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151.
CunDe Xiao ZhongQin Li Lin Zhao ShiChang Kang YuanQing He Xiang Qin XiaoBo He 《寒旱区科学》2012,4(1):0001-0012
In coordination with Global Cryosphere Watch (GCW) initiated by World Meteorology Administration (WMO), a regional observation
network is proposed based on existing stations/sites over High Asia and cryospheric elements required by GCW. Thus,
High Asian Cryosphere (HAC) network is preliminary designed, composing of seven "supersites", each containing several reference
sites. The network covers major mountain ranges in High Asia, such as East Tianshan, Qilian, Tanggula, Nyainqentanglha,
Himalayas as well as the central and eastern Qinghai-Xizang (Tibet) Plateau. Although multiple cryospheric elements were observed
at the existing HAC network, many others, which are required by Integrated Global Observation System-Cryosphere
Theme (IGOS-Cryosphere), are not yet included. More comprehensive observations are necessary to be included into "supersites"
of HAC, so that the basic requirements for validation of satellite data, assimilation and coupled regional models can be met. 相似文献
152.
The observed South Asia High (SAH) center is characterized by two distinctive equilibrium modes
during boreal midsummer, namely the center of SAH is located between 82.5o--92.5oE for the
Tibetan Plateau mode and between 55o--65oE for the Iranian Plateau mode, respectively. The
present study describes the ability of 15 coupled general circulation models (CGCM) used in the Intergovernmental
Panel on Climate Changes (IPCC) 4th Assessment Report to reproduce the observed bimodality of the SAH. These models
reveal a wide range of skill in simulating this bimodality. Nearly half of the models reproduced the bimodality,
while the other half of the models did not simulate well these two modes whereas usually preferring one
mode. The models that reproduced the bimodality of the SAH present similar horizontal and vertical
circulations as those features from the NCEP reanalysis data. The results from these models identify
the warm characteristics of the SAH and indicate that these two modes have different dynamic and
thermodynamic properties.
Different characteristics of the simulated sensible heat and latent heat related to precipitation
partly contribute to the difference in the simulations of the SAH bimodality. The majority of these
models that prefer to simulate the Tibetan Plateau mode produce a small sensible heat flux difference
between the Iranian Plateau and the Tibetan Plateau, and also generally simulate a very strong false
precipitation center over the east of the Tibetan Plateau, which indicates strong latent release and
thereby contributes to the preference of the SAH center on the Tibetan Plateau. Whereas, the models
that reproduce the bimodality of the SAH tend to simulate large precipitation over the southern Himalayas
and no obviously false precipitation is produced over the east of the Tibetan Plateau. In addition,
the models resolution may also have important impacts on the simulations of precipitation. 相似文献
153.
北极海冰对2008年1月乌拉尔高压异常的影响 总被引:1,自引:1,他引:0
2008年1月我国南方发生了大范围的雨雪冰冻灾害天气,造成此次灾害的一个重要原因是乌拉尔高压异常的长期维持,而作为下垫面的海洋,2007/2008冬季环北欧海海冰异常偏少。观测资料合成分析表明,乌拉尔山地区出现高压异常与巴伦支海和喀拉海的海冰偏少存在密切对应关系。利用大气环流模式试验研究了(90°W~60°E)区域海冰异常对大气的影响,模拟结果显示海冰对乌拉尔高压异常有正的贡献,线性模式诊断表明天气尺度瞬变波是海冰影响乌拉尔高压异常的一种重要机制。 相似文献
154.
Features of atmospheric circulation and thermal structures are discussed using the NCAR/NCEP
data to reveal the reasons for the late onset and anomalous southward persistence of the South China Sea
Summer Monsoon (SCSSM) in 2005. The results show that three factors are crucial. First, a strong
Arabian High overlaps with a high-latitude blocking high and channels strong cold air to southern Asia.
