Large Anomalies in Lower Stratospheric Water Vapor and Ice During the 2015-2016 El Niño

Winter 2015/2016 experienced a strong El Niño that was heavily observed by aircraft, radiosonde and satellite platforms. During this event, lower stratospheric water vapor and ozone measurements from the Microwave Limb Sounder satellite instrument and stratospheric ice measurements above the tropopause from the Cloud-Aerosol Aerosol Lidar with Orthogonal Polarization (CALIOP) were highly anomalous. In this presentation, we will examine the water vapor fields in detail.

To first order, the tropical cold point tropopause temperature field regulates the amount of water vapor entering the stratosphere by controlling the amount of dehydration in the rising air. However, unusually high altitude evaporating convective ice might also have a role in hydrating the stratosphere. The El Niño of 2015-2016 produced decadal record amounts of water vapor entering the stratosphere in the Western Pacific, as well as convective cloud ice observed 1-2 km above the environmental cold-point tropopause in the Central Pacific. This coincides with a zonally asymmetric tropopause temperature response, consisting of cold anomalies in the Central Pacific and warm anomalies in the Western Pacific. A trajectory-based analysis that simulates dehydration based solely on large-scale reanalysis temperature and wind fields can account for only about 0.5-0.6 ppmv of the observed tropical lower stratospheric moistening of ~0.9 ppmv observed by MLS at 82 hPa during this event. This suggests that unresolved dynamical processes associated with convection and/or sublimation of lofted ice particles also contributed to lower stratospheric moistening. These observations suggest that convective moistening could contribute to climate change-induced stratospheric water vapor increases.