John J. Carroll

The spatial variation of ozone climatology on the Western slope of the Sierra Nevada

Abstract The spatial variability of ozone climatology is described for six remote sites on the western slope of the Sierra Nevada. A statistical analysis was applied to determine relationships between ozone concentrations and atmospheric variables, as well as relationships among sites. The sites, whose locations vary in latitude, elevation, and topography, show considerable variability in climatological patterns and statistics. However, the stations fall into two general groups: those with a distinct diurnal ozone pattern and those with a flat diurnal ozone pattern. Diurnal variations among sites appear to depend primarily on topographic setting rather than on remoteness from urban sources.

Potential impacts of climate change on citrus and potato production in the US

Abstract Potential impacts of global climate change on fruit and vegetable yield in the US were investigated through simulations of citrus and potato. Simulated treatments included combinations of three increased temperature regimes (+ 1·5, + 2·5 and + 5·0°C), and estimates of the impact of three levels of atmospheric carbon dioxide (440, 530, and 600 ppm) in addition to control runs representing current climatic conditions. Adaptive planting dates of −28, −14, + 14 and + 28 days were included in the potato simulations for current and increased temperature regimes. Twenty-two sites were simulated for citrus yields and 12 sites for potato, using climate records from 1951 to 1980. Response surfaces were developed for all combinations of increased temperature and CO 2 . Results of citrus simulations without CO 2 -induced yield improvement indicate that production may shift slightly northward in the southern states, but yields may decline in southern Florida and Texas due to excessive heat during the winter. CO 2 effects tended to counteract the decline in simulated citrus yields. Fall potato production under current management practices appears vulnerable to an increase in temperature in the northern states; increased CO 2 and changes in planting date were estimated to have minimal compensating impacts on simulated potato yields.

Relationships of ozone exposure to pine injury in the Sierra Nevada and San Bernardino Mountains of California, USA.

Hourly ambient ozone exposure data and crown injury measurements were gathered in the Sierra Nevada and San Bernardino Mountains of California to develop relationships between the Ozone Injury Index (OII), the Forest Pest Management Index (FPM), chlorotic mottle, fascicle retention (OII index components) and cumulative ambient ozone indices for Pinus ponderosa Dougl. ex Laws and Pinus jeffreyi Grev. and Balf. Eleven sites located in the mixed conifer forest near ambient ozone monitoring sites were evaluated annually for 4 years. Four other sites in the San Bernardino Mountains were evaluated for 1 year. Analyses showed OII to be functionally equivalent (r2 = 0.96) to the FPM, and to depend only on fascicle retention and chlorotic mottle (R2 = 0.95) of the fourth whorl (or if four whorls are not present at the site, then the last whorl present for the majority of trees). Significant associations were found between OII and 4-year 24-h. summer SUM0, SUM06, W126 and HRS80 ozone indices. Three sites had higher levels of cumulative chlorotic mottle for individual whorls and larger numbers of trees with visible crown injury than other sites with similar cumulative ambient ozone levels. Including an indicator variable to discriminate between these two groups of sites increased R2 and decreased root mean square (RMSE) for all indices, especially SUM0 (R2 = 0.93, RMSE reduced by 46%).

Global transmissivity and diffuse fraction of solar radiation for clear and cloudy skies as measured and as predicted by bulk transmissivity models

Abstract Measurements of cloudiness and of global, direct, and diffuse radiation taken over a 13 mo period at Davis, CA, are analyzed in terms of global transmission (Kt) and diffuse fraction (Kd) for clear sky conditions and for various cloudiness conditions. A number of global transmission clear sky models are compared with observations for ranges of total water column and turbidity and some are found to give representative values for the global radiation at the ground. The dependence of the diffuse fraction on global transmission is found to be best represented by linear formulae—with different dependencies found for clear and cloudy conditions. Global transmission models are also compared with observations for cloudy conditions and found to give representative values of cloud transmissivities if climatological differences in the cloudiness at the measurement site and those sites used to calibrate the cloud models are considered. These results support the use of routine instantaneous surface meteorological data to calculate the most likely instantaneous global and diffuse radiation on a horizontal surface in the absence of any radiation measurements. These calculated irradiances are best used for solar energy system dynamic modeling in which system responses to typical sequences in meteorological conditions are being examined.

Agroclimatic modeling for the simulation of phenology, yield and quality of crop production. I. Citrus response formulation

This paper describes the development of basic simulation concepts that can be used in models aimed at forecasting. The objective is to demonstrate the utility of considering the crops basic environmental requirements or “climatic normals” in producing a self-contained comprehensive model. We seek to develop a model in which regularly measured weather data can be used to provide information on the crop performance. Following an abbreviated overview of modeling alternatives, the model design is described. The results of this study are a set of criteria and functions needed to predict the temporal evolution of phenological stages, fruit growth, fruit maturation, and fruit coloration for two varieties of oranges (Navel and Valencia). The major factors considered are the effect of temperature and solar radiation on flowering time, and flowering duration and the number of flowers; the effect of past stress, temperature, evaporation, wind, and rain, planting density, and tree age on fruit set. Given the number of fruits set, growth, maturation and coloration are modeled as responding primarily to temperature and water balance. Possible damage due to freezes is also modeled. These form the basis of a time dependent model (reported elsewhere) which uses daily air temperature and wind data for the prediction of these quantities. These criteria and functions are derived from an extensive body of published observations from many parts of the world, and are selected to be variety specific and independent of local climatology or other site-specific effects.

