Nonhydrostatic Numerical Simulation On The Developing Structure And Mechanism Of The Heavy Rainfall Mesoscale System

The structure and mechanisms of two types of heavy rainfall mesoscale systems occurred in China have been studied in details by using observational analyses, numerical simulations and thermodynamic-dynamic diagnoses. The following eight issues have been mainly discussed and studied in this dissertation:1. The research on two types of heavy rainfall systems with a landing typhoon metamorphic low and typical Mei-Yu frontLanding typhoon metamorphic low and typical Mei-Yu front, two important types of the heavy rainfall synoptic systems, always result in severe floods in China. Therefore, we selected two related heavy-rainfall cases ( "96.8" landing typhoon metamorphic low and "98.7" Mei-Yu front with the low vortex-shear line) to investigate and study in this thesis. The results from observational analyses, numerical simulations and thermodynamic-dynamics diagnoses for the two heavy rainfall events indicated that the heavy rainfall were directly related to the genesis and intensive development of the MaCS and MpCS. However, there were still some large differences in the genesis, development and its structure evolution of the two types of heavy rainfall systems.2. The study on the structure and developing mechanisms of the meso-α scale heavy rainfall systems of the "96.8" landing typhoon metamorphic lowA heavy rainfall event occurred in Henan, Hebei and Shanxi Provinces during the period from 3 to 5 August 1996, resulted in severe flood catastrophe in China. Satellite cloud image analyses showed that the event was directly related to the genesis and intensive development of the MaCS formed in landing typhoon metamorphic low.Synoptic observational analyses showed that "96.8" rainstorm occurred under a favorable circulation pattern formed by the interactions between the large- and mesoscale synoptic systems as well as the high-, middle- and low latitude circulation systems. The stable gross col field and the interaction between a northward moving typhoon-low and its eastern lateral Pacific subtropical high were the large- and meso-scale circulation conditions. The unique dynamical and thermodynamical structures of the MaCS formed in landing typhoon metamorphic low were directly responsible for this rainstorm event.We have successful simulated this event using a nonhydrostatic numerical model MM5.V3 with a two-way interactive nesting mesh method. Results from the simulations revealed that: the developing typhoon-low had α structure of the cyclonic vorticity column with warm center and high humidity. At the lower levels, the vorticity column was the moist convective instability and the moist potential vorticity was negative;Strong vertical ascending motion, strong divergence at upper levels, strong convergence at thelower levels and the development of the convective cloud cluster were intercoupling;the intensive southern wind jet accompanied by the typhoon-low was not only the necessary interaccompanying and intercoupling conditions on the development and maintenance of the typhoon-low and convective cloud cluster, but it also transported the moisture source and heat energy essential prerequisite for the "96.8" extraordinary rainstorm.3. The study on the structure and developing mechanisms of the meso-p scale heavy rainfall system of the, 'j'98.7" Mei-Yu front with the low vortex-shear lineLarge-, meso- scale synoptic systems and cloud image analyses indicated that the "98.7" extraordinary heavy rainfall event was closely related to the genesis, development of a short wave trough on 500 hPa, a low vortex-shear line on 700 hPa and a Mei-Yu front system on surface, but it also directly related to the successive genesis and intensive development of MaCS and MpCS along the low vortex-shear line.Simulations using MM5.V3 with full moist physics schemes, four-dimensional data assimulation (FDDA) of analysis nudging and two way interactive nesting mesh method in two- or triple- or quartet- nest grid, especially in a very high horizontal resolution (nest subdomain D04 with 2km horizontal resolution) revealed that: (1) The intensive development of a meso-p shear line at low levels along the Changjiang River in the east Hubei and the occurrence of a convergence center were in directly relationship with the genesis and development of a meso-P low vortex;(2) The vertical structure of the intensive development on the meso-p shear line showed that the intensive convergence and divergence layers were reiteration and coupling with strong ascending motion. The strong vorticity, potential vorticity and convergence layers were inter-adjointing while the moist potential temperature center at low levels and the saturated vapor belt at middle levels were coexistence;(3) The vertical structural features of the genesis on the meso-p low vortex indicated that the divergence and ascending motion developed in double-branches column while the vorticity and potential vorticity developed in one branch column;the high moist energy column had a coupling double-branches development while the moisture channel had a step slantwise ascending development;(4) The vertical structures of the developing meso-p low vortex revealed the intercoupling development between the V-letter columns of the divergence and strong ascending motion;the vorticity and potential vorticity had double-branches columns;the band of the step slantwise ascending moisture channel became wider and deeper during the period of intensive double-branches column of high moisture energy. Meanwhile, the low vortex extremely developed and reached its strongest with its typical structure. (5) The genesis and developing field structure of the low vortex cloud water and rain water were developed from belt to column while the snow and cloud ice at upper levels exhibited a belt development. (6) There were considerable consistent corresponding relationship among the belt, centers of heavy rainfall and high value 6e on 700 hPa. The centers of heavy rainfall located the north side of the jet stream;the distribution of potential vorticity (PV) at lower levels was almost coincidence with the distribution of the simulated precipitation, suggesting the development of mesoscale system was related to the genesis of PV belt.4. Thermodynamic diagnoses of the heat and moisture budgets on the genesis and development of the "98.7" meso-fi scale heavy rainfall systemAnalyses of diagnostic apparent heat sources Qi and apparent moisture sink Q2 showed that the regions of high value of the total latent heat plus surface fluxes were consistent with the corresponding intensive regions of "98.7" heavy rainfall;The deep and thick heating layer in the mjdtlle troposphere was the mainly thermodynamic mechanism for the cumulus convective activation, the persistent genesis and