名词解释

地转风 空气质点受水平气压梯度力与水平地转偏向力的共同作用而运动,当二力达到平衡时的风叫做地转风。地转风是理论条件下的风,风速的大小与方向不随时间变化。离地面1—2千米以上,不受地面摩擦影响的自由大气的风与地转风接近,可称为准地转风。地转风平行于等压线吹,当我们背风而立,右手一方     

考虑空气对流运动的阵风风速计算

众所周知,在同样的气压梯度下暖半年地面风速值特别是阵风风速值白天大于夜间(有时大1—2倍)。风速的这种增大现象和空气的垂直对流运动有关。从实质上说,空气的上升和下降运动就是由空气输送总速度的垂直分量或是由风的垂直分量引起的。强对流中,风速上升分量可超过10米/秒。     

三峡坛子岭单点地面矢量风分析

利用UVW三轴风速仪三峡坛子岭单点地面风观测资料分析了三峡坝区地面风速量值、风向风速出现频率分布、风的日变化规律等，并根据这些观测资料、结合一些地形风理论知识和观测现象推测了三峡坛子岭附近地面风平面流场特征，从而揭示了河道地形回流风这一特殊小地形下的局地风现象。三峡坛子岭附近地面的这种回流风尺度在百米到千米量级，与由于地形热力因子引起的山地风不同，是由于小地形的动力作用引起的，其风向与长江河道引导的山地风相反。     

尘卷风的形成、结构和卷起沙尘过程的数值研究

文中应用数值算法对尘卷风的发展过程进行了模拟计算与分析。通过模拟计算得到了尘卷风的内部详细结构和运动过程。研究表明尘卷风是由于地面局部增热不均匀而形成的一种特殊的旋转对流运动。在尘卷风形成的过程中 ,外围空气通过贴近地面的薄层被地面加热后流向中心部位 ,外围空气的旋转能量在中心部位得到加强形成尘卷风 ,其旋转能量是热泡原来具有的旋转能量的局部集中和一部分势能转化而形成的 ,其旋转方向是由热对流泡的初始旋转方向所决定。尘卷风是一种类兰金涡 ,旋转速度和压力的分布具有兰金组合涡的特点 ;在成熟阶段 ,尘卷风的详细结构可以粗略地分为 4个区域———地面附近的气流汇聚区域、柱状的涡核区域、旋风与地面作用形成的转角风区域以及涡核外部的外围气流区域。转角区域可以细分为两个子区域———外围的方位角风区域(在该区域 ,上升气流运动方向与轴线之间有一定的夹角 ,称为方位角 )和中心的下沉停滞气流区域。尘卷风中心的低压和急速的上升气流可使大量沙尘扬起 ,不同直径的沙尘颗粒在尘卷风的作用下运动轨迹不同 ,因此卷起不同大小沙尘的尘卷风的外形也是不同的。     

河西走廊西部一次极端大风天气过程3次风速波动的动力条件分析

利用自动气象站、高空探测和NCAR/NCEP再分析资料,对2017年5月1-3日河西走廊西部极端大风天气的影响系统、3次风速波动和动力条件等方面进行了分析。结果表明:在阻塞高压发展加强和冷涡的异常南压作用下,冷平流和动量下传是河西走廊西部持续大风形成的关键因素;第一次大风波动主要与地面变压风有关,动量下传在第二、三次大风波动中起重要作用;在高空急流入口区中心及左侧伴生的下沉运动能有效将高空动量下传到500 h Pa,低层不稳定层结发展的动量交换作用和热力、动力条件下所产生的垂直运动使中低空动量下传至近地面;前倾槽所形成的涡度平流上负下正结构极有利于动量下传,垂直方向上涡度平流梯度越大、梯度大值中心越低,越容易引发河西走廊西部近地面极端大风。     

雾霾天气个例气象条件对比分析

应用常规观测资料、NCEP 1°×1°再分析资料和L波段探空资料从环流形势、扩散条件和边界层特征3个方面对2013年两次雾、霾天气个例进行对比分析,结果表明:500hPa西北气流冷平流、地面弱风场、垂直速度呈弱上升-下沉的垂直分层特点和逆温是两次雾、霾天气出现和维持的共同特征。地面西北风、850hPa弱冷平流、近地层浅薄的接地逆温(100~200m)和湿层与霾天气对应,地面偏东风、850hPa暖平流、925hPa以下深厚的悬浮逆温(400m)和湿层与雾天气对应,霾过程较雾过程逆温强度强,上升运动高度高。消散时雾较霾下沉运动中心高度低,强度弱;霾消散时接地逆温特征变化不大,雾消散时悬浮逆温有底部抬升和大气稳定层结向中性层结转变的变化特征;但均有下沉气流接地、垂直风切变较强和高层低露点干空气下传到地面的特点。     

