Lecture 3 Ice Flashcards
Where does thermal energy come from?
Radiant energy from the sun warms the earth’s atmosphere and surface (water and soil) and becomes heat energy
3 mechanisms that transfer heat energy through the atmosphere (3)
- Conduction = molecule to molecule exchange
- Convection =movement of a fluid (water or air)
- Radiation = transfer of energy by
electromagnetic waves
Conduction (3)
Rate of heat transfer depends on whether the substance is a good conductor:
Air is a poor thermal conductor since on a cold winter day not much heat lost to the surrounding air
Snow is a poor conductor = makes igloos a useful house
Convection (3)
- A phenomenon in fluids or gases
- The fluid or gas is set into motion called a current
- These moving currents are convection
How convection works (heater) (3)
heats the air, it becomes less dense and rises
– Cool air moves in to replace the air that rose
– Generates the air flow
Radiation (6)
- Energy carried by electromagnetic waves (Light, microwaves, radio waves, x-rays)
- Most electromagnetic radiation from the sun is in the form of visible light
- Every object is emitting electromagnetic waves regardless of temperature
- Most things emit primarily in the infrared (Night vision goggles, etc. detect infrared)
- Wavelength is related to vibration frequency
- Heat energy absorbed by land and oceans averages 51% of incoming solar energy
Absorbing radiation (4)
- Things also absorb radiation If they didn’t, they would run out of energy to emit
- Good emitters are also good absorbers
- A good absorber reflects very little energy (Think about dark pavement)
- A poor absorber reflects a lot of energy (Snow doesn’t melt in sunshine even though
1400 watts/meter2 of energy are hitting it)
Radiation at night (3)
- At night, objects receive no input energy from the sun
- Objects are warmer than outer space, so they continue to radiate energy
- Thus, they cool off e.g., Ground radiates heat = if cloudy, reflected back if no cloud, sky is heat sink
How temperatures on earth vary (2 - 1 then 3)
Over space:
* Poles are colder than the equator
Over time:
* Day/night
* Seasonally
* Ice age
Arctic definition (3)
- Geophysicist – region north of Arctic Circle. ie the southernmost latitude at which the sun can remain continuously above or below the horizon for 24 hours
-Climatologist – region with mean temp < 10degrees C in warmest month (July)
- Ecologist – region lying north of poleward limit of trees (tree line)
Earth’s 5 circles of latitude (5)
- the arctic circle
-the tropic of Cancer
-The equator
-The tropic of Capricorn
-the Antarctic circle
Polar Night / polar day
Polar Night = 24 hours of darkness
Polar Day = 24 hours of light, where the sun never goes bellow the horizon
Areas within the Arctic and Antarctic circles have at least 1 day each year with a polar day or night
Polar Day vs the equator (2)
-The Arctic can receive more daily solar energy than the equator!
-On average, the equator receives the most solar energy on Earth
However, in a 24 hour period during a “Polar Day”, the Arctic’s maximum solar energy is higher than the equator’s!
Why are higher latitudes colder? (3)
-Angle of energy reaching north spreads energy over greater area = energy per square meter is less
– Sun has more atmosphere to travel through
– Long nights in winter meaning Less sunlight reaches surface and More heat lost at night than gained in the day
What causes the seasons (3)
-Tilt of Earth on axis and its Orbit around the sun
As Earth orbits, it stays tilted in same direction
* Hemisphere tilted towards sun = summer
* Hemisphere tilted away from sun = winter
If tilt increases, then you will have more regions with constant sunlight in the summer (polar day) and more regions with constant darkness in the winter (polar nights). Therefore the Arctic circle would increase.
Why do Ice ages occur (2)
- Due to Small changes in earth’s orbit around sun called Milankovitch cycles
- Pleistocene glaciations are Thought to have been a change in the orbital path
of the Earth around the sun.
The 3 Milankovitch cycles
Eccentricity – orbit varies from circular to oval. 100k year cycle
Tilt - ranges from 22.1 degrees to 24.5 degrees. Larger angle = more seasonal variation. 41k year cycle
Precession – earth wobbles as it rotates. 26k year period with a Different North star!
Sea Ice (4)
- High albedo = keeps the ocean surface from warming
- Water getscaught up in ice = keeps sea levels low
- Sea ice does not merely grow and melt in one place, it’s almost constantly in motion (pack ice) except in coastal regions where ice grows out from, and stays attached to, the shore (fast ice)
-Many Animals and plants depend on sea ice (ie polar bears and seals)
Polynyas
- Persistent open water surrounded by ice (like a lagoon but ice instead of land)
- sustained by winds or ocean heat
- often occur near coasts, fast ice, or ice shelves
- Incredibly important habitats for many arctic organisms
Polynyas
- Persistent open water surrounded by ice (like a lagoon but ice instead of land)
- sustained by winds or ocean heat
- often occur near coasts, fast ice, or ice shelves
- Incredibly important habitats for many arctic organisms
Forces acting on Sea Ice (5)
- Wind
- Ocean Currents
- Coriolis Force
- Internal Ice Stress
- Sea Surface Tilt
Wind and Sea Ice (4)
– primary force responsible for ice motion
- timescale of days or weeks
- rough ice surface is affected more
- sea ice that drifts freely moves at 2% of the wind speed
Ocean currents and sea ice (3)
- typically act in the opposite direction of the wind force
- act as a drag on the wind-driven sea ice motion
- important in longer-term ice motion (monthly to yearly)
Coriolis force and sea ice (3)
- causes objects to accelerate because of the rotation of the earth.
- in the Northern Hemisphere, causes objects to deflect to the right
- increases toward the poles – plays an important role in determining sea ice motion
Internal Ice Stress (4)
- measure of the compactness, or strength, of the ice – quite variable
*resistance to the motion caused by the wind force - Stress is minimal when the sea ice pack is loosely compacted and can flow freely (e.g., in summer), but can be high when the ice is compact and cannot flow
*strength of ice depends primarily on its thickness. Thin ice breaks apart easily under compression
Sea Surface Tilt (3)
- differences in sea level caused by small differences in gravity
- Geoid – undulating surface results from the uneven distribution of mass within and on the surface of Earth
- also uneven heating, salinity variations, and currents, especially near coastal regions or ice shelves
- small force compared to wind and current forces, but can affect sea-ice motion over months or years
