Topic Author
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Joined: Thu Dec 30, 1999 5:04 pm

HELP: A Geography Question

Sun Mar 11, 2001 6:02 pm

I am going to have a geography exam!!

My question: what is the difference between "trough of low pressure" and "cold front", besides their appearance on the synoptic chart.

Can anyone help me to answer it!
Thanks a lot for answering me!
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Joined: Wed Sep 27, 2000 8:17 am

RE: HELP: A Geography Question

Sun Mar 11, 2001 7:00 pm

Geography? Not exactly.

Well, anyway, a trough of low pressure is an elongated area of lower pressure.

A cold front is associated with an area of low pressure. It marks a steep boundary where cold is replacing warm (Warm and moist air is found ahead of the front while cool and dry area is found behind). Along the front, the warm, humid air often rises very high due to the sharp angle of the boundary, and condenses into towering cumulus or cumulonimbus clouds that have the potential to create thunderstorms. A narrow band of heavy precipitation, often in the form of rain showers, usually accompanies the front, often, but not always a short distance behind the frontal boundary.

RE: HELP: A Geography Question

Sun Mar 11, 2001 7:33 pm


Pretty much correct! Meteorology is included in most Geography syllabuses these days.

A cold Front is dynamic, and therefore moves across latitude and longitude; a trough is mostly stationary, with winds blowing anticlockwise and towards the centre.

The latter appears as an elongated stretch of concentric circles (the circles being isobars).

We get both in the UK, and frequently, and thus we get some of the most depressing weather (apart from Ireland and Iceland Big grin )
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Joined: Wed Sep 27, 2000 8:17 am

RE: HELP: A Geography Question

Sun Mar 11, 2001 8:37 pm

Capt---You are correct, but it is confusing, because "trough" seems to be used in two related, but slightly different ways.

A trough of low pressure is symbolized by a dashed purple line on most weather maps. It is connected to the area of low pressure. The cold front is also stemming from the center of low pressure, symbolized by a blue line with triangular barbs indicating the direction of movement. Inclement weather can occur with both, but it tends to be more severe with a cold front. In a sense they are both extended areas of low pressure, but a cold front signifies a definite boundary between warm and cold air.

Isobars are just lines connecting areas of equal pressure. Yes, you do see concentric circles radiating out from an area of low pressure or high pressure for obvious reasons. The isobars help you to identify how strong/widespread the area of low/high pressure is.

A trough can also be used to describe a dip in the jet stream, which allows cooler air from the North to extend further south. Ridges (when the jetstream bows to the north) and troughs occur in a fairly regular pattern along our polar jetstream. The constant variation in the speed, direction and location of wave formations along the jetstream leads to much of the variety to our weather patterns.

If anyone has more info, I'd appreciate it, because troughs have always confused me, especially with their "double-meaning"
Topic Author
Posts: 244
Joined: Thu Dec 30, 1999 5:04 pm

RE: HELP: A Geography Question

Mon Mar 12, 2001 5:41 pm

First of all, thanks a lot of answering my question. I become more clear about the idea.  Smile/happy/getting dizzy
I have just sat the geog exam, fortunately, they didn't ask the difference between the two.  Smile/happy/getting dizzy
However, it seems that the idea between TROUGH and COLD FRONT is still quite confusing as both are at the convergence of a warm moist air current with a dry cold current.
Besides, when I read my book, I saw the axis of the through connect with the cold front, which is originated from a temperate cyclone. it seems to make the case more confusing.

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