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18 Cards in this Set
- Front
- Back
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Define: Atmospheric Pressure
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Force per unit area exerted by the weight of the air at a specific level
105.1.1 |
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Define: Station Pressure
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Actual atmospheric pressure at the elevation of the observing station
105.1.1 |
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Define: Mean Sea Level Pressure
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Atmospheric pressure reduced to mean sea level
105.1.1 |
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Give 3 units of pressure measurement, and state the standard atmospheric pressure value for each
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- Hectopascal (hPa), 1013.0, used on weather charts
- Kilopascal (kPa), 101.3, used for general public - Inches of Mercury ("Hg), 29.92, used for altimeters 105.1.2 |
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Explain the relationship between station pressure and elevation
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The higher the station elevation, the lower the pressure
105.1.3 |
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Describe what mean sea level pressure represents on surface weather maps
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Station pressure plus an imaginary column of air extending from station level down to sea level
105.1.4 |
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Define: Isobar (4 points)
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- lines joining points of equal pressure at MSL
- measured in hPa - analyzed on met charts to identify pressure systems - spaced every 4 hPa above and below the 1000 hPa reference point 105.2.1 |
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State the isobaric interval on Canadian surface weather maps
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Drawn at 4 hPa intervals above and below the value of 1000 hPa
105.2.2 |
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Define: Highs, lows, troughs, and ridges and state how they are labelled on weather maps
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Low - region of relatively low pressure, pressure values decreasing towards the center, labelled "L"
High - region of relatively high pressure, pressure values increasing towards the center, labelled "H" Trough - valley of low pressure area, a bulge in the side of a low pressure area Ridge - ridge of high pressure area, a bulge in the side of a high pressure area 105.2.3 |
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Describe the horizontal extent of low and high pressure areas
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- high pressure systems always hundreds of km in diameter
- low pressure systems vary in size from a couple of meters to hundreds of km 105.2.4 |
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Describe the character of air movement within high and low pressure areas and the general associated weather conditions
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High pressure area - clockwise circulation, usually clear weather
Low pressure area - counter clockwise circulation, usually cloudy weather 105.2.5 |
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Define pressure gradient
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Rate of change of pressure with horizontal distance
105.2.7 |
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Identify areas of weak/strong pressure gradient on a surface map
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Strong gradient - isobars are close
Weak gradient - isobars are far apart 105.2.8 |
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Define pressure tendency
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Rate of change of pressure with time at a station
105.3.1 |
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List the terminology used when the central pressure is changing in time with a low or high pressure system
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- deepening
- filling - weakening - building 105.3.2 |
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List the three causes of pressure variations over time
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- movement of pressure systems
- variation in intensity of systems - diurnal variations in pressure 105.3.3 |
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Describe the usual displacement of pressure systems
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West to east
105.3.4 |
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Describe diurnal pressure variations and state their basic cause and their typical range
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- due to day-night atmospheric temperature fluctuation
- two pressure max at 10am/10pm - two pressure min at 4am/4pm - can be +/- 2.5 hPa 105.3.5 |