Comparison of leapfrog, Smolarkiewicz, and MacCormack schemes applied to nonlinear equations

Abstract The MacCormack scheme is a finite-difference scheme widely used in the aerospace simulations. It is a two-step algorithm, and contains a small amount of implicit numerical diffusion that makes it numerically stable without having to use any explicit filtering. It uses a nonstaggered grid. A detailed comparison with the leapfrog and Smolarkiewicz schemes is presented using the nonlinear advection equation and the Euler equations for a variety of conditions at different Courant numbers. Of the schemes tested, the unfiltered leapfrog is the least acceptable for the solution of nonlinear equations. Although it is numerically stable for linear problems, when used to solve nonlinear equations (without using any explicit filtering) it becomes numerically unstable or nonlinearly unstable. Furthermore, it introduces large phase errors, and produces better results with small Courant numbers. The MacCormack scheme is nonlinearly stable, produces modest amounts of numerical dispersion and diffusion, has no p...

Agroclimatic modeling for the simulation of phenology, yield and quality of crop production

In our previous paper of this series, a set of criteria and functions were formulated to predict the temporal evolution of phenological stages, fruit growth, and fruit maturation for two varieties of oranges: Navel and Valencia. The present paper reports the development of a working model employing these criteria and functions, and an evaluation of the performance of the model. The model is capable of simulating the effects of management practices, such as fertilizer application or disease and pest control, but in the simulations reported here, only the local meteorologial effects are modeled. Available observations of the time of flowering and the time of maturity are compared with model predictions of these parameters in a variety of climatic regions for which daily meteorological data are available. The model tends to initiate flowering about a week earlier than observed. The time to maturity is predicted to be well within the observed range of this parameter in each climatic region. Simulation of fruit growth also agrees well with observations, but with a tendency to continue higher than observed growth rates at maturity, resulting in about a 9% over-estimate of final fruit size. Simulation of 20 years of average yields in several climatically diverse regions compare quite well with observed yields when the meteorological data is complete and representative of the whole region, when the bearing acreage in the region is stable and the region itself is homogeneous. Major climatic events and their effects on yield are well represented in the model. Average yields are slightly higher than observed, a result of excessive growth rates in the final stages, and the interseasonal variation is smaller in the model than in the observations, a result of using average, conservative functions to simulate real processes.

Application of the MacCormack Scheme to Atmospheric Nonhydrostatic Models

Abstract In a previous paper, the authors discussed the numerical properties of the MacCormack scheme, a finite-difference technique widely used in aerospace simulations. Here the authors report results of its application to the simulation, in two dimensions, of the development of a fully compressible buoyant bubble. The model uses the fully compressible Navier-Stokes equations applied to an inviscid, adiabatic atmosphere. It uses a nonstaggered grid. Both lateral and top boundary conditions are open and essentially reflection-first. The model produced reasonable solutions with no explicit numerical filtering. In regions with locally steep gradients, the MacCormack scheme produces numerical oscillations that locally distort the solution but do not lead to numerical unstability. These results are compared with those of Droegemeier and of Carpenter et al., who show results using a filtered staggered leapfrog scheme. The fields computed by both schemes are very similar, with those, from the filtered leapfrog...

The dependence of open field burning emissions and plume concentrations on meteorology, field conditions and ignition technique

A program of field and laboratory measurements of emissions from the burning of agricultural residues (primarily cereal straw and stubble) and plume behavior is described. Relationships investigated include the dependence of total emissions and plume concentrations on fuel management, field ignition technique and ambient meteorological conditions. Total particulate emissions (by mass) were found to increase strongly with increasing residue moisture content but are reduced to one half through the use of a backfire field ignition technique versus the head fire ignition method. Increased emissions from headfires is attributable to smoldering in the burned over areas. Backfire fuel consumption rates are typically about one-fifth that for headfires, resulting in a further reduction of particle concentrations in backfire plumes. Increased fuel loading reduces emissions, especially for headfires. The mass median diameter of particles from either fire ignition technique is less than 0.2 μm and in the average about one half of these particles are chloroform soluble. CO and gaseous hydrocarbon emissions were also found to be directly proportional to residue moisture content, but independent of field ignition technique. Plume rise is maximized (ground level concentration minimized) by using headfires in light winds (<4 m s−1). At higher wind speeds, limited plume rise and increasing fumigation increases ground level concentrations but this can be minimized through the use of backfires. As the effluent plume ages, the size spectrum shifts to smaller diameters suggesting significant evaporation with time. The results of fuel drying studies and cost analyses for the various techniques are also presented.

A High-Resolution Air Pollution Model Suitable for Dispersion Studies in Complex Terrain

Abstract The development of an air pollution transport model that uses an expanding terrain-following coordinate with high resolution in analytic form near the surface and a high-order accurate transport algorithm is described. The model is designed to be internally consistent in the application of numerical methods, computationally efficient, and suitable for pollutant dispersion studies in complex terrain. The application of the time-splitting Warming–Kutler–Lomax advection scheme is examined in both rotational and deformational flows for its conservation and stability properties. It is found that the combination of this scheme with a short-wave filter makes the integration mass conserving and dispersion free. The model is applied to some hypothetical cases that represent the typical phenomena occurring over mountains. The model proves to be capable of simulating realistic planetary boundary layer structure and stability variation, hydrostatic mountain waves, thermally induced mountain–valley winds, and...