Monitoring Moisture Transport into the Arctic UTLS and Its Role in Cloud Formation

The investigation of cloud formation mechanisms in the UTLS (Upper-Troposphere/Lower-Stratosphere) is a core activity of our SACIA (Signatures of Aerosol-Cloud Interaction over the Arctic) project. Aerosol transport along potential temperature lines inside the Arctic dome, with subsequent subsidence to the tropopause was demonstrated in previous communications. We hypothesize that water vapor, the cardinal driver of cloud formation, should follow similar transport paths. In this study, we focus on illustrating such a mechanism and its contribution to cloud nucleation. To this end, the period following the energetic Kasatochi (Aleutian Islands, 52^oN) volcano eruption of 8^th August, 2008 was particularly revealing. The long-range moisture transport and lifting dynamics are brought into relief by the temperature and humidity profiles provided by the NOAA Atmospheric Infrared Sounder (AIRS) and the Advanced Microwave Sounding Unit (AMSU) aboard the Aqua satellite. These profiles provide a particulate dynamics context for the Calipso lidar and CloudSat radar profiles acquired about a minute later along their common A-train orbit. The temporal evolution of the water vapor condensation process at the tropopause is also observed by the ground-based lidar (CRL or CANDAC Rayleigh-Mie-Raman Lidar) and radar (MMCR or Milli-Meter Cloud Radar) at the Eureka Weather Station (80^oN). The moisture dynamics at the cloud interface can be investigated using high resolution radiosondes profiles.

In order to understand how the Kasatochi mechanisms might be generalized, we applied the same investigative framework to the August 2017 pyrocumulonimbus (pyroCb) forest firestorm in Western Canada, along with recent (intense) pyroCb and volcanic (Raikoke) events in the summer of 2019. In these cases the moisture profiles were provided by the Cross-track Infrared Sounder (CrIS) and the Advanced Technology Microwave Sounder (ATMS) aboard the Suomi NPP satellite.