影响高空探测高度的若干因素及提高探测高度的对策

通过对高空探测高度的分析可知：降水、净举力和空气阻力、球炸率是影响探测高度的主要因素，针对各个影响因素，找出提高探测高度的方法。     

浅析影响高空探测高度的因子

1引言随着科技的发展和社会的进步,人们对气象信息的需求日益增加。探空工作的目的就是为了测定自由大气中不同高度的气象要素以了解大气结构,为做天气预报提供重要参考资料。所以对探空资料的完整性就有了更高的要求,探测高度越高为服务对象提供的资料就越多,如何提高探测高度确保探空质量是探空工作的首要任务。了解到影响探测高度的主要因素,才能够知道如何提高探空高度。     

浅谈提高气球探测高度的几点体会

从气球的贮存、充灌、升速控制、净举力计算等方面对影响气球探测高度的主要因素进行了分析,并着重阐述了通过对净举力的修正来提高探测高度的方法和一些体会.     

提高探空气球探测高度的方法

高空气象要素的收集和整理对研究大气中各种物理过程及天气预报服务是非常重要的。尽可能地获取最大垂直范围内的探测资料,就必须提高气球的飞升高度。在此对影响气球上升高度的因素做了具体分析,并提出相应的处理方法。     

探测气球施放高度的技术探讨

高空气象探测是天气预报保障工作的基础,其探测高度和探测要素的准确性,对国民经济建设和航空兵活动具有十分重要的意义。我区鞍山场站气象雷达站为提高探测气球的施放高度,确保探测质量,从1982年到1986年,针对影响施放高度的各种因素进行了一系列的研究和探讨。在严格执行《规范》规定的基础上,作了综合性的技术改进,通过5年多的实际验证.效果良好。1983—1989年的平均施放高度为25121米,比1982年以前的平均施放高度提高了4251米。这一施放高度     

高空气象探测施放高度的差异分析

球皮质量、氢气纯度、净举力是影响高空气象探测施放高度的关键因素．雷达故障、大风、强降水天气,充球净举力等是造成不同台站问探测高度差异的重要原因。     

L波段探空雷达探测高度偏低分析

海拉尔站L波段雷达探测高度经常出现偏低现象,为弄清探测高度偏低的具体原因,通过ASOM系统统计分析了该站探空和测风数据,并从多个可能造成雷达探测高度偏低的成因分别进行分析,发现造成海拉尔站L波段雷达探测高度偏低的主要原因为:(1)探空仪突然变性;(2)1600g探空气球在冬季的施放高度偏低;(3)海拉尔站值班大楼在固定方位、仰角区间内会对探空信号造成遮挡。     

合理施加净举力,提高探测高度

探测高度是高空测报的主要指标,也是我区的一大难关。从1980—1989年,全区年平均探空达2500米以上的仅有两年。那么它受哪些因素的影响呢?除了球皮质量和天气情况外,合理施加净举力是提高探测高度的重要一环。下面结合理论和实践对这一问题作初步探讨。     

提高气球探测高度的措施

1　选择合适的净举力气球升速的快慢决定于净举力的大小。海口站地处沿海地区 ,在冬春季节天气一般较稳定 ,有时即使下毛毛雨、小雨 ,对气球升速影响不大 ,这时净举力不宜太大 ,一般控制在 12 0 0 ｇ左右 ,气球升速保持在 35 0～ 40 0米/分 ,即可延长球炸时间 ,提高探测高度。夏季是雷暴、台风盛行季节 ,气球探测高度较低 ,这时净举力要增大 ,以免气球下沉 ,导致重放球。据经验总结的各种天气条件下选用的净举力见附表。不同天气条件下选用的净举力ｇ气球型号晴天或云较薄小雨或云较厚中　雨大雨、暴雨、台风12 0或 750 12 0 0 13 0 0 150 0…     

