An example of attenuation by wet snow on a radar dome

Abstract

A case study of the degradation of weather radar data by the accretion of wet snow on a radar dome is presented as a precautionary example to radar users. During the ERICA field program in 1989, accumulated precipitation on the radome at Halifax, Nova Scotia, attenuated signal in a distinctive, pie‐shaped sector on the upwind side of the radar.     

Simulation of a Stably Stratified Atmospheric Boundary Layer Using One-Dimensional Turbulence

One-dimensional turbulence (ODT) is a single-column simulation in which vertical motions are represented by an unsteady advective process, rather than their customary representation by a diffusive process. No space or time averaging of mesh-resolved motions is invoked. Molecular-transport scales can be resolved in ODT simulations of laboratory-scale flows, but this resolution of these scales is prohibitively expensive in ODT simulations of the atmospheric boundary layer (ABL), except possibly in small subregions of a non-uniform mesh.Here, two methods for ODT simulation of the ABL on uniform meshes are described and applied to the GABLS (GEWEX Atmospheric Boundary Layer Study; GEWEX is the Global Energy and Water Cycle Experiment) stable boundary-layer intercomparison case. One method involves resolution of the roughness scale using a fixed eddy viscosity to represent subgrid motions. The other method, which is implemented at lower spatial resolution, involves a variable eddy viscosity determined by the local mesh-resolved flow, as in multi-dimensional large-eddy simulation (LES). When run at typical LES resolution, it reproduces some of the key high-resolution results, but its fidelity is lower in some important respects. It is concluded that a more elaborate empirically based representation of the subgrid physics, closely analogous to closures currently employed in LES of the ABL, might improve its performance substantially, yielding a cost-effective ABL simulation tool. Prospects for further application of ODT to the ABL, including possible use of ODT as a near-surface subgrid closure framework for general circulation modeling, are assessed.     

An objective classification system of air mass types for Szeged, Hungary, with special interest in air pollution levels

Summary This paper determines the characteristic air mass types over the Carpathian Basin for the winter (December, January, and February) and summer (June, July and August) months dependant on levels of the main air pollutants. Based on the ECMWF data set, daily sea-level pressure fields analysed at 00 UTC were prepared for each air mass type (cluster) in order to relate sea-level pressure patterns with the level of air pollutants in Szeged. The data comprise daily values of twelve meteorological and eight pollutant parameters for the period 1997–2001. Objective definition of the characteristic air mass types is achieved by using the methods of Factor Analysis and Cluster Analysis. According to the results, during the winter months five air mass types (clusters) were detected based on higher concentrations of primary pollutants that occur with high irradiance and low wind speed. This is the case when an anticyclone is found over the Carpathian Basin and over the region south of Hungary, influencing the weather of the country. Low levels of pollutants occur when zonal currents exert influence over Hungary. During the summer months anticyclones and anticyclone ridge situations are found over the Carpathian Basin. (During the prevalence of anticyclone ridge situations, the Carpathian Basin is found at the edge of a high pressure centre.) As a result of high irradiance and very low NO levels, secondary pollutants are highly enriched.     

Petrology of ultramafic and mafic xenoliths in picrite of Kahoolawe Island,Hawaii

A picrite lava (22 wt% MgO; 35 vol.% ol) along the western shore of the1.3–1.4 Ma Kahoolawe tholeiitic shield, Hawaii, contains small xenoliths of harzburgite, lherzolite, norite, and wehrlite. The various rock types have textures where either orthopyroxene, clinopyroxene, or plagioclase is in a poikilitic relationship with olivine. The Mg#s of the olivine, orthopyroxene, and clinopyroxene in this xenolith suite range between 86 and 82; spinel Mg#s range from 60 to 49, and plagioclase is An_75–80. A ⁸⁷Sr/⁸⁶Sr ratio for one ol-norite xenolith is 0.70444. In comparison, the host picrite has olivine phenocrysts with an average Mg# of 86.2 (range 87.5–84.5), and a whole-rock ⁸⁷Sr/⁸⁶Sr ratio of 0.70426. Textural and isotopic information together with mineral compositions indicate that the xenoliths are related to Kahoolawe tholeiitic magmatism, but are not crystallization products of the magma represented by their host picrite. Rather, the xenoliths are crystalline products of earlier primitive liquids (FeO/MgO ranging 1 to 1.3) at 5–9 kbar in the cumulate environment of a magma reservoir or conduit system. The presence of ultramafic xenoliths in picrite but not in typical Kahoolawe tholeiitic lava (6–9 wt% MgO) is consistent with replenishment of reservoirs by dense Mg-rich magma emplaced beneath resident, less dense tholeiitic magma. Mg-rich magmas have proximity to reservoir cumulate zones and are therefore more likely than fractionated residual liquids to entrain fragments of cumulate rock.     

