Science unit 9.3

• Axis


  Imaginary line connecting North Pole to South Pole
• Earth's rotation


  Rotates on its axis once per day
• Sun "rises" in the East, "sets" in the West
• For us, the sun rises over the Atlantic Ocean to our East, sets over the Appalachian Mountains to our West
• Earth's axis tilt


  Causes the seasons
• The Earth's axis is not straight up-and-down… it's actually ~23.5° off-center
• As Earth orbits the sun, the north end of Earth's axis points in the same direction, but the orientation of Earth's axis changes relative to the sun over the course of a year
• Axis orientation DOES NOT CHANGE!!
• Earth's revolution


  Revolves around the sun once per year
• Rotation


  An object spinning around its own center of mass or axis
• Revolution


  One object moving in a circular path around another object
• The earth travels around the sun due to the sun's gravitational attractive force exerted on the earth
• It takes the Earth 365.242189 days (or 365 days, 5 hours, 48 minutes, and 45 seconds) to make a complete revolution; this is why we have a leap year every 4 years
• Latitudes


  • Different parts of Earth receive different amounts of sunlight depending on the season
  • Areas closer to the equator (lower latitudes) receive more direct sunlight year-round
  • Areas near the poles (higher latitudes) receive highly varying amounts of sunlight… "polar day" and "polar night"!
• This is why the equator is warmer, and the poles are cooler
• Climate


  Depends on the amount of incoming vs outgoing solar radiation (referred to as "global heat budget")
• The angle at which sunlight hits Earth's surface depends on the latitude!
• North Pole slanted away from the sun's rays, South Pole slanted towards the sun's rays
• Solstice


  • Occurs when the sun is directly overhead at latitude 23.5°N or 23.5°S
  • Solstices are when the sun's location are the farthest north or south from the Equator
  • Also the "longest" and "shortest" days of the year
• Summer Solstice happens in June in New Jersey (Northern Hemisphere), LOTS of daylight
• Winter Solstice happens in June in Australia (Southern Hemisphere), LOW AMOUNT of daylight
• Equinox

  • Halfway point from one solstice to the other
  • At an equinox, neither hemisphere is tilted towards the sun, and the lengths of daylight and darkness are approximately equal
• Autumn and Spring Equinoxes have equal number of hours of day and night (Approx. 12 hours, depending on latitude)
• Weather


  Short-term events in temp, precipitation, etc. Based on latitude, altitude, and proximity to water
• Climate


  Long-term trends in weather over larger areas, typically measured over the span of years (typically ~30 years)
• Earth's climate has a history of changing
• Köppen Climate System


  • Divides climates into 5 main groups based on criteria (usually temperature) which allows for different vegetation growth
  • Zone A: Tropical/equatorial
  • Zone B: Arid/dry
  • Zone C: Warm/mild temperate
  • Zone D: Continental
  • Zone E: Polar
• Climate change is affecting NJ faster than much of the rest of the United States. New Jersey has warmed up faster than any other U.S. state by average air temperature over a 100-year period beginning in the early 20th century… about 3°F in the last century (2× as much as the rest of the country)
• Major impacts in NJ

  • Rainfall → erosion + coastal flooding → tourism + food!
  • Coastal flooding → water sources and power plants!
  • Loss of barrier islands → increased inland storm damage!
• Paleodata (paleoclimatology)


  Data from older sources that give us hints about what the climate, or other variables, was like
• Paleodata sources

  • Different carbon isotopes
  • Ice cores (trapped air bubbles!)
  • Tree ring data (slow growth in winter vs. fast growth in summer)
  • Varves (layers in glacial lake sediments have annual patterns)
• Warm summers produce a thick deposit of sediment. These alternate with thin, clay-rich layers deposited in cool winters
• Milankovitch Cycles


  • Describe how relatively slight changes in Earth's movement affect the planet's climate
  • Cycles caused by changes in the shape of the Earth's orbit around the sun, tilt of the Earth's rotation axis, and wobble of our axis
• Eccentricity Cycle (Elliptical Cycle)


  About every 100k years. When the Earth orbit is elliptical we spend less time close to the sun in the span of a year (less solar energy, tends to cool the Earth)
• Obliquity Cycle (Axis Tilt)


  About every 41,000 years. Axis tilt can change up to 2.5 degrees. Increased obliquity can cause summers to be warmer and winters to be colder
• Precession Cycle (Wobble)


  About every 26,000 years. Wobble of Earth's axis driven by tidal forces which are influenced by the sun and moon. Earth is not perfectly round so gravity tugs the axis over time creating the wobble cycle. Can affect seasons!
• Ice Age


  • A period of time where global temps drop so much that glaciers advance and encompass over one third of Earth's surface
  • A "glacial" period is the period of time where glacial advancement occurs
  • An "interglacial" period is the warmer period of time in an ice ages when glaciers retreat and sea levels rise
• Earth is currently in an interglacial period
• The last glacial period began about 100,000 years ago and lasted until 25,000 years ago
• Other Factors That Affect Weather

  • Change in solar output (every ~11 years the sun grows brighter and then dims)
  • Change in plate tectonics (changes where oceans are and how ocean currents flow)