Collaborative Research: Aerosol Properties and Autoconversion during Cold-Air outbreak Experiment in the Sub-Arctic Region (CAESAR)

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Arctic climate is changing at a faster pace than anywhere on Earth. Climate projections indicate that the Arctic will continue to warm, but uncertainties arise due to questions about the future behavior of Arctic clouds. An area of primary uncertainty is the properties of clouds that form during cold-air outbreaks, where very cold airmasses over the Arctic ice move southward over the relatively warm open ocean. This award will help to provide observational data of these clouds (and precipitation) and the exchange of energy between the ocean and atmosphere during the Cold-Air outbreak Experiment in the Sub-Arctic Region (CAESAR), which will be conducted in Spring 2024 out of northern Scandinavia. The observations collected during CAESAR will be used in an effort to better understand the characteristics of the cold-air outbreak system, and the Arctic climate system more broadly, in order to inform climate models and projections. The project will also help to improve forecasting of weather hazards with significant relevance to naval operations, commercial shipping, and coastal communities. The broader field effort includes significant opportunities for students and early-career scientists, international collaboration, and public outreach. One specific goal of this award is the development of interactive worksheets/notebooks for courses, based on the CAESAR project. This award will contribute to the CAESAR goal of examining the impact of varying aerosol conditions in the upstream Arctic boundary layer on ice initiation, cloud liquid water, and snow growth mechanisms in a range of wind and temperature regimes. In particular, the measurements provided through this project will target two critical knowledge gaps: 1) understanding the budget of marine boundary layer (MBL) cloud condensation nuclei (CCN) sources, and 2) providing observational constraints on CCN-limited aerosol indirect effect. The project will support the deployment of two CCN counters, a scanning mobility particle sizer (SMPS), an ultra-high sensitivity aerosol spectrometer (UHSAS), and a single particle soot photometer (SP2). The research team will contribute two value-added products to support the overall CAESAR objectives: quality-controlled cloud condensation nuclei activation spectra to support aerosol-cloud-precipitation modeling investigators and derived cloud droplet number probability distribution functions to support observational and modeling colleagues.Primary funding for this project comes from the Physical and Dynamic Meteorology program with partial funding from the Arctic Natural Sciences program. The deployment of observational assets for CAESAR is being funded by the Facilities for Atmospheric Research and Education program.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.