Increasing Water Vapor in the Stratosphere and Mesosphere After 2002

Water vapor (H₂O) measurements made by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument between 2002 and 2018 and by the Aura Microwave Limb Sounder (MLS) instrument between 2004 and 2018 are analyzed to determine the linear trend and solar cycle response of H₂O in the stratosphere and mesosphere. Both SABER and MLS show a rapid global H₂O increase of 5–6% per decade in the lower stratosphere after the 2001 drop. The increasing zonal mean H₂O at 40°N in SABER and MLS is consistent with the Boulder frost point hygrometer data in the lower stratosphere. The global distribution of SABER and MLS H₂O trends are positive at most altitudes and latitudes, and they peak in the tropical lower stratosphere. In the mesosphere the SABER H₂O trend is 0.1–0.2 ppmv per decade and the MLS H₂O trend is 0.2–0.3 ppmv per decade. The trend and solar cycle response derived from the observations are compared against the Whole Atmosphere Community Climate Model (WACCM). The solar cycle response of H₂O from WACCM agrees with SABER and MLS. The linear H₂O trend from WACCM does not show the observed increase in the lower stratosphere.