Shouting Gao

Cloud-resolving modeling of convective processes

Preface.- Introduction.- 1. Model and Physics.- 2. Analysis Methodology.- 3. Comparison between Simulations and Observations.- 4. Surface Rainfall Processes.- 5. Tropical Cloud Clusters.- 6. Cloud Radiative and Microphysical Processes.- 7. Convective, Moist and Dynamic Vorticity Vectors.- 8. Diurnal Variations of Tropical Oceanic Convection.- 9. Precipitation Efficiency.- 10. Air-Sea Coupling.- 11. Climate Equilibrium States.- 12. Remote Sensing Applications.- 13. Future Perspective of Cloud-Resolving Modeling.- Abbreviations and Acronyms.

Impacts of Ice Microphysics on Rainfall and Thermodynamic Processes in the Tropical Deep Convective Regime: A 2D Cloud-Resolving Modeling Study

Abstract The effects of ice microphysics on rainfall and thermodynamic processes in the tropical deep convective regime are examined based on hourly zonal-mean data from a pair of two-dimensional cloud-resolving simulations: one simulation with ice clouds and the other without ice clouds. The model is integrated for 21 days with the imposed large-scale vertical velocity, zonal wind, and horizontal advections obtained from the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment. The experiment without ice clouds produces a larger amount of cloud water and a smaller surface rain rate than the experiment with ice clouds because of the exclusion of vapor deposition processes in the experiment without ice clouds. The experiment without ice clouds produces cold and moist states simply because it generates a smaller cloud heating rate and consumes a smaller amount of vapor than does the experiment with ice clouds.

Effects of Diurnal Variations on Tropical Equilibrium States: A Two-Dimensional Cloud-Resolving Modeling Study

Abstract Effects of diurnal variations on tropical heat and water vapor equilibrium states are investigated based on hourly data from two-dimensional cloud-resolving simulations. The model is integrated for 40 days and the simulations reach equilibrium states in all experiments. The simulation with a time-invariant solar zenith angle produces a colder and drier equilibrium state than does the simulation with a diurnally varied solar zenith angle. The simulation with a diurnally varied sea surface temperature generates a colder equilibrium state than does the simulation with a time-invariant sea surface temperature. Mass-weighted mean temperature and precipitable water budgets are analyzed to explain the thermodynamic differences. The simulation with the time-invariant solar zenith angle produces less solar heating, more condensation, and consumes more moisture than the simulation with the diurnally varied solar zenith angle. The simulation with the diurnally varied sea surface temperature produces a colde...

Precipitation Modeling and Quantitative Analysis

-Precipitation Modeling with Cloud-Resolving Model.- -Precipitation Equations and Process Analysis.- -Tropical Precipitation Processes.- -Effects of Sea Surface Temperature.- -Effects of vertical wind shear.- -Microphysical and Radiative Effects of Ice clouds.- -Cloud Radiative Effects.- -Precipitation Efficiency.- -Sensitivity of Precipitation Modeling to Uncertainty of Initial Conditions.

Time-Expanded Sampling for Ensemble Kalman Filter: Assimilation Experiments with Simulated Radar Observations

A time-expanded sampling approach is proposed for the ensemble Kalman filter (EnKF). This approach samples a series of perturbed state vectors from each prediction run not only at the analysis time (as the conventional approach does) but also at other time levels in the vicinity of the analysis time. Since all the sampled state vectors are used to construct the ensemble, the number of required prediction runs can be much smaller than the ensemble size and this can reduce the computational cost. Since the sampling time interval can be adjusted to optimize the ensemble spread and enrich the ensemble structures, the proposed approach can improve the EnKF performance even though the number of prediction runs is greatly reduced. The potential merits of the time-expanded sampling approach are demonstrated by assimilation experiments with simulated radar observations for a supercell storm case.

