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 re-radiated 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
• 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
saturation water vapor pressure (X 100)
• 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