Twitter index: September 11, National Day of Catalonia

Trending topics #Remember911, "Torres Demelas," "World Trade Center" and "11 de Setembro" are all being used to mark the anniversary.

Meanwhile, Catalonian microbloggers are wishing one another "Feliç Diada" to mark the National Day of Catalonia.

Boy band One Direction also makes an appearance among the top ten topics, as Indonesian Twitter users express their love for the band with the hashtag #IndonesiaCintaOneDirection.

The top 10 most talked about topics on Twitter on September 11 at 1:00pm GMT are:

1. #Remember911
2. #WordsISayWhenImMad
3. #IndonesiaCintaOneDirection
4. 11 de Setembro
5. Feliç Diada
6. Salvador Allende
7. Torres Gemelas
8. World Trade Center
9. Hi Love
10. Feliz Martes