Valley winds in the mount Rainier area

Summary Four summer seasons of field work near Mt. Rainier have shown that a well-developed valley wind system tends to have the following features: Airflow within a valley is up the valley during the day and down it at night and is compensated by a return flow (anti-wind) at a higher level. The layers occupied by the two flows are of approximately equal thickness, and the boundary between them is generally at, or somewhat below, ridgeheight. Above the anti-wind, the flow depends on the large-scale synoptic situation.Horizontal wind speed in these two layers is greatest slightly below the center of each layer. Speeds reach a maximum in early afternoon and just beforce sunrise. The reversal between day and nighttime flows is almost simultaneous everywhere in the valley, about an hour after sunnet and sunrise.Vertical transport of air between the two layers appears to be localized, mainly in the neighborhood of the ridges. Slope winds apparently feed the vertical currents. Speed fluctuations, having a period of about 20 minutes, were observed in drainage winds near the surface at night.When a well-developed wind system occured in one valley, well-developed systems tended to occur in other valleys in the same area.

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Zusammenfassung Beobachtungen im Verlaufe von vier Sommern im Mount-Rainier-Gebiet zeigten ein gutentwickletes Talwind-System mit folgenden Eigenschaften: Die Luft im Tale bewegt sich tags talaufwärts und nachts talabwärts; diese Strömung wird kompensiert durch ein Gegenwind-System in größerer Höhe. Die vertikale Erstreckung der übereinander liegenden Strömungen ist etwa gleich, und ihre Grenzfläche liegt, im allgemeinen, in oder etwas unter der Höhe der Bergkämme. Oberhalb des Gegenwindes beherrscht die weiträumige synoptische Situation die Strömung.Die Horizontalgeschwindigkeit ist für beide Windsysteme am größten etwas unter dem Zentrum der betreffenden Schicht. Geschwindigkeitsmaxima werden am frühen Nachmittag und kurz vor Sonnenaufgang erreicht. Der Umschlag von Tag- zu Nachtströmungen erfolgt nahezu gleichzeitig in allen Teilen des Tales, und zwar je etwa eine Stunde nach Sonnenaufgang bzw. Sonnenuntergang.Der vertikale Luftmassenaustausch zwischen beiden Schichten erfolgt im wesentlichen oberhalb der Bergkämme. Dieser vertikale Kammwind wird von unten durch den Hangwind ernährt. Im nächtlichen Fallwind wurden Geschwindigkeits-Variationen mit einer Periode von etwa 20 Minuten beobachtet.Wenn gut entwickelte Wind-Systeme in einem Tal vorkommen, kann man auch in anderen Tälern gut entwickelte Systeme erwarten.

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Résumé Des observations faites durant quatre étés dans la région du Mount Rainier ont montré la présence d'un système bien développé de brises de vallée et de montagne. Ce système a les particularités suivants: Le courant est dirigé vers l'amont durant la journée, vers l'aval durant la nuit. Ces courants sont compensés par un système de vents contraires à grande altitude. Le développement vertical des deux courants est à peu près identique et la surface qui les sépare est située, en général, à l'altitude des crêtes ou légèrement au-dessous. Le courant situé au-dessus du ven contraire est déterminé par la situation synoptique générale.La vitesse horizontale du vent est maximum pour les deux systèmes un peu au-dessous du centre de la couche correspondante. Les plus grandes vitesses se mesurent au début de l'après-midi et peu avent le lever du soleil. Le passage de la brise de vallée à la brise de montagne ou vice versa s'opère presque simultanément en tous les points de la vallée et cela approximativement une heure après le lever, respectivement le coucher du soleil.L'échange vertical des masses d'air entre les deux couches se fait principalement au-dessus des crêtes. Ce vent vertical de crêtes est alimenté d'en bas par le courant remontant les pentes. Dans le cas du vent nocturne descendant, on a observé des variations de vitesse ayant une périodicité de 20 minutes environ.Si l'on observe dans une vallée déterminée un système bien développé de brises de vallée et de montagne, on peut s'attendre à ce que des systèmes semblables se retrouvent également dans d'autres vallées de la même région.

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With 9 Figures

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Contribution No. 97, department of Atmospheric Sciences, University of Washington, Seattle, USA.

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This research was aided by the U.S. Air Force Cambridge Research Laboratories under AF Contract 19 (604)-7201, Project 7655, Task 7655.     

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Sources and distribution of organic matter in northern Patagonia fjords,Chile (∼44–47°S): A multi-tracer approach for carbon cycling assessment

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Possible remnants of a frozen mud lake in southern Elysium, Mars

In this work we estimate the minimum persistence time of subsurface ice in water rich sediment layers remaining after sublimation of a martian lake. We simulate sublimation of ice from layers of different granulations and thicknesses. Presented results assume insolation and atmospheric conditions characteristic for the present day southern Elysium, where data from Mars Express have identified surface features possibly indicating the very recent presence of a frozen body of water [Murray et al., 2005. Nature 434, 352-356]. The age of these features is estimated to be several million years. On this time scale, we find that most of the water ice must have sublimated away, however remnant ice at a few percent level cannot be excluded. This amount of water ice is sufficient for chemical cementation of the observed features and explains their relatively pristine appearance, without significant signs of erosion.