Variability of subtropical upper tropospheric humidity

The largest climatological mean values occur over the central-eastern Pacific and Atlantic oceans, where there is also large day-to-day variability.

In contrast, there are smaller mean values, and smaller variability that occurs at lower frequency, over the Indian and western Pacific oceans. These differences in the distribution and variability of subtropical RH are related to differences in the key transport processes in the different sectors. The large variability and intermittent high and low RH over the central-eastern Pacific and Atlantic oceans are due to intrusions of high potential vorticity air into the subtropics.