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Latitudinal Heat Imbalances
Current Weather
Finish Surface Energy Balance
Controls of Air Temperature
Tropics vs. Middle and High Latitudes
Mechanisms of Polar Heat Transport
For Next Class: Read Chapter 6
Thin Ice Screening at 7 PM on September 2
Bowen RatioBowen ratio = (sensible heating)/(latent heating)
High Bowen ratio implies more sensible heating than latent heating (i.e., deserts)
Low Bowen ratio implies more latent heating than sensible heating (i.e., oceans or water bodies)
© AMS 3
Heat Imbalance: Atmosphere vs. Earth’s Surface
Simplified Surface Energy Balance
NET R =
+SW (insolation)
–SW (reflection)
+LW (infrared)
–LW (infrared)
Figure 4.16
Global NET Radiation
Figure 4.17
Describe the spatial patterns: which areas have the highest net radiation? Why? The lowest? Why?
Latitude and Temperature
Figure 5.4
January Temperatures
Figure 5.14
July Temperatures
Figure 5.17
Global Temperature Ranges
Figure 5.19
Where is the coldest location in the world likely to be in January? Why?
In July? Why?
Which location has the greatest annual temperature range? Why?
Temperature
General circulation of the atmosphere and ocean is driven by latitudinal heating imbalances (i.e. surplus in tropics and deficit in polar regions)
12© AMS
Heating Imbalance: Tropics vs. High Latitudes
Poleward heat transport brought about by• Air mass exchange• Storm systems• Ocean circulation
13© AMS
Heating Imbalance: Tropics vs. High Latitudes
Heat Transport by Air Mass Exchange• Air Mass: huge volume of air covering thousands
of square kilometers that is relatively uniform horizontally in temperature and humidity
Properties depend largely on characteristics of source region
14© AMS
Source regions of air masses that regularly invade North America
15© AMS
Heating Imbalance: Tropics vs. High Latitudes
Heat Transport by Storms• Acquisition and subsequent release of latent heat
in migratory storm systems transports heat to the poles
• Tropical storms and hurricanes are greater contributors to poleward heat transport than ordinary middle latitude storms
Blizzard of 1993
Developed in association with an extremely amplified Rossby Wave. Note the strong cold front in Honduras!
18© AMS
Heating Imbalance: Tropics vs. High Latitudes
Heat Transport by Ocean Circulation• Contributes to poleward heat transport via wind-
driven surface currents and the deeper thermohaline circulation
Surface water that is warmer than the overlying air is a heat source for the atmosphere
Surface water that is cooler than the overlying air is a heat sink for the atmosphere
19© AMS
Heating Imbalance: Tropics vs. High Latitudes
Heat Transport by Ocean Circulation• Thermohaline
circulation: density-driven movement of water masses, traversing the lengths of the ocean basins
Also known as the meridional overturning circulation (MOC)
The Gulf Stream
Figure 5.10
Sea-Surface Temperatures
Figure 5.11