It is true that P is more common in cold areas (Scandinavia for example) where there is less sun hours, and also that P exacerbated in the winter and tends to remit in the summer. However, these are only a part of the reasons for P activity, and in Israel, where I practice we have a lot of immigrants from cold and more polar areas who's P exacerbates, continues, and most of them don"t get a remission just from relocating. One positive point thaugh... We have the Dead Sea...
Dr. Gilead