应用卫星资料分析苏州夏季城市热岛效应

利用苏州2004-2007年自动气象站资料以及购自中国科学院对地观测与数字地球科学中心的Landsat 5卫星(25 m分辨率)资料,分析研究苏州地区城市热岛总体特点以及分布规律,并对可能变化做一些探讨.分析认为,由于城市热岛效应,苏州地区气温呈中间高两侧低的分布特征,气温高值中心呈西北-东南走向,沿太湖及沿江地区气温相对较低;苏州城市地表温度呈明显的放射型分布,以市区中心向四周呈放射状分布.     

苏州—无锡—常州城市带热岛效应个例研究

应用WRF(weather research and forecasting)及其耦合的多层城市冠层模式BEP(building energy parameterization),对2013年8月13日长江三角洲地区一次高温天气过程进行了模拟。此次过程盛行东南风,风向与苏州—无锡—常州城市带走向一致。模拟结果表明:苏州—无锡—常州城市带热岛效应明显,热岛强度向下游城市逐渐增加;在东南风作用下,三座城市的热岛连成一片,形成了一个更强大的热岛环流。夜晚,边界层逐渐趋于稳定,热岛环流减弱,有利于热岛温度向下游地区输送。热岛效应导致城市边界层高度明显上升。白天太湖产生强盛的湖风对其周边城市影响显著,来自太湖的冷气团导致无锡和常州边界层内热岛强度明显下降,抑制城市热岛向上发展,削弱了无锡与常州两城市热岛间的联系。白天太湖使得无锡和常州边界层高度明显下降。     

苏州-无锡-常州城市带热岛效应个例研究

应用WRF（weather research and forecasting）及其耦合的多层城市冠层模式BEP（building energy parameterization）,对2013年8月13日长江三角洲地区一次高温天气过程进行了模拟.此次过程盛行东南风,风向与苏州-无锡-常州城市带走向一致.模拟结果表明：苏州-无锡-常州城市带热岛效应明显,热岛强度向下游城市逐渐增加;在东南风作用下,三座城市的热岛连成一片,形成了一个更强大的热岛环流.夜晚,边界层逐渐趋于稳定,热岛环流减弱,有利于热岛温度向下游地区输送.热岛效应导致城市边界层高度明显上升.白天太湖产生强盛的湖风对其周边城市影响显著,来自太湖的冷气团导致无锡和常州边界层内热岛强度明显下降,抑制城市热岛向上发展,削弱了无锡与常州两城市热岛间的联系.白天太湖使得无锡和常州边界层高度明显下降.     

A Radar-Based Investigation of Lake Breezes in Southern Manitoba,Canada

Lake breezes are thermally direct circulations that form as a result of the differential heating of land and water and are important in modifying local climate and triggering convection; they have also been linked to tornadogenesis. Although lake breezes are generally well understood, studies of smaller lakes have been relatively scarce, and none have examined lake-breeze circulations in southern Manitoba even though they are seemingly apparent on weather radar. The objectives of this paper are to provide a radar-based analysis of lake-breeze frequency and characteristics in southern Manitoba, determine the detectability of lake-breeze fronts using the radar analysis with data collected in 2013, assess the types of lake-breeze circulations that occur, and examine the meteorological conditions in which they occur. Between 2008 and 2013, lake-breeze fronts were noted on 205 days using radar over the summer months, accounting for 37% of study days, with an average of 11–12 days with lake-breeze fronts each month. These findings agree fairly well with, and are only slightly less than, frequencies reported for Lake Michigan but are lower than the most recent findings for southern Ontario. In an effort to validate the results, a broad comparison between the radar analysis and a more complete analysis using satellite and surface stations is provided for 2013 demonstrating that radar is more useful for detecting lake breezes around Lake Manitoba than around Lake Winnipeg. Lake-breeze circulations originating on Lake Manitoba and the Shoal lakes were classified into three types. The distribution of types for the Shoal lakes was similar to previous findings by other authors with “moderate deformation” circulations being the most frequent. Finally, a brief meteorological analysis was completed for each month of this study. The results of the analysis were inconclusive with no single meteorological factor being consistently well correlated to higher or lower lake-breeze frequency.     

