The fast Ice Nucleus chamber FINCH

We present first results of our new developed Ice Nucleus (IN) counter FINCH from the sixth Cloud and Aerosol Characterization Experiment (CLACE 6) campaign at Jungfraujoch station, 3571 m asl. Measurements were made at the total and the ICE CVI inlet. Laboratory measurements of ice onset temperatures by FINCH are compared to those of the static diffusion chamber FRIDGE (FRankfurt Ice Deposition Freezing Experiment). Within the errors of both new instruments the results compare well to published data.     

Ice‐edge upwelling off the Newfoundland coast during LIMEX

Abstract

Analysis of CTD, Batfish and drifter data collected in the southern Labrador marginal ice zone during LIMEX (Labrador Ice Margin Experiment) in 1987 shows strong evidence of upwelling at the ice edge. The most clear indication of the upwelling is the rise of isopycnals and the increase of surface density near the ice edge. The upwelling zone has a width of 6 km extending from the ice edge, and an upwelling depth of at least 100 m. The existence of the upwelling zone along the ice edge is shown to be related to the character of the ice edge. Upwelling is more likely to occur at sharp and compacted ice edges. A two‐dimensional coupled ice‐ocean dynamical model of a continuously stratified ocean with a coastal boundary on a sloping bottom is used to study the dynamics of ice‐edge upwelling. The model results are in qualitative agreement with observations. A sensitivity analysis of the model is presented.     

Detection of the Labrador current using ice‐floe movement in synthetic aperture radar imagery and ice beacon trajectories

Abstract

Two sets of Synthetic Aperture Radar (SAR) images were collected, as part of the Labrador Ice Margin Experiment (LIMEX), over the Newfoundland Shelf on consecutive days in April 1990. Ice movement is detected from the displacement of ice floes between the two images sets and compared with ice drift data from six satellite‐tracked beacons and in situ CTD data. The ice velocity data derived from the SAR images and the beacons are used to generate a map of ice velocity vectors. A streamfunction map of ocean currents is produced by removing the direct wind‐driven component in the ice movement data, and by using an objective analysis method. The resulting flow pattern contains the offshore branch of the Labrador Current with a speed of 30 to 50 cm s^?1. The current closely follows the shelf break topography from north to south through the study area (47–50.5°N) as a continuous flow. In comparison, if the wind effect was not removed from the ice velocity data, the calculated Labrador Current north of 50°N would stray from the shelf break. The position of the current axis and the current speed derived from the ice movement data are in good agreement with the geostrophic current computed from the CTD data.     

Time-dependence of sea-ice concentration and multiyear ice fraction in the Arctic Basin

The time variation of the sea-ice concentration and multiyear ice fraction within the pack ice in the Arctic Basin is examined, using microwave images of sea ice recently acquired by the Nimbus-5 spacecraft and the NASA CV-990 airborne laboratory. The images used for these studies were constructed from data acquired from the Electrically Scanned Microwave Radiometer (ESMR) which records radiation from earth and its atmosphere at a wavelength of 1.55 cm. Data are analyzed for four seasons during 1973–1975 to illustrate some basic differences in the properties of the sea ice during those times. Spacecraft data are compared with corresponding NASA CV-990 airborne laboratory data obtained over wide areas in the Arctic Basin during the Main Arctic Ice Dynamics Joint Experiment (1975) to illustrate the applicability of passive-microwave remote sensing for monitoring the time dependence of sea-ice concentration (divergence). These observations indicate significant variations in the sea-ice concentration in the spring, late fall and early winter. In addition, deep in the interior of the Arctic polar sea-ice pack, heretofore unobserved large areas, several hundred kilometers in extent, of sea-ice concentrations as low as 50% are indicated.     

Ice‐floe collisions interpreted from acceleration data during LIMEX ‘89

Abstract

Wave‐induced ice motions measured during the Labrador Ice Margin Experiment (LIMEX ‘89) were interpreted to determine the cause and the frequency of collisions between floes. The LIMEX acceleration data were acquired with an optimal resolution near the predominant wave frequency and did not contain information above 0.5 Hz. It was therefore possible to establish the frequency of collisions, but not the magnitude of the events. Events were defined by any contact between floes in a wave cycle, and the distribution of times between events indicates that floes are more likely to collide in adjacent wave cycles than if the events were independent. Periods of continuous and intermittent collisions were related to the wave characteristics, and the frequency of events increased with a decrease in air temperature and an increase in local wind speed. Contrary to expectations, there was not a positive relation between collision frequency and wave amplitude.     

