According to the Poincare Hopf theorem, we know that the sum of the indices of the critical points of a flow over the 2-sphere is 2. I conclude that we can have one critical point having index 2, or two critical points having index 1 (e.g. the flow of west winds). But doesn't the flow of east winds over the sphere create two critical points of index -1? Or is it not possible to have such a vector field on the 2-sphere?
2026-04-05 20:04:34.1775419474
Poincare Hopf: possible vector fields on the 2-sphere
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The flow of east winds over the sphere that you wrote seems the following picture.
The index of this flow must be $1$, not $-1$. Then the sum of indices of critical points is $2$.
The index $-1$ is the following picture.