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.     

Impact of non-outbreak insect damage on vegetation in northern Europe will be greater than expected during a changing climate

Background insect herbivory, in addition to insect outbreaks, can have an important long term influence on the performance of tree species. Since a projected warmer climate may favour insect herbivores, we use a dynamic ecosystem model to investigate the impacts of background herbivory on vegetation growth and productivity, as well as distribution and associated changes in terrestrial ecosystems of northern Europe. We used the GUESS ecosystem modelling framework and a simple linear model for including the leaf area loss of Betula pubescens in relation to mean July temperature. We tested the sensitivity of the responses of the simulated ecosystems to different, but realistic, degrees of insect damage. Predicted temperature increases are likely to enhance the potential insect impacts on vegetation. The impacts are strongest in the eastern areas, where potential insect damage to B. pubescens can increase by 4–5%. The increase in insect damage to B. pubescens results in a reduction of total birch leaf area (LAI), total birch biomass and birch productivity (Net Primary Production). This effect is stronger than the insect damage to leaf area alone would suggest, due to its second order effect on the competition between tree species. The model's demonstration that background herbivory may cause changes in vegetation structure suggests that insect damage, generally neglected by vegetation models, can change predictions of future forest composition. Carbon fluxes and albedo are only slightly influenced by background insect herbivory, indicating that background insect damage is of minor importance for estimating the feedback of terrestrial ecosystems to climate change.     

Sensitivity of high-resolution Arctic regional climate model projections to different implementations of land surface processes

This paper discusses the effects of vegetation cover and soil parameters on the climate change projections of a regional climate model over the Arctic domain. Different setups of the land surface model of the regional climate model HIRHAM were realized to analyze differences in the atmospheric circulation caused by (1) the incorporation of freezing/thawing of soil moisture, (2) the consideration of top organic soil horizons typical for the Arctic and (3) a vegetation shift due to a changing climate. The largest direct thermal effect in 2 m air temperature was found for the vegetation shift, which ranged between −1.5 K and 3 K. The inclusion of a freeze/thaw scheme for soil moisture shows equally large sensitivities in spring over cool areas with high soil moisture content. Although the sensitivity signal in 2 m air temperature for the experiments differs in amplitude, all experiments show changes in mean sea level pressure (mslp) and geopotential height (z) throughout the troposphere of similar magnitude (mslp: −2 hPa to 1.5 hPa, z: −15 gpm to 5 gpm). This points to the importance of dynamical feedbacks within the atmosphere-land system. Land and soil processes have a distinct remote influence on large scale atmospheric circulation patterns in addition to their direct, regional effects. The assessment of induced uncertainties due to the changed implementations of land surface processes discussed in this study demonstrates the need to take all those processes for future Arctic climate projections into account, and demonstrates a clear need to include similar implementations in regional and global climate models.     

Identification of geomorphic process units in Kärkevagge, northern Sweden, by remote sensing and digital terrain analysis

Sediment transport processes in the Kärkevagge are investigated concerning their spatial and temporal characteristics due to long–term monitoring. Within this study remote sensing techniques and GIS modelling in connection with geomorphic mapping are applied for identification and characterization of geomorphic process units. Relationships between geomorphometric parameters and slope processes like solifluction, talus creep and rockfall have been analysed. Multitemporal Landsat–TM5 scenes are used as source for landcover characteristics (Normalized Difference Vegetation Index) after preprocessing involving orthorectification and topographic normalization in order to remove possible terrain–induced effects. Additionally, a digital elevation model with a resolution of 20 m for the Kärkevagge catchment is developed and parameters like slope gradient, slope aspect and profile curvature are extracted as input for the analysis of the sediment transport system. The combination of landcover information, geomorphometrical and topological features allows the definition of areas for single process activities. They show specific sediment displacement characteristics depending on material conditions, topological and geometrical features. Geomorphic process units, which show a homogenous composition, are extracted from these available layers.     

