15 research outputs found

    A synthetic analysis of seasonal influences in the effects of land use on the urban thermal regime

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    A simple digital surface climate simulator is employed as the vehicle for the exploration of some relationships between land-use and the urban climate. Specifically the simulator indicates that the physical roots of the urban ‚Äúheat island effect‚ÄĚ are significantly seasonally variable. Ein einfacher numerischer Simulator des Bodenklimas wurde zur Erforschung des Zusammenhanges zwischen Bodennutzung und Stadtklima verwendet. Im besonderen zeigte dieser Simulator, da√ü die physikalischen Grundlagen der st√§dtischen ‚ÄěW√§rmeinsel‚ÄĚ in signifikanter Weise jahreszeitlichen Einfl√ľssen unterliegen.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41666/1/704_2005_Article_BF02243185.pd

    The effect of iteration frequency on a numerical model of near-surface ice segregation

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    It is possible to construct numerical models of the ice segregation process. However, the model is a discrete approximation of a nonlinear continuous process and thus is subject to somewhat more pronounced effects of node geometry and calculation frequency than linear models. The model more closely simulates natural frozen soil structure when vapor phase transport is included in the model structure. An iteration frequency of 10 s appeared sufficient to yield realistic results with the exponentially spaced node geometry employed in these tests.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23588/1/0000550.pd

    A simple energy balance model of ice segregation

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    Step functions of normal frost front advance in dry and wet soils are reviewed and used to introduce the geometry of the soil frost system. An energy balance equation at the initiation of ice lens growth is developed using simple physical assumptions. This model is then employed to simulate the effects of varied surface temperature depression and water table depth on the timing, position and rate of ice lens growth. Lowering the water table delays the onset of segregation but the initial heave rates are all above half a meter per year in the region examined.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23250/1/0000183.pd

    The simulation and implications of thermal plumes produced by Arctic construction in smooth terrain

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    In smooth snow covered Arctic terrain human construction produces extreme local variations in the aerodynamic roughness length. These features have been identified on thermal imagery and simulated on a digital computer. The analysis of these features provides a powerful tool for (1) assessing the spatial-temporal integrity of meteorological sites, (2) identifying cultural features in snow covered flat terrain in the relatively low resolution thermal imagery which will be acquired from spacecraft in the next decade, and (3) assessing and attenuating the environmental impact resulting from Arctic construction. Auf glattem, schneebedecktem Terrain der Arktik werden durch Bauten extreme lokale √Ąnderungen in der aerodynamischen Bodenrauhigkeit hervorgerufen. Dieser Effekt konnte sowohl auf Temperaturabbildungen als auch durch numerische Modellrechnungen nachgewiesen werden. Die Analyse dieses Effekts kann dazu verwendet werden, um a) die r√§umliche und zeitliche Repr√§sentanz von meteorologischen Stationen zu beurteilen, b) Spuren menschlicher Bet√§tigung in schneebedecktem, ebenem Terrain aus Temperaturabbildungen niedriger Aufl√∂sungsgenauigkeit festzustellen, die von zuk√ľnftigen Satelliten geliefert werden, und c) den Umweltseinflu√ü arktischer Bauwerke abzusch√§tzen.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41667/1/704_2005_Article_BF02243186.pd

    A simulation model of river ice cover thermodynamics

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    A model of ice cover thermodynamics was used to simulate ice growth and decay along the international section of the St. Lawrence River for winter 1980-1981. This winter was chosen because of the exceptionally cold weather in December and January, and because of the abnormally warm air temperatures during the second half of February. At the air-ice interface, the model computes the surface energy transfer components and a resulting equilibrium surface temperature. At the lower boundary, an empirical algorith simulates the turbulent transfer of heat from the water. Within the ice, and implicit numerical solution to the general heat diffusion equation is used, permitting stable solutions for a variety of time intervals and node distances within the model. The model was used to simulate ice growth and decay at five sites characterized by their flow velocity, the date of ice-cover formation, and the water temperature regime. The model adequately represented growth rates at all five sites, but produced decay rates slower than those observed. Simulated breakup was 1-7 days later than observed, presumably because mechanical weakening of the ice was not taken into consideration. During the growth period, the model is far more sensitive to the values assigned to ice properties than it is to the error range in the meteorological variables. During the breakup period, the most sensitive boundary variable is water temperature.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25721/1/0000278.pd

    Modeling the annual thermal regime of lake Ohrid, Yugoslavia, using daily weather data

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    The time-dependent characteristics of the five weather variables which control the annual thermal response of Lake Ohrid are analyzed in detail. These are daily values for solar radiation, air temperature, humidity, wind speed and cloud cover. A simple numerical model of the lake's thermal response, forced by thermally driven density mixing, is developed and tested using observed thermal profiles for verification. The numerical model successfully reproduces the major features of the lake's thermal regime over a 6 y period from 1972 to 1977, the average root mean square value for the simulated profiles being 1.2[deg]C with extremes of 2.2 and 0.3[deg]C and a standard deviation of 0.4[deg]C.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24043/1/0000292.pd

