Ch 7a: Atmosphere Flashcards
Extent of Atmosphere
Thins upward, 500 km merges with vacuum of space, 5% of the volume of Earth.
Atmosphere Pressure and Density
gases are highly compressible, density increases downward.
Measuring Pressure:
Aneroid barometers, mercury barometers
Average pressure at sea level:
760 mm mercury, 101.325 kPa
Temperature measures:
average kinetic energy of molecules
Heat refers to:
total energy of all molecules
Temperature and Elevation:
four layers based on temperature changes: troposphere, stratosphere, mesosphere, thermosphere.
Troposphere:
16 km thick at equator, 10 km at poles. Top surface is tropopause. Heated from below, reradiated. Contains most weather
Stratosphere:
extends from top of troposphere to ~50km. Temperature increases upward due to absorption of solar UV energy by ozone. Upper boundary is stratopause.
Mesosphere:
temperature decreases upwards to ~80km.
Thermosphere:
Heating of gas molecules by EMR. Temperature is high, scare molecules so total heat content very low.
Composition of the atmosphere:
gases and aerosols.
Gases:
mainly nitrogen, oxygen, argon, water vapour.
Aerosols:
water droplets, solid particles
Greenhouse Gases, waves
incoming solar energy is mainly short wave. Radiated by ground is long wave. Absorbed by 5 greenhouse gases:
5 Greenhouse Gases:
carbon dioxide, water vapor, methane, nitorus oxide, ozone.
Absorption of solar energy and gases:
different gases absorb different parts of Sun’s energy spectrum. Absorbed energy is converted to heat within atmosphere.
Behavior of water:
water can exist in the atmosphere in 3 phases. Phase transformation involves latent heat.
Water Vapor varies between __%-__%.
varies between 0.3%-4.0%. Typically quoted as partial pressures. (Dalton’s Law of partial pressures)
Saturation Pressure:
dry air in contact with water or ice. Partial pressure of VP increases
When evaporation and condensation are balanced:
air is saturated, VP=SVP
Relative Humidity (RH):
RH = (VP/SVP) * 100%. Dew point.
RH changes when:
water vapour amount or temperature changes
Adiabatic temperature change AKA
Adiabatic lapse rates
Adiabatic temperature change
as air masses rise, pressure falls and expansion occurs. Temperature decreases at -1C per 100m
Adiabatic cooling of rising air causes condensation
condensation releases latent heat energy. Offsets adiabatic cooling.
Total energy of atmosphere is …
approx constant. Energy is continuously redistributed through circulation (atmospheric and oceanic)
Atmospheric circulation
As air is intensely heated near equator: expansion generates a region of low pressure. Air tends to rise because of its buoyancy. Creates pressure-gradient flow. High P regions to low P regions.
Temperature varies dramatically with …
with location and elevation; affects pressure. Significant for weather studies, aviation.
Isobars
contours of air pressure
Geostrophic flow:
rotating earth, pressure gradient flow is modified by the coriolis effect.
When flow is parallel to isobars:
pressure gradient is exactly balanced by Coriolis effect, flow is straight (geostrophic flow)
Near-surface flow
Air flow near surface is not exactly geostrophic due to friction.
Distribution of high and low pressure
ITCZ, sub-tropical high, subpolar low, converging tropical and polar air masses meet at polar front, polar high.
ITCZ =
Inter tropical convergence zone.
Air masses control…
control weather conditions. Up to 2000 km wide.
Air masses characterized by:
temperature, specific humidity, origin (M or C)
Define air fronts
they mark boundaries between air masses
air masses do not…
merge well
warm - cold contact
High speed winds, strong T and P changes –> jet stream
Frontal Zone Classification
depends mainly on the direction of air mass movement. Contact region is usually inclined
Front types:
cold, warm, stationary, occluded
Warm Front:
warm air advances on cold, warm air mass flows over cold
Cold Front:
Cold air advances on warm, cold air mass flows under warm
Stationary Front:
a front that is not moving
Occluded Front:
when a cold front overtakes a warm front
Wind speed and direction:
direction wind comes from, typical wind speeds average 10-30 kmh.
