Balanced Vortex: Suggestions for Teacher

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This experiment exhibits a number of important principles of rotating fluid dynamics including conservation of angular momentum and balance of forces.  Here we will focus on the role of rotation in influencing the motion, by defining a non-dimensional number as the ratio of two timescales, the so called Rossby number

Ro= τtankmotion

where  τtank is the rotation period at which the cylinder/tank is spun and τmotion is the period of the circular motion set up in the tank, which can be measured by tracking the paper dots.
For more on background theory for curved flow – see theory.


Here we describe three activities illustrating how to use the concept of  Rossby number to draw analogy between the tank experiment and observed hurricane data.

Activity 1:  and introductory activity making use of a set of four experiments yto introduce the concept of Rossby number – see  Balanced Vortex matrix(pdf).

Activity 2 : an example, using  Hurricane Bertha,  on how to use real observed wind from scatterometer imagery to calculate Rossby number in function of radius – see Balanced Vortex and Hurricanes wind(pdf).

Activity 3: a more general activity,  making use of scatterometer imagery:
1. Choose an hurricane case from the Scatterometer Imagery of Historical Storms
2. Plot the surface winds at different times along the path of the hurricane
3. Choose a specific time and download the wind data to compute the Rossby number in function of radius – see instructions  (you need Matlab for this part)
4. Discuss how the hurricane data compare to the radial inflow experiment.

Interesting case studies:
Hurricane Katrina (Aug’05): NASA-EO, NCDC
Super-typhoon Ioke (Sept’06): satellite loop, NASA-EO, QuickScat
Hurricane Dean (Aug 07): satellite loop, NCDC, NASA-EO, QuickScat
Hurricane Bertha (Jul 08) NASA-EO