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1.
In this study, the movement of polar lows is addressed from a novel and perspicuous viewpoint. The usual assumption has been that these mesoscale systems are, to a first approximation, advected by the larger scale flow in which they are embedded. However, when there are two or more polar lows in the same vicinity, binary interactions between pairs of polar lows can cause a cyclonic co-rotation of the pair. In geographic coordinates these interactions can appear as unusual loops, twists and turns in the low tracks, due to the interplay between the cyclonic co-rotation and the translation of the binary pair by the ambient flow. However when the tracks are replotted in centroid relative coordinates, a mutual rotation is unmistakable. Satellite imagery from several case studies has been examined to accurately determine the polar low tracks, and thus the co-rotations. Using surface wind observations, a theoretical rotation rate can be estimated, based on barotropic vortex dynamics. There is a good correspondence between the observed and calculated rotation rates. Recognizing the existence of binary interactions between polar lows emphasises the connection between polar lows and tropical cyclones, where binary interactions have been described in several studies. Indeed, in the cases studied here, binary interactions are strongest during the secondary (convective) stage of polar low development where the lows are somewhat analogous to arctic hurricanes. 相似文献
2.
The Atlantic inflow in the Fram Strait(78°50′N) has synoptic scale variability based on an array of moorings over the period of 1998–2010. The synoptic scale variability of Atlantic inflow, whose significant cycle is 3–16 d, occurs mainly in winter and spring(from January to April) and is related with polar lows in the Barents Sea. On the synoptic scale, the enhancement(weakening) of Atlantic inflow in the Fram Strait is accompanied by less(more)polar lows in the Barents Sea. Wind stress curl induced by polar lows in the Barents Sea causes Ekman-transport,leads to decrease of sea surface height in the Barents Sea, due to geostrophic adjustment, further induces a cyclonic circulation anomaly around the Barents Sea, and causes the weakening of the Atlantic inflow in the Fram Strait. Our results highlight the importance of polar lows in forcing the Atlantic inflow in the Fram Strait and can help us to further understand the effect of Atlantic warm water on the change of the Arctic Ocean. 相似文献
3.
傅刚 《中国海洋大学学报(自然科学版)》1999,(1)
论述有关发生在高纬度海洋上的极地低压研究的最新进展。不仅涉及观测研究,而且对有关的动力学机制和数值模拟也进行了介绍。因日本海沿岸各国的经济活动越来越活跃,而对发生在日本海上的极地低压进行了专门讨论。 相似文献
4.
Convective cloudiness in the Atlantic sector of the Arctic is considered as an atmospheric spatially self-organized convective field. Convective cloud development is usually studied as a local process reflecting the convective instability of the turbulent planetary boundary layer over a heated surface. The convective cloudiness has a different dynamical structure in high latitudes. Cloud development follows cold-air outbreaks into the areas with a relatively warm surface. As a result, the physical and morphological characteristics of clouds, such as the type of convective cloud, and their geographical localization are interrelated. It has been shown that marginal sea ice and coastal zones are the most frequently occupied by Cu hum, Cu med convective clouds, which are organized in convective rolls. Simultaneously, the open water marine areas are occupied by Cu cong, Cb, which are organized in convective cells. An intercomparison of cloud statistics using satellite data ISCCP and ground-based observations has revealed an inconsistency in the cloudiness trends in these data sources: convective cloudiness decreases in ISCCP data and increases in the groundbased observation data. In general, according to the stated hypothesis, the retreat of the sea-ice boundary may lead to an increase in the amount of convective clouds. 相似文献
5.
Smirnova J. E. Zabolotskikh E. V. Bobylev L. P. Chapron B. 《Izvestiya Atmospheric and Oceanic Physics》2016,52(9):1128-1136
Izvestiya, Atmospheric and Oceanic Physics - In this study polar lows over the Nordic Seas for the period of 1995–2008 have been detected and studied using the Special Sensor Microwave Imager... 相似文献
6.
7.
Zenith Total Delay (ZTD) observations and model calculations are used to analyze a mesoscale convective system which yielded a large amount of precipitation over a short period of time in the north-western Mediterranean. ZTD observations are derived from the GPS signal delay whereas the ZTD model results are calculated by means of the MM5 mesoscale model.
