Crustal thickness estimation beneath the southern central Andes at 30°S and 36°S from S wave receiver function analysis

We have used the S wave receiver function (SRF) technique to investigate the crustal thickness beneath two seismic profiles from the CHARGE project in the southern central Andes. A previous study employing the P wave receiver function method has observed the Moho interface beneath much of the profiles. They found, however, that the amplitude of the P to S conversion was diminished in the western part of the profiles and have attributed it to a reduction of the impedance contrast at the Moho due to lower crustal ecologitization. With SRF, we have successfully detected S to P converted waves from the Moho as well as possible conversions from other lithospheric boundaries. The continental South American crust reaches its maximum thickness of ∼70 km (along 30°S between 70°W and 68.5°W) beneath the Principal Cordillera and the Famatina system and becomes thinner towards the Sierras Pampeanas with a thickness of ∼40 km. Negative phases, possibly related to the base of the continental and oceanic lithosphere, can be recognized in the summation traces at different depths. By comparing our results with data obtained from previous investigations, we are able to further constrain the thickness of the crust and lithosphere beneath the central Andes.     

On the existence of a relation between the Kolmogoroff and von Kármán constants

A model is described, in which the mean vertical wind profile and turbulence spectra at different heights are calculated for a turbulent boundary layer without thermal stratification. The model makes use of Heisenberg's formula for the transfer of turbulent energy and is based on the assumption of a constant shearing stress in that boundary layer. As a result, a logarithmic wind profile follows with 0.39 as the value of von Kármán's constant, which is — in this model — strongly related to the inertial subrange of the turbulent energy spectra and therefore to the Kolmogoroff constant.This paper is based on studies done by the author during a one-year visit to CSIRO Division of Meteorological Physics, Aspendale, Australia, and was presented at the AGARD Specialists Meeting on The Aerodynamics of Atmospheric Shear Flows sponsored by the Fluid Dynamics Panel at Munich, Germany, during 15–17 Sept. 1969.     

Historical changes in sediments of Pyramid Lake,Nevada, USA: consequences of changes in the water balance of a terminal desert lake

Sediment cores from the shallow and deep basins of Pyramid Lake, Nevada, revealed variations in composition with depth reflecting changes in lake level, river inflow, and lake productivity. Recent sediments from the period of historical record indicate: (1) CaCO₃ and organic content of sediment in the shallow basin decrease at lower lake level, (2) CaCO₃ content of deep basin sediments increases when lake level decreases rapidly, and (3) the inorganic P content of sediments increases with decreasing lake volume. Variations in sediment composition also indicate several periods for which productivity in Pyramid Lake may have been elevated over the past 1000 years. Our data provide strong evidence for increased productivity during the first half of the 20th Century, although the typical pattern for cultural eutrophication was not observed. The organic content of sediments also suggests periods of increased productivity in the lake prior to the discovery and development of the region by white settlers. Indeed, a broad peak in organic fractions during the 1800's originates as an increase starting around 1600. However, periods of changing organic content of sediments also correspond to periods when inflow to the lake was probably at extremes (e.g. drought or flood) indicating that fluctuations in river inflow may be an important factor affecting sediment composition in Pyramid Lake.     

Grundlagen einer synoptisch-statistischen Theorie der Druckänderungen

Zusammenfassung Es werden die Grundlagen einer synoptisch-statistischen Theorie der Druckänderungen entwickelt. Diese beruht im wesentlichen auf folgenden Annahmen: Zwischen zwei um ein bestimmtes Zeitintervall auseinanderliegenden Werten eines meteorologischen Elementes (im vorliegenden Fall der Höhe der 850 mb-Druckfläche) an einem gegebenen Punkt des Feldes besteht eine Korrelation. Die dazu gehörende Regressionsbeziehung kann auf Grund allgemein gültiger Prinzipien abgeleitet werden. Es erübrigt sich in einem solchen Fall, auf die komplizierten, ohne wesentliche Vereinfachungen kaum lösbaren, thermo-hydrodynamischen Gleichungen einzugehen. Die verwendeten allgemeinen Prinzipien sind: Erhaltungstendenz von Druckanomalien (bezogen auf langjährige Normalwerte), Ausgleichstendenz für bestehende räumliche Druckgegensätze, Kompensation oder Gegenläufigkeit bestimmter Abläufe, d. h. ein Mechanismus, der entgegengesetzte Effekte bezüglich eines meteorologischen Elementes in der vertikalen und horizontalen Verteilung verursacht. Es kann gezeigt werden, daß eine entsprechende Regressionsbeziehung aufzustellen ist, die den beiden ersten Prinzipien genügt. Untersuchungen über das dritte Prinzip sind noch nicht abgeschlossen. Die Erhaltungstendenz wurde bereits vonNamias erfolgreich für die Konstruktion von Trendkarten verwendet. Um eine entsprechende Beziehung abzuleiten, die dem Ausgleichsprinzip gerecht wird, wurde eine Korrelation zwischen einem räumlichen und einem zeitlichen Mittelwert mittels einer hinreichend großen Anzahl von Beobachtungen hergeleitet. Auf diese Weise wird es möglich, eine Prognosenformel aufzustellen für eine über einen Zeitraum von 24 Stunden gemittelte Vorhersagekarte. Die praktische Anwendung dieser Formel wird an Hand von 10 Wetterlagen überprüft. Die Korrelationskoeffizienten für die Treffsicherheit der Prognose liegen zwischen 0,86 und 0,98

