Upper air soundings taken every three hours are used to examine a cold front of average intensity over a period of 24 hours. Vertical cross sections of potential temperature and wind and horizontal analyses are compared and adjusted until they are consistent with one another. These analyses are then used to study the evolution of the front. The front is found to consist of a complex system of fronts occurring at all levels of the troposphere. Low level fronts are strongest at the surface and rapidly weaken with height. Fronts in the middle and upper troposphere are much more intense. The warm air ahead of the fronts is nearly barotropic while the cold air behind the fronts is baroclinic through deep layers. A deep mixed layer is observed to grow in this cold air. Examination of cross sections of potential temperature and potential vorticity indicates that the air in at least the upper portions of the upper level fronts originates in the stratosphere. No evidence is found, however, of an extrusion of stratospheric air to very low levels. Diabatic processes seem to destroy the extrusion as it descends. The structure of the upper level fronts is complex. These fronts are observed to split apart, recombine, and descend to low elevations. This descent is due to the incorporation into the front of pre-existing stable/baroclinic layers. An equation for parcel-following frontogenesis in isentropic coordinates is developed and applied. No single process was found to be dominant in changing frontal intensity. Frontogenesis occurs on the leading edge of the fronts and frontolysis on the trailing edge. The magnitudes of the computed frontogenesis decrease downstream from the axis of the upper level trough. Isentropic trajectories are constructed in order to verify the computed values of parcel-following frontogenesis. Poor correlations are found between the computed and trajectory-following values of frontogenesis. This is believed to be due to nonlinearities in the field of frontogenesis and to errors in the trajectories. Such nonlinearities cast doubt on the usefulness of conventional data for the study of frontogenesis. Vertical velocities are computed using a kinematic technique. Reasonable fields of vertical velocity are obtained in the vicinity of the fronts and jet streaks. Good correlations are found between the vertical displacement between endpoints of the trajectories and the value of computed vertical velocity integrated over the path of the trajectory. The field of vertical velocity is also found to be highly nonlinear. / Graduation date: 1977

The numerical analysis of thermal convection in porous media, heated from below, and assuming Darcy flow conditions, involves the solving of a set of non-linear equations for the temperature and flow fields. The condition of criticality determining the onset of convection is obtained by linearization and the solving of an eigenvalue problem of the fourth order. The smallest eigenvalue represents the critical Rayleigh number. The shape of the critical temperature and flow fields is then obtained from the linear set. In most practical cases, the problem setting is such that closed analytical solutions cannot be derived. The difficulties of solving the convection equations can be overcome by using the Galerkin finite-element method. The method allows the solution of both the linear set and also the more complete non-linear set of equations at various boundary conditions and taking variations in the material parameters into account. In this thesis, the Galerkin method is used to solve the convection equations for infinitely long porous vertical or semi-vertical slabs with prescribed temperatures at the top and bottom surfaces. The first set of models investigated involve boundary walls that are impermeable to the fluid but perfectly conducting to heat. The critical Rayleigh numbers and critical temperature and flow fields are obtained for such slabs with various aspect ratios. The results show that the critical number is raised by 200 to 400% as compared with published data for similar slabs with thermally non-conducting walls. The results are generalized by investigating cases of slabs with (1) three types of vertically varying permeability, (2) by taking the temperature dependence of the fluid properties into account, (3) by including non-linear terms, and finally, (4) a few cases of slabs with boundary walls of finite thermal conductivity are investigated. The results are applicable to a number of situations in geothermal areas. A brief discussion of two such cases is given, that is, (1) the estimating of the critical permeability profile for the East geothermal field in the Imperial Valley and (2) the computation of a temperature cross section in the Cumali geothermal field in Turkey. / Graduation date: 1979

Data assimilation in Numerical Weather Prediction (NWP) optimally blends observations with atmospheric model data in order to obtain the best possible initial state for an atmospheric model prediction. Specification of error characteristics is an important part of data assimilation. This thesis is concerned with representation of background error standard deviations, with handling of observations, and with observation error characteristics. The research includes both the study of basic assimilation problems within the framework of an idealised quasi-geostrophic model and the development of assimilation algorithms for a full scale limited area high resolution forecasting system. It is shown in this thesis that an accurate representation of background error standard deviations is important for the quality of NWP forecasts. In particular the effect of introducing a time-dependency is investigated and a novel approach to relate the flow-dependency of background error standard deviations to an Eady baroclinic instability measure is developed. The Eady based flow-dependent background error representation is demonstrated to have a positive impact on NWP, as compared to horizontally and temporally independent background error statistics. An alternative method, based on on-line error estimation and maximum likelihood theory, is proven to be able to represent the flow-dependency of background error standard deviations and encouraging results are obtained within the quasi-geostrophic model framework. Furthermore, it is shown that a proper observation handling is an important part of data assimilation. The treatment of error characteristics is specifically shown to be of major importance when exploiting the potential benefit of radar radial wind observations within data assimilation.

