Ocean dynamics and acoustic fluctuations in the fram strait marginal ice zone

Acoustic waves transmitted over a 100-kilometer path in the Fram Strait marginal ice zone undergo Doppler shifts and fluctuations around these shifts, the former due to quasi-steady motion of both acoustic source and receiver and the latter to unsteady motions of the water column and ice cover. Internal waves and differential Doppler shift usually account for such fluctuations in the deep temperate ocean but only partially explain the results obtained in the marginal ice zone. There the fluctuations are more energetic and may be caused alternatively or additionally by comparably energetic fluctuations in ice-edge eddies or other mesoscale motions.     

Norwegian remote sensing experiment in a marginal ice zone

The Norwegian Remote Sensing Experiment in the marginal ice zone north of Svalbard took place in fall 1979. Coordinated passive and active microwave measurements were obtained from shipborne, airborne, and satellite instruments together with in situ observations. The obtained spectra of emissivity (frequency range, 5 to 100 gigahertz) should improve identification of ice types and estimates of ice concentration. Mesoscale features along the ice edge were revealed by a 1.215-gigahertz synthetic aperture radar. Ice edge location by the Nimbus 7 scanning multichannel microwave radiometer was shown to be accurate to within 10 kilometers.     

Ocean circulation: its effects on seasonal sea-ice simulations

A diagnostic ice-ocean model of the Arctic, Greenland, and Norwegian seas is constructed and used to examine the role of ocean circulation in seasonal sea-ice simulations. The model includes lateral ice motion and three-dimensional ocean circulation. The ocean portion of the model is weakly forced by observed temperature and salinity data. Simulation results show that including modeled ocean circulation in seasonal sea-ice simulations substantially improves the predicted ice drift and ice margin location. Simulations that do not include lateral ocean movment predict a much less realistic ice edge.     

各向异性强度对冷冻浓缩过程冰晶生长影响的相场法模拟

针对各向异性参数与实际物性参数的关系无法用试验方法准确获得的问题,采用描述相变微观结构的相场模型,探讨各向异性强度对冰晶生长形貌和冰晶的溶质分布的影响,确定模型中各向异性强度系数的合理取值。结果表明:各向异性强度系数取值大小对冰晶的形貌有很大影响,取值越大,冰晶的二次分枝越发达,且尖端速度波动的幅值越大,但对冰晶大小影响不大;各向异性强度系数取值大小对冰晶的溶质分布也有较大影响,取值越大则冰晶前沿溶质越富集,溶质分布波动范围越大。各向异性强度系数取值范围为0.010~0.025时,模拟获得的形貌与低温显微镜下观察到的冰晶生长形貌试验结果较为吻合,能够较真实地反映冷冻浓缩过程冰晶生长形貌。     

Unusual radar echoes from the greenland ice sheet

Airborne radar images of part of the Greenland ice sheet reveal icy terrain whose radar properties are unique among radar-studied terrestrial surfaces but resemble those of Jupiter's icy Galilean satellites. The 5.6- and 24-centimeter-wavelength echoes from the Greenland percolation zone, like the 3.5- and 13-centimeter-wavelength echoes from the icy satellites, are extremely intense and have anomalous circular and linear polarization ratios. However, the detailed subsurface configurations of the Galilean satellite regoliths, where heterogeneities are the product of prolonged meteoroid bombardment, are unlikely to resemble that within the Greenland percolation zone, where heterogeneities are the product of seasonal melting and refreezing.     

Rapid bottom melting widespread near Antarctic Ice Sheet grounding lines

As continental ice from Antarctica reaches the grounding line and begins to float, its underside melts into the ocean. Results obtained with satellite radar interferometry reveal that bottom melt rates experienced by large outlet glaciers near their grounding lines are far higher than generally assumed. The melting rate is positively correlated with thermal forcing, increasing by 1 meter per year for each 0.1 degrees C rise in ocean temperature. Where deep water has direct access to grounding lines, glaciers and ice shelves are vulnerable to ongoing increases in ocean temperature.     

Radar mapping of mercury: full-disk images and polar anomalies

A random-code technique has been used at Arecibo to obtain delay-Doppler radar images of the full disk of Mercury. Anomalously bright features were found at the north and south poles. The north polar feature is oblong (4 degrees by 8 degrees ) and offset from the pole. The smaller south polar feature is mostly confined to the floor of the crater Chao Meng-Fu. The polar locations and radar properties of these features indicate that they may be produced by volume scattering in ice. The images also reveal a variety of more subdued reflectivity features ranging in size from hundreds to thousands of kilometers; some of these appear to have an impact origin.     

