Water Cycle: Global Circulation Driven by convection (flow to transport heat) Sun’s energy input is 1370W/m 2 at Earth’s orbital distance –Q: How much energy does Earth emit compared to solar energy input?

Water Cycle: Global Circulation Energy input is not uniform over Earth’s surface  more heating at equator, less at poles

Latitudinal Energy Balance Energy input&loss nonuniform over Earth’s surface  atmosphere+ocean circulation transport heat towards poles

??? What would temperature at poles be on an Earth with no atmosphere and oceans, when compared to actual Earth? During winter? During summer? What would effect of ice be on Earth’s absorption of solar energy? What is effect of greenhouse gases in atmosphere on surface energy balance? On surface temperature? How does a greenhouse gas work? (or a greenhouse?)

Mean Annual Heat Balance Atmosphere blocks incoming solar radiation AND creates greenhouse effect 23% of incoming solar energy goes into evaporating water (~1 ton/m 2 -year)

Water Cycle: Global Evaporation Solar Input leads to evaporation (change from liquid to gas) (Area Earth Disk)(Energy for evaporation) (Earth Surface Area) (Latent Heat of evaporation) Rate =

Latitudinal Energy Balance Energy input & loss are nonuniform over Earth’s surface  atmosphere+ocean circulation transport heat towards poles Radiated Energy proportional to T 4 (e.g. hotter surface radiates more energy)

Mean Annual Heat Balance Atmosphere blocks incoming solar radiation AND creates greenhouse effect 23% of incoming solar energy goes into evaporating water (~1 ton/m 2 -year)

Earth’s Rotation makes things more interesting… If non- rotating Actual rotating

Coriolis Effect

Earth’s Rotation makes things more interesting… If non- rotating Actual rotating

Cellular Structure of atmospheric circulation

Equatorial InterTropical Convergence (ITC) Annual change in ITC responsible for monsoon season

ITC Change generates Monsoon Annual change in ITC responsible for monsoon season

Polar Convergence (Front + Jetstream) 1

Polar Convergence (Front + Jetstream) 2

Ocean Circulation: Another heat transport engine (driven by changes in heat and salinity& wind drag) El Nino year (weaker trades & no upwelling off S. Am.) Wind-induced upwelling off S. Am.

Ocean Surface Currents

Salt makes a big difference because seawater evaporation changes the density of the remaining seawater Typical fresh water has 0.02% dissolved salt (density  =1 ton/m 3 ) Typical salt water has 3.5% dissolved salt ions (  = ton/m 3 ) (evaporation makes the leftover water denser as it does not remove salts)

Ocean variations in Salinity (%) Poles have less evaporation, more precipitation (relative to evaporation), and fresher water… Salinity(ppt)

Ocean variations in Temperature Seawater at poles is colder than in tropics (cooling water generally makes it denser but below 5°C waters density decreases with further cooling) Ice-shelves freezing makes underlying water saltier & denser (cold+salty=> densest!)

Polar downwelling (driven by polar cooling) Densest water finds the bottom where it spreads out, next densest tends to float above densest, and so on…

Freshwater carried eastward by rainclouds Global conveyer belt Deepest Antarctic bottom-water takes ~1000 years to mix in Flow in conveyor is about 15 times larger than flow of all rivers

Global climate