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Meteorology Lecture 1
Weather and Climate Review
What drives our weather?
• The sun
• Insolation – solar energy reaching the Earth
• Remember the sun’s output can vary, which impacts weather on Earth– e.g. The Little Ice Age
Folklore: Sirius – The Dog Star
• Thought to produce heat at the end of summer
• Worshipped by numerous civilizations
• The “Dog Days of Summer”
Sirius
Sun
What about the Moon?
• Does it warm the Earth?
• Why does it glow?Albedo – % of insolation an object reflects
High – light surfacesLow – dark surfaces
Solar Radiation and Earth’s Surface
Why do we have seasons?
Sun conditions at the Solstices and Equinoxes
Solar declination: latitudinal change ofatitudinal change of subsolar pointssubsolar points
Energy Pathways
Figure 4.1
Heat Transfer
• Heat – energy produced by the motion of molecules and atoms in a substance
• 4 ways to transfer heat:
1. Radiation – electromagnetic waves (sunlight)
2. Conduction – energy moved from high to low
3. Convection – vertical movement of energy
4. Advection – horizontal movement of energy
Earth’s Modern Atmosphere
• The atmosphere is absolutely essential for life on Earth
• Earth’s atmosphere exists in a series of spheres or layers that grade into one another
• Layers: Composition, temperature, and function
Protective Atmosphere
Figure 3.6
Energy Balance in the Troposphere • Greenhouse Effect – where gases
(carbon dioxide, water vapor, methane, nitrous oxide, and CFCs) absorb insolation and reradiate it back to Earth in longer wavelengths thereby warming the lower troposphere
• The Greenhouse Effect and Atmospheric Warming– Atmosphere absorbs heat energy– Atmosphere delays transfer of heat from
Earth into space
Local Factors Influencing Air Temperature
• Urban Effect– Urban Heat Island
• Darker surfaces – less reflection• Less forest cover• Less water on surface• Heat from human energy use
The Urban Environment
Figure 4.21
Urban Heat Island
Figure 4.22
Global NET R
• Surfaces lose heat in one of 3 ways:– Latent heat of evaporation – energy released
as water changes state; can’t feel it– Sensible heat – heat you can feel and
measure; convection and conduction– Ground heating and cooling – energy stored
during warm periods and released during cool periods
Radiation Budgets
Figure 4.20
El Mirage, CA
Pitt Meadows,BC
Principal Temperature Controls
• Latitude
• Altitude
• Cloud Cover
• Land-Water Heating Differences
Latitude and Temperature
Figure 5.4
• Latitude – Affects insolation– Sun angles– Daylength
Altitude
Figure 5.5
• Altitude – High altitude has greater daily range– High altitude has lower annual average
Cloud Cover
Land–Water Heating Differences
• Evaporation (= latent heat)
• Transparency (= penetration of insolation)
• Specific heat (differs among objects)
• Movement (= vertical mixing)
• Ocean currents and sea surface temperatures(= spread of energy spatially)
All this leads to this important concept:Marine vs. continental effects
Land–Water Heating Differences
Figure 5.7
Global Temperature Ranges
Figure 5.17
Atmospheric Pressure Systems
High-pressure system-also called anticyclone-circulating body of air-descending air-clockwise circulation innorthern hemisphere
Low-pressure system-also called cyclone-circulating body of air-rising air-counterclockwise circ. in northern hemisphere
Atmospheric Pressure Map
Isobars – lines of equal air pressure on a map
Wind DirectionWinds are named according to the direction FROM which they are blowing
Direction of Air Flow• Unequal heating of land surfaces
• Pressure gradient force – air flows from high to low
• Coriolis force – deflection or change in direction caused by Earth’s rotation
• Frictional forces – places a drag on that air flow
Pressure Gradient Force
Fluctuations in the Pressure Gradient
High pressure to low pressure, perpendicular to isobars
Coriolis Force•Due to Earth’s rotation
•Pulls wind to right in northern hemisphere
•Pulls wind to left in southern hemisphere
•Strongest at poles
•None at equatorCoriolis Force
Frictional Forces
• Near surface, friction (f) works against pressure gradient force (pgf), so resulting wind direction is between pressure gradient force and coriolis force (cf)
pgf
f
cf – northern hemisphere
WIND
Three Forces Combined
Rossby Waves
Figure 6.17
Strong boundaries often
occur between warm and cold
air. In the mid-latitudes, the
polar front marks this thermal
discontinuity at the surface.
The Polar Front and Jet Streams
Relative Humidity• Relative humidity is the indication of how
close the air is to saturation and when condensation will begin
• Dew-point temperature not really a temperature, but a measure of moisture content
• When air temperature tries to decrease below the dew point, surplus water vapor is removed from the air by condensation
Relative Humidity
Figure 7.8
Cooling
Warming
Actualwater vapor
Hydrologic Cycle