Notes for Sept. 19-21

For the next couple of class sessions we will discuss radiation balance and global temperature patterns, taking us through chapter 4 and chapter 5. The following topics are covered in the textbook, picking up where we left off in last week's notes:

Chapter 4 - Atmosphere and surface energy balance

• Interactions and transformations of radiant energy
• radiation primer
• concept of radiation balance
• lecture notes on radiation balance from Karen Lemke's course
• global distribution of insolation
• transmission of radiant energy
• reflection and albedo
• refraction
• scattering and diffuse radiation
• absorption and conversion to heat
• Transformations of heat energy
• sensible heat and latent heat
• conduction, convection, advection
• longwave radiation and the "greenhouse effect"
• Global average shortwave and longwaveradiation balance
• Local daily radiation balance and temperature cycle
• Global patterns of net radiation, latent heat, and sensible heat
• Clear-sky net radiation and the role of cloud forcing
• The urban environment as a heat island

• Factors controlling global temperature patterns:
• Latitude
• Altitude
• Cloud cover
• Land-water contrasts, continental vs. maritime conditions
• role of specific heat
• latent heat of evaporation
• light penetration through water/dispersal of radiant energy through greater depth
• advection/circulation: advection of heat by global ocean currents
• temperature trends associated with marine-continental contrasts
• Isotherm maps, global temperature distributions and seasonal patterns of change (among other things, notice the location of the "thermal equator" in figs. 5-11 and 5-13)
• Comparison of northern and southern hemisphere patterns
• Spatial pattern of maximum temperature ranges


Temperature is largely a function of radiation balance, the difference between what comes in and what goes out; as we will see, there are strong latitudinal gradients in net radiation, with a surplus near the equator and a deficit near the poles, and this in turn causes a net heat flow from low latitudes toward high latitudes. This ultimately is what drives the general circulation of the atmosphere and oceans, although the way in which it leads to the generation of winds and ocean currents is not nearly so straightforward as you might think.

As we will see (and as we have already mentioned in class once or twice), the temperature patterns are not strictly a function of latitude. Land-water contrasts play a large role, and in that context remember that the northern and southern hemispheres are almost mirror images of each other: the northern hemisphere is dominated by land masses in the middle and high latitudes, and the pole is open water surrounded by continents. The southern hemisphere is mostly water, but has a land mass sitting at the pole and surrounded by ocean. In addition to land-water contrasts, there is also a strong influence due to the nature of the ocean currents, which in turn are driven by wind patterns. This accounts for the fact that England and northern Europe, as well as Pacific northwestern Canada and coastal Alaska, have fairly temperate climates although they are at high latitudes.

These patterns can be seen in satellite images and maps showing sea-surface temperatures, among other things, and before long we will begin looking at some of the more complex phenomena affecting the general circulation and global weather patterns.