The heat engine framework is examined in terms of large-scale atmospheric convection in order to investigate several theoretical and modeling issues related to the steady-state convecting atmosphere. Applications of the heat engine framework to convective circulations are reviewed. It is shown that this framework provides fundamental insights into the nature of various atmospheric phenomena and estimates of their potential intensity. The framework is shown to be valid for both reversible and irreversible systems; the irreversible processes' sole effect is to reduce the thermodynamic efficiency of the convective heat engine. The heat engine framework is then employed to demonstrate that the two asymptotic limits of quasi-equilibrium theory are consistent. That is, the fractional area covered by convection goes to zero, σ → 0, as the ratio of the convective adjustment to large-scale time scale (e.g. radiative time scale) go to zero, tADJ/tLS →0 , despite recent arguments to the contrary. Furthermore, the heat engine framework is utilized to develop a methodology for assessing the strength of irreversibilities in numerical models. Using the explicit energy budget, we derive thermodynamic efficiencies based on work and the heat budget for both open (e.g., the Hadley circulation) and closed (e.g., the general circulation) thermodynamic systems. In addition, the Carnot efficiency for closed systems is calculated to ascertain the maximum efficiency possible. Comparison of the work-based efficiency with that of the efficiency based on the heat budget provides a gauge for assessing how close to reversible model-generated circulations are. A battery of experiments is carried out with an idealized GCM. The usefulness of this method is demonstrated and it is shown that an essentially reversible GCM is sensitive (i.e., becomes more irreversible) to changes in numerical parameters and horizontal resolution.

This research extends an observation program that recorded the night airglow from a Tucson ground station using an imaging spectrograph known as GLO. GLO was designed at the Lunar and Planetary Laboratory of the University of Arizona to observe auroral and airglow emissions, and recorded midlatitude airglow data near equinox during Space Shuttle mission STS-69 in September 1995. GLO observations from the shuttle recorded the night airglow layer seen edge on at the Earth's limb. These observations from orbit exhibit a fundamentally different picture of the night airglow compared to observations from the ground. GLO data also represent the first simultaneous optical measurements of airglow emissions over the spectral range from 1150 to 9000 A, showing global emission variations in the night sky. Intensity variations are not correlated among emitting species, implying greater dynamism and more complex chemical interactions in the airglow than previously assumed. Although other researchers have described observations of organized waves and tides in the night airglow, these prior observations are sporadic or averaged over long time periods. The night sky intensity variations recorded by GLO do not exhibit any obvious relationship to atmospheric tides. They may instead be the result of a chaotic superposition of upward and downward vertical motions. This upwelling and subsidence may cause the decoupling of airglow emissions in the O2 Atmospheric band, the OH Meinel band, and the atomic oxygen green line at 5577 A. Emission enhancements with maxima-to-minima ratios of 4 to 12 depending on emitting species, have been observed in the GLO data. Emissions in the O2 Atmospheric band system and the OI (5577 A) green line show a greater dynamic range of variation than the OH Meinel band system. The chemistry along a limited line-of-sight can be explained by classical airglow chemistry, but only over a limited altitude range. Dynamic effects in the 80 to 100 km region are sufficiently chaotic to present mixed results when inferring chemical processes as a function of altitude.

The development and investigation of a new technique for measuring tropospheric concentrations of hydroxyl radicals (OH) is presented. The technique is based on the near-infrared fluorescence of IR125 which is quenched upon reaction with OH. IR125, is shown to react with OH, and be sufficiently less reactive with other tropospheric oxidants that when exposed to tropospheric air samples, changes in the dye fluorescence are related to the ambient OH concentration. A near-infrared fluorimeter was constructed to determine IR125 concentrations. Detection of 10-12 M IR125 in solution was obtained. This sensitivity allows observation of changes in IR125 concentrations due to reaction with typical tropospheric OH concentrations. Changes in the fluorescence of IR125 when sampling the ambient air using dye impregnated quartz wool cartridges were shown to follow predicted OH concentrations for the observed environmental conditions. Photodecomposition by sunlight and reaction with other, longer lived, oxidants were accounted for in determining the IR125 response to OH. An OH source of known concentration to calibrate the IR125 response based on the photolysis of HONO or H2 was constructed. A photochemical computer model developed and used to determine the steady-state OH concentrations was validated by the successful prediction of concentrations of some cogenerated compounds. This OH source was not compatible with the sampling technique using dye impregnated quartz wool cartridges, because of the overwhelming interference caused by suspected heterogeneous reactions of the precursors. Absolute calibration remains to be completed.