苏州夏季城市热岛现状及影响因子分析研究

利用2007年夏季常规和自动站气象观测资料,分析研究苏州城市热岛及其与影响因子关系.气温分布表明,市中心干将桥气温相对较高,而靠近太湖的新区镇湖镇、东山等郊区气温相对较低.苏州城市热岛强度日变化呈现双峰分布,两个峰值分别出现在10时和20时左右,最低值出现在16时左右.热岛强度与气象条件关系分析表明:(1)热岛强度受云量的影响较大;(2)与城区气温分布关系密切,相关系数为0.62;(3)与风向有关,城区风向为西风时的热岛强度大于东风时热岛强度;而城区热岛强度与风速关系不明显.另外相关站点的合理选取对城市热岛研究也十分重要.     

High Resolution Deterministic Prediction System (HRDPS) Simulations of Manitoba Lake Breezes

The Effects of Lake Breezes On Weather–Manitoba (ELBOW-MB) field project, conducted around Lakes Manitoba and Winnipeg in July 2013, was the first in-depth field study of lake breezes in Manitoba, Canada. Using observational data collected during ELBOW-MB and output from the 2.5?km Canadian High Resolution Deterministic Prediction System (HRDPS), comparisons were made between HRDPS output and observational data to determine whether the HRDPS can simulate Manitoba lake breezes. The model comparisons considered various lake-breeze characteristics, such as depth, inland penetration distance, and initiation and dissipation time. In addition, cross-sections of lake-breeze circulations were analyzed. The results show that the HRDPS was able to correctly simulate lake breezes, or lack thereof, in 78% of cases on Lake Winnipeg and 68% of cases on Lake Manitoba. Modelled lake-breeze initiation and dissipation times were found to be too early in some cases and too late in others when compared with observations. Overall, it was found that the HRDPS was able to simulate most aspects of lake breezes, although inland penetration distance was one characteristic that the HRDPS was not able to simulate realistically.     

一维热扩散湖模式在太湖的应用研究

利用在太湖获得的2010年8月11-28日的观测资料研究了一维热扩散湖模式在太湖的适用性,通过对比模拟进一步研究了影响太湖湖表温度模拟的主要因子。该湖模式对太湖最初的模拟结果并不理想,模拟的湖表面温度与观测有较大的系统性偏差,温度的日变化幅度与观测相比也偏小。通过分析该模式对太湖的模拟效果不理想的可能原因,针对太湖的生态环境和污染情况,设计了18个测试参数的敏感性试验,从敏感性试验的结果分析得到,适用于太湖的、依赖于湖泊类型的3个参数应做如下修改:消光系数（η₀）应放大3倍,湖泊表层吸收的太阳辐射系数（β）应取0.8,粗糙长度（z₀）采用公式计算得到。用新得到的适用于太湖的3个参数,模拟得到的结果与最初的模拟结果和观测资料对比,发现采用新的参数后,模拟结果比最初的模拟结果有了很大的改进,模拟的湖表温度基本接近观测,模拟的湖水垂直剖面时间序列图也跟观测吻合得较好,随之的感热、潜热通量的模拟也都与观测接近。最后,对输入湖模式的主要大气参量（太阳辐射、2 m气温及风场）±10%的误差引起的模式模拟的湖表面温度误差进行分析,结果表明该湖模式对大气强迫场的误差敏感度不高;相比之下,模拟结果对风场敏感性最小,对辐射和气温的敏感度相当。     

临太湖局地平原区人居环境的自然适宜性评价——以吴江区为例

本文以苏州市吴江区为例,利用1971—2016年吴江区常规气象观测资料、2004—2016年吴江区自动气象观测数据、2016年吴江区各镇人口和面积数据、2016年ASTER GDEM 高程数据和Landsat 8 OLI_TIRS卫星遥感数据,将湖陆风指数引入人居自然环境适宜性评价体系,建立缓冲区后,分别计算气候适宜性指数、地被指数、水文指数、湖陆风指数和人居环境自然适宜性综合指数,在此基础上,分区分级评价了吴江区人居环境的自然适宜性。研究结果表明:(1)吴江区人居环境自然适宜度从西部往东部逐渐递减。(2)一般适宜区主要位于吴江区的东北部和东南局地,中度适宜区分布在中北部和南部,较高适宜区位于中部以西太湖沿岸,高度适宜区位于紧临太湖的西南地区,极高适宜区位于西南角局部地区。(3)引入湖陆风指数后,评价结果能更好地反映临湖平原的湖陆风环流对局地气候所起的关键作用。(4)建立缓冲区后的水文指数分布能够更客观地反映吴江区不同尺度水体分布对人居环境自然选择的影响。     

