QX气象Meteorological Monthly1000-0526气象编辑部中国北京qx-40-10-116510.7519/j.issn.1000-0526.2014.10.001P434研究论文Articles高原东南缘大气近地层湍能特征与边界层动力、热力结构相关特征Relationship Between Turbulent Energy in the Near-Surface Layer and Atmospheric Boundary Layer Thermodynamic Structure over the Southeastern Side of Tibetan Plateau徐祥德XUXiangde
Based on the data observed from an intensive GPS sounding experiment and the comprehensive measurements of boundary layer in Dali of Yunnan Province during March, May and July 2008, the heights of CBL (convective boundary layer) and SBL (stable boundary layer) are calculated with approaches of temperature gradient and inversion layer strength and sensible heat flux, latent heat flux, turbulent kinetic energy, shear item and buoyancy item are obtained with eddy-correlation method. The apparent heat source Q1, which is calculated from the NCEP reanalysis data, presents the similar diurnal cycles to the turbulent energy components and turbulent flux, reflecting a close connection of the plateau's heat source variations with the diurnal changes in turbulent transport of hydrothermal process in the underlying surface. The comprehensive analysis on the vertical profiles of variables about turbulence and thermodynamics reveals the significant correlations among sensible heat flux, latent heat flux, apparent heat source and buoyancy item, implying an important contribution of thermodynamic turbulence transport to the Q1 in the near-surface layer over the southeastern edges of the Tibetan Plateau. The buoyancy item and turbulent energy play an important role in formation of the near-surface Q1, vortex dynamics, thermodynamic mixing structure. The lower layer Q1 and moisture sink are closely associated with the boundary layer height. This comprehensive analysis describs a physical linkage of thermodynamic turbulence transport with atmospheric heat source, vortex dynamical process and thermodynamic mixing layer structure to understand the interaction of turbulence-convection and atmospheric thermodynamic process in the active convection region over the southeastern edges of the Tibetan Plateau.
湍流通量湍能分量大气动力热力结构边界层高度turbulent fluxturbulent energy componentatmospheric dynamicthermodynamic structureboundary layer height国家自然科学基金重点项目41130960公益性行业(气象)科研专项GYHY201406001中日合作计划JICA项目国家自然科学基金重点项目(41130960)、公益性行业(气象)科研专项(GYHY201406001) 和中日合作计划JICA项目共同资助引言
高原热力强迫作用可驱动高原地区特殊的热对流输送,强烈的湍流混合可构成深厚对流混合热力边界层,亦可称对流边界层(convective boundary layer,CBL)。Flohn (1968) 根据卫星云图估算高原地区积雨云密度,强调高原东南部巨大的积雨云对上层大气输送热量的烟囱效应;在高原腹地中尺度积云对流系统发展,状如爆米花状,称为高原“爆米花”云(Xu et al,2002),高原“爆米花”中尺度对流系统发展有明显的“萌芽”阶段。高原东南缘为对流云频发区,该区域对流云团构成的大气视热源Q1、水汽汇Q2类似“CISK”自激反馈机制(Xu et al,2014),构成高原区域特殊的“大气涡旋结构”。位于对流层中部青藏高原白天强辐射背景下可形成发展旺盛的对流边界层,夜间高原地面强烈冷却效应却形成相对弱的稳定边界层(stable boundary layer,SBL),此两类高度“落差”日变化的边界层结构类似日周期振荡大气“抽吸泵”特征(Wu et al,1998),探讨高原边界层影响因素亦是剖析高原大气结构及其影响关键科学问题之一,数值模拟试验研究可揭示出高原较高边界层不仅决定了高原局地强对流结构和垂直运动分布特征,而且可显著影响高原周边及其下游地区大气环流异常状况(卓嘎等,2002)。
根据第二次青藏高原试验加密探空与垂直高分辨探空观测资料的分析,已发现高原存在深厚的混合层,在此层内低层中小尺度湍流结构形成或合并成大直径热泡对流单体,若干对流单体合并成对流云团,在云团内部发生充分的对流混合。因此可观测到深厚的垂直缓变或不变的层次,这里称为对流混合层。表明高原地区存在深厚的Ekman “抽吸泵”的动力机制(Xu et al,2002;周明煜等,2000)。
(a) Cross section of apparent (6 h interval) heat source (Q1) (unit:10-4 K·s-1) from NCEP reanalysis data,
(b) time series of (30 min) heat flux and latent heat flux (unit: W·m-2),
(c) shear term and buoyancy term (unit: m2·s-3) calculated by eddy covariance method,
(d) cross sections of potential temperature θ (unit: K),
(e) specific humidity q (unit: g·kg-1) observed by (6 h interval) GPS Soundings (* represens 14:00 CBL height, ☆ represens 02:00 SBL height)
(a) Vertical correlational profiles between turbulent flux, turbulent kinetic energy (TKE), components in TKE equation and apparent heat source (Q1); (b) 800 hPa Q1 and 600 hPa Q1 scatter diagram; (c) vertical correlational profiles between heat flux and delayed 1-3 days apparent heat source (Q1) at 14:00 in spring 2008
Cross section of apparent heat source (Q1) (unit:10-4 K·s-1) from NCEP reanalysis data in (a) April and (c) May; daily precipitation in (b) April and (d) May 2008 (Dali * represens 14:00 NCEP PBL height)
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