(AP01)大气概述 大气物理学课件

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,大气物理学,Atmospheric Physics,主讲：刁一伟,Email:,大气物理学 Atmospheric Physics,课程属性: 学科必修课/主干课,学 时: 51,考试方式：平时成绩考勤、作业等20%，课堂笔试80%,预修课程：高等数学、普通物理学、大气探测学,适用专业：大气科学专业,教 材：盛裴轩,毛节泰等编著,大气物理学,北京大学,出版社, 2003,课程性质及考核方式,课程的性质和任务,大气物理学是一门气象专业根底课。学习该课程是为了使学生了解和掌握大气物理学各个方面的根底知识和根底理论,为学习后行课、专业课打下坚实根底。本门课主要介绍大气的组成和结构、大气静力学、大气辐射、大气热力学、云雾降水物理学等。,教材和主要参考书,华莱士、霍布斯著，王鹏飞等译，大气科学概观，上海科学技术出版社，1981.,徐绍祖主编：大气物理学根底，气象出版社，1993.,徐玉貌、刘红年、徐桂玉编著：大气科学概论，南京大学出版社，2000.,第一章 大气概述,一、定义,主要研究地球,大气现象与过程,的物理机制和规律。,大气现象与过程：大气中流体运动、光象、电象、热现象、相变过程、辐射过程。,二、分支,大气动力学、大气光学、大气电学、大气热力学、云降水学、大气辐射学,:/,Earth System Science,The study of the relationships among system components, and the influence of many processes (including life) on the evolution of the global environment.,意大利天文学家,伽利略,(16世纪)：温度计。,意大利数学及物理学家,托里塞利,(17世纪)：水银气压计。,法国数学及哲学家,帕斯卡和笛卡尔,(17世纪)：气压随高度变化。,英国科学家,霍克,(17世纪)：风速计。,德国物理学家,华氏,(18世纪)：定华氏温标。,法国化学家,查尔斯,(18世纪)：温度与固定体积空气的关系。,瑞典天文学家,摄氏,(18世纪)：定摄氏温标。,美国科学家,富兰克林,(18世纪)：防风筝入雷暴证明闪电来源。,瑞士地质及气象学家,笛绍高斯,(18世纪)：毛发湿度计。,气象参数温、压、湿、风等的度量与天气现象的关系开始被建立。,三、大气物理学开展简史,近代大气物理学起始阶段18世纪中叶20世纪中叶,1752, 美国,Franklin,第一次用风筝探明雷击的本质就是电.,1871, 英国物理学家,Rayleigh,解释了天空兰色的现象.,1908,年，德国物理学家,G. Mie,解决了球形粒子的散射问题,18591901,年,这两位德国物理学家开创了辐射定律,Max Karl Ernst Ludwig Planck,18581947,德国物理学家量子力学的开创人,G.R. Kirchhoff,18241887,德国物理学家,云物理学研究的形成,云物理的根底和开端：18801881，英国物理学家J. Aitken等指出了凝结核在雾滴形成中的重要作用。1911，创造云室，因此获1927年诺贝尔物理学奖。,云物理学是研究云的形成过程及其组成、性质、结构和分布，它是20世纪40年代就已形成的一门分支学科。,大气物理学高速开展阶段20世纪中叶以来,具有重大实际应用问题的需要大大加速了大气物理学的开展。,1. 云物理学,1946年，美国物理学家, 发现干冰可以催化云产生降水。发现碘化银可作为人工冰核大大鼓励了科学家们进行人工影响云雨的勇气与信心，促使云降水物理学获得了重大开展。到了90年代，由于云和降水的物理过程和化学过程研究的掀起，云物理学增添了不少研究新内容，因此，云物理学也称为云降水物理学。由于旱涝灾害和雹灾等气候和天气灾害的严重性，人工增雨、消雹作业在许多地区的开展，使得云降水物理学获得新的开展，特别是人工影响天气试验的成功，说明在局部地区，人类可以在某种程度上控制天气的变化。因此，云降水物理学的建立以及人工影响天气的试验的成功也是20世纪大气科学的重大研究进展之一。,2. 大气污染与边界层物理,由于大气边界层是大气污染的主要源地，而大气边界层主要特点是它的湍流性，因此，从20世纪60年代开始，关于边界层结构、特性的探测和分析研究得到很大开展，并且应用到大气环境的研究，特别是开展了大气边界层污染物扩散特性的研究；到了8090年代，边界层大气污染的区域输送及模拟，大气污染的预测和调控机理的研究得到很大开展。因此，边界层物理学应用到大气环境的分析、模拟、预测和调控，这也是20世纪大气科学的一个重要应用研究成就。,第二次世界大战以后，随着分子光谱学和光谱分析技术的开展，大气各种成分的辐射特性及其在大气中的传输研究在20世纪5O60年代掀起高潮，并且，这些研究广泛应用于气象卫星对地球和大气的天基遥感。这不仅使其它大气科学分支学科大大开展，也使得大气物理学本身得到开展。到了20世纪9O年代，大气辐射的测量已成为大气和地球系统天基遥感的重要手段，这是20世纪大气科学应用研究的重要进展之一。大气辐射在气候系统中的作用：由于在20世纪8O年代以后，温室气体CO2和痕量气体O3、CH4,在大气中浓度的改变引起全球增暖和人类生存环境的变化，并对全球环境变化产生了严重影响，这个问题引起世界上许多国家科学家的关注，因此，关于这些气体浓度改变的气候效应的研究使得大气辐射学的研究迅速开展。这不仅使得大气物理学的研究更深入，也使得大气物理过程与大气动力过程的研究相结合。,3. 大气辐射学,第一节 大气的起源和演化,1.1 地球的形成,Origin of the Solar System and Earth,Cloud of gas and space dust (nebula) began to contract about 4.6 billion years ago,The Nebular Hypothesis,2006年08月24日北京时间晚间9:30，第26届国际天文学联合会IAU大会就有关行星新定义的决议草案进行了表决，通过新的行星定义。国际天文从而确认太阳系只有8颗行星，冥王星遭到彻底“降级。冥王星被排除在行星行列之外，而将其列入“矮行星。现在太阳系的天体包括：八大行星，矮行星和小天体。