Midterm I Review

Topics we have discussed Atmospheric sciences at a glance Evolution of the atmosphere What cause the four seasons? What is the greenhouse effect? What set the atmosphere in motion?

The mission of the atmospheric sciences is to understand and predict weather, climate, and related disasters

Atmospheric sciences at a glance Atmosphere: A mixture of gas molecules, microscopically small particles of solid and liquid, and falling precipitation Meteorology: The study of the atmosphere and the processes that form weather Weather: The state of the atmosphere at a given time and place Climate: The statistical properties of the atmosphere. (i.e. averages and variability) Weather- and climate-related disasters: tropical cyclones, tornados, floods, droughts, winter storms, extreme heat, extreme cold, lightning, El Nino, global warming

Atmospheric sciences at a glance (cont) The modern climatology (meteorology) was born in the 1940s (a very young science!), but has been growing very fast! Now we have a global observational network with many satellites, ships, radars and surface stations, as well as very comprehensive prediction models running on the world’s largest computers. The current status of weather and climate predictions: (1) weather prediction good to 10 days, (2) tropical cyclone prediction good in track but not in intensity, (3) climate prediction good to two seasons, (4) climate change projections have a 3-fold difference in magnitude. The main reasons of the difficulties: (1) Teleconnection problem, (2) Feedback problem, and (3) Subgrid-scale problem.

Evolution of the atmosphere –The standard units of measurements (SI) –Earth’s three atmospheres: 1st: 4.6 billion years ago, H, He Transition: formation of magnetic field, volcano activities 2nd: 4 billion years ago, CO 2, H 2 O, N 2 Transition: emergence of life, formation of ocean 3rd: 400 million years ago, O 2 Important event: formation of seven continents –What is the residence time? What is the difference between the permanent and variable gases? Name 3 of each. What are the most and second most abundant gases? –Given that variable gases are so rare, why are they considered at all? How are CO 2 and O 3 changing?

Standard units of measurement SI (System International) QuantityNameUnitsSymbol Lengthmetermm Masskilogramkgkg Timesecondss TemperatureKelvinKK Densitykilogramkg/m 3 kg/m 3 per cubic meter Speedmeter perm/sm/s second Forcenewtonm.kg/s 2 N PressurepascalN/m 2 Pa EnergyjouleN.mJ PowerwattJ/sW

Evolution of the Sun and the Earth The Earth was born 4.6 billion years ago.

Permanent gases and variable gases Residence time: The amount of time a gas is in the atmosphere The permanent gases: gases having long residence times (N 2 =42,000,000 y, O 2 =5,000 y), % of total atmosphere mass The variable gases: Gases generally having shorter residence times (H 2 O=10 days, CO 2 =150 y).

Importance of the Variable Gases CO2 and water vapor are the major greenhouse gases Water can exist in all three states on Earth. Global water cycle is the process of water being cycled from the planet to the atmosphere and back again. O3 protects us against harmful ultraviolet radiation

What cause the four seasons? – What is energy? 3 methods of energy transfer – The names of the 6 wavelength categories in the electromagnetic radiation spectrum – The wavelength range of Sun (shortwave) and Earth (longwave) radition – The two basic motions of the Earth – What causes the seasons: the Earth’s tilt and the 3 ways it affects the solar insolation

Methods of Energy Transfer Conduction –Molecule to molecule transfer –Heat flow: warm to cold –e.g. leather seats in a car Convection –transferred by vertical movement –physical mixing –e.g. boiling water Radiation –propagated without medium (i.e. vacuum) –solar radiation provides nearly all energy –The rest of this chapter deals with radiation

The Electromagnetic Spectrum The limitations of the human eye! Sun = “shortwave” ( μm) Peak 0.5 μm (green) Earth = “longwave” (4-100 μm) Peak 10 μm (infrared)

The Earth’s two basic motions: revolution with a period of 1 year, and rotation with a period of 1 day. The change of seasons is caused by the Earth’s 23.5 o tilt from the line perpendicular to its orbit plane (toward the sun during summer), which affects the receipt of solar insolation in three ways: 1.Length of Daylight period 2.Angle at which sunlight hits the surface (“Beam Spreading”) 3.Thickness of atmosphere through which sunlight must travel (“Beam Depletion)

What is the greenhouse effect? Earth ’ s energy balance at the top of the atmosphere and at the surface. What percentage of solar energy is absorbed by the surface? Atmospheric influences on radiation (3 ways) What cause the greenhouse effect? What are the major greenhouse gases? Why is methane important and what contributes most to methane production? The three types of atmospheric scattering. What causes the blue sky? Why causes the reddish-orange sunsets? Basic characteristics of global temperature distribution (T decreases poleward, isotherm shifts seasonally, T over land > over ocean in summer).

