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A trough is an elongated area of low pressure (rising air). It can be identified as an area on a local synoptic chart where the isobars form a 'finger' coming out of a low pressure system or into a high pressure system.
On a global scale, the equatorial trough is an extensive area of low pressure that extends right around the earth in the equatorial regions. It is the result of the solar heating of the equatorial regions causing the surface air to rise.
A ridge is an elongated area of high pressure (sinking air). It can be identified as an area on a local synoptic chart where the isobars form a 'finger' coming out of a high pressure system or into a low pressure system.
On a global scale, the subtropical ridge is an extensive area of high pressure that extends right around the earth north and south of the equatorial regions. It is caused by air sinking back to the surface after it has risen at the equatorial trough.
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