用线性模式分析形成相当正压性的物理因子

用两层的线性准地转模式讨论了形成大气环流异常的相当正压性的物理因子。指出大气扰动的水平尺度、β效应和热成风,即平均西风在垂直方向上的梯度,是形成相当正压性的三个最主要的因子。另外还讨论了相当正压性所造成的对流层中层的流函数和厚度场的同相关系。最后指出了线性模式的缺陷。     

夏季副热带相当正压切变线的动力学性质

切变线风场除伴随温度锋区出现以外，也可以在夏季副热带大尺度弱环境风场中伴随狭窄、深厚的强对流加热带而出现。后者的结构是相当正压的（本文称为EBtSL）。除Rossby数Ro=O(du/dt)/f0U以外，决定带状准二维运动系统性质的另一个重要参数是H=(CZ/f0l)2，EBtSL的特点是在跨带水平尺度#Al#a收缩的同时，铅直尺度Z（无量纲）并不随之收缩，因而H～10（斜压锋面，H≤1）。在这种情况下，即使非绝热加热率比温度平流大一个量级，且Ro=10-1／2；O(|d→Va／dt)=10-1／2O(|d→Vg／dt)已不符合经典的地转动量近似，但仍旧能够成为排除重力-惯性波的准平衡运动系统。变化的欧拉时间尺度仍取决于平流，即EBtSL能持续地容纳特大的潜热释放（和降水）。本文给出EBtSL的发展方程和次级环流方程，讨论了EBtSL的基本动力学性质。这些结果把关于典型EBtSL的一系列观测事实逻辑地联系起来，并给予理论解释，表明EBtSL是一种特别有利于持续大暴雨的动力学结构。 典型的EBtSL是长江流域梅雨晚期自由大气层的切变线。其初生机制是低层干-湿气团界带紧南侧бθe/бy2负值最大轴附近的带状CISK。自由大气层中EBtSL形成后，在边界层维持着浅薄温度锋区。本文结合Arakawa-Schubert平衡理论，简要讨论了关于这种系统的动力学全貌。     

亚欧及北太平洋相当正压层高度的分析及数值模拟

本文利用相当正压层方法,分析了亚欧及北太平洋中纬度地区47个站点的相当正压层高度,其结果与文献[1]类似。计算表明:亚欧及北太平洋的相当正压层高度平均位于359hPa,略去高原站点后,平原地区的平均高度为374hPa。相当正压层是一个波动很大的不同气压的曲面,并随地区和季节变化较大。高原和西风急流的强弱可能都是其影响因子,尤其是高原的作用值得进一步探讨。数值模拟也证实了300hPa上Rossby波比500hPa效果好。     

相当正压Rossby波和斜压Rossby波相互转换的分析

利用由两层准地转模式简化的低谱模式，得知相当正压结构Ｒｒｏｓｓｂｙ波为平衡态，讨论了具有相当正压结构的Ｒｏｓｓｂｙ波存在所需条件；并以定常Ｒｏｓｓｂｙ波（相当正压结构）为基态，导出反映高低层Ｒｏｓｓｂｙ波位相变化的振荡方程，指出高低层位相差的变化与垂直切交流的扰动、平均层上流函数和热成风流函数波动部分振幅扰动（Ａ’和Ｂ’）的关系，说明相当正压结构和斜医结构的Ｒｏｓｓｂｙ波是相互转换的。     

相当湿位涡异常与梅雨锋暴雨分析

基于位涡异常与中尺度对流系统发展密切相关的分析事实,以及中尺度天气的发生发展的过程中水汽的重要作用,在引入水汽变化方程的基础上,导出了非均匀饱和大气中的相当湿位涡方程,进而分析了引起相当湿位涡异常的主要因子。依据相当湿位涡包含动力因子、热力因子和水汽因子的特点,利用相当湿位涡及增量对一次梅雨锋暴雨进行诊断和模拟分析,初步揭示了相当湿位涡及其增量对梅雨锋强降水的指示意义,相当湿位涡及其增量大值区对未来1～3小时的强降水具有较好的指示作用。针对梅雨锋暴雨,可以将梅雨湿度锋与相当湿位涡相结合作为强降水短时临近预报的一个指标。      

