Oceanography Lecture Notes Outline
I. Contents - Topics
Covered
Structure of
the Atmosphere
Composition
of Air
Atmospheric
Pressure
Winds and the
Coriolis Effect
Global Wind
Bands
Seasonal
Variability in Winds
Effects and
Features of Wind
Hurricanes
Clouds,
Weather, and Climate
II. Structure of the Atmosphere
A. The Atmosphere Consists of a Series of Layers
1. The layers of the atmosphere
are defined by temperature shifts
·
Troposphere (clouded layer)
Ø Temperature decreases with elevation
Ø The layer where “weather” occurs
·
Stratosphere (ozone layer)
Ø Temperature increases with altitude
Ø Little circulation in stratosphere
Ø Exceptions are injections of volcanic eruptions
·
Mesosphere
Ø Temperature decreases with increasing altitude
·
Thermosphere
Ø
Temperature increases with
increasing altitude
2. The atmosphere is warmed at the surface and cooled at the
top
B. The Atmosphere is Density Stratified
1. The atmosphere is most
compressed at the surface
2. Pressure decreases with altitude
III. Composition and Properties of Air
A. Air is
Composed of Transparent, Odorless Gases
1. Nitrogen – N2 - (78.1%)
2. Oxygen – O2
- (20.9%)
3. Other gases: Ar (0.9%); CO2 , water vapor, and
inert gases (variable ~ avg. 1.4%)
4. Variable amounts of dust particles
Ø Terrigenous materials from land (wind-carried)
Ø Sea salt from ocean surface
B Atmospheric Pressure Varies Both
Vertically and Horizontally
1. Measure of air density
2. Pressure increases when
cooled or when water vapor content decreases
3. Air density decreases
when air is warmed
4. Standard surface air
pressure is 760 mm mercury (Hg)
5. High pressure zone
defined as > 760 mm Hg
6. Low pressure zone
defined as < 760 mm Hg
7.
Geographically-continuous regions of equal surface pressure are represented on
maps as isobars
IV. Winds on a Rotating Earth and THe Coriolis
Effect
A. Winds on a
Non-rotating Earth Would Be Fairly Simple
1. Hemispherical
atmospheric circulation systems
2. Large wind cells
in each (northern and southern) hemisphere
3. Warm air rises at the equator, cools as water vapor
condenses as rain
4. Dry air rising aloft cools, then sinks at the poles
5. Surface winds blow from the equator to the poles
B.
Winds on a Rotating Earth Are More Complex
1. Equator moves eastward at 1700
kilometer/hour
2. Rotational decreases poleward (with
increasing latitude)
Ø 850 km/hr at 60o N and S latitude
3. Earth rotation causes deflection of moving
objects relative to Earth’s surface
Ø Moving objects are deflected to the right in the
northern hemisphere
Ø Moving objects are deflected to the left in the
southern hemisphere
C.
The Deflection of Objects on a Rotating Sphere is Called the Coriolis Effect
1. The
Coriolis Effect is a special term for the effects of global-scale centrifugal
forces on Earth
2. Moving air and ocean water masses are
significantly affected by centrifugal forces
3.
Moving air masses move along curved paths (deflected) instead of straight
paths.
4.
The Coriolis Effect greatly complicates the Earth’s wind patterns
Ø Hemispherical wind cells get divided into
several smaller latitudinal systems
V. Latitudinal WInd Bands
A.
Latitudinal Wind Bands are Deflected by Coriolis Effect
1. Winds veer
to the right in northern hemisphere
2. Winds veer to the left in the
southern hemisphere
B.