Towards an integration of process measurements, archive analysis and modelling in geomorphology — the Kärkevagge experimental site, Abisko area, northern Sweden

The analysis of Holocene geomorphic process activity demands long–term data sets, which are available for the Kärkevagge catchment due to 50 years of intensive geomorphologic field studies. This data set is used in combination with additional field measurements, remote sensing and digital elevation model (DEM) analysis to provide input data for modelling Holocene valley development. On the basis of this information, geomorphic process units (GPUs) are defined by means of GIS modelling. These units represent areas of homogeneous process composition that transfer sediments. Since the data base enables the quantification of single processes, the interaction of processes within the units can also be quantified. Applying this concept permits calculation of recent sediment transfer rates and hence leads to a better understanding of actual geomorphic landscape development activity. To extrapolate these data in time and space the process–related sediments in the valley are analysed for depth and total volume, primarily using geophysical methods. In this fashion the validity of measured process rates is evaluated for the Holocene time scale. Results from this analysis are exemplified in a cross–profile showing some of the principal sediment units in the valley. For example, the measured modern rates on a slush torrent debris fan seem to represent the Holocene mean rate. This approach should also be suitable for revealing Holocene geomorphic landscape development in terms of climate change.     

Potential impact of climate change on ecosystems of the Barents Sea Region

The EU project BALANCE (Global Change Vulnerabilities in the Barents region: Linking Arctic Natural Resources, Climate Change and Economies) aims to assess vulnerability to climate change in the Barents Sea Region. As a prerequisite the potential impact of climate change on selected ecosystems of the study area has to be quantified, which is the subject of the present paper. A set of ecosystem models was run to generate baseline and future scenarios for 1990, 2020, 2050 and 2080. The models are based on data from the Regional Climate Model (REMO), driven by a GCM which in turn is forced by the IPCC-B2 scenario. The climate change is documented by means of the Köppen climate classification. Since the multitude of models requires the effect of climate change on individual terrestrial and marine systems to be integrated, the paper concentrates on a standardised visualisation of potential impacts by use of a Geographical Information System for the timeslices 2050 and 2080. The resulting maps show that both terrestrial and marine ecosystems of the Barents region will undergo significant changes until both 2050 and 2080.     

Assessment of diel chemical and isotopic techniques to investigate biogeochemical cycles in the upper Klamath River,Oregon, USA

The upper Klamath River experiences a cyanobacterial algal bloom and poor water quality during the summer. Diel chemical and isotopic techniques have been employed in order to investigate the rates of biogeochemical processes.Four diel measurements of field parameters (temperature, pH, dissolved oxygen concentrations, and alkalinity) and stable isotope compositions (dissolved oxygen–δ¹⁸O and dissolved inorganic carbon–δ¹³C) have been performed between June 2007 and August 2008. Significant diel variations of pH, dissolved oxygen (DO) concentration, and DO–δ¹⁸O were observed, due to varying rates of primary productivity vs. respiration vs. gas exchange with air. Diel cycles are generally similar to those previously observed in river systems, although there are also differences compared to previous studies. In large part, these different diel signatures are the result of the low turbulence of the upper Klamath River. Observed changes in the diel signatures vs. sampling date reflect the evolution of the status of the algal bloom over the course of the summer.Results indicate the potential utility of applying diel chemical and stable isotope techniques to investigate the rates of biogeochemical cycles in slow-moving rivers, lakes, and reservoirs, but also illustrate the increased complexity of stable isotope dynamics in these low-turbulence systems compared to well-mixed aquatic systems.     

Nitrogen loading to Pleasant Bay, Cape Cod: application of models and stable isotopes to detect incipient nutrient enrichment of estuaries

To test and refine methods to detect nutrient enrichment and resulting eutrophication, we applied the Waquoit Bay nitrogen loading model (NLM) and Estuarine loading model (ELM) to estuaries of Pleasant Bay that receive increasing but low N loads (25-199 kg N ha(-1) yr(-1)) from land. Contributions of wastewater to these estuaries increased from 7% to 63% as N loads increased, and modeled estimates of dissolved inorganic nitrogen in the water were within approximately 27% of measured values. N isotopic signatures in suspended and benthic organic matter and in tissue of quahogs increased as wastewater contributions to N loads increased, with clams approximately 4 per thousand heavier than organic matter, indicating that even at these low N loads, N from land-derived sources moved detectably up the food web. These results extend the application of NLM and ELM to detect incipient levels of N enrichment and demonstrate that these models can be used in conjunction with isotope measurements as the basis for food web analyses in a system exposed to relatively lower N loads than previously studied.