Mysteries of the tropical lower stratosphere: trends and cycles

While the lower stratosphere is expected to cool as a result of ozone depletion and increases in greenhouse-gas concentrations, the temperature record from radiosondes shows an unexpected time profile, especially pronounced over the western Pacific region. Trends were small or non-existent until the early 1990s, and strongly negative (up to 3 K per decade) thereafter. At the midlatitude edge of the tropics (e.g., Hawaii) the long-term record since 1980 shows a cyclical sawtooth pattern, with 8- to 10-year cooling intervals separated by more rapid recoveries. These characteristics will be described and discussed, and the possible connection to sea-surface temperatures in the tropical Pacific will be explored.