Download Review Radiation: Why are winter temps in the Northern

Review
Radiation:
● Why are winter temps in the Northern Hemisphere colder even though we are closer to
the sun at that time?
● Both distance and angle of incidence of the solar beam are important. The angle of
incidence and length of the day has a larger effect on the seasons than the change of
distance wrt. the sun.
● What does radiation balance imply about the total incoming vs.outgoing radiation.
● what would the peak wavelength of emission be for clouds, earth surface, sun?
Climate:
● Difference between GH effect and an actual GH?
● If H2O is the biggest GH gas in the atmosphere, why are we so concerned about CO2?
● Ice-albedo feedback.
● WV feedback
Optical phenomena:
We beat that to death last week. . .
Important things:
● Refraction occurs when light (radiation) enters a medium of different density. As it
slows down its trajectory bends towards the normal created by the interface of the two
media. Shorter, higher energy wavelenghts are refracted mrore than larger
wavelenghts.
● Reflection
● Dispersion
● Scattering:
● Releigh: Blue is scattered more than reds (explains why sky is blue).
● Rainbows
● Sundog
● preferential orientation of hexagonal snow plates all oriented in a single plane.
● mirage
● typical case: cool over warm (more dense over less dense)
● this is an inferior mirage
● opposite of general atmoshere: decreasing density with height
● we see the sky in the location of the ground
● Superior mirage: objects appear lower than they actually are
● mountains & stars
● Green Flash
● Blue-green bent more so it is still visible longest after the son has actually set.
Atmospheric Circulation:
● Key point to remember: circulation can occur on a variety of scales
● Global scale
● Stage 1: Without rotation
● Warm air at the equator-->rising (why? warm air less dense)
● Cool air sinks at the poles
● Stage 2: With rotation
Hadley Cells: Winds deflected to the right in the NH; left in S.H.
Because of the speed of rotation and the size of the earth, there are three cells
that develop: Hadley, Ferrel, and Polar. Be able to draw these and the
associated climatologic surface winds. Know where you might find climatologic
highs and lows and how this might affect climatology (location of
deserts/rainforest/westerlies).
● Intertropical Convergence Zone (ITCZ): A convergence of equatorward flow.
● What affects its location: Distribution of land masses and season.
● Why is there a jet stream
● jet is found in the region of strong temp gradient.
● Why is jet stronger in winter than in summer?
● Monsoon circulation
● Air Masses
● Source regions
● rel. uniform geographical characteristics
● large area
● away from jet
● classification
● continental vs. maritime
● polar vs. tropical
● Why doesn't Seattle get the really cold stuff.
● Boundaries btwn air masses are fronts.
Scale of ~1000km
● Fronts
● Why might we expect the precipitation to start more gradually as a warm front
approaches than as a warm front approaches? Ans. The slope is less steep.
● Bergen Model for lifecycle of storm
● Start with polar front (a boundary between warm and arctic air)
● Disturbance forms along it and grows
● Eventually the storm occludes as the cold front catches up to the warm front.
Local scale
● Diurnal winds
● Sea breeze: Warmer over land during day, cooler over water
● Land breeze: Cooler over land, warmer over water
● What influence do these breezes have on time of max & min temperatures.
● Is the Sound Breeze a sea breeze or land breeze? Why do we typically get sea
breezes rather than land breezes in Seattle?
● Slope and Mountain-Valley winds
● Key concept: Cooler air is denser and sinks; warmer air is less dense and
rises.
● Convergence of upslope flows caused by heating of mountainsides often
produces convection.
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Thunderstorms:
● Requirements:
● Instability in the vertical (temps decrease rapidly with height)
● Sufficient low level moisture (Gulf of Mexico is a great moisture source).
● Lifting to initiate instability (often there is a layer of stability that a parcel needs
to break through before getting into the unstable layer). Fronts, mountains, and
sea breeze circulations all provide a source of vertical motion.