Wind speed indicators: half notch
8 kmh, 5 knots
Wind speed indicators: full notch
16 kmh, 10 knots
Wind speed indicators: triangular wedge
80 kmh, 50 knots
Wind chill
skin cools faster in moving air, boundary layer of very slow moving air acts as an insulator.
Wind chill equivalent temperature:
windchill factor
Factors controlling wind speed and direction:
pressure gradient, coriolis effect, friction, topography
Cyclones:
large (500-2000km wide) wheels of air.
Cyclones: pressure info
Have LOW pressure centre, wind crosses pressure isobars at an angle into the low. Net inflow of air.
Cyclones may:
contain clouds and ppte, possibly high winds.
Cyclones rotate
anticlockwise (in the N.H.) around surface LOW pressure centre
Anticyclones rotate
clockwise (in the N.H.) around surface HIGH pressure centre.
Anticyclones: pressure info
wind crosses pressure isobars at an angle, net outflow of air.
Anticyclones may:
contain clearing and little cloud development or ppte.
Global wind patterns:
trade winds, westerlies, monsoons
Regional to local:
breezes, katabatic winds, adiabatic winds
Tradewinds:
easterlies, reliable rarely shift direction
ITCZ:
(intertropical convergence zone), air moves upwards creating: clouds and rain and tropical forests. Double band of clouds, Doldrums.
Doldrums are:
equatorial regions of light ocean currents and winds within the intertropical convergence zone
Westerlies:
in the temperate zone (mid-latitude). Migrating, rotating cyclones. More fickle than the reliable easterly winds. Often controlled by the jetstream.
Monsoons winds
seasonal migration of pressure belts reverses wind direction. Affect India, Australia, W. Africa. Migration of the ITCZ.
Basic causes of cloud formation
density differences, frontal confrontation, large scale obstacles, convergence.
Cloud development:
lifting of air relating to pressure temperature and SVP drops.
Clouds occur when–
RH increases until 100%, condensation: nucleation of tiny water droplets. Droplets increase size by collision and recirculation in the system by updrafts.
Cloud classification based on:
shape, altitude or position, vertical development. Amount of possible rain, snow or hail, causal origin.
Cloud types:
cirrus clouds (>6km), Stratus clouds, cumulus clouds, Altus clouds (2-6km), Nimbus clouds.
Severe storms
:name given to a weather system that may be an immediate threat to life or property.
Snow and freezing rain
raindrops also form from melting snowflakes, supercooled liquid raindrops may freeze when falling on a cold surface.
Ice:
cloud droplets condense on condensation nuclei
If T
form supercooled cloud droplets
If T
form ice crystals on ice nuclei
Hail:
raindrops fallings into air colder than 0C may freeze into ice pellets. Ice pellets that are > 5 mm are called hail stones
Thunderstorms:
Moist, unstable vertically lifted air masses. Common olong cold fronts where mT meets cP
Condensation & latent heat
latent heat
Air mass thunderstorm:
(Local Thunderstorm): most common, often single cell, width=height (10km), duration (60min), occur when wind changes with height are small
Organized thunderstorm:
rotating supercell or several multicells. Often associated with mid-latitude cyclone cold fronts, well established anvil. Duration (2-6hrs) Wind changes with height are large.
Lightning, upper portion:
mainly positively charged
Lightning, lower portionL
mainly negatively charged
Electric sparks:
charge accumulations > insulation ability of air
Tornadoes - waterspouts
grey, rotating funnels extending from stormbase downwards. Often small, usually visible for only a few minutes. Can leave a large swath of destruction. Classification based on Fujita Scale
Hurricanes
Tropical cyclones, winds are > 32.6m/s. Name based on where it formed. Classified on Saffir-Simpson scale
Anatomy of a hurricane
About 500-1000km wide and last about 7-10 days. Sinking motion in the inner eye (20-40km diam) Low pressure centre. Rising motion and strong winds in the eyewall region.
Adiabatic winds:
winds moving up a slope
Katabatic winds:
winds moving down a slope
