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1.
This paper evaluated the performance of a coupled modeling system, Weather Research and Forecasting (WRF)/Urban Canopy Model (UCM), in the simulation of a heat wave event which occurred around Guangzhou during late June through early July, 2004. Results from three experiments reveal that the UCM with new land data (E-UCM) reproduces the best 2-m temperature evolution and the smallest minimum absolute average error as compared with the other two experiments, the BPA-Bulk Parameterization Approach with new land data (E-BPA) and the UCM with original U.S. Geological Survey land data (E-NOU). The E-UCM is more useful in capturing the temporal and spatial distribution of the nighttime Urban Heat Island (UHI). Differences in surface energy balance between the urban and suburban areas show that low daytime albedo causes more absorption of solar radiation by urban areas. Due to the lack of vegetation which inhibits cooling by evapotranspiration, most of the incoming energy over urban areas is partitioned into sensible heat flux and therefore heats the surface and enhances the heat wave. During nighttime, the energy in the urban area is mainly from soil heat flux. Although some energy is partitioned as outgoing long wave radiation, most of the soil heat flux is partitioned into sensible heat flux due to the small latent heat flux at night. This leads to the development of nighttime UHI and the increase of the magnitude and duration of heat waves within the municipality.  相似文献   

2.
Heat flux data collected from the Baiyangdian Heterogeneous Field Experiment were analyzed using the footprint method. High resolution (25 m) Landsat-5 satellite imaging was used to determine the land cover as one of four surface types: farmland, lake, wetland, or village. Data from two observation sites in September 2005 were used. One site (Wangjiazhai) was characterized by highly heterogeneous surfaces in the central area of the Baiyangdian: lake/wetland. The other site (Xiongxian) was on land with more uniform surface cover. An improved Eulerian analytical flux footprint model was used to determine “source areas” of the heat fluxes measured at towers located at each site from surrounding landscapes of mixed surface types. In relative terms results show that wetland and lake areas generally contributed most to the observed heat flux at Wangjiazhai, while farmland contributed most at Xiongxian. Given the areal distribution of surface type contributions, calculations were made to obtain the magnitudes of the heat flux from lake, wetland and farmland to the total observed flux and apportioned contributions of each surface type to the sensible and latent heat fluxes. Results show that on average the sensible heat flux from wetland and farmland were comparable over the diurnal cycle, while the latent heat flux from farmland was somewhat larger by about 30-50 W m-2 during daytime. The latent and sensible fluxes from the lake source in daytime were about 50 W m-2 and 100 W m-2 less, respectively, than from wetland and farmland. The results are judged reasonable and serve to demonstrate the potential for flux apportionment over heterogeneous surfaces.  相似文献   

3.
Climate effects of land use change in China as simulated by a regional climate model (RegCM2)are investigated. The model is nested in one-way mode within a global coupled atmosphere-ocean model(CSIRO R21L9 AOGCM). Two multi-year simulations, one with current land use and the other with potential vegetation cover, are conducted. Statistically significant changes of precipitation, surface air temperature, and daily maximum and daily minimum temperature are analyzed based on the difference between the two simulations. The simulated effects of land use change over China include a decrease of mean annual precipitation over Northwest China, a region with a prevalence of arid and semi-arid areas;an increase of mean annual surfaoe air temperature over some areas; and a decrease of temperature along coastal areas. Summer mean daily maximum temperature increases in many locations, while winter mean daily minimum temperature decreases in East China and increases in Northwest China. The upper soil moisture decreases significantly across China. The results indicate that the same land use change may cause different climate effects in different regions depending on the surrounding environment and climate characteristics.  相似文献   

