Another Final Exam Question This is the 5th of what will probably be a total of 7
questions
Assume that a cloud-to-ground discharge occurs 250 km from one of
the sensors in the National Lightning Detection Network.
Before being used to estimate the peak currents for the strokes in
the discharge, the measured peak B field ampltitudes would be
range normalized to 100 km and a correction for attenuation of the
signal by propagation would be made. Discuss how these are
both done. What relation would then be used to determine the
peak current values?
Final Exam Short Answer Questions
You will most likely be asked to answer 4 or 5 of these (*'d
questions appeared on the Spring 2013 Final Exam)
1. What two parameters of the lightning
return stroke current waveform are responsible for producing high
voltages on a grounded down conductor connected to a lightning
rod? Give typical values for these two parameters.
2*. A cloud-to-ground discharge has a duration
that is usually less than 1 second. Why does the thunder
last much longer than that?
3*. Explain how the Optical Transient Detector
and the Lightning Imaging Sensor on satellites are able to detect
lightning optical signals during the day against the very bright
background of sunlight reflected by the top of the thunderstorm
cloud.
4*. Explain why a series of lightning rods
installed on the roof of a building might adequately protect
against high current amplitude return strokes but not against the
lower current amplitude strokes.
5*. Why would two down conductors in the
lightning protection system sketched below be preferable to just a
single down conductor?
6*. What do you think is the simplest and
most effective way of protecting sensitive home electronics
from damage during a lightning storm?
7. A two station network of magnetic
direction finders would not do a very good job locating
lighting that strikes on the baseline between the two
stations. Why is this? What two ways are there
that the magnetic direction finder data could be used to
improve the accuracy of locations on the baseline.
8. Where are the highest lightning flash
densities found in the world? Is there more lightning
over the land or over the ocean? When during the year
does the peak lightning activity occur?
9. Describe the sequence of events that
occur during a rocket triggered lightning discharge. In
what way(s) is a triggered discharge different from a natural
cloud-to-ground discharge? In what way(s) are the two
kinds of discharges similar?
10. Describe how lightning return stroke
currents can be measured directly and remotely.
Over the weekend I had a look at the Franklin Lecture
delivered at the 2012 Fall American Geophysical Union Meeting
in San Francisco. The
lecture "Lightning and Climate" was delivered by Earle
Williams from MIT. The lecture is packed with
interesting information and ideas. We'll watch perhaps
the first half of the lecture in class on Monday.
