Oceanography Set 2

Weather and High and Low Pressure Systems

• High pressure: typically associated with dry, sunny weather

• Low pressure: typically associated with rain or snow

• Lines of equal atmospheric pressure are “isobars”

  • Where isobars are closely spaces, wind will be strong (large changes in atmospheric pressure)

Atmospheric pressure

• A column of cool, dense air causes high pressure at the surface and sinking air (air molecules far apart) 

• A column of warm, less dense air causes low pressure at the surface and rising air (air molecules close together)

What tool is used to measure pressure?

Barometer

Wind

Moves of areas from high pressure to low pressure

Sea breeze

• During the day, land is warmer than the water which causes sea breeze (off shore to on shore) 

• During the night, the water is warmer than the land, causes land breeze (weak winds at night) 

• Land absorbs more heat (urban areas warmer than rural)

What drives sea breeze?

Uneven heating drives local wind patterns 

Monsoons: like a continental, seasonal scale sea breeze

• Land surface warming up in the summer → late may, june, july, surface becomes very warm and the ocean is still relatively cool, causes air to rise and forms low pressure over the surface of the land, high pressure over the ocean

• Subtropical monsoonal circulation driven by difference between land and oceans response to solar heating

Hurricanes are very powerful low-pressure systems

• 1 bar = 1000 mb (average) 

• 950 mb and below = atmospheric pressure for hurricanes (Hurricane Katrina: 902 mb)

Typhoon

Same thing as a hurricane but in the pacific ocean

Knots

•  Nautical miles per hour 

• 1 knot is 1.15 mph or 1.8 kph 

What drives a hurricane?

• Starts as a low pressure system 

• Fueled by heat from the warm ocean → causes air to rise and then suck into the low pressure system 

• Go from East to West then curve up to the Northeast 

• NEVER crosses the equator → coriolis effect rotates COUNTER CLOCKWISE

Bermuda High

• Air circulates clockwise around the high-pressure system

• When strong and well-developed:

  • Steers storms westward then northward

  • Moves west along the west coast of Africa

Why do hurricane rotate counterclockwise in the Northern Hemisphere?

• Warm, moist air rises (less dense)

• Surrounding tropical air rushes in and causes strong winds

• Air is deflected to the right by the Coriolis effect → counterclockwise spin

What ocean is associated with Hurricanes?

Atlantic Ocean: from Huracan, Taino god of wind

What ocean is associated with Typhoons?

Pacific Ocean: from Chinese word “great wind”

What ocean is associated with Cyclones?

Indian Ocean

Why don’t hurricanes cross the equator?

Coriolis effect weakens → no rotation

Hurricane Hazards

• High winds

• Strong pressure gradient

• Intense rainfall

Storm surge

• Caused by low pressure and onshore winds

• Dome of water up to 1 meter (3.3 ft) in open sea

• Influenced by:

  • Wind-driven surge

  • Pressure surge

Northwest quadrant hurricane region

Significant storm surge

Northeast quadrant hurricane region

Greatest winds, strongest surge, highest tornado risk

Southwest quadrant hurricane region

Southeast quadrant hurricane region

Strong winds, dangerous surge

Eye wall hurricane region

Most violent part of storm

What affects storm surge intensities?

Shoreline geography affects severity of the surge

Saffir-Simpson Hurricane Wind Scale

Ranks hurricanes Category 1–5 based on wind speed and damage potential

New Bedford, Massachusetts Hurricane Barrier

• Built a hurricane barrier in the early 1960s

• Constructed after repeated hurricane damage in the 1930s-40s

 The 4 Branches of Oceanography

1. Chemical oceanography

2. Physical oceanography

3. Geological oceanography

4. Biological oceanography