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311.
CryoSat-2卫星海冰区域波形识别及海冰干舷高确定 总被引:1,自引:0,他引:1
利用40%阈值法对CryoSat-2卫星波形数据进行重跟踪,将波形特征参数和海冰浓度相结合,对海冰和Lead(浮冰之间的开阔水域)进行有效识别。利用沿轨前后搜索算法计算海冰干舷高,并引用AWI结果,绘制2011~2013年北冰洋多年冰区域和一年冰区域平均海冰干舷高变化趋势图。比较本文结果与AWI结果的各年同期数据,验证本文结果的可靠性。 相似文献
312.
Impacts of Two Ice Parameterization Schemes on the Cloud Microphysical Processes and Precipitation of a Severe Storm in Northern China
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A severe storm that occurred over Beijing in northern China on 23 June 2011 was simulated with two different ice crystal parameterization schemes(the DeMott scheme and Meyers scheme) by using the Regional Atmospheric Modeling System. Compared with the DeMott scheme, the simulation results with the Meyers scheme have the following characteristics:(1) Updrafts are stronger and more numerous;(2) The cloud is better organized and contains a greater peak of ice-phase hydrometeor mixing ratios;(3) Cloud water and hail mixing ratios increase while graupel mixing ratios decrease;(4) The surface precipitation is initially greater. However, at the end of the simulation, less precipitation is produced. In short, the differences between the two schemes are not obvious, but the De Mott scheme has a relatively more reasonable result. 相似文献
313.
Arctic sea ice and Eurasian climate: A review 总被引:12,自引:0,他引:12
GAO Yongqi SUN Jianqi LI Fei HE Shengping Stein SANDVEN YAN Qing ZHANG Zhongshi Katja LOHMANN Noel KEENLYSIDE Tore FUREVIK SUO Lingling 《大气科学进展》2015,32(1):92-114
The Arctic plays a fundamental role in the climate system and has shown significant climate change in recent decades,including the Arctic warming and decline of Arctic sea-ice extent and thickness. In contrast to the Arctic warming and reduction of Arctic sea ice, Europe, East Asia and North America have experienced anomalously cold conditions, with record snowfall during recent years. In this paper, we review current understanding of the sea-ice impacts on the Eurasian climate.Paleo, observational and modelling studies are covered to summarize several major themes, including: the variability of Arctic sea ice and its controls; the likely causes and apparent impacts of the Arctic sea-ice decline during the satellite era,as well as past and projected future impacts and trends; the links and feedback mechanisms between the Arctic sea ice and the Arctic Oscillation/North Atlantic Oscillation, the recent Eurasian cooling, winter atmospheric circulation, summer precipitation in East Asia, spring snowfall over Eurasia, East Asian winter monsoon, and midlatitude extreme weather; and the remote climate response(e.g., atmospheric circulation, air temperature) to changes in Arctic sea ice. We conclude with a brief summary and suggestions for future research. 相似文献
314.
P. Buford Price 《Planetary and Space Science》2010,58(10):1199-1206
Despite the fact that microbial cells are unlikely to be found in the Martian soil in the near future, this paper is written on the assumption that some of the seasonally varying concentration of Martian methane is due to ongoing methanogenesis. It is first pointed out that life might have arisen on Mars first and been transported to Earth later. A case is made that an icy origin of life is more likely than a hot origin, especially if biomolecules take advantage of the high encounter rates and stability against hydrolysis, and that microorganisms feed on the ions that comprise eutectic solutions in ice. Although certain difficulties are avoided if RNA and DNA grow while adsorbed on clay grains, double strand-breaks of microbial DNA due to alpha radioactivity are a far greater threat to microbial survival on clay or other rock types than in ice. Developing a relation between the rate of microbial metabolism in ice and the experimentally determined rate of production of trapped gases of microbial origin, one can estimate the concentration of methanogens that could account for the methane production rate as a function of temperature of their habitat. The result, of order 1 cell cm−3 in the Martian subsurface, seems an attainable goal provided samples are taken from at least 1 or 2 m below the hostile surface of Mars. Instruments on NASA’s 2011 Mars Science Lab will measure stable isotopes for methane, water, and carbon dioxide, which on Earth served to distinguish abiotic, thermogenic, and microbial origins. Future measurements of chirality of biomolecules might also provide evidence for Martian life. 相似文献
315.
The current sheet in Earth’s magnetotail often flaps, and the flapping waves could be induced propagating towards the dawn and dusk flanks, which could make the current sheet dynamic. To explore the dynamic characteristics of current sheet associated with the flapping motion holistically and provide reasonable physical interpretations, detailed direct calculation and analysis have been applied to one approximate analytic model of magnetic field in the flapping current sheet. The main results from the model demonstrate: (1) the magnetic fluctuation amplitude is attenuated from the center of current sheet to the lobe regions; The larger wave amplitude would induce the larger magnetic amplitude; (2) the curvature of magnetic field lines (MFLs), with maximum at the center of current sheet, is only dependent on the displacement Z along the south-north direction from the center of current sheet, regardless of the tilt of current sheet; (3) the half-thickness of neutral sheet, h, the minimum curvature radius of MFLs, Rcmin, and the tilt angle of current sheet, δ, satisfies h=Rcmin cos δ; (4) the gradient of magnetic strength forms a double-peak profile, and the peak value would be more intense if the local current sheet is more tilted; (5) current density j and its jy, jz components reach the extremum at the center of CS. j and jz would be more intense if the local current sheet is more tilted, but it is not the case for jy; and (6) the field-aligned component of current density mainly appears in the neutral sheet, and the sign of it would change alternatively as the flapping waves passing by. To check the validity of the model, one simulation on the virtual measurements has been made, and the results are in well consistence with actual observations of Cluster. 相似文献
316.
