AMS Weather Studies Introduction to Atmospheric Science 4

AMS Weather Studies Introduction to Atmospheric Science, 4 th Edition Chapter 2 Atmosphere: Origin, Composition, and Structure © AMS 1

Case-in-Point § Weather and climatic issues in one part of the world can affect those in another part § North African dust storms can affect the weather and air quality of the southeastern U. S. § Dust can harbor microscopic disease-causing organisms § This dust may be harming coral reefs in the Caribbean § This dust may increase the frequency of red tides © AMS 2

Driving Question § What is the composition and structure of the atmosphere? – This chapter covers: § Evolution of the atmosphere § How meteorologists monitor the atmosphere – At the surface – Upper-air § The temperature profile of the atmosphere § The thermal subdivisions of the atmosphere § Electromagnetic characteristics of the upper atmosphere © AMS 3

Atmosphere, Weather, and Climate § Atmosphere – – – Gases and suspended particles ½ of the mass is found in the lower 5500 m (18, 000 ft) 99% of the mass is below 32 km (20 miles) § Weather – The state of the atmosphere at a given time and place – Variables – temperature, humidity, cloudiness, precipitation, wind speed, wind direction § Climate – Weather conditions at a location over a specified time period plus weather extremes at that locale – Computed over a 30 year period, beginning with the 1 st year of a decade § Climatology is the study of climate, climate controls, variability (change) over space & time © AMS 4

Evolution of the Atmosphere § Primeval phase – Gases surrounding Earth were primarily helium plus hydrogen compounds § Methane and ammonia § Eventually, these escaped to space – 4. 4 billion years ago, there was enough gravity to retain an atmosphere – Rocks outgassed as they solidified and cooled § Primarily carbon dioxide, nitrogen, and water vapor § Trace amounts – methane, ammonia, sulfur dioxide – Water vapor was broken into hydrogen and oxygen by UV radiation © AMS 5

Evolution of the Atmosphere § Primeval phase, continued – 4. 5 – 2. 5 billion years ago, sun was much fainter § Earth was not cooler due to CO 2 (greenhouse gas) – CO 2 combined with rainwater to form carbonic acid § This reacted with rocks, locked carbon in the rocks, so there was less in the atmosphere § Living organisms took CO 2 out of the atmosphere via photosynthesis, locking carbon into carbohydrates – Oxygen became the 2 nd most abundant gas in the atmosphere § Nitrogen is 1 st. It is an out-gassing product that is relatively inert – CO 2 has been a minor component of the atmosphere for the last 2. 5 billion years § Fluctuations play important roles in climate change © AMS 6

Evolution of the Atmosphere § Modern phase – Lower atmosphere (to 80 km or 50 miles) circulates and maintains uniform ratios of gasses § Homosphere – Above this, gases separate based on weight § Results in stratified layers § Heterosphere – Nitrogen ≈ 78%, Oxygen ≈ 21% of the homosphere § Argon < 1% § CO 2 <. 04% © AMS 7

Note – this deals with dry air. Water vapor varies greatly, and is not included in the table © AMS 8

Evolution of the Atmosphere § § § Modern phase, continued O 2 in the homosphere O in the heterosphere – 150 km (95 miles) above Earth’s surface – UV radiation splits O 2 § Other planets’ atmospheres are much different § May have started the same § Earth’s atmosphere also has aerosols – Liquid and solid particles – Sources § Wind erosion of soil § Volcanic eruptions © AMS ■ Forest fires ■ Ocean spray ■ Agricultural & industrial activities 9

Evolution of the Atmosphere § Modern phase, continued – Water vapor § By volume, < 4% of the lowest 1 km of the atmosphere § Necessary for clouds and precipitation – CO 2 – even though <. 04%: § Required for essential function to all life – photosynthesis – Both CO 2 and water vapor absorb and emit infrared radiation § Keeps the lower atmosphere warm § Allows for life to exist © AMS 10

Air Pollution § An air pollutant is an aerosol or gas that occurs at a concentration that threatens the well-being of living organisms – Most are human-made, some are natural § Dust storms, volcanoes, pollen, decay of plants/animals § Primary air pollutants – Harmful immediately as emitted § Secondary air pollutants – Harmful after combination with one or more substances – Photochemical smog © AMS 11

Air Pollution § The Environmental Protection Agency (EPA) – Standards for 6 air pollutants § carbon monoxide § nitrogen oxides lead ■ particulates ■ ozone ■ sulfur dioxide ■ – Primary air quality standards § Maximum exposure levels humans can tolerate without ill effects – Secondary air quality standards § Maximum exposure levels allowable to minimize the impact on crops, visibility, personal comfort, and climate – Compliance with standards © AMS § Attainment areas – geographic regions where standards are met or below § Non-attainment areas – geographic regions where the primary standard is not met 12

Investigating the Atmosphere § Scientists (including meteorologists) use the scientific method – Identify questions related to the problem – Propose an answer to one of the questions § This is an educated guess – State the educated guess in a manner that can be tested § This is the hypothesis – Predict the outcome as if the hypothesis were correct – Test the hypothesis to see if the prediction is correct – Reject or revise the hypothesis if the prediction is wrong § An hypothesis that stands the test of time is a scientific theory © AMS 13

Atmospheric models § Scientific models are approximations or simulations of a real system § The Earth-atmosphere system can be scientifically modeled – A conceptual model is an abstract idea that represents some fundamental law or relationship § Example – the geostrophic wind model – A graphical model compiles and displays data in a format that readily conveys meaning § Example – a weather map – A physical model is a miniaturized version of a system © AMS § Example – a tornado vortex chamber – next slide 14

