This paper addresses and documents a number of issues related to the implementation of an advanced land surface–hydrology model in the Penn State–NCAR fifth-generation Mesoscale Model (MM5). The concept adopted here is that the land surface model should be able to provide not only reasonable diurnal variations of surface heat fluxes as surface boundary conditions for coupled models, but also correct seasonal evolutions of soil moisture in the context of a long-term data assimilation system. In a similar way to that in which the modified Oregon State University land surface model (LSM) has been used in the NCEP global and regional forecast models, it is implemented in MM5 to facilitate the initialization of soil moisture. Also, 1-km resolution vegetation and soil texture maps are introduced in the coupled MM5–LSM system to help identify vegetation/water/soil characteristics at fine scales and capture the feedback of these land surface forcings. A monthly varying climatological 0.15° × 0.15° green ...

https://www.sjsu.edu/people/frank.freedman/courses/metr130/s1/Paper-Chen-and-Dudhia---MWR.pdf

Coupling an Advanced Land Surface–Hydrology Model with the Penn State–NCAR MM5 Modeling System. Part I: Model Implementation and Sensitivity

This paper presents a range of applications of the Regional Atmospheric Modeling System (RAMS), a comprehensive mesoscale meterological modeling system. Applications discussed in this paper include large eddy simulations (LES) and simulations of thunderstorms, cumulus fields, mesoscale convective systems, mid-latitude cirrus clouds, winter storms, mechanically- and thermally-forced mesoscale systems, and mesoscale atmospheric disperision. A summary of current RAMS options is also presented. Improvements to RAMS currently underway include refinements to the cloud radiation, cloud microphysics, cumulus, and surface soil/vegetative parameterization schemes, the parallelization of the code, development of a more versatile visualization capability, and research into meso-α-scale cumulus parameterization.

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A comprehensive meteorological modeling system?RAMS

We tested four land surface parameterization schemes against long-term (5 months) area-averaged observations over the 15 km × 15 km First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) area. This approach proved to be very beneficial to understanding the performance and limitations of different land surface models. These four surface models, embodying different complexities of the evaporation/hydrology treatment, included the traditional simple bucket model, the simple water balance (SWB) model, the Oregon State University (OSU) model, and the simplified Simple Biosphere (SSiB) model. The bucket model overestimated the evaporation during wet periods, and this resulted in unrealistically large negative sensible heat fluxes. The SWB model, despite its simple evaporation formulation, simulated well the evaporation during wet periods, but it tended to underestimate the evaporation during dry periods. Overall, the OSU model ably simulated the observed seasonal and diurnal variation in evaporation, soil moisture, sensible heat flux, and surface skin temperature. The more complex SSiB model performed similarly to the OSU model. A range of sensitivity experiments showed that some complexity in the canopy resistance scheme is important in reducing both the overestimation of evaporation during wet periods and underestimation during dry periods. Properly parameterizing not only the effect of soil moisture stress but also other canopy resistance factors, such as the vapor pressure deficit stress, is critical for canopy resistance evaluation. An overly simple canopy resistance that includes only soil moisture stress is unable to simulate observed surface evaporation during dry periods. Given a modestly comprehensive time-dependent canopy resistance treatment, a rather simple surface model such as the OSU model can provide good area-averaged surface heat fluxes for mesoscale atmospheric models.

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Modeling of land surface evaporation by four schemes and comparison with FIFE observations

The increasing demand by the scientific community, policy makers, and the public for realistic projections of possible regional impacts of future climate changes has rendered the issue of regional climate simulation critically important. The problem of projecting regional climate changes can be identified as that of representing effects of atmospheric forcings on two different spatial scales: large-scale forcings, i.e., forcings which modify the general circulation and determine the sequence of weather events which characterize the climate regime of a given region (for example, greenhouse gas abundance), and mesoscale forcings, i.e., forcings which modify the local circulations, thereby regulating the regional distribution of climatic variables (for example, complex mountainous systems). General circulation models (GCMs) are the main tools available today for climate simulation. However, they are run and will likely be run for the next several years at resolutions which are too coarse to adequately describe mesoscale forcings and yield accurate regional climate detail. This paper presents a review of these approaches. They can be divided in three broad categories: (1) Purely empirical approaches, in which the forcings are not explicitly accounted for, but regional climate scenarios are constructed by using instrumental data records or paleoclimatic analogues; (2) semiempirical approaches, in which GCMs are used to describe the atmospheric response to large-scale forcings of relevance to climate changes, and empirical techniques account for the effect of mesoscale forcings; and (3) modeling approaches, in which mesoscale forcings are described by increasing the model resolution only over areas of interest. Since they are computationally inexpensive, empirical and semiempirical techniques have been so far more widely used. Their application to regional climate change projection is, however, limited by their own empiricism and by the availability of data sets of adequate quality. More recently, a nested GCM-limited area model methodology for regional climate simulation has been developed, with encouraging preliminary results. As it is physically, rather than empirically, based, the nested modeling framework has a wide range of applications.

