The most interesting thing about the windsurfing chart is the seasonal peaks. Obviously the Euros dig their gear out each summer and post like crazy then put their gear away and go skiing or snowboarding.
Search for "windsurfing, skiing, snowboarding" and the trends are almost perfectly complimentary, although the magnitude of the snow sports is much bigger than windsurfing.
CMC said...
... The Google trends does not monitor how many people visit Windsurfing sites as a whole only how many Google the term itself. ...
Google does indirectly monitor traffic to web sites. The number of searches is only part of it.
Google has software bots that trawl through web pages and counts the number of links to a web site from other web sites. The one with the most links is the most popular. It then applies that popularity factor to the links so the most popular site linked to by the most other popular sites is even more popular and appears at the top of the Google listings.
Every time you post a link to a web site counts as another vote for that web site so the more people looking at and sharing and posting on a web site, the more it features in Google's results.
This is why forums often get strange posts for products. The link to the product gets multiplied by the popularity of the forums and the products get bumped up in the Google results.