The mei-yu front heavy rainstorms occurred over Nanjing on 3-5 and 8-9 July 2003 and were simulated in this paper using the Weather Research and Forecasting Model (WRFv3.1) with various mesoscale convection parameterization schemes (MCPSs). The simulations show that the temporal and spatial evolution and distribution of rainstorms can be modeled; however, there was incongruity between the comparative simulations of four different MCPSs and the observed data. These disparities were exhibited in the simulations of both the 24-hour surface rainfall total and the hourly precipitation rate. Further analysis revealed that the discrepancies of vertical velocity and the convective vorticity vector (CVV) between the four simulations were attributed to the deviation of rainfall values. In addition, the simulations show that the mid-scale convection, particularly the mesoscale convection system (MCS) formation, can be well simulated with the proper mesoscale convection parameterization schemes and may be a crucial factor of the mei-yu front heavy rainstorm. These results suggest that, in an effort to enhance simulation and prediction of heavy rainfall and rainstorms, subsequent studies should focus on the development and improvement of MCPS.

Diagnostic Analyses of the Modified Convective Vorticity Vector in Non-uniformly Saturated Moist Flow

AbstractBecause the real atmosphere is non-uniformly saturated, the generalized potential temperature is introduced. The convective vorticity vector, which can depict the occurrence and development of mesoscale deep convective systems, is modified and re-derived in a nonuniformly saturated moist atmosphere (C*). Then, a case study is performed for a frontal rainfall event which occurred near the middle and lower reaches of the Yangtze River in China. The diagnostic results of C* show that, in the lower troposphere, the vertical component of C* (C*z ) can diagnose developments and movements of precipitation and convection better than those of Cm (Cmz, in saturated moist flow) and C (Cz, in dry flow). C*z is a good predictor for precipitation analyses as well.

Diagnostic analysis of the asymmetric structure of the simulated landfalling typhoon “Haitang”

The landfalling processes of Typhoon “Haitang” near Lianjiang of Fujian Province of China from 00 UTC 19 to 12 UTC 20 July 2005 were reproduced by using the nesting non-hydrostatic WRF model and data assimilation technology (Level II Doppler radar data of Changle of Fujian Province are assimilated to the simulation every one hour from 01 to 06 UTC 19 July 2005). The mesoscale structure and evolution of the typhoon before, during, and after its landfall were discussed. The simulation data show that the assimilation experiment with the high temporal-and-spatial-resolution radar radial velocity and reflectivity data can produce much better simulation of the typhoon track, intensity evolution and landfalling location than the control experiment without assimilating radar data. By using the assimilation experimental data, the mesoscale fine-mesh structure and evolution before and after typhoon landfall were analyzed. Because of the influence of sea–land thermodynamic difference, two asymmetric convective regions were located at ocean and land, respectively. To better understand and investigate the asymmetric-structure characteristics of the landfalling typhoon, several dynamical diagnostic tools, the helicity ( H), the moist potential vorticity (MPV), the convective vorticity vector (CVV), the moist vorticity vector (MVV), which are associated with the development of strong convections, are introduced. Further analysis illuminates that the distributions of these physical diagnostic parameters are totally asymmetric, and subsequently, the associated convections also show distinct asymmetry.

A phase analysis of vorticity vectors associated with tropical convection

Three new vorticity vectors have been proposed by Gao et al to study the two-dimensional tropical convection. In the present paper, phase relations between surface rain rate and the vorticity vectors are analysed with the calculations of lag correlation coefficients based on hourly zonally-averaged mass-integrated cloud-resolving simulation data. The cloud-resolving model is integrated with the vertical velocity, zonal wind, horizontal thermal and moisture advections, and sea surface temperature observed and derived from tropical ocean global atmosphere – coupled ocean atmosphere response experiment (TOGA-COARE) for 10 days. Maximum local increase of the vertical component of the convective vorticity vector leads maximum surface rain rate by 2 hours mainly due to the interaction between vorticity and zonal gradient of ice heating. While maximum local increase of the vertical component of the moist vorticity vector leads maximum surface rain rate by 2 hours mainly because of the interaction between zonal specific humidity gradient and zonal buoyancy gradient. And the maximum local decrease of the zonal component of the dynamic vorticity vector leads maximum surface rain rate by 2 hours mainly due to the interactions between vorticity and vertical pressure gradient as well as vorticity and buoyancy.

Diagnostic analysis of mesoscale rainstorms in the Jiang-Huai valley of China with convective vorticity vector

By the vector product of absolute vorticity vectors and equivalent potential temperature gradients, a new vector, convective vorticity vector (CVV) is readdressed after Gao et al., and is applied to the study of the development and movement of mesoscale rainstorms in the Jiang-Huai valley of China by using high-resolution simulation data with PSU/NCAR MM5 briefly. The results show that the CVV, especially its vertical component which is closely related to interactions between vertical secondary circulations and horizontal equivalent potential temperature gradients, may be a good tracer and diagnostic tool in the study of mesoscale rainstorms in the Jiang-Huai valley of China. And the main physical processes responsible for the variations of the vertical component of the CVV are discussed briefly based on its tendency equation proposed in this article.

A convective vorticity vector associated with tropical convection: A two‐dimensional cloud‐resolving modeling study

Although dry/moist potential vorticity (( · ∇θe)/ρ) is a useful physical quantity for meteorological analysis, it cannot be applied to the analysis of two‐dimensional (2‐D) simulations. A new vorticity vector ( × ∇θe)/ρ (convective vorticity vector (CVV)) is introduced in this study to analyze 2‐D cloud‐resolving simulation data associated with 2‐D tropical convection. The cloud model is forced by the vertical velocity, zonal wind, horizontal advection, and sea surface temperature obtained from the Tropical Ocean‐Global Atmosphere (TOGA) Coupled Ocean‐Atmosphere Response Experiment (COARE) and is integrated for a selected 10‐day period. The CVV has zonal and vertical components in the 2‐D x‐z frame. Analysis of zonally averaged and mass‐integrated quantities shows that the correlation coefficient between the vertical component of the CVV and the sum of the cloud hydrometeor mixing ratios is 0.81, whereas the correlation coefficient between the zonal component and the sum of the mixing ratios is only 0.18. This indicates that the vertical component of the CVV is closely associated with tropical convection. The tendency equation for the vertical component of the CVV is derived and the zonally averaged and mass‐integrated tendency budgets are analyzed. The tendency of the vertical component of the CVV is determined by the interaction between the vorticity and the zonal gradient of cloud heating. The results demonstrate that the vertical component of the CVV is a cloud‐linked parameter and can be used to study tropical convection.