    An algorithm for clustering profile data and its application to near-surface ice content data from wet coastal tundra soils near Barrow, Alaska

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    An algorithm to cluster profile data into groups that minimize the sum of the intra-group variances was applied to near-surface soil ice content data collected near Barrow, Alaska, in wet tundra terrain. When the algorithm was requested to produce 2‚Äď5 groups and group mean profiles, the results were consistant with the modern theory of ice segregation. This process produces much of the variability of near surface soil ice stratigraphy in nature. These results strengthen the case for employing the algorithm on other profile data sets as an aid in hypothesis formulation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43194/1/11004_2005_Article_BF01032216.pd

    URBAN TERRAIN CLIMATOLOGY AND REMOTE SENSING *

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    . Urban areas have been conceived of as monolithic heat islands because traditional ground observation techniques do not lend themselves to more specific analyses. Observations of urban energy-exchange obtained from calibrated electro-optical scanners combined with energy budget simulation techniques provide tools to relate the urban land use mosaic to the heat island phenomenon. Maps of surface energy-related phenomena were made from airborne scanner outputs for selected flightpaths across the city of Baltimore, Maryland. Conditions for the flight time were simulated according to the various types of land use using an energy budget simulation model which lends itself to extrapolation of simulated grid-point conditions into a map form. Maps made by simulation compare sufficiently well with those made by aerial observation to encourage further refinement of the simulation approach.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72392/1/j.1467-8306.1976.tb01110.x.pd

    Soil temperature and electric potential during diurnal and seasonal freeze-thaw

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    Combined measurements of soil temperature and electric potential in the upper 15 cm of a glacial sandy-loam soil were made during the winters of 1986-1987 and 19871988 at the University of Michigan Botanical Gardens using an electronic data acquisition system at frequencies varying from 10 min to daily (midnight). Most of the data was collected at hourly intervals.Analysis of temperature-potential time series at two locations with probes at (0, 3, 6, 9) and (0, 5, 10, 15) cm depths indicated that the variation of electric potential relative to the potential of a 1.5 m ground spike could be interpreted as the response of an electrolytic concentration cell without transference formed by a probe and the ground spike. As the electrolyte concentration is much greater at the ground spike, and electric potential varies inversely with concentration, the potentials at the soil probes varied over the range of approximately 300-700 mV in a manner consistent with the behavior of a concentration cell.The rapid and systematic pattern of potential variation during freeze-thaw events demonstrates that the effects of electrolyte concentration and dilution are products of evaporation-distillation, the melting of frost-purified ice, soil water advection to the freezing-evaporating region, concentrated electrolyte expulsion from the freezing region and the infiltration of rain and snow melt waters.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27857/1/0000269.pd

    The observation and simulation of diurnal surface thermal contrast in an Alaskan alpine pass

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    A simple surface climate simulator was employed in the analysis of thermal regimes in rough alpine terrain at Chitistone Pass, Alaska. The simulator favorably abstracts observations of thermal regimes on flat and sloping surfaces with variable thermal and radiative properties. It is shown that slope and exposure control variations in surface thermal regimes. The simulator predicts these controls and it is suggested that simulation of surface thermal regimes can be performed before and after field investigations, thus increasing the effective information content of thermal maps acquired using aircraft and orbital platforms. It is concluded that the removal by spatial filtering of the low frequency effects of slope and exposure on thermal maps is necessary before site material effects can be discriminated and analyzed. Ein einfaches Rechenmodell des Bodenklimas wurde auf die Analyse des Temperaturregimes im unebenen Terrain des Chitistone-Passes in Alaska angewandt. Das Modell bildet die beobachteten Temperaturregime ebener und geneigter Bodenfl√§chen mit ver√§nderlichen W√§rmeleit- und Strahlungscharakteristiken zufriedenstellend ab. Es wird gezeigt, da√ü Hangneigung und Hanglage im wesentlichen das Bodentemperaturregime bedingen. Das Modell sagt diese Bedingungsfaktoren richtig voraus. Es wird daher vorgeschlagen, da√ü Modellrechnungen vor und nach Feldmessungen angestellt werden sollten, um den effektiven Informationsgehalt der Temperaturverteilungskarten zu erh√∂hen, die von Flugzeugen oder Satelliten vermessen wurden. Es wird darauf hingewiesen, da√ü die Unterdr√ľckung niederfrequenter Effekte von Hangneigung und Hanglage auf die kartographisch festgehaltene Temperaturverteilung notwendig ist, bevor Bodenbeschaffenheitseffekte diskriminiert und analysiert werden k√∂nnen. Diese Unterdr√ľckung kann durch r√§umliche Filterung geschehen.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41669/1/704_2005_Article_BF02243725.pd
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