| The mesosphere is characterized by a marked decrease in temperature that is carried through from the stratopause. |
| The base of the mesosphere is defined as the temperature maximum existing at the top of the stratosphere, with the boundary between the two regions usually called the stratopause. |
| After the peak, the stratopause descended further, the upper stratosphere warmed, and the lower mesosphere cooled. |
| In answer to your question about how the water vapour gets that high, water vapour is thrown into the stratopause by volcanic eruptions and remains trapped. |
| As for the northern hemisphere, there is general cooling of the atmosphere, i.e., around the stratopause and in the lower stratosphere from September to December-January. |
