Non-Divergent and Irrotational
Flows in
Hurricane Jimena at 1930
UTC on 23 September 1991
The two panels below show the radial and vertical variation of the zonal wind component averaged around the storm center at a given height and radius from storm center. The left panel shows the non-divergent flow, determined by finding a wind solution that most closely matches the Doppler observations while having a vertical wind everywhere of zero (and thus a horizontal wind divergence of zero as well). The right panel shows the irrotational or divergent-only component of the wind, determined by subtracting the non-divergent field from the full three-dimensional flow that includes vertical wind and horizontal divergence.
At larger radii the divergent
flow tends to add to the non-divergent flow, while at smaller radii (inside
the eyewall), the divergent flow opposes the non-divergent flow.
Thus the divergent flow (associated mostly with eyewall convection) tends
to reduce the shear near the center, thus protecting the core.
This protection can be seen
in the full analysis (the sum of the two analyses shown above) shown below.
Note the decreased shear near the center compared with the non-divergent
analysis above.