Latitudinal effects Intensity of insolation is not the same at all latitudes Earth is roughly spherical, so insolation passing through 1 m 2 screen –Illuminates an area = 1 m 2 where surface is perpendicular to radiation (near equator) –Illuminates an area = 1 m 2 x (1/sin45°) = ~ 1.4 m 2 where surface is inclined ~45° to radiation (at 45° latitude) –Illuminates an area = 1 m 2 x (1/sin30°) = ~ 2 m 2 where Earth’s surface is inclined ~30° to radiation (at 60° latitude), Moving from the equator to the poles, insolation per unit area decreases uniformly

Latitudinal effects Intensity of insolation is not the same at all latitudes because earth is roughly spherical Compare what happens to insolation passing through a screen, held perpendicular to radiation path, with an area = 1 m 2 –Where Earth’s surface is perpendicular to radiation (near equator), insolation illuminates an area = 1 m 2 –Where Earth’s surface is inclined ~45° to radiation (at 45° latitude), insolation illuminates an area = 1 m 2 x (1/sin45°) = ~ 1.4 m 2 –Where Earth’s surface is inclined ~30° to radiation (at 60° latitude), insolation illuminates an area = 1 m 2 x (1/sin30°) = ~ 2 m 2 Moving from the equator to the poles, insolation per unit area decreases uniformly

More latitudinal effects Amount of energy radiated to space also varies with latitude, although effect is not as pronounced –Near poles, average temperature = O°C = 273°K –Near equator, average temperature = 3O°C = 303°K –Radiated heat flux is proportional to temperature raised to the fourth power –Taking the ratio of temperatures 273°K/303°K = 0.909, and raising that ratio to the fourth power, one gets 0.68 –Difference in the radiated heat flux on the order of 32% –This compares with the difference in heat received from the sun, which is >50% Polar atmosphere radiates more energy to space than it receives - must balance this deficit

Effects of latitudinal inequities in heating and cooling Differential heating & cooling lead to –Atmospheric circulation or prevailing wind patterns –General oceanic circulation pattern Both move or transport heat from low latitudes to high latitudes, attempting to balance the discrepancy between incoming heat & re- radiated heat

Atmospheric circulation pattern, I The equatorial zone Near equator, energy absorbed exceeds energy radiated to space Air warms, rises, then expands & cools, so water vapor condenses to form clouds and rain Between 10°-15°N & 10°-15° S latitude, have uniformly high temperatures, relatively low barometric pressure, and many low pressure storms We call this region of equatorial lows the doldrums The warm air rises to tropopause, where it separates into N & S directed flow parallel to ground surface

Atmospheric circulation pattern, I The equatorial zone By the time air at tropopause reaches 30°N or S, it has cooled enough that is now more dense than the surrounding air, & so it sinks Sinking air is compressed & heats up Yields warm air masses with low relative humidity at 30°N or S Regions at 30°N or S dominated by relatively high barometric pressure & little precipitation We call this region of subtropical highs the horse latitudes

Atmospheric circulation pattern, I The equatorial zone Between 30° N or S & the equator, air at surface moves from subtropical highs to equatorial lows Consistent winds toward the equator create a zone of intertropical convergence Moving air masses experience the Coriolis effect, creating the northeasterly winds in the northern hemisphere & the southeasterly winds in the southern hemisphere We call these winds the NE & SE trade winds This large-scale pattern of circulating air is the Hadley cell

The Coriolis effect Originates because earth spins on its rotational axis Angular rate of movement to E is constant along a longitude line, but absolute rate of movement to E depends upon latitude At the equator, absolute rate is 1670 km/hr At 30° N (or S), it is 1446 km/hr As a mass of air or water moves from the equator to 30°N or S, inertia of the mass of water or air causes the mass to appear (from a vantage point away from earth) to veer to the right in the northern hemisphere or to veer to the left in the southern hemisphere

Atmospheric circulation pattern, II The temperate zone Between 30° & 60°N or S, air at surface moves from subtropical highs to sub-polar regions of lower barometric pressure Moving air masses experience the Coriolis effect, creating the mid-latitude westerlies Relatively humid air rises in sub-polar lows centered over 60°N or 60°S Some air flows back toward subtropics along the tropopause We call this large-scale pattern of circulating air the Ferrell cell

Atmospheric circulation pattern, III, The polar zone Air rises to tropopause in Ferrell cell; flows N or S Air moving along tropopause toward the poles cools, & eventually becomes dense enough that it sinks over poles This creates a region of dry, cold air centered over each pole called the polar high Between 60° & 90°N or S, air at surface moves from polar highs to sub-polar lows Coriolis effect leads to the polar easterlies This large-scale pattern of circulating air is the Polar cell

Relative amounts of heat transfered Air circulates more rapidly than sea water but water has a higher heat capacity Circulation of sea water, where it is well developed, carries heat from one place to another more effectively than circulation of air Between 0°& 30°N or S, sea water circulation is well-developed, & oceanic currents are responsible for the bulk of the pole-ward transfer of heat At higher latitudes, sea water circulation is less well organized, & atmospheric circulation accomplishes more pole-ward heat transfer

Sea surface temperatures Sea water T varies with position in oceans Amount of insolation absorbed depends upon angle of incidence –With normal incidence, 98% of insolation enters water & 2% is reflected –With oblique incidence, more light is reflected –Warming concentrated at low latitudes Light penetrates no more than 500 m, so therefore only warms surface waters Have surface zone ( 18°C) & deep zone, the lower reaches of the oceans, where water temperatures are low (<3°C)

Vertical temperature gradient Between surface zone & deep zone, T changes rapidly with increasing depth Region with steep T gradient = thermocline zone –Thermoclines common in the tropics & the subtropics –Thermoclines occur seasonally in mid-latitudes –Thermoclines are rare at high latitudes Thermoclines usually create a region of rapid increase in sea water density, called a pycnocline In such cases, the ocean is stably stratified