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

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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