UNDERSTANDING EARTH’S SYSTEMS GLOBAL CLIMATE UNDERSTANDING EARTH’S SYSTEMS

Global Circulation Although the loss and gain of radiation is balanced over the entire climate system, no one part of the planet’s surface is in equilibrium at a given time.

Global Circulation The solar radiation hitting the Earth is unequal…WHY? Earth is oblate (slightly flattened)

The Earth is tilted and rotating and revolving Winter (Northern Hemisphere tilts away from sun) Spring (sun aims directly at equator) Summer (Northern Hemisphere tilts toward sun) Fall (sun aims directly at equator) 23½° To Polaris The tilt (23½° inclination) causes the seasons The Earth is tilted and rotating and revolving

Solar Heating of Earth Varies with Latitude The atmosphere reflects, scatters and absorbs solar radiation. At high latitudes solar radiation travels a longer path through atmosphere. Equal amounts of sunlight are spread over a greater surface area near the poles than in the tropics. Ice near the poles reflects much of the energy that reaches the surface there.

Heat Redistributed Heat gained at Equatorial latitudes Heat lost at higher latitudes Winds and ocean currents redistribute heat around the Earth Oceans do not boil away near the equator or freeze solid near the poles because heat is transferred by winds and ocean currents from equatorial to polar regions.

Physical Properties of the Atmosphere: Density Warm, low density air rises Cool, high density air sinks Creates circular- moving loop of air (convection cell)

Physical Properties of the Atmosphere: Water Vapor Cool air cannot hold much water vapor, so is typically dry Warm air can hold more water vapor, so is typically moist Water vapor decreases the density of air

Physical Properties of the Atmosphere: Pressure A column of cool, dense air causes high pressure at the surface, which will lead to sinking air A column of warm, less dense air causes low pressure at the surface, which will lead to rising air

Physical Properties of the Atmosphere: Movement Air always moves from high-pressure regions toward low-pressure regions Moving air is called wind

Atmospheric Circulation (convection) Heated air rises at equator Cooler air descends at poles Maximum Sun warming

The Coriolis Effect As Earth rotates, different latitudes travel at different speeds The change in speed with latitude causes the Coriolis effect Coriolis Effect: Coriolis effect is an inertial force described by the 19th-century French engineer-mathematician Gustave-Gaspard Coriolis in 1835. Coriolis showed that, if the ordinary Newtonian laws of motion of bodies are to be used in a rotating frame of reference, an inertial force--acting to the right of the direction of body motion for counterclockwise rotation of the reference frame or to the left for clockwise rotation--must be included in the equations of motion. The effect of the Coriolis force is an apparent deflection of the path of an object that moves within a rotating coordinate system. The object does not actually deviate from its path, but it appears to do so because of the motion of the coordinate system.

The Coriolis Effect The rotation of the Earth deflects the path of moving objects. As observed from space, cannonball 1 (shot northward) and cannonball 2 (shot southward) move as we might expect; that is, they travel straight away from the cannons and fall to Earth. Observed from the ground, however, cannonball 1 veers slightly east and cannonball 2 veers slightly west of their intended targets. The effect depends on the observer’s frame of reference.

The Coriolis effect The Coriolis effect Is a result of Earth’s rotation Causes moving objects to follow curved paths: In Northern Hemisphere, curvature is to right In Southern Hemisphere, curvature is to left Changes with latitude: No Coriolis effect at Equator Maximum Coriolis effect at poles

Add rotation Add land mass Unequal heating and cooling of the Earth

Wind Belts of the World

The Total Atmosphere Effect Global air circulation as described in the six-cell circulation model. Air rises at the equator and falls at the poles, but instead of one great circuit in each hemisphere from equator to pole, there are three in each hemisphere.

Cell Circulation Centers on the Meteorological (Not Geographical) Equator

Ocean Currents

Why is Ocean Circulation Important? Transport ~ 20% of latitudinal heat Equator to poles Transport nutrients and organisms Influences weather and climate Influences commerce

Ocean Currents Surface Currents Deep Water Currents The upper 400 meters of the ocean (10%). Wind-driven currents occur in the uppermost 100 m or less Deep Water Currents Thermal Currents (90%) Density differences causes by salinity and temperature produce very slow flows in deeper waters.

Current Gyres Gyres are large circular-moving loops of water Five main gyres (one in each ocean basin): North Pacific South Pacific North Atlantic South Atlantic Indian Generally 4 currents in each gyre Centered about 30o north or south latitude

Lost at Sea

North Pacific Subtropical Gyre “Great Pacific Garbage Patch” Estimate: 46,000 pieces of floating garbage/mi2. 135° to 155°W and 35° to 42°N

Upwelling and Downwelling Vertical movement of water Upwelling = movement of deep water to surface Hoists cold, nutrient-rich water to surface Produces high productivities and abundant marine life Downwelling = movement of surface water down Moves warm, nutrient-depleted surface water down Not associated with high productivities or abundant marine life

El Niño-Southern Oscillation (ENSO) El Niño = warm surface current in equatorial eastern Pacific that occurs periodically around Christmastime Southern Oscillation = change in atmospheric pressure over Pacific Ocean accompanying El Niño ENSO describes a combined oceanic-atmospheric disturbance

Forecast El Niño will likely peak during the Northern Hemisphere winter 2015-16, with a transition to ENSO-neutral anticipated during the late spring or early summer 2016. The expectation that this El Niño could rank among the top three strongest episodes as measured by the 3-month SST departures in the Niño 3.4 region going back to 1950.

Forecast Seasonal outlooks generally favor below-average temperatures and above-median precipitation across the southern tier of the United States, and above-average temperatures and below-median precipitation over the northern tier of the United States.

Normal El Niño Occurs during December 2 to 7 year cycle 1997

El Niño events over the last 55 years El Niño warmings (red) and La Niña coolings (blue) since 1950. Source: NOAA Climate Diagnostics Center http://esminfo.prenhall.com/science/geoanimations/animations/26_NinoNina.html

Effects of severe El Niños

Effects of El Niño Hurricanes: Below normal number of tropical storms/hurricanes in the Atlantic, although this does not imply any limits on the strength or location of any given tropical system. Monsoons: A drier-than-normal North American Monsoon, especially for Mexico, Arizona and New Mexico. Drought: A drier-than-normal fall and winter in the U.S. Pacific Northwest. Wintertime Storms: A wetter-than-normal winter in the Gulf Coast states from Louisiana to Florida, and in central and southern California if El Nino is strong. Warmer Temperatures: A warmer than normal late fall and winter in the northern Great Plains and upper Midwest.

Scientists are still working on the puzzle Scientists are still working on the puzzle. The IPCC’s 5th Assessment Report is planned for 2013-2014. Climate models are being improved, more data is being collected. However, the puzzle is already complete enough to know we need to take action.