Tornado Vortex Chamber © AMS 15

Atmospheric Models § Meteorologists today use numerical models rather than physical models – Mathematical equations represent relationships among system variables § Example – a global climate model and rising CO 2 § All other climate variables are held constant § CO 2 is increased § Results are noted – All have inherent errors § Accuracy of component equations may be a problem © AMS 16

Monitoring the Atmosphere § Surface observations – Systematic observations in some areas as far back as 1644 -45 in North America § Old Swedes Fort (Wilmington, DE) had 1 st systematic observations – Philadelphia began in 1731 – Charleston, SC – 1738 – Cambridge, MA – 1753 – New Haven, CT – 1781 – uninterrupted to today © AMS 17

Monitoring the Atmosphere § Surface observations, continued – – – Army monitored weather to compare with troop health Mid-1800 s – national network of volunteer observers 1849 – telegraph companies transmitted weather conditions free of charge – 1860 s – loss of ships in Great Lakes § Government took a greater role in forecasting – 1870 – President Ulysses S. Grant established 24 stations under the auspices of the U. S. Army Signal Corps – 1891 – transferred from military to civilian hands © AMS § New weather bureau under U. S. Department of Agriculture 18

Monitoring the Atmosphere § Surface observations, continued – Transferred to Commerce Department in 1940 – 1965, Weather Bureau reorganized into the National Weather Service (NWS) § Under Environmental Science Services Administration (ESSA), which became National Oceanic and Atmospheric Administration (NOAA) – 1990 s – NWS modernized and expanded © AMS § Today, 123 NWS Forecast Offices (see next slide) § Added Automated Surface Observing Systems (ASOS) 19

NWS Forecast Offices © AMS 20

Automated Surface Observing System (ASOS) © AMS 21

Cooperative Observer Network § The NWS also has a Cooperative Observer Network – Member stations record daily precipitation and max/min temperatures for hydrologic, agricultural, and climatic purposes © AMS 22

Upper Air Observations § Kites were used early on – 1749, Glasgow, Scotland, Alexander Wilson – 1752, Benjamin Franklin, demonstrated electrical nature of lightning § Balloons – Manned balloon, 1804, Gay-Lussac & Biot § Air samples taken, measured temperature and humidity up to 7, 000 m (23, 000 ft) – Manned balloon, 1862, Glaisher & Coxwell § Weather measurements to 9000 m (29, 500 ft) § Nearly perished from cold and oxygen deprivation § Kites carried the first thermograph aloft in 1894 § 1907 -1933 – box kites with meteorographs, up to 3000 m (10, 000 ft) © AMS 23

Upper Air Observations § Radiosondes – Invented in late 1920 s – Transmits altitude readings (soundings) of: § Temperature ■ Dewpoint ■ Air pressure – Data is received immediately § No need to recover equipment – Rawinsonde § § § A radiosonde that is tracked by direction-finding antennas Provides data on wind direction and speed Dropwindsonde is not launched with a balloon § It is dropped from an aircraft on a parachute – These devices are launched simultaneously worldwide © AMS § Launched at 0000 Z and 1200 Z § Only 20% of the devices are recovered 24

Upper Air Observations Launching a radiosonde © AMS radiosonde 25

Upper Air Observations Data from radiosonde shown in a Stüve diagram © AMS Locations of radiosonde observation stations 26

Remote Sensing § Measurement of environmental conditions by processing signals that are either emitted by an object or reflected back to a signal source – Radar – Satellites © AMS 27

Temperature Profile of the Atmosphere § Troposphere – Lowest layer – Where almost all weather occurs – Temperature decreases with altitude § Generally, but with frequent exceptions (e. g. , inversion, isothermal layer) § Average temperature drop is 6. 5 °C/1000 m (3. 5 °F/1000 ft) – ~ 6 km (3. 7 mi) thick at the poles, ~20 km (12 mi) thick at the equator – Upper boundary/transition zone to next layer is called the tropopause © AMS 28

Temperature Profile of the Atmosphere § Stratosphere – – – Next higher level Goes from troposphere up to ~ 50 km (30 mi) In lower stratosphere, temperature is constant § This is an isothermal condition – Above 20 km (12 mi), temperature increases with increasing altitude § Stratosphere is warmed by the energy released by ozone absorbing UV radiation – Stable conditions are ideal for jet aircraft travel, but can cause trapping of pollutants (e. g. from volcanic eruptions) in lower stratosphere – Upper boundary/transition zone to next layer is called © AMS the stratopause 29

Temperature Profile of the Atmosphere § Mesosphere – – – Next higher level Goes from stratopause up to about 80 km (50 mi) Temperature once again decreases with increasing altitude in this layer § Thermosphere – Next higher level – Temperatures are isothermal (constant temperature condition) in the lower thermosphere – Temperatures rise rapidly above that § Air temperature particularly sensitive to incoming solar radiation § Temperature is more variable than in other regions © AMS 30

Air Temperature and Altitudinal Relationships in the Atmosphere © American Meteorological Society © AMS 31

The Ionosphere and the Aurora § The ionosphere is located mostly in thermosphere – High concentration of ions and electrons § Electrically-charged atomic-scale particles § Caused by solar energy stripping electrons from oxygen and nitrogen atoms and molecules – Leaves a positive charge – Auroras are found in the ionosphere § Caused by solar wind – Sub-atomic, super-hot, electrically charged particles § Earth’s magnetic field deflects the solar wind – Makes a teardrop-shaped cavity known as the magnetosphere © AMS § Auroras are only visible at the higher latitudes 32

The Ionosphere and the Aurora Average variation of particle density with altitude in the ionosphere © AMS 33

The Ionosphere and the Aurora § The magnetosphere is caused by the deflection of the solar wind by Earth’s magnetic field Aurora borealis © AMS 34

The Ionosphere and the Aurora The Northern Hemisphere auroral oval, an area of continuous auroral activity © AMS 35