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981.
982.
Effects of mesoscale sea-surface temperature fronts on the marine atmospheric boundary layer 总被引:1,自引:0,他引:1
Eric D. Skyllingstad Dean Vickers Larry Mahrt Roger Samelson 《Boundary-Layer Meteorology》2007,123(2):219-237
A numerical modelling study is presented focusing on the effects of mesoscale sea-surface temperature (SST) variability on
surface fluxes and the marine atmospheric boundary-layer structure. A basic scenario is examined having two regions of SST
anomaly with alternating warm/cold or cold/warm water regions. Conditions upstream from the anomaly region have SST values
equal to the ambient atmosphere temperature, creating an upstream neutrally stratified boundary layer. Downstream from the
anomaly region the SST is also set to the ambient atmosphere value. When the warm anomaly is upstream from the cold anomaly,
the downstream boundary layer exhibits a more complex structure because of convective forcing and mixed layer deepening upstream
from the cold anomaly. An internal boundary layer forms over the cold anomaly in this case, generating two distinct layers
over the downstream region. When the cold anomaly is upstream from the warm anomaly, mixing over the warm anomaly quickly
destroys the shallow cold layer, yielding a more uniform downstream boundary-layer vertical structure compared with the warm-to-
cold case. Analysis of the momentum budget indicates that turbulent momentum flux divergence dominates the velocity field
tendency, with pressure forcing accounting for only about 20% of the changes in momentum. Parameterization of surface fluxes
and boundary-layer structure at these scales would be very difficult because of their dependence on subgrid-scale SST spatial
order. Simulations of similar flow over smaller scale fronts (<5 km) suggest that small-scale SST variability might be parameterized
in mesoscale models by relating the effective heat flux to the strength of the SST variance. 相似文献
983.
A microscale three-dimensional urban energy balance model for studying surface temperatures 总被引:1,自引:2,他引:1
A microscale three-dimensional (3-D) urban energy balance model, Temperatures of Urban Facets in 3-D (TUF-3D), is developed
to predict urban surface temperatures for a variety of surface geometries and properties, weather conditions, and solar angles.
The surface is composed of plane-parallel facets: roofs, walls, and streets, which are further sub-divided into identical
square patches, resulting in a 3-D raster-type model geometry. The model code is structured into radiation, conduction and
convection sub-models. The radiation sub-model uses the radiosity approach and accounts for multiple reflections and shading
of direct solar radiation. Conduction is solved by finite differencing of the heat conduction equation, and convection is
modelled by empirically relating patch heat transfer coefficients to the momentum forcing and the building morphology. The
radiation and conduction sub-models are tested individually against measurements, and the complete model is tested against
full-scale urban surface temperature and energy balance observations. Modelled surface temperatures perform well at both the
facet-average and the sub-facet scales given the precision of the observations and the uncertainties in the model inputs.
The model has several potential applications, such as the calculation of radiative loads, and the investigation of effective
thermal anisotropy (when combined with a sensor-view model). 相似文献
984.
F. Couvreux F. Guichard V. Masson J.-L. Redelsperger 《Boundary-Layer Meteorology》2007,123(2):269-294
This study focuses on the intrusion of dry air into the convective boundary layer (CBL) originating from the top of the CBL.
Aircraft in-situ measurements from the IHOP_2002 field campaign indicate a prevalence of negative skewness of the water vapour
distribution within the growing daytime CBL over land. This negative skewness is interpreted according to large-eddy simulations
(LES) as the result of descending dry downdrafts originating from above the mixed layer. LES are used to determine the statistical
properties of these intrusions: their size and thermodynamical characteristics. A conditional sampling analysis demonstrates
their significance in the retrieval of moisture variances and fluxes. The rapid CBL growth explains why greater negative skewness
is observed during the growing phase: the large amounts of dry air that are quickly incorporated into the CBL prevent a full
homogenisation by turbulent mixing. The boundary-layer warming in this phase also plays a role in the acquisition of negative
buoyancy for these dry tongues, and thus possibly explains their kinematics in the lower CBL. Budget analysis helps to identify
the processes responsible for the negative skewness. This budget study underlines the main role of turbulent transport, which
distributes the skewness produced at the top or the bottom of the CBL into the interior of the CBL. The dry tongues contribute
significantly to this turbulent transport. 相似文献
985.
Lisa K. Whalley Kate L. Furneaux Tom Gravestock Helen M. Atkinson Catherine S. E. Bale Trevor Ingham William J. Bloss Dwayne E. Heard 《Journal of Atmospheric Chemistry》2007,58(1):19-39
A Laser Induced Fluorescence (LIF) instrument has been developed to detect iodine monoxide (IO) radicals in the atmosphere.
