Both at the surface and also in the top atmosphere, meteorologist constantly refer to "high" and also "low" pressure systems. However, we look at them indigenous two various perspectives.

You are watching: On a map a line indicating constant pressure is called:

At soil level, we look for air push values as they relate come "sea level" which provides us v a picture of the fads at the surface. Utilizing sea level (elevation = zero) together the typical baseline we room able to make an interpretation of different pressure values in between stations. So, ~ above all surface charts, the key of the "surface" is taken into consideration zero feet.

The lines drawn on surface charts connecting areas of equal push are called isobars. "Iso" method equal and "bar" is the unit whereby we measure pressure. Therefore, an isobar is a heat representing the location where the press is same (the same) follow me that line.

Typical levels of consistent pressure charts through each mirroring different aspects of the atmosphere.

When we study the atmosphere yet the altitude at which any particular pressure value occurs will differ from reporting terminal to reporting station.

These transforms in altitude represent various air densities in the atmosphere. Remind that as air temperature decreases the air's thickness increases.

This means the altitude whereby any details pressure occurs will certainly be lower in the environment when the air is colder. Conversely, higher air temperatures an outcome in lower densities which increases the altitude of press levels.

This is why, as a rule, the atmosphere decreases in elevation from the equator toward the poles.

Therefore, we attract lines on constant pressure chart to represent the altitude in ~ which that details pressure occurred. These lines are referred to as isoheights, present of same height.

By convention meteorologists simply refer to isoheight lines as 'contours'. This lines room analogous come topographic charts. In essence, top air charts display the setting in three dimensions.

By spring at this contours us observe trends of higher heights (called ridges) and lower heights (called troughs). These ridges and also troughs drive the we experience at the surface.

Learning Lesson: Pie in the Sky


Wind flow from a ridge towards a trough is to decrease in height above the surface. Vice versa, wind flow from a trough right into a ridge is boosting in height.

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Between the colder, more dense air and also the warmer, less dense air is the place of the greatest adjust (gradient) in heights of any certain pressure level.