4.
Dealing with the regional land surfaces heat fluxes over inhomogeneous land surfaces in arid and semi-arid areas is an important but not an easy issue. In this study, one parameterization method based on satellite remote sensing and field observations is proposed and tested for deriving the regional land surface heat fluxes over inhomogeneous landscapes. As a case study, the method is applied to the Dunhuang experimental area and the HEIFE (Heihe River Field Experiment, 1988-1994) area. The Dunhuang area is selected as a basic experimental area for the Chinese National Key Programme for Developing Basic Sciences: Research on the Formation Mecbanism and Prediction Theory of Severe Climate Disaster in China (G1998040900, 1999-2003). The four scenes of Landsat TM data used in this study are 3 June 2000,22 August 2000, and 29 January 2001 for the Dunhuang area and 9 July 1991 for the HEIFE area. The regional distributions of land surface variables, vegetation variables, and heat fluxes over inhomogeneous landscapes in arid and semi-arid areas are obtained in this study.  相似文献   

5.
Due to the higher temporal and spatial resolution and the better integrality of long-term satellite infrared(IR) Brightness Temperature(TBB) data,a climatology of deep convection during summer over South China and the adjacent waters is presented in this paper based on the 1-hourly infrared IR TBB data during June-August of 1996-2007(except 2004).The results show that the geographic distribution of deep convection denoted by TBB ≤-52℃ over South China and the adjacent waters are basically consistent with previous statistical results based on surface thunderstorm observations and low-orbit satellite lightning observations.The monthly,ten-day,five-day and diurnal variations of deep convection in this region are focused on in this paper.There are 5 active deep-convection areas in June-August.The monthly variations of the deep convection are closely associated with the large-scale atmospheric circulations.The deep convection over the land areas of South China is more active in June while that over the South China Sea is more active in July and August.The development of deep convection is prominently intermittent and its period is about 3 to 5 five-day periods.However,the deep convection over the coastal areas in South China remains more active during summer and has no apparent intermittence.The ten-day and five-day variations of deep convection show that there are different variations of deep convection over different areas in South China and the adjacent waters.The tendency of deep convection over the land areas of South China is negatively correlated with that over the South China Sea.The diurnal variations of deep convection show that the sea-land breeze,caused by the thermal differences between land and sea,and the mountain-valley breeze,caused by the thermal differences between mountains and plains or basins,cause deep convection to propagate from sea to land in the afternoon and from land to sea after midnight,and the convection over mountains propagates from mountains to plains after midnight.The different diurnal variations of deep convection over different underlying surfaces show that not only there are general mountainous,marine and multi-peak deep convection,but also there is longer-duration deep convection over coastal areas and other deep convection triggered and maintained by larger-scale weather systems in South China during summer.  相似文献   

6.
The influence of urban intensity on fog evolution in the Beijing-Tianjin-Hebei (BTH) region (China) is investigated numerically with the the Weather Research and Forecasting (WRF) model coupled with the urban canopy parameterization-building energy model (UCP- BEM) urban physics scheme. The experiments were designed with a focus on the influence of different urban intensities, which are represented by a different fractional coverage of natural land, buildings, and energy consumption inside buildings in an urban environment. The results of this study indicate that urban areas notably influence fog evolution when natural land is reduced to a small fraction (e.g., less than 10%). Developed land changes fog evolution through urban effects. Higher urban intensity (HUI) generally results in warmer temperatures and lower wind speeds throughout the day, while inhibiting morning specific humidity loss and afternoon specific humidity gain because of the HUI effect on surface heat flux, surface roughness, and surface moisture flux. HUI leads to later and weaker liquid water content formation, with a higher liquid water content base, primarily due to its effect on near surface temperatures. This finding implies that HUI may inhibit the conditions for fog formation. In addition, urban areas with equal natural and developed land coverage seem to greatly enhance the upward surface moisture flux, which is attributed to the combination of a relatively large potential evaporation on developed land and an ample moisture supply from natural land. As a result, the specific humidity increases in the afternoon.  相似文献   