RELAXING ASSUMPTIONS OF PERFECT INFORMATION IN PARK VISITATION MODELS*

Variables related to urban park awareness are identified and methods for relaxing assumptions of perfect information in park use models are discussed. Park awareness is related to park characteristics (age and degree of development of the park), population characteristics (race, age, length of residence, recreation participation), and distance. Park attributes are stronger predictors of both park awareness and use than is distance. These findings parallel similar research on the cognitive aspects of shopping decisions.     

Storminess and vulnerability along the Atlantic coastlines of Europe: analysis of storm records and of a greenhouse gases induced climate scenario

Identification of the distinctive circulation patterns of storminess on the Atlantic margin of Europe forms the main objective of this study; dealing with storm frequency, intensity and tracking. The climatology of the extratropical cyclones that affect this region has been examined for the period 1940–1998. Coastal meteorological data from Ireland to Spain have been linked to the cyclone history for the North Atlantic in the analysis of storm records for European coasts. The study examines the evolution in the occurrence of storms since the 1940s and also their relationship with the North Atlantic Oscillation (NAO). Results indicate a seasonal shift in the wind climate, with regionally more severe winters and calmer summers established. This pattern appears to be linked to a northward displacement in the main North Atlantic cyclone track.

An experiment with the ECHAM4 A-GCM at high resolution (T106) has also been used to model the effect of a greenhouse gases induced warming climate on the climatology of coastal storms in the region. The experiment consists of (1), a 30-year control time-slice representing present-day equivalent CO₂ concentrations and (2), a 30-year perturbed period corresponding to a time when the radiative forcing has doubled in terms of equivalent CO₂ concentrations. The boundary conditions have been obtained from an atmosphere-ocean coupled OA-GCM simulation at low horizontal resolution. An algorithm was developed to allow the identification of individual cyclone movements in selected coastal zones. For most of the northern part of the study region, covering Ireland and Scotland, results describe the establishment by ca. 2060 of a tendency for fewer but more intense storms.

The impacts of these changes in storminess for the vulnerability of European Atlantic coasts are considered. For low-lying, exposed and ‘soft’ sedimentary coasts, as in Ireland, these changes in storminess are likely to result in significant localised increases in coastal erosion.     

Groundwater sustainability and groundwater/surface-water interaction in arid Dunhuang Basin,northwest China

The Dunhuang Basin, a typical inland basin in northwestern China, suffers a net loss of groundwater and the occasional disappearance of the Crescent Lake. Within this region, the groundwater/surface-water interactions are important for the sustainability of the groundwater resources. A three-dimensional transient groundwater flow model was established and calibrated using MODFLOW 2000, which was used to predict changes to these interactions once a water diversion project is completed. The simulated results indicate that introducing water from outside of the basin into the Shule and Danghe rivers could reverse the negative groundwater balance in the Basin. River-water/groundwater interactions control the groundwater hydrology, where river leakage to the groundwater in the Basin will increase from 3,114?×?10⁴ m³/year in 2017 to 11,875?×?10⁴ m³/year in 2021, and to 17,039?×?10⁴ m³/year in 2036. In comparison, groundwater discharge to the rivers will decrease from 3277?×?10⁴ m³/year in 2017 to 1857?×?10⁴ m³/year in 2021, and to 510?×?10⁴ m³/year by 2036; thus, the hydrology will switch from groundwater discharge to groundwater recharge after implementing the water diversion project. The simulation indicates that the increased net river infiltration due to the water diversion project will raise the water table and then effectively increasing the water level of the Crescent Lake, as the lake level is contiguous with the water table. However, the regional phreatic evaporation will be enhanced, which may intensify soil salinization in the Dunhuang Basin. These results can guide the water allocation scheme for the water diversion project to alleviate groundwater depletion and mitigate geo-environmental problem.     

Environmental geochemistry of the River Gomti: A tributary of the Ganges River

Water and sediment samples collected from the Gomti River, a tributary of the Ganges River system, during the postmonsoon season have been analyzed to estimate major elemental chemistry. Water chemistry of the River Gomti shows almost monotonous spatial distribution of various chemical species, especially because of uniform presence of alluvium Dun gravels throughout the basin. The river annually transports 0.34×10⁶ tonnes of total suspended material (TSM) and 3.0×10⁶ tonnes of total dissolved solids (TDS), 69 percent of which is accounted for by bicarbonate ions only. Samples collected downstream of the city of Lucknow show the influence of anthropogenic loadings for a considerable distance in the river water. Na⁺, Cl^–, and SO₄ ^2– concentrations build up downstream. The bed sediment chemistry is dominated by Si (36 percent), reflecting a high percentage of detrital quartz, which makes up about 74 percent of the mineralogy of the bed sediments in the River Gomti. The average Kjeldahl nitrogen concentration (234 g/g) indicates indirectly the amount of organic matter in the sediments. The Hg concentration in sediments has been found to be higher (average 904 ppb) than the background value. The suspended sediments are well sorted, very finely skewed, and extremely leptokurtic, indicating a low energy condition of flow in the Gomti River. The influence of chemical loads in the Gomti has been found to be small or nonexistent on the Ganges River, perhaps because the water discharge of the Gomti (1.57 percent) to the Ganges is quite low.