Effect of convection on the summertime extratropical lower stratosphere

Satellite and in situ water vapor and ozone observations near the base of the overworld (theta approximate to 380-K potential temperature) are examined in summertime northern midlatitudes, with a focus on how their horizontal variations are influenced by deep convection. We show that summertime convection has a significant effect on the water vapor budget here, but only a small effect on the ozone budget. Using a simple model, we estimate that convection increases model extratropical water vapor at 380 K by 40% but decreases model extratropical ozone by only a few percent, relative to what would occur without convection. In situ data show that this convective injection occurs up to at least similar to390 K. This raises the possibility that the convectively moistened air might travel isentropically to the tropics and ascend into the stratospheric overworld without passing through the cold point. We argue that trends in convective moistening should be examined as possible contributors to observed trends in lower stratospheric water vapor, at least during summer months.