Screening effects on road surface temperature and road slipperiness

Summary The effect of screening on road surface temperatures during day time conditions is studied. Data from the Swedish Road Weather Information System (VVIS) are used and differences in road surface temperature between sites screened from the sun and well exposed sites are analysed. Six stations in the counties of Skaraborg and Älvsborg are used. The main factors determining the shadow patterns analysed are type and orientation of the screening objects, solar elevation and cloudiness and sky-view factor. The solar elevation and cloudiness determine the potential maximum differences in road surface temperature, while shape and orientation of the screening obstacle determine the occurrence and duration of the shadow pattern. The study shows that the maximum differences in road surface temperature during the day at screened sites are strongly correlated to the daily maximum solar elevation during a given period. It is evident that, when the cloud cover increases, the temperature divergence at screened sites is progressively reduced. The maximum road surface temperature difference occurring during the day has also been shown to have a significant effect on the road surface temperature after sunset at the screened site. The road surface temperature at a screened site is kept at a low level compared with the well exposed station site till after sunset but if the sky-view factor is small the road surface temperature difference can be reduced.With 8 Figures     

相似集合预报方法在北京区域地面气温和风速预报中的应用

相似集合是近年来提出的一种基于相似理论、大数据挖掘和集合预报思路的统计释用方法。文中首先介绍了相似集合的基本原理,并应用该方法对北京快速更新循环数值预报系统（BJ-RUC）v3.0预报地面要素开展了订正释用试验。结果表明,相似集合订正后,在0—36 h预报时段内,10 m风速的均方根误差降低44%,2 m气温的均方根误差降低22%,均方根误差均显著减小。对比测站预报误差的水平分布,相似集合方法的应用对于提升非城区站点的10 m风速预报、复杂地形区域的2 m气温预报具有更为明显的效果。相同预报因子的相似集合和支持向量机方法对模式10 m风速和2 m气温预报均具有显著且相似的订正效果,但相似集合方法具有计算资源需求较少、不需要大量人工干预的优势。相似集合方法形成的集合较好地模拟了模式平均误差的增长情况,集合离散度与集合平均均方根误差表现出理想的统计一致性,即相似集合方法在形成确定性预报的同时,还能够提供预报要素的不确定性或概率信息。因此,相似集合方法在模式预报订正及释用方面具有广阔的应用前景。      

Local surface temperature change due to expansion of oil palm plantation in Indonesia

A high world demand for crude palm oil has caused a reduction in the area of Indonesia’s tropical rainforests over the past several decades. Our hypothesis is that the expansion of the area devoted to oil palm plantations at the expense of primary and secondary tropical rainforests will increase the local surface temperature. While similar studies of other crops have been reported, this is the first time this particular hypothesis has been investigated and reported using the remote sensing methods described in this paper. In this study, we used remotely sensed data to quantify land use changes from tropical rainforests to oil palm plantations, calculated the surface temperature from thermal infrared data supplied by band 6 of the Landsat 5 Thematic Mapper (TM) and Landsat 7 Enhanced Thematic Mapper Plus (ETM+), examined the correlations of surface temperature to foliage cover, and conducted field work to verify the results obtained using the remotely sensed data. For this study, we used a new spectral index, Principal Polar Spectral Greenness (PPSG), that is potentially more sensitive than other index to small changes in foliage cover at high cover levels. The outcome of satellite image processing is only 0.2 °C different from direct temperature measurement in the field. Our study indicated that less density of the closed-canopy composition of oil palm trees resulted in higher surface temperature.     

冬季高速公路路桥温度变化规律及能量平衡分析

利用2009年10月-2010年3月湖北省武英高速凤凰关水库自动气象站逐时路、桥面温度和常规气象资料,分析了冬季典型天空状况（晴空、阴天）和天气过程（雾、降雨、降雪）中气温、路面温度和桥面温度的变化规律。结果表明,夜间桥面温度与气温接近,比路面温度低2℃,桥面0℃以下的低温维持时间为路面维持时间的2倍左右。利用下垫面能量平衡模型,分别计算冬季夜间晴空和阴天时路、桥面辐射能量收支变化情况,分析了夜间路面和桥面温度变化差异的原因,并对桥面比路面更易结冰的现象给出了理论解释。     

A study of the relation between the surface wind at Trawsfynydd Power Station and nearby topography

Trawsfynydd Power Station (52.9N, 04.0W) lies in a hilly region in northwest Wales. Certain local effects on the surface wind at the power station are revealed by comparing the surface wind there with the surface wind at Valley (53.3N, 04.5W), a well-exposed coastal site only about 50 km to the northwest. Tentative explanations are given for the occurrence of the observed local effects in terms of nearby topography.     

