AP01大气概述课件

1、大气物理学Atmospheric Physics主讲: 刁一伟 Tel: 58731592Addr:气象楼809Email: ,课程属性: 专业基础课 学 时: 48 考试方式：平时20%，期中20%，期末60% 预修课程：高等数学、普通物理学 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,课程性质和目标：大气物理学是一门气象专业基础课。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基础知识和基础理论,为学习后行课、专业课打下坚实基础。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、

2、云雾降水物理学等。 本课程主要讲述：大气中各种气体成分的性质、各种气象要素的定义与计算、大气的垂直分层；大气静力学；大气热力学的基本概念和基本定律、各种热力过程和温湿参量；大气层结稳定度；辐射的基本概念和基本定律、太阳短波辐射在大气中的传输、地球长波辐射在大气中的传输；大气的基本运动；云物理学等大气学科的基础知识。,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：大气物理学基础，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,0.1 定义 主要研究地球大气现象与过程的物理机

3、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。 0.2 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,http:/www.earthsystemschool.mpg.de/web/imprs_profile.jpg,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

4、 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。,0.3 大气物理学发展简史,近

5、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,云物理的基础和开端：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。

6、1911，T.R.Wilson发明云室，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。,大气物理学高速发展阶段（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发展。,1. 云物理学 1946年，美国物理学家I.Langmuir, V.J.Schaefer发现干冰可以催化云产生降水。B.Vonnegut发现碘化银可作为人工冰核大大激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发展。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

7、，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发展，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发展，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

8、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发展。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发展，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发展，也使得大气物理学本身得到发展。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

9、，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发展。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

10、 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 a

11、t 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 le

12、vel 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

13、- 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

14、 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,1.2 大气的演化,第一代大气：氢、氦、氖等气体组成，

15、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

16、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 atmospher

17、es 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 in-falling gas is heated so much by collisions that it is immediately expelled as an outgoing wind.,Secondary Origin of the AtmosphereThe

18、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” volati

19、les 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 g

20、eneral 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 t

21、hese volcanic gases ? Yes. What kind of gases are ejected during a volcanic eruption? Mainly H2O, CO2, SO2, Cl, N2, 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 atmos

22、phere keeps evolving. The first to go was H2O, 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 CO2 SO2, and Cl (which would eventually form NaClremembe

23、r the ocean water is salty?).,N2 became the dominant gas in our atmosphere mainly because of its low water solubility! Nice story, but where is O2 ? 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 liv

24、es 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.

25、 Eventually the atmosphere would accumulate about 20% of free oxygen (so aerobic life forms can survive!). The appearance of O2 also made the formation of O3 possible which further shields solar UV and protects life forms on the earth surface.,大气演化小结,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

26、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，大部分仍留在大气中，成为现代大气中的主要气体成分。,Ph

27、otosynthesis 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。,Perm

28、anent Constituents (residence time 10 millions of years) 78% of nitrogen (N2) 21% of oxygen (O2) 1% of argon (A) 0.034% of CO2 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) H2O and Some trace gases (

29、such as sulfur dioxide (SO2), ammonia (NH3), nitrogen dioxide (NO2), etc. Aerosol particles - liquid droplets and solid particles Semi-permanent Constituents e.g., methane (CH4), CO, H2,2）按浓度（单位为体积混合比）来分，分为：,主要气体：浓度1%，包括N2、O2、Ar 微量气体：1ppm1%，包括CO2、CH4、Ne、 He、 Kr、水汽 痕量气体： 1ppm,2.2.2 90km以上大气,1）空气分子大部分

30、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,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。 3）空气密度 标准状态（p=1013.25hPa, t=0）下，干空气密度为1.29kg/m3 4）平均分子量 90km以下，空气平均分子量为28.966，不随高度变化；90km以上，随高度递减。,2.2.3 有关概念及其它特征,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