● Distribution
● Why does the SE really get it? Bermuda high brings in low level moisture and
the surface temperatures are hot --> unstable lapse rate.
● Why don't we get many T-storms here in the NW?
● Types of T-storms:
● Air Mass
● Develop in humid air masses, usually away from fronts and other large-scale
features.
● Stages
● 1) Rising motion (due to instability; buoyant)
● 2) Mature Stage: Precipitation starts falling, bringing with it a downdraft.
Gust front forms at leading edge of downdraft as it splays upon hitting the
ground. The gust front often can be seen with the roll cloud.
● 3) How does it die? Gust front eventually blocks the updraft that feeds the
storm.
● Severe T-Storms
● Associated with hail, tornadoes, and strong winds
● They last significantly longer and are larger than air mass thunderstorms.
● Actually develop a circulation or meso-cyclone.
● Need extreme or very high humidity to fuel storms.
● How do these storms maintain strength while their counterparts die off?
● Large vertical wind shear to counteract the rotational motion produced by
the gust front.
● Tornadic storms develop hook echo on the doppler radar (tornado often forms
in the hook and can be identified by the rapidly changing wind direction).
● Know that the Fujita scale describes tornado intensity.
● You should know why certain regions are more favorable for tornadoes. . .
● What are those regions?
● Lightning
● A discharge of electricity accompanying T-storms
● 3 Types: Cloud to cloud, cloud to ground, within cloud
● Heat up air very rappidly; we know that heating-->expansion
● Pressure surge created gives us thunder.
● Speed of light: 186,000 miles/s (we see flash nearly instantaneously)
● Speed of Sound: 1,100 ft/s (for every 5 secs --> 1 mile distant).
● Theory for charge separation:
● Ice-coated snow particles, called graupel act as dipoles with charge separation.
When smaller particles (moving upward in an updraft) collide with downwardmoving larger graupel particles, the larger particles gain electrons (neg charge)
and the smaller particles are now with fewer electrons (positive charge).
● Overall, the lower part of the cloud is negatively charged (inducing a positive
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charge on the ground) and the upper portion is positively charged.
● Steps in development
● Stepped leader forms in quick bursts
● They get close enough to the surface tht the resistance of the air is no longer
sufficient to prevent the release of the charge differential.
● Return Stroke: surge of neg charge (electrons) from cloud to ground.
Hail
● Can grow to be much larger than rain drops because ice is much more tightly
bonded.
● Form due to cyclic up and down drafts
● Often see banding of clear layers (melt freezes) and opaque layers (forming
directly from vapor). You don't need to know these details.
Hurricanes
● Can cause damage in a variety of ways: Wind, rain, and most importantly storm
surge.
● Saffir-simpson scale provides an idea of storm intensity:
● Category I-V
● Higher categories have stronger winds and lower pressures, but are much less
frequent.
● Smaller than mid-lattitude cyclone (only ~500km across), but usually more intense.
● Structure definined by convective elements: Eye wall and spiral bands.
● Aiurflow: Counterclockwise inflow at low levels and then outflow above.
● Hurricanes need water with very warm sea surface temperatures. Why?
● The release of latent heat as this warm, moist air rises fuels the storm.
● Start with a low at the surface; air converges and rises; eventually we reach
saturation, causing the release of latent heat which warms the atmosphere; a
warmer atmosphere expands and causes outflow aloft, reducing the weight of the
column and decreasing the pressure at the surface, causing even more inflow and
convergence. . .
● Origin of Atlantic Hurricanes: Tropical waves off the coast of Africa
● How do the energy souces of hurricanes differ from mid-lattitude cyclones?
● Hurricanes use mostly latent heat.
● Mid-lattitude cyclones feed off of temperature gradients.
● Extra-tropical transition is where these hurricanes change their fundamental
source of energy, going from latent heat to temp gradients. Extra-tropical
cyclones can be quite powerful and typically have no shortage of moisture.
● Where won't we get hurricanes in spite of warm surface water temps?
● Hint: Coriolis force is close to zero, where?