,Structure of the Earth,The innermost layer, or core, is under such intense pressure that it has remained,partly solid at the centre,. It is made up of nickel and iron and has an estimated temperature of,4000,kelvin,.,The solid inner part of the core is around,2500,kilometres,(1600 miles) in diameter and accounts for just 1.7% of the total mass of the planet. Outside the solid inner layer of the core, a molten outer level has a thickness of 2200,kilometres,(1,400 miles) making up about 31% of the mass.,Beyond the outer core is the mantle, the largest single part of the planet. It is semi-solid, with a rockier composition than the metallic core. The mantle which is composed mainly of magnesium, silicon and oxygen - makes up around 82% of the volume and 67% of the mass of Earth. It can be divided into three separate regions: the lower mantle, the transition zone and the upper mantle.,Moving towards the Earths surface, a thin, rocky layer of crust is found. It is made up of a number of elements, mainly silicon and oxygen, with the next most common being,aluminium, iron, calcium, sodium and magnesium. The crust varies in thickness over the Earths surface, from as little as 7km in some oceanic regions to 70,kilometres,under the mountain ranges.,Major events in Earths development,大气的演化,第一代大气：氢、氦、氖等气体组成，称为原始大气阶段Primordial Atmosphere。,第二代大气：氮、二氧化碳、甲烷、氨和水汽，称为次生大气阶段Secondary Primitive Atmosphere。,现代大气：氮和氧气为主，称为今日大气阶段Current Atmosphere。,Primordial atmosphere, Where did it go?,When the earth (and other planets) formed, it must have been solidified and surrounded by a primordial atmosphere (mainly H,2, He).,This primordial atmospheres of the inner planets were was probably wiped out completely during the stage when the sun evolved to the stage of a,T-Tauri,star.,At this stage, the sun would have ejected substantial mass from its surface in form of violent solar winds.,Thus the current atmospheres of the inner planets are secondary.,In young systems, gravity causes a gas cloud to condense. The situation then usually becomes quite complex, as some of the infalling gas is heated so much by collisions that it is immediately expelled as an outgoing wind.,Secondary Origin of the Atmosphere,The role of volcanoes,The volatile-rich debris bombarded the earth surface day and night in form of meteors. Their potential energies were converted into kinetic energies and eventually heats on the surface.,At higher temperature, volatiles started to be released from the debris. These “degassed volatiles eventually evolved into the present atmosphere.,In fact, the degassing process (in form of tectonic activity) is still going on at present day, although its intensity and frequency are both much less than they were before,Mt. Pinatubo eruption,A cross-section of an oceanic ridge/rise shows its general features (above).,Oceanic ridges/rises are called spreading centers because this is where two plates are moving apart. It is an area of plate divergence where new crust is added to the diverging plate edges.,Evolution of the Secondary Atmosphere,Are you saying that our atmosphere came from these volcanic gases ?,Yes.,What kind of gases are ejected during a volcanic eruption?,Mainly H,2,O, CO,2, SO,2, Cl, N,2, in that order, and bunch of other trace gases and particles.,So they are really different from our atmosphere!,Yes, but you have to remember that this was only the beginning. The atmosphere keeps evolving. The first to go was H,2,O, because the earths atmosphere can only hold a small amount of water vapor (the saturation value). The excess water vapor would condense and precipitate (rain), Oceans!,The rain water also dissolved CO,2,SO,2, and Cl (which would eventually form NaClremember the ocean water is salty?).,N,2,became the dominant gas in our atmosphere mainly because of its low water solubility!,Nice story, but where is O,2,?,In the early atmosphere, there was little free oxygen. It was even slightly reducing. This is in fact beneficial for life to form, as the primitive lives would have difficulties to survive in an oxidizing atmosphere. Under this reducing environment, life forms evolved and finally green plants appeared.,The chlorophylls in green plants make the photosynthesis possible. During this process (in the presence of sunlight, of course) oxygen is released. Eventually the atmosphere would accumulate about 20% of free oxygen (so aerobic life forms can survive!).,The appearance of O,2,also made the formation of O,3,possible which further shields solar UV and protects life forms on the earth surface.,現在一般科學界認為地球在45億年前生成時是沒有大氣的，而地球大氣的形成主要是經由火山爆發將地殼內具揮發性物質噴出的結果。然而火山爆發所噴出的混合氣體成分主要為水氣(85%)、二氧化碳(10%)、以及少量的氮氣、硫或硫化物(二氧化硫和硫化氫)。值的特別注意的自由氧根本上是不存在的。這些成分和現在地球大氣的成分差別很大。,地球大氣的源起,大气演化,1、原始地球上无大气、无海洋；火山爆发频繁发生。,2、火山喷发形成原始大气，主要由水汽、CO2、氮和硫或硫化物。没有氧气。,大量水汽造成长时间降雨，持续了几千年推测，形成原始海洋，生命就在原始海洋中形成。,3、生命的光合作用使大气圈中出现了氧气。,约2030亿年前，原始植物开始通过光合作用释放少量的O2，随着O2的大量增加，导致高空大气形成O3层，从而过滤了太阳的紫外辐射，这样使得大量植物从海洋深处逐渐向陆地推进，最后形成愈来愈多的O 愈来愈少的辐射 接受更多的可见光 更加丰富的植物 释放更多的O2。,大约在4亿年前，伴随着地球生物的演化过程，才逐渐形成现在地球大气的状态。,从火山喷发出来的氮，由于其化学惰性及其在水中的低溶解度，大局部仍留在大气中，成为现代大气中的主要气体成分。,Photosynthesis releases oxygen to the atmosphere,第二节 大气组成,地球大气是由多种,气体,以及漂浮于其中的固态、液态等,颗粒物质,组成的。,2.1 气体成分,90km以下干洁大气均匀混合，称为均匀层。,2.1.1 90km以下大气的气体成分,1按大气成分在大气中的停留时间可分为：,定常成分：浓度的时空变化不明显的气体成分。寿命在104107a，主要包括N2、O2、惰性气体Ar等。,可变成分：寿命几年到几十年。例如，CO2、O3、CH4，H2等。,快变成分：短寿命小于1年，如H2O，CO，NO，NO2，HNO3，SO2，H2S和气溶胶等。