Upper air density derived from the orbits of Discoverer satellites and its variation with latitude     

B. R. May 《Planetary and Space Science》1964,12(12):1179-1185

Observations on artificial satellites have been used to investigate how the air density at heights between 190 and 260 km varies with latitude The Discoverer series of satellites was used because the position of their perigees moved over the latitude range from 80°S to 80°N.

It is concluded that the air density at a fixed height is a function of latitude and is about 30 per cent smaller at the poles than at the equator. This result is applicable to a local time of 14^h in the years 1959–1960: it is different from that obtained by Groves who concluded that the density is independent of latitude.  相似文献   

Land reform in Namaqualand, 1994–2005: A review     

Harry May  Edward Lahiff 《Journal of Arid Environments》2007,70(4):782

With the transition to democracy in 1994, South Africa was faced with an enormous challenge in redressing the highly unequal and racialized pattern of land rights inherited from the colonial and apartheid past. In Namaqualand, a history of land dispossession and racial segregation presented the new government with a complex set of problems, which led to a series of distinct policy responses within the context of the wider national land reform programme. Land reform in Namaqualand aims to impact positively on local people's access to land, improve livelihood opportunities and develop the local economy. Unique features of the land reform process in Namaqualand include the reform of tenure in the former Coloured Rural Areas, the prominent role played by local municipalities and the heavy reliance on municipal commonage as a form of landholding. This study provides and overview of the process of land reform in Namaqualand since 1994, considering the three elements of tenure reform, land redistribution and restitution of historical land rights. It concludes that, while considerable progress has been made in provision of additional land to historically disadvantaged communities, obstacles remain in the area of post-transfer support to new and emerging farmers.  相似文献   

Estimation of fault-zone conductance by calibration of a regional groundwater flow model: Desert Hot Springs,California   总被引：1，自引：2，他引：1  

Alex Mayer  Wesley May  Chad Lukkarila  Jimmy Diehl 《Hydrogeology Journal》2007,15(6):1093-1106

The hydraulic conductance of a large fault zone has been estimated by calibrating a regional groundwater flow model. Drops in groundwater elevations of over 80 m have been observed along a 15-km length of the Mission Creek fault, California, USA. The large drops in elevation are attributed to the reduced hydraulic conductivity of the fault materials. A conceptual and numerical model of the two hydrologic subbasins in Desert Hot Springs, separated by the Mission Creek fault, was developed. The model was used to estimate the hydraulic conductance along the fault. The parameter estimation involved calibrating the model with observed groundwater elevations from over 40 locations over a 60-year period. The fault hydraulic conductances were estimated assuming a linear trend in the fault length, yielding variations in the fault hydraulic conductance of about an order of magnitude along the fault length (2?×?10^?11–4?×?10^?10 1/s). When an average fault thickness of 35 m is assumed, the fault hydraulic conductivity values are estimated to be from three to five orders of magnitude lower than the surrounding materials. A sensitivity analysis indicated that assumptions made in the conceptual model do not significantly affect estimated fault hydraulic conductances.  相似文献   

THE ASIAN TSUNAMI, ACADEMICS AND ACADEMIC RESEARCH     

Sophia Buranakul  Carl Grundy-Warr  Ben Horton  Lisa Law  Jonathan Rigg  May Tan-Mullins 《Singapore journal of tropical geography》2005,26(2):244-248

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Coupling of the Perturbed C–N–P Cycles in Industrial Time     

Abraham Lerman  Fred T. Mackenzie  L. May Ver 《Aquatic Geochemistry》2004,10(1-2):3-32

Coupling of the C–N–P biogeochemical cycles is effected by the dependence of the land and aquatic primary producers on the availability of N and P. In general, the Redfield ratios C:P and N:P in the reservoirs supplying nutrients for primary production on land, in the oceanic coastal zone, and in the surface ocean differ from these ratios in the land phytomass and aquatic plankton. When N:P in the source is higher than in primary producers, this results in a potential accumulation of some excess nitrogen in soil water and coastal water, and increased denitrification flux to the atmosphere. The oceanic coastal zone plays an important role in the coupled C–N–P cycles and their dynamics because of its intermediate position between the land and oceanic reservoirs. These coupled cycles were analyzed for the last 300 years of exposure to four human-generated forcings (fossil fuel emissions, land use change, chemical fertilization of land, and sewage discharge to the coastal zone) and global temperature rise. In the period from 1700 to 2000, there has been a net loss of C, N, and P primarily from the land phytomass and soil humus, despite the rise in atmospheric CO₂, increased recycling of nutrients from humus, chemical fertilization, and re-growth of forests on previously disturbed land. The main mechanisms responsible for the net loss were increased riverine transport to the coastal zone of dissolved and particulate materials and, for N, increased denitrification on land. The oceanic coastal zone gained N and P, resulting in their accumulation in the organic pool of living biomass and dissolved and reactive particulates, as well as in their accumulation in coastal sediments from land-derived and in situ produced organic matter. Pronounced shifts in the rates and directions of change in some of the major land reservoirs occurred near the mid-1900s. Denitrification removes N from the pool available for primary production. It is the strongest on land, accounting for 73–83% of N removal from land by the combined mechanisms of denitrification and riverine export.  相似文献   

Simulation of the variability and extremes of daily rainfall during the Indian summer monsoon for present and future times in a global time-slice experiment   总被引：1，自引：1，他引：1  

