Evaluation of mid-depth currents of NCEP reanalysis data in the tropical Pacific using ARGO float position information

1. Introduction The reanalysis dataset (Ji et al., 1995; Kalnay et al., 1996) offered by the National Centers for Environ- mental Prediction (NCEP) has been applied widely in relevant multidisciplinary research. Along with in- creasingly extensive observa…     

北半球E-P通量分析及其与副热带高压的关系

利用北半球1951－2000年冬季（1月）200hPa,500hPa的月平均资料，计算出E－P通量，并根据平均环流的E－P通量剖面图，研究了北半球冬季在大地形作用下，波动对基本气流的作用，以及波流相互作用下行星波的传播。北半球冬季平均E－P通量的辐合辐散与地形作用形成的大槽大脊相对应，其强度也与槽脊的强度相一致。另外，根据多年夏季（7月）的月平均高度场、风场及降水资料得到E－P通量和副热带高压的关系，进一步得到E－P通量与异常天气的关系。     

自动与人工观测降雨量的差异及相关性

利用全国627个基准、基本站2005年自动与人工雨量业务观测资料, 分析了业务上自动与人工观测的降雨量的差异以及引起差异的原因, 并分析了自动观测与人工观测的降雨量的相关性。结果表明:自动观测比人工观测的日降雨量平均偏高0.12 mm, 标准差为0.70 mm, 相对偏高1.42%。627个站中, 80%的站自动与人工观测的年降雨量差值在5%以内; 近4%的站年降雨量差值在10%以上。年降雨量相对差值较大的站, 其年降雨量均较小。空间采样差、20:00 (北京时) 定时观测中人工与自动观测时间的不一致以及其他突发事件均会导致自动与人工测量的日降雨量的差异, 甚至显著差异。由于观测仪器不同引起的降雨测量系统误差差别, 导致自动与人工观测降雨量的系统偏差。自动观测与人工观测的日降雨量呈线性相关, 相关系数为0.9988。     

Seasonal temperature and precipitation variability during the last 60?years in a Mediterranean climate area of Northeastern Spain: a multivariate analysis

This paper presents the analysis of mean daily temperature and precipitation from 1950 to 2010 in an area with Mediterranean climate of NE Spain including some coastal areas near Barcelona and the Penedès and Camp de Tarragona Depressions located between the Coastal Mountain Range and the Mediterranean Sea. Their variability, with especial attention to the frequency of extreme events, was analysed by using 18 indexes: seven for temperature and 11 for precipitation were analysed for four meteorological observatories. A multivariate analysis was performed in order to analyse the temperature and precipitation trends. During the analysed period, an increase in mean annual maximum temperature was observed in all observatories ranging between 1.5 and 2.2°C associated with an increase in the number of days with high extreme temperatures. Minimum temperature only increased significantly in the coast observatories (about 1.4°C). By seasons, temperature trends were greater at Vilafranca del Penedès and Barcelona observatories and lower at Reus airport. Maximum spring temperature increased between 1.5 and 2.5°C, summer temperature increased between 1.6 and 2.5°C and autumn temperature increased by up to 2.2°C. Precipitation presented a high variability from year to year, without significant trends. The most significant results were related to the dry conditions observed in spring 2000s, the wet conditions recorded in summer 2000s and 1980s and the longer dry periods in autumn 2000s. The increase of temperatures determined the increase of evapotranspiration, and due to the higher irregular distribution, water deficits for crop development were recorded. An advance of phenological dates and a reduction of grape yield are associated to climate trends.     

相对湿度自动与人工观测的差异分析

利用四川135个站自动与人工第二年平行观测相对湿度(下文简称湿度)资料,就自动与人工观测相对湿度的差异及引起差异的原因进行了分析。结果表明:相对湿度自动与人工观测相比,日平均值平均偏低2.7270%、月平均值平均偏低2.7970%、年平均值平均偏低2.7472%。56.35%的时次自动观测湿度值与人工观测湿度值的差值在5%以内,86.66%的时次自动观测湿度值与人工观测湿度值的差值在10%以内,2.61%的时次自动观测湿度值与人工观测湿度值的差值在20%以上。自动与人工观测湿度的差值无明显地域性差异。湿球纱布包扎不规范、纱布不清洁,干湿球温度表人工读数误差,干湿球温度表的通风状态,观测时间的不一致,自动观测在高湿状况下的非线性以及其他原因均会导致自动与人工观测湿度产生差异,甚至是显著差异。     

