Refer to figures.
Note: This is a different version of question 502084 which may come up in exams. We have a small amount of feedback for this question, so it may be different to exactly what you see in the exam. Please send us any further exam feedback via the comments, by email to [email protected] or using the exam feedback section of your dashboard, thanks!

POLAR FRONT DEPRESSIONS. These move eastwards along the semi stationary front “Polar front” which is located between 35°N and 65°N (higher latitudes in Summer, lower in Winter).

An air mass is simply a large portion of air in the Earth's atmosphere, defined by where it has been "formed" (a high pressure, stable source region where it develops its initial characteristics) and the track it has taken to get somewhere. For Western Europe, the air masses are classified as T(Tropical), P(Polar) and A(Arctic) - in terms of their thermal qualities - and c(continental) or m(maritime) - in terms of their water content. Note that Artic air is from directly North of Europe, whereas Polar air is from the Polar cell fo the atmosphere, so source regions like Siberia or Northern Canada/Greenland.

The Polar front splits Sub-tropical air (which we refer to as Tropical for European air masses) from Polar air. Therefore, when a Polar front depression forms (in the North Atlantic specifically), the warm sector to the South of the depression is that Tropical air, whereas the rest of the depression is surrounded by the Polar air. Therefore, in this question;

(1) is Tropical (T) air in the warm sector,
(2) is Polar (P) air ahead of the depression (East), and
(3) is the Polar (P) air behind the depression (West).

(4) is a little more complicated. It is the air North of the depression. From the options, we have already narrowed down the correct answer, and that states that the air North of the depression "may be" Arctic (A). This is not always the case, but certainly possible, especially in Winter when Artic air can easily flow down from the North Pole. Often, for a new depression, this air would also be Polar, but later down the life cycle, it can drag Artic air down to it. Also, the question says "may be", rather than "is", which we are happy to consider as being correct.