Large values of the root-mean-square (rms) differences between the ZTD derived from the observations and the modeling are found for the maximum activity of the mesoscale convective system. It appears that the average bias between observations and modeling results is slightly affected (20%) by the passage of the storm system which is associated to the water vapor variability of the atmosphere.
We have analyzed the ZTD differences in terms of the two components: the Zenith Hydrostatic Delay (ZHD) and the Zenith Wet Delay (ZWD). The hydrostatic error is mainly caused by the differences between the elevation of the GPS stations and the model topography and is reduced when using a more accurate topography data set. We propose a correction for this error assuming hydrostatic equilibrium. The remaining average ZTD difference is associated to the ZWD and is mainly generated by inaccuracies of the mesoscale model to predict the water vapor content during the rainfall event. 相似文献
Large values of the root-mean-square (rms) differences between the ZTD derived from the observations and the modeling are found for the maximum activity of the mesoscale convective system. It appears that the average bias between observations and modeling results is slightly affected (20%) by the passage of the storm system which is associated to the water vapor variability of the atmosphere.
We have analyzed the ZTD differences in terms of the two components: the Zenith Hydrostatic Delay (ZHD) and the Zenith Wet Delay (ZWD). The hydrostatic error is mainly caused by the differences between the elevation of the GPS stations and the model topography and is reduced when using a more accurate topography data set. We propose a correction for this error assuming hydrostatic equilibrium. The remaining average ZTD difference is associated to the ZWD and is mainly generated by inaccuracies of the mesoscale model to predict the water vapor content during the rainfall event. 相似文献
8.
《Marine and Petroleum Geology》2003,20(6-8):861-882
Hyperpycnal flows form in the marine environment when river discharge enters the ocean with suspended concentrations in excess of 36 kg m−3 due to buoyancy considerations, or as little as 1–5 kg m−3 when convective instability is considered. They form at a river mouth during floods of small to medium size rivers including extreme events such as jökulhaups, dam breaking and draining, and lahars. Associated with high-suspended concentration, they can transport considerable volume of sediment to ocean basins. The typical deposit or hyperpycnite sequence is a compound of a basal coarsening-up unit, deposited during the waxing period of discharge, and a top fining-up unit deposited during the waning period of discharge. Hyperpycnites differ from other turbidites because of their well-developed inversely graded facies and intrasequence erosional contacts. These observations lead to a complete redefinition and interpretation of fine-grained turbidites. Hyperpycnite stacking can locally generate high-sedimentation rates, in the range of 1–2 m per 100 year. Because hyperpycnites are related to climate through flood frequency and magnitude, their record should vary with sea level and climate change. They can also be associated with proximal ice-melting settings. Hyperpycnal flows could also be involved in the formation of meandering canyons and channels. 相似文献
9.
A statistical mechanism that explains the formation of probability distribution functions of thermals according to temperature fluctuations is considered. In the proposed approach based on the Boltzmann-Jaynes variational method, a statistical ensemble of convective thermals is characterized by a class of stationary probability densities that depend on temperature fluctuations. It is assumed that the probability density functions of this class may depend on the potential energy, as well as on the available potential energy. For a class of stationary probability density functions, the entropy functional is defined to be an analogue of the Boltzmann H-entropy. The equilibrium distributions of thermals according to temperature fluctuations correspond to the most probable distributions that yield a maximum of the entropy functional. The exponential and normal distributions of thermals according to temperature fluctuation that are constructed using the variational method quite adequately approximate field atmospheric observations, as well as the results of laboratory modeling. 相似文献
10.
