THE IMPACT OF MOUNTAIN TO BASIN WINDS ON THE DIURNAL VARIATION IN FOG OVER THE SICHUAN BASIN, CHINA

There is an increased demand for the accurate prediction of fog events in the Sichuan Basin (SCB) using numerical methods. A dense fog event that occurred over the SCB on 22 December 2016 was investigated. The results show that this dense fog event was influenced by the southwest of a low pressure with a weak horizontal pressure gradient and high relative humidity. This fog event showed typical diurnal variations. The fog began to form at 1800 UTC on 21 December 2016 (0200 local standard time on 22 December 2016) and dissipated at 0600 UTC on 22 December 2016 (1400 local standard time on 22 December 2016). The Weather Research and Forecasting model was able to partially reproduce the main features of this fog event and the diurnal variation in the local mountain to basin winds. The simulated horizontal visibility and liquid water content were used to characterize the fog. The mountain to basin winds had an important role in the diurnal variation of the fog event. The positive feedback mechanism between the fog and mountain to basin winds was good for the formation and maintain of the fog during the night. During the day, the mountain to basin wind displayed a transition from downslope flows to upslope flows. Water vapor evaporated easily from the warm, strong upslope winds, which resulted in the dissipation of fog during the day. The topography surrounding the SCB favored the lifting and condensation of air parcels in the lower troposphere as a result of the low height of the lifting condensation level.     

气旋爆发性发展过程的动力特征及能量学研究

本文对不同路径的爆发性气旋进行了动力特征及能量学研究。发现高空大值位涡空气的下伸是气旋爆发性发展的一个重要条件。初生气旋逐渐向强位涡区移近并形成上下位涡区相接的形势。使气旋迅速发展。高空急流与气旋发展有密切关系。发展中的气旋明显地向着急流左侧的辐散区移动。急流的突然加强及高空强风动量的不断下传，构成了下层的强风带及上下一致的急流结构。能量学研究指出在气旋发展前气旋内散度风动能向旋转风动能的转换突然增强。散度风动能在爆发气旋发展时有明显增长。     

山东大风天气的低频特征及机理分析

利用山东省122个国家级地面气象观测站的风速数据与欧洲中期天气预报中心(ECMWF)提供的ERA-interim再分析数据,采用小波分析、带通滤波等方法对2015年9月—2020年9月山东的大风天气及相应的低频大气环流形势进行分析.结果表明,近几年山东的大风天气有增加的趋势,春季大风发生频次最多,秋季最少;山东半岛东部...     

夏季长江淮河流域异常降水事件环流差异及机理研究

长江、淮河同处东亚中纬度,天气过程的大尺度环流背景相似,大量相关研究基本是把江淮流域天气气候事件作为一个整体研究,然而对长江、淮河流域夏季降水的时空变化进行分析发现,长江、淮河流域夏季异常降水事件有各自不同的年际、年代际变化特征,但环流差异及成因并不十分清楚。本文根据中国台站降水资料及NCEP/NCAR再分析资料,利用物理量诊断和现代统计学等方法,重点分析长江、淮河流域梅雨期降水异常事件发生时南北半球大气环流内部动力过程的差异及成因。研究指出:长江（淮河）流域梅雨期降水异常偏多年500 hPa位势高度场亚洲中高纬度环流呈现为南北向（东西向）的波列与东亚中高纬鄂霍茨克海阻塞频次增多（减少）以及200 hPa高度场上东亚副热带高空西风急流强度加强（减弱）、稳定（移动）有关;长江（淮河）流域梅雨期降水异常偏多年主要水汽来源与南半球澳大利亚高压、马斯克林高压位置偏东（西）造成西太平洋150°E～180°（阿拉伯海50°E～60°E）地区越赤道气流加强有关。长江（淮河）流域梅雨期异常降水事件大气环流内部动力过程最显著的差异表现为:东亚副热带高空西风急流加强（减弱）以及南半球澳大利亚高压、马斯克林高压位置偏东（西）。     

Air Pollution Transport in an Alpine Valley: Results From Airborne and Ground-Based Observations

An observational dataset from a wintertime field campaign in the Inn Valley, Austria, is analysed in order to study mechanisms of air pollution transport in an Alpine valley. The results illustrate three types of mechanisms: transport by a density current, back-and-forth transport by valley winds, and transport by slope winds. The first type is associated with an air mass difference along the valley. Cooler air located in the lower part of the valley behaves like a density current and produces the advection of pollutants by upvalley winds. In the second type, strong horizontal gradients in pollution concentrations exist close to ground. Multiple wind reversals result in a back-and-forth transport of pollutants by weak valley winds. In the third type, upslope winds during daytime decrease low-level pollution concentrations and cause the formation of elevated pollution layers.     