An all solid-state Nd:YAG pumped Ti:Sapphire laser operating at approximately 445 nm was used to excite the (2,0) band of
the IO A2Π3/2 ← X2Π3/2 electronic transition, with off-resonance fluorescence in the (2,5) band detected at 521 nm. The sensitivity of the instrument
was determined by calibration. IO (between 10 and 150 pptV) was generated following the 184.9 nm photolysis of N2O/CF3I/N2 mixtures with O3 actinometry used to determine the photolysis flux. The detection limit was determined to be 0.3 pptV for a 300 s integration
period, with an uncertainty of 23% (1σ). The instrument was deployed in August/September 2006 during the RHaMBLe (Reactive Halogens in the Marine Boundary Layer)
campaign in Roscoff, France. Located on a small jetty, a few metres from the water’s edge at high tide, the instrument measured
significant levels of IO on 11 days, with a maximum of 27.6 ± 3.2 pptV observed on one day (averaged over 10 s) representing
the highest IO mixing ratio recorded in the marine boundary layer to date. IO displayed a clear diurnal profile with a maximum
at low tide during the daytime. These results represent the first point measurements of IO in the atmosphere by LIF. 相似文献
986.
不同区域气候模式对中国地区温度和降水的长期模拟比较 总被引:19,自引:9,他引:19
利用亚洲区域模式比较计划RMIP第二阶段五个区域模式和一个变网格全球模式,对中国地区1988年12月~1998年11月十年模拟的平均温度和降水结果,分析比较了不同区域气候模式对中国地区温度和降水的模拟能力。研究结果表明:几乎所有模式都能模拟出中国地区多年平均温度和降水的基本空间分布形态,但模式模拟的温度普遍偏低,在大部分区域,大多数模式模拟的降水偏多,而且不同模式之间存在较大差别。模式能较好地反映出中国地区温度的年际变化,对夏季降水的年际变化模拟较差,对冬季模拟较好。 相似文献
987.
使用国家气候中心的区域气候模式对1961~1990、2001~2030年湖北省逐月气温、降水量的预估值(格点0.5°×0.5°,A2情景),以1961~1990年湖北省平均温度和平均降水量为基准,计算并分析未来30年(2001~2030年)及每10年年平均气温、降水量变化趋势。结果表明:(1)未来30年湖北省年平均气温普遍呈上升趋势,上升幅度在0.19~0.39℃之间,平均0.27℃,鄂南增温比鄂北快,其中2021~2030年增幅最大,2001~2010年增幅最小;(2)年平均降水量湖北省大部呈减少趋势,表现出南增北减、东增西减的特点,2001~2010年变化不大,2011~2020年绝大多数站点均有不同幅度增加,2021~2030年全省各地呈一致的下降趋势,湖北省南涝北旱趋势将有所加剧。 相似文献
988.
对住宅小区的侧墙绿化墙面与裸露墙面温湿度的对比分析发现,侧墙绿化可以有效地改善墙体的温湿度状况;同时通过观测爬墙虎的蒸腾速率,推算出其对环境的降温增湿效果;并通过有侧墙绿化与无侧墙绿化室内温湿度分析比较,说明侧墙绿化对室内温湿度的影响。 相似文献
989.
对宁夏20个测站1961—2004年的冬季负积温EOF分析表明,冬季的冷趋势具有明显的大尺度特征,在近40 a逐渐变暖。据累积距平显示,l986年出现了突变,之前,冬季气温偏低,具体表现为冷冬年全部分布在此时段,之后偏暖,90年代以后出现暖冬的频次明显增加。≤0℃持续日数具有明显的年代际变化,2001—2004年比60年代平均减少了13.5 d。在80%保证率下,全区≤0℃持续日数和负积温依地势自北向南增多,引黄灌区最少,中部干旱带次之,南部黄土丘陵区相对最多。 相似文献
990.
利用常规的天气图、卫星云图和物理量诊断对2004年春季两次持续性增温过程及降水天气进行诊断分析,结果表明:两次增温过程的降水强度、范围和落区等差异显著。前者造成了陕西历史上最早的暴雨过程,并有冰雹相伴;后者则为一般性降水。在春季降水过程中,当南海和菲律宾附近有热带低压云系存在时,对陕西的强降水有增幅作用;来自孟加拉湾700 hPa的偏西南急流和来自南海850 hPa的偏东南急流直伸到陕西的位置决定强降水的落区。700 hPa正涡度中心与垂直运动的上升区配合很好,涡度随着暴雨的临近明显增大,正涡度的增长,有利于对流的发展。 相似文献