On the deterioration of icebergs in the marginal ice zone

Abstract

During the Labrador Ice Margin Experiment (LIMEX) of March‐April 1989, the International Ice Patrol (IIP) of the United States Coast Guard deployed two satellite‐tracked TIROS Arctic Drifter (TAD) platforms on two medium‐sized tabular icebergs. The icebergs were drifting in sea ice of about 9/10 concentration east of Newfoundland. These deployments were part of an experiment to examine differential sea‐ice/iceberg motion during spring conditions near the ice margin. Sea‐ice concentration and movement data were collected concurrently by other LIMEX investigators.

The TADs, deployed on 11 March 1989, were tracked using the ARGOS data collection and location system carried on two NOAA polar‐orbiting satellites of the TIROS family. For two months following the deployment, IIP periodically attempted to relocate the icebergs during routine aerial iceberg patrols. One of the TADs stopped transmitting on 23 April 1989 probably because of a major calving event that resulted in the TAD being crushed. As of 24 April the drift rate of the other TAD nearly doubled compared with its drift rate prior to that date, indicating that it had fallen off the iceberg and was floating on water. By 24 April there was no sea ice near either of the two icebergs.

The TAD data provide a unique datasetfor modelling the deterioration of icebergs while they emerge out of the marginal ice zone and travel in open water. It is shown that a good knowledge of the environmental conditions, pariicularly water temperature and sea state, are critical to model successfully the deterioration and calving of the two icebergs.     

A simulation of sea‐ice motion and distribution off Newfoundland during LIMEX,March 1987

Abstract

A coupled ice‐ocean dynamical model is applied to the simulation of sea‐ice motion and distribution off Newfoundland during the Labrador Ice Margin Experiment (LIMEX), March 1987. In the model, the ice is coupled to a barotropic ocean through an Ekman layer that deepens with increasing wind speed. A 6‐hourly gridded wind dataset was used as input to drive the ice and the ocean. The results show that ice velocities with ice‐ocean coupling are appreciably higher than those without coupling because of the generation of wind‐driven coastal currents. This suggests that coupled ice‐ocean dynamics should always be considered in short‐term sea‐ice models. The model gives reasonable agreement with the observed ice edge except in the southern boundary where ice‐melt has a strong influence on the ice‐edge position. Ocean currents, sea level and ice velocities computed from the model are in qualitative agreement with limited current‐meter, tide‐gauge, and ice drifter trajectory data.     

Changes in the Wetlands of Andalusia (Doñana Natural Park, SW Spain) at the End of the Little Ice Age

The Little Ice Age is a climatic period still insufficiently known. This ignorance is more marked in the case of Andalusia (southern Spain), where only recent works throw any light on the topic. Our studies, primarily from the perspective of botany and changes in the plant landscape, reveal the effects that this period had in these latitudes, and in particular on the Doñana Natural Park (SW Spain). This work shows an aridization in climatic conditions coinciding with the end of the Little Ice Age. The results corroborate the most recent theses on this period in Spain. Furthermore, the effects on the marsh areas studied lead us to conclude that the interpretation of the Little Ice Age in these southern latitudes should be different to that normally given for more northerly latitudes – much better known and more studied than the Mediterranean regions.     

Observations of longitudinal roll vortices during arctic cold air outbreaks over open water

An evolving convective Arctic planetary boundary layer (PBL) containing longitudinal roll vortices (rolls) was observed with aircraft data during the 1983 Marginal Ice Zone Experiment and the 1984 Arctic Cyclone Experiment.The PBL is observed to grow rapidly as the very cold and dry air flows off the ice over the relatively warm water. There is very large sensible heat flux, a result of the large surface-air temperature differences. Coherent structures were identified in these PBL's by use of power, coherence squared and phase spectra of the data. A systematic method of separating the rolls from organized thermal plumes was devised, based on theoretical characteristics for roll circulations and the resulting modified mean wind profile. The rapid mixing by the rolls aids in the establishment of equilibrium and an observed adiabatic modified mean Ekman layer. Rolls that form in a thermally neutral atmosphere over ice have different characteristics than those that appear in the unstable stratification over water. The rolls become increasingly more convective in character with distance from the ice edge. They have aspect ratios (wavelength/PBL height) that decrease with distance from the ice edge in agreement with linear theory. This is in contrast to the cloud street wavelength to inversion height ratio which is observed to increase downwind from the ice edge.     

Variability of Sea-Ice Extent in Baffin Bay over the Last Millennium

Comparison of an ice core glaciochemical time-series developed from thePenny Ice Cap (PIC), Baffin Island and monthly sea-ice extent reveals astatisticallysignificant inverse relationship between changes in Baffin Bay spring sea-iceextent andPenny Ice Cap sea-salt concentrations for the period 1901–1990 AD.Empiricalorthogonal function analysis demonstrates the joint behavior between changesin PICsea-salt concentrations, sea-ice extent, and changes in North Atlanticatmosphericcirculation. Our results suggest that sea-salt concentrations in snowpreserved on thePIC reflect local to regional springtime sea-ice coverage. The PIC sea-saltrecord/sea-ice relationship is further supported by decadal and century scalecomparisonwith other paleoclimate records of eastern Arctic climate change over the last700 years. Our sea-salt record suggests that, while the turn of the century wascharacterized bygenerally milder sea-ice conditions in Baffin Bay, the last few decades ofsea-ice extentlie within Little Ice Age variability and correspond to instrumental recordsof lowertemperatures in the Eastern Canadian Arctic over the past three decades.     