Impact of katabatic winds on the environment of Neanderthals during the Middle Palaeolithic in westernmost Europe

Compilation of the offshore and onshore altitudinal limits of the loess deposits of western France and southern England shows that they were deposited by low-level wind fields. These relate to (i) the deflation of silt-rich sediment extracted from the outwash plains of the not far distant British–Irish Ice Sheet and from the palaeo-rivers of the Channel, and (ii) the existence of north and north-western palaeo-winds deduced from particle size analysis and heavy mineral distribution, and suggest (iii) that loess particles were transported by strong katabatic winds blowing from the northern ice-covered regions towards Brittany and Normandy. Comparison between the main orientation of Neanderthal shelters and the direction of the katabatic winds shows that they were perpendicular to each other. The dominant orientation of the shelters was apparently ruled by these winds. A small-scale study concentrating on the penultimate glaciation shows that in contrast to Brittany and Normandy where loess deposits accumulated on north-facing cliffs, in England the same particles were deposited on the leeside of the hills. The existence of deflation zones, violently swept by Marine Isotope Stage 6 katabatic winds south of the British–Irish ice sheet, was probably at the origin of the restricted number of Neanderthals at that time in England. © 2021 John Wiley & Sons, Ltd.     

Shocks and shells in hot star winds

Radiation-driven winds of hot, massive stars showvariability in UV and optical line profiles on time scales of hours to days.Shock heating of wind material is indicated by the observed X-ray emission. We present time-dependent hydrodynamical models of these winds, where flowstructures originate from a strong instability of the radiative driving. Recent calculations (Owocki 1992) of the unstable growth of perturbations were restricted by the assumptions of 1-D spherical symmetry and isothermality of the wind. We drop the latter assumption and include the energy transfer in the wind. This leads to a severe numerical shortcoming, whereby all radiative cooling zones collapse and the shocks become isothermal again. We propose a method to hinder this collapse. Calculations for dense supergiant winds then show: (1) The wind consists of a sequence of narrow and dense shells, which are enclosed by strong reverse shocks (with temperatures of 10⁶ to 10⁷ K) on their starward facing side. (2) Collisions of shells are frequent up to 6 to 7 stellar radii. (3) Radiative cooling is efficient only up to 4 to 6R _*. Beyond these radii, cooling zones behind shocks become broad and alter the wind structure drastically: all reverse shocks disappear, leaving regions ofpreviously heated gas.     

Along-Channel Winds in Howe Sound: Climatological Analysis and Case Studies

This paper examines along-channel winds within Howe Sound, British Columbia, Canada, that occur from both the interior plateau out toward the coast as outflows and from the coast inland as inflows. First, the relationships between along-channel winds and pressure, temperature, and humidity are explored in Howe Sound–Cheakamus Valley. The pressure gradients between Pam Rocks and Squamish and Pam Rocks and Pemberton have the strongest correlations with outflow strength and that between Pam Rocks and Squamish has the strongest correlation with inflow strength. Outflows (inflows) have lower (higher) temperatures and dew point temperatures, except for the inflows in summer, which have lower dewpoint temperatures than the overall mean. Second, two case studies of outflow events are presented and described during the period of intensive observations prior to and during the Vancouver 2010 Winter Olympics. The January 2010 outflow event is caused by a zone of strong across-barrier mean sea level pressure gradient. The pressure gradient is formed behind an Arctic front that moved southward across Howe Sound. The February 2010 outflow event is caused by an approaching sea level low pressure centre from the Pacific that formed a northeast–southwest mean sea level pressure gradient across southern British Columbia. In the January case, the outflow layer is about 1.5?km deep, while it is shallower in the February case. Only the January outflow case exhibits hydraulic behaviour.     

Air-Sea Interactions under the Existence of Opposing Swell

Data of a comprehensive laboratory study on the coexistent system of wind waves and opposing swell (Mitsuyasu and Yoshida, 1989) have been reanalyzed to clarify the air-sea interaction phenomena under the coexistence of wind waves and swell. It is shown that the magnitude of the decay rate of swell due to an opposing wind is almost the same as that of the growth rate of swell caused by a following wind, as measured by Mitsuyasu and Honda (1982). The decay rate is much smaller than that obtained recently by Peirson et al. (2003), but the reason for the disagreement is not clear at present. The effect of an opposing swell on wind waves is very different from that of a following swell; wind waves are intensified by an opposing swell while they are attenuated by a following one. The phenomenon contradicts the model of Phillips and Banner (1974), but the reason for this is not clear at this time. The high-frequency spectrum of wind waves shows a small increase of the spectral density. Wind shear stress increases a little due to the effect of opposing swell. The intensification of wind waves by opposing swell and the small increase of the spectral density in a high-frequency region can be attributed to the increase of wind shear stress. Such organized phenomena lead to the conclusion that the hypothesis of local equilibrium for pure wind waves (Toba, 1972) can also be satisfied for wind waves that coexist with opposing swell. The recent finding of Hanson and Phillips (1999) can be explained by this mechanism.