25 research outputs found
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An investigation of flow regimes affecting the Mexico City region
The Mexico City region is well-known to the meteorological community for its overwhelming air pollution problem. Several factors contribute to this predicament, namely, the 20 million people and vast amount of industry within the city. The unique geographical setting of the basin encompassing Mexico City also plays an important role. This basin covers approximately 5000 km{sup 2} of the Mexican Plateau at an average elevation of 2250 m above sea level (asl) and is surrounded on three sides by mountains averaging over 3500 m asl, with peaks over 5000 m asl. Only to the north is their a significant opening in the mountainous terrain. Mexico City sprawls over 1000 km{sup 2} in the southwestern portion of the basin. In recent years, several major research programs have been undertaken to investigate the air quality problem within Mexico City. One of these, the Mexico City Air Quality Research Initiative (MARI), conducted in 1990--1993, was a cooperative study between researchers at Los Alamos National Laboratory and the Mexican Petroleum Institute. As part of this study, a field campaign was initiated in February 1991 during which numerous surface, upper air, aircraft, and LIDAR measurements were taken. Much of the work to date has focused upon defining and simulating the local meteorological conditions that are important for understanding the complex photochemistry occurring within the confines of the city. It seems reasonable to postulate, however, that flow systems originating outside of the Mexico City basin will influence conditions within the city much of the time
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The mutual evolution of mountain waves and katabatic flow
Typically, katabatic flows have been studied in their least complicated or idealized state. Further, these flows are generally regarded as having simple forcing and non-turbulent structure due to the strong atmospheric stability they are bedded within. Somewhat analogously, mountain waves and their effects have been mostly studied in their idealized state, i.e. for constant upstream flow and stability. Even in the numerous cases where these two atmospheric phenomena have been studied in their realistic state, seldom has their mutual interaction been considered. One exception that includes numerical modeling is Gross (1990). The express purpose of this work is to examine how each of these phenomena interact with each other in an evolving nocturnal atmosphere. This work is motivated by observations from the Atmospheric Studies in Complex Terrain (ASCOT) Program which clearly indicate non-idealized behavior in katabatic flows. Although numerous idealized simulations were also completed, discussion here focuses on the most realistic simulations of the case night 3--4 September 1993. This night was dominated by clear skies and light near surface winds. A high pressure system to the southwest of Colorado caused northwesterly flow at {approximately} 7 m s{sup {minus}1} upstream of the Rockies with a Froude number of 0.45 overnight. ASCOT observations indicated that katabatic and mountain wave flow were occurring
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Dynamical processes in undisturbed katabatic flows
Idealized analytical investigations of katabatic slope flows have usually sought to simplify the analysis by either assuming a particular force balance amenable to analytical solution or using integral (or bulk) models. In each case, steady state conditions are evaluated, with occasional exception. Historically, the modeling of idealized katabatic flows has focused analysis of model time where steady state conditions have been achieved. To investigate the true dynamics of evolving undisturbed katabatic flow, the Regional Atmospheric Modeling System (RAMS) is used. As described in Pielke et al (1992) RAMS is a prognostic numerical model that contains the three-dimensional primitive equations in terrain-following, non- hydrostatic, compressible form. In addition to standard variables, RAMS was configured to output the various components of the governing equations with high temporal resolution. Each of the simulations used idealized 2000m high mountain topography of a given slope (1{degree}, 2.5{degrees},5{degrees}, or 10{degrees}) on either side of the peak. In the 3-d simulations this mountain becomes an infinite north-south ridge (cyclic boundary conditions in the N-S direction). Vertical grid spacing was set to 20m for the first 500m {delta}z increases to a maximum of 400 m over 72 grid points to 10.5 km. Horizontal grid spacing was 500 m and the number of east-west grid points was 701, 301, 201 and 201 for the 1 {degree}, 2.5{degrees}, 5{degrees} and 10{degrees} mountains, respectively. Only results from the homogeneous with a vertical structure as follows: 0.0 m s{sup -1} to 3000 m AGL, standard atmospheric {theta} lapse rate of 2.5 K km {sup - 1} to 3000 m AGLl, standard atmospheric {theta} lapse rate of 3.4 K Km {sup -1} above that. The simulations ran for 12 hours after model sunset ({similar_to}1800 MST) so that only longwave radiative effects were active