Influence Diagrams for Representing Uncertainty in Climate-Related Propositions

In order to respond to policy questions about the potential impacts of climate change it is usually necessary to assemble large quantities of evidence from a variety of sources. Influence diagrams provide a formal mechanism for structuring this evidence and representing its relationship with the climate-related question of interest. When populated with probabilistic measures of belief an influence diagram provides a graphical representation of uncertainty, which can help to synthesize complex and contentious arguments into a relatively simple, yet evidence-based, graphical output.Following unusually damaging floods in October–November 2000 the UK government commissioned research with a view to establishing the extent to which the floods were a manifestation of hydrological climate change. By way of example application, influence diagrams have been used to represent the evidential reasoning and uncertainties in responding to this question. Three alternative approaches to the mathematization of uncertainty in influence diagrams are demonstrated and compared. In situations of information scarcity and imprecise expert judgements, methods based on interval probabilities have proved to be attractive. Interval probabilities can, it is argued, represent ambiguity and ignorance in a more satisfactory manner than the conventional Bayesian alternative. The analysis provides a quantified commentary on the uncertainties in the conclusion that the events of October–November 2000 were extreme, but cannot in themselves be attributed to climate change.     

四川自动与人工观测气温的差异分析

利用四川135个站自动与人工第2年平行观测气温资料,就自动与人工观测的气温的差异、引起差异的原因进行了分析。结果表明:气温各项目的自动观测比人工观测平均偏高,平均差值基本在0.2℃以内;气温、日最高、日最低的自动与人工观测比较,差值在±0.2℃之间的分别占58.71%、51.58%、62.68%,自动与人工观测值一致的分别占15.07%、12.16%、14.78%;自动与人工观测气温之间的对比差值存在明显的日变化,无明显的季节性和地域性差异;两种观测体制在观测时间上、观测方式上、测温传感器安装位置上,以及感应元件和测温原理的不同、仪器误差、热滞效应,都会造成观测结果出现差异。      

采用TIPEX科学试验资料对1998年7月长江特大暴雨系统的梅雨期区域边界水汽输送模型及其数值试验

采用1998年第二次青藏高原大气科学实验(TIPEX)现场观测资料,包括加密探地面与探空观测、系留气球资料及遥感和高原试验中的中日合作研究(GAME/Tibet)基地Doppler雷达资料对青藏高原上空发展的积云对流系统及其生成和移动进行监测,讨论了与1998年长江下游暴雨的关系。结果表明:1)卫星云图动态分析及TBB资料制作的Hovmoller时空剖面分析表明,1998年7月下旬的长江暴雨洪水系统可追溯到高原。2)对上述TBB分析的云团在安多站过境时段(7月18-19日)进行Doppler跟踪,Doppler雷达回波跟踪分析揭示出,这种在高原中部地区发展和东移、加强的回波十分频繁。TIPEX多种仪器联合观测资料的综合分析可捕捉高原对流系统的生消和移动轨迹,对诊断预测高原系统对其下游的影响很有价值。3)综合分析上述TIPEX同时段地面和高空加密观测报告的时空剖面发现,高原腹地区(那曲地区)对流云系频繁发展,与准静止的地面风场辐合的维持有关。高原地面风场的动力辐合、高原上空风场垂直切变以及高原西风增湿过程所提供的高原水汽输送对1998年长江暴雨的发展与加强起重要作用。4)对高原水汽垂直分布的中尺度过滤分析发现,高原水汽的高值与低值随时间的交替变化,清楚地揭示了生命史为几小时的次天气尺度的波动。高原中尺度波动东移的揭示进     

天气雷达组合风场显示产品的检验评估

采用绝对误差、相对误差、皮尔逊相关系数、样本数量分布图等统计方法对中国气象局气象探测中心下发的2012年8月至2017年7月天气雷达组合风场显示产品进行质量评估,结果表明:①该产品与探空风场有较高的相关性,两种资料没有系统性差异,风向相关性优于风速;②随高度升高,该产品和探空资料的相关系数变差,500hPa以下高度的风场数据可用性较高;③产品质量与降水有着密切的关系,天气尺度的稳定性降水有利于提高风场反演质量,非气象回波、强对流天气情况下雷达反演风场质量均会下降。④产品质量与地形复杂程度有一定的关系。     