Observations of Lake-Breeze Events During the Toronto 2015 Pan-American Games

Enhanced meteorological observations were made during the 2015 Pan and Parapan American Games in Toronto in order to measure the vertical and horizontal structure of lake-breeze events. Two scanning Doppler lidars (one fixed and one mobile), a C-band radar, and a network including 53 surface meteorological stations (mesonet) provided pressure, temperature, humidity, and wind speed and direction measurements over Lake Ontario and urban areas. These observations captured the full evolution (prior, during, and after) of 27 lake-breeze events (73% of observation days) in order to characterize the convective and dynamic processes driving lake breezes at the local scale and mesoscale. The dominant signal of a passing lake-breeze front (LBF) was an increase in dew-point temperature of \(2.3 \pm 0.3 \,^{\circ }\hbox {C}\), coinciding with a \(180^{\circ }\) shift in wind direction and a decrease in air temperature of \(2.1 \pm 0.2 \,^{\circ }\hbox {C}\). Doppler lidar observations over the lake detected lake breezes 1 hour (on average) before detection by radar and mesonet. On days with the synoptic flow in the offshore direction, the lidars observed wedge-shaped LBFs with shallow depths, which inhibited the radar’s ability to detect the lake breeze. The LBF’s ground speed and inland penetration distance were found to be well-correlated (\(r = 0.78\)), with larger inland penetration distances occurring on days with non-opposing (non-offshore) synoptic flow. The observed enhanced vertical motion \(({>} 1\hbox { m s}^{-1})\) at the LBF, observed by the lidar on 54% of lake-breeze days, was greater (at times \({>} 2.5\hbox { m s}^{-1}\)) than that observed in previous studies and longer-lasting over the lake than over land. The weaker and less pronounced lake-breeze structure over land is illustrated in two case studies highlighting the lifetime of the lake-breeze circulation and the impact of propagation distance on lake-breeze intensity.     

Simulation and Exploration of the Mechanisms Underlying the Spatiotemporal Distribution of Surface Mixed Layer Depth in a Large Shallow Lake

The aquatic eco-environment is significantly affected by temporal and spatial variation of the mixed layer depth(MLD) in large shallow lakes.In the present study,we simulated the three-dimensional water temperature of Taihu Lake with an unstructured grid with a finite-volume coastal ocean model(FVCOM) using wind speed,wind direction,short-wave radiation and other meteorological data measured during 13-18 August 2008.The simulated results were consistent with the measurements.The temporal and spatial distribution of the MLD and the possible relevant mechanisms were analyzed on the basis of the water temperature profile data of Taihu Lake.The results indicated that diurnal stratification might be established through the combined effect of the hydrodynamic conditions induced by wind and the heat exchange between air and water.Compared with the net heat flux,the changes of the MLD were delayed approximately two hours.Furthermore,there were significant spatial differences of the MLD in Taihu Lake due to the combined impact of thermal and hydrodynamic forces.Briefly,diurnal stratification formed relatively easily in Gonghu Bay,Zhushan Bay,Xukou Bay and East Taihu Bay,and the surface mixed layer was thin.The center of the lake region had the deepest surface mixed layer due to the strong mixing process.In addition,Meiliang Bay showed a medium depth of the surface mixed layer.Our analysis indicated that the spatial difference in the hydrodynamic action was probably the major cause for the spatial variation of the MLD in Taihu Lake.     

Sea and Lake Breezes: A Review of Numerical Studies

Numerical studies of sea and lake breezes are reviewed. The modelled dependence of sea-breeze and lake-breeze characteristics on the land surface sensible heat flux, ambient geostrophic wind, atmospheric stability and moisture, water body dimensions, terrain height and slope, Coriolis parameter, surface roughness length, and shoreline curvature is discussed. Consensus results on the influence of these geophysical variables on sea and lake breezes are synthesized as well as current gaps in our understanding. A brief history of numerical modelling, an overview of recent high-resolution simulations, and suggestions for future research related to sea and lake breezes are also presented. The results of this survey are intended to be a resource for numerical modelling, coastal air quality, and wind power studies.     