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Summary The idea of a synoptic-statistical theor of pressure variations is outlined. This theory is based upon the assumption that a closs correlation exists between two values of a meteorological quantity (in our special case the height of the 850 mb-contours) separated by a given time interval at a given point and that the appropriate regression line can be obtained with the aid of general principles. Then it is unnecessary to consider the complicated thermo-hydrodynamical equations which can hardly be solved without essential simplifications. The general principles used are: Principle of persistence tendency of pressure anomalies (with regard to long range period normals), principle of equalization tendency of existing pressure differences, principle of compensation i. e. a mechanism which produces contrary effects with regard to the vertical and also horizontal distribution of the meteorological quantity under consideration. It is shown that a relation for regression lines can be found making use of the first and second principle. Investigations concerning the third principle are not yet finished. The persistence tendency has been used successfully byNamias for constructing trend charts. In order to obtain a relation which allows for the effect of equalization of pressure differences a correlation is derived between space and time means using a suffiently large number of observations. By this way it is possible to set up a prognostic formula for a 24 hours mean prebaratic. The practical application of the formula is proved for 10 weather situations. The resulting correlation coefficients for the skill of the forecast range between 0,86 and 0,98.

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Résumé L'auteur développe une théorie reposant sur les varations de pression considérées du point de vue synoptique et statistique. Il admet qu'entre deux valeurs consécutives de la hauteur de la surface isobare de 850 mb en un point fixe existe une corrélation dont on peut déduire une relation de régression. Il est inutile dans ce cas de se servir des équations thermo- et hydrodynamiques insolubles sans simplifications importantes. Les principes généraux retenus sont: tendance à la persistance des anomalies de pression (relatives à des moyennes pluriannuelles), tendance à la compensation des différences de pression spatiales, compensation ou opposition de certains processus, c'est à dire un mécanisme qui provoque des effets opposés d'un élément météorologique dans la verticale et dans l'horizontale. Il est possible d'établir une relation de régression satisfaisant les deux premiers principes; les recherches concernant le troisième principe ne sont pas encore achevées. La tendance à la persistance a été déjà utilisée avec succès parNamias pour dresser des cartes d'évolution. Pour obtenir une relation satisfaisant le principe de compensation, on a établi une corrélation entre une moyenne spatiale et une moyenne temporelle à l'aide d'un nombre suffisant d'observations. De la sorte il devient possible d'écrire une formule de prévision pour une carte de prévision relative à un intervalle de 24 heures. On vérifie la formule sur 10 cartes synoptiques. Les coefficients de corrélation pour la probabilité de réussite de la prévision varient entre 0,86 et 0,98.

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Mit 11 Textabbildungen     

Über die Voraussage zeitlich gemittelter Höhenkarten für Zwecke mittelfristiger Wetterprognosen

Zusammenfassung Eine Überprüfung der vonNamias abgeleiteten Formel zur Konstruktion sogenannter Trendkarten an Hand 20 ausgewählter Höhenkarten in der Zeit vom November 1955 bis Mai 1956 ergab eine vollkommene Bestätigung der vonNamias für Amerika angegebenen Korrelationskoeffizienten und des Faktors der entsprechenden Regressionsgleichung für den mitteleuropäischen Raum, obwohl die Untersuchungen sich auf die 850 mb-Topographie bezogen zum Unterschied vonNamias, der die 700 mb-Fläche zugrunde legte. Durch eine sinngemäße Kombination der in der synoptischen Praxis üblichen Konstruktionsmethode für 24 stündige Vorhersagekarten mit statistischen Überlegungen über die Abweichungen vom Normalwert gelingt die Ableitung einer Prognosenformel für eine dreitägige Mittelkarte, die als Grundlage für mittelfristige Wetterprognosen (Halbwochenprognosen) Verwendung findet. Die Formel weist gegenüber der Trendformel vonNamias den Vorteil auf, daß sie mit praktisch derselben Treffergenauigkeit einen wesentlich größeren Vorhersagezeitraum erfaßt.