Second, the Tibetan Plateau has a bigger snow cover than usual in spring and the melting of snow cools
down the surface. Third, the Somali Jet breaks out at a much later date, being not conducive to convection
over Indochina. The former two factors restrict atmospheric sensible heating over the Tibetan Plateau and
nearby regions while the third one limits latent heating over Indochina. All of the factors slow down
atmospheric warming and postpone the onset of SCSSM. Long after the onset of SCSSM, strong cold air
over India advances the Southwest Monsoon northward slowly, resulting in weaker convection and latent
heating over the Tibetan Plateau and nearby areas. The negative feedback conversely inhibits further
northward movement of Southwest Monsoon. 相似文献
155.
This paper investigates the interannual variation of the West Pacific Subtropical High (WPSH)
intensity based on the data compiled by the Chinese National Climate Center. Monthly reanalysis data
from National Centers for Environmental Prediction and National Center for Atmospheric Research
(NCEP/NCAR) are also used to study the lead-lag relationship between WPSH intensity and surface heat
flux anomalies. The three major findings are as follows: First, WPSH intensity presents good seasonal
persistence, especially from winter to the ensuing summer. Persistence is more significant after 1977,
especially from spring to summer, and from summer to autumn; persistence of anticyclonic anomalies are
significantly better than cyclonic anomalies. Second, surface heat flux tends to present opposite anomalous
patterns between the strong and weak years of the WPSH intensity, which is especially valid at the latent
heat flux over the ocean. Simultaneous correlations between surface heat flux and WPSH intensity in each
of the seasons are marked by similar key areas. Finally, surface heat flux from the preceding winter of a
strong summer WPSH is quite similar to strong spring WPSH, but the positive anomalies over the
northwest Pacific and south of Japan are notably stronger. The situations in the weak years are similar
except for those over the northwest Pacific: winter surface heat flux shows negative anomalies for a weak
spring WPSH, but positive anomalies for a weak summer WPSH. It is suggested that surface heat flux in
the previous winter plays an important role in maintaining the WPSH intensity in the ensuing spring and
summer. 相似文献
156.
华南地区汛期极端降水的概率分布特征 总被引:18,自引:2,他引:16
利用1960-2005年华南地区71个测站的逐日降水量资料和NCEP/NCAR南半球月平均海平面气压场再分析资料,采用Le Page榆验、广义极值分布等统计诊断方法,研究了华南地区近46 a前汛期(4-6月)和后汛期(7-9月)极端降水的时空变化及概率分布特征.并讨论了南半球澳大利亚高压和马斯克林高压强度指数与华南汛期暴雨日数间年代际变化的关系.结果表明:(1)1992年华南地区降水发生了由减少趋势到增多趋势的突变,降水趋势发生突变后前汛期极端降水量和日极端降水强度有所下降,而后汛期则是显著增强.(2)华南汛期年平均日最大降水量、50 a一遇日最大降水量极值和暴雨日数的空间分布特征相似,即前汛期的空间分布自南向北呈现"低-高-低"的分布趋势,后汛期呈现由沿海到内陆的"高-低"的分布趋势.(3)1992年发生突变后,前、后汛期年平均日最大降水量和年平均暴雨日数显著增加和减少的空间分布基本一致.(4)就年代际变化而言,南半球澳大利亚高压和马斯克林高压的强度变化是华南汛期降水异常的重要气候背景,即当两高压处在同时增强时期时,华南前汛期极端降水处于偏少阶段,后汛期则处于偏多阶段. 相似文献
157.