ANDREW RUSSELL GERAINT VAUGHAN EMILY G. NORTON HUGO M. A. RICKETTS CYRIL J. MORCRETTE TIM J. HEWISON KEITH. A. BROWNING ALAN M. BLYTH 《地球，A辑:动力气象学与海洋学》2009,61(2):250-263
A narrow line of convective showers was observed over southern England on 18 July 2005 during the Convective Storm Initiation Project (CSIP). The showers formed behind a cold front (CF), beneath two apparently descending dry layers (i.e. sloping so that they descended relative to the instruments observing them). The lowermost dry layer was associated with a tropopause fold from a depression, which formed 2 d earlier from a breaking Rossby wave, located northwest of the UK. The uppermost dry layer had fragmented from the original streamer due to rotation around the depression (This rotation was also responsible for the observations of apparent descent—ascent would otherwise be seen behind a CF). The lowermost dry layer descended over the UK and overran higher θ w air beneath it, resulting in potential instability. Combined with a surface convergence line (which triggered the convection but had less impact on the convective available potential energy than the potential instability), convection was forced up to 5.5 km where the uppermost dry layer capped it. The period when convection was possible was very short, thus explaining the narrowness of the shower band. Convective Storm Initiation Project observations and model data are presented to illustrate the unique processes in this case. 相似文献
11.
北极极端气旋过程能够反映北极气候变化特征并对北极水文气象要素的调节具有重要影响,其活动及大气环流形势特征值得关注。利用美国国家环境预报中心(National Centers for Environmental Prediction,NCEP)与美国国家大气研究中心(National Center for Atmospheric Research,NCAR)提供的逐日再分析资料定义北极超强气旋(Arctic Super Cyclone, ASC)过程,结合美国国家冰雪数据中心(National Snow and Ice Data Center, NSIDC)基于NCEP/NCAR再分析资料追踪识别的北半球气旋及特征资料,分析了ASC的活动特征及其大气环流特征。结果表明:判别ASC的北极最低气压5%阈值具有显著的冬季低夏季高的单峰型季节变化特征,冬季ASC的强度远强于夏季;ASC多从大西洋扇区经北欧海?巴伦支海?喀拉海输入到极区,也存在少部分极区原生或太平洋扇区输入;ASC多生成于两大洋急流轴或急流出口区北侧,极少数生成于大陆或中低纬度,且绝大多数在极区消亡难以回到中纬度。极区原生ASC频数占总数约1/3,整体没有显著增减趋势,但长生命史ASC频数以0.49次/(10 a)的趋势增多,表明其持续时间增长。ASC频数与北极涛动(Arctic Oscillation, AO)在冬季相关性很好,其大气环流形势回归场中极区海平面出现低压低温异常,高空极涡加深且两大洋急流偏北,中纬度急流主轴偏弱;ASC的生成发展不仅有利于AO向正位相转变,同时AO正位相下也有利于ASC活动的增强,ASC活动是AO位相变化的潜在指标。 相似文献
12.
In this paper a new nondestructive damage identification method is introduced. The method based on flexibility matrix can be used to detect and locate structm＇al damage and evaluate the severity of damage in legs of jacket platforms by modal parameters of a structure. With the modal data for only the few lower modes in both the intact and damaged states, the one-dimensional and two-dimensional distributed curvatures can be used to analyze damage location and the severity. Instead of directly comparing the curvatures before and ＇after damage, the method here uses modal parameters only in the damaged structure to detect the damage and it consists of three parts. First, ilexibility matrix is obtained by use of the absolute maximum in each column. Second, because the legs of jacket platforms are the pipe-like structure, the circumferential flexibility curvature matrix is obtained by use of the circular curvature. At last, equivalent curvature ratio is defined and the curve meaning equivalent curvature ratio and the severity of damage relationship for one element is given through the data of damage severity from ten percent to ninety percent by numerical simulation. Many existing damage detection methods need two steps, locate the damage firstly and evaluate the severity of the damage. However, the method present- ed! in this paper can locate and then evaluate the severity of damage at the same time. The numerical analysis results in- dicate that the present method is effective, useful and only need the first and the second mode data of the structure. 相似文献
13.