A Theoretical Study of Cold Air Damming with Upstream Cold Air Inflow

Abstract The previously developed two-layer model of cold air damming is extended to include upstream cold air inflow. The upper layer is an isentropic cross-mountain flow. The lower layer is a cold boundary layer flow partially blocked by a two-dimensional mountain with a cold dome formed on the windward side of the mountain. The interface represents a sloping inversion layer coupling the two layers. The shape of the interface can be approximated by a cubic polynomial, and the interfacial coupling condition yields a set of algebraic equations that quantify the scale and intensity of the dammed flow as functions of the external parameters characterizing the environmental conditions. It is found that the cold dome shrinks as the Froude number increases or, to a minor degree, as the Ekman number decreases or/and the upstream inflow veers from northeasterly to southeasterly (with respect to a longitudinal mountain to the west). The mountain-parallel jet speed increases as the Ekman number decreases or/and th...

On the parameterization scheme of gravity wave drag effect on the mean zonal flow of mesosphere

Based on McFarlane’s parameterization scheme of gravity wave drag, a refined gravity-wave-drag scheme is presented. Both the drag effect of the momentum flux and the dissipation effect of gravity wave breaking on the mean zonal flow are included in the refined parameterization scheme. The dissipation effect can be formulated with the gravity wave numbers and the mean quantities. The refined parameterization scheme may represent a complete drag effect of stationary gravity wave breaking on the mean zonal flow.

An Analytic Model of Cold Air Damming and Its Applications

Abstract It is shown that the geometric shape of the cold dome in the two-layer model of cold air damming of Xu can be described approximately by a cubic polynomial and thus a set of coupled algebraic equations can be derived to quantify the scale and intensity of cold air damming as functions of the external parameters that characterize the environmental flow. In particular, these functions are easily computed and plotted in the parameter space, showing quantitatively how the cold dome width (scaled by the Rossby radius of deformation) and mountain-parallel jet speed change with the Froude number, surface roughness, inertial aspect ratio, and incident angle of the upstream inflow. The results also show that the cold dome width and mountain-parallel jet speed are insensitive to the depth of the upper-layer cross-mountain flow if the cross-mountain flow is sufficiently deep. The surface roughness and inverse inertial aspect ratio are found to have nearly the same control on the cold dome width and mountain...

A Diagnostic Study of the Asymmetric Distribution of Rainfall during the Landfall of Typhoon Haitang (2005)

The precipitation during landfall of typhoon Haitang (2005) showed asymmetric structures (left side/right side of the track). Analysis of Weather Research and Forecasting model simulation data showed that rainfall on the right side was more than 15 times stronger than on the left side. The causes were analyzed by focusing on comparing the water vapor flux, stability and upward motion between the two sides. The major results were as follows: (1) Relative humidity on both sides was over 80%, whereas the convergence of water vapor flux in the lower troposphere was about 10 times larger on the right side than on the left side. (2) Both sides featured conditional symmetric instability [MPV (moist potential vorticity) <0], but the right side was more unstable than the left side. (3) Strong (weak) upward motion occurred throughout the troposphere on the right (left) side. The Q vector diagnosis suggested that large-scale and mesoscale forcing accounted for the difference in vertical velocity. Orographic lift and surface friction forced the development of the asymmetric precipitation pattern. On the right side, strong upward motion from the forcing of different scale weather systems and topography caused a substantial release of unstable energy and the transportation of water vapor from the lower to the upper troposphere, which produced torrential rainfall. However, the above conditions on the left side were all much weaker, which led to weaker rainfall. This may have been the cause of the asymmetric distribution of rainfall during the landfall of typhoon Haitang.

An experiment study of lee vortex with large topography forcing

This paper, relates the lee vortex which is triggered when the rotating and stratified flow passes over the large obstacle by using towing tank and based on the similarity. The results show that Froude number Fr is the most important parameter, and, in the rotating case, the lee vortex is easily triggered, because the rotating may, on one hand, lead to downward flow, on the other hand, induce lee vortex through generating geostrophic vorticity. Even in the non-rotating case, the lee vortex can be still formed, as long as both Froude number Fr and stratification parameter N are appropriate. For the formation mechanism of the lee vortex, there are obvious differences in the rotating case compared with the non-rotating case. In the non-rotating case, the tilting term of the perturbation vorticity is a dominant factor of inducing the lee vortex. However, in the rotating case, effect and the convergence of perturbation vorticity are dominant factors.