HIGH AND LOW PRESSURE SYSTEMS

HIGH AND LOW PRESSURE SYSTEMS1

9 PM SURFACE WEATHER CHART2Isobars-lines of equal pressure Barometric pressure, measured from barometers at various weather stations and various heights by using weather balloons

LOW PRESSURE SYSTEMS

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LOW PRESSURE SYSTEMS

4A low is where the pressure is lower than the surrounding areaMove counter-clockwise (cyclonic) in Northern Hemisphere.Lower level convergence (air coming together) upper level divergence (moving away)

LOW PRESSURE SYSTEMS

5As air converges at the surface, it is forced up along with moisture and clouds are formedThis is why low pressure is often associated with bad weatherThis surface convergence also leads to frontal systems. Frontal systems are divisions of temperatures, along with wind shifts.Frontal systems include cold fronts, warm fronts, occluded fronts and stationary fronts.LOW PRESSURE SYSTEMS6Due to the cyclonic nature of lows, cold air is likely found to the north and west while warm moist air is generally found to the south and east of the low pressure center.

LOW PRESSURE SYSTEMS

7Examples of semi-permanent low pressure systems- Sea breeze/land breeze

LOW PRESSURE SYSTEMS

8Semi-permanent systems occur in the Southwest U.S. desert as well as MexicoHeat from the sun during the day creates low pressureOften dust devils are created (TURBULENT!)

LOW PRESSURE SYSTEMS

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LOW PRESSURE SYSTEMS10Hurricanes are extreme low pressure centers--Need to have very warm waters-- Winds aloft (upper atmosphere) need to be calm--Need an existing low or disturbance--Occurs on water due to absence of friction--Tight pressure gradient--Low stacks from surface to 300 mbEXTREME LOW11

HURRICANE KATRINA12HIGH PRESSURE SYSTEMA high is where the pressure is higher than the surrounding area also called an anticyclone.Air moves in a clockwise direction in Northern HemisphereIn a high pressure area, the air is descending. Convergence aloft (upper air) and divergence at the surface.As the air descends it warms and generally keeps clouds from forming.Highs are generally associated with good weather. 13Semi permanent high over us is called the Bermuda High (Subtropical High).HIGH PRESSURE SYSTEMS

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3-D CYCLONES15

CONVERGENCE AND DIVERGENCE16

SURFACE WEATHER CHART17

LABEL THE HIGH AND LOW!18

QUESTIONS???

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