The influence of inter-annually varying albedo on regional climate and drought

Albedo plays an important role in land–atmosphere interactions and local climate. This study presents the impact on simulating regional climate, and the evolution of a drought, when using the default climatological albedo as is usually done in regional climate modelling, or using the actual observed albedo which is rarely done. Here, time-varying satellite derived albedo data is used to update the lower boundary condition of the Weather Research and Forecasting regional climate model in order to investigate the influence of observed albedo on regional climate simulations and also potential changes to land–atmosphere feedback over south-east Australia. During the study period from 2000 to 2008, observations show that albedo increased with an increasingly negative precipitation anomaly, though it lagged precipitation by several months. Compared to in-situ observations, using satellite observed albedo instead of the default climatological albedo provided an improvement in the simulated seasonal mean air temperature. In terms of precipitation, both simulations reproduced the drought that occurred from 2002 through 2006. Using the observed albedo produced a drier simulation overall. During the onset of the 2002 drought, albedo changes enhanced the precipitation reduction by 20 % on average, over locations where it was active. The area experiencing drought increased 6.3 % due to the albedo changes. Two mechanisms for albedo changes to impact land–atmosphere drought feedback are investigated. One accounts for the increased albedo, leading to reduced turbulent heat flux and an associated decrease of moist static energy density in the planetary boundary layer; the other considers that enhanced local radiative heating, due to the drought, favours a deeper planetary boundary layer, subsequently decreasing the moist static energy density through entrainment of the free atmosphere. Analysis shows that drought related large-scale changes in the regional climate favour a strengthening of the second mechanism. That is, the second mechanism is stronger in a drought year compared to a normal year and this difference is larger than for the first mechanism. When both mechanisms are active, the second mechanism tends to dominate across the model domain, particularly during the 2002 drought period. The introduction of observed inter-annual variations in albedo produces an enhancement of the first mechanism and a weakening of the second mechanism during the onset of the drought.     

Turbulence Structure Within and Above a Canopy of Bluff Elements

Measurements of turbulence structure in a wind-tunnel model canopy of bluff elements show many of the features associated with vegetation canopies and roughness sublayers but also display features more characteristic of the inertial sublayer (ISL). Points of similarity include the existence of an inflexion point in the space-time averaged streamwise velocity at the canopy top, the variation with height of turbulent second moments and the departure of the turbulent kinetic energy budget from local equilibrium in and just above the canopy. Quadrant analysis shows characteristic dominance of sweep over ejection events within the canopy although sweeps are more frequent than usually seen in vegetation canopies. Points of difference are a u′, w′ correlation coefficient that is closer to the ISL value than to most canopy data, and a turbulent Prandtl number midway between canopy and ISL values. Within the canopy there is distinct spatial partitioning into two flow regimes, the wake and non-wake regions. Both time-mean and conditional statistics take different values in these different regions of the canopy flow. We explain many of these features by appealing to a modified version of the mixing-layer hypothesis that links the dominant turbulent eddies to the instability of the inflexion point at canopy top. However, it is evident that these eddies are perturbed by the quasi-coherent wakes of the bluff canopy elements. Based upon an equation for the instantaneous velocity perturbation, we propose a criterion for deciding when the eddies linked to the inflexion point will dominate flow structure and when that structure will be replaced by an array of superimposed element wakes. In particular, we show that the resemblance of some features of the flow to the ISL does not mean that ISL dynamics operate within bluff-body canopies in any sense.     