W. May 《Climate Dynamics》2004,22(2-3):183-204

In this study the simulation of the variability and extremes of daily rainfall during the Indian summer monsoon for the present-day and the future climate is investigated. This is done on the basis of a global time-slice experiment (TSL) with the ECHAM4 atmospheric general circulation model (GCM) at a high horizontal resolution of T106. The first time-slice (period: 1970–1999) represents the present-day climate and the second (2060–2089) the future climate. Moreover, observational rainfall data from the Global Precipitation Climatology Project (GPCP, 1997–2002) and rainfall data from the ECMWF re-analysis (ERA, 1958–2001) are considered. ERA reveals serious deficiencies in its representation of the variability and extremes of daily rainfall during the Indian summer monsoon. These are mainly a severe overestimation of the frequency of wet days over the oceans and in the Himalayas, where also the rainfall intensity is overestimated. Further, ERA shows unrealistically heavy rainfall events over the tropical Indian Ocean. The ECHAM4 atmospheric GCM at a horizontal resolution of T106, on the other hand, simulates the variability and extremes of daily rainfall in good agreement with the observations. The only marked deficiencies are an underestimation of the rainfall intensity on the west coast of the Indian peninsula and in Bangladesh, an overestimation over the tropical Indian Ocean, due to an erroneous northwestward extension of the tropical convergence zone, and an overestimation of the frequency of wet days in Tibet. Further, heavy rainfall events are relatively strong in the centre of the Indian peninsula. For the future, TSL predicts large increases in the rainfall intensity over the tropical Indian Ocean as well as in northern Pakistan and northwest India, but decreases in southern Pakistan, in the centre of the Indian peninsula, and over the western part of the Bay of Bengal. The frequency of wet days is markedly increased over the tropical Indian Ocean and decreased over the northern part of the Arabian Sea and in Tibet. The intensity of heavy rainfall events is generally increased in the future, with large increases over the Arabian Sea and the tropical Indian Ocean, in northern Pakistan and northwest India as well as in northeast India, Bangladesh, and Myanmar.  相似文献   

Discovery of the “Phantom” dinoflagellate in Chesapeake Bay     

Alan J. Lewitus  Roman V. Jesien  Todd M. Kana  JoAnn M. Burkholder  Howard B. Glasgow  Eric May 《Estuaries and Coasts》1995,18(2):373-378

Since its discovery in natural estuarine habitat of North Carolina in 1991, the widespread impact of the toxic dinoflagellate, Pfiesteria piscicida (gen. et sp. nov.), popularly called the “phantom” dinoflagellate, on North Carolina fish stocks has been established, yet little is known about its influence outside of North Carolina estuaries. Here, we document the presence of P. piscicida in Chesapeake Bay. A fish kill was observed after inoculating an aquarium containing mummichogs with sediment samples from Jenkins Creek, a brackish creek (salinity 11‰) of the Chesapeake Bay system. P. piscicida was the cause of the kill, as supported by morphological, physiological, and histological evidence. The appearance and behavior of the algae and symptoms associated with fish mortality were consistent with those previously observed in P. piscicida-associated aquaria fish kills in North Carolina. The discovery of P. piscicida in Chesapeake Bay supports the speculation that these toxic dinoflagellates have a dramatic and far-reaching impact on fish stocks in shallow, eutrophic estuaries along the eastern United States.  相似文献   

A time-slice experiment with the ECHAM4 AGCM at high resolution: the impact of horizontal resolution on annual mean climate change   总被引：2，自引：0，他引：2  

W. May  E. Roeckner 《Climate Dynamics》2001,17(5-6):407-420

 The climate response to increasing levels of atmospheric greenhouse gases, prescribed according to the International Panel of Climate Change (IPCC) scenario IS92a, is studied in two model simulations. The reference simulation is a transient response experiment performed with a medium-resolution (T42) coupled general circulation model of the atmosphere and ocean (ECHAM4/OPYC) developed at the Max-Planck-Institute for Meteorology. For two 30-year “time slices”, representing the present-day climate and the future climate at the time of effective CO₂ doubling, the annual mean climate states are compared with those obtained from the high-resolution (T106) ECHAM4 model forced with monthly sea surface temperatures and sea-ice from the coupled model. The large-scale changes in temperature, zonal wind, sea-level pressure and precipitation are broadly similar. This applies, in particular, to the respective zonal means. In general, except for precipitation, the responses in the time-slice experiments are slightly weaker than those simulated in the coupled model due to a smaller effect of the horizontal resolution on the simulations of the future (warmer) period than on the simulations of the present period. On a regional scale, the impact of horizontal resolution is smaller in the Southern than in the Northern Hemisphere, where the response differences are caused mainly by changes in the positions of the stationary waves. Although the precipitation responses are broadly similar, there are few notable exceptions such as a more pronounced maximum over the equatorial oceans in the T106 experiment but a weaker response over low-latitude land areas. Differences in precipitation response are found especially in areas with strong topographical control such as South America, for example. Received: 17 January 2000 / Accepted: 7 July 2000  相似文献   

TOPOGRAPHIC SURVEYING: THE JUBILEE LINE EXTENSION SURVEY     

D. Stevens  W. M. McKay  M. R. May 《The Photogrammetric Record》1992,14(79):85-98

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A Field Experiment to Study the Behavior of Tetrachloroethylene Below the Water Table: Spatial Distribution of Residual and Pooled DNAPL   总被引：6，自引：0，他引：6  

Bernard H. Kueper  David Redman  Robert C. Starr  Stanley Reitsma  May Mah 《Ground water》1993,31(5):756-766

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