Simulation of iceberg drift as a component of ice monitoring in the West Arctic

Discussed is the hydrodynamic model of iceberg drift. Presented are the examples ofits use in operational practice for predicting iceberg drift in the Kara Sea and for enhancing ice monitoring in the Barents Sea.     

Medium-range forecasts of large ice cover discontinuities for hydrometeorological support of navigation in the Arctic basin

A brief characteristic of the Arctic ice cover discontinuities (ICD) is given. Their practical importance for vessels operating in this region as well as necessity of forecasting such indicators as the prevailing disposition of discontinuities and location of zones of their formation and closure are noted. The forecasting technique is based on the method of complex analogs. A summary of forecasts produced for the Arctic navigation areas since 1991 is provided. It is shown, that recent upgrading of the original methodology allowed to produce forecasts in on-line mode, to present digital maps of the forecast data, and to transfer them directly to the vessel’s automated workplace. A number of practical examples are presented for illustrating the navigation efficiency if forecast and actual ICD data are used. The results of forecast verification are given.     

The sea ice mass budget of the Arctic and its future change as simulated by coupled climate models

Arctic sea ice mass budgets for the twentieth century and projected changes through the twenty-first century are assessed from 14 coupled global climate models. Large inter-model scatter in contemporary mass budgets is strongly related to variations in absorbed solar radiation, due in large part to differences in the surface albedo simulation. Over the twenty-first century, all models simulate a decrease in ice volume resulting from increased annual net melt (melt minus growth), partially compensated by reduced transport to lower latitudes. Despite this general agreement, the models vary considerably regarding the magnitude of ice volume loss and the relative roles of changing melt and growth in driving it. Projected changes in sea ice mass budgets depend in part on the initial (mid twentieth century) ice conditions; models with thicker initial ice generally exhibit larger volume losses. Pointing to the importance of evolving surface albedo and cloud properties, inter-model scatter in changing net ice melt is significantly related to changes in downwelling longwave and absorbed shortwave radiation. These factors, along with the simulated mean and spatial distribution of ice thickness, contribute to a large inter-model scatter in the projected onset of seasonally ice-free conditions.     

An investigation of climate drift in a coupled atmosphere-ocean-sea ice model

Climate drift is a common and serious problem in most state-of-the-art coupled atmosphere-ocean-sea ice models. We consider the nature of climate drift in such a model, and in particular address the question of whether or not climate drift is inherent to the model, or whether the drift can be averted by a suitable choice of initial conditions or coupling procedure. The synchronous approach to coupling was adopted in which the ocean, atmosphere and sea ice models were spun-up independently to equilibrium using climatological forcing fields. The models were then coupled and integrated forward in time. Several experiments were performed which were designed to assess the impact of different coupling methodologies and changes in the initial conditions of the component models on the climate drift of the system. The results of our experiments indicate that climate drift is a problem inherent to the coupled model in that systematic errors in the components lead to incompatibilities in the surface fluxes required by the component models to maintain realistic climatologies. We conclude that climate drift can be averted only if the parameterizations of certain important physical processes are improved which should have the effect of reducing or eliminating these incompatibilities.     

An unusual anomaly of ice conditions in the eastern seas of the Russian Arctic and in the arctic basin in summer 2007

It is demonstrated that during the whole annual cycle of ice cover evolution in 2006–2007 in the eastern seas of the Russian Arctic and in the Arctic basin, the factors whose effect led to the formation of an extremely large anomaly of ice conditions in summer 2007 were revealed. By the end of summer, the ice melted on the huge water area of 3500000 km². In September, the ice edge between the meridians of 150° E-170° W reached the parallel of 85° N. The estimates of the open water area being formed due to the ice melting and its drifting edge shift are given.     

Modeling of fast ice evolution in the Arctic seas

A one-dimensional model of fast ice wind-induced break-up developed before was adapted for two-dimensional case that enabled to explain many regularities of this phenomenon. A numerical scheme is proposed of the integration of the acting stresses and potential resistivity by the fast ice area as well as the method for taking into account the correlation between the wind direction and prevailing coastline orientation that enables to simulate practically any combination of tensile and shearing stresses in the basins of arbitrary shape. The seasonal variability of strengthening ice properties is taken into account. All numerical tests carried out within the frameworks of this investigation demonstrated the qualitative and, partly, quantitative similarity of computation results and regularities observed in nature. The model sensitivity to the variation of some parameters is studied. The limits of model applicability are discussed and the directions of further research are proposed.     

Numerical modeling of ice drift in the Sea of Azov

Considered is the dependence of the evolution of the ice drift velocity field in the Sea of Azov on the direction and duration of the impact of wind of constant intensity based on the constructed two-dimensional mathematical model.     

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.     