An ensemble strategy for high-resolution regional model forecasts

Summary An ensemble methodology is proposed for very high-resolution regional model Quantitative Precipitation Forecasts. To facilitate a systematic study, the model and the boundary conditions are assumed to be perfect. The generation of perturbations is derived on the basis that the largest errors in precipitation forecasts at very high resolutions arise from miss-specified diabatic heat sources and sinks which feedback erroneously to the grid scale variables in the initial state. This methodology is tested in a Proxy Observed System Simulation Experiment (POSSE) involving an intense cyclone over eastern Canada. The perturbations of wind and temperature in this ensemble strategy are obtained as normalized coefficients of a Combined Empirical Orthogonal Function analysis of the difference fields between the control and the diabatically initialized model runs. These perturbations are added to and subtracted from the control initial state to obtain a set of two perturbed initial states. Several such perturbed initial states are obtained from initializing observed rain rates at different times close to the time of the analysis. The results from the POSSE reveal that the Quantitative Precipitation Forecast of the ensemble mean outperforms the control model run. Received August 8, 2000/Revised November 1, 2000     

Checking for model consistency in optimal fingerprinting

 Current approaches to the detection and attribution of an anthropogenic influence on climate involve quantifying the level of agreement between model-predicted patterns of externally forced change and observed changes in the recent climate record. Analyses of uncertainty rely on simulated variability from a climate model. Any numerical representation of the climate is likely to display too little variance on small spatial scales, leading to a risk of spurious detection results. The risk is particularly severe if the detection strategy involves optimisation of signal-to-noise because unrealistic aspects of model variability may automatically be given high weight through the optimisation. The solution is to confine attention to aspects of the model and of the real climate system in which the model simulation of internal climate variability is adequate, or, more accurately, cannot be shown to be deficient. We propose a simple consistency check based on standard linear regression which can be applied to both the space-time and frequency domain approaches to optimal detection and demonstrate the application of this check to the problem of detection and attribution of anthropogenic signals in the radiosonde-based record of recent trends in atmospheric vertical temperature structure. The influence of anthropogenic greenhouse gases can be detected at a high confidence level in this diagnostic, while the combined influence of anthropogenic sulphates and stratospheric ozone depletion is less clearly evident. Assuming the time-scales of the model response are correct, and neglecting the possibility of non-linear feedbacks, the amplitude of the observed signal suggests a climate sensitivity range of 1.2–3.4 K, although the upper end of this range may be underestimated by up to 25% due to uncertainty in model-predicted response patterns. Received: 9 December 1997 / Accepted: 24 December 1998     

A global ocean temperature and altimeter data assimilation system for studies of climate variability

 An ocean data assimilation (ODA) system which can assimilate both temperature and altimeter observations has been applied to the global ocean and tested between January 1993–October 1996. A statistical method has been used to convert sea surface height (SSH) anomalies observations from TOPEX/POSEIDON into synthetic temperature profiles. The innovative aspect of this method is the introduction of time dependency in the correlations used to transform the altimeter observations into temperature corrections. The assimilation system is based on a univariate variational optimal interpolation scheme applied to assimilate both in situ and synthetic temperature profiles. In addition, a longer global analysis for the upper-ocean temperature starting from January 1979 and ending November 1997, has been produced to examine the skill of sea temperature assimilation with a rather simple and practical method. The temperature analysis shows encouraging improvement over a corresponding ocean simulation when compared to independent (not assimilated) temperature data both at seasonal and interannual time scales. However, the univariate data assimilation of hydrographic data does not result in an improvement of the velocity field. In fact the assimilation of sparse in situ data can introduce unrealistic spatial variability in the temperature field which affects the velocity field in a negative way. This deficiency is partially overcome when we also assimilate altimeter observations since the coverage is complete and uniform for this data. In particular, our study shows that temperature corrections due to the altimeter signal have a positive impact on the current system in the tropical Pacific. Received: 28 May 2000 / Accepted: 6 November 2000     

The Impact of Agricultural Practices in China on Land-Atmosphere Interactions

Human-induced land use changes and the resulting alterations in vegetation features are major but poorly recognized drivers of regional climatic patterns.In order to investigate the impacts of anthropogenically-induced seasonal vegetation cover changes on regional climate in China,harmonic analysis is applied to 1982-2000 National Oceanic and Atmospheric Administration(NOAA) Advanced Very High Resolution Radiometer(AVVHRR)-derived normalized difference vegetation index(NDVI) time series(ten day interval data).For two climatic divisions of South China,it is shown that the first harmonic term is in phase with air temperature,while the second and third harmonics are in phase with agricultural cultivation.The Penman-Monteith Equation and the Complementary Relationship Areal Evapotranspiration(CRAE) model suggest that monthly mean evapotranspiration is out of phase with temperature and precipitation in regions with signiffcant second or third harmonics.Finally,seasonal vegetation cover changes associated with agricultural cultivation are identiffed:for cropped areas,the temperature and precipitation time series have a single maximum value,while the monthly evapotranspiration time series has a bimodal distribution.It is hypothesized that multi-cropping causes the land surface albedo to sharply increase during harvesting,thereby altering the energy distribution ratio and contributing to observed seasonal vegetation cover changes.     