The research described in this dissertation is predicted on the hypothesis that remotely sensed information on vegetation cover classes can be used to improve the representation of heterogeneous continental surfaces in global climate models. The problem it addressed was that current understanding of soil-vegetation-atmosphere interactions is considered only to be relevant to small plots of uniform vegetation with dimensions of the order 10-1000 m but, in order to provide realistic simulation of climate, General Circulation Models require description of such interactions for large areas of mixed vegetation with dimensions of the order 100-1000 km. The methods used to investigate this issue was to create and apply a coupled model that provided realistic representation of both surface and atmospheric boundary layer processes, and to use this model to simulate surface-atmosphere interactions with explicit representation of patches of vegetation on the one hand, and with a single, area-average representation of exchanges on the other. These modeling studies were given credibility by initiating and validating the coupled model using appropriate data from the FIFE site in Kansas and the ABRACOS site in Brazil. The results showed that when quite simple aggregation rules are used to derive the effective area-average values of the vegetation-related parameters, these parameters give adequate simulation of surface-atmosphere interactions. These aggregation rules were then applied using remotely sensed maps of land cover to derive parameter values. Significant differences were found in the resulting parameters, and in the surface energy fluxes and modeled climate calculated using those parameters. Thus, it has been shown that remotely sensed data can indeed be used to improve the representation of heterogeneous land surfaces in global climate models using the methods developed in this research, and that using these data significantly alters the simulated global climate.

A Snow-Atmosphere-Soil Transfer (SAST) model has been developed to extend the point snowmelt model to vegetated areas using the parameterization concepts of the Biosphere-Atmosphere Transfer Scheme (Dickinson et al. 1993). The model applications for short-grass and forest fields show that the simulated surface temperature, albedo, and snow depth have close agreement with observations. In addition, because of biases in simulated runoff in the high-latitudes, a Shuffled Complex Evolution (Sorooshian et al. 1993) scheme for automatic calibration has been connected with the SAST model to determine the realistic distribution of runoff components from different soil layers and search the optimized parameter set. The calibrated runoff closely matches observations. Because the Community Climate Model version 3 (CCM3) coupled with the SAST model overestimates snow depth and precipitation and underestimates surface temperature over the Rocky Mountains, remotely sensed snow depth data have been assimilated in the model to alleviate model discrepancies based on energy and mass balances. The improved surface temperature simulations result from the decreased snowmelt and albedo in winter and spring and from the weakened evaporation in summer due to drier soil. Meanwhile, modeled summer precipitation over the Rocky Mountains has a minor improvement. The relationship between the variations of tropical Pacific SST and snowpack anomalies in the western United States (U.S.) has been studied by comparing observations and CCM3 output. The results indicate that in the northwestern U.S., the warm tropical Pacific phase of the El Nino-Southern Oscillation (ENSO) is associated with diminished snowpack while its cool phase is related to enhanced snowpack. This relationship is largely determined by winter precipitation variability for the observations; however, it relies heavily on the variations of temperature due to the biases in atmospheric patterns for the model output. In the southwestern U.S., positive snowpack anomalies for both observations and simulations result from the strong warm phase of the ENSO and negative ones are connected with exaggerated local precipitation in fall.

The North American Monsoon System (NAMS) is an important climatological feature of much of southwestern North America because it is responsible for large portions of the annual rainfall in many otherwise arid and semi-arid environments. This dissertation explores issues related to numerical simulation of the North American Monsoon climate. Simulation studies using both an atmospheric general circulation model (AGCM) and a regional climate model (RCM), forced by model analyzed boundary conditions, are presented. The RCM was run for a single season with three different convective parameterization schemes for a single season to assess the sensitivity to convective representation. The main conclusion from these simulations was that substantial differences in both the time-integrated thermodynamic and circulation structures of the simulated July 1999 NAM atmosphere evolve in the simulations when different convective parameterization schemes (CPSs) are used. All simulations reproduced the maximum of precipitation along the western slope of the Sierra Madre Occidental. However, root mean squared errors and model biases in precipitation and surface climate variables were substantial, and showed strong regional dependencies between each of the simulations. There are large differences in the modeled monthly-total surface runoff between simulations. These differences appear to be more closely related to differences in local, precipitation intensity than to time-average or basin-average intensity. It was found that many features of the North American Monsoon were poorly simulated by the AGCM used in its current configuration when using a yearly repeating cycle of sea-surface temperatures. In particular, the model is unable to simulate the regional patterns of monsoon circulation and rainfall. Modeled rainfall over the southwest U.S. and Mexico is much too low, while tropical precipitation is overestimated. Anomalous sea-surface temperature forcing in the Pacific Ocean also induced model responses that resemble observed responses suggesting that sea-surface temperatures may play a modest role in establishing the monsoon circulation and hence in the generation of monsoon rainfall.

