The Need for Continued Stratospheric Water Vapor Measurements

A section on stratospheric water vapor has been included in the BAMS State of the Climate report since 2010. It is significant from a climate standpoint because stratospheric water vapor modulates Earth’s climate directly through long-wave radiative processes, and indirectly through its influence on stratospheric ozone abundance. An increase in stratospheric water vapor will radiatively warm the troposphere and cool the stratosphere. Water vapor abundance also has an impact on ozone chemistry. The eruption of Hunga Tonga in January 2022 resulted in the largest stratospheric water vapor perturbation observed in the satellite era. Changes in tropopause temperature associated with climate change are also expected to force changes in stratospheric water vapor.

Near-global measurements by satellites began in late 1978 with seven months of Limb Infrared Monitor of the Stratosphere measurements that provided the first insights into the global budget. Longer-term datasets from satellite-borne instruments have been available since 1984, with the Aura Microwave Limb Sounder (MLS) launched in 2004 providing extensive global coverage. However, the Aura MLS is reaching end of lifetime, and there may be a gap in global coverage that would degrade the long term stratospheric water vapor climate data record.

This presentation will discuss the outlook for continued stratospheric water vapor measurements, and provide recommendations for enhancing the ground based network to allow the long term stratospheric water vapor record to maintain its current high quality.