Benthic communities colonizing two different typologies of artificial structures, Tecnoreef® pyramids (PY), and plinth modules (PL), differing for material and shape, were investigated for three years after their deployment on a soft bottom offshore Pedaso (Western Adriatic Sea). The aims were to describe the colonization patterns of benthic assemblages on the two artificial modules, to highlight possible differences between them and to detect the effectiveness of the artificial reef on the ecosystem functioning.The composition of the benthic communities settled on the two types of artificial substrates was different especially just after the reef deployment. Abundance and species richness were higher on PL in the first two years, while an explosion of individuals characterized PY in the third year. This suggested a delay of about one year in the colonization processes on PY likely due to the material and shape. The community settled of the artificial structures was dominated by hard-substrate species which are commonly absent in the natural environment. The occurrence of these organisms enriched the local soft-bottom communities and contributed to habitat diversification. This, together with the importance of these species in the diet of a few reef-dwelling fish, confirms the trophic role and the ecological importance of artificial reefs in areas characterized by soft seabed. 相似文献
14.
3‐dimensional variational algorithms are widely used for atmospheric data assimilation at the present time, particularly on the synoptic and global scales. However, mesoscale and convective scale phenomena are considerably more chaotic and intermittent and it is clear that true 4‐dimensional data assimilation algorithms will be required to properly analyze these phenomena. In its most general form, the data assimilation problem can be posed as the minimization of a 4‐dimensional cost function with the forecast model as a weak constraint. This is a much more difficult problem than the widely discussed 4DVAR algorithm where the model is a strong constraint. Bennett and collaborators have considered a method of solution to the weak constraint problem, based on representer theory. However, their method is not suitable for the numerical weather prediction problem, because it does not cycle in time. In this paper, the representer method is modified to permit cycling in time, in a manner which is entirely internally consistent. The method was applied to a simple 1‐dimensional constituent transport problem where the signal was sampled (perfectly and imperfectly) with various sparse observation network configurations. The cycling representer algorithm discussed here successfully extracted the signal from the noisy, sparse observations 相似文献
15.
锯缘青蟹卵黄发生期卵巢和肝胰腺脂类的变化 总被引：16，自引：0，他引：16
锯缘青蟹2次卵巢发育时的卵黄发生旺期与卵黄发生初期相比,卵巢指数和卵巢脂肪含量(%卵巢干重或湿重)均显著增加,积累了大量的脂类,而这一时期的肝胰腺指数和肝胰腺脂肪含量均无显著变化,说明在卵黄发生时期,肝胰腺吸收的脂肪均及时转运到正在发育的卵巢.卵黄发生期,卵巢或肝胰腺磷脂/总脂的百分含量,均无显著变化,肝胰腺中游离脂肪酸逐步增加,甚至在卵黄发生后期超过甘油三酯的含量.卵黄发生阶段,无论肝胰腺或卵巢,其磷脂长链多不饱和脂肪酸显著高于中性脂,而饱和脂肪酸含量相对较低;肝胰腺脂类脂肪酸组成的最主要变化是中性脂的n3系列的长链多不饱和脂肪酸,尤其是C22:6n3显著降低.卵黄发生初期,肝胰腺磷脂与卵巢中性脂的脂肪酸组成(肝胰腺转运脂肪时,首先要将吸收或储存的脂类转换成磷脂,才能运出)无显著差异,但卵黄发生旺期,肝胰腺磷脂的长链多不饱和脂肪酸显著高于卵巢中性脂的含量.文中讨论了这些变化的原因. 相似文献
16.
G. S. Golitsyn 《Izvestiya Atmospheric and Oceanic Physics》2008,44(5):537-547
Similarity and dimension considerations applied to convection in a rotating fluid allows one to estimate the sizes and horizontal velocities of generated vortices. To do this, it is necessary to know the buoyancy flux in the fluid and the angular velocity of fluid rotation [1, 2]. The author’s preliminary efforts [3] have shown that the sizes, wind speeds, and total kinetic energy can thus be estimated correctly for tropical cyclones (TCs), as well as for polar lows (PLs) (which are often called explosive mesocyclones because they take just a few hours to develop). In this study, the sensible and latent heat fluxes for U = 33 m/s and the related buoyancy fluxes are estimated on the basis of climatology, bulk formulas, and the velocity scale of convection in a rotating fluid. In the tropics, at hurricane wind speeds U ≥ 33 m/s and climatological air humidity r = 80%, the total heat flux at the water surface temperature T s ≥ 26°C becomes equal to or greater than 700 W/m2. Due to the Clausius-Clapeyron equation, the latent heat flux to the atmosphere (the main part of the flux in the tropics) decreases substantially at lower values of T s. Thus, an energy flux from the ocean to the atmosphere of 700 W/m2 or greater should be regarded as the first necessary condition for TC genesis instead of the temperature T s. Low static stability, which must be at least half its climatological value as estimated here, is another necessary condition [4]. In polar regions, total fluxes roughly twice those in the tropics are needed for the formation of explosive mesocyclones, PLs, which is explained by the much smaller role of latent heat, greater geostrophicity, and stronger static stability of the atmosphere there. Enthalpy fluxes and wind speeds are interrelated: the larger the flux is, the stronger the convection, the higher the concentration of angular momentum in an ascending convective air column, and the greater the azimuthal velocity in the vortex are, which in turn enhances the transfer of energy from the ocean. Considering the problem with the use of simple analytic relations makes it possible, for the first time, to find a numerical criterion for their generation. It is hoped that this material may be useful for educational purposes as well. 相似文献
17.
