Some examples of river-capture in the Peak District     

William Platt 《Proceedings of the Geologists' Association. Geologists' Association》1935,46(1):40-42

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Occurrence of polar stratospheric clouds at Kiruna     

C.-F. Enell  Å. Steen  T. Wagner  U. Frieß  K. Pfeilsticker  U. Platt  K.-H. Fricke 《Annales Geophysicae》1999,17(11):1457-1462

Polar stratospheric clouds (PSCs) are often observed in the Kiruna region in northern Sweden, east of the Scandinavian mountain range, during wintertime. PSC occurrence can be detected by ground-based optical instruments. Most of these require clear tropospheric weather. By applying the zenith-sky colour index technique, which works under most weather conditions, the data availability can be extended. The observations suggest that PSC events, especially of type II (water PSCs) may indeed more common than predicted by synoptic models, which is expected because of the frequent presence of mountain-induced leewaves. However, it will be of importance to increase the density of independent observations.  相似文献   

Phenological Responses to ENSO in the Global Oceans     

M.-F. Racault  N. Menon  T. Platt 《Surveys in Geophysics》2017,38(1):277-293

Phenology relates to the study of timing of periodic events in the life cycle of plants or animals as influenced by environmental conditions and climatic forcing. Phenological metrics provide information essential to quantify variations in the life cycle of these organisms. The metrics also allow us to estimate the speed at which living organisms respond to environmental changes. At the surface of the oceans, microscopic plant cells, so-called phytoplankton, grow and sometimes form blooms, with concentrations reaching up to 100 million cells per litre and extending over many square kilometres. These blooms can have a huge collective impact on ocean colour, because they contain chlorophyll and other auxiliary pigments, making them visible from space. Phytoplankton populations have a high turnover rate and can respond within hours to days to environmental perturbations. This makes them ideal indicators to study the first-level biological response to environmental changes. In the Earth’s climate system, the El Niño–Southern Oscillation (ENSO) dominates large-scale inter-annual variations in environmental conditions. It serves as a natural experiment to study and understand how phytoplankton in the ocean (and hence the organisms at higher trophic levels) respond to climate variability. Here, the ENSO influence on phytoplankton is estimated through variations in chlorophyll concentration, primary production and timings of initiation, peak, termination and duration of the growing period. The phenological variabilities are used to characterise phytoplankton responses to changes in some physical variables: sea surface temperature, sea surface height and wind. It is reported that in oceanic regions experiencing high annual variations in the solar cycle, such as in high latitudes, the influence of ENSO may be readily measured using annual mean anomalies of physical variables. In contrast, in oceanic regions where ENSO modulates a climate system characterised by a seasonal reversal of the wind forcing, such as the monsoon system in the Indian Ocean, phenology-based mean anomalies of physical variables help refine evaluation of the mechanisms driving the biological responses and provide a more comprehensive understanding of the integrated processes.  相似文献   

An Evaluation of an Object-Oriented Paradigm for Land Use/Land Cover Classification∗     

Rutherford V. Platt  Lauren Rapoza 《The Professional geographer》2013,65(1):87-100

Object-oriented image classification has tremendous potential to improve classification accuracies of land use and land cover (LULC), yet its benefits have only been minimally tested in peer-reviewed studies. We aim to quantify the benefits of an object-oriented method over a traditional pixel-based method for the mixed urban–suburban–agricultural landscape surrounding Gettysburg, Pennsylvania. To do so, we compared a traditional pixel-based classification using maximum likelihood to the object-oriented image classification paradigm embedded in eCognition Professional 4.0 software. This object-oriented paradigm has at least four components not typically used in pixel-based classification: (1) the segmentation procedure, (2) nearest neighbor classifier, (3) the integration of expert knowledge, and (4) feature space optimization. We evaluated each of these components individually to determine the source of any improvement in classification accuracy. We found that the combination of segmentation into image objects, the nearest neighbor classifier, and integration of expert knowledge yields substantially improved classification accuracy for the scene compared to a traditional pixel-based method. However, with the exception of feature space optimization, little or no improvement in classification accuracy is achieved by each of these strategies individually.  相似文献   

Automated flash flood warning systems     

Rutherford H. Platt 《Applied geography (Sevenoaks, England)》1987,7(4)

