Why do the same vegetables taste better in the north wind than in the south wind? What is the reason? Is it an illusion?

This is not an illusion. Scrubbed vegetables are delicious and have scientific basis.

Under the influence of mild atmosphere and decreased photosynthesis, the organic acids produced by plants themselves were effectively inhibited and digested, which greatly reduced the acidity and astringency of the taste.

In order to resist the cold, the plant nerve itself will convert starch into powdered sugar, which will make the taste sweet.