Sub-kilometer length scales in coastal waters

Patchiness or spatial variability is ubiquitous in marine systems. With increasing anthropogenic impacts to coastal resources and coastal systems being disproportionately large contributors to ocean productivity, identifying the spatial scales of this patchiness, particularly in coastal waters, is of critical importance to understand coastal ecosystem dynamics. The current work focuses on fine scale structure in three coastal regions. More specifically, we utilize variogram analyses to identify sub-kilometer scales of variability in biological and physical parameters measured by an autonomous underwater vehicle (AUV) in the Mid-Atlantic Bight, Monterey Bay, and in San Luis Obispo Bay between 2001 and 2004. Critical scales of variability in density, turbidity, fluorescence, and bioluminescence are examined as a function of depth and distance offshore. Furthermore, the effects of undersampling are assessed using predictive error analysis. Results indicate the presence of scales of variability ranging from 10s to 100s of meters and provide valuable insight for sampling design and resource allocation for future studies.     

不同时空尺度的泥石流预报技术体系

降水诱发的泥石流是我国主要的泥石流灾害类型。降水是该类泥石流灾害预报的关键动态因子,不同的降水监测和预报技术与方法决定了泥石流预报的不同时空尺度。分析了不同降水监测和预报技术的时空尺度和时空分辨率,并以此为基础,结合下垫面条件分析,建立了不同时空尺度的泥石流预报体系框架:大中区域泥石流预报(数值天气预报)─中小区域泥石流预报(多普勒天气雷达)─单沟泥石流预报(多普勒天气雷达和地面降水遥测)。具体的技术体系包括下垫面条件分析、降水监测和预报方法以及预报结果的表述与发布。     

Aircraft Observations of the Development of Thermal Internal Boundary Layers and Scaling of the Convective Boundary Layer Over Non-Homogeneous Land Surfaces

This study investigates the convective boundary layer (CBL) that develops over anon-homogeneous surface under different thermal and dynamic conditions. Analysesare based on data obtained from a Russian research aircraft equipped with turbulentsensors during the GAME-Siberia experiment over Yakutsk in Siberia, from April to June 2000.Mesoscale thermal internal boundary layers (MTIBLs) that radically modified CBLdevelopment were observed under unstable atmospheric conditions. It was found thatMTIBLs strongly influenced the vertical and horizontal structures of virtual potentialtemperature, specific humidity and, most notably, the vertical sensible and latent heatfluxes. MTIBLs in the vicinity of the Lena River lowlands were confirmed by clouddistributions in satellite pictures.MTIBLs spread through the entire CBL and radically modify its structure if the CBL isunstable, and strong thermal features on the underlying surface have horizontal scalesexceeding 10 km. MTIBL detection is facilitated through the use of special parameterslinking shear stress and convective motion.The turbulent structure of the CBL with and without MTIBLs was scaled usingthe mosaic or flux aggregate approach. A non-dimensional parameterL_Rau/L_hetero (where L_Rau is Raupach's length and L_hetero is the horizontal scale of the surface heterogeneity)estimates the application limit of similarity and local similarity scaling models forthe mosaic parts over the surface. Normalized vertical profiles of wind speed, airtemperature, turbulent sensible and latent heat fluxes for the mosaic parts withL_RauL_hetero < 1 could be estimated by typical scalingcurves for the homogeneous CBL. Traditional similarity scaling models for the CBLcould not be applied for the mosaic parts with L_Rau/L_hetero > 1.For some horizontally non-homogeneous CBLs, horizontal sensible heat fluxes werecomparable with the vertical fluxes. The largest horizontal sensible heat fluxes occurred at the top of the surface layer and below the top of the CBL.Formerly affiliated to the Frontier Observational Research System for Global ChangeFormerly affiliated to the Frontier Observational Research System for Global Change     

大气中的波流相互作用研究进展

简要回顾了近年来关于波动同纬向平均流相互作用的研究进展,重点讨论了E-P通量和波作用守恒理论的研究进展,同时,还介绍了波流作用稳定性问题的理论研究动态.     

非静力模式中几种垂直网格计算特性的对比研究

从非静力滞弹性方程组出发，将惯性重力波的水平波长分几百公里、几十公里和几公里三种情况，从频率、群速和各速的垂直尺度范围等方面对现有的几种垂直网格进行比较讨论。结果表明：在非静力模式中，CP网格和LZ网格适合于各种不同水平尺度惯性重力波的模拟；L网格和LY网格适合于水平尺度为几十公里以上的惯性重力波的模拟；LTS网格和CPTS网格比较适合于水平尺度的几十公里以下的惯性重力波的模拟。     