提高探空气球施放高度的再探讨

对影响高空气象探测高度的因素进行分析,提出提高气球施放高度的相应对策。     

Variability of the Mixed-Layer Height Over Mexico City

The diurnal and seasonal variability of the mixed-layer height in urban areas has implications for ground-level air pollution and the meteorological conditions. Measurements of the backscatter of light pulses with a commercial lidar system were performed for a continuous period of almost six years between 2011 and 2016 in the southern part of Mexico City. The profiles were temporally and vertically smoothed, clouds were filtered out, and the mixed-layer height was determined with an ad hoc treatment of both the filtered and unfiltered profiles. The results are in agreement when compared with values of mixed-layer height reconstructed from, (i) radiosonde data, and (ii) surface and vertical column densities of a trace gas. The daily maxima of the mean mixed-layer height reach values \(> 3\hbox { km}\) above ground level in the months of March–April, and are clearly lower (\(< 2.7\hbox { km}\)) during the colder months from September–December. Mean daily minima are typically observed at 0700 local time (UTC ? 6h), and are lowest during the winter months with values on average below 500 m. The data presented here show an anti-correlation between high-pollution episodes and the height of the mixed layer. The growth rate of the convective mixed-layer height has a seasonal behaviour, which is characterized together with the mixed-layer-height anomalies. A clear residual layer is evident from the backscattered signals recorded in days with specific atmospheric conditions, but also from the cloud-filtered mean diurnal profiles. The occasional presence of a residual layer results in an overestimation of the reported mixed-layer height during the night and early morning hours.     

编程求解混合层高度的方法

在t-lnp图上利用08时、14时气压和最低气温、最高气温，经过坐标转换求解早晨、中午混合层的气压和温度，然后根据等温大气压高公式计算混合层高度。该计算方法用VB6．0编程，可自动从当日报文中读取数据，计算出混合层高度值，也可根据数值预报结果计算次日混合层高度。     

An Independent Method to Determine the Height of the Mixed Layer

A method for the independent evaluation ofmixed-layer (ML) height, zi, has beenproposed. The ML height is determined bythe functional relationshipszi = 0.75 z/nv max or 0.53 z/nu max in which, z is a measuring height; nv max and nu max are normalized peak frequencies of lateral velocity component, v, and longitudinal velocity component, u, spectra at height z in the surface layer respectively. Using Doppler sodar data, the technique was shown to be feasible; it is easy to apply to micro-meteorological field experiments and works even for the ML top above the range of the sodar.     

探空高度与雷达高度的比较研究

利用2009年1月南京探空站L波段高空探测的试验记录,以GPS所测的高度数据作为标准,分别从探空高度和雷达高度作了详细分析.结果表明:探空高度与GPS高度的差值随着探测高度的升高而增大,并且随着高度升高,增大的幅度越快;雷达高度与GPS高度的差值有正有负,随着探测高度的升高,总体上高度差值变大,且差值变化幅度出现较大起伏,其稳定性较差.100 hPa以下,探空高度比雷达高度的可信度大,选取探空高度较好;100hPa以上,雷达高度比探空高度可信度大,选取雷达高度较好.     

Determining Boundary-Layer Height from Aircraft Measurements

The height of the atmospheric boundary layer (ABL) is an important variable in both observational studies and model simulations. The most commonly used measurement for obtaining ABL height is a rawinsonde profile. Mesoscale or regional scale models use a bulk Richardson number based on profiles of the forecast variables. Here we evaluate the limitations of several frequently-used approaches for defining ABL height from a single profile, and identify the optimal threshold value for each method if profiles are the only available measurements. Aircraft measurements from five field projects are used, representing a variety of ABL conditions including stable, convective, and cloud-topped boundary layers over different underlying surfaces. ABL heights detected from these methods were validated against the ‘true’ value determined from aircraft soundings, where ABL height is defined as the top of the layer with significant turbulence. A detection rate was defined to denote how often the ABL height was correctly diagnosed with a particular method. The results suggest that the temperature gradient method provides the most reasonable estimates, although the detection rate and suitable detection criteria vary for different types of ABL. The Richardson number method, on the other hand, is in most cases inadequate or inferior to the other methods that were tried. The optimal range of the detection criteria is given for all ABL types examined in this study.     

The Height Correction of Similarity Functions in the Stable Boundary Layer

Empirical similarity functions of the Richardson number, obtained from bin-averaged data in the lower part of the stable boundary layer, show an undesired dependence on height at which the observations are collected. A correction of this flaw is proposed and tested by employing the neutral mixing length l _o as a similarity scale for height. The function of height describing l _o is assumed to be linear in the surface layer, and approaching a specified value with increasing height. The modification does not alter the dependence of similarity functions on the Richardson number, and is shown to be supported by the Cooperative Atmospheric-Surface Exchange Study-1999 (CASES-99) data.     

