Diurnal momentum budget analysis of thermally induced slope winds

Summary  Data measured during the TRACT field campaign at various stations along a 7.5° steep and west-northwest facing slope of the Black Forest mountain range (Germany) are used to analyze the thermal structure and the momentum budget associated with thermally induced slope winds. Acceleration of the air close to the ground is found to be directed nearly vertically downward during the night and nearly vertically upward during the day, rather than parallel to the slope. This means that during the night the airflow is deflected by the slope surface in the down-slope direction, whereas during daytime stable stratification above the heated slope layer is required to establish up-slope flow parallel to the slope. The diurnal cycle of the momentum budget of the along-slope wind component near the surface is analyzed in detail with respect to the driving forces (buoyancy and pressure gradient force) and friction. It is found that a small imbalance between forcing and friction is responsible for the diurnal change in slope flow intensity. The along-slope components of the horizontal pressure gradient force and the buoyancy force are shown to have the same order of magnitude. This means that for small to moderate slope angles the pressure gradient force cannot be neglected as is done in some analytical slope wind models. The reaction time of the slope flow to changes in forcing is estimated to be in the range of 30 to 120 seconds, which confirms the empirically known fact that slope winds react very quickly. Received December 1, 1999 Revised June 13, 2000     

Evaluation of Modeled Spatially and Temporarily Highly Resolved Emission Inventories of Photosmog Precursors for the City of Augsburg: The Experiment EVA and Its Major Results

Emission inventories of NO_x, CO, and individual volatile organic compounds (VOC), highly resolved in space and time, belong to the most important input parameters for chemistry and transport models (CTM) used for ozone prediction. Because of the decisive influence of the input quality on the outcome of CTM simulations, the quality of emission inventories has to be assessed. This paper presents an experimental evaluation of the highly resolved emission inventories for the city of Augsburg. The emissions of the city, determined in March and October 1998 using mass balance and tracer techniques, and derived from the measured receptor concentration ratios, were compared with emissions modeled from an emission inventory. The modeled CO emissions were in agreement with the measured ones within the combined experimental and model uncertainties. More detailed CO emission model simulations suggest that the tendency of calculated CO emissions being smaller than the measured ones may be due to higher traffic activity in Augsburg. Modeled NO_x emissions were in agreement with the measured ones within the combined experimental and model uncertainties. Large deviations between modeled and measured values have been found for some individual NMHC compounds. The measured NMHC emission fingerprints were dominated by mobile sources. Substantial model predicted NMHC emissions from the solvent use could not be detected by measurements suggesting that they may not be correctly represented by the emission model.     

Mesoscale Heat Transport Over Complex Terrain By Slope Winds – A Conceptual Model And Numerical Simulations

Vertical heat fluxes induced by mesoscale thermally driven circulations maycontribute significantly to the subgrid-scale fluxes in large-scale models (e.g.,general circulation models). However, they are not considered in these modelsyet. To gain insight into the importance and possible parameterisation of themesoscale flux associated with slope winds, an analytical (conceptual) modelis developed to describe the relationship between the mesoscale heat flux andatmospheric and land-surface characteristics. The analytical model allows usto evaluate the mesoscale flux induced by slope winds from only a few profilemeasurements within a domain. To validate the analytical model the resultingheat flux profiles are compared to profiles of highly resolved wind and temperaturefields obtained by simulations with a mesoscale numerical model.With no or moderate synoptic wind the mesoscale heat flux generated by the slopewind circulation may be as large as, or even larger than, the turbulent fluxes at thesame height. At altitudes lower than the crest of the hills the mesoscale flux is alwayspositive (upward). Generally it causes cooling within the boundary layer and heatingabove. Despite the simplifications made to derive the analytical model, it reproducesthe profiles of the mesoscale flux quite well. According to the analytical model, themesoscale heat flux is governed by the temperature deviation at the slope surface, thedepth of the slope-wind layer, the large-scale lapse rate, and the wavelength of thetopographical features.     

Modification of air flow over an escarpment — Results from the Hjardemål experiment

Mean flow, turbulence, and surface pressure measurements over an escarpment are presented. The speed-up in the mean wind field shows the known dependence on stratification. Cross-sections of the standard deviation of horizontal and vertical wind components and of the friction velocity are derived from the data and compare favorably with the numerical model of Zeman and Jensen (1987). The modification of turbulent power spectra at intermediate frequencies can be explained by rapid distortion theory. At very low frequencies, there is a quasi-stationary response to the disturbance. Except for speed-up and standard deviations of the wind components, which are also shown for downslope wind, all results in this paper refer to upslope winds.An analysis of the vertical momentum flux reveals that upstream of the escarpment, most of the flux is transported in sweeps of fast, sinking motion to the ground. Downstream of the escarpment, ejections of slow, rising motion dominate the turbulent transport.     

