Hi.

 

The first; what size of a mylar mirror "umbrella" held by a reasonably far positionable satellite could produce a ~500 Km Ø shadow on earth?

 

And the other; would such shade cool the sea surface a few degrees if projected several days on a path, enough to somewhat decrease the intensity of a hurricane ?

 

Miguel

As far is I know, the sun is far enough away from the earth to make the light waves from the sun almost parallel. If this is true, then the umbrella would need to be around 500km to produce a 500km shadow.

 

As for the second point, warm water in the ocean tends to exist in streams of current, so shading just the path of a hurricane wouldn't help. You'd have to cool the current, wherever that was coming from.

 

I may be wrong