环太湖地区气候变化特征研究

根据1971—2010年环太湖地区苏州、常州、长兴等9个气象台站日平均气温和日降水量资料,采用EOF正交经验分析法、线性倾向率法、小波分析法和Mann-Kendall检验法研究了环太湖地区近40 a来的气候变化特征。结果表明:1) 1971—2010年间,环太湖地区整体上呈增暖趋势,环太湖地区的季节性增暖存在空间差异,西北部的气温在春、夏季明显升高,而东南部则在秋、冬季明显增暖,1990年前后该地区的增暖率存在完全相反的空间分布。2)该40 a中,降水表现为北部增加,南部减少。整个环太湖地区的降水在冬季普遍呈现增加趋势,春、夏季降水的空间分布差异性大于秋、冬季。3) M orlet小波分析结果表明,环太湖地区年平均温度存在16～17 a和6 a、26 a左右的变化周期;年降水量存在15～16 a和24 a的强显著性变化周期,各地区在年均温、年降水量周期振荡的强度上存在一定的差异。4) Mann-Kendall突变检验显示,1971—2010年环太湖地区各站点均表现为气温由低向高的突变,突变发生在1992—1993年。     

太湖沿岸湿沉降的化学特性及水体酸化的趋势

通过对太湖沿岸湿沉降的实际监测，运用统计学方法研究了太湖沿岸3个测点自2002年7月至2003年6月大气降水pH值和化学离子组成，并结合文献和太湖水体的常规观测资料，分析了太湖流域大气降水酸化的趋势及地表水酸化的状况。结果表明：太湖地区的酸雨比较严重，沿岸酸沉降具有普遍现象；大气降水中主要阴离子是SO4^2-，约占全部测定阴离子的48％。Ca^2＋是主要的阳离子，约占全部阳离子的37％；太湖酸雨频率及酸雨强度近20a来有增强的趋势，但水体pH变化不大，水体有轻微酸化的迹象。     

夹卷对郊外大气边界层内臭氧影响的数值模拟研究

夹卷是大气边界层与自由大气进行能量和物质交换的重要途径,对边界层动力结构及边界层内温度、水汽和各种污染物浓度有重要影响。利用化学-地表-大气-土壤(CLASS)模式定量评估了夹卷过程对远郊地区大气边界层内臭氧（O₃）浓度的影响并与大气化学反应贡献进行了对比,结合地面O₃、NO_x及边界层高度、位温和比湿等观测资料和再分析资料对CLASS模拟结果进行了定量评估。结果表明:CLASS模式能较为真实地模拟夹卷和大气光化学反应对远郊地区大气边界层臭氧浓度的影响,且当自由大气层内臭氧浓度达到一定值时,两者对边界层内臭氧峰值影响相当。数值试验结果进一步揭示,夹卷对控制氮氧化物（NO_X）和可挥发性有机物(VOC_S)排放源控制效果有重要影响,且当夹卷区内O₃跳跃值增大到一定时,可完全抵消源排放减排控制的效果。本研究旨在表明,为有效控制近地层臭氧浓度,在制定人为污染源减排措施时必须考虑自由大气层臭氧的夹卷贡献。      

Numerical simulation of the impact of urban non-uniformity on precipitation

To evaluate the influence of urban non-uniformity on precipitation, the area of a city was divided into three categories (commercial, high-density residential, and low-density residential) according to the building density data from Landsat satellites. Numerical simulations of three corresponding scenarios (urban non-uniformity, urban uniformity, and non-urban) were performed in Nanjing using the WRF model. The results demonstrate that the existence of the city results in more precipitation, and that urban heterogeneity enhances this phenomenon. For the urban non-uniformity, uniformity, and non-urban experiments, the mean cumulative summer precipitation was 423.09 mm, 407.40 mm, and 389.67 mm, respectively. Urban non-uniformity has a significant effect on the amount of heavy rainfall in summer. The cumulative precipitation from heavy rain in the summer for the three numerical experiments was 278.2 mm, 250.6 mm, and 236.5 mm, respectively. In the nonuniformity experiments, the amount of precipitation between 1500 and 2200 (LST) increased significantly. Furthermore, the adoption of urban non-uniformity into the WRF model could improve the numerical simulation of summer rain and its daily variation.     

Evaluation of the Influence of Aquatic Plants and Lake Bottom on the Remote-Sensing Reflectance of Optically Shallow Waters

Abstract

Aquatic plants and lake bottoms in optically shallow waters (OSWs) wield great influence on reflectance spectra, resulting in the inapplicability of most existing bio-optical models for water colour remote sensing in lakes. Based on radiative transfer theory and measured spectra from a campaign for Lake Taihu in October 2008, absorption and backscattering coefficients were used to simulate the remote-sensing reflectance, which are considered to be reliable if matched to their measured counterparts. Several cases of measured spectra at different depths, Secchi disk depth transparency, and aquatic plant height and coverage were analyzed thoroughly for spectral properties. The contribution of aquatic plants was evaluated and compared with the measured and simulated remote-sensing reflectance values. This is helpful for removing the influence of aquatic plants and lake bottoms from the spectra and for constructing an improved chlorophyll a retrieval model for OSWs, such as that for Lake Taihu, China.     