Approaches to the simulation of regional climate change: A review

This paper uses published work to demonstrate the link between surface moisture and heat fluxes and cumulus convective rainfall. The Earth's surface role with respect to the surface energy and moisture budgets is examined. Changes in land-surface properties are shown to influence the heat and moisture fluxes within the planetary boundary layer, convective available potential energy, and other measures of the deep cumulus cloud activity. The spatial structure of the surface heating, as influenced by landscape patterning, produces focused regions for deep cumulonimbus convection. In the tropics, and during midlatitude summers, deep cumulus convection has apparently been significantly altered as a result of landscape changes. These alterations in cumulus convection teleconnect to higher latitudes, which significantly alters the weather in those regions. The effect of tropical deforestation is most clearly defined in the winter hemisphere. In the context of climate, landscape processes are shown to be as much a part of the climate system as are atmospheric processes.

/pdf/influence-of-the-spatial-distribution-of-vegetation-and-wpcwspo5ja.pdf

Influence of the spatial distribution of vegetation and soils on the prediction of cumulus Convective rainfall

The current study provides an evaluation of thermally induced circulation over flat terrain due to nonuniform horizontal distribution of soil moisture availability. Additionally, the effect of soil moisture availability on the thermally induced upslope flow during the daylight hours is examined. The results indicate that in flat terrain, which has a nonhomogeneous moisture availability, the intensity of thermal circulations approaches that of sea-breeze circulations for the case of large contrasts. Even small amounts of water in thesoil, adjacent to dry areas, can still result in a significant mesoscale flow. The upslope flow has been indicated to be perturbed significantly when the moisture availability ii~creases or when the horizontal contrast of soil moisture availability becomes large.

Evaluation of Soil Moisture Effects on the Generation and Modification of Mesoscale Circulations

The influence of cold pools downstream of mesoscale mountain barriers on downslope winds and flushing is investigated in this study by means of a numerical mesoscale model. The model is compared with existing analytical and numerical solutions. It is found that the numerical model produces phases and amplitudes of nonlinear mountain waves reasonably well. The solutions show that the structure of mountain waves can be modified greatly by the presence of the cold pool. When a cold pool is present downstream of the mountain, the development of a large amplitude mountain wave is inhibited. In the absence of surface heating, downslope winds associated with a mountain wave can be prevented from penetrating the cold pool to reach the surface and flush out the very stable cold air, particularly when the synoptic pressure gradient is oriented so as to continuously replenish the cold air. Results also suggest that shear-induced turbulent mixing at the top of the cold air has little effect on flushing. Base...

Influence of Cold Pools Downstream of Mountain Barriers on Downslope Winds and Flushing

The exact solution of the nonhydrostatic pressure residual (total pressure perturbation minus hydrostatic pressure perturbation) in Defant's linear model is derived. The quasi-nonhydrostatic residual, introduced by Pielke, and the pressure-correction term by Orlanski are compared with the exact residual for varying physical situations. It is found that, within the linear framework, nonhydrostatic effects generally become relatively more important when the environmental stability is near the neutral state and/or the associated horizontal length scale is several kilometers or smaller. The residual components associated with buoyancy and horizontal momentum are the two important physical mechanisms contributing to the generation of nonhydrostatic effects. In a near-neutral environment, a pressure residual must include the horizontal momentum nonhydrostatic residual in order to approximate more accurately the nonhydrostatic effects, while in a sufficiently stable environment the total pressure tends ...

A Method to Determine Nonhydrostatic Effects within Subdomains in a Mesoscale Model

The development of the “midchannel eddy” over the Santa Barbara Channel represents a mesoscale response of the large-scale airflow to the combination of the diurnal heating cycle over land surfaces, the curvature of the coastline, and the orientation of major ridges with respect to the coastline. In this paper we analyze and discuss the results of a numerical simulation of mesoscale airflow over the Santa Barbara Channel and adjacent land areas on 23–24 September 1985, with emphasis upon nocturnal mesoscale eddy development. Simulated winds are compared with SCCCAMP 1985 wind observations. Both simulation and observations indicate inception of a midchannel eddy in the vicinity of Santa Barbara during the late evening of 23 September, followed by westward and southward expansion of the eddy. Our analyses indicate that simulated midchannel eddy development is associated with the following sequence of events: 1) offshore-directed flow develops over coastal ridges in the early evening, associated wit...

A Numerical Study of Mesoscale Eddy Development over the Santa Barbara Channel

An analysis of the mesoscale airflow patterns in the south-central coast air basin (SCCAB) was performed using data collected during the 1985 South-Central Coast Cooperative Aerometric Monitoring Program (SCCCAMP). Airflow within the SCCAB is strongly influenced by the diurnal sea-breeze/land-breeze cycle and by slope flows that develop along the steep terrain. Mesoscale airflow features observed during the four intensive monitoring periods include eddies along the coast and over the Santa Barbara Channel. An analysis of the transport patterns indicated that both recirculation of pollutants within the SCCAB and transport of pollutants from the south coast air basin (SOCAB) contributed to the observed high ozone concentrations on the intensive monitoring days.

Robert C. Kessler

Papers

Evaluation of Soil Moisture Effects on the Generation and Modification of Mesoscale Circulations

Influence of Cold Pools Downstream of Mountain Barriers on Downslope Winds and Flushing

A Method to Determine Nonhydrostatic Effects within Subdomains in a Mesoscale Model

A Numerical Study of Mesoscale Eddy Development over the Santa Barbara Channel

Analysis of Mesoscale Airflow Patterns in the South-Central Coast Air Basin during the SCCCAMP 1985 Intensive Measurement Periods