Ocean/ice interaction at the base of deep-drafted Antarctic ice shelves modifies the physical properties of inflowing shelf
waters to become Ice Shelf Water (ISW). In contrast to the conditions at the atmosphere/ocean interface, the increased hydrostatic
pressure at the glacial base causes gases embedded in the ice to dissolve completely after being released by melting. Helium
and neon, with an extremely low solubility, are saturated in glacial meltwater by more than 1000%. At the continental slope
in front of the large Antarctic caverns, ISW mixes with ambient waters to form different precursors of Antarctic Bottom Water.
A regional ocean circulation model, which uses an explicit formulation of the ocean/ice shelf interaction to describe for
the first time the input of noble gases to the Southern Ocean, is presented. The results reveal a long-term variability of
the basal mass loss solely controlled by the interaction between waters of the continental shelf and the ice shelf cavern.
Modeled helium and neon supersaturations from the Filchner–Ronne Ice Shelf front show a “low-pass” filtering of the inflowing
signal due to cavern processes. On circumpolar scales, the simulated helium and neon distributions allow us to quantify the
ISW contribution to bottom water, which spreads with the coastal current connecting the major formation sites in Ross and
Weddell Seas.
相似文献
Christian B. RodehackeEmail: |
317.
On the recent warming of the southeastern Bering Sea shelf 总被引:1,自引:0,他引:1
P.J. Stabeno N.A. Bond S.A. Salo 《Deep Sea Research Part II: Topical Studies in Oceanography》2007,54(23-26):2599
During the last decade, the southeastern Bering Sea shelf has undergone a warming of 3 °C that is closely associated with a marked decrease of sea ice over the area. This shift in the physical environment of the shelf can be attributed to a combination of mechanisms, including the presence over the eastern Bering Sea shelf of a relatively mild air mass during the winter, especially from 2000 to 2005; a shorter ice season caused by a later fall transition and/or an earlier spring transition; increased flow through Unimak Pass during winter, which introduces warm Gulf of Alaska water onto the southeastern shelf; and the feedback mechanism whereby warmer ocean temperatures during the summer delay the southward advection of sea ice during winter. While the relative importance of these four mechanisms is difficult to quantify, it is evident that for sea ice to form, cold arctic winds must cool the water column. Sea ice is then formed in the polynyas during periods of cold north winds, and this ice is advected southward over the eastern shelf. The other three mechanisms can modify ice formation and melt, and hence its extent. In combination, these four mechanisms have served to temporally and spatially limit ice during the 5-year period (2001–2005). Warming of the eastern Bering Sea shelf could have profound influences on the ecosystem of the Bering Sea—from modification of the timing of the spring phytoplankton bloom to the northward advance of subarctic species and the northward retreat of arctic species. 相似文献
318.
The Whippoorwill Formation is a gleyed diamicton that is present locally within bedrock depressions beneath the oldest glacial till in northern Missouri, USA. Stratigraphy, paleomagnetism, and cosmogenic-nuclide burial ages show that it was deposited between the Matuyama-Gauss magnetostratigraphic boundary at 2.58 Ma and the first advance of the Laurentide ice sheet into Missouri at 2.47 ± 0.19 Ma. High cosmogenic-nuclide concentrations also show that the constituents of the Whippoorwill Formation experienced long exposure at a stable landscape surface with erosion rates of 1-2 m/Ma. However, cosmogenic-nuclide concentrations are invariant with depth below the Whippoorwill Formation surface, indicating active mixing of the soil profile shortly before burial by till. The Whippoorwill Formation retains numerous features indicative of cryoturbation. Therefore, we interpret it as a buried Gelisol, a soil formed under periglacial conditions in the presence of permafrost. At the onset of Northern Hemisphere glaciation, climate cooling established permafrost conditions and accelerated erosion by inducing landscape instability. Thus, weathered regolith materials were mobilized and redeposited by gelifluction shortly before the ice sheet overrode the landscape. 相似文献
319.
320.
Sea ice growth and consolidation play a significant role in heat and momentum exchange between the atmosphere and the ocean. However, few in situ observations of sea ice kinematics have been reported owing to difficulties of deployment of buoys in the marginal ice zone (MIZ). To investigate the characteristics of sea ice kinematics from MIZ to packed ice zone (PIZ), eight drifting buoys designed by Taiyuan University of Technology were deployed in the open water at the ice edge of the Canadian Basin. Sea ice near the buoy constantly increased as the buoy drifted, and the kinematics of the buoy changed as the buoy was frozen into the ice. This process can be determined using sea ice concentration, sea skin temperature, and drift speed of buoy together. Sea ice concentration data showed that buoys entered the PIZ in mid-October as the ice grew and consolidated around the buoys, with high amplitude, high frequency buoy motions almost ceasing. Our results confirmed that good correlation coefficient in monthly scale between buoy drift and the wind only happened in the ice zone. The correlation coefficient between buoys and wind was below 0.3 while the buoys were in open water. As buoys entered the ice zone, the buoy speed was normally distributed at wind speeds above 6 m/s. The buoy drifted mainly to the right of the wind within 45° at wind speeds above 8 m/s. During further consolidation of the ice in MIZ, the direct forcing on the ice through winds will be lessened. The correlation coefficient value increased to 0.9 in November, and gradually decreased to 0.7 in April. 相似文献