Lecture 12 - A World of Changing Environments Flashcards
What are the Key Elements of the Climate?
-Temperature
-Humidity
-Precipitation (type, frequency and volume)
-Atmospheric pressure
-Wind (speed and direction)
What Factors Affect the amount of Energy reaching/ leaving Earth?
-Orbital forcing
-Atmospheric composition
-Earth’s albedo
-Solar flux
-Ocean circulation
-Earth’s energy balance = balance between incoming UV and outgoing infrared
What is Orbital Forcing?
-How Milankovic cycles impact the seasonality and location of solar energy around the Earth
What are Kepler’s Laws of Planetary Motion?
-First Law = each planet’s orbit about the sun is an ellipse
-Second Law = planets do not move with constant speed along their orbits (northern hemisphere winter is shorter than the winter and vice versa)
Milankovic Cycles: Orbital Eccentricity
-Periodicity = 100,000 years
-When the Earth’s orbit is most elliptical, the amount of solar energy received at the perihelion would be in the range of 20-30% more than at the aphelion
Milankovic Cycles: Axial Tilt/ Obliquity
-Periodicity of 41,000 years
-Low obliquity means less difference between seasons (mild summers and winters)
-High obliquity means greater difference between seasons (warm summers and cold winters)
Milankovic Cycles: Precession of the Equinoxes
-Periodicity of 26,000 years
-A slow and continual change of the direction of the rotational axis
-Similar to wobbling a spinning top
-Position of the Earth during its orbit changes over time, affecting when radiation is received and where
How do Winds Operate?
-They impact rainfall patterns
-Wind direction is always high pressure to low pressure
What is the ITCZ?
-A low pressure, high temperature belt which follows the position of the overhead sun
-Rapid rising moist, warm air results in high rainfall
-It is a driver of the Trade Winds
-The Trade Winds converge at the ITCZ from the Southern and Northern Hemisphere
What is the Sub-Tropical High Pressure belt?
-Air here is sinking
-Very dry
-Follows movement of the ITCZ
-Trade Winds are generated here which move towards the low pressure ITCZ (like a convection current)
What are the Trade Winds?
-Surface winds as air moves back towards the equator
-They follow movement of the ITCZ
-Winds pick up moisture and air is forced upwards as the winds converge (at the ITCZ)
-This rising air causes cloud formation
How does Rainfall Occur Locally?
-Air rises due to convection, frontal activity (cool air meeting warm air) and orography (air meeting the land and forced upwards, e.g. the Lake District)
Why do Sea-Surface Temperature vary Spatially?
-Temperature regions, e.g the North Atlantic Drift
-Warm sst = high rates of evaporation which results in high rainfall on adjacent land
-Cool sst = low evaporation and low rainfall/ desertic conditions on adjacent land
Describe Antarctic Bottom Water and Thermohaline Circulation
-Antarctica is separated from the Deep Southern Ocean by a shallow continental shelf
-Waters are exchanged here between the deep ocean and the shallow shelf, forming the Antarctic Cross Shelf Circulation:
-Dense water leaves the shelf as
Antarctic bottom water (this will
then flow at the bottom of all
oceans
-relatively warm water from the
Southern Ocean (modified
circumpolar deep water/ MCDW)
comes onto the continental shelf,
bringing heat to the ice shelves
What is the Importance of the Antarctic Cross-Shelf Circulation?
-Antarctic cross-shelf circulation influences the water that transports heat, carbon, and nutrients around the globe
-It also influences basal melting of Antarctic floating ice and therefore the stability of the entire Antarctic ice sheet
