I'm just starting to study meteorology and keep getting these terms pop up. I can understand that cyclones, in the northern hemisphere are anti-clockwise in direction and are areas of low pressure. However, I cannot get my head around troughs and depressions? Whats the difference and why are there so many terms?
Thanks in advance.
Thanks in advance.
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In Norwegian, we say: Dear children have many names. It is the same for meteorology: we love to give them different names and we don't always agree on the names! ;-)
Any place that has an atmospheric pressure at sea level that is less than 1,013.25 hPa, could be called, a cyclone, a low pressure or a depression - period!
The word, cyclone, comes from the Greek for, a twist. As such, any low pressure that generates a spinning geostrophic wind, can be called, a cyclone. The opposite, a high pressure, is then called a anticyclone.
A depression is simple the French name we give to a low pressure. (French is my mother tongue). But in English, it is mostly used for what we call, in French, un marais depressionaire, which means: a large region of low but not too deep pressure.
A trough should be easy to understand; it is the opposite of a ridge: a "valley" of low pressure between two high pressures.
And now comes the question: When is this or that world used? Well, it is up to the person drawing the synoptic map: some may think it is necessary to write a "L" there, to show the center of a new shallow low pressure center, and someone else thing it is too early or not necessary.
It is the same for clouds. Someone may call this cloud for an alto-cumulus while another person may call it a strato-cumulus. The thing is, it may be a stratiform cloud but to know that, you must know if there is an inversion at altitude and you can't know that from observing from the ground. Likewise, an alto- cloud is a cloud over 6,500 ft AGL and, from the ground you can measure that.
Any place that has an atmospheric pressure at sea level that is less than 1,013.25 hPa, could be called, a cyclone, a low pressure or a depression - period!
The word, cyclone, comes from the Greek for, a twist. As such, any low pressure that generates a spinning geostrophic wind, can be called, a cyclone. The opposite, a high pressure, is then called a anticyclone.
A depression is simple the French name we give to a low pressure. (French is my mother tongue). But in English, it is mostly used for what we call, in French, un marais depressionaire, which means: a large region of low but not too deep pressure.
A trough should be easy to understand; it is the opposite of a ridge: a "valley" of low pressure between two high pressures.
And now comes the question: When is this or that world used? Well, it is up to the person drawing the synoptic map: some may think it is necessary to write a "L" there, to show the center of a new shallow low pressure center, and someone else thing it is too early or not necessary.
It is the same for clouds. Someone may call this cloud for an alto-cumulus while another person may call it a strato-cumulus. The thing is, it may be a stratiform cloud but to know that, you must know if there is an inversion at altitude and you can't know that from observing from the ground. Likewise, an alto- cloud is a cloud over 6,500 ft AGL and, from the ground you can measure that.