04Precipitation

04Precipitation - ESM 203: Atmospheric circulation and...

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ESM 203: Atmospheric circulation ESM 203: Atmospheric circulation and precipitation and precipitation Jeff Dozier and Thomas Dunne Fall 2007
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2 Circulation driven by radiation imbalance Circulation driven by radiation imbalance with latitude with latitude 0 30 60 90 latitude Absorbed solar radiation Emitted infrared radiation excess deficit
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3 Effects of spatially variable heating on a Effects of spatially variable heating on a uniform, non-rotating Earth uniform, non-rotating Earth Heating at equator and cooling near poles would cause a single convection cell in the atmosphere if Earth were covered with a uniform surface and if Earth did not rotate Duxbury, A.C. & Duxbury, A. B. (1989) An Introduction to the World’s Oceans
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4 Movement across Earth’s rotating surface Movement across Earth’s rotating surface A substance that moves across Earth’s rotating surface moves from a place where the planet is rotating at one speed to a position where it is rotating at a different speed (measured in m/s, not in radians/s or deg/s) Ignoring friction, if an air parcel moves directly north in N hemisphere, it begins with a faster W E velocity than does the place it is heading for. Also, as it moves “inward” relative to Earth’s axis of rotation the air’s rotation speeds up because its angular momentum (m ω r, where ω is angular velocity) must remain constant, like a spinning skater. Duxbury, A.C. & Duxbury, A. B. (1989) An Introduction to the World’s Oceans From the point of view of an observer on the surface, the air appears to move to the right
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5 Coriolis force Coriolis force Displacement of the air parcel is to the right in N hemisphere appears to be subject to a [Coriolis] force that increases with increasing latitude and air speed Using same reasoning, imagine the effect on air moving south (toward faster rotating surface) in the N hemisphere In the S hemisphere, the sense of the force is reversed (i.e. to left) whether moving north or south Duxbury, A.C. & Duxbury, A. B. (1989) An Introduction to the World’s Oceans
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6 Coriolis force on a rotating disk Coriolis force on a rotating disk Definitions : velocity of rotation v = ω r, ω = angular velocity (rad sec -1 ) r = radius of rotation angular momentum = vr = ω r 2 Conserving angular momentum with change Δ r=r 0 -r requires ω r 0 2 = ( ω + Δω ) r 2 = ( ω + Δ v/r)r 2 , where Δ v is relative velocity caused by Δ r from r 0 to r Solving, Δ v = ω ( r 0 2 /r - r) r 0 r
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7 Effect of latitude, Coriolis force on a Effect of latitude, Coriolis force on a sphere sphere Equator N latitude true direction of Coriolis force the horizontal (only important) component, proportional to sin(latitude)
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8 Coriolis force and cooling of air raised at equator Coriolis force and cooling of air raised at equator disrupt the simple circulation of a non-rotating Earth disrupt the simple circulation of a non-rotating Earth Air rising at Equator moves N and increasingly to E while
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This note was uploaded on 08/06/2008 for the course ESM 203 taught by Professor Dozier,dunne during the Fall '07 term at UCSB.

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04Precipitation - ESM 203: Atmospheric circulation and...

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