Air Temperature Data The Controls of Temperature Outline for Lesson 5 2/11/03 World Distributions of Temperature

Chapter 3 Temperature Daily mean Daily temperature range Monthly mean Annual mean Annual temperature range. Temperature is one of the most basic elements of weather…. Mean temperatures are good for making comparisons; temperatures ranges give us an idea of extremes which are important to understand the weather and climate of an area.

Death Valley, California Highest accepted temperature in the Western Hemisphere (57°C/134°F)………why? -Very low elevation (53m below sea level) -It is a desert -Mountains to the west shield Death Valley from the moderate, moist Pacific air. Few clouds.

Isotherms: Lines of Equal Temperature

Given equal amounts of radiation it is the controls of temperature that determine what the temperature average and range will be for an area. Recall from Chapter 2 that latitude, and the corresponding sun angle, determines in general what areas will be warm (lower latitudes, i.e. the tropics) or cool (higher latitudes, i.e. the poles). However, not all lines of latitude have the same temperature profile. Therefore, latitude is not the only factor that controls temperature. What are the other controls of temperature ? The Controls of Temperature

Differential heating of land and water Ocean Currents Altitude Geographic position Cloud cover and albedo Controls of Temperature Include:

1. One reason water heats more slowly than land is that it is a mobile medium. The ability to convectively mix allows heat to be distributed through more volume than conduction. Incoming solar radiation heats the water and land but different energy transfer processes contribute to different rates of heating between land and water. Convective heat transfer allows for deeper mixing (more efficient) hot cold Conductive heat transfer is shallow (less efficient) watersolid Differential Heating of Land and Water

watersolid The opacity of water is less than that of land. Therefore, radiation is able to penetrate deeper into water which more evenly distributes the radiative energy. 2. Solar radiation only reaches a few centimeters into land while, depending on the clarity, solar radiation can reach several meters into water. The result is that a greater volume of water is heated at a slower rate. The smaller volume of land however attains higher temperatures. 0 5m depth Differential Heating of Land and Water

3. Specific heat: the heat (heat energy) need to raise the temperature of one gram of a substance 1° C. The higher the heat capacity the more energy needed to raise the temperature of that substance.

4. Evaporation is greater from water than land. A change of phase from liquid to gas (evaporation) requires energy that does not contribute to a rise in temperature. Conversely when gas is converted to a liquid (condensation), or liquid to solid (freezing) energy is liberated. Graph of the temperature of a water versus heat added. The water starts out in the form of ice. As heat is added its temperature increases linearly until the ice reaches the melting point. Additional heat added does not raise the temperature of the sample but, instead, causes some ice to melt. Once all of the ice has melted, additional heat goes into raising the temperature of the water. A similar phenomenon occurs when the water vaporizes. ice water steam

Convective heat transfer in water Opacity of water High Specific Heat of water Energy of Evaporation/Condensation of water all contribute to the fact that water warms and cools more slowly than land, which can greatly effect the climate and daily weather. How?

Water tends to moderate the temperature of a region. Other factors (i.e. latitude) being equal, a city near water will experience warmer winters and cooler summers than a city inland. Same latitude, different proximity to water

The Southern Hemisphere is comprised of nearly 80% water, ~20 % more than the Northern Hemisphere The difference in heating between land and water can also explain the different latitudinal heating between the Northern and Southern Hemisphere. Its all a matter of scale

Because the Northern Hemisphere has more land than the Southern hemisphere it has a steeper slope than the Southern Hemisphere.

The prevailing winds drive the surface ocean currents. The general circulation of the atmosphere is in response to the unequal heating of the Earth by the Sun. There is an energy surplus in tropics and a deficit in the Mid Latitudes and Poles. Yet the Tropics are not getting progressively warmer nor are the Mid Latitudes or Poles getting colder….. Ocean Currents

OK, we know that land heats up and cools down much faster than water, and we know that the prevailing winds and ocean currents help to maintain the earth’s energy balance. Which contributes more to the transfer of energy. Wind currents or ocean currents?

Air CurrentsOcean Currents 75 % 25 % Global Heat Transport The exchange of energy by the winds and currents equalizes the latitudinal imbalances. Winds can move much faster (vertically and horizontally)

Ocean Surface Currents Mean Jan Temp (°C) ~0°C ~4.8°C Warm ocean surface currents effect the climate in middle latitudes whereas cold ocean currents moderate tropical regions.

Monthly mean for Rio de Janeiro, Brazil and Arica, Chile. Both cities are coastal and both near sea level. Ocean Currents can effect average temperature

Hot (28°C) Cold (9°C) Ben Franklin’s depiction of the Gulf Stream The Gulf Stream transports heat from the lower latitudes toward the North Pole.

How Altitude Affects Temperature Height (km) Guayaquil (alt:29m ) Quito (alt: 2800m )

Recall that the lapse rate is –6.5°C/km. An altitude difference of 2.8km should correspond to a temperature change of ~18°C. 2.8km x (-6.5 °C/km)= 18.2°C Yet the difference is only 12.2°C….why? An increase is elevation also increases the amount of incoming radiation because there is less atmosphere to reflect or absorb the incoming radiation. As a consequence, mountain locations experience wide daily temperature ranges.

Geographic Position Eureka experiences ocean breeze whereas New York City mostly land breeze. windwardleeward Mountains act like a barrier. Most of the moisture is left on the windward side (Seattle). Coastal AreasMountain Barriers

Cloud cover and albedo Cloud cover can be important because many clouds have a high albedo. During the day clouds reflect solar radiation. Temperatures are lower than if there were clear skies. During the evening, clouds absorb the terrestrial radiation radiation. Temperatures are higher than if there were clear skies.

The Daily cycle of temperature at Peoria, Illinois for 2 July days. On the clear day there is a wider spread in temperature than on the cloudy day. Cloud cover and albedo

In Rangoon, the highest monthly mean temperature occurs during April and May rather than July and August (as is the case in most locations in the Northern Hemisphere). The reason is that during the summer months the extensive cloud cover increases the albedo which reduces the incoming radiation Competing Factors in Temperature Control

World Temperature Distributions World mean sea level temperature in January in °C. World mean sea level temperature in July in °C. isotherms trend east to west decreasing temperature toward the Poles “hot” and “cold” spots” migrate with the suns vertical rays

The hottest and coldest places are over land. Warm ocean currents moving to the Poles warm the air. Equatorial bound currents Help cool the air. World Temperature Distributions

World mean sea level temperature in January in °C. World mean sea level temperature in July in °C. Equatorial temperatures do not fluctuate significantly (there are no seasons). 25 °C -40 °C 10 °C Middle and higher latitudes have much stronger seasonal signals.