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601.
Analysis of the wind field and heat budget in an alpine lake basin during summertime fair weather conditions 总被引:2,自引:0,他引:2
M. Kossmann A. P. Sturman P. Zawar-Reza H. A. McGowan A. J. Oliphant I. F. Owens R. A. Spronken-Smith 《Meteorology and Atmospheric Physics》2002,81(1-2):27-52
Summary ?Observational data collected in the Lake Tekapo hydro catchment of the Southern Alps in New Zealand are used to analyse the
wind and temperature fields in the alpine lake basin during summertime fair weather conditions. Measurements from surface
stations, pilot balloon and tethersonde soundings, Doppler sodar and an instrumented light aircraft provide evidence of multi-scale
interacting wind systems, ranging from microscale slope winds to mesoscale coast-to-basin flows. Thermal forcing of the winds
occurred due to differential heating as a consequence of orography and heterogeneous surface features, which is quantified
by heat budget and pressure field analysis.
The daytime vertical temperature structure was characterised by distinct layering. Features of particular interest are the
formation of thermal internal boundary layers due to the lake-land discontinuity and the development of elevated mixed layers.
The latter were generated by advective heating from the basin and valley sidewalls by slope winds and by a superimposed valley
wind blowing from the basin over Lake Tekapo and up the tributary Godley Valley.
Daytime heating in the basin and its tributary valleys caused the development of a strong horizontal temperature gradient
between the basin atmosphere and that over the surrounding landscape, and hence the development of a mesoscale heat low over
the basin. After noon, air from outside the basin started flowing over mountain saddles into the basin causing cooling in
the lowest layers, whereas at ridge top height the horizontal air temperature gradient between inside and outside the basin
continued to increase.
In the early evening, a more massive intrusion of cold air caused rapid cooling and a transition to a rather uniform slightly
stable stratification up to about 2000 m agl. The onset time of this rapid cooling varied about 1–2 h between observation
sites and was probably triggered by the decay of up-slope winds inside the basin, which previously countered the intrusion
of air over the surrounding ridges. The intrusion of air from outside the basin continued until about mid-night, when a northerly
mountain wind from the Godley Valley became dominant. The results illustrate the extreme complexity that can be caused by
the operation of thermal forcing processes at a wide range of spatial scales.
Received June 25, 2001; Revised December 21, 2001 相似文献
602.
Thermodynamic characteristics and temporal variation of alpine lake breezes in the eastern Southern Alps are examined. Research was conducted in a large glacially excavated basin dominated by an 87 square kilometre melt-water lake as part of a study of windblown dust dispersion. The surrounding mountain ranges were found to shelter the lake basin from most synoptic winds, thereby allowing local and regional thermally generated circulations to develop to ridge height, approximately 1300m above the surrounding landscape. During favourable synoptic conditions the local lake breeze becomes embedded within the regional valley wind forming an extended lake breeze. Tethersonde flights during these conditions made using a kite based sounding system identified both stable internal (SIBL) and thermal internal boundary layer (TIBL) conditions over the down wind shoreline. Two equations for estimating the height of both boundary-layer types were tested against observations and found to provide good first order predictive estimates of boundary-layer height. 相似文献
603.
604.
605.