山区为什么会出现焚风？

“焚风”,顾名思义,就是火一样的风,是一种过山后变为暖热、干燥的地方性风。那么,为什么气流越过山脉会出现焚风呢?这是由于气流越过高山,出现下沉运动造成的。从气象学上讲,某一团空气从地面升到高空,每升高1 0 0 0m ,温度平均要下降6 5℃;相反,当一团空气从高空下沉到地面的时候,每下降1 0 0 0m ,温度约平均升高6 5℃。这就是说,当空气从海拔4 0 0 0～50 0 0m的高山下降至地面时,温度就会升高2 0℃以上,会使凉爽的气候顿时热起来。这就是产生“焚风”的原因。在我国,焚风地区也到处可见。如天山南北、秦岭脚下、川南丘陵、金沙江河谷、…     

不同下垫面湍流输送计算方法的研究

文章应用三种不同下垫面近地面层风速和温度梯度资料，代入风速和温度廓线公式，迭代求得感热通量及热量交换系数。确定Kh /Kw与稳定参数ξ的关系式。分别利用空气动力学方法和波文比能量平衡法计算潜热通量，并进行了比较。     

城市里的风

现代城市总是与分布稠密的人口、兴旺发达的工商业、高耸密集的建筑群以及错综复杂的交通设施分不开的。人类在创造城市的同时,也创造了城市特定的环境和特定的气候（如噪音、热岛效应等）。作为环境气象因子之一的城市里的风,也有着许多不同于乡村和其他地方的特点。由于热岛效应的影响,城市中的空气受热上升,郊区较冷的空气流向城市,因此在城市和郊区之间就形成了一个小型的局地环流,由此产生的风称作城市地面风（也称作“乡村风”）。这种风一般出现在大范围的风系较弱的晴朗天气条件下,风速一般不会超过2米每秒,风向则表现为城…     

扬沙与尘卷风不能同时记录

扬沙与尘卷风不能同时记录在审核地面气象观测记录报表时，发现有的站将扬沙与尘卷风同时记录。我们认为这种记录方法不合适，因为二者生成的天气条件不同。扬沙是由于风大将地面尘沙吹起，致使空气相当混浊，水平能见度小于１０．０ｋｍ的视程障碍现象。有扬沙时一般范围...     

湖南省森林火灾时空分布特征及其气象成因分析

利用湖南省2008-2017年10年森林火灾数据、卫星MODIS和VIIRS监测资料及常规气象资料，统计分析了湖南省森林火灾时空分布特征，分析结果表明：近10年湖南省森林火灾高发月份是2、3、4月， 3月最多，总次数为3800次，森林火灾在邵阳发生次数最多，郴州、长沙和永州次之。森林火灾受灾面积最大的是永州市、怀化市、邵阳市，达6800-7500公顷。重点分析了2018年2月14-19日湖南致灾严重的森林火灾过程与气象条件的关系，结果表明，森林火灾期间，气温偏高、相对湿度较小，降水量少，平均风速一般超过0.5m/s，火灾严重时段最大风速增大到6m/s左右，风向以偏东风和偏南风为主，湖南高低空受上下一致的西南风气流控制，天气形势较稳定。     

大兴安岭林区火灾特征及影响因子分析

对1970—2006年大兴安岭地区森林火灾过火次数与过火面积及其影响因子分析。结果表明：春季是大兴安岭地区火灾易发季节,4—6月易引发较大等级的森林火灾;雷击是引起该地区森林火灾的主要原因,雷击火灾多集中在春季和夏季, 6月份为雷击火多发月;年尺度上,降水量与过火次数显著相关,气温与过火面积显著相关;月尺度上,气温与过火次数显著相关,风速、相对湿度与过火面积显著相关;日尺度上,过火次数与最高气温显著相关,过火面积与相对湿度显著相关;但复相关系数较小,表明对森林火灾的预测不能仅仅选取气象因子,更要考虑火源及可燃物的影响。     