The hazard of flash flooding, affecting both remote upland stream valleys and urbanizing metropolitan watersheds, poses a need for rapid identification and analysis of sudden changes in stream flow to allow timely public warning. Since 1976, the US National Weather Service (NWS), in cooperation with various regional authorities, has developed a new, low-cost system in response to this need. This system, known as ALERT (Automated Local Evaluation in Real Time) employs stream and rain gauges equipped with self-activating radio transmitters which communicate with a central microcomputer. Using software calibrated to the watershed in question, predictions of downstream flood levels may be rapidly generated. This paper reviews the origins and technology of ALERT systems and reports on the experiences to date of 32 system users. The survey found a high level of satisfaction with ALERT, but uncertainty concerning the reliability of the systems, since few have yet been tested in actual flash floods.  相似文献   

THE LONDON SQUARE: Gardens in the Midst of Town. By Todd Longstaffe–Gowan     

Lorne Platt 《Geographical review》2013,103(2):308-310

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Diagnostic Properties of Phytoplankton Time Series from Remote Sensing     

Trevor Platt  Shubha Sathyendranath  George N. WhiteIII  César Fuentes-Yaco  Li Zhai  Emmanuel Devred  Charles Tang 《Estuaries and Coasts》2010,33(2):428-439

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Chronology of Sediment Deposition in Upper Klamath Lake, Oregon     

Steven M. Colman  J. Platt Bradbury  John P. McGeehin  Charles W. Holmes  David Edginton  Andrei M. Sarna-Wojcicki 《Journal of Paleolimnology》2004,31(2):139-149

A combination of tephrochronology and ¹⁴C, ²¹⁰Pb, and ¹³⁷Cs measurements provides a robust chronology for sedimentation in Upper Klamath Lake during the last 45 000 years. Mixing of surficial sediments and possible mobility of the radio-isotopes limit the usefulness of the ¹³⁷Cs and ²¹⁰Pb data, but ²¹⁰Pb profiles provide reasonable average sediment accumulation rates for the last 100–150 years. Radiocarbon ages near the top of the core are somewhat erratic and are too old, probably as a result of detrital organic carbon, which may have become a more common component in recent times as surrounding marshes were drained. Below the tops of the cores, radiocarbon ages in the center of the basin appear to be about 400 years too old, while those on the margin appear to be accurate, based on comparisons with tephra layers of known age.Taken together, the data can be combined into reasonable age models for each site. Sediments have accumulated at site K1, near the center of the basin, about 2 times faster than at site CM2, on the margin of the lake. The rates are about 0.10 and 0.05 cm/yr, respectively. The chronological data also indicate that accumulation rates were slower during the early to middle Holocene than during the late Holocene, consistent with increasing wetness in the late Holocene.  相似文献   

Dating high-grade metamorphism—constraints from rare-earth elements in zircon and garnet   总被引：32，自引：8，他引：24  

Martin?J.?WhitehouseEmail author  John?P.?Platt 《Contributions to Mineralogy and Petrology》2003,145(1):61-74

We integrate petrography and SIMS REE analyses of garnet and polyphase zircon from a pelitic granulite adjacent to the Ronda peridotite, Betic Cordillera, southern Spain to constrain the significance of zircon U-Pb geochronology. Sillimanite inclusions in garnet rims suggest that they grew during decompression, and Ca enrichment in their rims records initiation of partial melting. Chondrite-normalised REE profiles of zircon cores are typically magmatic (positive La to Lu slope and Ce anomaly), whereas overgrowths have flat or negatively sloping heavy-REE profiles (Gd-Lu). The presence of rimmed zircon grains only in the garnet rims and the matrix suggests that this zircon phase grew after garnet had already sequestered heavy REEs, a process documented here by progressive depletion of heavy REE in the garnets from centre to rim. Combined with the textural evidence, we suggest that the U-Pb age of 21.3ǂ.3 Ma obtained from the zircon rims dates a point on this decompression path rather than the peak metamorphic pressure.  相似文献   

Theoretical study of onset conditions for solar eruptive processes: Influence of the boundaries     

U. Platt  T. Neukirch 《Solar physics》1994,153(1-2):287-306

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