2016年6月赣北两次对流性暴雨过程对比分析

利用常规气象观测资料、NCEP 1°×1°FNL资料和多普勒雷达、卫星TBB等资料,对2016年6月1—2日和18—19日江西省北部两次对流性暴雨过程进行对比分析。结果表明,高空冷涡、西太平洋副热带高压、中低层急流、高空槽等共同作用导致两次暴雨发生。中层有冷空气影响,低层深厚西南急流维持时,更利于降水的对流性特征维持。两次暴雨过程强降水由低质心较强回波的“列车效应”造成。强降水回波带有多单体风暴和强降水超级单体风暴特征时,强降水效率更高。两次过程水汽收支中水汽通量散度项由正转负,水汽垂直输送项由负转正,中低层水汽辐合将低层大量水汽向上输送至中高层,利于强降水的形成。差动涡度平流中心与上升运动中心吻合,其导致垂直动力强迫,促进扰动不稳定和垂直运动的发展。强上升运动区南北两侧垂直经向环流和反环流的形成,为强暴雨的发生维持提供了持续的强水汽水平输送和辐合抬升条件。     

2013年初夏湖北两次低涡暴雨对比分析*

利用NCEP提供的高时空分辨率的GFS(Global Forecast System)0.5o×0.5o再分析资料和常规气象资料,对2013年初夏湖北两次低涡暴雨进行了对比分析。结果表明：（1）两次暴雨落区不同,5月暴雨由湖北西部向东北方向发展,主要位于湖北西部和中北部;而6月暴雨由湖北西南部向东发展,强降水主要位于湖北中部和东部。（2）两次暴雨落区不同是由于低涡移动的路径不同造成的,而低涡的移动路径受高低空配置的影响,不同的高低空配置导致这两次低涡暴雨的差异。（3）500hPa正的涡度平流使低涡移动发展,对低涡暴雨的发展和移动有很好的指导意义,而6月暴雨500hPa存在强正涡度平流中心,使低涡东移发展加强;另外,对流层低层温度平流对低涡的移动有引导作用。（4）边界层水汽辐合为低涡造成的强降水提供了充足的水汽条件。     

北半球中高纬月平均环流正压斜压动能的年变化特征

本文利用多年月平均资料计算了北半球中高纬月平均环流正压、斜压动能的年变化特征。结果表明无论正压、斜压动能都具有明显的年变化,而且两者的变化趋势也是一致的,但是正压动能要比斜压动能对总动能的贡献大得多。环流异常具有相当正压的垂直结构。有关结论可为长期数值预报模式的简化提供依据。     

低涡影响下的西北地区东部暴雨个例分析

利用常规气象观测资料、陕西区域自动站观测资料、多源融合逐小时0.05° ×0.05°格点降水资料、NCEP1° ×1°再分析资料和卫星探测资料对2019年8月2—4日西北地区东部一次由低涡向东北方向移动引发的暴雨过程进行了诊断分析.结果表明:500 hPa中纬度低槽、副热带高压、低槽携带的弱冷空气及来自台风外围和副高外...     

On the stability of equivalent modons

In the framework of the equivalent barotropic dynamics, we show that the kinetic energy and enstrophy a small scale perturbation superimposed on a large scale solitary wave do not grow in time as long as the perturbation scale remains much less than that of the wave. This property is proved to hold for the equivalent modons of Flierl et al. which therefore turn out to be resistant to small scale perturbations. These conclusions appear to explain the numerical results of McWilliams et al. on non divergent modons.     

An application of equivalent modons to atmospheric blocking

Certain consistent features are demonstrated between a particular strong, vortex pair atmospheric blocking pattern over the eastern North Atlantic Ocean and Europe during January 1963 and an equivalent modon solution of the inviscid equivalent barotropic equation. Modons are uniformly translating, shape preserving, non-linear analytic solutions. The equivalent barotropic model for the atmosphere is derived as a lowest-order truncation of an expansion and projection of the quasigeostrophic equations with the empirical orthogonal pressure modes of the troposphere. The horizontal and vertical structure of the blocking pattern, as well as its intensity, are consistent with the modon dispersion relation. On the other hand, there remain some uncertainties about whether the pressure profile of the mean zonal wind is consistent with modon requirements and whether a stationary theoretical solution adequately reflects the essential dynamics of a fluctuating and regenerative blocking pattern.     

Available equivalent potential energy in moist atmospheres

Summary The equivalent potential energy of the moist atmosphere is defined as the sum of its total potential energy and latent heat. The available equivalent potential energy is the amount of equivalent potential energy available for conversion into kinetic energy. For the isolated moist atmospheres, we may find the equivalent lowest state which is the limit of the states attained through all the actual processes involving water condensation and possesses the least equivalent potential energy. Thus, the maximum available equivalent potential energy with respect to the equivalent lowest state can be estimated for any provided initial state. This study may extend the understanding for the development of precipitation systems in the moist atmosphere.With 5 Figures     

