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21.
Richard Morrill 《The Professional geographer》1983,35(1):1-9
Geography is hurt by a widespread misunderstanding of its nature and accomplishments. The purpose here is to show how the seeming great diversity of geographic study is unified by a common concern with the meaning of place and the organization of space. Geography can be proud of its increasing contribution to knowledge and to society, but it must constantly guard the quality of its work. 相似文献
22.
Pollen-inferred vegetation and environmental changes in the central Tibetan Plateau since 8200 yr BP
LingYu Tang CaiMing Shen ChunHai Li JinLan Peng Hui Liu Kam-Biu Liu Carrie Morrill Jonathan T. Overpeck Julia E. Coel Bao Yang 《中国科学D辑(英文版)》2009,52(8):1104-1114
The ecotone between alpine steppe and meadow in the central Tibetan Plateau is sensitive to climate changes. Here we used
the pollen records from three lakes in this region to reconstruct the evolution of local vegetation and climate since 8200
cal. yr BP. The history of temperature and precipitation was reconstructed quantitatively with multi-bioclimatic indexes and
a transfer function from pollen records. Results show that the steppe/meadow dominated during the period of 8200–6500 cal.
yr BP, especially 8200–7200 cal. yr BP, indicating the central Tibetan Plateau was controlled by strong monsoon. The steppe
dominated during the periods of 6000–4900, 4400–3900, and 2800–2400 cal. yr BP. The steppe decreased gradually and the meadow
expanded during the period of 4900–4400 cal. yr BP. Three century-scale drought events occurred during 5800–4900, 4400–3900
and 2800 cal. yr BP, respectively. The first time when the regional climate shifted to the present level was at 6500 cal.
yr BP in the central Plateau. Since 3000 cal. yr BP, the temperature and precipitation have decreased gradually to the present
level. However, the cold climate between 700–300 cal. yr BP likely corresponds to the Little Ice Age.
Supported by Chinese Academy of Sciences 100 Talents Project (Grant No. 29082762), National Natural Science Foundation of
China (Grant Nos. 40671196, 40372085, 49371068, 49871078), and U.S. National Science Foundation (Grant Nos. ATM-9410491, ATM-008194) 相似文献
23.
Amy J. Wagner Carrie Morrill Bette L. Otto-Bliesner Nan Rosenbloom Kelsey R. Watkins 《Climate Dynamics》2013,41(11-12):2855-2873
Previous model experiments of the 8.2 ka event forced by the drainage of Lake Agassiz often do not produce climate anomalies as long as those inferred from proxies. In addition to the Agassiz forcing, there is new evidence for significant amounts of freshwater entering the ocean at 8.2 ka from the disintegration of the Laurentide ice sheet (LIS). We use the Community Climate System Model version 3 (CCSM3) to test the contribution of this additional meltwater flux. Similar to previous model experiments, we find that the estimated freshwater forcing from Lake Agassiz is capable of sustaining ocean and climate anomalies for only two to three decades, much shorter than the event duration of ~150 years in proxies. Using new estimates of the LIS freshwater flux (~0.13 Sv for 100 years) from the collapse of the Hudson Bay ice dome in addition to the Agassiz drainage, the CCSM3 generates climate anomalies with a magnitude and duration that match within error those from proxies. This result is insensitive to the duration of freshwater release, a major uncertainty, if the total volume remains the same. An analysis of the modeled North Atlantic freshwater budget indicates that the Agassiz drainage is rapidly transported out of the North Atlantic while the LIS contribution generates longer-lasting freshwater anomalies that are also subject to recirculation by the subtropical gyre back into the North Atlantic. Thus, the meltwater flux originating from the LIS appears to be more important than the Agassiz drainage in generating 8.2 ka climate anomalies and is one way to reconcile some model-data discrepancies. 相似文献
24.
