Download Lect 5 Climate

Lecture 5– Climate
Meteorology: Study of climate and weather
• Weather: daily variations in precipitation,
winds, temperature, etc.
Climate: overall combination of
temperature, precipitation, winds etc. of an
area/region
– Subject to many factors:
• microclimate
Climate Impacts life forms
Heating of the Earth
• Shortwave radiations most energetic
• about 51% reaches earth surface
• Albedo – surface reflectivity of earth
• Clouds
• Polar ice caps
• Deserts
• Greenhouse effect: trapped energy not reradiated to space
• Clouds
• Atmospheric gasses (chapter 30)
• Incoming radiation: short wave (high
temperature)
• Reflected radiations from earth: long wave
(low temperature)
• The sun emits electromagnetic radiation of a wide range of
wavelengths
• The wavelengths of 400 to 700 nanometers (nm) make up
visible light
– One nanometer is one-billionth of a meter (1 nm = 0.000000001 m)
• These same wavelengths are also called photosynthetically
active radiation (PAR)
– Used by plants to power photosynthesis
Seasons due to tilt of
earth
• Uneven heating drives
air circulation/ppt
patterns
• Warm, moist air rises.
• Adiabatic cooling:
moisture condenses and
falls as rain.
• Cooler, dry air falls back
to surface.
– Rainforests found near
equator.
– Major deserts found near
30o N / S.
• Northern
hemisphere
annual variations
in solar radiation
and temperature
• Adiabatic
temperature
changes: changes in
air temperature which
occur without a gain
or loss of heat energy
– due to
expansion/contraction
of air with altitude
• Air cools as it rises: for dry air ~ 10C/1000
meters
• Slower for moist air ~ 6C/1000 meters
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Uneven atmospheric heating  global air circulation and precipitation patterns
Hadley cells
Ferrell cells
Polar cells
ITCZ – Inter-tropical convergence zone – area over equator where Hadley cells
converge
Solar-Driven Air Circulation
h
Coriolis effect – prevailing wind/water movements
– caused by moving N or S on rotating Earth
• earth is rotating from left to right (eastwards)
– Motion faster at equator than towards poles (think parabola)
• so as one moves toward equator, one enters a faster region from a
slower one
– objects in motion seem to be deflected to left as they are moving slower (to
the right) than their surroundings
• moving away from equator, one enters a slower region from a
faster one
– objects in motion seem to be deflected to right as they are moving faster
(to the right) than their surroundings
• Relative humidity - amount of water vapor
in air relative to the amount it can actually
hold at that temperature
– Affects living things through evaporation and
condensation
RH =
current water vapor pressure
(X 100)
saturation water vapor pressure
• Ocean Currents: movement of large
masses of water
• Driven by:
– Uneven heating
– Steady winds, interrupted by land masses
– Thermohaline differences
• Gyres: large circular movements that
circulate around an oceanic basin
• counterclockwise in southern hemisphere
• clockwise in northern hemisphere
• Impact of Gyres
– move warm waters northward or southward 
warm the climate of the land
– example is the Gulf Stream in the North Atlantic, which
so warms western Europe that palm trees grow in
southern Ireland
– move cool water south
• Example: California Current  cools west
coastal climate
Rain shadow effect
Water in Air
• Evaporation: water converted from liquid to
gas as it enters air
• Energy requiring process (heat)
• Condensation: reverse
• Vapor pressure: pressure water exerts as an
independent component of the atmosphere
• ‘saturated’ atmosphere:
• evaporation = condensation
• Saturation vapor pressure (water vapor capacity
of air) = maximum amount of water that can
enter the atmosphere
• Function of temperature
• Fog: a visible aggregate of tiny water
droplets suspended in the air near the
ground
– Important to many species:
• California coastal redwood
• Soft or maritime chaparral community
– Human uses – fog nets
Saturation vapor pressure: function of
temperature
– As temp. drops amount of water that can be held in
the atmosphere drops – precipitation forms