https://www.gamespot.com/articles/pokemon-go-global-challenges-available-during-summ/1100-6460033/

Pokemon Go's Summer Tour 2018 kicks off this weekend with the Safari Zone live event in Dortmund, Germany, but even if you aren't able to attend in-person, you'll still have a chance to participate. The Pokemon Company announced that special Global Challenges will be underway during each of this summer's live events, with players all over the world contributing toward their success.

Each weekend that an event takes place, players will be divided up into four regions: the Americas; Europe, the Middle-East, and Africa; Asia-Pacific; and the "main research site," which is the location of the live event. Each region will strive to complete their own challenges, which will contribute to the global progress and unlock bonus rewards in the game. If players manage to earn bonus rewards during all three events, then Niantic teases an Ultra Bonus will be unlocked--although what that will be remains a mystery.