Download Investigation 7A and 7B

Investigation 7A: Precipitation Patterns
The purpose of investigation 7A is to describe different mechanisms leading to the formation of
clouds and precipitation in low pressure systems, locate areas of precipitation based on weather radar
depictions, and indicate the general relationship between the uplift of air and the formation of clouds
and precipitation. Questions 1-6 were answered in the introduction to this investigation. Then, Figures
1, 2, 3, and 4 were analyzed in order to answer questions 7-21.
There are many factors that contribute to rain and snow fall. The uplift and cooling of air by
expansion is one of the main acts that forms clouds and precipitation. An upward branch on convection
current, uplift of air along the windward slopes of a mountain range, or convergence of surface winds
may also play a part in clouds and precipitation. A front is a line drawn on a surface weather map that
marks narrow transition zone between air masses differing in density. A huge volume of air is called an
air mass. A mass of cold, dry air is denser than a mass of warm, humid air. Ascending unsaturated air is
compressed, cooling at about 10 degrees Celsius per 1000 meters of ascent. The warmer air rising above
the frontal surface expands and cools as it ascends, and its relative humidity increases. If saturation is
achieved, clouds develop. The rain or snow comes from those clouds.
I would have my high school mathematics students analyze Figures 1, 2, 3, and 4 to investigate
precipitation patterns. After speaking briefly about how clouds form and why rain happens, students
would take the class period to look at the different maps in order to draw conclusions about
precipitation.
Investigation 7B: Doppler Radar
The purpose of investigation 7B is so describe aspects of the actual wind that are detected by
Doppler radar, determine the speed of the wind toward or away from the radar site, and to construct
the wind pattern as detected by Doppler radar. Figures 1a and 1b were analyzed in order to answer
questions 1-11. Red and green pencils were used to denote certain things on Figure 1a and Figure 1b.
Figures 2, 3, and 4 were used to answer questions 12-26.
The Doppler effect is the change in frequency of a sound or electromagnetic wave reaching a
receiver when the receiver source is moving relative to one another. A frequency shift occurs when a
radar signal is reflected from a moving target. If the moving target is moving toward the radar, the
reflected signals returned to the radar have a higher frequency then if the target was stationary. If the
target is moving away from the radar, then the returned signal’s frequency is lowered. Doppler radar is
used in order to detect severe weather conditions such as a tornado. Doppler radar can only detect
motions that are directly toward or away from the radar. In the example with the mesocyclone, the
Doppler radar senses no wind speed at the points were the wind path blows perpendicular to the radar
beam. Doppler radar is sensitive enough to detect microwave energy returned from dust, insects, and
temperature/humidity changes in the air providing a clear air return.
Typically, students seem to be very interested in tornados and thunder storms. I would have
students do the Figure 1a and 1b exercise to understand Doppler Radar. Then students can use
geometry to figure out how far away the tornado is or the circumference of the tornado. Then, students
can analyze Figures 2, 3, and 4 in order to make inferences about weather conditions and Doppler radar.