The Variations in Middle and Upper Stratospheric Water Vapour over the Past Two Decades

The radiative and chemical interactions of stratospheric water vapour (SWV) mean that SWV has a significant influence on the climate. Based on the Stratospheric Water and OzOne Satellite Homogenized (SWOOSH) SWV data (100-1 hPa, 60 degrees S to 60 degrees N), variations in the middle and upper SWV are mainly investigated over the past two decades. Water vapour variations below 10 hPa are found to result from upward transport of the lower SWV. Using empirical orthogonal function analysis and regression analysis of the anomalous upper SWV variability, it is found that upper SWV variations have an 11-year period controlled by the solar cycle as well as a 2-year cycle regulated by the quasi-biennial oscillation (QBO). Our results also show that state-of-the-art chemistry-climate models perform poorly in simulating the upper SWV variations. It is possibly because the effect of lower-middle SWV changes on the upper SWV variations is too strong in the simulations.