TOPOGRAPHIC DEPENDENT HORIZONTAL LOCALIZATION SCALE SCHEME IN GRAPES-MESO HYBRID EN-3DVAR ASSIMILATION SYSTEM

Based on the GRAPES-MESO hybrid En-3DVAR (Ensemble three-dimension hybrid data assimilation for Global/Regional Assimilation and Prediction system) constructed by China Meteorological Administration, a 7-day simulation (from 10 July 2015 to 16 July 2015) is conducted for horizontal localization scales. 48h forecasts have been designed for each test, and seven different horizontal localization scales of 250, 500, 750, 1000, 1250, 1500 and 1750 km are set. The 7-day simulation results show that the optimal horizontal localization scales over the Tibetan Plateau and the plain area are 1500 km and 1000 km, respectively. As a result, based on the GRAPES-MESO hybrid En-3DVAR, a topography-dependent horizontal localization scale scheme (hereinafter referred to as GRAPES-MESO hybrid En-3DVAR-TD-HLS) has been constructed. The data assimilation and forecast experiments have been implemented by GRAPES-MESO hybrid En-3DVAR, 3DVAR and GRAPES-MESO hybrid En-3DVAR-TD-HLS, and then the analysis and forecast field of these three systems are compared. The results show that the analysis field and forecast field within 30h of GRAPES-MESO hybrid En-3DVAR-TD-HLS are better than those of the other two data assimilation systems. Particularly in the analysis field, the root mean square error (RMSE) of u_wind and v_wind in the entire vertical levels is significantly less than that of the other two systems. The time series of total RMSE indicate, in the 6-30h forecast range, that the forecast result of En-3DVAR-TD-HLS is better than that of the other two systems, but the En-3DVAR and 3DVAR are equivalent in terms of their forecast skills. The 36-48h forecasts of three data assimilation systems have similar forecast skill.     

Wavelet analysis of rainfall variation in the Hebei Plain

Rainfall is an important climate factor, which has significant impacts on agricultural production and na-tional economic development[1]. Being part of the North China Plain, the Hebei Plain is an agricultural region. Under the continental monsoon climate, it is cold and dry in winter, hot and rainy in summer, and its variable rainfall is concentrated in summer. Droughts and floods occur frequently and impose sig-nificant impacts on agricultural production. Studies on the characteristics and …     

空间数据问题与GIS发展的思考

讨论了GIS空间数据的几个理论问题:空间数据概念的完整性,空间数据量,面向多维空间、动态分析的空间数据结构,以及GIS空间数据的初始化和空间尺度等;深入探讨GIS在解决这些问题时所面临的困惑,并在分析了GIS所需的空间数据基础上定义了位、邻、近、势4类空间关系数据,由此探讨了地图代数作为一种解决思路的可行性及其若干特点。     

An Analysis of Sonic Anemometer Observations In Low Wind Speed Conditions

When the wind speed decreases below a certain value (1–2 m s^-1) meandering (low frequency horizontal wind oscillations) starts to prevail. In these conditions it becomes difficult to define a precise mean wind direction and to estimate the airborne dispersion. To study the wind and turbulence characteristics during meandering, two sonic anemometer datasets, containing hourly wind observations, were analysed: the first one, lasting 1 year, was recorded in complex terrain (Graz, Austria) and the second one, lasting about 1month, was recorded in a rather flat area (Tisby, Sweden). It was found that meandering seems to exist under all meteorological conditions regardless of the stability or wind speed and it was confirmed that meandering sets a lower limit for the horizontal wind component variances. Further, it was found that the autocorrelation functions of the horizontal wind components, computed for the low wind cases, show an oscillating behaviour with the presence of large negative lobes. Two different relationships from the literature, and relevant to these oscillatory aspects, were fitted to the data. They contain two parameters: one associated and relevant to the classical integral time scale and the second with meandering occurrence. Based on these relationships, expressions for the mean square displacement of particles _y²(t) were also derived.     

Coastline configuration disrupts the effects of large-scale climatic forcing, leading to divergent temporal trends in wave exposure

Both climate change and the North Atlantic Oscillation (NAO) may influence coastal systems by altering wave exposure. The effects of such climatic forcing are often coherent over relatively large geographic areas. Temporal trends in wave exposure at any particular shore are, however, the result of an interaction between site-specific fetch characteristics and changes in wind climate. This leads to contrasting trends in wave exposure at locations separated by no more than a few kilometres. Wave exposures were estimated at locations around a sea lough over 32 years to characterise these scales of variability. Locations separated by approximately 5 km had independent dynamics with respect to the temporal trend (correlation range −0.35 to 0.44) and to associations with the NAO (correlation range −0.18 to 0.40). Wave exposure can therefore be increasing for a section of shore while nearby areas have the opposite trend. Mean exposure at a location was not a good predictor of the temporal trend. More exposed sites were, however, sensitive to variations in the strength of the NAO. The reduction of large scale forcing to small-scale variability has implications for the detection and mitigation of potential climate change impacts.