The Canadian boreal snow water equivalent band

Abstract

Satellite and conventional snow water equivalent (SWE) dataseis reveal a well‐defined zone of high winter season SWE (>100 mm) that extends across the northern boreal forest of Canada. SWE coefficient of variation (CV) patterns derived from a monthly averaged (1978–2002) passive microwave derived time series show a high degree of interannual variability across open prairie, southern boreal, and open tundra regions of North America while SWE across the northern boreal forest was highly invariant. The potential existence of a consistent SWE zone resistant to interannual climatic variability over the past 25 years is intriguing in the context of the sensitivity of snow cover to climate variability and change. A ground sampling campaign conceived specifically to evaluate SWE distribution across the northern boreal forest was conducted in northern Manitoba during the 2003–04 winter season. Data from this survey confirmed the SWE gradient across the boreal forest, although satellite‐derived retrievals for the tundra were consistently low.

A series of Canadian Regional Climate Model (CRCM) simulations were conducted to identify feedbacks between the atmosphere and land surface for a domain focused on the northern boreal forest. A control simulation produced monthly patterns of SWE distribution that closely matched the passive microwave retrievals. Water budget computations showed the SWE accumulation pattern to be a function of the modelled regional precipitation pattern, and not the result of surface processes such as melt or evaporation/sublimation. Mean monthly patterns of 850‐hPa fronto genesis forcing corresponded closely to the patterns of accumulated SWE suggesting that lower tropospheric frontal activity was responsible for the snowfall events that led directly to the deposition of the northern boreal SWE band. CRCM sensitivity experiments were conducted with perturbed land cover and terrain. Only subtle differences in SWE accumulation and frontogenesis patterns relative to the control run were found when complete grassland cover was prescribed, though removing orography greatly enhanced the magnitude and zonal extent of the SWE band.     

THETAPLOT,an equivalent potential temperature diagram

Summary THETAPLOT is a diagram useful for the display and analysis of atmospheric thermodynamic soundings, particularly in relation to conditionally and convectively instable summertime weather situations. The basic coordinates of THETAPLOT are the equivalent potential temperature and the negative logarithm of pressure. The body of the diagram contains families of curves of constant potential temperature, mixing ratio and temperature. From any given sounding, three curves are plotted on the diagram: 1) Theta-ed, the equivalent potential temperature of air saturated at its dew point temperature; 2) Theta-e, equivalent potential temperature; and 3) Theta-es, the saturated equivalent potential temperature. The winds are plotted along the margin of the diagram.With 5 Figures     

关于霜形成时温、湿条件的讨论

1引言在审地面气表的过程中,发现勃利县2003年10月4日出现霜,而最低地温却>0℃,由此引起了对霜形成时温、湿条件的讨论,并对历史资料中出现霜的记录进行了统计分析,找出在最低地温≥0℃以及相对湿度不大的情况下出现霜的原因,因而得出将此日的霜做为正确记录处理的结论。     

The Bayliss-Isaacson algorithm and the constraint restoration method are equivalent

Summary Bayliss and Isaacson (1975) method of modifying any given difference scheme so as to ensure total conservation of the appropriate physical invariants is shown to be equivalent to the constraint restoration method of Miele et al. (1968, 1969) subject to the requirement of least-square change of the state-vector coordinates.Both methods are applied to enforce conservation of total energy and potential enstrophy in global shallow-water equations models. Some algorithmic differences between the methods are discussed as well as some implications of a posteriori enforcement of conservation of integral invariants on the performance of meteorological numerical weather prediction (NWP) models and the internal energy distribution.With 2 Figures     

郑州强对流天气成因分析

对2004年郑州出现的7次强对流天气过程的天气形势、影响系统及稳定度的分析结果表明：华北低涡和NW气流形势下存在着低层升温、高层降温机制,使大气层结趋于不稳定,当测站高低空温差或温度平流差达到一定量值,且近地层存在辐合系统时,易出现强对流; SW气流或高压控制时,大气高温高湿,具有较强不稳定能量,若850 hPa或地面出现辐合系统时,易产生强对流;地面湿度连续数天加大或保持在某一值域,其上空温湿24 h变化呈上趋冷下趋暖或上趋干下趋湿并达到一定量值,预示强对流的发生;700～500 hPa湿度明显减小,24 h温度露点差加大4 ℃以上,或近地层θse≥350K,中低层Δθse≥26 K,θse小值位于700 hPa或500 hPa,其厚度≥2000 m,易出现强雷雨大风; 700 hPa以下t-td≤4.3 ℃,或连续4天850 hPa t-td≤7 ℃、700 hPa t-td≤5 ℃、500 hPa t-td≤9 ℃,PW≥12,可预示短时暴雨的出现.