Optical depths at visible and infrared wavelengths obtained in Tucson, Arizona before and after the Pinatubo eruption in June 1991 have been used to investigate the characteristics of the stratospheric aerosols due to the Pinatubo eruption. The intrusion of the Pinatubo aerosols over Tucson first occurred on July 26, 1991 when the spectral optical depth values rose to two to four times their normal values. In general, there was a pattern of increase between June 1991 and April 1992, and a gradual decrease after April 1992. The stratospheric Pinatubo aerosol in April 1992 was characterized by a typical columnar total number density on the order of 8.78 x 106 in the size range of 0.2-0.7 μm. The total number density decreased to the order of 9.28 x 105 by April 1994. Simulations of the size distribution using a simple polydisperse coagulation and fallout model showed that both of the processes played a very important role in the evolution and transport of the particles in the interval from April 1992 to March 1993. A strong seasonal variation was observed in the aerosol optical depth data. The values are higher in the winter and spring and lower in the summer and fall. This variation is explained by more effective transport of particles from the tropics poleward in the winter and spring than in the summer and fall. We also observed that there was a reduction in stratospheric ozone associated with the Pinatubo aerosols, possibly because of the extra sites available for heterogeneous chemical reactions. The reduction was more noticeable in the spring and summer than in other seasons. The magnitude of the ozone reduction was in a good agreement with other studies.

Thirteen years of satellite-based total ozone measurements, extending from January 1979 through December 1991, are analyzed with a multiple regression statistical model to isolate the components of interannual variability associated with (1) linear trends and (2) the 11-year variation in solar ultraviolet irradiance. Lower stratospheric temperature and geopotential height data obtained from satellite- and ground-based sources are analyzed in similarly, providing a comprehensive assessment of the interannual variability in the lower stratosphere over the 1979-1991 period. The results of the statistical analyses indicate coherent variations in ozone, temperature, and geopotential height at extratropical latitudes in NH winter which are related to both the trend and solar-cycle components; the amplitudes of these variations exhibit pronounced spatial dependences. A three-dimensional mechanistic ozone transport model is used to describe the spatial distribution of total ozone in NH winter using observed lower stratospheric temperature and geopotential height fields. Application of this model on a year-to-year basis demonstrates that a large percentage of the observed interannual variability in the spatial distribution of total ozone is directly associated with changes in the dynamical structure of the lower stratosphere. The influence of dynamical variability on zonal mean total ozone is also investigated using an empirical approach. From the results of the observational and modeling studies, it is concluded that changes in the dynamics of the lower stratosphere over the 1979-1991 period have contributed significantly to the observed total ozone trends in the Northern Hemisphere. In contrast, the observed variability in total ozone associated with the 11-year solar cycle could not be explained in terms of a systematic variation in the dynamical forcing of the lower stratosphere in-phase with the 11-year cycle.

This research focuses on the numerical simulation of a rare, high-latitude hail storm observed during the CAGES (Canadian GEWEX Enhanced Study) field experiment. On 11 May 1999, a shortwave trough moved northward from British Columbia and continued its passage over the Northwest Territories. A hail storm developed in an environment of small convective available potential energy. To understand the processes responsible for the formation of the storm, the Canadian Mesoscale Compressible Community Model (MC2) is used to simulate the case. The addition of a second soil type to the lower boundary of the model allows for a realistic simulation of the location and time of the storm. The results indicate that the dynamics associated with the shortwave trough, coupled with diurnal heating effects over the more realistic soil type, produced the weakly-forced hail storm that passed directly over Fort Simpson, Northwest Territories.

The precipitations on meteorological scanning radar may comes from different altitudes and different process. The challenge for operational meteorology is to assess the part of this precipitation which will reach the ground and at what place. Many factors influence the difference between radar data and ground data: partial beam filling, attenuation and beam blocking, bright band enhancement, wind transport of the precipitation, growth or decay of the drops/flakes below the lowest elevation angle of the radar. An important case for operational meteorology is that of light snow aloft whose base has an horizontal slope toward the ground: "snow virgas". I will use the output of two vertical pointing radar in this thesis to find what happens in those trails and try to explain the influencing mechanisms. I will also describe an algorithm that attempts to predict the place where the snow will reach the ground using McGill University scanning radar. My study shows that the slope of the snow virgas is essentially due to the transport by winds in saturated airmasses and evaporation of flakes in unsaturated ones. Finally, finding the slope of the virgas toward the ground, by an automatic algorithm, is extremely difficult on a scanning meteorological radar due to its coarse resolution.