北京城市高温遥感指标初探与时空格局分析 总被引:4,自引:2,他引:2
利用北京高温天气下的NOAA18/AVHRR卫星资料与气象台站资料,分析了日最高气温与遥感反演的城市地表温度的关系,初步确定了地表高温阈值并建立了高温遥感指标,并利用1989~2008年(缺2002年)6~9月NOAA/AVHRR资料开展了北京地区高温时空格局分析研究。指标初步研究表明:北京气温高温值为35、37、40°C对应的遥感地表高温值分别为44、47、52°C,可以较好地适用于北京平原地区;利用该阈值建立的地表高温强度指标(LSHI)对北京平原高温的监测与气象台站高温监测基本一致,而高温比例指数指标(LSHP)能有效反映出城市高温空间强弱和时间差异。北京遥感地表高温空间格局分析显示:夏季(6~8月)旬平均遥感地表温度≥44°C年出现概率不超过50%,广泛分布于城区和平原区;旬平均遥感地表温度≥47°C年出现概率不超过40%,集中于北京五环内;旬平均遥感地表温度≥52°C年出现概率不超过15%,集中于城区;6~9月高温出现的概率高值区一般都集中于五环内,其中旬平均遥感地表温度≥44°C、≥47°C、≥52°C的出现概率分别为80%~100%、60%~80%、10%~40%。 相似文献
158.
Day-to-day precipitation data of Junes during the 43 years of 1958-2000 from stations to the
south of Yangtze River are used to divide regions and run statistical analysis of sustained torrential rainfall
processes. A preliminary analysis is then made based on it and the results show that June is the month in
which torrential rains in the southern half of China take place frequently and sustained torrential rains
occur at the same time in South China and the area to the south of Yangtze River. In addition, the analysis
gives the basic features of sustained torrential rains of June in China and their interannual variability
patterns, with the suggestion that the amount of these events increases significantly after the 1990s. Lastly,
the sustained torrential rains occurring in Junes of 1994, 1998 and 2005 in the southern half of China are
taken as examples in the research on the basic patterns and formation mechanisms of the evolution of
double rain-bands during the rain season in South China and the area to the south of Yangtze River. The
analysis shows that the large scale environment field in which sustained torrential rains occur is related to
the stable sustaining of the South Asia High and upper level jet streams. 相似文献
159.
Abdel-Zaher M. Abouzeid Douglas W. Fuerstenau 《International Journal of Mineral Processing》2009,93(1):59-65
Attempts at improving comminution machines generally have been directed towards increasing the performance efficiency, particularly increasing throughput rate and decreasing energy consumption. The latest and most successful new comminution technology has been the high-pressure grinding rolls (HPGR), which have proved to be highly efficient in energy consumption and to have a relatively high throughput rate at low steel consumption. Already used extensively in cement plants worldwide, the first HPGRs in the mineral industry were installed in plants processing diamond ores. They are now finding their way into the large-scale base-metal mining industry. Since feed constituents in natural ores vary in their physical properties such as hardness, plasticity and brittleness, the present paper is concerned with an investigation of the behavior of a heterogeneous feed as it passes through the HPGR. The effect of feed composition on operational parameters, the energy efficiency of comminution, and energy distribution among the feed components is addressed. Mineral particles with high hardness act as energy transfer agents in the roll gap and enhance the grinding of softer mineral particles in a mixed feed. 相似文献
160.
Jaqueline C. Rodrigues Tania Maria Haas Costa Márcia R. Gallas Celso C. Moro 《Physics and Chemistry of Minerals》2009,36(8):439-446
We investigate the structural evolution of synthetic layered double hydroxides (LDH) samples, processed at room temperature
and high-pressure (up to 7.7 GPa) in a toroidal chamber with two pressure-transmitting media, lead and graphite, using X-ray
diffraction, thermogravimetry and N2-adsorption isotherms techniques. The X-ray patterns of compacted samples show a decrease in the peak intensities. For both
pressure-transmitting media, our samples revealed a reduction of the basal d-spacing for the (003) plane when processed at
7.7 GPa. The expected high-pressure-induced amorphization was not observed. Surprisingly, we find high-pressure processing
to have a strong influence on the memory effect of the LDH, due essentially to the reduction of the surface area and pore
closing. Even when immersed in water, our samples did not recover the LDH structure, when either calcined at 450°C and compacted
at 7.7 GPa, or calcined at 700°C and immediately compacted at 2.5 and 7.7 GPa. 相似文献