Week 5: Global temperature - Ocean and atmospheric circulation

Tending the wild: keeping the river

Yurok living on the Klamath river
- river provides food (salmon caught with dip nets)
- law enforcement surrounds a birthday party fishing for salmon - they start singing and police get scared and leave
- the indigenous people have to fight for their river
- tons of fish killed after farmers dump run off into the river
- trees should have been culturally burnt - cooling the water temp but hasn't seen fire in 100 years
- river has been warming
- protesting to remove dams

Key takeaways:

- reduced summer river flows leading to increased stress on fish and other species
- higher temperatures and longer dry seasons increase wildfire risk and impair water quality in streams

temperature anomalies

How different temperatures are from what they are normally.
- We typically use a 30-year mean temperature value as an estimate of what is “normal”. We then look at the annual average temperature and subtract the 30-year mean value to determine how different a particular year is from what is normal.
- Positive values indicate years that are hotter and negative values indicate years that are cooler.

How to measure global average temp:

1. Measure temperature above land and the ocean in thousands of places around the world.

2. Subtract the temperature you measure at each location from the usual temperature on that day. The difference is called the anomaly.

3. Repeat steps 1 and 2 for each day of the year.

4. Divide the planet into a grid of 2592 squares. Calculate the average temperature anomaly for each square. At the end of the year, you will have 946080 temperature anomalies.

5. Take the average of all temperature anomalies from all over the world. Compare this with other years.

Hadley cells

largest cells
- warm air spreads out towards the poles, gradually cooling and sinking then moves back to the equator

tropopause

acts as a lid to the lowest part of the atmosphere, which contains all of our weather

polar cells

smallest cells
- cold dense air flows at low levels towards north or south
- as the air leaves the polar region, it warms and rises, returning to poles at high levels

ferrel cells

in between polar and Hadley
- unlike polar and Hadley, ferrel cells are NOT driven by temperature

The Coriolis effect

- refers to an apparent deflection of a moving object that occurs due to the rotation of the earth. For example, air moving in the northern hemisphere appears to be deflected to the right and air moving in the southern hemisphere is deflected left.

polar front jet stream

results where ascending air from the Ferrel and Polar cells meet. This is called the polar front and is characterized by steep temperature gradients which create the fast flowing air of the jet stream.

the subtropical jet stream

occurs because of the conservation of angular momentum which causes the Coriolis effect to increase towards the poles. By the subtropics, air is moving eastwards creating the subtropical jet stream.

Intense cloud cover over India in July

The intense cloud cover you observe over India in July is the result of differences in heating over the Indian Ocean and the land mass that is India. In summer the land heats more quickly than the oceans creating a low pressure system over India that draws moisture-rich air from the oceans. This moisture-rich air cools rapidly as it is pushed upwards by the Himalayas causing intense rainfall. These rainfall events are referred to as monsoons.

how surface ocean currents are caused

Surface ocean currents are caused by atmospheric circulation and tides. Currents near shore are influenced by winds and tides, whereas currents out at sea are mainly affected by winds.

gyres

- clockwise in northern hemisphere
- counterclockwise in southern hemisphere

the global conveyor belt

thermohaline circulation of deep water and surface currents = winding loop - GCB
- carries nutrients for ocean life
- longest current in the world
- only moves a couple cm per second
- rising sea temps are causing it to slow down

Thermohaline circulation

Thermohaline circulation is driven by differences in temperature and salinity, which affect the density of water. Cold, saline water is more dense than warm, fresh water. Waters arriving in the north from the equator are cooled and salty and therefore sink – this is what drives the global conveyor belt which is a giant current system moving energy around the planet.

El Nino

upwelling occurs across the tropical pacific
- warm water of the coast of Asia/Australia (west)
- cooler water in the east of of South America
- The warmer water in the west causes more rainfall and storms above it
EL NINO:
- trade winds weaken
- warm west water swaps over to east and so does the warm weather
- El Nino years are the warmest on record
- peaks around Christmas time and lasts for several months
EL NINA:
- trade winds become stronger and warm water in the west gets pushed towards western pacific
- makes colder, stormier weather