31、。 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；在地球系统的水循环中起重要角色。,*接下来分别讨论各主要气体成分*,地球水循环,大气中的水汽约为26.6万亿吨。 全球平均气柱内的水汽总量为27kg/m2,水汽的分布,二氧化碳 Carbon Dioxide,如果地球周围不被大气层包围的话，地球表面的等效温度大约是19。但实际观测到的地球表面温度约为15。远高于辐射平衡温度，这主要是由于大气的存在使地球表面的平衡的温度升高了。大气对太阳的短波辐射是透明的，而对地球表面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

32、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。,Enhanced Greenhouse Effect,The current concentration of CO2 is about 365 p

33、pm (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

34、the period 1990 to 2100.,CO2 lags temperature - what does it mean? The skeptic argument. An article in Science magazine illustrated that a rise in carbon dioxide did not precede a rise in temperatures, but actually lagged behind temperature rises by 200 to 1000 years. A rise in carbon dioxide levels

35、 could not have caused a rise in temperature if it followed the temperature. (Joe Barton) What the science says. When the Earth comes out of an ice age, the warming is not initiated by CO2 but by changes in the Earths orbit. The warming causes the oceans to give up CO2. The CO2 amplifies the warming

36、 and mixes through the atmosphere, spreading warming throughout the planet. So CO2 causes warming AND rising temperature causes CO2 rise. Over the last half million years, our climate has experienced long ice ages regularly punctuated by brief warm periods called interglacials. Atmospheric carbon di

37、oxide closely matches the cycle, increasing by around 80 to 100 parts per million as Antarctic temperatures warm up to 10C. However, when you look closer, CO2 actually lags temperature by around 1000 years. While this result was predictedtwo decades ago(Lorius 1990), it still surprises and confuses

38、many. Does warming cause CO2 rise or the other way around? In actuality, the answer is both.,Figure 1: Vostok ice core records for carbon dioxide concentration (Petit 2000) and temperature change (Barnola 2003).,Interglacials come along approximately every 100,000 years.This iscalled the Milankovitc

39、h cycle,brought on by changes in the Earths orbit. There are three main changes to theearths orbit. The shape of the Earths orbit around the sun (eccentricity) varies between an ellipse to a more circular shape. The earths axis is tilted relative to the sun at around 23. This tilt oscillates between

40、 22.5 and 24.5 (obliquity). As the earth spins around its axis, the axis wobbles from pointing towards the North Star to pointing at the star Vega (precession).,Figure 2: The three main orbital variations. Eccentricity: changes in the shape of the Earths orbit.Obliquity: changes in the tilt of the E

41、arths rotational axis. Precession: wobbles in the Earths rotational axis. The combined effect of theseorbital cycles cause long term changes in the amount of sunlight hitting the earth at different seasons, particularly at high latitudes. For example, around 18,000 years ago, there was an increase i

42、n the amount ofsunlight hitting the Southern Hemisphere during the southern spring. This lead to retreating Antarctic sea ice and melting glaciers in the Southern Hemisphere.(Shemesh 2002). The ice loss had a positive feedback effect with less ice reflecting sunlight back into space (decreased albed

43、o). This enhanced thewarming.,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 Glacie

44、r,1986 Hubbard Glacier blocks Russell Fjord,2002 Hubbard Glacier blocks Russell Fjord again 2003 Glacier has retreated,Ozone， 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 240-32

45、0nm harmful) radiation，Protects from skin cancer, etc,How is ozone formed ?,UV radiation strikes the O2 molecule and splits it, atomic oxygen associates itself with another O2 molecule simplistic version,Source, sink and reservoirs,Ozone is in a fluid state of creation and destruction,(from WMO Repo

46、rt 2003),How is ozone destroyed ?,Ozone Destruction Cycle 2The 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 propell

47、ant 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),Ozone Depletion,Growth of the Antarctic ozone hole over 20 years, as observed by the sate

48、llite,Darkest blue areas represent regions of maximum ozone depletion.,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 vorte

49、x”. 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 n

50、ot 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,

51、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

52、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 ni

53、trogen 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 clou

54、ds” (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

55、 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

56、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

57、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

58、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 Organi

59、sation (WMO reports #25, #37),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,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 analysi