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Ch 09 - Atmospheric Circulation and Weather Systems11th Fundamentals of Physical Geography
Atmospheric Pressure
What is 'Atmospheric Pressure', and what instruments are used to measure it?
What is 'Atmospheric Pressure', and what instruments are used to measure it?
DEFINITION
Atmospheric Pressure
- Definition: The weight of a column of air contained in a unit area from the mean sea level to the top of the atmosphere.
- Standard Value: At sea level, the average pressure is 1,013.2 millibars (mb).
- Measurement Instruments:
- Mercury Barometer
- Aneroid Barometer
- Key Characteristic: Pressure is always highest at the Earth's surface (due to gravity compressing the air) and decreases with altitude.
Prism Memory Hook
Sea Level Standard: 10-13-2 (1,013.2 mb)
Standard Atmosphere Data
At 10 km altitude (the cruising height of commercial jets), how do the atmospheric pressure and temperature compare to sea level?
At 10 km altitude (the cruising height of commercial jets), how do the atmospheric pressure and temperature compare to sea level?
DATA
Standard Atmosphere Vertical Profile
- Sea Level Baseline: Pressure is ~1013 mb and average temperature is 15.2°C.
- At 5 km Altitude: Pressure halves to ~540 mb, temperature drops to -17.3°C.
- At 10 km Altitude: Pressure drops to roughly one-fourth, at 265 mb, and temperature plunges to -49.7°C.
- Significance: This rapid decrease in pressure and temperature dictates aviation engineering and upper-atmospheric circulation.
Prism Memory Hook
At 10km up, pressure is a quarter and temp is minus fifty.
Vertical Variation of Pressure
If pressure decreases rapidly with height, creating a strong upward gradient, why don't we experience constant, powerful upward winds?
If pressure decreases rapidly with height, creating a strong upward gradient, why don't we experience constant, powerful upward winds?
CONCEPT
Vertical Pressure Gradient and Hydrostatic Balance
- Rate of Decrease: In the lower atmosphere, pressure drops roughly 1 mb for every 10 meters increase in elevation.
- The Paradox: The upward vertical pressure gradient force is mathematically much stronger than horizontal gradients.
- The Balancing Act: We do not experience violent updrafts because this strong upward force is almost perfectly balanced by an equal and opposite Gravitational Force pulling the air down.
- Result: This state of equilibrium is called Hydrostatic Balance.
Prism Memory Hook
Gravity anchors the sky.
Also in this chapter
61 more cards to study in Prism
- 4Isobars: Low vs. High Pressure Systems
- 5Forces Driving Surface Wind
- 6Pressure Gradient Force (PGF)
- 7Frictional Force
- 8The Coriolis Force: Directional Deflection
- 9Coriolis Force: Magnitude by Latitude
- 10Coriolis Application: Aviation & Artillery
- 11Geostrophic Wind
- 12Convergence and Divergence
- 13The Rotating Tank Experiment
- 14Drivers of General Circulation
- 15World Pressure Belts
- 16The Hadley Cell
- 17Ferrel and Polar Cells
- 18Land and Sea Breezes
- 19Mountain and Valley Winds
- 20Katabatic Winds
- 21Adiabatic Warming (Chinook/Foehn Winds)
- 22Air Masses
- 23Air Mass Source Regions
- 24The Mid-Latitude Source Gap
- 25Classification Codes of Air Masses
- 26Fronts and Frontogenesis
- 27Frontolysis
- 28Four Types of Fronts
- 29Cold Front vs. Warm Front Weather
- 30Extra-Tropical Cyclones
- 31Life Cycle of a Mid-Latitude Cyclone
- 32Regional Names of Tropical Cyclones
- 33Prerequisites for Tropical Cyclones
- 34Energy Source of Tropical Cyclones
- 35Cyclone Structure: The Eye
- 36Cyclone Structure: The Eye Wall
- 37Cyclone Dimensions & Recurvature
- 38Cyclone Landfall and Dissipation
- 39Storm Surge
- 40Cyclonic vs. Anticyclonic Circulation
- 41Comparing Cyclones: Origin Environment
- 42Comparing Cyclones: Frontal Systems
- 43Comparing Cyclones: Direction of Movement
- 44Comparing Cyclones: Area, Violence, & Lifespan
- 45Comparing Cyclones: Thermodynamic Cores
- 46The Purpose of Storms (Energy Balance)
- 47Thunderstorms
- 48Hailstorms
- 49Lightning Intensity and Trends
- 50Tornadoes
- 51Atmosphere-Ocean Interaction
- 52Forces Driving Ocean Currents
- 53Thermohaline Circulation
- 54The Desiccating Effect of Ocean Currents
- 55Ocean Currents: Fog Formation and Fishing Grounds
- 56El Nino & Southern Oscillation (ENSO)
- 57Seasonal Winds: The Monsoon Concept
- 58The ITCZ and the Monsoon Trough
- 59Monsoon Onset and Withdrawal Timelines
- 60Pulsations: Active vs. Break Monsoon
- 61Spatial Distribution of Monsoon Rainfall
- 62Impact of El Nino on the Indian Monsoon
- 63Climate Change and Monsoon Trends
- 64Mission Mausam (Current Affairs)
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11th Fundamentals of Physical Geography
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