Chapter 2 - Climate Systems Today Flashcards
How does solar radiation arriving differ to back radiation emitted?
Earth has maintained a constant temperature through time, thus must be losing an equal amount of heat; back radiation. It occurs at a longer wavelength than incoming short wave radiation.
What kind of radiation is trapped by greenhouse gases, and what is the climatic impact?
95% of longwave radiation is trapped. Radiation is retained within climate system and reradiated back to Earth. Makes surface temps 31 degrees warmer than it would be.
What different and opposing roles do clouds play in the climate system?
Cold cloud tops emit radiation back to space and offset retained radiation to keep balance. However, clouds also trap outgoing radiation. Relative strength of these mechanisms varies with region and season.
How does back radiation add to effects of uneven solar heating (pole-equator imbalance)?
Higher latitudes receive less radiation due to less direct angle. The effect of this is amplified by high albedo of ice and snow reflecting radiation; positive feedback.
What causes air to rise from Earth’s surface?
Air is heated, expands in volume and rises due to lighter density. This air carries sensible heat in convection.
What causes the monsoon circulation to reverse from summer to winter
During summer, air circulation is upwards over land due to low pressure and downwards over the ocean as pressure increases. During winter the exact opposite occurs due to the slow thermal response of the ocean which is now warm relative to land, thus heat rises
Describe the main path by which heat is transported to poles
Hadley cells. Heat rises at tropics (ITCZ), sinks at subtropics as pressure increases. Fronts at middle and high latitudes then move warm air polewards, and cold air towards to equator.
Why does rain fall on the sides of mountains in the path of winds from nearby oceans?
As moist air driven up mountains rise and cool, water vapour condenses and precipitates
How do low level winds create spinning gyres in subtropical oceans?
Result from an initial drag of winds on the ocean surface and of the Coriolis deflection of the moving water
Why does deep water form today at higher latitudes?
- Initially acquire salinity from strong evaporation in the subtropics. Then frigid airmasses extract sensible heat to increase density
- Increased density resulting from salt rejection
Intense cooling in gaps in extensive sea-ice cover
What is the impact of sea ice on the atmosphere?
Seals off underlying ocean from interacting with atmosphere, thus heat cannot be released. High albedo of ice reflects radiation; positive feedback loop. Can cool surface temps by 30 degrees
What parts of ice sheets gain and lose mass?
Glaciers accumulate mass at cold, high elevations. Snow turns to ice and flows to lower elevations where melting occurs (ablation zone).
Accumulation occurs due to persistence of ice through summer at subfreezing temps. Ablation occurs due to temps exceeding freezing point/calving (shedding of ice bergs)
What regions of the ocean are most productive?
Upwelling in eastern equatorial Pacific and Atlantic oceans increases photosyynthesis and thus productivity in these regions
(upwelling returns nutrients to the surface and replaces those delivered to continental shelves etc.)
What explains discrepancy between projected and actual earth temperature when accounting for back radiation?
Greenhouse gasses; they adsorb 95% of back radiation. Increase global temps by 31 degrees.
Where is most radiation stored?
Low latitude oceans - high heat capacity and high receival of radiation
Methods of heat transport through the atmosphere?
Sensible heat = conduction and convection. Involves no change in state and can be directly sensed
Latent heat = requires a change in state. e.g. evaporation of water
How can salinity increase?
Evaporation at low latitudes or salt rejection (stores freshwater in ice and leaves salty) at high latitudes
How can density increase?
Increase salinity or cool the water (compressible, less volume). Cooling occurs when warm water is carried poleward or when cold air masses travel to low latitudes
Why is there no deep water at low latitudes?
Not high enough salinity and surface waters are not dense
Why are air temperatures in high latitudes with ice so low?
As ice cover seals off air/water interactions. Typically this interaction keeps the lower atmosphere a similar temp to sea, but with the ice cover air temps can decrease by 30 degrees
Why do extremes in ice cover lag behind radiation?
This is because large inputs and extractions of heat calories are required to from and melt sea ice .
Also this process involves heat exchange with the slow-responding ocean which has a very high heat capacity
What are the conditions needed for ice accumulation?
Temperature needs to be cold enough for snow to fall AND persist through the summer
What are the conditions needed for ice ablation?
- Temperatures exceed freezing point
- Absorption of radiation
- Uptake of sensible/latent heat delivered by warm air masses
- Summer rain across ice
Calving = shedding of icebergs
Why is there not abundant photosynthesis in surface waters?
Due to a lack of nutrients N and P
- Phytoplankton use nutrients
- Sink when they die
- Decompose releasing nutrients into deeper ocean
Where upwelling occurs, nutrients brought back to surface
Factors effecting poleward heat flow?
- Shape of continents
- In north Atlantic -circulation cell (surface water sinks below 2km and is compensated by surface waters in the south - thermohaline flow)
Mediterranean overflow water sinks due to?
winter chilling and strong evaporation
how can small scale warming occur at ice sheets?
- Gaps (leads) in ice cover produced by changing winds allow some heat exchange
- Pools on ice cover which form during winter may darken ice, allowing more absorption of radiation
why do ice streams occur?
- Weight of ice sheet melts bottom creating layer of water
- Meltwater may cause soil to loose cohesiveness - deformable bed
