Self-study
Discharges of lightning from a volcanic ash cloud occur only when the cloud’s highest point exceeds an altitude of 5 kilometers. █████ ██████████ ██████ █████████████ ████ ████████ ██ ███ ███ █████ █████ ██████ ██████ ███████ █████ ███ ███████ ███ ████████ ██ ███ ███████ ███ ██ ██ ███ █████████ ██ ███ █████ ██ ███ ██████ █████ █████████ █████████ ████ ███ █████████ ██ ███ ████ ████████ █████████ ██ ███ ████████ ██ ███ ███████
Summary
In areas without weather radar, lightning discharge is our only reliable way of finding ash cloud altitude, because we can deduce altitude from the clouds that emit lightning discharge.
Notable Assumptions
There are a few assumptions. Among them:
1) The author is assuming that lightning discharge is the only alternative to weather radar.
2) The author is assuming that lightning discharge is an option in the areas without weather radar.
17.
Which one of the following ██ ██ ██████████ ████████ ██ ███ █████████
a
The highest point ██ ███ ████████ ███ █████ ████ ██████████ ██████ ██ ████████ ██ █ ███████████
The negation of (A) is that not all ash clouds will exceed 5 km. Phrased differently, some ash clouds won’t exceed 5 km. This does not ruin the argument that, in some cases where we do not have weather radar, lighting discharge may be our only option for determining altitude.
b
Lightning discharges can ██ ████████ ██ ████ ███████ ██ █████ ███████ █████ ██ ████████████
This is necessary. If (B) is negated, and lightning discharge is not an option for any of the places where we don’t have weather radar, then this argument is ruined.
c
Weather radar is ██ ████ ████████ ██ ███████████ ███ ████████ ██ ████████ ███ ██████ ████ ██ ██ ██ ███████████ ███ ████████ ██ ███████ ███████
We are not comparing ash clouds to regular clouds, Also, we are not concerned with accuracy.
d
A volcanic ash █████ █████ ███████ █████ ███████ ██ ████████ ██ █ ██████████ ██ ██████ ██ ██ ██ █████ ██████ ██████ ███ █████ ██ ███████ ██████
The author is not trying to discredit the usability of weather radar. She is looking at areas where weather radar isn’t an option, and saying that lightning discharge is our only option in those cases.
e
Lightning discharges are ██ ████ ████████ ███ █████ ████████ ███ ██████ ████ ███ █████ ████████ ███ ███████
We are not comparing small and large ash clouds. If (E) is negated, and large ash clouds have lightning discharge equally or more frequently than small ash clouds, the argument is unharmed.