A Note on the Role of Meridional Wind Stress Anomalies and Heat Flux in ENSO Simulations

Four comparative experiments and some supplementary experiments were conducted to examine the role of meridional wind stress anomalies and heat flux variability in ENSO simulations by using a high-resolution Ocean General Circulation Model （OGCM）. The results indicate that changes in the direction and magnitude of meridional wind stress anomalies have little influence on ENSO simulations until meridional wind stress anomalies are unrealistically enlarged by a factor of 5.0. However, evidence of an impact on ENSO simulations due to heat flux variability was found. The simulated Nino-3 index without the effect of heat flux anomalies tended to be around 1.0° lower than the observed, as well as the control run, during the peak months of ENSO events.     

A three-dimensional numerical sensitivity study of mesoscale circulations induced by circular lakes

Summary A three-dimensional mesoscale planetary boundary layer model with theE- turbulence closure is used to simulate airflow over a lake of circular shape. A series of model sensitivity studies are performed to examine the effects of lake-land temperature difference, ambient wind magnitude and direction, lake size, surface roughness, the Coriolis force and baroclinic ambient wind conditions on mesoscale lake circulations.The lake-land temperature difference is essentially the basic energy source driving the mesoscale circulations over the lake on synoptically undisturbed days. A lake-breeze convergence zone is predicted by the model due to the differential heating between the land and the water. It is found that spatial and temporal variations of this convergence zone and associated convection are strongly controlled by the direction and the magnitude of the ambient wind. Under southeasterly and southwesterly ambient winds, the lake-breeze convergence zone and the associated convection occur primarily along up wind and lateral sides of the lake with reference to the general direction of the ambient flow. In contrast to the southeasterly and southwesterly ambient winds, the lake-breeze convergence zone and the convection are predicted all around the coastline of the lake under calm wind.The model also predicts a cloudless region over the lake in all the case studies due to divergent nature of the lake-breeze circulation. The lake size is found to have a significant effect in intensifying convection. Surface roughness over the land surface is found to be important in determining the intensity of the convection. The combined effect of the Coriolis force and the differential surface roughness between land and water appear to be the responsible mechanism for producing the asymmetric shape of the lake-breeze convergence zone around the symmetric circular lake. Finally, it was found that an initial baroclinic flow has different mesoscale lake-breeze circulation patterns as compared to an initial barotropic flow.With 16 Figures     

2012年太湖蒸发量变化特征及蒸发模型评估研究

湖泊蒸发是全球能量分布,水文循环的重要组成部分,同时是气候及生态系统环境变化的指示因子。运用太湖湖上观测平台大浦口站2012年涡度相关数据分析了太湖蒸发量的月变化及日变化特征,并评估了11种蒸发模型。结果表明：太湖2012年总蒸发量为1066.2 mm。潜热通量是太湖净辐射能量分配中的主导项, 2012年太湖地区潜热通量占净辐射通量的91.9%。2～7月为太湖水体储热阶段,当净辐射在7月达到最大值时,蒸发值也达到最大值;净辐射8月开始减少,至12月达到最小值,期间湖体储热释放,使得蒸发量在2月才达到最小值。采用涡度相关系统观测太湖蒸发量的数据评估了11种蒸发模型,分别从年蒸发总量和蒸发量月变化特征来探讨模型对于太湖蒸发量计算的适用性,其中以波文比能量平衡模型表现最好,与涡度相关观测值的相关系数为0.99,中心化均方根误差为4.50 mm month^-1。     

A modelling investigation into lake-breeze development and convection triggering in the Nam Co Lake basin,Tibetan Plateau

This paper uses the cloud resolving Active Tracer High-resolution Atmospheric Model coupled to the interactive surface model Hybrid in order to investigate the diurnal development of a lake-breeze system at the Nam Co Lake on the Tibetan Plateau. Simulations with several background wind speeds are conducted, and the interaction of the lake breeze with topography and background wind in triggering moist and deep convection is studied. The model is able to adequately simulate the systems most important dynamical features such as turbulent surface fluxes and the development of a lake breeze for the different wind conditions. We identify two different mechanisms for convection triggering that are dependent on the direction of the background wind: triggering over topography, when the background wind and the lake breeze have the same flow direction, and triggering due to convergence between the lake-breeze front and the background wind. Our research also suggests that precipitation measurements at the centre of the basins on the Tibetan Plateau are not representative for the basin as a whole as precipitation is expected to occur mainly in the vicinity of the topography.