Non-dimensional wind and temperature profiles in the atmospheric surface layer: A re-evaluation

Previous results of non-dimensional wind and temperature profiles as functions of ( = z/L) show systematic deviations between different experiments. These discrepancies are generally believed not to reflect real differences but rather instrumental shortcomings. In particular, it is clear that flow distortion has not been adequately treated in most previous experiments. In the present paper, results are presented from a surface-layer field experiment where great care was taken to remove any effects from this kind of error and also to minimize other measuring errors. Data from about 90 30-min runs with turbulence measurements at three levels (3, 6, and 14 m) and simultaneous profile data have been analysed to yield information on flux-gradient relationships for wind and temperature.The flux measurements themselves show that the fluxes of momentum and sensible heat are constant within ± 7% on average for the entire 14 m layer in daytime conditions and when the stratification is slightly stable. For more stable conditions, the flux starts to decrease systematically somewhere in the layer 6 to 14 m. From a large body of data for near-neutral conditions (¦¦ 0.1), values are derived for von Kármán's constant: 0.40 ± 0.01 and for _h at neutrally, 0.95 ± 0.04. The range of uncertainty indicated here is meant to include statistical uncertainty as well as the effect of possible systematic errors.Data for _m and _h for an extended stability range (1 > > – 3) are presented. Several formulas for _m and _h appearing in the literature have been used in a comparative study. But first all the formulas have been modified in accordance with the following assumptions: = 0.40 and ( _h ) _{= 0} = 0.95; deviations from this result in the various studies are due to incomplete correction for flow distortion. After new corrections are introduced, the various formulas were compared with the present measurements and with each other. It is found that after this modification, the most generally used formulas for _m and _h for unstable conditions, i.e., those of Businger et al. (1971) and Dyer (1974) agree with each other to within ± 10% and with the present data. For stable conditions, the various formulas still disagree to some extent. The conclusion in relation to the present data is not as clear as for the unstable runs, because of increased scatter. It is, however, found that the modified curve of Businger et al. (1971) for _h fits the data well, whereas for _m , Dyer's (1974) curve appears to give slightly better agreement.     

Development of sea surface temperature,surface wind and divergence anomalies during a composite ENSO episode

Summary The interannual variations in sea surface temperature (SST) in the equatorial east Pacific, which are dominated by the El Niño phenomenon, are shown for the period 1870–1983. Since 1870 25 significant warm events have occurred. These events are classified as weak, moderate, strong and very strong, according to the normalized SST anomalies in the region 130° W–80° W, 0°–5° S.The spatial and temporal development of a composite El Niño/Southern Oscillation (ENSO) episode, based on 10 very strong or strong events, is presented in terms of SST, surface wind and divergence anomalies for the tropical Pacific (10° N–30° S). During its evolution the following phases are distinguished: Antecedent Conditions, Onset Phase, Peak Phase, Mature Phase and Dissipation Stage.Some aspects of ocean-atmosphere interaction associated with this evolution and, more specifically, the initiation of the composite event, are described. Seasonally varying feedback processes between SST, surface wind and convergence anomaly patterns in the western Pacific/Indonesian region suggest a possible mechanism for the initiation of typical ENSO events.

