An observational study of wind-induced waving of plants

The motions of individual plants and the turbulence statistics of surface winds measured near the top of a canopy are obtained over a wheat field and a rush field. Two typical cases of motions of individual plants are presented. The displacements of the ear of wheat (the plant height is 1.0 m) showed a natural oscillation in wind speeds of 1.6 m s^–1 measured at a height of 30 cm over a wheat canopy, while displacements of the stem of a rush plant were closely related to the fluctuations of surface winds in wind speeds of 1.7 m s^–1 measured at the top of the rush plant. The power spectra of displacements of a rush plant seem to support the negative seven-third power hypothesis proposed by Inoue. The frequency responses of displacements of plants to fluctuations of the instantaneous momentum flux are also presented.     

An Observational Study of Wind-Induced Waving of Plants

The motions of individual plants and the turbulence statistics of surface winds measured near the top of a canopy are obtained over a wheat field and a rush field. Two typical cases of motions of individual plants are presented. The displacements of the ear of wheat (the plant height is 1.0 m) showed a natural oscillation in wind speeds of 1.6 m s⁻¹ measured at a height of 30 cm over a wheat canopy, while displacements of the stem of a rush plant were closely related to the fluctuations of surface winds in wind speeds of 1.7 m s⁻¹ measured at the top of the rush plant. The power spectra of displacements of a rush plant seem to support the negative seven-third power hypothesis proposed by Inoue. The frequency responses of displacements of plants to fluctuations of the instantaneous momentum flux are also presented.     

The damping of a group of sea waves

The signals from a wave probe, a buoy-mounted sensor at the water surface, and a three-component sonic anemometer were recorded during the passage of a discrete group of waves which were travelling against a light wind. Cross spectra between the wave signals and the pressure and sonic anemometer signals were obtained and are interpreted.Bedford Institute contribution No. 226.This work forms part of a Ph.D. dissertation at the Institute of Oceanography, University of British Columbia.     

A Gcm Study of the Impact of Greenhouse Gas Increase on the Frequency of Occurrence of Tropical Cyclones

In order to make inferences on the possible future changes of tropical cyclogenesis frequency, we apply the diagnostic computation of the Yearly Genesis Parameter (YGP) proposed by Gray (1975) to the large-scale fields simulated by a GCM. The YGP is an empirical diagnostic of the frequency of Tropical Cyclones (TCs) based on six physical parameters computed from seasonal means of atmospheric and oceanic variables. In this paper, we apply the YGP diagnostic to the results of three climate simulations performed with the atmospheric General Circulation Model (GCM) of Météo-France: ARPEGE-Climat. In a control simulation of the current climate, it is shown that the model has a realistic tropical climatology and that the computed YGP reproduces the geographical distribution of the tropical cyclogenesis frequency. The YGP is then applied to two simulations corresponding to two scenarios of doubled carbon dioxide concentration. The two experiments differ by the sea surface temperatures (SSTs) used as a lower boundary condition. In both simulations the YGP gives a large increase of total cyclogenesis frequency, but without extension of the area of possible cyclone genesis. The increase in YGP is due essentially to the contribution of the ocean thermal energy factor in the thermodynamical potential. The dynamical parameters, on the contrary, limit the cyclogenesis increase and are a major explanation of the difference between the two experiments. This is in agreement with the results of the previous similar study of Ryan et al. (1992) concerning the importance of large-scale atmospheric circulation modifications on tropical cyclone climatology. After discussing the observed relationships between ocean surface temperature and large-scale convection, and questioning the use of a fixed temperature threshold in the diagnosis of tropical cyclone frequency, we propose a modification to the YGP consisting in replacing the thermodynamical potential by a term proportional to the convective precipitation computed by the GCM. For the simulation of the present climate this modification affects only marginally the geographical distribution of tropical cyclone genesis, but for the doubled CO₂ case, the modified YGP diagnoses a more limited increase in TC genesis in the Northern Hemisphere and a small reduction in the Southern Hemisphere, which seems in better agreement with other recent modelling studies with high resolution climate models (Bengtsson et al., 1996). We conclude that the modified YGP based on convective precipitation could serve as a useful diagnostic of tropical cyclone genesis, and should be tested in simulations with other GCMs.     

