is the study of the oceans and is vital in understanding weather and
climate as well.
play 3 important roles in determining weather and climate:
are the source of atmospheric water vapor
exchange energy with the atmosphere
transfer heat poleward through ocean currents
oceans provide the majority of water needed to form precipitation.
average, the ocean gains energy during the summer and loses it in winter,
and the maximum exchanges of energy occur in the Northern Hemisphere
winter to the east of North America and Asia
where warm ocean currents flow poleward.
maintaining the Earth’s radiation balance, around 30° latitude, the ocean
and atmosphere each transport about the same amount of heat, whereas Equatorward
of 30°, the ocean transfers the majority of heat required to maintain
oceans and atmosphere work together to maintain balance, through winds,
currents, and atmospheric conditions.
ocean can be classified into three different vertical zones based on
Zone-uniform or mixed layer, constant temperature due to wind mixing,
around 2% of world’s ocean waters are within this zone.
- Deep Zone- bottom layer, below 1000
meters, cold water at temperatures between 1° and 3° C, temperature is
uniform in this layer.
transition zone between Surface and Deep layer, temperature decreases
rapidly with depth down to 1000 meters.
zones can change depending on latitude, although the deep zone is the same
in all regions (Polar, Mid-latitude, and Tropical).
between the atmosphere and ocean occur at the surface and result in the
transfer of heat and moisture, so Sea Surface Temperature (SST)
distribution is important.
Ocean Current is a massive, ordered pattern of water flow. They closely resemble surface wind
general, warm currents tend to flow poleward or westward, while cold
currents tend to flow toward the Equator.
an ocean circulation that forms a closed loop that stretches across and
entire ocean basin.
currents generally flow at an angle of around 45° to the wind to the right of the wind in the Northern Hemisphere and to the left of the wind in the Southern Hemisphere, due to
Coriolis and Friction forces.
Spiral- the progressive turning of ocean currents from the surface down to
100 meters due to the combined effect of wind on the sea surface and the
Coriolis Force. The top layer is
driven by surface wind and each layer below it is driven by frictional
drag of the layer above.
Transport- the effect of the Ekman Spiral to move water masses at a right
angle (90°) to the direction of the surface wind. In the NH, it is to the right, in the SH
to the left.
a wind driven ocean circulation pattern in which cold, nutrient-rich ocean
waters are forced up to the surface as a consequence of Ekman Transport.
is very important for marine organisms at the surface and if it ceases, it
can have catastrophic effects on coastal regions.
El Nino and La Nina
- El Nino
is a natural, periodic warming of the equatorial Pacific Ocean between South America and the Date Line. It is an excellent example of
ocean/atmosphere interaction and its effect on climate.
under normal conditions, SSTs off of Peru are cold due to coastal
upwelling, and waters in the western Equatorial Pacific are warm. The westerly (east to west) trade winds
also push the water westward raising the level of the ocean one half meter
higher than around South America’s
western coast. Due to the water’s
warmth over the western Pacific, more precipitation also occurs.
- An El
Nino event is triggered when the trade winds weaken or reverse direction
and blow from west to east, bringing with it warmer waters towards South
America, along with increased precipitation.
El Nino, two distinct changes occur in the equatorial Pacific
coastal waters are replaced by warm waters in the eastern Pacific
height of the ocean surface drops over Indonesia
(western Pacific) and rises in the eastern Pacific (South America),
forcing the thermocline to lower near South America
and prevent upwelling.
changes can affect the global weather patterns by changing the Subtropical
Jet, which can then change the weather of the mid-latitudes region, not
just the tropics.
Nino warming occurs periodically every 2 to 7 years.
Southern Oscillation is the seesaw in atmospheric pressure between the
western and eastern Pacific that is commonly associated with El Nino and
La Nina. It is measured through the
Southern Oscillation Index (SOI).
Nino and the Southern Oscillation can often occur together, but also can
happen separately. When they occur
together it is called ENSO.
Nina- cooler-than-normal sea surface temperatures in the eastern tropical Pacific Ocean.