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Zusammenfassung Die interannuären Variationen der Meeresoberflächentemperatur (SST) im äquatorialen Ostpazifik, die von dem El Niño-Phänomen dominiert werden, werden für die Periode 1870–1983 aufgezeigt. Seit 1870 traten 25 signifikante Ereignisse auf. Diese Ereignisse werden entsprechend den normierten SST-Anomalien in der Region 130° W–80° W, 0°–5° S als schwach, mittel, stark und sehr stark klassifiziert.Die räumliche und zeitliche Entwicklung einer Komposit-El Niño/Southern Oscillation (ENSO)-Episode, die auf 10 sehr starken bzw. starken Ereignissen basiert, wird anhand von SST-, Bodenwind- und Divergenzanomalien für den tropischen Pazifik (10° N–30° S) dargestellt. Während ihrer Entwicklung werden die folgenden Phasen unterschieden: Vorausgehende Bedingungen, Einsetzphase, Spitzenphase, Reifestadium und Auflösungsstadium.Einige Aspekte der Wechselbeziehungen Ozean—Atmosphäre werden im Zusammenhang mit der Entwicklung und insbesondere der Auslösung des Komposit-Ereignisses beschrieben. Jahreszeitlich variierende Rückkopplungsprozesse zwischen SST-, Bodenwind- und Konvergenzanomalien in der westpazifischen/indonesischen Region stellen einen möglichen Mechanismus für die Auslösung typischer ENSO-Ereignisse dar.

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With 9 Figures     

基于1988-2017年CCMP数据的浙江沿海海表风速变化及成因

利用1988-2017年CCMP海表风速（Cross Calibrated,Multi-Platform Ocean Surface Wind Velocity）逐月数据、沿海气象站实测风速数据及NCEP/NCAR再分析资料,分析了CCMP海表风速数据在浙江省沿海区域的适用性、浙江省沿海海表风速的年际变化特征及其可能成因。结果表明,利用CCMP海表风速数据与浙江省沿海典型气象站（嵊泗站、普陀站、大陈站、玉环站和洞头站）观测的海表风速进行对比发现,两套资料的风速变化趋势基本一致,且两者风速值偏差较小;利用CCMP海表风速研究浙江沿海风速年际变化特征是合理可信的。CCMP风速距平场的EOF分析结果显示：第一模态的方差贡献率达90.9%,空间场呈一致变化型;第二模态的方差贡献率仅为6.09%,空间场呈偶极子变化型。根据第一模态的方差贡献率和空间场的分布来看,可将浙江沿海全海域风速作为一个整体来研究。1988-2017年浙江沿海CCMP年平均风速序列表明,2002年前后海表风速发生了一次由上升到下降的趋势转变;分析海陆温度变化发现,引起浙江沿海海表风速变化的可能原因是陆地温度上升过快。     

Variation in wind velocity over water

Starting from the equations of motion and continuity, a theoretical model is deduced in this paper for the variation in wind velocity over water caused by abrupt changes in surface roughness and temperature when air flows from land to water, based on the consideration that the turbulent exchange coefficient varies with height and distance from the upwind edge. According to the computation of this model, the variation in wind velocity over water, as the drift of air is from land to water, occurs mainly in the first few kilometers from the upwind edge. The wind velocity over water increases to a maximum when the air over land is stable, it tends to moderate when neutral condition is reached, and least variation is shown in unstable condition. And when the air over land is unstable the wind velocity is less over water than over land in strong winds, but some-what greater in light winds.     

Effects of regional temperature,wind speed and soil wetness on spatial structure of surface air temperature

Summary Climate parameters are usually collected on some grid or pattern that is supposed to represent the unobserved neighborhood. Spatial dependence is a measure of the extent to which observed data represent the unobserved neighborhood. Geostatistical analyses provide procedures for measuring spatial dependence. In this study, semivariograms were estimated from hourly observations of screen-height air temperature obtained from a dense meteorological observation network. The range and spatial component normalized by the sill were estimated from the semivariogram in order to obtain information on the spatial structure of the air temperature. Zones of spatial correlation were delineated, using the range of the semivariogram. Scales of spatial correlation depended on the regional mean air temperature and regional wetness at the ground. The range or spatial scale for data collected in winter was larger than those in summer. The range under wet conditions was larger than under dry conditions. Effects of regional wind speed on range were different, depending on the regional mean air temperature. The normalized spatial component was used as an index for measuring continuities on the interpolation surface. The normalized spatial component generally increased as the range increased.With 5 Figures     

Variation in summer surface air temperature over Northeast Asia and its associated circulation anomalies

