The in class lecture of Wednesday, February 11th dealt with the "Impact of Clouds on the
Radiation Balance" on Earth. Dr. Takle discussed how the variation in cloud existence,
size, altitude, and density in locations around the world have a significant impact the
temperature.
The lecture began with a discussion of how the temperature of a body and its energy
radiation are related. Energy radiated is proportional to the temperature raised to the
four power. Therefore the warmer the body, the more it radiates.
For the remainder of the class, satellite images of longwave radiation (in W/m) for
different situations. Images of diurnal range of clear-sky for April 1985 shows that the
deserts of the earth have the largest range in temperature. This is partly due to absence
of clouds, and mostly due to the absence of water vapor (most important greenhouse gas) in
the air. Water vapor radiates energy BACK to earth at night, keeping the surface
temperature from dropping significantly. When clouds are included for the same satellite
images, the range of temperatures decreases.
Dr. Takle also went to one of the hotlink to show the class
some up to date images of the earth. Some of these includes the current cloud cover. The
impression I got was that clouds are very difficult to measure and model, but are
extremely important in daily climatic events.
--- Matt Bryner
Today in class we covered the impact of clouds on radiation balance. We primarily
focused on long wave radiation. First, an equation was given, which showed the important
fact that the amount of energy radiated by something is proportional to the temperature it
was raised to the fourth power. This, in a simplified manner, demonstrates the way that
satellites work.
For most of the period, we observed and discussed satellite images. One displayed
diurnal (daytime vs. nighttime) ranges of the earth, ignoring cloud cover. The highest
energy levels were found to be in desert regions, due to the great fluctuation of
temperature between the hot days and cool nights. The tropic regions, on the other hand,
had low energy levels, as there is not a great temperature flux. This is because of the
high level of humidity in these regions. The vegetation releases large amounts of water
vapor (the most important greenhouse gas), which absorbs energy and re-radiates it to the
ground (desert regions have little water vapor in the air). We then examined diurnal
ranges with cloud cover. Here, the areas of high energy were greatly reduced. This shows
that clouds radiate a significant amount of energy back to the ground. We also observed
maps showing the variability in outgoing long-wave radiation from year to year. This
showed that in the summer months, there is very little variation between years, while
during the winter months, there is a large change, especially in the Pacific Ocean region,
due to the influence of El Nino storms.
--- Shane Brockshus
Pre-Class Preparation
Objectives Class images
