Problem with Trim or Split

Hi all,

I want to trim an ellipsoid with a closed curve on the surface (as shown in the pictures). As a result the ellipsoid / the area inside the closed curve is interrupted by the meridian curve of the ellipsoid. The area inside the closed curve is divided into two pices.

Does anybody know how to fix this problem? Why does the meridian curve interact with a trimming or splitting process?

I think this problem was discussed before but I could not find a solution.

thanks :-)