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Summary Using 20 different contour charts during the period from November 1955 to May 1956 the formula for the construction of socalled trendcharts, primarily derived byNamias, has been verified for Central Europe though the investigations were based upon data from the 850 mb-level instead of the 700 mb-level used byNamias. Through a combination of the synoptic method for construction of forecast maps 24 hours in advance with statistic considerations about the departure from normals a formula is finally derived for a forecast of a three day mean chart. This formula has been successfully used for an extended forecast half week in advance. The described method shows an essential improvement upon theNamias procedure since a much greater forecast period can be obtained with almost the same accuracy.

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Résumé La formule établie parNamias en vue de construire les cartes d'évolution a fait l'objet d'un examen critique fondé sur la discussion de vingt cartes d'altitude de la période de novembre 1955 à mai 1956. Les valeurs des coefficients de corrélation données par cet auteur pour l'Amérique du Nord ainsi que le coefficient de l'équation de régression correspondante ont été confirmés pour l'espace européen, bien que les topographies étudieés n'aient pas été les mêmes (850 mb au lieu de 700 mb). Combinant les méthodes usuelles de construction des cartes de prévision de vingt-quatre heures à des critères statistiques d'écart à la normale, l'auteur établit une formule de prévision destinée à calculer une carte moyenne de trois jours servant de base à la prévision à moyenne échéance. Cette formule présente sur celle deNamias l'avantage d'atteindre une plus longue période de prévision avec une égale exactitude.

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Herrn Prof. Dr.H. Ficker zum 75. Geburtstag gewidmet.     

Radar observations of precipitation production in thunderstorms

Abstract

Precipitation production is investigated for 9 intense thunderstorms that developed over the Lowveld in South Africa. A C‐band radar is used to observe the 3‐dimensional reflectivity pattern. Using an empirical relation between reflectivity factor and precipitation content and integrating over the storm volume provides an estimate of the total precipitation content aloft. Likewise, an area integration of the instantaneous rain rate at cloud base yields an estimate of the rate of total outflow. At their maturing stage, the storms had precipitation contents of 0.2 to 5.0 Tg and rainfall rates of about 0.3 to 2.0 Gg s^?1. The total accumulation of rain at the ground ranged from 1 to 10 Tg. The characteristic storm updraft, defined as the ratio of the area‐averaged rainfall rate to the volume‐averaged precipitation content, was about 5 ms^?1 for all storms. The time evolution of integral storm parameters is also presented and related to the overall storm development. The precipitation production values observed in the Lowveld storms compares well with previous estimates reported for large thunderstorms observed in Alberta and New England.     

Verification of the Weather Research and Forecasting Model when Forecasting Daily Surface Conditions in Southern Alberta

The Weather Research and Forecasting (WRF) model was compared with daily surface observations to verify the accuracy of the WRF model in forecasting surface temperature, pressure, precipitation, wind speed, and direction. Daily forecasts for the following two days were produced at nine locations across southern Alberta, Canada. Model output was verified using station observations to determine the differences in forecast accuracy for each season.

Although there were seasonal differences in the WRF model, the summer season forecasts generally had the greatest accuracy, determined by the lowest root mean square errors, whereas the winter season forecasts were the least accurate. The WRF model generally produced skillful forecasts throughout the year although with a smaller diurnal temperature range than observed. The WRF model forecast the prevailing wind direction more accurately than other directions, but it tended to slightly overestimate precipitation amounts. A sensitivity analysis consisting of three microphysics schemes showed relatively minor differences between simulated precipitation as well as 2?m surface temperatures.     

Interpretation of shallow refraction seismic data by reflection/refraction tomography

A new algorithm for tomographic inversion of traveltimes of reflected and refracted seismic waves is developed. The inversion gives interface configurations and velocity distributions in layers. The important features of the algorithm are: (a) the inclusion of shot time delays in the list of unknown parameters; (b) the regularization is applied in such a way that the most probable model is characterized by the similarity of neighbouring interfaces. As the problem under consideration is non-linear, several iterations are necessary in order to obtain the final model. In the case of a very inexact initial model, a 'layer-by-layer' inversion strategy is recommended as a first inversion step. The inversion program is supplied with a user interface, thanks to which one can: (a) pick interactively and identify seismic traveltimes; (b) build and edit depth/velocity models; and (c) display calculated traveltime curves and compare them with picked traveltimes as well as with the original seismic sections. The efficiency of the inversion software developed is illustrated by a numerical example and a field example in which shallow seismic data are considered. Application to wide-aperture reflection/refraction profiling (WARRP) data is also possible.