* Wide range of spatial scales for vortices

o All require centripetal acceleration
o Magnitude of acceleration increases as spatial scale (radius) decreases

+ Centripetal Acceleration

o Impact of Coriolis felt primarily at larger scales

* Rossby Number Scale Ratio

o Measures importance of Coriolis relative to centripetal acceleration

+ For uniform rotating flow:

# Centripetal + pressure gradient + Coriolis = 0
# Gradient Wind Equation

o Ratio of Centripetal Acceleration to Coriolis Acceleration:

+ Ro = (V2/r) / (fV) = V / (fr)

o Radius of vortex is main source of variation

+ Radius ranges from meters to 1000s of kilometers
+ Velocities range from around 0.5 m/s to around 50 m/s

o Coriolis is weak force, only important for large scale flows

+ At 45oN: f = 1.03 X 10-4 rev/s
+ So fV = 5 X 10-5 m/s2 to 5 X 10-3 m/s2
+ Takes a long time to have a measureable impact

* Small Scale Vortices

o Ro >> 1 (r < 10km) - Cyclostrophic flow
o Coriolis not important so inward acceleration always caused by central low pressure
o No prererential direction for rotation
o Small scale vortices (e.g. dust devils) rotate either direction in either hemisphere and at equator

* Large Scale Vortices

o Ro << 1 (r > 1000km) - approaches geostrophic flow
o Slightly curved flow produced by small differences between Coriolis and pressure gradient
o Coriolis always deflects to right in Northern Hemisphere, to left in Southern Hemisphere
o Enforces preferential directions for rotation around central highs and lows

+ Counterclockwise around lows in Northern Hemisphere, clockwise in Southern Hemisphere
+ Clockwise around highs in Northern Hemisphere, counterclockwise in Southern Hemisphere

* Intermediate Scale Vortices

o Ro = O(1) (r = O(100km)) - Gradient wind flow
o Coriolis strong enough to enforce preferential directions of rotation