BCC_CSM北极海冰模拟性能的改进对东亚冬季气候模拟的影响

国家气候中心气候系统模式(BCC_CSM)将美国Los Alamos国家实验室发展的海冰模式CICE5.0替代原有的海冰模式SIS,形成一个新版本耦合模式,很好地提高了模式对北极海冰和北极气候的模拟能力.在此基础上,本文评估新耦合模式对1985-2014年东亚冬季气候的模拟性能,检验北极海冰模拟性能的改进对东亚冬季气候...     

针对冰盖的定向地球工程研究

针对冰盖的定向地球工程研究旨在增强冰盖稳定性和减缓冰盖物质流失,从源头上减少冰盖对海平面上升的贡献,有望为应对气候变化和保护海岸线争取几百年的时间。冰盖地球工程主要作用在冰底和冰架-海洋界面上,主要途径如下：(1)排干或冻结冰盖底部水来干燥冰床,增强冰盖底部摩擦力;(2)在海洋中建造人造岛来支撑漂浮的冰架;(3)在冰架前端建造水下隔离墙,阻止温暖的海水到达冰川底部以减缓其融化。冰盖地球工程包括数值模拟、方案设计、工程试验和政治法律等诸多方面的研究。国际上的研究团队正在开展数值模拟和方案设计方面的研究,工程试验和政治法律等方面的研究尚未起步。预计工程试验的难度阶梯很可能是从实验室试验开始,到小尺度的野外试验,接着到格陵兰冰盖的入海冰川,最后到南极冰盖的入海冰川。针对冰盖的定向地球工程研究很有可能成为21世纪全球变化领域新兴的研究方向。     

Criteria for the Onset of Significant Concentrations of Ice Particles in cumulus clouds

Field observations and measurements, reported from many locations around the world, are used to deduce the cloud depths (and cloud top temperatures) required for the Onset of Significant Concentrations of Ice Particles (OSCIP) in cumulus clouds. The results show that the OSCIP will generally occur if cloud top temperatures are between about −4° and −10°C. The results are compared with the criteria for the OSCIP proposed by Hobbs and Rangno (1985) and for the formation of high ice particle concentrations by riming-splintering.     

Estimating icing amounts caused by freezing precipitation in Canada

The Chaine and Skeates icing model is a semi-empirical model. It is based on the formulations proposed by McKay and Thompson (1969). Horizontal ice accretion thickness is assumed to be the observed precipitation amount adjusted by the appropriate ice density. Clear ice density is assumed to be 900 kg/m³. Vertical ice accretion thickness is proportional to precipitation rate and wind speed. Ice accretion occurs only at temperatures near or below freezing. All impinging water is assumed to turn into ice. The freezing fraction is assumed to be one. Horizontal and vertical ice thicknesses are changed into equivalent radial thickness (Chaine and Castonguay, 1974). All parameters used in this model can be derived from routinely observed meteorological data. Icing amounts estimated by this model are very sensitive to wind speed and precipitation rate. Model simulated 30-year return period equivalent radial ice amounts for 20 Quebec locations are compared with collocated Passive Ice Meter data and the results are found to be reasonable. The variation of ice amount with height can be estimated by a log function proportional to 10 m icing amounts, except in British Columbia. Also the 30-year return period equivalent radial ice estimates due to freezing precipitations for 303 locations in Canada are calculated and an Ice Map is plotted. In the future, more work needs to be done to estimate ice amounts due to other forms of icing such as in-cloud rime icing and wet snow. These quantities should be added to the current amounts to make the ice map complete. Anecdotal ice information should be collected to validate the map.     

对非球形冰晶94 GHz云雷达后向散射和衰减的研究

针对94 GHz毫米波云雷达的数据处理,基于离散偶极子近似法(DDA)计算了几种非球形冰晶的后向散射及衰减效率,探讨了不同冰云模型下冰云的雷达反射率因子(Z_e)和衰减系数(k)及冰水含量(IWC,记作W)的关系。结果表明:(1)形状对冰晶的散射及衰减效率与粒子大小有关。(2)在实际的冰云中,将六角形冰晶和椭圆冰晶看做同体积的球形粒子将低估其衰减和后向散射。将聚合物冰晶看做等体积球形,将高估其后向散射及衰减,子弹花冰晶的后向散射与同体积的球形相比有减小也有增大,但是衰减比同体积球形的小。(3)冰云模型对Z_e-k、Z_e-W关系具有较大影响,假设滴谱相同的条件下,得到了具体冰云模型下对应Z_e-k、Z_e-W关系的系数。这些探讨为我国W波段云雷达的数据处理提供了参考。     

