DEPRESSION, in meteorology, used to de scribe that form of pressure distribution which is represented by isobars (q.v.) having the form of a letter V and enclosing an area of low pressure. The central line, through the apex of the V's, is called the trough. The motion of the system is normally eastwards with the line of the trough remaining parallel to its earlier direction. If the trough runs north to south the winds in front of the V are largely from the south, and at the rear of the V are largely from the north. The change of wind experi
enced as the trough passes is often destructively sudden, and is usually accompanied by increased rainfall. (See SQUALL.) In general the weather sequence resembles that consequent on the passage of a circular depression and a V may usually be inter preted as a steeper gradient projection of a cyclonic system. The isobaric form contrasting with a V is termed a "wedge."