Mesoscale oceanographic processes beneath the ice of fram strait

A major component of the Fram Strait Marginal Ice Zone Experiment was the investigation of air-sea-ice interactions, processes, and circulation patterns found behind the local ice edge and on scales greater than 10 kilometers (mesoscale and large scale). Neutrally buoyant floats, ice-tethered cyclesondes, and helicopter-based measurements were used to obtain uniquely integrated and consistent views of the mesoscale ocean features beneath the ice cover of Fram Strait. Within the vicinity of the Yermak Plateau, three distinct regions of mesoscale motion were observed that coincided with the shallow topography of the plateau, the northward flowing Atlantic water over the western flank of the plateau, and the strong current-shear zone of the East Greenland Polar Front. A subice meander of the front was also observed, which was probably occluded subsequently.     

Changes in Atmospheric Circulation and Ocean Ice Cover over the North Atlantic During the Last 41,000 Years

High-resolution, continuous multivariate chemical records from a central Greenland ice core provide a sensitive measure of climate change and chemical composition of the atmosphere over the last 41,000 years. These chemical series reveal a record of change in the relative size and intensity of the circulation system that transported air masses to Greenland [defined here as the polar circulation index (PCI)] and in the extent of ocean ice cover. Massive iceberg discharge events previously defined from the marine record are correlated with notable expansions of ocean ice cover and increases in PCI. During stadials without discharge events, ocean ice cover appears to reach some common maximum level. The massive aerosol loadings and dramatic variations in ocean ice cover documented in ice cores should be included in climate modeling.     

南极普里兹湾关键物理海洋学问题研究进展及未来趋势

南极普里兹湾及其邻近海域关键物理海洋学问题包括水团特性、环流特征和冰架 海洋 海冰相互作用过程等。该海域水团可以分为南极表层水、绕极深层水、南极底层水、南极陆架水和南极冰架水等,受外部条件影响,这些水团时空变化显著。普里兹湾区域的环流以普里兹湾流涡,西向的沿岸流和东向的绕极流,以及两者之间的南极辐散带的环流为主要特征,地形是环流特征的关键影响因素。埃默里冰架 海洋的相互作用过程显著影响普里兹湾海域的水团特性和环流状况。冰泵机制,是埃默里冰架外海水进入冰穴,并引起冰架底部消融和冻结的重要原因。冰架 海洋 海冰相互作用形成的低温高盐水,是普里兹湾形成南极底层水的潜在因素之一。加强现场观测,并建立高分辨率的冰架 海洋 海冰耦合模型系统是研究普里兹湾海域物理海洋学关键过程和变化机制的重要手段,是南极研究的发展趋势。     

Spaceborne imaging radar: geologic and oceanographic applications

Synoptic, large-area radar images of the earth's land and ocean surface, obtained from the Seasat orbiting spacecraft, show the potential for geologic mapping and for monitoring of ocean surface patterns. Structural and topographic features such as lineaments, anticlines, folds and domes, drainage patterns, stratification, and roughness units can be mapped. Ocean surface waves, internal waves, current boundaries, and large-scale eddies have been observed in numerous images taken by the Seasat imaging radar. This article gives an illustrated overview of these applications.     

Radar images of Mars

Full disk images of Mars have been obtained with the use of the Very Large Array (VLA) to map the radar reflected flux density. The transmitter system was the 70-m antenna of the Deep Space Network at Goldstone, California. The surface of Mars was illuminated with continuous wave radiation at a wavelength of 3,5 cm. The reflected energy was mapped in individual 12-minute snapshots with the VLA in its largest configuration; fringe spacings as small as 67 km were obtained. The images reveal near-surface features including a region in the Tharsis volcano area, over 2000 km in east-west extent, that displayed no echo to the very low level of the radar system noise. The feature, called Stealth, is interpreted as a deposit of dust or ash with a density less than about 0.5 gram per cubic centimeter and free of rocks larger than 1 cm across. The deposit must be several meters thick and may be much deeper. The strongest reflecting geological feature was the south polar ice cap, which was reduced in size to the residual south polar ice cap at the season of observation. The cap image is interpreted as arising from nearly pure CO(2) or H(2)O ice with a small amount of martian dust (less than 2 percent by volume) and a depth greater than 2 to 5 m. Only one anomalous reflecting feature was identified outside of the Tharsis region, although the Elysium region was poorly sampled in this experiment and the north pole was not visible from Earth.     

