Download Air-Sea-Interaction-Lecture-Notes

AIR-SEA INTERACTION
I.
INTRODUCTION
A. Radiant energy heats up the atmosphere and colder air pockets sink, while
warmer air pockets rise, creating atmospheric winds
B. Since water is a liquid, atmospheric winds create most of the surface currents
and waves in the ocean
C. The high heat capacity of water allows for this constant exchange of energy
between the atmosphere and the ocean, leading to climate & weather patterns
II.
UNEVEN SOLAR HEATING ON EARTH
A. DISTRIBUTION OF SOLAR ENERGY
1. Earth is spherical, therefore radiant energy is not evenly distributed
everywhere
2. No matter if the Earth were tilted on its axis, or not, radiant energy hits
the Earth but at different angles (angle of incidence)
a. Think of the perpendiculars to Earth’s surface
3. As a result, radiation strikes Earth at high angles around the equator and
low latitudes, but decreases for high latitudes
a. The same amount of energy is given by the sun, but over a larger
area
b. Therefore, you have cooler temperatures the further away from
the equator
4. Earth’s atmosphere will actually absorb some radiation, so less radiation
strikes at high latitudes because there is more atmosphere
5. Albedo is the percentage radiation that is reflected
a. The average albedo is 30%
b. Albedo is higher at higher latitudes because larger angles and ice
has a higher albedo than soil
6. Since Earth is spinning, the angles of incidence change throughout the
day and thus, the amount of radiation received fluxuates hourly
7. Since Earth is tilted, the angles of incidence change throughout the year,
and thus, the amount of radiation received fluxuates
daily/weekly/monthly
B. EARTH’s SEASONS
1. Why do we have seasons?
a. http://www.youtube.com/watch?v=iMEfYLvxioc
2. Johannes Kepler discovered that the Earth revolves around the sun in an
elliptical fashion (called ecliptic)
a. What is the difference between an ellipse and a circle?
3. Earth is also tilted and therefore, Earth’s axis ALWAYS points in the same
direction (towards North Star)
a. At 23.5o
4. http://www.youtube.com/watch?v=rcquRMaVSKU&feature=related
5. VERNAL EQUINOX
a. March 21
b. All places experience equal night and day
c. In the Northern Hemisphere, it’s called the Spring Equinox
6. SUMMER SOLSTICE
a. June 21
b. Sun is directly over the Tropic of Cancer
c. Sun appears to pause at noon
7. AUTUMNAL EQUINOX
a. September 23
b. In the Northern Hemisphere, it’s called the Fall Equinox
8. WINTER SOLSTICE
a. December 22
b. Sun is directly over the Tropic of Capricorn
c. Summer for Southern Hemisphere
9. Arctic Circle versus Antarctic Circle (66.5o)
C. OCEANIC HEAT FLOW
1. Look at Figure 7-3 on p.197
2. Why doesn’t the equator keep getting warmer and the poles colder?
D. THE ATMOSPHERE: PHYSICAL PROPERTIES
1. http://www.youtube.com/watch?v=WaikvaAw2nk
2. COMPOSITION
a. The atmosphere consists mainly of Nitrogen and Oxygen
b. p. 197
c. Although the others are small, they can trap a lot of energy
i. How? Why?
3. TEMPERATURE
a. The troposphere (“tropo = turn”) is where all weather is produced
b. Don’t forget about the tropopause
c. p.198
4. DENSITY
a. Because of density, hot air rises and cool air sinks
b. This create a flow as the warm air eventually cools
c. A convection cell can be created in a room
5. WATER VAPOR CONTENT
a. Cool, dry air
b. Warm, moist air
c. Water vapor is less dense than air
i. When you boil something, where does the water vapor
go?
ii. Humid air is less dense than dry air
6. PRESSURE
a. Changes in air pressure can cause molecular density changes
i. What happens when there is a change in the density of
air?
ii. Cool, dense air causes high pressure at the surface, which
leads to sinking air
iii. Warm, less dense air causes lower pressure at the surface,
which leads to rising air
7. MOVEMENT
a. Air ALWAYS moves from high pressure to low pressure
i. Equilibrium idea again
b. A balloon deflates for this reason
III.