,Permanent Constituents,(residence time 10 millions of years), 78% of nitrogen (N,2,), 21% of oxygen (O,2,), 1% of argon (A),0.034% of CO,2,Other inert gases (e.g., helium (He), neon (Ne), krypton (Kr), xenon (Xe),Variable Constituents,(residence time usually a few days to a few weeks),H,2,O and Some trace gases,(such as sulfur dioxide (SO,2,), ammonia (NH,3,), nitrogen dioxide (NO,2,), etc.,Aerosol particles - liquid droplets and solid particles,Semi-permanent Constituents,e.g., methane (CH,4,), CO, H,2,2按浓度单位为体积混合比来分，分为：,主要气体：,浓度1%，包括N,2、,O,2、,Ar,微量气体：,1ppm1%，包括CO,2,、CH,4,、Ne、 He、 Kr、水汽,痕量气体：, 1ppm,2.2.2 90km以上大气,1空气分子大局部都发生离解；,2空气成分随高度的分布逐渐变成按分子量,或原子量大小排列。,从低层到高层依次为N2、O、 He、 H,2.2.3 有关概念及其它特征,1干洁大气: 不含水汽和悬浮颗粒物的大气称为干洁大气。,2相变特征：在地球大气温、压条件下，水汽是唯一能发生相变的气体成分。,4平均分子量,90km以下，空气平均分子量为，不随高度变化；90km以上，随高度递减。,3空气密度,标准状态p=1013.25hPa, t=0下，干空气密度为3,2.2.4 重要气体成分及其主要作用,1主要气体氮、氧,对生命活动有重要意义，但对天气、百万年尺度的气候变化没有什么作用。,2微量、痕量气体水汽、CO2 、O3,水汽是云和降水的源泉；,在全球能量平衡中起重要作用，影响地面和空气温度；,是地球系统的水循环中起重要角色。,大气中的水汽含量,大气中的水汽约为28万亿吨95万亿吨。,全球平均气柱内的水汽总量为27kg/m,2,水汽的空间分布,水汽绝大局部集中在对流层下半部，随高度增加而急剧减少，水汽实际上随地区和季节的差异有很大的变化。,水汽是天气变化中的重要角色，如果没有水汽，云雾雨雪等天气现象就不存在。,水汽在大气化学变化中也起着非常重要的作用。,二氧化碳 Carbon Dioxide,如果地球周围不被大气层包围的话，地球外表的等效温度大约是19。但实际观测到的地球外表温度约为15。远高于辐射平衡温度，这主要是由于大气的存在使地球外表的平衡的温度升高了。大气对太阳的短波辐射是透明的，而对地球外表的长波辐射不太透明，其性质如同温室的玻璃一样。所以，一般把大气的这种保温作用又称为“温室效应。把具有温室效应的气体统称为“温室气体。大气中的主要温室气体不是大气的主要成分，而是水汽，CO2，CH4，N2O，CFCs。,自然界的温室气体使地球保持适当的温度平均15，而适于人类和生物生存。但是当他们的浓度增加，将会使地球温度升高，改变气候及其他气象要素，特别是降水。,温室气体浓度增加，使全球平均地表温度升高，严格地说，这是在自然温室气体浓度之上增加的“增强温室效应，人们经常把增强二字省略，但不应忘记。,The current concentration of CO2 is about 365 ppm (part per million), as compared to,the pre-industrial concentration of about 285 ppm. This is an increase of about 28%.,This increase is primarily due to the burning of fossil fuels (also some loss of biomass),The globally averaged surface temperature is projected to increase by 1.4 to 5.8C over the period 1990 to 2100.,Fig. 1-4, p. 7,Fig. 1-3, p. 6,Increase in catastrophic flood events,Global average sea level has risen,and ocean heat content has increased,Increase in frequency and,intensity of droughts,Source: OSTP,Snow cover and ice extent have decreased,Body text,Hubbard Glacier, Alaska, USA,1985 Hubbard Glacier,1986 Hubbard Glacier blocks Russell Fjord,2002 Hubbard Glacier blocks Russell Fjord again,2003 Glacier has retreated,Body text,Apollo 17 Image of the Planet,Dec. 7, 1972.,This view of the Earth from space drove home how finite, interconnected and fragile our planet is.,Inspired Earth Day (4/22) Celebration in the United States.,Evidence from satellites of thinning of the Ozone layer led to the Montreal Protocol for reducing CFCs. It was signed in September 1987 and became effective in 1989.,Montreal Protocol,Ozone Depletion,Growth of the Antarctic ozone hole over 20 years, as observed by the satellite,Darkest blue areas represent regions of maximum ozone depletion.,How ironic . . .,at ground level, ozone is a health hazard，major constituent of photochemical smog,in the