Earth ’ s energy budget (averaged over the whole globe and over a long time At the top of the atmosphere (3-way balance): Incoming shortwave = Reflected Shortwave + Emitted longwave At the surface (5-way balance): Incoming shortwave = Reflected shortwave + Net emitted longwave (emitted - incoming) + Latent heat flux + sensible heat flux Sensible heat 7% Latent heat 23% Net Longwave 21% Yellow: shortwave Red: longwave

The greenhouse effect helps to keep the earth surface at a comfortable temperature. But when it’s too strong, the temperature becomes too warm. Transparent to solar (shortwave) radiation Opaque to earth’s (longwave) radiation Major GH gases: CO 2, H 2 0 (v), CH 4 Atmospheric absorption - The Greenhouse Effect

The importance of methane (CH 4 ) 23 times more powerful as a greenhouse gas than CO 2 The livestock sector is a major player, which accounts for 35-40% global anthropogenic emissions of methane (their burps!) The livestock sector is responsible for 18% of total greenhouse gas emissions, which is higher than transportation (cars, airplanes, etc) Therefore, consuming less meat is more efficient in reducing global warming than not driving cars.

What set the atmosphere in motion? How thick is the atmosphere compared to the earth’s thickness? Four layers of the atmosphere, what separate them? Definition of pressure and its unit. Definition of pressure gradient. Pressure gradient sets the air in motion. Equation of state (Relationship between P, ρ, and T) Vertical Pressure Distribution. How does pressure change with height? What is the hydrostatic equilibrium?

What set the atmosphere in motion? (cont.) Know the 3 Forces that affect wind speed /direction Especially work on Coriolis force, as this is the hardest to understand. Which direction is air deflected to by Coriolis force? What is the geostrophic balance? At which level is it valid? Difference between upper level and surface winds Does cyclones correspond to high or low surface pressure? Is the air moving clockwise or counter-clockwise around them? How about anticyclones?

Temperature Layers The names of the 4 layers What separate them? The approximate height of tropopause, stratopause and mesopause

The Equation of State Describes relationships between pressure, temperature, and density (Start w/ molecular movement in sealed container  Pressure proportional to rate of collisions between molecules and walls). At constant temperatures, an increase in air density will cause a pressure increase (Add more molecules  increase density  increase rate of collisions  raise pressure) Under constant density, an increase in temperature will lead to an increase in pressure ( Raise temperature  increase speed of molecules  increase rate of collisions  raise pressure) Pressure = density x temperature x 287 J kg -1 K -1 [ p = ρ T R ]

Vertical Hydrostatic Equilibrium Explains why air doesn’t continuously blow upward or get pulled downward The downward force of gravity (weight of parcel) is balanced by a strong vertical pressure gradient (VPG)  creates hydrostatic equilibrium Δ p/ Δ z= ρ g Vertical Pressure Gradient weight = of parcel ρgρgρgρg Δ p/ Δ z

Forces affecting the horizontal winds Horizontal pressure gradients responsible for wind generation Three forces affecting horizontal winds: 1.Pressure Gradient Force (PGF) 2.Coriolis Effect (CE) 3.Friction Force (FF) CE: The Earth’s rotation deflects any moving object to the right of its moving direction in NH (left in SH). Like walking in a turning bus. CE increases poleward (greatest at the poles, 0 at the equator), and increases with the speed of moving object

Geostrophic Balance (Geostrophic flow) PGF = - CE When the effects of friction can be neglected (such as in the upper air away from surface roughness), the wind speed/direction is simply a balance between the PGF and CE. Air motion is deflected by the Coriolis force to be perpendicular to PGF PGF

Cyclones, Anticyclones, Troughs and Ridges on weather charts Highest level   Lowest level Isobars usually closed off at lowest levels – Cyclones (low pressure), Anticyclones (high pressure)  High pressure areas (anticyclones) - clockwise airflow in the Northern Hemisphere (opposite flow direction in S. Hemisphere)  Low pressure areas (cyclones) - counterclockwise airflow in N. Hemisphere (opposite flow in S. Hemisphere) Isobars usually not closed off at highest levels – Troughs (low pressure), Ridges (high pressure)

About the midterm There will be ~40 multiple-choice questions Sample questions

1)In the SI system, the standard unit of length is: A) yard, B) meter, C) gram, D) pound. 2) Which of the following is NOT a variable gas? A) water vapor. B) nitrogen. C) carbon dioxide. D) ozone. 3)In the northern hemisphere, when the surface wind blows toward the east, the underlying ocean current flows toward: A) the west. B) the north. C) the southeast. D) the northwest. 4) Anticyclones: A) are associated with low-pressure systems in the northern hemisphere. B) experience Coriolis effects that deflect air to the left in the Northern Hemisphere. C) are associated with supersonic winds. D) are associated with counter-clockwise flow in the southern hemisphere.