Atmospheric excitation, or atmospheric disturbance, was an unnatural disturbance in the atmosphere which caused the weather to change. The Tenth Doctor's sonic screwdriver, the TARDIS, and moving a planet could all cause atmospheric excitation.
The Tenth Doctor used a device above the inside of the door of the TARDIS to excite the atmosphere, causing snow, in an attempt to cheer up Donna Noble (which, however, terrified her). (TV: The Runaway Bride)
The shifting of the Earth's location from the Medusa Cascade back to its original orbit caused rain. The Tenth Doctor said that there would be a lot of it, but it would eventually calm down. (TV: Journey's End)