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 Ratio
Bowen 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)
Heat Imbalance: Atmosphere vs.
Earth’s Surface
© AMS
3
Simplified Surface Energy Balance
NET R =
+SW (insolation)
–SW (reflection)
+LW (infrared)
–LW (infrared)
Figure 4.16
Global NET Radiation
Describe the spatial patterns: which areas have the
highest net radiation? Why? The lowest? Why?
Figure 4.17
Latitude
and
Temperature
Figure 5.4
January Temperatures
Figure 5.14
July Temperatures
Figure 5.17
Global Temperature Ranges
Figure 5.19
Temperature
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?
General
circulation of the
atmosphere and
ocean is driven by
latitudinal heating
imbalances (i.e.
surplus in tropics
and deficit in polar
regions)
Heating Imbalance: Tropics vs. High
Latitudes

Poleward heat transport brought about by
• Air mass exchange
• Storm systems
• Ocean circulation
© AMS
12
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

© AMS
Properties depend largely on characteristics of source
region
13
Source regions of air masses that regularly
invade North America
© AMS
14
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
© AMS
15
Blizzard of 1993

Developed in association with an extremely
amplified Rossby Wave. Note the strong cold front in
Honduras!
Heating Imbalance: Tropics vs. High
Latitudes

Heat Transport by Ocean Circulation
• Contributes to poleward heat transport via winddriven surface currents and the deeper
thermohaline circulation


© AMS
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
18
Heating Imbalance: Tropics vs. High
Latitudes

Heat Transport by
Ocean Circulation
• Thermohaline
circulation: densitydriven movement of
water masses, traversing
the lengths of the ocean
basins

© AMS
Also known as the
meridional overturning
circulation (MOC)
19
The Gulf
Stream
Figure 5.10
Sea-Surface Temperatures
Figure 5.11