A dissertation posted in partial fulfilment

of Doctor’s Amount of Philosophy in Meteorology

Department of Meteorology

A nonhydrostatic mesoscale statistical model is developed and simulations of numerous mesoscale phenomena by using this model are described.

The model is dependant on a quasi-nonhydrostatic equation system within the normalized pressure-sigma coordinates. The machine is freed from vertical seem waves but contains Lamb wave modes that are however considerably retarded in nonhydrostatic regime. An integration time step similar to those of an anelastic model system may be used when grid length is about a couple of kilometres. The present model includes also parameterized microphysical processes.

The answer process of the model is similar to that particular of the anelastic system in terrain-following height-coordinates. An elliptic equation needs to be solved for that geopotential height perturbation. Conventional finite differencing techniques are utilized with the exception of the advection of thermodynamical variables, in which the flux-remedied transport plan (FCT) is utilized. FCT eliminates the issue of ‘negative water’ generation and considerably increases the model precision. Radiative the weather is applied in the lateral limitations, and also at top of the boundary radiative condition is simulated by an absorbing layer. Subgrid scale turbulence is parameterizd while using deformation and Richardson number dependent formulation. Three water phases, i.e. water vapour, cloud water and rain water, can be found within the model with Kessler’s microphysics parameterizations being adopted.

Numerous two dimensional mesoscale troubles are studied while using model. They include, dry and moist gravity waves and related phenomena in stratified air streams flowing on the 2-D ridge, lengthy-resided squall line systems and deep orographic convection.

First of all, the model solutions of small amplitude mountain gravity waves in a variety of regimes are verified against analytical solutions and good agreement is located. The model will be accustomed to simulate the 1972 Boulder severe downslope windstorm and also the results lend further support to Smith’s nonlinear flow transition mechanism of severe downslope winds. Two occasions of mountain lee waves which happened within the west from the Uk will also be studied. The lee wave patterns observed from satellite are very well reproduced, and in addition, the results of mountain height and scales, orography spectrum and moisture condensation around the formation and evolution of trapped lee waves and connected clouds are examined.

A number of simulations of lengthy-resided squall lines is conducted which demonstrate particularly the function from the interaction between cold pool output and occasional-level ambient inflow, and also the mechanism through which this kind of interaction determines and maintains an ideal condition of squall line convection. It’s proven that it’s the momentum as opposed to the vorticity within the inflow that plays the important thing role. An ideal condition which are more intense, lengthy-lasting squall lines is suggested in line with the propagation speed from the cold pool. The sensitivities of convection to using FCT plan, to spatial resolution and also to diffusion will also be examined.

Deep orographic convection can also be studied while using sigma-coordinate model.

The Large Thompson storm that continued to be quasi-stationary around the upwind slope from the Front Selection of the Rocky Mountain tops and caused flash floods is simulated. A powerful and quasi-stationary storm is acquired when a remote orography profile can be used. A plateau type mountain is located to create fast-moving storm systems that is described with regards to the cold output strength. Experiments showing the result of modifications for an ambient sounding will also be presented and lastly the limitations of two-dimensionality around the storm simulations discussed.

Table of Contents

Chapter 1. General Introduction and also the Quasi-Non-Hydrostatic Equation System (PDF format ) (PS format )

Chapter 2. Model Equations and Statistical Formulation of Dynamic Processes (PDF format ) (PS format )

Chapter 3. Thermodynamics, Cloud Microphysics and Subgrid Scale Mixing (PDF format ) (PS format )

Chapter 4. Dry and Moist Flow over 2-D Orography: Mountain gravity waves and severe downslope winds (PDF format ) (PS format )

Chapter 5. Strong, Lengthy-resided Squall Lines: Two Dimensional Statistical Experiments (PDF format ) (PS format )

Chapter 6. Deep Orographic Convection: Statistical Study The Large Thompson Storm (PDF format ) (PS format )

Appendix A A short description from the leapfrog-trapezoidal transport formula, References yet others (PDF format ) (PS format )

This thesis could be referenced as:

Xue, M. 1989: A nonhydrostatic statistical model in sigma-coordinates and simulations of mesoscale phenomena. Ph.D thesis, Dept. of Meteorology, Studying College, 258pp.

You may also download the PDF and PS files from ftp://twister.ou peut-rrtre un.edu/pub/mxthesis .

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