Maxim I. Boyanov Edward J. O’Loughlin Jeremy B. Fein 《Geochimica et cosmochimica acta》2007,71(8):1898-1912
The chemical reduction of U(VI) by Fe(II) is a potentially important pathway for immobilization of uranium in subsurface environments. Although the presence of surfaces has been shown to catalyze the reaction between Fe(II) and U(VI) aqueous species, the mechanism(s) responsible for the enhanced reactivity remain ambiguous. To gain further insight into the U-Fe redox process at a complexing, non-conducting surface that is relevant to common organic phases in the environment, we studied suspensions containing combinations of 0.1 mM U(VI), 1.0 mM Fe(II), and 4.2 g/L carboxyl-functionalized polystyrene microspheres. Acid-base titrations were used to monitor protolytic reactions, and Fe K-edge and U L-edge X-ray absorption fine structure spectroscopy was used to determine the valence and atomic environment of the adsorbed Fe and U species. In the Fe + surface carboxyl system, a transition from monomeric to oligomeric Fe(II) surface species was observed between pH 7.5 and pH 8.4. In the U + surface carboxyl system, the U(VI) cation was adsorbed as a mononuclear uranyl-carboxyl complex at both pH 7.5 and 8.4. In the ternary U + Fe + surface carboxyl system, U(VI) was not reduced by the solvated or adsorbed Fe(II) at pH 7.5 over a 4-month period, whereas complete and rapid reduction to U(IV) nanoparticles occurred at pH 8.4. The U(IV) product reoxidized rapidly upon exposure to air, but it was stable over a 4-month period under anoxic conditions. Fe atoms were found in the local environment of the reduced U(IV) atoms at a distance of 3.56 Å. The U(IV)-Fe coordination is consistent with an inner-sphere electron transfer mechanism between the redox centers and involvement of Fe(II) atoms in both steps of the reduction from U(VI) to U(IV). The inability of Fe(II) to reduce U(VI) in solution and at pH 7.5 in the U + Fe + carboxyl system is explained by the formation of a transient, “dead-end” U(V)-Fe(III) complex that blocks the U(V) disproportionation pathway after the first electron transfer. The increased reactivity at pH 8.4 relative to pH 7.5 is explained by the reaction of U(VI) with an Fe(II) oligomer, whereby the bonds between Fe atoms facilitate the transfer of a second electron to the hypothetical U(V)-Fe(III) intermediate. We discuss how this mechanism may explain the commonly observed higher efficiency of uranyl reduction by adsorbed or structural Fe(II) relative to aqueous Fe(II). 相似文献
606.
Brent D. Turrin Fara Lindsay Jeremy S. Delaney Jisun Park Gregory F. Herzog Carl Swisher Jr Cyrena A. Goodrich 《Meteoritics & planetary science》2023,58(3):304-327
The Almahata Sitta (AhS) meteorite consists of disaggregated clasts from the impact of the polymict asteroid 2008 TC3, including ureilitic (70%–80%) and diverse non-ureilitic materials. We determined the 40Ar/39Ar release patterns for 16 AhS samples (3–1500 μg) taken from three chondritic clasts, AhS 100 (L4), AhS 25 (H5), and MS-D (EL6), as well as a clast of ureilitic trachyandesite MS-MU-011, also known as ALM-A, which is probably a sample of the crust of the ureilite parent body (UPB). Based on our analyses, best estimates of the 40Ar/39Ar ages (Ma) of the chondritic clasts are 4535 ± 10 (L4), 4537–4555 with a younger age preferred (H5), and 4513 ± 17 (EL6). The ages for the L4 and the H5 clasts are older than the most published 40Ar/39Ar ages for L4 and H5 meteorites, respectively. The age for the EL6 clast is typical of older EL6 chondrites. These ages indicate times of argon closure ranging up to 50 Ma after the main constituents of the host breccia, that is, the ureilitic components of AhS, reached the >800°C blocking temperatures of pyroxene and olivine thermometers. We suggest that these ages record the times at which the clasts cooled to the Ar closure temperatures on their respective parent bodies. This interpretation is consistent with the recent proposal that the majority of xenolithic materials in polymict ureilites were implanted into regolith 40–60 Ma after calcium–aluminum-rich inclusion and is consistent with the interpretation that 2008 TC3 was a polymict ureilite. With allowance for its 10-Ma uncertainty, the 4549-Ma 40Ar/39Ar age of ALM-A is consistent with closure within a few Ma of the time recorded by its Pb/Pb age either on the UPB or as part of a rapidly cooling fragment. Plots of age versus cumulative 39Ar release for 10 of 15 samples with ≥5 heating steps indicate minor losses of 40Ar over the last 4.5 Ga. The other five such samples lost some 40Ar at estimated times no earlier than 3800–4500 Ma bp . Clustering of ages in the low-temperature data for these five samples suggests that an impact caused localized heating of the AhS progenitor ~2.7 Ga ago. In agreement with the published work, 10 estimates of cosmic-ray exposure ages based on 38Ar concentrations average 17 ± 5 Ma but may include some early irradiation. 相似文献