When AM radio waves travel from a transmitter to a receiver far away, they
have to bounce off the underside of the ionosphere to reach the receiver.
The waves lose some of their energy each time they are reflected. Although
this is normally a small amount, less than 5%, it can be several times
larger than this during a solar storm. When solar flare erupt, the radiation
arrives at the Earth 8.5 minutes later and ionizes the D-layer located
just below the ionosphere closest to Earth. Radio signals passing through
this layer and bouncing off the ionosphere higher up, have some or all
of their intensity absorbed.
Objective
Students will calculate the ending percentage of radio wave strength at
the receiving station.
Introduce the concept of radio waves in the ionosphere. Be sure to include
a discussion about the waves reflecting off of the ionosphere layer and
the surface of the Earth, and the impact of a solar storm on these waves.
A blank transparency of the student page may be helpful for student visualization.
Explain that the radio waves normally lose about 5% each time they cross
the D-layer just below the ionosphere. During solar storms, the radio waves
can lose as much as 30% with each crossing of the D-layer.
Provide students with the examples given, and check for their understanding.
Allow sufficient time for the students to calculate the percentages, and
to determine the remaining signal strength at the receiver's location.
Discuss the loss of wave strength and how that may affect communication.
Some possible responses may include; mobile phone connections, AM radio
station signals, and military communications.
This lesson can conclude after the discussion, or the following additional
procedure may be performed: Group the students into pairs. Have them
measure the given angles. Challenge each pair to vary the angle of the
bounce to determine if there is an angle that will provide a stronger signal
strength. For example, adjust the angle from the transmitter to a smaller
degree, creating an isosceles triangle. This will change the number of
bounces to a fewer number of triangles, instead of the 8 given in the first
example. By decreasing the number of bounces, the signal strength is stronger
at the receiver's location. Adjusting the angle to greater than the original
will increase the number of bounces required, and in turn decrease the
signal strength at the receiver.
Example for one bounce with two passes through the
D-layer
Normal 5% loss:
100% x 0.95 = 95%
95% x 0.95 = 90% (Final)
Solar Storm 30% loss:
100% x 0.70 = 70%
70% x 0.70 = 49% (Final)
Conclusions
Students should learn about real everyday situations that occur with our
radio systems. From their discussion, they should address that during a
solar flare, the radio waves lose a great amount of strength. Students
should realize that solar flares greatly affect daytime long distance communication.
Return to the Table of Contents
This activity was developed by the NASA, IMAGE/POETRY
Teacher and Student Consortium.
For more information, and a list of other resources, visit
Introduction