S. V. Anisimov S. V. Galichenko N. M. Shikhova K. V. Afinogenov 《Izvestiya Atmospheric and Oceanic Physics》2014,50(4):390-398
The electric state of the middle-latitude convective atmospheric boundary layer (ABL) is investigated during a point in time when it is not disturbed by clouds, precipitation, mist, or industrial aerosols. A numerical model is developed that estimates the electroaerodynamic state of the convective ABL. The model is parameterized using results of field observations and laboratory experiments. According to the model, vertical profiles of atmospheric electric field strength, space charge density, electric conductivity, and atmospheric electric current density are calculated in the horizontally homogeneous approximation with a high space-time resolution. 相似文献
18.
Chunhui Tao Sheng Chen Edward T. Baker Huaiming Li Jin Liang Shili Liao Yongshun John Chen Xianming Deng Guoyin Zhang Chunhua Gu Jialin Wu 《Marine Geophysical Researches》2017,38(1-2):3-16
Seafloor hydrothermal polymetallic sulfide deposits are a new type of resource, with great potential economic value and good prospect development. This paper discusses turbidity, oxidation–reduction potential, and temperature anomalies of hydrothermal plumes from the Zouyu-1 and Zouyu-2 hydrothermal fields on the southern Mid-Atlantic Ridge. We use the known location of these vent fields and plume data collected in multiple years (2009, 2011, 2013) to demonstrate how real-time plume exploration can be used to locate active vent fields, and thus associated sulfide deposits. Turbidity anomalies can be detected 10 s of km from an active source, but the location precision is no better than a few kilometers because fine-grained particles are quasi-conservative over periods of many days. Temperature and oxidation–reduction potential anomalies provide location precision of a few hundred meters. Temperature anomalies are generally weak and difficult to reliably detect, except by chance encounters of a buoyant plume. Oxidation–reduction potential is highly sensitive (nmol concentrations of reduced hydrothermal chemicals) to discharges of all temperatures and responds immediately to a plume encounter. Real-time surveys using continuous tows of turbidity and oxidation–reduction potential sensors offer the most efficient and precise surface ship exploration presently possible. 相似文献
19.
通过迭代CFAR算法，本文发展了一种针对分块SAR图像的冰山检测方法。考虑到滑动窗口运算负担大、计算效率低，首先对SAR图像进行分块，以提取分块内的亮目标冰山。利用高斯模型表征后向散射系数的统计分布，冰山检测阈值可简单地表达为均值和方差的线性组合，将分块内像素逐个比对阈值以检测冰山。考虑到同一场景中尺寸变化大的冰山影响检测精度，以识别的冰山像素做种子执行区域生长，从而提取大尺寸的冰山。针对单个分块迭代上述处理，以降低高斯模型表征分块统计分布的误差，提高冰山检测精度。利用2013年11月22日和29日获取自极地海域的两景RADARSAT-2图像开展验证试验。结果表明，数量多、尺寸变化大并嵌入在海冰等极地常见情形下的冰山，能被文中方法有效识别，选取区域内正确率高达85%以上，且具有良好的运行效率。 相似文献
20.