This study investigates the interannual variation of summer surface air temperature over Northeast Asia(NEA) and its associated circulation anomalies.Two leading modes for the temperature variability over NEA are obtained by EOF analysis.The first EOF mode is characterized by a homogeneous temperature anomaly over NEA and therefore is called the NEA mode.This anomaly extends from southeast of Lake Baikal to Japan,with a central area in Northeast China.The second EOF mode is characterized by a seesaw pattern,showing a contrasting distribution between East Asia(specifically including the Changbai Mountains in Northeast China,Korea,and Japan) and north of this region.This mode is named the East Asia(EA) mode.Both modes contribute equivalently to the temperature variability in EA.The two leading modes are associated with different circulation anomalies.A warm NEA mode is associated with a positive geopotential height anomaly over NEA and thus a weakened upper-tropospheric westerly jet.On the other hand,a warm EA mode is related to a positive height anomaly over EA and a northward displaced jet.In addition,the NEA mode tends to be related to the Eurasian teleconnection pattern,while the EA mode is associated with the East Asia-Pacific/PacificJapan pattern.     

Joint multifractal description of the relationship between wind patterns and land surface air temperature

Land surface air temperature (SAT), registered at 1.25–2 m above the ground, is influenced by wind patterns. As a consequence, some phenomena such as urban heat islands and the formation of ground-level air pollutants are affected. Detailed understanding of the effects of wind circulations on SAT is convenient to improve the knowledge of these phenomena. Thus, the joint multifractal analysis has been applied to describe time series recorded at Cordoba (southern Spain) from 2001 to 2008 revealing the presence of seasonal patterns related with warm and cold winds blowing from the SW (later spring and summer) and NE (later autumn and winter), respectively, that provoke different heterogeneity in SAT values. In addition, the extreme high SAT values seem to be related with summer SW winds. However, the presence of rare low SAT values produced by NE winds is less relevant.     

Variations in momentum,mass and heat fluxes due to changes in the sea surface temperature of Hudson Bay

Abstract

The atmospheric model of Danard et al. (1983) is used to investigate the changes in heat, mass and momentum fluxes at the air‐sea interface in Hudson Bay when the seasonal sea surface temperature is varied. Comparisons of model predictions with data from a meteorological buoy located 400 km offshore showed that the model predicted the variations in wind speed and air temperature fairly well but underestimated their magnitudes. In addition it provided offshore heat and mass fluxes for which no direct observations were available.

The most important parameter determining air‐sea fluxes is the temperature difference between air and water. This determines the stability and the degree of vertical convection of the air. In the spring the colder water stabilizes the air, which depresses vertical convection. This reduces wind stress and evaporation while increasing the heat flux into the water. During the fall, the opposite occurs. The sea surface temperature is thus buffered against man‐made changes. When the temperature is decreased, for example, as the result of hydroelectric development in surrounding watersheds, the heat flux into the water increases while the wind stress decreases. Both effects increase the sea surface temperature, opposing the initial decrease. A one‐degree depression of sea surface temperature in summer is slowly offset by increased heating and no noticeable change in temperature remains at the end of the fall.     

孟加拉湾的叶绿素a,海表温度和风速的趋势

孟加拉湾（BoB）是一个高能量活跃的地区,其短期内的动态变化将对浮游环境产生巨大影响."风泵"能够在BoB海域导致垂直的混合从而影响海表温度和叶绿素浓度.本文对2006——2016年的月平均Aqua-MODIS叶绿素a （chl-a）浓度数据和Sea WiFS月度气候态数据进行了分析,研究了叶绿素浓度的时间/季节变化和温度以及风速的关系.基于季风期间的chl-a变异与海表温度（SST）,评估了在BoB海域它们之间的关系和变化.chl-a浓度值的趋势分析表明,该区域的垂直混合非常低,冬季最高,夏季最低.冬季最大chl-a浓度值为0.50 mg/m³,并且从2月开始下降到夏季季风期间.与冬季季风相比,夏季季风期间叶绿素表现出较低的浓度.在夏季季风期间,特别是在7月和8月,由于云层密集,卫星传感器无法准确捕获chl-a浓度值.chl-a浓度和SST之间相关系数R²值为0.218 1.     

