A 1951–80 global land precipitation climatology for the evaluation of general circulation models     

Mike Hulme 《Climate Dynamics》1992,7(2):57-72

Previous evaluations of model precipitation fields have suffered from two weaknesses; they have used only mean observed climatologies which have prevented an explicit evaluation of interannual variability, and they have generally failed to quantify the significance of differences between model and observed fields. To rectify these weaknesses, a global precipitation climatology is required which is designed with model evaluation in mind. This paper describes such a climatology representative of the period 1951–80. The climatology is based on historical gauge-precipitation measurements from over 2500 land-based station time series representing over 28% of the Earth's surface. It is necessarily biased towards terrestrial areas. The climatology (CRU5180) is derived from month-by-month gridbox precipitation estimates at 5° resolution. Although other global precipitation climatologies exist, this is the first one to have used a consistent reference period for each station, and to include the details of interannual variability. Fields of mean seasonal and annual precipitation and mean temporal variability are presented, and the variability of global-mean precipitation over 1951–80 assessed. The resulting mean monthly global precipitation fields are compared briefly with two other observed climatologies used for model evaluation, those prepared by Jaeger and Legates and Willmott. The global and hemispheric means, mean seasonal cycles, and spatial patterns of the three cimatologies are compared. Although based on a smaller set of stations than Legates and Willmott, the CRU5180 precipitation estimates agree closely with their uncorrected climatology.  相似文献   

Reply to P. I. A. Kinnell's comments on ‘the generation and redistribution of overland flow on a massive oxic soil in a eucalypt woodland within the semi-arid tropics of North Australia’, Mike Bonell and John Williams. Hydrological processes, 1, 31–46 (1986)     

Mike Bonell  John Williams 《水文研究》1989,3(1):97-100

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Automated classification of stellar spectra — II. Two-dimensional classification with neural networks and principal components analysis     

Coryn A. L. Bailer-Jones  Mike Irwin  & Ted von Hippel 《Monthly notices of the Royal Astronomical Society》1998,298(2):361-377

We investigate the application of neural networks to the automation of MK spectral classification. The data set for this project consists of a set of over 5000 optical (3800–5200 Å) spectra obtained from objective prism plates from the Michigan Spectral Survey. These spectra, along with their two-dimensional MK classifications listed in the Michigan Henry Draper Catalogue, were used to develop supervised neural network classifiers. We show that neural networks can give accurate spectral type classifications (σ₆₈= 0.82 subtypes, σ_rms= 1.09 subtypes) across the full range of spectral types present in the data set (B2–M7). We show also that the networks yield correct luminosity classes for over 95 per cent of both dwarfs and giants with a high degree of confidence.   Stellar spectra generally contain a large amount of redundant information. We investigate the application of principal components analysis (PCA) to the optimal compression of spectra. We show that PCA can compress the spectra by a factor of over 30 while retaining essentially all of the useful information in the data set. Furthermore, it is shown that this compression optimally removes noise and can be used to identify unusual spectra.   This paper is a continuation of the work carried out by von Hippel et al. (Paper I).  相似文献   

Sediment supply and climate change: implications for basin stratigraphy   总被引：8，自引：3，他引：5  

Mike R. Leeder  Tracey Harris  & Mike J. Kirkby 《Basin Research》1998,10(1):7-18

The rate of sediment supply from erosional catchment to depositional basin depends primarily upon climate, relief, catchment slope and lithology. It varies in both time and space. Spatial changes in erosion rates due to variations in lithology are illustrated by contrasting rates of drainage divide migration away from faults of known ages. Time variations in relative sediment supply are extremely complex and vary widely according to the direction and magnitude of climate change. In many parts of the Great Basin and south-western USA, glacial maximum climates were characterized by higher effective moisture and the altitudinal downward spread of woods and forests. Sparse data from alluvial fans indicate reduced sediment supply, despite the increased runoff evident from higher lake levels. The situation in Mediterranean areas is less clear, with rival climatic scenarios for vegetation ecotypes predicting contrasting runoff. In order to test these latter we run Cumulative Seasonal Erosion Potential [CSEP] experiments for present-day and a variety of full-glacial Mediterranean candidate climates. The results indicate the likelihood of enhanced sediment supply and runoff compared to the present day during full-glacial times for a cool wet winter climate and a reduction in sediment supply and runoff for a full-glacial cool dry winter climate. We then explore the consequences of such phase differences in sediment supply, and sea and lake levels for the stratigraphy of sedimentary basins. Highstands and lowstands of sea or lake may be accompanied by greater or lesser sediment and water supply, as determined by the regional climate and the direction of climatic change. Thus marine lowstands are not necessarily periods of great transfer of coarse clastic sediments to shelves and deep water basinal environments. Unsteady sediment supply has greatest implications for alluvial systems, in particular the effect that changing relative supplies of water and sediment have upon river and fan channel incision.  相似文献   