Comparison of areally averaged turbulent fluxes over non-homogeneous terrain: Results from the EFEDA-field experiment

In June 1991 the EFEDA-field experiment (ECHIVAL Field Experiment in a Desertification-Threatened Area) was carried out in the Spanish province Castilla-La Mancha, to improve the understanding of the interactions between the soil, the vegetation and the atmosphere.Here results of energy balance studies at the Barrax site are given, one of the three intensively studied experimental sites within Castilla-La Mancha. This area is characterized by a large fraction of irrigated fields (40%) while the remaining 60% was fallow land at the end of June 1991. The energy balances over these two characteristic land-use classes totally differ. While for the irrigated fields the evapotranspiration is dominant, for the non-irrigated fields the sensible and the soil heat fluxes dominate and the latent heat flux is nearly negligible.In order to achieve areally averaged turbulent fluxes, surface, SODAR and aircraft data have been used. Comparing the surface fluxes from all three facilities, it can be found that:The sensible heat flux estimation from SODAR (_w-method) gives reliable results when a calibration of _w is done with another independent system (e.g. aircraft).Aircraft measurements in conjunction with energy budget methods yield surface fluxes of sensible heat, which are about 20% lower than the areally averaged values calculated by the surface measurements. The areally averaged latent heat fluxes from aircraft and surface measurements agree better than the sensible heat fluxes.     

Predicting site-specific storm wave run-up

Natural Hazards - Storm wave run-up causes beach erosion, wave overtopping, and street flooding. Extreme runup estimates may be improved, relative to predictions from general empirical formulae...     

Calibration of electromagnetic seismographs by means of responses to release and shock tests

Summary The paper deals with the problems of fast determination of the magnification curve and of the partial constants of an electromagnetic seismograph by means of responses to release and shock tests, using a computer.     

Das Erdbeben von Guatemala vom 4. Februar 1976

Zusammenfassung Am 4. Februar 1976 erlitt der mittelamerikanische Staat Guatemala die wohl größten Erdbebenzerstörungen seiner Entwicklungsgeschichte. Ohne irgendwelche Warnungen durch Vorbeben wurden große Landesteile gegen 3 Uhr früh von einem Hauptbeben verwüstet, als dessen Folge 22 545 Menschen getötet und etwa 70 027 verletzt wurden. Der Gesamtschaden liegt in der Größenordnung von 2,2 Milliarden D-Mark, die kulturellen Sachwerte nicht mitgerechnet.Die Schadenszone erstreckt sich über eine Länge von rund 300 km und ist etwa 70 km breit, was einer Fläche von 21 000 km² entspricht.Das Erdbeben wurde verursacht durch einen linkslateralen, horizontalen Scherungsbruch entlang der Motagua-Verwerfung, Abb. 1, welche als Transformationsverwerfung die Nordamerikanische Kontinentalplatte von der Karibischen Platte trennt und vom Kaiman-Graben her auf das guatemaltekische Festland übergreift. Die an der Erdoberfläche sichtbare Länge des Scherangsbruches beträgt 150 bis 200 km. Die horizontalen Bodenverschiebungen betragen meist 40 bis 80 cm und erreichen vereinzelt bis zu 2 Meter. Dabei ist stets die nördliche Scholle nach Westen und die südliche Scholle nach Osten verschoben, wie es der Plattentektonik entspricht.

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On February 4, 1976 the Central American State of Guatemala suffered the greatest earthquake-destruction of its history. Without any foreshock warning, around three o'clock in the morning, the earthquake killed 22 545 people and aproximately 70 027 were injured. The total material earthquake damage is estimated at 2.2 milliards (american: 2.2 billions) German Marks, not counting the historical value of destroyed cultural monuments and others.The damaged zone is some 300 kms. long and about 70 kms. wide, what corresponds to an area of 21 000 kms².The Earthquake was originated by a horizontal, left-lateral shear breakage along the Motagua-Fault, Fig. 1, which separates as a transform fault the North American Continental Plate from the Caribbean Plate and which, coming from the CaymanTrough, continues into Guatemalan territory. The visible length of this left-lateral strike-slip fault is 150 to 200 kms. The horizontal displacements in soil are 40 to 80 cms. and in some places up to two meters. In all observed cases, the northern block was shifted towards West and the southern one towards East, in perfect agreement with Plate Tectonics.

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Resumen El día 4 de Febrero de 1.976, el Estado Centroamericano de Guatemala sufrió su probable mayor destrucción sísmica de su historia. Sin el aviso alguno de sismos premonitores, alrededor de las tres de la mañana fue devastado gran parte del país, en cuya consecuencia hubo 22.545 muertos y alrededor de 70.027 heridos. El daño total de las pérdidas se estima en el orden de 2.2 Mil Milliones de Marcos alemanes, no contando los valores culturales materiales.La zona de daños se extiende sobre una longitud de unos 300 KMS y con una anchura de unos 70 KMS, lo que corresponde a una área de 21 000 KMS².El terremoto fué originado por una fractura cortante, horizontal y lateral-izquierda a lo largo de la Falla Tectónica de Motagua, Fig. 1, la cual separa, como falla de transformatión, la Placa Continental Norteamericana de la Placa del Caribe, prolongándose desde la Fosa de Caimán hacia territorio continental guatemalteco. La longitud de la fractura cortante, visible en la superficie terrestre, es entre los 150 y los 200 KMS. Los desplazamientos horizontales del suelo son en la mayoría entre 40 y 80 cms y alcanzan en algunos casos hasta dos metros. Además, el bloque norte siempre es desplazado hacia el oeste y el bloque al sur de la falla hacia el este, como lo require la tectónica de placas de esa región.

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Singularity-free static centrally symmetric solutions of some fourth order gravitational field equations

The fourth order field equations proposed by TREDER with a linear combination of BACH 's tensor and EINSTEIN 's tensor on the left-hand side admit static centrally symmetric solutions which are analytical and non-flat in some neighborhood of the centre of symmetry.