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This bar indicates that you are within the PDS enterprise which includes 6 science discipline nodes and 2 support nodes which are overseen by the Project Management Office at NASA's Goddard Space Flight Center (GSFC). Each node is led by an expert in the subject discipline, supported by an advisory group of other practitioners of that discipline, and subject to selection and approval under a regular NASA Research Announcement.

Rossby Number

A small Rossby number indicates that the geostrophic approximation is valid ( i.e., du/dt = dv/dt = 0) and that the Coriolis acceleration, v · f, is greater than the horizontal fluid acceleration, du/dt.

Ro = (du/dt)/(v f) approx (v2/r)/(v f) = (v/r)/f = U/(f0 · L)

For the GRS, hurricanes, etc.

Ro = (Vt a/b2/eta3)/f

eta2 = [ cos2(theta) + (a4/b4) · sin2(theta) ] / [ cos2(theta) + (a2/b2) · sin2(theta) ]

where Vt is the tangential velocity, a is the semimajor axis, b is the semiminor axis, and theta is the angle between the semi-major axis and the direction of motion. Mitchell et al. 1981 JGR 86 p.8751.



terrestrialRed SpotFA/BC/DEsmall spots
Vt110 m/s120 m/s
a1.1E7 m4.9E6 m
Ro(0).36.36
Ro(90).04.08
g.lat22 S33 S40.5 S


Great Red Spot
40000 x 13000 km (1879-1882)
20-60 m/s velocity around spot, 6 day period
bounded by Jets at -19.5 (-60 m/s) and -27.0 (+50 m/s) graphic latitude
long drift = -3.4 m/s
± 1/2 degree longitude oscillation with 90 day period
anticyclonic (counterclockwise in southern hemisphere)