2011年8月28～29日本溪暴雨天气雷达回波特征分析

利用常规资料、卫星云图和营口多普勒雷达产品,对2011年8月28～29日发生在本溪地区的暴雨天气过程进行综合分析。结果表明,西风带低槽、低层切变线和副热带高压边缘强盛的暖湿气流共同影响造成了这次暴雨天气过程;在基本反射率图上,在混合性降水云系中存在强度为45～55 dBz的强回波中心,对流云团出现"列车效应"时有利于暴雨天气的发生;在多普勒速度图上,低空急流和逆风区是这次暴雨的重要特征。     

Fast recession of a west antarctic glacier

Satellite radar interferometry observations of Pine Island Glacier, West Antarctica, reveal that the glacier hinge-line position retreated 1.2 +/- 0.3 kilometers per year between 1992 and 1996, which in turn implies that the ice thinned by 3.5 +/- 0.9 meters per year. The fast recession of Pine Island Glacier, predicted to be a possible trigger for the disintegration of the West Antarctic Ice Sheet, is attributed to enhanced basal melting of the glacier floating tongue by warm ocean waters.     

Greenland Ice Sheet Surface Properties and Ice Dynamics from ERS-1 SAR Imagery

C-band synthetic aperture radar (SAR) imagery from the European Space Agency's ERS-1 satellite reveals the basic zonation of the surface of the Greenland Ice Sheet. The zones have backscatter signatures related to the structure of the snowpack, which varies with the balance of accumulation and melt at various elevations. The boundaries of zones can be accurately located with the use of this high-resolution imagery. The images also reveal a large flow feature in northeast Greenland that is similar to ice streams in Antarctica and may play a major role in the discharge of ice from the ice sheet.     

祁连山东段缀块水平冰雪景观变化的研究

采用美国陆地资源卫星两期卫星遥感图像,从缀块水平研究了祁连山东段地区1994-2008年的冰雪景观变化.研究结果表明,2008年祁连山东段地区冰雪景观与1994年同期相比,缀块总数量缩减了28.2%;冰雪景观总面积减少了19.6%;冰雪景观总体形状趋于复杂,10~100 hm2和1 000 hm2以上的缀块形状复杂度变大,<1hm2和100~1 000 hm2的缀块形状变化不显著;冰雪景观的总体破碎度减小,连接度增大,景观稳定性增加.     

2016年8月23-24日青海省河南县强降水天气诊断分析

利用常规观测资料、Micaps、卫星云图、多普勒雷达资料等,从环流背景、物理量、卫星云图、雷达回波等方面,对2016年8月23—24日青海省河南县出现的一次短时强降水天气进行分析,探讨造成此次强降水的主要成因。结果表明,在588 dagpm线副高控制范围内高湿高温状态下,冷暖空气的汇合以及切变辐合造成了此次对流不稳定;在具备充分水汽供应的条件下,垂直方向上低空辐合、高空辐散的配置为此次降水提供了动力条件。对流旺盛、雷达强回波带过境的地方会造成强降水。     

基于形态学梯度的细胞图像自动分割

提出一种自动分割细胞图像的方法,利用数学形态学梯度运算对图像边缘进行锐化。再利用判别分析法自动确定梯度图像阈值,经后处理,可得单像素宽度细胞图像边缘。该边缘可描述医学图像中细胞的有效区域,实现细胞图像自动分割。为验证该方法的有效性,对30幅实际细胞图像进行分割试验。结果表明,该方法对细胞图像分割有较好的适应能力。     

Placers of cosmic dust in the blue ice lakes of greenland

A concentration process occurring in the melt zone of the Greenland ice cap has produced the richest known deposit of cosmic dust on the surface of the earth. Extraterrestrial particles collected from this region are well preserved and are collectable in large quantities. The collected particles are generally identical to cosmic spheres found on the ocean floor, but a pure glass type was discovered that has not been seen in deep-sea samples. Iron-rich spheres are conspicuously rare in the collected material.     

长江口悬浮泥沙的MODIS影像遥感监测研究

通过对遥感监测泥沙原理和MODIS传感器特征的分析,应用不同时间的MODIS影像进行长江口及其附近海域的悬浮泥沙监测。结果表明:(1)长江口及其附近海域悬浮泥沙含量较高,其中杭州湾悬浮泥沙浓度高于长江口;(2)长江口及其附近海域水体中的泥沙由再悬浮形成,且冬季泥沙浓度和范围均大于春季;(3)入海径流与海洋动力是影响河口沿岸及近海水域水体悬浮泥沙含量的主要因素,其中海洋动力的潮流和波浪是主导控制因素。