Simulation of daily energy budget and mean soil temperatures at an arid site

Summary Soil temperature is often inadequately based upon relatively few measurements at widely dispersed locations. Within arid regions, such as the desert southwestern United States, soils, microclimates, and thus soil temperature may be markedly heterogeneous. Because extensive measurement of soil temperature is often not feasible, models are needed that simulate soil temperature based on readily available soil survey and above-ground weather information. This paper describes a simple energy-budget based model for simulating daily mean temperatures within a bare arid land soil. The model requires basic information on soil physical properties, and daily weather data including air temperature, windspeed, rainfall, and solar radiation to calculate daily surface energy budget components and surface temperature. One of two alternative numerical methods is then used to calculated subsurface temperatures. Tests of the model using 1987 daily temperature data from an arid site at Yuma, Arizona resulted in root mean square deviations within 1.4°C between daily modeled and measured temperatures at both 0.05 and 0.10 m depths. Sensitivity analysis showed modeled temperatures at 0.05 m depth to be most sensitive to parameters affecting the surface energy balance such as air temperature and solar radiation. Modeled temperatures at 1.0m depth were relatively more sensitive to initial temperature conditions and to parameters affecting distribution of energy within the profile such as thermal conductivity.With 3 Figures     

Effect of Surface Heterogeneity on the Boundary-Layer Height: A Case Study at a Semi-Arid Forest

We investigate the effects of an isolated meso-\(\gamma \)-scale surface heterogeneity for roughness and albedo on the atmospheric boundary-layer (ABL) height, with a case study at a semi-arid forest surrounded by sparse shrubland (forest area: \(28~\text{ km }^2\), forest length in the main wind direction: 7 km). Doppler lidar and ceilometer measurements at this semi-arid forest show an increase in the ABL height over the forest compared with the shrubland on four out of eight days. The differences in the ABL height between shrubland and forest are explained for all days with a model that assumes a linear growth of the internal boundary layer of the forest through the convective ABL upwind of the forest followed by a square-root growth into the stable free atmosphere. For the environmental conditions that existed during our measurements, the increase in ABL height due to large sensible heat fluxes from the forest (\(600~\text {W~m}^{-2}\) in summer) is subdued by stable stratification in the free atmosphere above the ABL, or reduced by high wind speeds in the mixed layer.     

Deriving characteristic parameters of the convective boundary layer from sodar measurements of the vertical velocity variance

This paper deals with the derivation of the convective mixing height and the characteristic convective velocity w _* from profiles of _w measured by sodar. The parameters were obtained by fitting an analytical profile to the observed data. Results were compared with values obtained by the meteorological preprocessor of a dispersion model and from noon radiosoundings. In addition, a Monte Carlo method was applied to study the influence of measurement errors. It turned out that it is inherently difficult to determine the depth of deep mixed layers from sodar measurements with a limited range, although the determination of w _* should be possible. However, a significant underestimation of _w , and thus w _*, was found, which is probably due to disproportional sampling of updrafts and downdrafts.     

Climate change and coastal flooding in Metro Boston: impacts and adaptation strategies

Sea level rise (SLR) due to climate change will increase storm surge height along the 825 km long coastline of Metro Boston, USA. Land at risk consists of urban waterfront with piers and armoring, residential areas with and without seawalls and revetments, and undeveloped land with either rock coasts or gently sloping beachfront and low-lying coastal marshes. Risk-based analysis shows that the cumulative 100 year economic impacts on developed areas from increased storm surge flooding depend heavily upon the adaptation response, location, and estimated sea level rise. Generally it is found that it is advantageous to use expensive structural protection in areas that are highly developed and less structural approaches such as floodproofing and limiting or removing development in less developed or environmentally sensitive areas.     

The upper limit of glaciation in the Himalayas

On the slopes of Himalayan Mountains there is a reduction and culmination of glaciation at 7000–7200 m asl. The presumed cause for this is that the surface temperatures on these slopes are too low for glaciation. This working hypothesis was verified with temperature measurements using collected infra-red radiation. The regression analysis of the measurements taken in the Mt. Everest region during sunny weather conditions of the post-monsoon season resulted in a 0°C line at 7000–7200 m asl. The coincidence of the 0°C line with the upper limit of glaciation is causally definable with the copula between the function of temperature and snow metamorphism: since it is too cold above 7000–7200 m asl, metamorphism into perennial or galcial ice through settling or sintering is absent or simply too slow. High relief and drifting hinder here the processes of ice-formation through pressure compaction of the dry-snow accumulation caused by molecular diffusion and recrystallization. Above 7200 m only continuous leeward accumulations of shifting snow on wall sections with moderate inclination lead to the formation of seracs. However, glaciation generally ceases at this level. This additionally confirms another study. It has been proven that Himalayan glaciers with catchment areas over 7000 m do not extend further downward than those glaciers whose catchment areas just reach this altitude. A break in balance at 7100 m asl is thereby confirmed, and the upper glacial limit is proven. Above the glacial region a rocky zo ne adjoins with pergelic conditions even in the surface layer. This zone is covered by snow during monsoon season only. Here, the weathering processes take place in an arid environment without thawing and purely by means of temperature variations below 0°C. They could correspond to those occurring on a larger scale on the planets of our solar system.A lowering of the upper glacial limit by at least 660 or 1200 m respectively, analogous to the Pleistocene snow-line depression reconstructed in S Tibet and the Central Himalayas, is assumed during the Ice Age.The author gratefully acknowledges the translation of this paper rendered by Dr. J. A. Hellen, Newcastle-upon-Tyne.     