松花江流凌预报自动化系统

利用５００ｈＰａ高度场５个相关区作为预报因子,建立流凌预报模型,根据此模型制作松花江流凌预报自动化系统,实现流凌专业预报自动化。     

Investigating the variability of the Arctic sea ice thickness in response to a stochastic thermodynamic atmospheric forcing

The natural low frequency variability of the sea-ice thickness in the Arctic is investigated based on a 10 000 years simulation with a one-dimensional thermodynamic sea-ice model forced by random perturbations of the air surface temperature and solar radiation. The simulation results suggest that atmospheric random perturbations are integrated by the sea-ice. Moreover those perturbations occurring at the onset of ice melting force the largest ice thickness anomalies, which are successively amplified in summer by the albedo feedback and damped in winter by the feedback of the heat conduction through the ice. They also result in a global shift of the melting season which, in the mean annual cycle, leads to earlier melting as compared to the mean climatological cycle. The power spectrum of the ice anomalies suggests that the thickness of the perennial ice should vary preferentially on a time scale of approximately 20 years. The shape of the spectrum is consistent with that of a first order Markov process in which the characteristic time scale of the ice fluctuations would be the relaxation time scale associated with the linear feedback. The equivalent Markov model is constructed by linearizing the ice growth rate anomaly equations and allows us to derive an analytical expression of the feedback and of the forcing of the anomalies. The characteristic time scale depends explicitly on those model parameters involved in the atmosphere-ice interaction but also on the mean seasonal characteristics of the forcing and of the ice thickness. Received: 18 August 1999 / Accepted: 10 May 2000     

中国北方暴雪的年代际变化及其与大气环流和北极海冰的联系

采用相关、回归等统计方法,对中国北方暴雪的年代际变化特征及其与大气环流和北极海冰的联系进行探讨。结果表明:中国北方冬季暴雪发生频次较高区域主要位于东北,在空间分布上呈现由西北向东南增加的态势,且存在明显的年代际变化特征:1965—1980年为东北暴雪少发期; 2002—2011年为东北暴雪多发期。分析表明:暴雪少发期,输送至东北的水汽较少;暴雪多发期,更多的水汽输送来自于西北太平洋,同时偏北气流引导的极地冷空气与偏南风引导的太平洋暖湿空气在东北地区汇合,提供暴雪频发的动力条件,造成东北暴雪出现年代际增多。此外,研究发现:前期秋季北极海冰的年代际减少与东北暴雪的年代际增加存在很好的相关性;秋季北极海冰异常偏少导致的大气环流异常主要表现为纬向西风减弱和NAO负位相,由此导致大气经向活动增强,利于极地冷空气向南入侵,且冷空气与暖湿空气在东北地区汇合,这是东北暴雪年代际增加的重要原因之一。     

Markov-chain simulation of particle dispersion in inhomogeneous flows: The mean drift velocity induced by a gradient in Eulerian velocity variance

The Langevin equation is used to derive the Markov equation for the vertical velocity of a fluid particle moving in turbulent flow. It is shown that if the Eulerian velocity variance _wE is not constant with height, there is an associated vertical pressure gradient which appears as a force-like term in the Markov equation. The correct form of the Markov equation is: w(t + t) = aw(t) + b _wE + (1 – a)T _L ( _wE ²)/z, where w(t) is the vertical velocity at time t, a random number from a Gaussian distribution with zero mean and unit variance, T _L the Lagrangian integral time scale for vertical velocity, a = exp(–t/T _L), and b = (1 – a ²)^1/2. This equation can be used for inhomogeneous turbulence in which the mean wind speed, _wE and T _L vary with height. A two-dimensional numerical simulation shows that when this equation is used, an initially uniform distribution of tracer remains uniform.     

SACOL站冰云粒子下降末速度的反演及其时空分布特征研究

冰云是影响气候变化最为重要的因子之一,其生命周期的变化在很大程度上决定了冰云的气候辐射效应。冰云粒子下降末速度是影响冰云生命周期的关键参数。为了开展对冰云粒子下降末速度的研究,利用兰州大学半干旱气候与环境监测站Ka波段毫米波云雷达2013年8月至2015年7月连续观测数据,反演了冰云粒子的下降末速度(V_t),并根据雷达反射率因子(Z)与V_t的关系计算了拟合因子a、b的值;在此基础上应用聚类分析方法,对比分析了4种不同特性冰云Z、V_t和拟合因子a、b的时、空分布特征,进而尝试通过参数垂直分布特征识别研究云中不同位置上云微物理过程的变化。结果表明:冰云粒子下降末速度的分布与雷达反射率因子有很好的对应,最大频率都出现在距离地面约7 km高度处,且具有显著的季节变化,粒子下降末速度在暖季较冷季可增大25%,峰值出现在6月和9月;云层较厚且持续时间长的第一、三类冰云,其雷达反射率因子、粒子下降末速度及拟合因子a和b的平均值都显著大于云层较薄且持续时间短的第二、四类云。垂直方向上,Z、V_t和拟合因子b从云顶到云...     