Atmospheric Circulation is Broken Up Into Six Major Wind Bands or Belts
1. Northeasterly and Southeasterly
Trades
·
Termed the “Hadley” cells
(0 - 30° latitude),
·
Separated by a belt of low
pressure called the equatorial
doldrums
Ø Coincides with the intertropical convergence zone (ITCZ)
·
Bordered on their high
latitude side by a subtropical
high pressure belt
·
Strong, steady wind system
·
Typically associated with
warm moist air
2. Northern and Southern Westerlies
·
Termed the “Ferrel” cells
(30 - 60° latitude)
·
Bordered on their high
latitude side by the Polar Front
·
Bordered on their low
latitude side by a subtropical
high pressure belt
·
Winter storm systems
typically ride this belt from west to east
3. The Northern and Southern Polar
Easterlies
·
Termed Polar cells (60 -
90° latitude)
·
Bordered on their low
latitude side by the polar jet stream
·
Consists of very cold dry
air
·
Winter storm systems
typically develop at the low latitude edge
of this belt
C. Air Either
Rises or Falls Where Latitudinal Wind Bands Meet
1. Equatorial warm
air rises, sinks at ~30°N
2. At 30°N some moves back towards equator as trade winds
Ø NE in northern hemisphere
Ø SE in S. hemisphere (directions from which they blow)
3. Trade winds converge at equator
Ø Intertropical convergence zone (ITCZ).
4. At 30°N the remaining air flows towards poles as the
Westerlies
5. Westerlies meet colder, dense air flowing
from poles towards equator
Ø These air masses converge at Polar (Antarctic) Front
D. Jet
Streams are Narrow Bands of Strong Winds at the Polar Front
1. Jet streams vary seasonally, as the cells migrate
2. The jet streams are typically found along the Polar Front
E. Winds
Influence Climate
1. Climate is the long-term averaged weather
2. Wind’s influence at mid-latitudes:
·
Low rainfall coupled with
high evaporation
·
Typically light and variable winds (horse latitudes)
·
Dominated by high
atmospheric pressure
3. Wind’s influence in equatorial regions:
·
High rainfall coupled with
cloudiness
·
Typically light and
variable winds (doldrums)
·
Dominated by low atmospheric pressure
VI. Seasonal variabilty in winds
A. Causes of
Seasonal Changes:
1. Caused by differential solar heating of ocean and land
2. Product of high heat capacity of water
B. Weather
Characteristics of Summer:
1. Low pressure areas over land caused by warm rising air
2. High pressure over ocean
C. Weather
Characteristics of Winter
1. Winter produces the opposite effect
·
High pressure areas over
land caused by cold sinking air
·
Low pressure over ocean
D.
Characteristics of Monsoons
1. Regional seasonal changes in winds
2. A result of continent configurations
3. Summertime pattern:
·
Warming land with rising
air draws cooler, moist air from ocean
·
Result yields monsoon rains
4. Wintertime pattern:
·
Winds reverse, cool
continental air is drawn towards ocean
·
Result is dry
weather.
E.
Characteristics of Local Wind Patterns Near Coastlines
1. Sea breeze pattern:
·
Warm land air rises,
replaced by cool sea air
·
Called onshore winds
·
Typically a daytime
phenomena
2. Land breeze pattern
·
sea air rises, replaced by
cool land air
·
Called offshore winds
·
Typically a nighttime phenomena
3. Fluctuation between sea and land breezes a daily
occurrence
VII. effects and features of wind
A. Mountain
topography Has an Effect on Surface Winds
1. Winds rise and cool, leading to condensation of water
vapor
2. Precipitation occurs on windward side of topographic high
3. Dry air found on
leeward side (this area termed the rain shadow)
B.
Characteristics and Significance of Jet Streams:
1. High speed winds of upper troposphere
2. Polar jet streams found at 60°N and 60°S
3. Steers storm systems within the Westerlies
4. Sub-tropical jet streams at 30°N and 30°S
5. Greatest oscillation in winter
VIII. Hurricanes
A. Hurricanes Form From Trade Winds in Equatorial
Regions
1. Initiated over warm waters (>27°C)
2. Begins as pressure disturbance (termed easterly wave)
3. Involves the convergence of rotating winds
4. Starts as low pressure with moist winds at 10 - 20°N and
S
·
Starts as tropical
depression
·
Builds to become tropical
storms
5. Becomes hurricanes when wind speed >75 knots
6. Moves westwards
7. Dissipates over land or cold water
IX. Clouds, Weather, and CLimate
A. Clouds Heat and Cool the Earth
1. Require condensation nucleii
2. Types of clouds:
·
cold air with precipitation
(cumulonimbus)
· warm air rises (nimbostratus, altostratus, cirrostratus and
cirrus).