迭部“4.15”森林大火的气象条件及EOS遥感监测

利用2003年4月15～18日甘南迭部重大森林火灾资料以及2002年5月-2003年4月气象资料，分析了火灾的天气气候成因，同时利用相应的EOS／MODIS遥感资料分析了前期土壤湿度以及着火状况。结果表明：冬、春季气温偏高、降水偏少，持续数月干旱是甘肃南部发生重大火灾的主要气候背景。西北区东部过渡季节干旱少雨的500hPa平均环流特征是欧亚大陆东岸大槽偏深、新疆脊偏强。北方冷空气底部锋区南压，青藏高原上偏南气流发展是甘肃南部火灾环流形势之一。气温持续上升、湿度持续下降是火灾发生、蔓延的重要条件。通过研究发现，EOS／MODIS资料能够较好地反映火灾前期的土壤湿度状况，是准确监测火灾发生、估算火区面积、强度和蔓延趋势最有效途径。     

Nighttime convection in the interior of a dense Douglas fir forest

Infrared radiative surface temperatures as observed over a dense Douglas fir forest during stable atmospheric conditions are analyzed. It is shown that the concept of a single surface temperature to describe both the thermal coupling and the radiative coupling between atmosphere and forest fails when longwave cooling is large and wind speeds are low. In such cases a decoupling of the radiative surface temperature from the air temperature aloft is observed. Conditions for decoupling are formulated in terms of an appropriate Richardson number. It is shown that a convective surface temperature comes into play that is coupled to the forest interior air temperature. Observed radiative surface temperature is then composed of this convective surface temperature and the aerodynamic surface temperature. Forest interior air temperature during nighttime is, in general, lower than air temperature above the canopy. A simple two-layer canopy model is used to explain this phenomenon in terms of the distribution of atmospheric sensible heat flux and storage heat flux over the two canopy layers.     

Estimating australian forest fire danger under conditions of doubled carbon dioxide concentrations

The most appropriate indices with which to quantify Australian bushfire danger are the McArthur fire danger meters. These meters use meteorological information to produce a fire danger index that is directly related to the chance of a fire starting - and to the severity of a fire once it has started. The Mark 5 forest-fire danger meter uses air temperature, relative humidity and wind speed, plus a drought factor that is calculated using daily rainfall and temperature information.Three years of daily data generated from the CSIRO four-level general circulation model, and thirty years of daily data generated from the CSIRO nine-level model were used to estimate the daily McArthur forest fire danger index for simulations corresponding to present conditions, and to those corresponding to doubled atmospheric CO₂. The performance of these models with respect to fire danger was tested by comparing the fire danger index for Sale (in the Eastern part of Victoria, South-eastern Australia) calculated from analysis of daily climatological data with the modelled annual cumulative forest fire danger index for the grid point that was representative of Sale. Data from both models for all Australian grid points were also examined. Both models predict an increase in fire danger over much of Australia for their doubled CO₂ scenarios.The results from the models confirm that annually averaged daily relative humidity is the single most important variable in the estimation of forest fire danger on an annual basis, yet the models tend to produce relative humidities that are slightly too low so that the fire danger is overestimated. A simple one-box model of evaporation indicates that the value of relative humidity to be expected under an altered climatic regime depends on the modelled relation between actual and potential evaporation, the present values of relative humidity and evaporation rate, as well as on the expected changes in wind speed.     

井冈山森林火灾与气象条件的相关分析

根据江西井冈山森林火灾资料,利用一元回归和逐步回归分析方法,对井冈山1991—2000年森林火灾发生期间的连旱日数、降水量、相对湿度、气温、风速5个主要气象指标进行分析,将各指标分别与火灾发生次数、森林受害面积进行回归计算,建立了利用连旱日数和降水量预测森林火灾受灾面积及发生次数的数学模型。模式运算结果表明,当火灾发生前15 d连旱日数增加时,火灾次数增加;当火灾发生前15 d连旱日数增加、降水量减少时,火灾面积增加。     

大兴安岭特大森林火灾气象成因的分析

本文分析了1987年5月大兴安岭特大森林火灾的气象成因。前期干旱、少雨及5月上旬气温的显著偏高，是发生特大火灾的气候背景。大兴安岭位于我国最北部，属于寒温带，年平均气温只有-3—-6 ℃，有机物分解缓慢，使林内可燃物越积越多，是发生火灾的物质基础。在已有大量火源存在的情况下，正逢有强干冷锋过境，平均风速达8—12 m/s，最大17.0 m/s，使火势急速蔓延，是造成特大森林火灾的最关键因素。地形与气温、积雪有密切关系，也对火场的蔓延有一定的影响。     

