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ESS 111 – Climate & Global Change
Lecture 1
Structure of the Atmosphere
Global Wind Belts
Where is the atmosphere?
Everywhere!Completely surrounds EarthHeld to Earth by gravitational attraction
What makes up the atmosphere?
Water Vapor
Location of this in the atmosphere is highly variable Significantly influences climate & weather
How?
Atmospheric Thickness
No defined top to the atmosphereThe atmosphere is very shallow—and is less than 2% of the Earth’s thickness
Over 90% ofatmosphere inthe lowest 16km& is where nearlyall weather occurs
Temperature Basics Temperature – measure of average kinetic energy (motion) of individual molecules in matterThree temperature scales (units): Kelvin (K), Celsius (C), Fahrenheit (F)
All scales are relative
degrees F = 9⁄5 degrees C + 32degrees K = degrees C + 273.15
Temperature Layers
Due to surface heating (Longwave, Latent heat, Sensible heat)
Due to ozone absorption of sunlight
Due to Solar winds, Cosmic rays
Temperature decreases with height in the Troposphere
Density & Pressure
Density & Pressure
Lower layers of atmosphere are compressed by air above it
This compression increases pressure & density of the lower layers of the atmosphere
What is atmospheric pressure?
Weight of the overlying airTaller the column of air above an object, the greater the air pressure exerted on that object
Standard Atmospheric Pressure
1013.25 mb1013.25 hPa29.92 inches of Hg
The Layers of the Atmosphere
Thermosphere
Troposphere
Lowest region of the atmosphereContains ½ of the Earth’s atmosphere
density density
Troposphere
Depth of tropopauseBetween the Troposphere & Stratosphere is the tropopauseHeight is variable – Thermal expansion & contraction
How do we determine where the tropopause is located?
Stratosphere
Temperature increases with an increase in altitude
What is this called?
Why is there a temperature inversion in the stratosphere?
Temp Inversion – temperature warms with height instead of cooling w/ heightOzone
Gas that absorbs ultraviolet (UV) solar energyIncreases the temperature of the air surrounds ozone
Mesosphere
Temperature decreases with an increase in altitudeWhere meteors burn up while entering the Earth’s atmosphere
Thermosphere
First exposed to the Sun's radiation and so is first heated by the Sun
Air is so thin that a small increase in energy can cause a large increase in temperature
Vertical Structure of the Atmosphere
Space shuttle Endeavour straddles mesosphere & stratosphere
Planetary WindsWell-defined pressure patterns exist across the Earth that induce the global wind patterns on the planet
Idealized Single-Cell Convection Model for a Planet
Features of the circulation pattern:
•horse latitude•trade winds•doldrums•prevailing westerlies•polar easterlies•polar front
The Three-Cell Model
Intertropical convergence zone (ITCZ) -- surface low pressure with clouds and rain
Subtropical high -- Air subsides (dry climate)
Hadley cell -- tropical convection cell
Ferrel cell -- southwesterly winds at surface
Polar cell -- northeasterly winds at surface
Observed Distribution of Pressure and Winds
(a) An imaginary uniform Earth with idealized zonal (continuous) pressure belts
(b) Actual planetary winds belts on Earth taking into account continents and ocean currents
Equatorial Low- warm air rising creates cell of low pressure.
Intertropical Convergence Zone (ITCZ)- referred to as the convergence zone because this region is where the trade winds converge. Ascending air leads to cloud formation which makes thisregion clearly visible on satellite imagery.
Subtropical Highs- These zones are caused primarily by Coriolis deflection which restricts upper-level winds from moving poleward.Subsiding air and divergent winds at the surface cause warm, cloud-free weather (many large desert areas are located along this latitudinal belt). Subtropical Highs tend to persist throughout the year, with the center of the high migrating, and are regarded as semi-permanent pressure systems.
Idealized Pressure Belts
Idealized Pressure Belts (cont.)
Subpolar Low – located around 50 to 60 latitude. Associated with the polar front. The belt of low pressure is formed by theinteraction (convergence) of the polar easterlies and the westerlies
Polar Highs – located over the poles! The process which producesthe polar highs is different than the process which produces thesubtropical highs. Surface cooling is the principle reason the polar high.
The ITCZ is a band of clouds across the tropics
ITCZ
The three-celled model vs. reality:
• Hadley cells are close approximations of real world equatorial winds
• Ferrel and polar cells do not approximate the real world winds very well at all
• Model is unrepresentative of westerly flow aloft
• Continents and topographic irregularities cause significant variations in real world wind patterns compared to the model
Semi-Permanent Pressure Cells are large areas of higher or lower atmospheric pressure than the surface average
They may be thermally induced (rising warm air or subsiding cold air) or they may be caused dynamically by converging or diverging wind patterns)
They fluctuate seasonally
Northern hemisphere semi-permanent cellsThe Aleutian, Icelandic, and Tibetan lows
Siberian, Hawaiian, and Bermuda-Azores highs
ITCZ (low)
Vertical structure and mechanisms
Hadley Cell (thermal): Heating in tropics forms surface low and upper level high air converges equatorward at surface, rises, and diverges poleward aloft descends in the subtropics
Ferrel Cell (dynamical): Dynamical response to Hadley and polar cells
Polar Cell (thermal): Driven by heating at 50 degree latitude and cooling at the poles
Average atmospheric air pressure and wind patterns in January
Average atmospheric air pressure and wind patterns in July