The petrography of Southern Tibet

Summary Mineralogical investigations of rock samples from the Transhimalaya and Tibetan Himalaya allow the conclusion that during the last glaciations in this area there was long distance glacial transport. The samples from the Mt. Everest group, the highest region of the continental crust, provide an account of the petrological data collected from this area. They depict a juxtaposition of sedimentary series and granitic intrusive bodies and also extreme tectonic action deep into their cystalline structure.     

Influence of low ozone episodes on erythemal UV-B radiation in Austria

This study investigates the influence of low ozone episodes on UV-B radiation in Austria during the period 1999 to 2015. To this aim observations of total column ozone (TCO) in the Greater Alpine Region (Arosa, Switzerland; Hohenpeissenberg, Germany; Hradec Kralove, Czech Republic; Sonnblick, Austria), and erythemal UV-B radiation, available from 12 sites of the Austrian UV-B monitoring network, are analyzed. As previous definitions for low ozone episodes are not particularly suited to investigate effects on UV radiation, a novel threshold approach—considering anomalies—is developed to provide a joint framework for the analysis of extremes. TCO and UV extremes are negatively correlated, although modulating effects of sunshine duration impact the robustness of the statistical relationship. Therefore, information on relative sunshine duration (SD_rel), available at (or nearby) UV-B monitoring sites, is included as explanatory variable in the analysis. The joint analysis of anomalies of both UV index (UVI) and total ozone (∆UVI, ∆TCO) and SD_rel across sites shows that more than 65% of observations with strongly negative ozone anomalies (∆TCO < −1) led to positive UVI anomalies. Considering only days with strongly positive UVI anomaly (∆UVI > 1), we find (across all sites) that about 90% correspond to negative ∆TCO. The remaining 10% of days occurred during fair weather conditions (SD_rel ≥ 80%) explaining the appearance of ∆UVI > 1 despite positive TCO anomalies. Further, we introduce an anomaly amplification factor (AAF), which quantifies the expected change of the ∆UVI for a given change in ∆TCO.

     

The microscale cooling effects of water sensitive urban design and irrigation in a suburban environment

There is still considerable uncertainty about precipitation at high elevation in mountain terrain due to the relatively few in situ measurements available and to the particular variability of the parameter. In this study, several spatialization techniques were tested, some for climatological time scale and others for daily fields, for precipitation over the western Alps for the period of 1990–2012. The study domain and period were chosen for the quality of available in situ observations and density of the network. First, a weather-type classification was established with a technique based on canonical correlation analysis combining large- and regional-scale data. The spatialization techniques applied for the climatological time scale were adapted from the Aurelhy method which uses elevation and principal components of the topography as predictors. The spatialization techniques applied to daily fields were based on kriging of daily rain gauges and used the climatological fields as predictors. This study aims to validate the advantage of using the climatology of the weather type of the day as predictor for daily fields over a monthly climatology. The climatology of the weather type of the day seems to demonstrate some small improvement.Finally, annual means over the period of 1990–2012 were produced using several methods, including some from accumulation of daily fields and others from the spatialization of in situ station means. Precipitation at high elevations and vertical climatological gradients were particularly scrutinized. Annual means based on sums of daily fields seem to have better performances.This paper only presents results for precipitation but temperature was also analysed.     

The Othris Ophiolite, Greece: A snapshot of subduction initiation at a mid-ocean ridge

The mantle section of the Tethyan-type Othris Ophiolite, Greece, records tectono-magmatic processes characteristic of both mid-ocean ridges and supra-subduction zones. The Othris Ophiolite is a remnant of the Jurassic Neotethys Ocean, which existed between Eurasia and Gondwanaland. Othris peridotites range from fertile plagioclase lherzolites to depleted harzburgites. Abundances of Al₂O₃ and CaO show well-defined inverse linear correlations with MgO, suggesting that the Othris peridotites formed as residua from variable degrees of partial melting.

Peridotites from the Fournos Kaïtsa and western Katáchloron sub-massifs are similar to abyssal peridotites and can be explained by a multistage model with some melting in the garnet stability field followed by moderate degrees of anhydrous near-fractional melting in the spinel stability field. In contrast, the peridotites from the Metalleio, Eretria, and eastern Katáchloron sub-massifs, and the Vourinos ophiolite are highly depleted and have extremely low concentrations of Al₂O₃ and heavy rare earth elements. These peridotites have enriched light REE contents compared to the middle REE. These residua are best modelled by hydrous melting due to a flux of slab-derived fluid to the mantle wedge during melting.

The occurrence of both styles of melting regimes within close spatial and temporal association in the same ophiolite is explained by intra-oceanic thrusting and forced subduction initiation at (or near) a mid-ocean ridge. Thus, the Othris Ophiolite, and probably Tethyan-type ophiolites in general, represent a transient phase of plate tectonic reorganisation rather than quasi-steady state plate tectonics.