Stability Dependence of Canopy Flows over a Flat Larch Forest

The dependence on atmospheric stability of flow characteristics adjacent to a very rough surface was investigated in a larch forest in Japan. Micrometeorological measurements of three-dimensional wind velocity and air temperature were taken at two heights above the forest, namely 1.7 and 1.2 times the mean canopy height h. Under near-neutral and stable conditions, the observed turbulence statistics suggest that the flow was likely to be that of the atmospheric surface layer (ASL) at 1.7h, and of the roughness sublayer (RSL) at 1.2h. However, in turbulence spectra, canopy-induced large coherent motions appeared clearly at both heights. Even under strongly stable conditions, the large-scale motions were retained at 1.2h, whereas they were overwhelmed by small-scale motions at 1.7h. This phenomenon was probably due to the enhanced contribution of the ASL turbulence associated with nocturnal decay of the RSL depth, because the small-scale motions appeared at frequencies close to the peak frequencies of well-known ASL spectra. This result supports the relatively recent concept that canopy flow is a superimposition of coherent motions and the ASL turbulence. The large-scale motions were retained in temperature spectra over a wider region of stability compared to streamwise wind spectra, suggesting that a canopy effect extended higher up for temperature than wind. The streamwise spacing of dominant eddies according to the plane mixing-layer analogy was only valid in a narrow range at near neutral, and it was stabilised at nearly half its value under stable conditions.     

重庆市森林火险变化特征及气象条件分析

利用重庆市34个气象站1961-2007年逐日气象观测资料以及同期NECP/NCAR逐月再分析数据,根据森林火险环境气象指数的定义,研究了重庆市森林火灾变化特征,并对春季和盛夏高森林火险等级下的典型年份的大气环流特征进行了分析。结果表明：重庆林火次数具有明显的年、季、月、日变化特征,盛夏（7-9月）和春季（2-4月）为2个高峰期,其林火次数占全年林火总数的78%,其中8月最多（占全年林火总数的18%）,午后是森林火灾多发时段;春季重庆市高森林火险的大气环流特征表现为：乌拉尔山、贝加尔湖和鄂霍茨克海地区500 hPa位势高度偏低,四川盆地高度场偏高,冷空气在中高纬地区堆积,天气活动主锋区偏北;盛夏重庆市高森林火险的环流特征为：巴尔喀什湖和鄂霍茨克海地区500 hPa位势高度显著偏低,朝鲜半岛位势高度显著偏高,西太平洋副热带高压位置偏北。     

Effect of Secondary Circulations on the Surface–Atmosphere Exchange of Energy at an Isolated Semi-arid Forest

Afforestation in semi-arid regions can potentially enhance the global carbon sink by increasing the terrestrial biomass. However, the survival of planted forests under such extreme environmental conditions is not guaranteed a priori, and critically depends on the surface–atmosphere exchange of energy. We investigate the pine forest Yatir in Israel, an example of a man-made semi-arid ecosystem, by means of large-eddy simulations. We focus on the interaction between surface–atmosphere exchange and secondary circulations that couple the isolated forest to the surrounding shrubland. The large-eddy simulations feature a grid resolution that resolves the forest canopy in several layers, and are initialized by satellite data and Doppler lidar, eddy-covariance and radiosonde measurements. We perform three large-eddy simulations with different geostrophic wind speeds to investigate the influence of those wind speeds on the surface–atmosphere exchange. We reproduce the measured mean updrafts above the forest and mean downdrafts above the shrubland, which increase in strength with decreasing geostrophic wind speed. The largest updrafts emerge above the older, denser part of the forest, triggering secondary circulations. The spatial extent of these circulations does not cover the entire forest area, although we observe a reduced aerodynamic resistance in the regions of updraft. Our simulations indicate that the enhanced surface–atmosphere exchange of the Yatir forest is not sufficient to compensate for the increased net radiation, due to the lower albedo of the forest with respect to the surroundings, resulting in higher air temperatures inside the forest. However, the difference between the forest and shrubland temperatures decreases with increasing geostrophic wind speed due to reduction in the aerodynamic resistance.