Elements of the theory of wavelike formation of cohesive mudflows in erosion areas

Presented are the dependences that allow judging as a rough approximation about the process of accumulation of the cohesive mud mass in mudflow areas till the complete formation of a mudflow in the erosion inset of the main riverbed of a mudflow type.     

A study of the effect of topography on the merging of vortices

Eight sets of numerical experiments are performed in 48 hours of integtation by using a barotropic primitive equation model with a topographic term so as to investigate the effect of topography on the merging of vortices. It is pointed out that the introduction of topography may change the track of vortices,and it causes the low vortices and vorticity lumps to be detained on the southeast side of the topography,thus creating a favorable condition for the merging of the low vortex and vorticity lumps. It is also shown that the effect of topography may cause double mergers of vortices in a horizontally shearing basic flow,and it can strengthen the low vortex remarkably.     

Identification of zones of atmospheric fronts as a problem of postprocessing the results of numerical prediction

Presented is a review of the results of the studies that have been carried out in recent 15 years at the Hydrometcenter of Russia and deal with the objective analysis of atmospheric fronts and with diagnostic computations on the base of the results obtained. A unique experiment on the quantitative estimation of the measure of subjectivity of the frontal analysis carried out by weather forecasters in operational mode was accomplished in the process of the method development. Differences turned out to be so significant that no concrete synoptic archive can be considered as a source of actual data on the position of fronts. At the same time, the degree of agreement between different forecasters concerning the position of primary cold and warm fronts remains practically significant. The statistical method of objective analysis of atmospheric frontal zones is worked out as a method of postprocessing the results of numerical forecast (objective analysis) of the fields of pressure (geopotential), temperature, and humidity. The proposed method was operationally tested and recommended for the operational use by the Roshydromet Central Methodological Committee for Hydrometeorological and Heliophysical Forecasts. The data on precipitation at the stations (a degree of precipitation intensity on the front characterizes its activity) are used as a predictant (criterion of the absence or presence of a front). The frontal parameter initially obtained as a probability of the fact that the forecaster draws the front through the given grid cell is (in its physical essence) a quantitative characteristic of baroclinity near the surface and in the layers of 850-500 and 925-700 hPa and of cyclonicity of the surface pressure field. This variable turned out to be an effective diagnostic characteristic of baroclinic forcing of vertical circulations and formation of clouds and precipitation in frontal zones. The spectra of the frequency of precipitation of various intensity for different seasons and regions of the European part of the former USSR are constructed using the long-term data on two main characteristics of precipitation forcing, namely, the frontal parameter and the height of the convection level. Given are other potential application areas of the frontal parameter including the verification of numerical models.     

Climate of scepticism: US newspaper coverage of the science of climate change

This two-part study integrates a quantitative review of one year of US newspaper coverage of climate science with a qualitative, comparative analysis of media-created themes and frames using a social constructivist approach. In addition to an examination of newspaper articles, this paper includes a reflexive comparison with attendant wire stories and scientific texts. Special attention is given to articles constructed with and framed by rhetoric emphasising uncertainty, controversy, and climate scepticism.     

WINDEX在民航济南机场的应用举例

WINDEX是1994年McCann提出的预报下击暴流潜势的一个新指数。通过分析2001年7月2日的一次强雷暴带来的下击暴流，发现WINDEX在我国某些地区(例如济南)可能有一定用处，值得进一步尝试。     

Characterisation and Simulation of the Multiscaling Properties of the Energy-Containing Scales of Horizontal Surface-Layer Winds

The multiscaling statistics of atmospheric surface-layer winds at low wavenumbers above farmland and in the lee of a mountain range were examined using a hot-wire and lightweight cup anemometer. It was found that the horizontal velocity spectra could be broken into high and low-wavenumber regimes according to the parameters given by this analysis. The low-wavenumber end of the spectrum possessed a spectral slope parameter that varied between values of 0.8 and 1.35 at the farmland site during the period of the experiment, and the high-wavenumber end – corresponding to the inertial range – possessed a spectral slope slightly greater than -5/3. The larger values for this parameter for the low-wavenumber end appeared to coincide with unstable conditions. In the lee of the mountain range, the low-wavenumber spectral slope parameter was larger still, at 1.45. The low-wavenumber signals over farmland were much less intermittent than inertial-range signals, but in the lee of the mountain range the intermittency increased. From this analysis, it was shown that the statistical properties of the recorded wind signal could be reproduced using a bounded random multiplicative cascade. The model was successfully used to simulate the wind velocity field directly, rather than simulating the energy dissipation field. Since the spectral slope parameter for low wavenumbers appeared to be a function of atmospheric stability, the method presented is a simple way of generating wind signals characteristic of a variety of atmospheric conditions.     