It is the counterpart of El Nino.
a La Nina, intense trade winds move warm waters towards Western Pacific,
and there is increased cold water upwelling in the eastern equatorial
Nina conditions typically last 9 to 12 month.
many cases, La Nina produces the opposite climate variations from El Nino.
oscillations similar to the El Nino-Southern Oscillation have been
uncovered in other areas of the world.
Pacific Decadal Oscillation (PDO) is the seesaw of atmospheric pressure
and SSTs that occurs over the North Pacific over periods of several
North Atlantic Oscillation (NAO) is an oscillation where atmospheric
pressure seesaws between the polar low near the North Pole and the
subtropical high over the Atlantic Ocean.
Tropical Cyclones: Hurricanes and Typhoons
Cyclones are circular low pressure storms with winds of at least 35 knots
(39 mph) which are driven by atmosphere-ocean interactions and originate
in the tropical oceans.
are tropical cyclones in the tropical regions of North and Central America.
are tropical cyclones in the region of the western Pacific.
cyclone is a center of low pressure.
Eye is the innermost part of a strong tropical cyclone’s center, and is
almost completely clear of clouds. Surrounding
the eye is the Eyewall, a
narrow, circular region of intense thunderstorms.
tropical cyclone must be powered by an energy source. This energy source is the large latent
heat of water.
tropical cyclone also adds fuel to itself by drawing surface air towards
its low pressure center, where the strong pressure gradient means the
means the winds grow stronger closer to the eye. As wind blows faster, more evaporation
occurs, and this means more water vapor in the air to fuel thunderstorms.
and Condensation are the keys to understanding the power of tropical
cyclones cannot develop in regions with SSTs lower than 26.5°C, so they
are constrained to the tropics region where warm SSTs produce more
evaporation. They are generally
only seen in the summer and fall seasons as well.
cyclones do not form near the Equator (within 5 degrees latitude) b/c the
Coriolis force is 0 and air tends to flow straight into low pressure centers,
so it feels up before the pressure can drop enough.
Eye of the storm is nearly calm and serves to break up the front and back
of the storm as it passes over. It
is calm because in this region air sinks instead of rising, making it very
the eye becomes very small and distinct, this is a sign of the storm
strengthening, when it becomes wider, it implies some weakening.
stronger the cyclone, the stronger the upper level High Pressure and
stronger surface Low Pressure.
shear is one way to break up a cyclone because the winds are changing fast
enough in the vertical to disrupt the vertical development of the storm.
heaviest rainfall is seen in Rainbands,
which spiral into and blend it with the eyewall.
strongest winds are seen on the north and east sides of the cyclone b/c
the storm’s forward motion adds or subtracts from the winds.
cyclones usually begin small as Tropical
Disturbances, or Easterly Waves in
the Atlantic Ocean.
- A Tropical Depression is the next
step in development, when cyclonic rotation is observed and a lower
pressure center is located.
that, the storm becomes a Tropical
Storm when winds reach a consistent speed of 35 knots.
- A Hurricane, or Typhoon, is classified when winds reach 65 knots, and this is
when the eye normally forms. There
are also SuperTyphoons (winds greater than 150 mph) in the Western
storms will lose their strength within a week, but some become
Extratropical Cyclones, a low
pressure system that forms outside of the tropics, and is usually
associated with cold air and fronts near its center.
Atlantic Hurricane Season starts on June 1st (typically in the Gulf of Mexico
or Western Caribbean) and lasts until
November 30th, however they can continue into December if SSTs
remain high enough and there is no wind shear present.
peak of hurricane activity in the tropical waters south and southeast of
is in mid-September.
80% of intense hurricanes in the Atlantic begin as Easterly Waves off the
coast of Western Africa and then drift
westward, also referred to as Cape Verde Hurricanes.
How do they cause destruction?
most obvious threat of a tropical cyclone is the powerful wind.
damage is classified using the Saffir-Simpson Scale, which rates
hurricanes on a scale of 1 to 5 based on the damage their winds would
cause upon landfall.
Surge is another threat where winds in a tropical cyclone push ocean water
in front of them, and the stronger the wind, the more water is piled up by
the winds, causing more flooding.
Surge is the deadliest weapon in the tropical cyclone’s arsenal, typically
causing 90% of all hurricane related deaths because water is heavier than
caused by heavy rains is another threat.