The Initiation of the "Little Ice Age" in Regions Round the North Atlantic

The "Little Ice Age" was the most recent period during which glaciers extended globally, their fronts oscillating about advanced positions. It is frequently taken as having started in the sixteenth or seventeenth century and ending somewhere between 1850 and 1890, but Porter (1981) pointed out that the "Little Ice Age" may 'have begun at least three centuries earlier in the North Atlantic region than is generally inferred'. The glacial fluctuations of the last millennium have been traced in the greatest detail in the Swiss Alps, where the "Little Ice Age" is now seen as starting with advances in the thirteenth century, and reaching an initial culmination in the fourteenth century. In the discussion here, evidence from Canada, Greenland, Iceland, Spitsbergen and Scandinavia is compared with that from Switzerland. Such comparisons have been facilitated by improved methods of calibrating radiocarbon dates to calendar dates and by increasing availability of evidence revealed during the current retreat phase. It is concluded that the "Little Ice Age" was initiated before the early fourteenth century in regions surrounding the North Atlantic.     

Ice‐band characteristics of the Antarctic seasonal ice zone observed using MOS MESSR images

Abstract

Ice‐band characteristics for the region off East Queen Maud Land in Antarctica were examined and their relationship with the wind conditions was assessed using a large number of Marine Observation Satellite (MOS) Multispectral Electronic Self Scanning Radiometer (MESSR) images received at Syowa Station during the period 1989–93. Analyses from 43 examples of bands captured from August to December suggest that ice‐band formation and band scale are affected by both wind speed and direction over approximately the preceding four days (defined as the effective wind). Ice‐band width and spacing are significantly correlated with the effective wind speed and the maximum wind speed during that period. The long axis of ice bands tends to be oriented at 70°‐90° (mean of 75°) to the right of the effective wind direction. The band scales decrease from winter (August) to summer (December) with typical band spacing of 4–6 km in winter and 1–2 km in summer. This seems to be primarily due to a decrease in ice floe size and partly due to a decrease in the effective wind speed from winter to summer. Band scale decreases from the ice interior to the ice edge under conditions of off‐ice winds.     

A warm and wet little climatic optimum and a cold and dry little ice age in the southern rocky mountains,U.S.A.

The zenith of Anasazi Pueblo Indian occupation in the northern Colorado Plateau region of the southwestern U.S.A. coincides with the Little Climatic Optimum or Medieval Warm Period (A.D. 900–1300), and its demise coincides with the commencement of the Little Ice Age. Indexes of winter (jet-stream derived) and summer (monsoon derived) precipitation and growing season length were developed for the La Plata Mountains region of southwestern Colorado. The results show that during the height of the Little Climatic Optimum (A.D. 1000–1100) the region was characterized by a relatively long growing season and by a potential dry farming zone or elevational belt (currently located between 2,000 m and 2,300 m elevation) that was twice as wide as present and could support Anasazi upland dry farming down to at least 1,600 m, an elevation that is quite impossible to dry farm today because of insufficient soil moisture. This expanded dry-farm belt is attributable to a more vigorous circulation regime characterized by both greater winter and summer precipitation than that of today. Between A.D. 1100 and 1300 the potential dry-farm belt narrowed and finally disappeared with the onset of a period of markedly colder and drier conditions than currently exist. Finally, when the Little Ice Age terminated in the mid A.D. 1800s and warmer, wetter conditions returned to the region, another group of farmers (modern Anglos) were able to dry farm the area.The U.S. Government right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged.     

Enhanced Arctic Ice Concentration Estimation Merging MODIS Ice Surface Temperature and SSM/I Sea-Ice Concentration

Ice concentration data from passive microwave sensors are not reliable during the summer melt season. In this study passive microwave ice concentration estimates are improved upon through the assimilation of ice surface temperature data from the Moderate-Resolution Imaging Spectroradiometer (MODIS). Ice concentration from the analysis is converted to ice extent and compared with data from the Interactive Multisensor Snow and Ice Mapping System (IMS). Ice concentration analysis from data assimilation is in better agreement with the IMS data than the original passive microwave data, with the largest improvements occurring during sea-ice melt.     

全球多源海冰密集度融合资料研制试验

为了发展一套全球多源海冰密集度逐日融合资料,以欧洲气象卫星应用组织(EUMETSAT)海洋海冰应用中心(OSI SAF)海冰密集度数据、中国国家卫星气象中心(NSMC)的MWRI和VIRR全球海冰密集度数据、美国国家冰雪数据中心(NSIDC)的NISE海冰密集度数据、美国国家冰中心(NIC)的IMS北半球海冰数据为观测...