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Ytzhaq Mahrer

Abstract

A numerical model for the prediction of mulched soil temperature has been developed. The model takes into consideration environmental condition as well as physical characteristics of both the mulch material and the soil. The ability of the model to predict the temperature of the mulched and unmulched soil is tested.

It is shown that soil temperatures of a wet mulched soil are significantly increased, primarily due to the elimination of evaporation and partly due to the greenhouse effect of the polyethylene film. In the case of a dry mulched soil the greenhouse effect is dominant. Thus a smaller temperature increase is obtained.

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Ytzhaq Mahrer and Roger A. Pielke

Abstract

A hydrostatic three-dimensional primitive equation model, which includes topography and detailed boundary layer parameterization, has been developed to simulate the lower tropospheric flow overv Barbados on synoptically undisturbed days. Observations indicate that on such days island precipitation shows a distinct nighttime maximum. Using observed data for the initial conditions, the model is fast integrated to a steady-state solution, whereupon a diurnal temperature wave is imposed on the island surface. Three experiments are run: 1) with a realistic representation of the terrain and shape of Barbados, 2) with no terrain but a realistic shape, and 3) with a cross section of Barbados where three-dimensional asymmetries of terrain and coastline are ignored. Results indicate that topography is an important factor in the modification of low-level flow over Barbados, only in a three-dimensional reputation don upward motion develop downwind of the west coast, as observed, and the nocturnal rainfall maximum may be attributed to a moister nighttime low-level environment as compared to the day. Additional meteorological observations are needed to verify certain aspects of the model predictions.

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Ytzhaq Mahrer and Roger A. Pielke

Abstract

Upstream interpolation with a cubic spline is used to integrate the advective terms in a two-dimensional hydrostatic primitive equation model. The model is applied to study the problems of air flow over a mountain, and sea and land breezes. Results are compared against existing numerical models and against an identical model which uses a simple upstream differencing scheme for the advective terms. It was found that under certain atmospheric conditions, where the atmosphere is being continuously forced, accurate results may be obtained near the surface even with the simple upstream scheme. Also it is shown that a sophisticated planetary boundary layer parameterisation is needed in order to obtain accurate results in both the lower and upper troposphere.

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Roger A. Pielke and Ytzhaq Mahrer

Abstract

This paper uses a prognostic equation suggested by Deardorff for the, growth of the planetary boundary layer to close the parameterization scheme for vertical turbulent mixing in the planetary boundary layer. The following major conclusions are obtained:

  1. The prognostic equation for the growth of the planetary boundary layer is much superior to the diagnostic form used earlier by Pielke.

  2. The growth of the planetary boundary layer into a region with substantial vertical shear of the horizontal wind markedly alters the locations of sea-breeze convergence zones.

  3. By improving the boundary layer parameterization scheme given in Pielke, the simulation of vertical turbulent mixing by eddy coefficients which are a function of distance from the ground results in predictions which are as good as those obtained with Deardorff's much more sophisticated model, and agree favorably with those observed during Day 33 of the Wangara experiment.

  4. The effect of decreasing the resolution from 31 levels to 8 levels in the boundary layer parameterization scheme does not seriously degrade the solutions, implying that the scheme discussed in this paper is a useful tool to represent the heated boundary layer in mesoscale models.

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Roger A. Pielke and Ytzhaq Mahrer

Abstract

An improved version of the mesoscale model, originally developed by Pielke (1974), is used to predict the sea breeze circulations over south Florida for a synoptically undisturbed day during the summer of 1973. Radar and surface observations are used to quantitatively verify the model results and to improve our understanding of the physical processes which occur over the region.

Among the improvements to the model are the incorporation of a surface heat budget, longwave and shortwave radiative fluxes, a prognostic equation for the depth of the planetary boundary layer, as well as a more accurate numerical representation of the advective and diffusive terms in the model. Despite these significant changes in the model, however, the predicted sea breeze circulation pattern is still quite similar to the earlier simulations.

Among the conclusions of this study are the following:

1) As shown in earlier experiments, the agreement between predicted convergence zones and shower distribution improves during most of the afternoon. Although the specific locations of shower occurrence cannot be predicted, the general regions of preferred convective rain activity are simulated with skill by the model.

2) The surface winds and temperature predictions have some skill except in or near regions of showers where local cumulonimbus circulations dominate.

3) Mesoscale moisture flux through the approximate cloud-base level is shown to precede the occurrence of rain in the NOAA south Florida cloud seeding area during the morning and early afternoon.

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Roger A. Pielke, Richard T. McNider, Mordecay Segal, and Ytzhaq Mahrer

A modelling approach is presented that appears to have the potential to provide reliable assessments of pollution concentration in coastal zones and complex terrain, where the assumptions behind current operational air quality models often are inadequate. With the use of a numerical mesoscale model (NMM), physically consistent flow fields can be predicted, thereby providing higher spatial and temporal resolution in the meteorological fields than would be available from a limited number of observation points. These predictions are used to calculate mean trajectories of pollutant parcels, as well as to provide quantitative estimates of pollution concentration using two techniques.

One technique, most relevant for point and line sources, uses mean and fluctuating velocities as derived from the mesoscale model in order to estimate the spread of pollutant, while the second, which is applicable mainly to area sources, utilizes the advection-diffusion equation.

Considering the scarcity of meteorological observational data with adequate spatial and temporal resolution along coastal regions and in irregular terrain, the approach outlined in this paper can be supportive and complementary to the conventional observationally oriented air quality assessments. Additionally, this technique can be utilized as a guide in the estimation of the optimal spatial resolution required in applied and research-oriented air quality observation networks.

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