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Assessing the interaction of mountain waves and katabatic flows using a mesoscale model
This paper has two main purposes. The first is to evaluate the interaction of two common complex terrain meteorological phenomena, katabatic flow and mountain waves. Although occasionally investigated together, generally, the large body of literature regarding them has treated each individually. The second purpose is to show the reader the utility of extracting high time resolution data sets of (1) standard meteorological variables, and (2) seldom used, components of the model equations. Using such time series, significant variability is found in the evolving, clear sky, nocturnal boundary layer, when meteorological variability is generally considered to be at its lowest point diurnally. The approach is to use results from three, 3-d, realistic topography simulations produced by the Regional Atmospheric Modeling System (RAMS). RAMS is a primitive equation mesoscale model formulated in {sigma} coordinates. The model is set up with five nested grids that focus on Eldorado Canyon, which is embedded in the Front Range slope of Colorado. On the finest grid {Delta}x = {Delta}y = 400 m and {Delta}z = 20 m for the lowest 400 m above ground level (AGL). The three simulations were: (1) a realistic simulation; (2) the same as (1) but without radiative forcing (referred to as mountain wave only or MWO) and (3) the same as (1) but without boundary nudging and no initial winds (referred to as katabatic flow only or KFO). The case night is 3--4 Sep 1993 from the Atmospheric Studies in Complex Terrain (ASCOT) 1993 field program near Rocky Flats, Colorado. Both mountain waves and katabatic flows were occurring on this night
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The importance of model resolution for predicting precipitation and runoff in complex terrain
As the demand for limited stores of fresh water grows, optimum use of water resources becomes paramount, especially in arid and semi-arid regions of the world. In order to make the best use of these limited resources, it is important to understand the entire hydrologic cycle in these regions and to be able to explore the potential effects of increased use and of changes in the regional climate. As part of Los Alamos' coupled environmental modeling initiative, the authors are linking a suite of environmental models to simulate the hydrologic cycle within river basins. Their goal is to produce a fully interactive coupling of atmospheric, surface hydrology, river, and groundwater models to allow feedbacks throughout the system. This paper focuses on the interaction between the atmospheric and surface hydrology models. The role of the complex topography in determining the spatial distribution of winter precipitation is investigated through sensitivity tests carried out using different horizontal resolutions in the modeling system
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Regional-scale simulations of the western United States climate
Mesoscale models can provide a sufficiently detailed regional climatology. From these pioneering studies, we were inspired to begin to develop regional climatologies with the Colorado State University Regional Atmospheric Modeling System (CSU-RAMS). Our major goal is to develop a better understanding of the hydrologic cycle in the mountainous, arid west. An advantage of using the RAMS code is that we can generate detailed descriptions of precipitation processes, which will hopefully translate into realistic surface yields of both rain and snow. In the ensuing sections, we first describe the model and its microphysics parameterizations, then continue with our methodology for incorporating large-scale data into the model grid. Preliminary results demonstrating the mesoscale variation of precipitation over the mountainous western US are then presented. The model framework for the present study incorporates a three-dimensional, terrain-following non-hydrostatic version of the code. The simulation includes topography derived from a 5-minute global data set with a silhouette averaging scheme that preserves realistic topography heights. This height data is then interpolated to the model grid. 13 refs., 8 figs
Ranking committees, income streams or multisets
Committee, Income stream, Multiset, Utility, Representable linear order, Risk aversion, D71,
Measuring opportunity inequality with monetary transfers
Equality of opportunity, Inequality measurement, Opportunity sets, D63, D71,