THE CORIOLIS EFFECT
A. Balloon Demonstration (EXAMPLE ONLY!)
1. In the Northern Hemisphere, it goes to the right
2. In the Southern Hemisphere, it goes to the left
B. VELOCITIES AT DIFFERENT POINTS ON EARTH
1. Imagine a person standing still very close to the north pole.
a. How much did he/she actually travel in a day?
2. Imagine a person standing still at the equator.
a. How much did he/she actually travel in a day?
IV.
ATMOSPHERIC CIRCULATION CELLS
A. CIRCULATION CELLS
1. Over the Equator, there is a lot of radiation
2. As a result, air decreases density, expands and rises
a. This creates low pressure at the Equator, called the equatorial low
3. As air rises, the pressure is lower, and it cools
a. The water vapor it contains condenses and falls as rain
4. Because it is cooler at the poles, the air mass travels north or south
5. However, at some point, the air cools enough to become denser than the
surrounding air, so it begins to descend, completing the circulation cell,
which are called Hadley cells
6. This descending air mass toward the surface creates high pressure at 30 o
(the point where the air cools enough to become denser than the
surrounding air), called subtropical highs and polar highs
a. Descending air is quite dry and tends to warm under its own
weight
b. Thus, dry, clear, fair, clear-sky conditions occur
7. Since this air mass is descending and creating a high pressure zone, air
masses on the other sides of 30o, are pulling away from another area,
creating another Ferrell Cell (range of about 30o)
8. These 60o marks are the subpolar lows
a. Weather is dominated by cloudy conditions with lots of
precipitation due to rising air cools and cannot hold its water
vapor
9. This process creates another Hadley cell, leaving the far-reaching 30o
marks as the final Polar cells
B. WIND BELTS
1. Hadley cells (moving air masses) obviously create wind patterns
2. TRADE WINDS
a. The wind belts between the equator and 30o are called such
b. Since air is sinking at 30o and rising at the Equator, the air mass
moves from the 30o mark to the Equator
c. The Coriolis Effect moves these air masses to the right in the
Northern Hemisphere and to the left in the Southern Hemisphere
d. We usually name motion from its point of origin
e. In the Northern Hemisphere, since it is moving to the right, it is
coming from a NE direction, so we call these the NE Trade Winds
f. In the Southern Hemisphere, since it is moving to the left, it is
coming from a SE direction, so we call these the SE Trade Winds
3. WESTERILES
a. Between 300 and 60o, winds are moving from the high pressure
zone (30o) to the low pressure zone (60o)
b. In the Northern Hemisphere these winds are moving to the right
(due to Coriolis), from a SW position, and are thus called the
prevailing westerlies
c. In the Southern Hemisphere these winds are moving to the left
(due to Coriolis), from a NW position, and are thus called the
prevailing westerlies
4. EASTERLIES
a. Between 600 and the poles, winds are moving from the high
pressure zone at the poles to the low pressure zone at 60o
b. In the Northern Hemisphere these winds are moving to the right
(due to Coriolis), from a NE position, and are thus called the polar
easterlies
c. In the Southern Hemisphere these winds are moving to the left
(due to Coriolis), from a SE position, and are thus called the polar
easterlies
C. BOUNDARIES
1. AT EQUATOR
a. This is called the doldrums (dull) due to lack of winds
b. This is also called the Intertropical Convergence Zone (ITCZ)
c. Plenty of rain, so no worries about being stranded
2. AT 30o
a. These are called the horse latitudes
b. High pressure and clear, dry, fair conditions dominate
c. Horses were thrown overboard to conserve freshwater
3. AT 60o
a. These are called polar fronts
b. Cloudy conditions and lots of precipitation
4. AT POLES
a. “Cold deserts”
D. HOW IT ALL ACTUALLY WORKS
1. This is an idealized situation
2. It actually has varying possibilities
a. Seasonal changes vary year to year
b. Global warming hits different spots differently
c. Lower heat capacity of rock compared to seawater make air over
continents colder in winter and warmer in summer than air over
oceans
i. Uneven distribution of land and ocean
d. p.205
V.
