EQ: What are high and low pressure centers? Classroom Unsquared

Remember air masses? They are large domes of air with a certain temperature and moisture content. They are several miles thick and hundreds of miles wide. Ground Hometown, USA Air mass Where would the air pressure at the ground be the highest? H Yes, where the air mass is thickest, in the center. The “swimming pool” of air is deepest there, so the weight of the air compresses the air more at the surface in the center. Compressed air wants to push outward, so a High Pressure center occurs!

How would we draw a high pressure center on a map? We would use isobar lines, lines of equal pressure. Wherever an isobar is drawn, that tells you the pressure at that location. Here is a Barometric Pressure Map. Pressure is measured in millibars, or mb for short. 1,010 mb is about normal pressure. A H C D If you were standing at each of the lettered locations, what would the air pressure be? A ? B ? C ? D ? 1016 mb 1020 mb 1014 mb 1009 mb B

Here are 2 air masses side-by-side. Which direction or directions will the surface winds blow in these air masses? Show with arrows. Ground Hometown, USA Air mass H H Yes, the winds will blow outward from the Highs, because the compressed air creates a force that pushes air outwards. What would we call the area between the Highs where the air masses are less thick? L A Low Pressure Center Which direction will air move at the center of the Highs and Low? Air will sink in the Highs and rise in the Low to form convection cells.

Remember the Coriolis Effect cause by the Earth’s rotation? What effect will that have on the winds blowing in the Highs and Lows? Here are a High and Low pressure center on a Barometric Pressure map. We know that air flows outward from the High and inward to the Low. But the Coliolis Effect makes the winds turn right in the northern hemisphere. So… HL So winds blow clockwise and out around Highs and counterclockwise and in around Lows!