stratosphere, it absorbs potentially harmful ultra-violet (UV 240-320nm harmful) radiation，Protects from skin cancer, etc,How is ozone formed ?,UV radiation strikes the O,2,molecule and splits it, atomic oxygen associates itself with another O,2,molecule ,simplistic version,Source, sink and reservoirs,Ozone is in a fluid state of creation and destruction,The Chlorine Catalytic Cycle,(from,WMO Report 2003,),The Nitrogen Catalytic Cycle,The Catalyst,(from,The Earth System,),Chlorine Sources,(from,WMO Report 2003,),Man-Made Sources for CFCs,There are two kinds of CFCs: freon-11 (CCl3F) and freon-12 (CCl2F2).,Freon-11 has been used:,(1) as a propellant in spray cans,(2) as a blowing agent for producing foams,(3) to clean semiconductor chips.,Freon-12 has been used as,(1) a refrigerant,(2) working fluid in most car air conditioners.,(from,The Earth System,),Special Features of Polar Meteorology,During the winter polar night, sunlight does not reach the south pole. A strong circumpolar wind develops in the middle to lower stratosphere. These strong winds are known as the “polar vortex. This has the effect of isolating the air over the polar region.,Since there is no sunlight, the air within the polar vortex can get very cold. So cold that special clouds can form once the air temperature gets to below about -80C. These clouds are called,Polar Stratospheric Clouds,but they are not the clouds that you are used to seeing in the sky which are composed of water droplets. PSCs first form as nitric acid trihydrate. As the temperature gets colder however, larger droplets of water-ice with nitric acid dissolved in them can form. These PSCs are crucial for ozone loss to occur.,So, we have the first few ingredients for our ozone loss recipe. We must have:,Polar winter leading to the formation of the polar vortex which isolates the air within it.,Cold temperatures; cold enough for the formation of Polar Stratospheric Clouds. As the vortex air is isolated, the cold temperatures persist.,The Polar Vortex,The wintertime circulation over the South Pole is characterized by a gigantic whirlpool of cold and dense air, called the polar vortex.,The cold and dense cold air in the middle of the vortex is subsiding.,The sinking air carries cloud particles along with it.,Remove odd nitrogen from the stratosphere.,Very little ozone and odd nitrogen can be brought into the south pole.,Polar Stratospheric Clouds (PSCs),In winter the polar stratosphere is so cold (80 or below) that certain trace atmospheric constituents can condense.,These clouds are called “polar stratospheric clouds (PSCs).,(Sweden, January 2000; from NASA website),How PSCs Affect Ozone Hole,The ice crystals in the polar stratospheric clouds provide surface for the ozone depletion surface to occur