THE OCEANS, WEATHER AND CLIMATE
A. DIFFERENCE BETWEEN WEATHER AND CLIMATE
1. Weather describes the conditions of the atmosphere at a given time and
place
2. Climate is the long-term average of weather
B. WINDS
1. Air moves away from high pressure to low pressure
2. In the Northern Hemisphere, it curves to the right toward the low
pressure, creating a counterclockwise (or cyclonic) flow
3. In the Northern Hemisphere, it curves to the left away from the high
pressure, creating a clockwise (anticyclonic) flow
4. SEA BREEZES AND LAND BREEZES
a. They are called from whence they came
b. Land heats up 5 more times than the water due to water’s high
heat capacity
c. During afternoon, warm air rises over land, causing low pressure,
causing the higher pressure over the water to swoop in over the
land from the sea, called a sea breeze
d. The inverse happens during the evening and at night as the land
cools much faster than the water
C. STORMS
1. Storms, in general, are atmospheric disturbances characterized by strong
winds, precipitation and often thunder and lightning
2. Air masses tend to go east
3. Jet stream - a fast moving, narrow easterly flowing mass that creates
warm and cold fronts
D. HURRICANES (TROPICAL CYCLONES)
1. To be covered in another lecture, though you need to know the material
for the test
E. THE OCEAN’s CLIMATE PATTERNS
1. Just like land, oceans have climate patterns as well
2. Even when idealized, they are less direct (p. 215)
3. EQUATORIAL REGION
a. Major air movement is upward
b. Surface winds are weak
c. Air is saturated with water vapor
d. Lots of precipitation
e. Surface salinity relatively low
4. TROPICAL REGIONS
a. Up to Tropic lines
b. Strong trade winds
c. Moderately rough seas
d. Precipitation varies from top to bottom
5. SUBTROPICAL REGIONS
a. Belts of high pressure are centered here
b. Dry, descending air produces little precipitation
c. High rate of evaporation
d. Leading to high salinity
6. TEMPERATE REGIONS
a. aka mid-latitudes
b. strong prevailing westerlies
c. severe storms are common
d. precipitation is heavy
7. SUBPOLAR REGIONS
a. Extensive precipitation
b. Sea ice covers the subpolar ocean in winter, but melts in the
summer
c. Icebergs are common
8. POLAR REGIONS
a. Surface temperatures at or near freezing
b. Covered in ice throughout the year
c. No sunlight during winter, constant sunlight during summer
VI.
SEA ICE
A. DEFINITION
1. Low temperature high-latitude areas cause permanent (or nearly so) ice
covering the sea surface
2. This is called sea ice
3. This is to differentiate from icebergs, which calve off of glaciers
B. SEA ICE FORMATION
1. Sea ice begins as hexagonal water crystals
2. They grow more and more until they become slushy water (frazil or
grease ice)
3. The slushy water then turns into a sheet of ice
4.
5.
6.
7.
Wind stress and wave action break up this thin sheet into round disks
This is called pancake ice
As it cools, pancake ice coalesces to become ice floes (less than 10 km)
Sea ice formation increases the salinity of water underneath, which
increases the density, making that water sink
8. As it sinks, it is replaced by lower density water which has a higher
freezing point, and therefore freezes, creating a cycle
C. SEA ICE IN THE ARCTIC OCEAN
1. PACK ICE
a. Floating ice that has been driven together into a single mass
b. Commonly forms around the margins of the Arctic
c. Expansion of ice floes that began to raft onto one another as they
expand
2. POLAR ICE
a. Thicker than pack ice
b. Melting may produce “holes” called polynyas
c. Circles clockwise around the Arctic
3. FAST ICE
a. This develops in the winter from the shore out to the pack ice
b. Completely melts during the summer
c. It is connected to the shore or sea-floor (held fast there)
D. SEA ICE NEAR ANTARCTICA
1. Limited to pack ice and fast ice since there is Antarctica
2. But, it is temporary
3. Strong winds prevent formation of pack ice at locations
VII. ICEBERGS
A. DEFINITION & PROPERTIES
1. Bodies of floating ice broken away from a glacier
2. Formed by vast ice sheets on land, which grow from accumulation of
snow and slowly flow outward to sea
3. http://www.youtube.com/watch?v=ewHIo2ekU4g&noredirect=1
4. http://www.youtube.com/watch?v=JmhnS96m9Ck&feature=related
5. http://www.youtube.com/watch?v=Sh271FAVZ0o&noredirect=1
B. RMS Titanic
1. Operated by White Star Line, she left from England to US across the
North Atlantic in April 1912
2. http://www.youtube.com/watch?v=tq7KbXFens8&feature=related
C. SHELF ICE
1. In Antarctica, glaciers cover the entire continent
2. The edges form thick floating sheets of ice called shelf ice
3. 90% of their mass shows