Question 1

True or False: as a parcel of air rises through the atmosphere it expands and cools, and as a parcel of air sinks it is compressed and warms.

Accepted Answer

True This adiabatic behaviour — cooling on the way up, warming on the way down, purely from the change in pressure with height rather than any heat being added or removed — is the starting point for understanding atmospheric stability. Everything about whether a sky stays calm or builds into a thunderstorm follows from how a rising or sinking parcel's temperature compares to the air around it.

Question 2

When taking a visual position fix using two compass bearings of charted objects, why is a third bearing often taken if a suitable object is available?

Accepted Answer

Two bearings give a position at their intersection, but a third bearing forms a small triangle ("cocked hat") where the three position lines meet — the size of this triangle gives a visual indication of the likely accuracy of the fix and any compass error, helping the navigator judge how much to trust the result A two-bearing fix gives a single intersection point with no indication of error; a third bearing reveals a "cocked hat" whose size is a practical, visual guide to the fix's reliability.

Question 3

Using the "rule of twelfths" to estimate the height of tide between low water and high water, what fraction of the total tidal range is gained during the first hour after low water?

Accepted Answer

1/12 of the range The rule of twelfths approximates the rise/fall over each hour of a (roughly) 6-hour tide as 1, 2, 3, 3, 2, 1 twelfths — so the first hour accounts for 1/12 of the total range, the slowest rate of change near the turn of the tide.