对地面温度异常情况的处理

从众多的地面温度观测记录来看，发现了很多地面最高温度表的记录和地面最低温度表的记录，分别比下午和上午地面0cm的值偏低和偏高许多，或者下午（上午）地面0cm温度表与地面最高温度表（地面最低温度表）读数相差较大的异常情况。以下就对这些情况出现的原因及处理方法提出一些看法和见解。     

Diurnal and seasonal variations of wind farm impacts on land surface temperature over western Texas

This paper analyzes seasonal and diurnal variations of MODerate resolution Imaging Spectroradiometer (MODIS) land surface temperature (LST) data at ~1.1 km for the period of 2003–2011 over a region in West-Central Texas, where four of the world’s largest wind farms are located. Seasonal anomalies are created from MODIS Terra (~10:30 a.m. and 10:30 p.m. local solar time) and Aqua (~1:30 a.m. and 1:30 p.m. local solar time) LSTs, and their spatiotemporal variability is analyzed by comparing the LST changes between wind farm pixels (WFPs) and nearby non wind farm pixels (NNWFPs) using different methods under different quality controls. Our analyses show consistently that there is a warming effect of 0.31–0.70 °C at nighttime for the nine-year period during which data was collected over WFPs relative to NNWFPs, in all seasons for both Terra and Aqua measurements, while the changes at daytime are much noisier. The nighttime warming effect is much larger in summer than winter and at ~10:30 p.m. than ~1:30 a.m. and hence the largest warming effect is observed at ~10:30 p.m. in summer. The spatial pattern and magnitude of this warming effect couple very well with the geographic distribution of wind turbines and such coupling is stronger at nighttime than daytime and in summer than winter. Together, these results suggest that the warming effect observed in MODIS over wind farms are very likely attributable to the development of wind farms. This inference is consistent with the increasing number of operational wind turbines with time during the study period, the diurnal and seasonal variations in the frequency of wind speed and direction distribution, and the changes in near-surface atmospheric boundary layer (ABL) conditions due to wind farm operations. The nocturnal ABL is typically stable and much thinner than the daytime ABL and hence the turbine enhanced vertical mixing produces a stronger nighttime effect. The stronger wind speed and the higher frequency of the wind speed within the optimal power generation range in summer than winter and at nighttime than daytime likely drives wind turbines to generate more electricity and turbulence and consequently results in the strongest warming effect at nighttime in summer. Similarly, the stronger wind speed and the higher frequency of optimal wind speed at ~10:30 p.m. than that at ~1:30 a.m. might help explain, to some extent, why the nighttime LST warming effect is slightly larger at ~10:30 p.m. than ~1:30 a.m. The nighttime warming effect seen in spring and fall are smaller than that in summer and can be explained similarly.     

对地面温度异常情况的处理

从众多的地面温度观测记录来看,发现了很多地面最高温度表的记录和地面最低温度表的记录,分别比下午和上午地面0cm的值偏低和偏高许多,或者下午(上午)地面0cm温度表与地面最高温度表(地面最低温度表)读数相差较大的异常情况.以下就对这些情况出现的原因及处理方法提出一些看法和见解:     

An updated estimation of radiative forcing due to CO2 and its effect on global surface temperature change

New estimations of radiative forcing due to CO2 were calculated using updated concentration data of CO2 and a high-resolution radiative transfer model. The stratospheric adjusted radiative forcing (ARF) due to CO2 from the year 1750 to the updated year of 2010 was found to have increased to 1.95 Wm－2, which was 17% larger than that of the IPCCs 4th Assessment Report because of the rapid increase in CO2 concentrations since 2005. A new formula is proposed to accurately describe the relationship between the ARF of CO2 and its concentration. Furthermore, according to the relationship between the ARF and surface temperature change, possible changes in equilibrium surface temperature were estimated under the scenarios that the concentration of CO2 increases to 1.5, 2, 2.5, 3, 3.5 and 4 times that of the concentration in the year 2008. The result was values of +2.2℃, +3.8℃, +5.1℃, +6.2℃, +7.1℃ and +8.0℃ respectively, based on a middle－level climate sensitivity parameter of 0.8 K (Wm－2)－1, Non－equilibrium surface temperature changes over the next 500 years were also calculated under two kinds of emission scenarios (pulsed and sustained emissions) as a comparison, according to the Absolute Global Temperature change Potential (AGTP) of CO2. Results showed that CO2 will likely continue to contribute to global warming if no emission controls are imposed, and the effect on the Earth－atmosphere system will be difficult to restore to its original level.