The methods previously used to determine the momentum and kinetic energy of throughfall drops in the field do not account for the drop's shape at impact or for the variations of the drop's velocity caused by chaotic air currents. The drop's shape at impact is critical because it influences the drop's measurable momentum, kinetic energy, impact force, and the amount of soil that can be displaced by the falling water drop. Since the momentum and kinetic energy of raindrops and throughfall drops are used as indices of soil particle displacement the most accurate momentum and kinetic energydata would be required to produce the most accurate estimate of soil particle displacement. The purpose of this project was to develop and utilize a simple digital electronic instrument which could be used in the field to directly measure the momentum of throughfall drops and raindrops. The instrument consisted of a voltage amplifier, voltage comparator, reference voltage, digital counting circuit and a digital display. The instrument was activated by an impact sensor constructed from an 8.0 ohm, 5.0 inch diameter audio speaker. A falling water drop's momentum was quantified as the amount of time (milliseconds) that the speaker's amplified voltage exceeded the reference voltage. The instrument displayed the drop's momentum as a function of time which was recorded and later converted into units of momentum (g*m/s) by an empirically determined calibration curve. The instrument was utilized in Benton County, Tennessee by measuring raindrop momenta during a single storm event and the throughfall drops produced by commercially planted loblolly pine trees and indigenous deciduous trees. The substitution of the loblolly pine for the deciduous trees represents a human induced change of the vegetation which could have an impact on the drainage basin's erosional characteristics. The purpose of the investigation was to determine if there were any differences between the sample means. The sample having the highest mean momentum would have the greatest potential to dislocate soil particles and cause subsequent soil erosion. The analysis of the sample data revealed that both of the throughfall drop momentum sample means (evergreen: 0.602 g*m/s, deciduous: 0.355 g*m/s) were greater than the raindrop momentum sample mean, 0.02 8 g*m/s. The differences between the sample means suggested that the throughfall drops have a greater potential to displace soil particles and cause subsequent soil erosion than the raindrops that produced the throughfall drops. Also, the evergreen throughfall drop momentum sample had the highest mean of the three samples, indicating that the evergreen throughfall drops had the greatest potential to displace soil particles. The nonparametric Wilcoxon rank sum test was used to determine if the samples' respective population means were equal. The results of the Wilcoxon test indicated that both of the throughfall drop momentum population means were greater than the raindrop momentum population mean, thus reaffirming the results of the sample data analysis. However, the test indicated that the throughfall drop momentum population means were equal, suggesting that the evergreen and deciduous throughfall drops have equal potential to dislocate soil particles and cause subsequent soil erosion.

The urban heat island is an area restricted to a city center where the temperatureis higher than its surrounding environment. The greatest temperature difference isfound at night when the weather is calm and the sky is clear of clouds. There are twomajor causes behind this phenomena and the first one is the use of energy forheating of houses. The heat leaks through the walls of the buildings and warms upthe surrounding mass of air. The second one is the use of building material whichstore the suns radiation on daytime and releases the heat during night. The heatisland leads to larger costs for cooling buildings. It also has an effect on humanhealth, since increased temperatures lead to heat stress which may be fatal. Thisreport aims to investigate if there is an urban heat island located over Uppsala cityand how it can affect daily life for the citizens. To find out how big the urban heatisland effect is in Uppsala city, a number of temperature measurements whereconducted. The results show that there is a visible temperature difference betweenurban and rural areas.

In the atmosphere vertical extended layers that are in the state of super saturation with respect to ice can appear; these layers have been termed ice-supersaturated layers (ISSL). If an aircraft passes through an ISSL, persistent condensation trails can form. These contrails absorb the long wave radiation from the earth and reflect the incoming short wave radiation from space. The absorbing effect of the long wave radiation is although greater than the reflecting effect of the short wave radiation and therefore these contrails increase the greenhouse effect.This study contain statistics of when ice-supersaturated layers occur in the Swedish airspace, based on data from balloon soundings that take place each day at four locations in Sweden. The soundings that are used in this report were carried out from January 2006 to December of 2010. The results show that ISSL are more common in the Swedish airspace than expected. The layers are by average 42 hPa thick, located at the height of 339 hPa and are present in 44 % of the soundings. / I atmosfären kan det uppkomma vertikalt utsträckta skikt som är övermättade med avseende på is; dessa lager har blivit benämnda som ice-supersaturated layers (ISSL). Om ett flygplan flyger igenom dessa ISSL luftmassor kan permanenta kondensationsstrimmor bildas.Dessa kondensationsstrimmor absorberar den långvågiga strålningen från jorden och reflekterar den inkommande kortvågiga strålningen från rymden. Den absorberande effekten är större än den reflekterande effekten, vilket bidrar till en förstärkning av växthuseffekten. Den här studien innehåller statistik för när dessa ISSL uppkommer i det Svenska luftrummet, baserat på data från ballongsonderingar som var utförda från Januari 2006 till December 2010. Resultatet från denna statistik visar att ISSL är mer vanliga i det Svenska luftrummet än förväntat. Lagren är i medeltal 42 hPa tjocka, placerade på 339 hPa höjd och förekommer i 44 % av sonderingarna.

Thesis (M.S.)--Texas A & M University, 2003. / "Major Subject: Meteorology." Title from author supplied metadata. Includes bibliographical references.

Thesis (M.S.)--Brigham Young University. Dept. of Electrical and Computer Engineering, 1999. / Includes bibliographical references (p. 129-131).

No description available.

The application of the thermal wind equation to daily analysed data provides the basis for computed ageostrophic wind fields. The numerical integration used in computing the geostrophic wind avoided any subjectivity but led frequently to an upward amplification of the error field. The study shows the tropopause and the jet streams as generators of strong ageostrophic wind. The same equation applied to mean data shows a general long period geostrophic balance, but there are signiticant seasonal differences and the tropopause remains a permanent zone of ageostrophic wind. [...]