more easily.,On these cloud surfaces, certain forms of chlorine that do not react with ozone are converted into forms that do.,Polar stratospheric clouds set up the stage for massive destruction of ozone to happen when sunlight returns in the spring.,Recipe for the Ozone Hole Formation,The polar winter leads to the formation of the polar vortex which isolates the air within it.,Cold temperatures form inside the vortex; cold enough for the formation of Polar Stratospheric Clouds (PSCs). As the vortex air is isolated, the cold temperatures and the PSCs persist.,Once the PSCs form, heterogeneous reactions take place and convert the inactive chlorine and bromine reservoirs to more active forms of chlorine and bromine.,No ozone loss occurs until sunlight returns to the air inside the polar vortex and allows the production of active chlorine and initiates the catalytic ozone destruction cycles.,Ozone loss is rapid. The ozone hole currently covers a geographic region a little bigger than Antarctica and extends nearly 10km in altitude in the lower stratosphere.,What is being done,?,First global agreement - restrict CFCs - Montreal Protocol - 1987,European Community countries have even stricter measures,Was anticipated - recovery of the ozone layer within 50 years of 2000,World,Meteorological Organisation,(,WMO reports #25, #37,),Fig. 1-8, p. 10,Fig. 1-9, p. 11,2.2.5 大气气溶胶 Aerosol,大气中分散、悬浮有液体或固体微粒时的气体和悬浮物的总体系称为,大气气溶胶,。而其中的悬浮物就称为,气溶胶粒子,。,1,、,定义：,现在普遍采用最早由Donnan在第一次世界大战期间的研究工作中，把aero同sol相联而得的术语aerosol。 尺度范围：1nm-100m,What are aerosols?,Source: Posfai et al., JGR, 2003,Sample from a biomass fire collected on a filter,filter strands,Aerosol properties,Li et al 2003,Chemical and mineralogical analysis of individual mineral dust particles, E. Ganor, Z. Levin, P. Formenti and Y. Rudich, JGR, 2000,MINERAL DUST PASSING OVER LAND,Mark! Highly Non- Spherical Shapes!,2、分类,1云降水学分类按半径分类,2大气环境学分类,TSP、降尘、PM10、尘粒、粉尘、灰等。,爱根核,：半径在,到,微米之间。,大 核,：半径在,到,1,微米之间。,巨 核,：半径大于,1,微米。,Aerosols,PARTICLES SUSPENDED IN THE ATMOSPHERE,DIAMETERS MEASURED IN MICRONS ONE MILLIONETH OF A METER.,CAN MODIFY THE AMOUNT OF SOLAR ENERGY THAT REACHES THE SURFACE.,CAN ACT AS CONDENSATION NUCLEI FOR CLOUD DROPLETS.,PRIMARY SOURCES:,SEA SALT SPRAY,WIND EROSION,VOLCANOES,FIRES,HUMAN ACTIVITY,3、大气气溶胶粒子的源和汇,土壤岩石风化及火山喷发的尘埃,烟尘及工业粉尘,海末破裂干涸成核,气,-,粒转化,微生物、孢子、花粉有机物质点,宇宙尘埃,1源,据估计，全球气溶胶质粒主要是自然界产生的，人工来源仅为自然来源的五分之一。,2汇,即气溶胶粒子被移出大气的过程。,对流层大气中质粒的移出或消失可以通过,上层大气的泄漏，也可以在地面沉积。,按是否有水质粒参与，分为干沉降、湿沉降。,干沉降过程：指质粒在干的状况下移出大气的过程。包括重力下沉、附粘移出。,湿沉降过程：指质粒受雨雪或云雾滴等影响而下沉到下垫面移出大气的过程。包括凝长下沉、碰并下沉。云内去除和云下去除,4、大气气溶胶粒子在大气过程中的作用,1在云雾降水中的作用,可作为水汽凝结和凝华以及水滴冻结的核心，即局部大气气溶胶粒子可作为CCNcloud condensation nuclei)或IN (ice nuclei),2对大气辐射过程的影响,吸收和散射太阳辐射，影响大气温度的垂直分布。,3对大气光学特性的影响,对太阳光的散射和吸收，会影响大气能见度。还会影响天空颜色。一些光学现象的出现，也与它们的作用有关。