development of severe rainstorm;The relative cool layer in the upper troposphere provided a favorable thermodynamic unstable condition for intensive cumulus convection over the heavy rain areas. The condensation latent heating of cumulus convective in the lower and middle troposphere was not only heating the middle troposphere atmosphere, but also heating the upper environment atmosphere through transporting heat to upper levels;the double-peak structure of Q2 at the early stage of heavy rainfall was relevant to drying associated with convective condensation of both stratocumulus in the lower levels and cumulus in the middle levels;the peak value of Q2 in the middle levels was basically corresponding with that of Qi;the deep and thick drying layer of Q2 was consistent with the deep and thick condensation heating layer of Qi.5. Dynamic diagnoses on change-rate of vorticity and divergence for the genesis and development of the "98.7" meso-fi scale heavy rainfall systemThe results from the diagnostic vorticity and vorticity change-rate (vorticity sources) indicated that one of the mainly physical mechanism of the persistent development of the low vortex-shear line was the superposition and coupling of positive vorticity centers over the upper and lower of the regions of Wuhan periphery;diagnoses of the total vorticity sources revealed that there was an almost vertical volume of high positive vorticity sources value generating and maintaining from low to upper levels over Wuhan periphery during the intensive genesis and development of the abrupt heavy rainfall. The vertical structure and evolution of the positive vorticity centers of the formation and development of the vorticitiy were consistent with that of the total vorticity sources, suggesting that the total vorticity sources played important roles in the genesis and development of the mesoscale low vortex, which was also a key dynamic mechanic of the persistent of the mesoscale system of the heavy rainfall. As for the contributions to the vortictiy change-rate, the divergence term was very important below 650hPa, but from 650hPa to 200hPa, vertical vorticity advection term was bigger than divergence term, the value of the horizontal advection was also positive. The divergence term was negative between 450hPa-250hPa, but the twisting term was negative through all the troposphere. Near the surface level, the factors of vertical vorticity and horizontal advection had almost no contribution to the vortictiy change-rate. The time-mean and perturbation of vorticity change-rate played important roles in the genesis of the low vortex at the beginning stage;The relative numeric of the nonlinear interactive vorticity change-rate was the most important component during the intensive development of the rainfall.The results from diagnostic divergence change-rate showed that the genesis and development of strong convergence centers and belt were related to the genesis anddevelopment of mesoscale vortex along shear line during the heavy rainfall. It indicated that the centers and their belt of the negative divergence change-rate in the lower level was in direct related to the genesis and development of mesoscale vortex along shear line by calculating the divergence equation. Moreover, the velocity advection divergence term was very important to the convergence for low level divergence, then the next large contribution was from ageostrophic vortictiy, and their negative belt was corresponding with the rainfall belt. At the same time, the p term in the divergence equation plays minor contribution to the divergence change-rate of the factors, which can be neglected.6. Dynamic diagnoses on frontogenesis and MPV for the genesis and development of the "98.7" Mei-Yu front with the low vortex-shear lineThe diagnoses from the frontogenetical function showed that the existence of frontogenesis nearby the north side of Wuhan-Huangshi played an important dynamic role in the maintenance and development of Meiyu front. Above the surface, the diabatic term was very crucial for the frontogenesis and the deformation and convergence of wind field was important too.The diagnoses of Moist Potential vorticity (MPV) showed that the low level negative MPV was correspondence with the rainfall belt, which indicated the moist symmetric instability was one of the possible mechanism of the convective along the Meiyu front precipitation belt. The heavy rain would be easily happened when the low level pressure was moist static instability and triggered vertical motion induced by moist symmetric instability.o7. A conceptual model of the meso-fi scale heavy rainfall system and study f Quantitative Precipitation Forecast (QPF)MM5.V3 with full moist physics scheme run in two-way interactive triple nest grid domains was used to simulate "98.7" heavy rainfall. Obviously, the simulations improved and the results was better than using two nest grid domains, especially the nest subdomain D03 with 6.6km horizontal resolution better revealed the four dimension thermodynamic and dynamic structure during the genesis and development of meso-p heavy rainfall system, and was able to successful reproduce maximum accumulated precipitation at 60hr and 72hr. We formed a conceptual picture based on to the simulations.The similar model run in two way with quartet nest grid as well as FDDA of analysis nudging was also used to simulate "98.7" heavy rainfall event. It showed that the simulation largely improved than previous simulations in two- and triple- nest grid, especially, the nest subdomain D04 with 2km horizontal resolution was able to simulate more correct heavy rainfall area and precipitation. It further revealed the structures and evolution of the genesis and development on meso-p systems producing intensive heavy rainfall. The simulative results also indicated that the development of a multiple nest technology with high temporal and spatial resolution and the application of FDDA method will be helpful to understand the structure and evolution of the genesis and development on the meso-P severe convective systems in more details, moreover, it willfurther enhance predictive capability for heavy rainfall area and precipitation as well as QPF.8. An investigation of probability on interlink mechanism between tropospheric precipitation and stratospheric ozoneA probability on interlink mechanism was investigated based on a correlation analysis of some observational fact between tropospheric precipitation and stratospheric ozone. Also we showed some relative modeled results using a 3D chemical transport model (CTM) SLIMCAT which is a power tool and world widely used to study ozone in the high- and middle- latitude regions. Furthermore, we made some possible explanations between the connection between tropospheric precipitation and stratospheric ozone. Further studies need to be done on this issue.