THETAPLOT,an equivalent potential temperature diagram

Summary THETAPLOT is a diagram useful for the display and analysis of atmospheric thermodynamic soundings, particularly in relation to conditionally and convectively instable summertime weather situations. The basic coordinates of THETAPLOT are the equivalent potential temperature and the negative logarithm of pressure. The body of the diagram contains families of curves of constant potential temperature, mixing ratio and temperature. From any given sounding, three curves are plotted on the diagram: 1) Theta-ed, the equivalent potential temperature of air saturated at its dew point temperature; 2) Theta-e, equivalent potential temperature; and 3) Theta-es, the saturated equivalent potential temperature. The winds are plotted along the margin of the diagram.With 5 Figures     

华南黑碳气溶胶浓度与南海夏季风关系的年代际突变

利用重建的华南区域黑碳气溶胶(Black Carbon,BC)浓度资料,分析其与南海夏季风在年际尺度上的关系.结果 表明,华南区域BC浓度与南海夏季风的关系在2000年前后有明显的突变,由显著负相关变为显著正相关,即由高BC浓度弱季风变为高BC浓度强季风.通过合成对比分析,发现1988-1999年(第一时间段)的华南B...     

1979—2018年5—8月中国东北冷涡建立的客观识别方法及变化特征

东北冷涡是中国东北地区重要的天气系统,采用欧洲中期天气预报中心（ECMWF）提供的ERA-Interim一日4次再分析资料,并改进现有的客观识别方法,将分析天气图的思路运用于对冷涡的客观识别中,检索出1979—2018年夏季（5—8月）516个东北冷涡过程。为了研究冷涡生成位置的差异,以45°N线为X轴,125°E线为Y轴将研究区划分为4个象限。结果表明:夏季东北冷涡生成位置以第2象限（西北部）最多,第4象限（东南部）最少,冷涡以向东移动为主。夏季东北冷涡的平均生命期为3.2 d,各象限生成的冷涡平均生命期有较大差异,第2象限最长,平均约为3.5 d;第4象限最短,平均约为2.9 d。72.1%的冷涡过程生命期少于4 d。夏季各月第2象限生成的冷涡频数均远多于其他3个象限,且具有很明显的逐月递减的季节内变化特征。东北冷涡的生成位置和频数具有明显的年代际变化,5月,1998—2007年偏北,2008—2018年偏南;6月,1980—1998年南移,2008—2018年北移,1993—2003年以偏东为主,2004—2018年以偏西为主;7月,1998—2010年北移,1985—2000年偏西,2005—2012年偏东;8月,2002—2010年偏北,2009—2018年偏东。就频数而言,特别是第2象限生成的冷涡,其年代际变化在季节内存在明显不一致,5月,1979—1985年冷涡偏多,1986—1992年冷涡偏少;6月,1979—1992年偏多,1993—2018年偏少;7月,1980—1991年偏多,1992—2000年偏少。      

安徽省夏季降水区域特征

用R型因子分析的方法对1957-2000年安徽省16个测站的夏季降水资料进行研究,应用因子荷载点聚图将观测站点进行区域划分,找出每个区域内的代表观测站,统计各分区夏季降水特征、夏季降水长期趋势变化、区域旱涝特征及年代际变化.结果表明:安徽省夏季降水可以划分为3个区.其中砀山、滁州和宁国可以分别作为它们的标准站.研究指出,40多年3个区的夏季降水特征差别较大:1区夏季降水量最少,2区居中,3区最多,其中6月3个区差别最明显;1区、2区夏季降水量长期趋势变化不明显,而3区表现为明显的正趋势变化;2区是降水异常的多发区,更容易发生干旱与洪涝;1区中在1957-1970年和1991-2000年旱涝较频繁,而在2区和3区中,旱、涝频数随时间变化总体趋势是从旱向涝转变的.