Extreme Outliers in Lower Stratospheric Water Vapor Over North America Observed by MLS: Relation to Overshooting Convection Diagnosed From Colocated Aqua-MODIS Data

F Werner; M J Schwartz; N J Livesey; W G Read; M L Santee

doi:10.1029/2020GL090131

Extreme Outliers in Lower Stratospheric Water Vapor Over North America Observed by MLS: Relation to Overshooting Convection Diagnosed From Colocated Aqua-MODIS Data

Geophys Res Lett. 2020 Dec 28;47(24):e2020GL090131. doi: 10.1029/2020GL090131. Epub 2020 Dec 19.

Authors

F Werner¹, M J Schwartz¹, N J Livesey¹, W G Read¹, M L Santee¹

Affiliation

¹ Jet Propulsion Laboratory California Institute of Technology Pasadena CA USA.

Abstract

Convectively injected water vapor (H₂O) in the North American (NA) summer lowermost stratosphere results in significant outliers in the 100-hPa H₂O measurements from the Aura Microwave Limb Sounder (MLS). MLS statistics from 15 years confirm that the NA region contains over 60% of global 100-hPa H₂O > 12 ppmv, despite having only ∼1.8% of all MLS observations. A profile sampled in August 2019 stands out, with $H_{2} O = 26.3$ ppmv, far exceeding the prior record and the median ∼4.5-ppmv abundance in NA. This particular outlier is associated with a large overshooting convective event (OCE) that spanned multiple U.S. states and persisted for several hours. Colocation of the MLS data over NA with cloud observations from Aqua's Moderate Resolution Imaging Spectroradiometer (MODIS) reveals the unique character of this case, as only 2.3% of MLS profiles are as close to an OCE and only 0.024% of OCEs cover as large an area within a 500-km perimeter of a profile.

Keywords: MLS; MODIS; overshooting convection; retrieval; stratosphere; water vapor.