Currents and Climate

The Atmosphere Air masses move vertically if: change in temperature change in concentration of water vapor (each causing density to change) Vertical movements usually restricted to troposphere

Water vapor decreases air mass density Water vapor continuously evaporating from sea and land surface Water molecules are lighter than N2 and O2 Atmospheric convection caused by: Heating Evaporation As air decreases in density It rises Expands (pressure decreases as you rise in the atmosphere) Cools Becomes supersaturated with water and it soon rains

Water and Heat Budgets Enough water is evaporated from land and oceans each year to cover the world 1m deep! 93% comes from the ocean 30% of all that is evaporated falls on land Filling lakes, streams, rivers Returns to ocean as run-off Incoming solar radiation ~25% absorbed by atmosphere and converted to heat ~50% absorbed by oceans and land ~25% is reflected back out to space At poles – more heat is lost to space than is received At equator – more heat is received than is lost to space

Climatic Winds Heat transfer from ocean to atmosphere causes convection Horizontal movements = wind 3 convection cells formed Hadley Ferrel Polar Ferrel cells lie between Hadley and Polar Between cells, winds are generally calm

Climate and Ocean Surface Water Properties Ocean surface water salinity determined by differences in evaporation and precipitation rates Except near continents where freshwater run-off is high Highest in subtropics and polar regions Low rainfall Lower in mid-latitudes High rainfall; low evaporation Lower at equator Evaporation is reduced by persistent cloud cover Ocean surface water temperatures generally decrease with latitude This pattern distorted by upwelling

Land-Ocean-Atmosphere Interactions Earth’s surface heats by day, cools by night Due to high “latent heat”, ocean surface water temperature varies little in this cycle Land varies more During day: land next to ocean heats loses some heat to air Air rises Replaced by cooler air from over ocean = SEA BREEZE

During night: land next to ocean cools rapidly Air over ocean warmer, rising Air moves from land to sea = LAND BREEZE

When moving moist air masses meet a mountain: Coastal fogs form when warm moist air from ocean passes over cold coastal water mass as it enters a sea breeze system When moving moist air masses meet a mountain: They rise and cool, causing rain Occurring on the windward side After crossing the mountain, and having lost much water, the air mass descends, is compressed, and warms, has become arid Occurring on the leeward side

The real question boils down to: How do interactions between the ocean and atmosphere impact worldwide weather and short-term climate variability?

What is climate? Weather at a particular location averaged over about 30 years

Factors that shape climate: Latitude Elevation Topography Proximity to large bodies of water Earth’s surface characteristics Net incoming solar radiation Long-term average atmospheric circulation Prevailing ocean circulation

Ocean’s Role Cover’s ~ 71% of Earth’s surface Absorbs most of sun’s energy shining on it (reflecting little) Carries this heat with it in currents Greenhouse gases: Source of major greenhouse gas – H2O vapor Regulates another greenhouse gas – CO2 Colder water contains more CO2

THE OCEAN AND CLIMATE CHANGE

How we know our ocean/atmospheric past: Historical documents Fossils Rocks Pollen Tree growth rings Glacial ice cores Deep sea sediment cores

Sea level predicted to rise The ocean’s role Takes up 56.2% of CO2 (compared to terrestrial sinks of 13.7%) Sea level predicted to rise Melting of polar ice sheets Melting of mountain glaciers Thermal expansion of sea water Shrinkage of Artic Sea ice (a major reflector of sunlight) Impacts Increased coastal erosion Inundation of some islands, wetlands, estuaries Disrupt marine ecosystems

STORMS

Tropical Cyclones/Hurricanes Storm system Characterized by: low pressure center thunderstorms strong wind flooding rain Feed on heat released when moist air rises (water vapor releases heat as it rises, cools, condenses)

Factors necessary for tropical cyclone formation: Water Temperature At least 26.5 °C to depth of 50 m Rapid Cooling with Heating Allows release of heat of condensation High Humidity Continued next slide…..

Distance Away from Equator Low Wind Shear High shear is disruptive to the storm’s circulation Distance Away from Equator More that 500 km or 5 degrees of latitude Allows Coriolis effect to deflect winds Pre-existing System of Disturbed Weather

Storm Classification

Tropical Depression Organized system of clouds and thunderstorms Maximum sustained winds <38 mph

Tropical Storm Maximum sustained winds increase to between 39-73 mph

Hurricane System with sustained winds of >74 mph Hurricance Classification Category 1: 74-95 mph Category 2: 96-110 mph Category 3: 111-129 mph Category 4: 130-156 mph Category 5: 157 mph or higher

Wind Simulator

Eye and Inner Core Sinking air at the center If winds strong enough eye will form Heaviest wind damage occurs at eye wall

Landfall Storm’s center crosses coastline Coastal areas will “feel” it coming hours before landfall

Coastal Effects Can produce powerful winds and torrential rain Can produce high waves and damaging storm surge

Inland Effects Damage to vehicles, building, bridges, etc. Possible flying projectiles. Heavy rains can produce significant flooding and storm surges can produce extensive coastal flooding up to 25 miles from the coast line. Historically resulting in 90% of cyclone deaths In the last two centuries, tropical cyclones have been responsible for 1.9 million deaths

Hurricane Season Our Season- June 1 to November 30

Dissipation occurs when: Moves over land, depriving itself of warm-water. Remains in the same area of ocean too long mixing the upper 30 meters of water (water becomes too cool). Moves into water < 26.5 °C

Long Term Trends More intense hurricanes are expected over next century due to global climate change – the earth’s warming due to increasing levels of greenhouse gases in the atmosphere.

Helpful Hurricanes? Relieve drought conditions. Help maintain equilibrium in Earth’s atmosphere and maintain relatively stable and warm temperature worldwide.

http://www.youtube.com/watch?v=zP4rgvu4xDEHurricane!