7.
With the data from the Tropical Cyclone Yearbooks between 1970 and 2001, statistical analyses were performed to study the climatic features of landfall TCs (noted as TCs hereafter) in China with particular attention focused on landfall frequency, locations, sustaining, decaying, transition, intensification and dissipation etc. The results indicate that the sustaining periods of TC over land are quite different for different landfall spots, and increased from Guangxi to Zhejiang. The most obvious decreasing of TC intensity occurs mainly within 12 hours after landfall. The stronger a TC is,the more it decays. The areas over which TCs are dissipated can be in Heilongjiang, the northernmost, and Yunnan, the westernmost. Besides, Guangxi is an area with high dissipating rate and subject to TC dissipation as compared with the other coastal regions.  相似文献   

8.
Based on LIS/OTD gridded lightning climatology data, ERA5 reanalysis data, and MODIS atmosphere monthly global products, we examined latitudinal and daily variations of lightning activity over land, offshore areas, open sea, and all marine areas (i.e., the aggregate of open sea and offshore areas) for different seasons over the Pacific Ocean and the adjacent land areas at 65°N-50°S, 99°E-78°W, and analysed the relationships of lightning activity with CAPE (Convective Available Potential Energy) and AOD (Aerosol Optical Depth). At any given latitude, the lightning density is the highest over land, followed by offshore areas, all marine areas and the open sea in sequence. The lightning density over land is approximately an order of magnitude greater than that over all marine areas. Lightning activity over land, offshore areas, open sea, and all marine areas varies with season. The diurnal variation of lightning density over land has a single-peak pattern. Over the offshore area, open sea, and all marine areas, lightning densities have two maxima per day. The magnitude of the daily variation in mean lightning density is the largest over land and the smallest over the open sea. The lightning density over the Pacific Ocean and adjacent land areas is significantly and positively correlated with CAPE. The correlation is the strongest over land and the weakest over the open sea. Cloud Base Height (CBH) may affect the efficiency of CAPE conversion to updraft. CAPE has a positive effect on lightning activity and has a greater impact on land than on the ocean. Over the sea, both CAPE and AOD can contribute to lightning activity, but the magnitudes of the influence of CAPE and AOD on lightning activity remain to be determined. Lightning activity over land and sea is a result of the combined action of AOD and CAPE.  相似文献   

9.
This paper describes the application of the variance method for flux estimation over a mixed agricultural region in China. Eddy covariance and flux variance measurements were conducted in a near-surface layer over a non-uniform land surface in the central plain of China from 7 June to 20 July 2002. During this period, the mean canopy height was about 0.50 m. The study site consisted of grass (10% of area), beans (15%), corn (15%) and rice (60%). Under unstable conditions, the standard deviations of temperature and water vapor density (normalized by appropriate scaling parameters), observed by a single instrument, followed the Monin-Obukhov similarity theory. The similarity constants for heat (CT ) and water vapor (Cq) were 1.09 and 1.49, respectively. In comparison with direct measurements using eddy covariance techniques, the flux variance method, on average, underestimated sensible heat flux by 21% and latent heat flux by 24%, which may be attributed to the fact that the observed slight deviations (20% or 30% at most) of the similarity “constants” may be within the expected range of variation of a single instrument from the generally-valid relations.  相似文献   

10.
The impacts of three periods of urban land expansion during 1990–2010 on near-surface air temperature in summer in Beijing were simulated in this study, and then the interrelation between heat waves and urban warming was assessed. We ran the sensitivity tests using the mesoscale Weather Research and Forecasting model coupled with a single urban canopy model,as well as high-resolution land cover data. The warming area expanded approximately at the same scale as the urban land expansion. The average regional warming induced by urban expansion increased but the warming speed declined slightly during 2000–2010. The smallest warming occurred at noon and then increased gradually in the afternoon before peaking at around 2000 LST—the time of sunset. In the daytime, urban warming was primarily caused by the decrease in latent heat flux at the urban surface. Urbanization led to more ground heat flux during the day and then more release at night, which resulted in nocturnal warming. Urban warming at night was higher than that in the day, although the nighttime increment in sensible heat flux was smaller. This was because the shallower planetary boundary layer at night reduced the release efficiency of near-surface heat. The simulated results also suggested that heat waves or high temperature weather enhanced urban warming intensity at night. Heat waves caused more heat to be stored in the surface during the day, greater heat released at night, and thus higher nighttime warming. Our results demonstrate a positive feedback effect between urban warming and heat waves in urban areas.  相似文献   

