Twitter study of tweet volume by time of day and day of year in New York, Tokyo, Istanbul, and São Paulo: "We see different patterns of activity between the four cities. For example, waking/sleeping times are relatively constant throughout the year in Tokyo, but the other cities exhibit seasonal varia- tions. We see that Japanese users’ activities are concentrated in the evening, whereas in the other cities there is more usage during the day. In Istanbul, nights get shorter during August; Sa ̃o Paulo shows a time interval during the afternoon when tweet volume goes down, and also longer nights during the entire year compared to the other three cities." http://www.umiacs.umd.edu/~jimmylin/publications/Rios_Lin