Richard Morrill 《Geographical review》2013,103(3):315-335
The evolution of Seattle's “Central Area” or “CD” is traced for eighty years from 1930 through 2010. Relevant theory about social and economic discrimination and urban development is presented first. This is followed by a brief history of the Central Area as a black community and a review of relevant literature. The changing distribution of the Central Area is presented through a series of maps, from an unexpected origin and development in a relatively desirable area east of downtown Seattle to its gradual displacement far southward, as central Seattle experienced gentrification. This spatial change is evaluated with respect to the expectations from theory presented earlier. 相似文献
25.
The collapse of the Olive View Hospital Psychiatric Day Clinic is studied using three biaxial force-deflection models to represent the columns of the building. These models are: shear collapse, elastic and inelastic. The biaxial models for shear and inelastic behaviour are new developments and are useful for non-linear structural dynamic studies. In the present study, the shear collapse model is intended to represent the actual prototype behaviour. The inelastic model, which is based on a hardening rule of plasticity, is used to study the performance of a hypothetical structure with the same storey shear capacity as the prototype but which exhibits ductile behaviour. The prototype structure had a base storey shear capacity of 25 per cent, and actually failed by shearing of all of the first floor columns. In the present study, the shear collapse model predicted this behaviour even with the El Centro accelerogram as input. This result may have far-reaching significance because many low-rise reinforced concrete buildings which were designed according to recent codes have similar storey shear capacity coefficients and column properties. According to this study, such buildings may collapse even in a moderate earthquake. In the inelastic representation, the structure was found to have a base storey shear capacity of 80 per cent when moment hinging was assumed to occur at the top and bottom of the columns. Even with this high strength capacity, the permanent offset computed from the inelastic model corresponded to a ductility factor of 5 when the Pacoima Dam accelerogram was used as input. On the basis of damage to other structures observed on the site, it seems likely that ground motion of about the Pacoima Dam intensity occurred at Olive View. From this it is concluded that a low-rise ductile frame concrete building, even with this high shear force capacity, may not prove satisfactory for hospital use when subjected to strong ground motion. 相似文献
26.
The LASCO-C3 coronagraph on SOHO, launched in December 1995, has been collecting images of the corona and background star
fields in a regular manner since 1996. This instrument contains a number of broadband filters with various passbands in the
range between 400 and 1100 nm. The filter used most often has been the Clear filter (400–900 nm) but there are four other
filters with about 100 nm passbands that are also used periodically. Preliminary calibration of the C3 optical system was
done before flight and a number of techniques that use star intensities or magnitudes and position have been applied during
flight. In order to understand the long-term behavior of the C3 instrument, we have recently performed an analysis of LASCO
data that examines the observed intensities of a set of moderately bright stars whose spectra is known from 13 color photometry.
Using these star spectra and the observed count rates we have derived the photometric calibration factors of the C3 coronagraph
for all five color filters with an absolute precision of about ± 7%. Observations with the Clear filter have been used to
look for long-term trends in the instrument sensitivity. The observations indicate a very slight decrease in the instrument
sensitivity of about 3.5% over the 8 years studied here. 相似文献
27.
Climate Dynamics - The East Asian winter monsoon (EAWM) exhibits significant variability on intraseasonal, interannual, and interdecadal time scales and the variability can be extended to Holocene... 相似文献
28.
Richard L. Morrill 《The Professional geographer》1979,31(1):55-65
The recent phenomenon of relative metropolitan decline and non-metropolitan growth is set into two broader frameworks: first, decentralization is an expected consequence of earlier industrialization and metropolitanization; and, second, the change follows a parallel shift in power, industrialization, and urbanization from the core to the periphery of the country. Evidence is found for both. The older industrial states thus exhibit non-metropolitan growth, whereas many newly industrializing states continue to show vigorous metropolitanization. 相似文献
29.
Richard Morrill 《The Professional geographer》2006,58(2):155-160
Browning's classic 1974 map of Megalopolis, covering the growth of Megalopolis from 1950 to 1970, is updated through 2000. The color map depicts the extent and expansion of Megalopolis for three time periods, 1950–1970, 1970–1990, and 1990–2000. Discussion relates the growth of Megalopolis to social and economic forces influencing urbanization in the United States in the latter half of the twentieth century. 相似文献