4. Results

Animation 2: Advection of passive contours (GIF animation; 1990kB).
The contour positions are displayed from t = 0.0 to t = 10.0 at an interval of 0.1 . Fluid in y < 0 at initial time is colored light blue.

- Passive contours clearly show the flow in other regions than the patch contour where little interest was put on in the previous analyses.

- The fluid are deformed even while the elliptical vortex keeps its shape. Especially at the edge of the ellipse, the fluid outside the vortex is dragged and stretched out.

- Fluid particles are stretched near the sreamlines containing the stagnation points in the co-rotating frame analyzed in section 4.2 .

- A complex flow pattern is produced after the streamer formation. There are many indications of stretching and folding.

- This stretching is also recognized as the time evolution of the length of each passive contour. ( Note that the area between two contours is preserved due to the nondivergent fluid. )