用曙暮光时的天光光强反演平流层气溶胶散射系数廓线

本文基于对曙暮光问题的系列研究,提出一个用曙暮光时的光强观测资料反演平流层气溶胶垂直分布的方案.然后在用Monte-Carlo计算程序模拟分析Koomen等人1951年曙暮光观测资料的基础上,对此资料实施了反演试验,并给出了反演基本结果和误差分析.结果表明此法是有效的,能为平流层气溶胶过去几十年的长期变化提供反演方法.     

气候变化对家燕物候期的影响分析

对镇江地区1984—2019年家燕物候资料(始见、绝见期)及同期气温、降水、日照等气象资料对比分析,结果表明:近36 a镇江地区家燕始见期在波动变化中呈提前的趋势,以4 d/10 a的速率提前.绝见期在波动变化中呈推后的趋势,以5 d/10 a的速率推后.间隔期在波动变化中呈延长的趋势,以9 d/10 a的速率延长;近...     

A numerical experiment of cyclogenesis and the development of disturbances

A numerical experiment has been carried out to study the mechanism of cyclogenesis and the develop-ment of disturbances. First, an idealized field of temperature and pressure is designed, which is very similar to the actual synoptic situation, consisting of the jet-like zonal circulation with some nonzonal waves superim-posed on it. Prediction is made by using a six-level splitting primitive model with the idealized field as an initial one. The results show that if a disturbance like a frontal zone in the lower troposphere is superim-posed on the zonal circulation, a frontal cyclone will quickly develop and then gradually become an oc-cluded one. Its life cycle is similar to that of the actual frontal cyclone on the synoptic map. However, if there is a disturbance superimposed on the zonal circulation in the middle troposphere, the cyclone with weaker intensity will be slowly formed near the surface. Finally, if the initial disturbance is located at the high-level, a situation like a cut-off low rather than a frontal cyclone will develop.     

On the use of marine radar imagery for estimation of properties of the directional spectrum of the sea surface

Abstract

The “sea clutter” observable on a standard marine navigation radar has long been recognized as a potential source of information about sea state. In the last decade a number of researchers have published “directional wave spectra” calculated from marine radar images. Our group has continued this line of research using a unique radar system that digitizes and stores radar images eight bits deep directly related to the strength of the radar backscatter.

Our system was deployed on the CSS Hudson during the Grand Banks ERS‐1 SAR Wave Spectrum Validation Experiment cruise in November 1991. We collected in excess of 3000 sea surface backscatter images. From this dataset we have produced a number of directional spectra in an effort to understand the performance of the sensor and to compare it with other wave determining instruments and models.

Analysis has shown a strong azimuthal asymmetry both in the strength of the backscattered signal and in the relative strength of spectral peaks. This asymmetry is similar inform to that observed in scatterometer data. Unbiased estimation of the “true” image spectrum requires removal of these asymmetries. This estimation has been accomplished through calculation and removal of a non‐linear multi‐parameter least‐squares model of the backscatter from each image, and averaging of spectra from many look directions. The resulting spectra compare favourably with those calculated from directional wave buoy data, satellite and aircraft SARs and other directional wave measurements and models.     

