A miniature three-dimensional anemometer for use within and above plant canopies

A miniature anemometer has been designed for the measurement of turbulent transport within canopies. The sensing element utilizes a relatively new concept in hot-film anemometry, in which the angular measurement is derived from the non-uniformity in heat transfer coefficient around the circumference of the cylindrical hot-film. The element is split along its length to form two separate conducting films and the relative magnitudes of the heat convected from each side are used to calculate the elevation angle of the wind. An electromechanical servosystem operated by a second split-film keeps the sensing head facing into the wind. The anemometer measures all three components of velocity over the complete solid angle without octant ambiguity and at velocities as low as 20 cm s^–1. It is a research instrument and because of its non-linear response characteristics, data handling is best accomplished by digital computer.The response of the split-film elements extends to high frequencies. The servo-system follows turbulent fluctuations up to approximately 5 Hz and keeps the probe within a few degrees of the wind at all times. In field tests, total wind speed and wind component measurements compared well with more conventional anemometers; eddy-correlation measurements of shear-stress with the split-film anemometer were in good agreement with measurements from a shear stress lysimeter and from a pressure-sphere anemometer.     

Coments on “derivation of water vapor fluxes from lidar measurements” by W. E. Eichingeret al.

Eichingeret al. (1993) discuss the use of a Raman lidar for measurements of water vapor fluxes and suggest that the method is superior to the use of standard micrometeorological, point sensor measurements. Although the lidar shows considerable promise for some purposes, we believe that their criticisms of point sensors are not warranted; that there are difficulties with their application of dissipation techniques to extract fluxes; and that they misinterpret the existence of plume structures as statistically significant spatial variations of turbulent fluxes.     

A comparison of some aerodynamic resistance methods using measurements over cotton and grass from the 1991 California ozone deposition experiment

Measurements of dry, deposition velocities (V _d ) of O₃ (using the eddy correlation technique) made over a cotton field and senescent grass near Fresno California during July and August 1991 were used to test some dry deposition velocity models. Over the cotton field, the observed maximum daytimeV _d was about 0.8 cm s^–1 and the average nighttime value was about 0.2 cm s^–1. Over the grass, daytime values averaged about 0.2 cm s^–1 and nighttime values about 0.05 cm s^–1. Application of a site-specific model known as ADOM (Acid Deposition and Oxidant Model) over the cotton field generally overestimated the observations except for a few hours in the afternoon when the observations were underestimated The overestimation was attributed to inadequacies in the surface resistance formulation and the underestimation to uncertainties in the aerodynamic formulation. Unlike previous studies which focused on the role of surface resistance, we perform additional tests using a large variety of aerodynamic resistance formulae, in addition to those in ADOM, to determine their influence on the modelledV _d of O₃ over, cotton. Over grass, ADOM considerably overestimated the observations but showed improvement when other surface resistance formulations were applied.     

Duricrust development and valley evolution: Process–landform links in the kalahari

Duricrusts are an important landscape component of the Kalahari region of central southern Africa. Their exposures within the dry valleys (mekgacha) of the Kalahari provide some of the most widespread surface outcrops of the terrestrial Jurassic to Holocene Kalahari Group sediments. Exposures have been extensively used in the construction of lithostrati-graphic sequences, on the assumption that valley systems have incised their courses through a pre-existing duricrust sequence. Recent work, however, has identified the role of groundwater erosion processes in valley development, which may have influenced duricrust formation. Studies of duricrusts from boreholes drilled within two mekgacha show that duricrust type is intrinsically related to the presence of a valley. Analyses of calcretes and silcretes in a series of profiles and thin sections from the Letlhakeng area of Botswana also indicate extensive alteration and diagenesis in association with former higher water tables. Sedimentary sequences within duricrust host materials can be identified but there is no evidence for correlation of duricrust cements between exposures. Profile studies from the Auob Valley in Namibia, however, suggest that this valley has incised through a sequence of duricrusts. Caution is advised in future attempts to correlate duricrust types on the basis of valley exposures, with the recommendation that where such exposures are used in a lithostratigraphic context, only duricrust host material characteristics and not cementing materials should be considered.     

Two “S-type” granite suites with low initial 87Sr/86Sr ratios from the New England Batholith,Australia

Two “S-type” (pelitic) granite suites from the New England Batholith, N.S.W., have Upper Carboniferous ages, indicating that they predate by 40 m.y. the intrusion of hornblende biotite granites, and are the oldest plutons of the batholith. Mineralogically and geochemically both suites have “pelitic” characteristics, one suite containing an Al-rich biotite, muscovite and cordierite, the other an Al-rich biotite and rare pyrope-almandine garnet. Low initial ⁸⁷Sr/⁸⁶Sr ratios of 0.706 for both suites probably reflect the volcanoclastic nature and young age of the sedimentary source of these granites at the time of melting. The age of the suites coincides with the last stages of (Andean type?) volcanism along an andesite/dacite volcanic chain to the west, suggesting an origin for the “S-type” granitic magma by partial melting of deformed sediments marginal to a continental region.     

The city in an era of restricted car usage: Some further observations and policy responses

This paper is written in response to a previous one by LEE and WOOD (Geoforum, 11, 17–29, 1980) in which they outlined some possible effects of future oil shortages on urban form and social structure. Australian cities appear to be among those likely to be most seriously affected and evidence presented here indicates that some adjustments within the urban housing market are already beginning to take place. However, according to the trade-off model of residential structure, the effects of increased travel costs on household income distribution patterns are likely to be less far-reaching than Lee and Wood suggest. The reactions of some Australian planning authorities are also outlined.     

Multivariate analysis of sedimentary environments using grain-size frequency distributions

Multivariate statistics were used to characterize and test the effectiveness of grain-size frequencies as environmental discriminators. Sediment from the following two depositional systems along eastern Lake Michigan were studied: (1) a closed system with respect to available grain sizes (Little Sable Point), and (2) an open system (Sleeping Bear Point-Manitou Passage). Principal components analysis shows that grain-size distributions are composed of two or more subgroups that reflect surface creep bedload, mixed suspension bedload, and uniform suspension. Discriminant function and principal latent vector analyses of the Little Sable Point environments show that, when available sediment is limited with respect to grain size (0.5 φto 3.0 φ), similar size distributions can occur in environments supposedly characterized by different energy conditions. Sediment in the Sleeping Bear Point-Manitou Passage system is not restricted to available grain sizes and the environments discriminated very well (α < 0.001). The grain-size distributions are such that they reflect differences in energy conditions within the environments. It is apparent that the grain sizes available to a depositional system control to a great extent the effectiveness of environmental discrimination.