11.
To address the deficiency of climatological research on tropical cyclones(TCs) influencing China, we analyze the distributions of TCs with different intensities in the region, based on the best-track TC data for1949–2011 provided by the Shanghai Typhoon Institute. We also present the distributions of 50- and 100-yr return-period TCs with different intensities using the Gumbel probability distribution. The results show that TCs with different intensities exert distinctive effects on various regions of China and its surrounding waters. The extreme intensity distributions of TCs over these different regions also differ. Super and severe typhoons mainly influence Taiwan Island and coastal areas of Fujian and Zhejiang provinces, while typhoons and TCs with lower intensities influence South China most frequently. The probable maximum TC intensity(PMTI) with 50- and 100-yr return periods influencing Taiwan Island is below 890 hPa; the PMTI with a50-yr return period influencing the coastal areas of Fujian and Zhejiang provinces is less than 910 hPa, and that with a 100-yr return period is less than 900 hPa; the PMTI with a 50-yr return period influencing the coastal areas of Hainan, Guangdong, and the northern part of the South China Sea is lower than 930 hPa,and that with a 100-yr return period is less than 920 hPa. The results provide a useful reference for the estimation of extreme TC intensities over different regions of China.  相似文献   

12.
Atmospheric turbulence measurements made at the U.S. Army Corps of Engineers Field Research Facility (FRF) located on the Atlantic coast near the town of Duck, North Carolina during the CASPER-East Program (October–November 2015) are used to study air–sea/land coupling in the FRF coastal zone. Turbulence and mean meteorological data were collected at multiple levels (up to four) on three towers deployed at different landward distances from the shoreline, with a fourth tower located at the end of a 560-m-long FRF pier. The data enable comparison of turbulent fluxes and other statistics, as well as investigations of surface-layer scaling for different footprints, including relatively smooth sea-surface conditions and aerodynamically rough dry inland areas. Both stable and unstable stratifications were observed. The drag coefficient and diurnal variation of the sensible heat flux are found to be indicators for disparate surface footprints. The drag coefficient over the land footprint is significantly greater, by as much as an order of magnitude, compared with that over the smooth sea-surface footprint. For onshore flow, the internal boundary layer in the coastal zone was either stable or (mostly) unstable, and varied dramatically at the land-surface discontinuity. The offshore flow of generally warm air over the cooler sea surface produced a stable internal boundary layer over the ocean surface downstream from the coast. While the coastal inhomogeneities violate the assumptions underlying Monin–Obukhov similarity theory (MOST), any deviations from MOST are less profound for the scaled standard deviations and the dissipation rate over both water and land, as well as for stable and unstable conditions. Observations, however, show a poor correspondence with MOST for the flux-profile relationships. Suitably-averaged, non-dimensional profiles of wind speed and temperature vary significantly among the different flux towers and observation levels, with high data scatter. Overall, the statistical dependence of the vertical gradients of scaled wind speed and temperature on the Monin–Obukhov stability parameter in the coastal area is weak, if not non-existent.  相似文献   

13.
登陆我国热带气旋的统计特征   总被引:32,自引:14,他引:32  
NCAR(National Center for Atmospheric Research)在1990年代发展起来的多普勒雷达四维变分分析系统(The four-dimensional Variational Doppler Radar Analysis System,简称VDRAS),采用四维变分(4D—VAR)资料同化技术和云尺度数值模式及其伴随模式,利用单部或多部多普勒雷达观测资料,反演对流尺度风暴的动力结构和微物理结构,包括三维风场、温度场、气压场和微物理量场。本文介绍了VDRAS的基本原理、个例试验和实时运行等概况,旨在随着我国新一代天气雷达建设的逐步完成,为应用我国新一代天气雷达的观测资料,开展4D-VAR方法的研究和应用提供一些参考或借鉴。  相似文献   