Estimation of impact of climate change on the peak discharge probability of the river Rhine

RHINEFLOW is a GIS based water balance model that has been developed to study the changes in the water balance compartments of the river Rhine basin on a monthly time basis. The model has been designed to study the sensitivity of the Rhine discharge to a climate change. The calculated discharge has been calibrated and validated on the period 1956 to 1980. For this period the model efficiency of RHINEFLOW is between 0.74 and 0.81 both for the entire Rhine and for its tributaries. Also calculated values for variations in other compartments, e.g. snow storage and actual evapotranspiration, were in good agreement with the measured values.Since a high correlation between monthly discharge and peak discharge was found for the period 1900–1980 The RHINEFLOW model is used to assess the probability of exceedence for discharge peaks under possible future climate conditions.The probabilities of exceedence were calculated from the conditional probabilities of peak discharges for a series of 15 classes of monthly discharges. Comparison of a calculated frequency distribution of high discharge peaks with observed peaks in a test series showed that the method performs well.Scenarios for temperature changes between 0 °C and plus 4 °C and precipitation changes between plus 20% and minus 20% have been applied. Within this range flood frequencies are more sensitive for a precipitation change than for a temperature change. The present two-year return period peak flow (6500–7000 m³/s) decreases by about 6% due to a temperature rise of 4 °C; a precipitation decrease of 20% leads to 30% lower two-year peaks whilst 20% precipitation increase raises them by approximately 30%.Application of a Business As Usual (BAU) and an Accelerated Policy (AP) climate scenario resulted in a significant increase in probability of peak flows for the BAU scenario, while for the AP scenario no significant change could be found. Due to sampling errors, accurate estimations of recurrence times of discharge peaks7000 m³/s require a longer sampling time series than 90 years. For management purposes the method can be applied to estimate changes of probabilities of events with a relatively long recurrence time.     

清远地区“2019·02·20”降雹天气过程特征分析

基于清远连州双偏振雷达探测资料、清远探空资料和地面观测资料,对2019年2月20日陆续发生在阳山、连山、连南、连州的冰雹天气过程天气背景、雷达回波和双偏振特征进行了分析。结果表明:风暴发生在南支槽加深东移,西南低空急流发展和低层切变线南压的大尺度环流背景下,锋面低槽触发使其对流发生。“上干下湿”的典型大气层结结构、适宜的高度(0℃层高度在3.7~4.2km、-20℃层高度在6.8~7.1km)、低层的弱逆温层,均有利于能量聚集迸发。在回波强度大于50dBz区域中,有明显的三体散射、气旋式辐合、回波悬垂和有界弱回波区等特征;其中阳山降雹单体VIL值随时间的变化趋势与风暴强度的变化趋势成正比,且具有水平反射率因子高、差分反射率低(-1~0.5dB),相关系数较低(0.8~0.94)的典型双偏振特征。     

增强副热带高压对西南涡影响的数值试验

本文通过对伴随副热带高压（简称“副高”）东退而东移的一次典型西南涡天气过程（简称“20150721”过程）进行数值模拟,采用数值敏感性对比试验探讨了增大副高强度对这次东移西南涡的影响,得到以下结论:（1）副高强度增大以后,可长时间稳定维持,能对西南涡中尺度天气系统整个发展演变过程造成持续影响。西南涡路径和强度的变化直接改变了降水的落区和强度。（2）副高强度增大率先改变了环流场,使入侵的北风偏弱,西南引导气流偏强,最终导致西南涡发展偏弱、移速偏快。（3）环流场的改变直接影响到水汽输送、辐合辐散,从而进一步影响西南涡的发展演变过程。（4）副高强度增大以后,西南涡移速过快,导致了低涡中心与低层热力中心偏离,使得动力和热力中心不完全匹配,由此削弱西南涡发展强度。     

“艾云尼”台风龙卷天气过程分析

利用常规观测、地面自动气象站、多普勒天气雷达、现场灾调及互联网视频等资料,对2018年6月8日发生在广东省佛山市南海区大沥镇的1804号“艾云尼”台风龙卷天气过程进行分析。结果表明:龙卷发生在台风“艾云尼”登陆后前进方向的右后侧,强度为EF1级。高层辐散抽吸、中低空强劲的东南风急流叠加和地面中尺度辐合线的抬升触发作用是其有利的环流背景。对流参数表现为弱的对流有效位能和对流抑制能量、强低层风垂直切变、低抬升凝结高度和大的风暴相对螺旋度。产生龙卷的风暴为低质心微超级单体风暴,龙卷出现在钩状回波的弱回波区内。速度图上中气旋提前龙卷约30 min,临近龙卷发生时中气旋旋转速度增至最强,尺度缩小,底高降至最低,对龙卷预警有一定指示作用。