Measurements and Parametrizations of the Atmospheric Boundary-Layer Height at Dome C,Antarctica

An experimental campaign, Study of the Atmospheric Boundary Layer Environmental at Dome C, was held during 2005 at the French-Italian station of Concordia at Dome C. Ground-based remote sensors, as well as in situ instrumentation, were used during the experimental campaign. The measurements allowed the direct estimation of the polar atmospheric boundary-layer height and the test of several parametrizations for the unstable and stable boundary layers. During the months of January and February, weak convection was observed while, during the polar night, a long-lived stable boundary layer occurred continuously. Under unstable stratification the mixing-layer height was determined using the sodar backscattered echoes and potential temperature profiles. The two estimations are highly correlated, with the mixing height ranging between 30 and 350 m. A simple prognostic one-dimensional model was used to estimate the convective mixing-layer height, with the correlation coefficient between observations and model results being 0.66. The boundary-layer height under stable conditions was estimated from radiosounding profiles as the height where the critical Richardson number is reached; values between 10 and 150 m were found. A visual inspection of potential temperature profiles was also used as further confirmation of the experimental height; the results of the two methods are in good agreement. Six parametrizations from the literature for the stable boundary-layer height were tested. Only the parametrization that considers the long-lived stable boundary layer and takes into account the interaction of the stable layer with the free atmosphere is in agreement with the observations.     

An Auxiliary Tool to Determine the Height of the Boundary Layer

Results from radiosoundings, performed both over land and over sea, show that the ascent rate of a radiosounding balloon, the vertical velocity of the balloon, can be used to determine the height of the boundary layer. In many cases the balloon has a higher ascent rate in the boundary layer and a lower, less variable, ascent rate above. The decrease in ascending velocity appears as a jump at the top of the boundary layer. Two examples of potential temperature profiles for unstable stratification and one profile for stable conditions are shown with the corresponding ascent rates. A comparison between the boundary-layer height determined from potential temperature profiles and from ascent rates is presented for a larger dataset. The different ascent rates of the balloon in the boundary layer and above can be explained by a decrease in drag on the balloon in combination with a lowering of the critical Reynolds number in the boundary layer caused by turbulence. Hence, by simply logging the time from release of a radiosonde, it is possible to obtain additional information that can be used to estimate the height of both the unstable and stable boundary layers.     

Aerodynamic Scaling for Estimating the Mean Height of Dense Canopies

We used an aerodynamic method to objectively determine a representative canopy height, using standard meteorological measurements. The canopy height may change if the tree height is used to represent the actual canopy, but little work to date has focused on creating a standard for determining the representative canopy height. Here we propose the ‘aerodynamic canopy height’ h _a as the most effective means of resolving the representative canopy height for all forests. We determined h _a by simple linear regression between zero-plane displacement d and roughness length z ₀, without the need for stand inventory data. The applicability of h _a was confirmed in five different forests, including a forest with a complex canopy structure. Comparison with stand inventory data showed that h _a was almost equivalent to the representative height of trees composing the crown surface if the forest had a simple structure, or to the representative height of taller trees composing the upper canopy in forests with a complex canopy structure. The linear relationship between d and z ₀ was explained by assuming that the logarithmic wind profile above the canopy and the exponential wind profile within the canopy were continuous and smooth at canopy height. This was supported by observations, which showed that h _a was essentially the same as the height defined by the inflection point of the vertical profile of wind speed. The applicability of h _a was also verified using data from several previous studies.     

CloudSat云底高度外推估计的可行性分析

云底高度对于全球辐射平衡以及航空飞行均具有重要影响。针对CloudSat与MODIS主、被动观测的优缺点,本文提出了利用MODIS云分类信息进行CloudSat云底高度外推估计的技术。首先使用MODIS和CloudSat数据,利用回归分析方法比较了基于云类型（CSAT）与基于距离（MSAT）的云底高度估计方法的优劣。此外,分析了中国及周边地区CloudSat各类云云底高度的均一性特征。最后,利用CloudSat各类云云底高度的统计特征,建立了一种基于云类型和距离权重的云底高度估计方法,并对该方法进行了验证和分析。结果表明,利用该方法得到的MODIS各类云云底高度估计误差的标准差均小于1.5 km,除了积雨云在观测点与待测点距离大于400 km的估计误差均值稍大于1.5 km外,各种情况下其他各类云的云底高度估计误差的均值均小于1.5 km。