,4对大气电学特性的影响,5在大气化学过程中的作用,Images taken between April 29 and May 5, 2005 shows dust from the Gobi Desert crossing the Pacific, well on its way to North America.,Transboundary:,Dust over the Pacific,Sand storm from China,Hansen figure,Hansen et al., Earths Energy Imbalance: Confirmation and Implications,Science, 2005.,虹和霓含七种色光的太阳光线，射入大气中的水滴(雨滴或雾滴)，各种色光经历折射和反 射后，可在雨幕或雾幕上形成彩色光弧环。当光弧环对观测者所张的角半径约42度，光环的彩色排序是内紫外红时，称为虹。在虹的外面，有时还出现较虹弱的彩色光环，光环对观测者所张的角半径约为52 度，彩色环的排序与虹相反即内红外紫，称为霓或副虹。虹和霓都要背对太阳而立才能观察到。在夏日的黄昏，西方放晴而东方天空有云 雨时，最易看到虹和霓。,2.2.6 大气中的一些光学现象,A primary and a secondary rainbow,内红外紫的晕是阳光或月光透过云中的冰晶时发生折射和反射形成,均匀云滴(水滴或冰晶)的衍射，结果会在月亮或太阳周围紧贴月盘或日盘,形成内紫外红的彩环称为华，是均匀云滴(水滴或冰晶)的衍射,第三节 大气的垂直结构,大气上界：,物理现象上界为1200km( 极光出现高度；,大气密度上界为20003000km ( 接近于星际气体密度1个/cm3的高度。,分层标准：按大气的属性进行分层,1按温度随高度的变化。,2按大气成分组成情况或称按空气平均分子量随高度变化分均匀层、非均匀层。,分层标准：按大气的属性进行分层,1按温度随高度的变化。,2按大气成分组成情况或称按空气平均分子,量随高度变化分均匀层、非均匀层。,3按电离状况分为电离层和非电离层,4按大气的光化学反响分：,臭氧层1050km)、非臭氧层,5按大气中电离气体运动受地磁场制约的情,况，还可以分出磁层。,地球大气根据温度、组成、电性的分层。电离层内带电离子密度有显着日变化,在白天D区对AM无线电波大量吸收,阻碍长距离传播;在夜晚AM无线电波可达F区可以传播较远.,地球大气带电粒子来源有四:太阳X光紫外线离子化空气分子;高能宇宙射线入侵至低层大气;陆地地壳放射性衰减;云内电荷别离.,Atmospheric Temperature Structure and Layers,1、对流层Troposphere12km以下,在赤道地区对流层顶的高度约,18,千米，中纬度地区约,12,千米，极地地区约,8,千米。夏季的对流层厚度大于冬季。,以南京为例，夏季的对流层厚度达,17,公里，而冬季只有,11,公里，冬夏厚度之差达,6,公里之多。,1)温度随高度的增加而降低，气温递减率为6.5/km。定义气温递减率：高度每升高单位高度气温降低的度数。,2)对流层中的垂直运动显著。,3)集中了80%的大气质量和几乎全部水汽。,4)云雾降水均发生在此层。,5)受地表影响最强烈，空气属性的水平分布很不均匀。,对流层特点,2、平流层 Stratosphere12km55km),125km以下温度递减率接近零，25km以上温度随高度明显增加。,2平流层气流运动主要以水平运动为主。,3水汽极少，颗粒物极少，能见度极好。,4大气污染物进入平流层后能长期存在。,mother-of-pearl (nacreous) clouds (mostly frozen sulfuric acid droplets),3、中层 Mesosphere85 km),1层内温度随高度增加而下降。reaching a minimum ( 100C) at about 85 km (the mesopause).,2空气的垂直对流运动强,故又称之为高空对,流层或上对流层。,4、热层 Thermosphere550km),1温度随高度增加而上升。,2高度电离。,3带电粒子运动受地球磁场的作用明显。,Above the mesosphere is the thermosphere where the temperature increases with height and can reach more than 1000C. The high temperature is caused by the heating of short wave solar radiation.,Will you feel cold or hot in the thermosphere?,Heat and temperature are not identical things!,Mohe China,Antarctic aurora,Boutin, Municipal beach of St-Prime Quebec Canada,5、外层 Exosphere 500 km 大气上界,1随高度升高气温增加不显著,2大气成分可以散逸到星际空间。,二、按电离状况分,地壳和大气中的放射性物质主要对低层大气的电离起作用，而它们的作用较弱，而宇宙线和太阳紫外线辐射对高层大气起作用，且作用较强。因此，大气中离子浓度低层低，高层高，据此分为：,中性层60km以下) 电离层60km以上,三、按大气中电离气体运动受地磁场制约的情况,1、非磁层500km以下,由于空气较稠密，带电粒子的运动主要受粒子间的碰撞支配。,2、磁层 Magnetosphere500km以上,本层内存在大量带电粒子，空气又稀薄，粒子间碰撞稀少，所以，带电粒子的运动主要受地磁场控制。,第四节 主要气象要素,气象要素：表征大气状态和现象的物理量。例如，气温、空气湿度、气压、风。,4.1 气温,4.1.1 定义：表示空气冷热程度的物理量,4.1.2 温标,摄氏温标,华氏温标,绝对温标,单位,K,常用符号,t,F,T,4.1.3 气温的度量,世界上的极端气温,气温的日变化,气温的日变化主要受地表日夜温差的影响，而地表温度的日变化和入太阳辐射以及出地球能量两者差值有关。,局部地形对气温的影响,在寒冷无风的夜晚，冷空气沉淀在山谷，造成谷底较斜坡冷的情形。在中纬度此较暖的斜坡区称之为温度带,(thermal belts), 可防止农作物遭霜害或冻伤。,果树加热器透过对流使上下空气循环，加热地表温度。混合下冷上暖空气的风机