14.
A Lagrangian model is applied to simulate the dispersion of passive tracers (in particular, water vapour) in coastal atmospheric boundary layers under onshore wind conditions. When applied to convective boundary layers over uniform surfaces, the model gives results in agreement with those of similar studies. Numerical simulation of turbulent dispersion in coastal areas also reproduces the basic features known from experimental studies. Under onshore wind conditions, the humidity field is plume-shaped with the maximum vertical transport being over land downstream of the coast line. The model shows that the surface sensible heat flux over land, the static stability of the onshore air flow and the onshore wind speed are the most important factors determining the basic features of turbulent dispersion in coastal areas.  相似文献   

15.
Although large-scale topography and land use have been properly considered in weather and climate models, the effect of mesoscale and microscale heterogeneous land use on convective boundary layer (CBL) has not been fully understood yet. In this study, the influence of semi-idealized strip-like patches of oases and deserts, which resemble irrigated land use in Northwest China, on the CBL characteristics, is investigated based on the Weather Research and Forecasting (WRF)-large eddy simulation (LES) driven by observed land surface data. The influences of soil water content in oases on aloft CBL flow structure, stability, turbulent kinetic energy (TKE), and vertical fluxes are carefully examined through a group of sensitivity experiments. The results show that secondary circulation (SC)/turbulent organized structures (TOS) is the strongest/weakest when soil water content in oases is close to saturation (e.g., when the oases are irrigated). With the decrease of soil water content in oases (i.e., after irrigation), SC (TOS) becomes weak (strong) in the lower and middle CBL, the flux induced by SC and TOS becomes small (large), which has a dramatic impact on point measurement of eddy covariance (EC) fluxes. The flux induced by SC and TOS has little influence on EC sensible heat flux, but great influence on EC latent heat flux. Under this circumstance, the area averaged heat flux cannot be represented by point measurement of flux by the EC method, especially just after irrigation in oases. Comparison of imbalance ratio (i.e., contribution of SC and TOS to the total flux) reveals that increased soil moisture in oases leads to a larger imbalance ratio as well as enhanced surface heterogeneity. Moreover, we found that the soil layer configuration at different depths has a negligible impact on the CBL flux properties.  相似文献   

16.
Although large-scale topography and land use have been properly considered in weather and climate models, the effect of mesoscale and microscale heterogeneous land use on convective boundary layer(CBL) has not been fully understood yet. In this study, the influence of semi-idealized strip-like patches of oases and deserts, which resemble irrigated land use in Northwest China, on the CBL characteristics, is investigated based on the Weather Research and Forecasting(WRF)-large eddy simulation(LES) driven by observed land surface data. The influences of soil water content in oases on aloft CBL flow structure, stability, turbulent kinetic energy(TKE), and vertical fluxes are carefully examined through a group of sensitivity experiments. The results show that secondary circulation(SC)/turbulent organized structures(TOS) is the strongest/weakest when soil water content in oases is close to saturation(e.g.,when the oases are irrigated). With the decrease of soil water content in oases(i.e., after irrigation), SC(TOS) becomes weak(strong) in the lower and middle CBL, the flux induced by SC and TOS becomes small(large), which has a dramatic impact on point measurement of eddy covariance(EC) fluxes. The flux induced by SC and TOS has little influence on EC sensible heat flux, but great influence on EC latent heat flux. Under this circumstance, the area averaged heat flux cannot be represented by point measurement of flux by the EC method, especially just after irrigation in oases. Comparison of imbalance ratio(i.e., contribution of SC and TOS to the total flux) reveals that increased soil moisture in oases leads to a larger imbalance ratio as well as enhanced surface heterogeneity. Moreover,we found that the soil layer configuration at different depths has a negligible impact on the CBL flux properties.  相似文献   

