Much like the oceans, the atmosphere on Earth oscillates on a global scale. The so-called atmosphere tides depend on the Sun’s heat and gravity, as well as the pull of the Moon and Earth’s own rotation. In the troposphere, scientists have identified a regular tide, which they call DW1, that has a 24-hour period and a zonal wave number of 1. Zonal wave number refers to the number of troughs and peaks that can be observed simultaneously in a wave as it circles the entire globe, meaning in this case that there is only one of each.
Click here for original story, Explaining thermal tides in the upper atmosphere during the 2015 El Niño
Source: Phys.org