INVITED EDITORIAL Clastic sediment supply to basins     

Niels Hovius  & Mike Leeder 《Basin Research》1998,10(1):1-5

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Use of annular flumes to determine the influence of current velocity and bivalves on material flux at the sediment-water interface   总被引：3，自引：0，他引：3  

John Widdows  Mary D. Brinsley  Peter N. Salkeld  Mike Elliott 《Estuaries and Coasts》1998,21(4):552-559

A benthic annular flume for both laboratory and in situ deployment on intertidal mudflats is described. The flume provides a means of quantifying material flux (i.e., biodeposition of suspended particulates, sediment resuspension, nutrients, oxygen, and contaminants) across the sediment-water interface in relation to changes in current velocity and benthic community structure and/or population density of key macrofauna species. Flume experiments have investigated the impact of the infaunal bivalveMacoma balthica and the epifaunal bivalveMytilus edulis on seston and sediment flux at the sediment-water interface. The bioturbatorMacoma was found to increase the sediment resuspension and/or erodability by 4-fold, at densities similar to those recorded at the Skeffling mudflat (Humber estuary) (i.e., >1000 individuals m^?2). There was a significant correlation between sediment resuspension andMacoma density (r=0.99; p<0.001), which supported previous in situ field observations indicating bioturbation byMacoma enhanced sediment erodability. Biodeposition rates (g m^?2 h¹) ofMytilus edulis andCerastoderma edule were quantified and related to changes in population density in a mussel bed (Cleethorpes, Humber estuary). Biodeposition rates were up to 40-times the natural sedimentation rates. At the highest mussel bed densities (i.e., 50–100% cover or >1400 mussels m^?2) the physical presence of this epifaunal bivalve on the sediment surface reduced erosion by 10-fold. The shift from net biodeposition to net erosion occurred at current velocities of 20–25 cm s^?1. These results demonstrate that infaunal and epifaunal bivalves can have a significant impact on seston flux or sediment deposition and on sediment resuspension or erodability in estuaries where there are extensive mudflats.  相似文献   

Semi-automated extraction of digital objective prism spectra     

Coryn A. L. Bailer-Jones  Mike Irwin  & Ted von Hippel 《Monthly notices of the Royal Astronomical Society》1998,298(4):1061-1068

We describe a method for the extraction of spectra from high-dispersion objective prism plates. Our method is a catalogue-driven plate solution approach, making use of the right ascension and declination coordinates for the target objects. In contrast to existing methods of photographic plate reduction, we digitize the entire plate and extract spectra off-line. This approach has the advantages that it can be applied to CCD objective prism images and spectra can be re-extracted (or additional spectra extracted) without having to re-scan the plate. After a brief initial interactive period, the subsequent reduction procedure is completely automatic, resulting in fully reduced, wavelength-justified spectra. We also discuss a method of removing stellar continua using a combination of non-linear filtering algorithms.   The method described is used to extract over 12 000 spectra from a set of 92 objective prism plates. These spectra are used in an associated project to develop automated spectral classifiers based on neural networks.  相似文献   

Editorial     

Mike Kirkby 《地球表面变化过程与地形》1981,6(2):101-101

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Chemical evolution of the early precambrian: edited by Cyril Ponnamperuma. Academic Press, 1977, 221 pp. $15.00 (Hard cover)     

George Pemberton 《Geochimica et cosmochimica acta》1980,44(10):1621-1622

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Seismic reflection coefficients from mantle fault zones   总被引：3，自引：0，他引：3  

Mike Warner &  Susan McGeary 《Geophysical Journal International》1987,89(1):223-230

Summary. Several bright reflections from structures within the mantle can be seen on BIRPS' deep seismic reflection profiles. We have calculated apparent reflection coefficients for the brightest of these events and obtain values around 0.1. It is not possible to produce such large reflections by either compositional layering or seismic anisotropy if olivine and pyroxene are the only significant minerals in the mantle. These large reflections can be produced by a mafic layer or a partially hydrated layer within normal peridotite. The brightest reflections seem to be best explained as major faults or shear zones within the mantle.  相似文献