一月北极海冰对六月亚洲-西太平洋环流的影响

本文应用统计学方法,分析一月北极海冰对六月亚洲—西太平洋环流的影响。结果表明两者存在相当密切的相关关系;这种关系在海平面气压场、500hPa和100hPa位势高度场上均有明显表现,在低层尤为明显;主要相关区正是对夏季风起决定性作用的区域。     

Sources of spread in simulations of Arctic sea ice loss over the twenty-first century

We show that intermodel variations in the anthropogenically-forced evolution of September sea ice extent (SSIE) in the Arctic stem mainly from two factors: the baseline climatological sea ice thickness (SIT) distribution, and the local climate feedback parameter. The roles of these two factors evolve over the course of the twenty-first century. The SIT distribution is the most important factor in current trends and those of coming decades, accounting for roughly half the intermodel variations in SSIE trends. Then, its role progressively decreases, so that around the middle of the twenty-first century the local climate feedback parameter becomes the dominant factor. Through this analysis, we identify the investments in improved simulation of Arctic climate necessary to reduce uncertainties both in projections of sea ice loss over the coming decades and in the ultimate fate of the ice pack.     

Enhanced alignment of plate ice crystals in a non-uniform electric field

An atmospheric electric field exerts a torque on both column and plate ice crystals. Columns tend to align along the direction of the field. One diameter of plate crystals also aligns parallel to a field, while a non-uniform diverging field leads to further orientation and proscribes a secondary orientation along the direction of least divergence. A laboratory investigation treats the electrical orientation of thin plate ice crystals in a non-uniform field as a two-step process. In the model, the average field provides the primary torque and aligns one diameter of the plate crystal while simultaneously a spatially varying component of the field aligns the perpendicular diameter. The first element of the process, the primary torque, has been investigated previously. The complete reorientation, caused by a secondary torque, is investigated herein. Experimentally a stronger field with sufficient non-uniformity is required to demonstrate the secondary torque. The realignment caused by this torque depends also on the strength of the aerodynamic torques on the falling ice crystals. Experiments in a laboratory cold chamber with small thin plate crystals in an electric field provided by a charged rod demonstrate crystal reorientation by changing the reflections of a beam of white light. A model incorporating electrical torques is applied to the laboratory observation and used to investigate the possibility of the effects occurring in the atmosphere. Fields near lightning strokes, which are strong but of short duration, may reorient small crystals. Larger crystal aggregates like planar snowflakes are governed by the same electrical torques. It is suggested that the secondary torque realignment might be observable for aggregates large enough to be detected by radar in cases pertaining to weaker but longer duration fields associated with cloud electrification. A simplification of the model is used to investigate electrically caused crystal motion and linear aggregation, with applications to the atmosphere and to lightning initiation.     

On the prediction of the kurtosis of velocity derivatives in a turbulent field

The prediction of the values of non-dimensional fourth-order moment (kurtosis) of the velocity derivative in a turbulent field is made under the assumption that the values of kurtosis depend on both the turbulence Reynolds number and the intermittency factor. The method consists of modeling a suitable probability density of the variable in a given turbulence Reynolds number and the intermittency factor. A crude model of the probability density function is derived, and the numerical calculations based on the model show excellent agreement with many of the experimental data. The analysis shows that the values of kurtosis depend strongly on the intermittency factor, and that depending on the value of the intermittency factor, it is entirely possible to have values of kurtosis as low as five in a flow with a turbulence Reynolds number of 5000.     

秋季北极海冰对中国冬季气温的影响

利用海冰资料、中国地面气候资料、环流特征量资料及NCEP/NCAR再分析资料,研究了秋季北极海冰变化对中国冬季平均气温、日气温变率以及异常低温天气的影响。分析结果表明,秋季北极海冰异常偏多年中国冬季常为暖冬;异常偏少年中国冬季常为冷冬,且异常低温天气出现频率更高,常发生低温灾害事件。秋季北极海冰通过影响后期的北半球极涡、东亚冬季风和西伯利亚高压进而影响中国冬季的平均气温,且通过影响冬季异常强西伯利亚高压的出现频次,影响中国冬季异常低温天气的发生频次。合成分析结果表明,秋季北极海冰异常偏少年的冬季,中国以北亚欧大陆高纬度的偏北风较强,且中国及其以北的中高纬度地区空气异常偏冷,导致极地和高纬度的冷空气易向南爆发,造成中国冬季气温偏低,异常低温天气频发。     

Structure of the vertical velocity field analyzed with a Doppler Sodar

Fifteen hours of Sodar echoes, collected during the 4th Environmental CEC Campaign at Turbigo, Italy, in September 1979, have been analyzed. We discuss the vertical profiles and the time evolution of the second and third statistical moments of the vertical component of wind velocity, measured at a rate of one height-profile every 6 s for a height range of 1000 m and a vertical resolution of 29 m. We also analyze the power spectra of the vertical velocity.