17.
In this study, the performances of the Community Atmosphere Model (CAM) and Pleim–Xiu (PX) surface layer parameterization schemes are investigated by using field observations. The parameterization schemes are evaluated against continuous momentum and sensible heat flux observations measured at two flat and homogeneous grassland sites in the suburb of Nanjing, eastern China. The observations were conducted from 30 December 2014 to 18 April 2017 at Jiangxinzhou and from 9 February 2015 to 26 March 2018 at Jiangning. It is found that the momentum flux is overall in good agreement with the observation, and the sensible heat flux is overestimated. The parameterizations of the momentum and sensible heat fluxes well capture the diurnal and seasonal patterns seen in the observations at the two sites. At Jiangxinzhou, the PX parameterization underestimates the momentum flux throughout the day and the CAM parameterization slightly overestimates it around the noon, while they underestimate the momentum flux throughout the year. The two parameterizations overestimate the sensible heat flux in the daytime as well as over the entire year. At Jiangning, the two parameterizations overestimate the momentum flux throughout the day and the sensible heat flux in the daytime, and overestimate both of them over the entire year. The two parameterizations are not significantly different from each other in reproducing the turbulent fluxes at the same site, while they perform differently at the two sites in terms of statistics. In addition, the parameterized fluxes increase with increased roughness length.  相似文献   

18.
本文采用美国台风联合警报中心整编的1981—2012年的best-track热带气旋资料、中国大陆743站逐日降水数据、亚太经合组织气候中心的北半球夏季季节内振荡(BSISO)指数和美国国家环境预报中心及大气研究中心的再分析资料,分析了中国东南部地区热带气旋暴雨特征及其与BSISO 8个位相的联系。结果表明:7、8月,中国东南沿海地区的热带气旋暴雨发生的频次最多,多个站点热带气旋暴雨占总暴雨频次的比例达40%以上。7、8月热带气旋暴雨主要发生于BSISO1的第1、2、7、8位相,发生的暴雨频次占总频次的78.4%,主要分布于福建省沿海地区和西南部;BSISO2的第5、6、7位相热带气旋暴雨发生的频次也较多,占总频次的73.6%,主要分布于福建省沿海地区及西南部和广东省西南沿海地区。对发生较多热带气旋暴雨的BSISO1和BSISO2位相背景下的环流合成异常的诊断显示,西北太平洋伸向中国东南沿海地区,大尺度引导气流为显著的异常东风带,有利于热带气旋登陆中国大陆;显著异常的纬向东风切变、气旋性相对涡度和整层水汽的异常辐合,有利于热带气旋登陆过程强度的维持,促使热带气旋暴雨发生在中国大陆。  相似文献   

19.
提取GLC2009土地覆盖数据,将其运用到WRF数值模式并与模式自带的MODIS、USGS土地覆盖进行对比,以海南岛做为研究区域,选择一次海风锋天气过程进行敏感性分析,结果表明:①GLC2009对海南岛农耕地、森林的划分最接近实际情况,在海南岛平原以及丘陵地带,MODIS和USGS划分的农耕地比例过高,而在山区森林比例偏低;②GLC2009、MODIS、USGS对海南岛北部的降水模拟出现了空报,但是GLC2009对东海岸的强降水模拟的较好,并避免了MODIS和USGS在海南西南部的降水空报的情况;③GLC2009模拟的10米风场清晰刻画了东海岸海风锋辐合,其相对合理的森林覆盖提高了地表粗糙度并增强了风场辐合、低反照率对地面气温的增加和海陆热力差异的增强有一定的促进作用。④GLC2009对这次海风锋过程中模拟的感热通量和潜热通量都要高于MODIS和USGS,这种陆气间的热通量交换利于强对流天气的触发,发展。  相似文献   

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