Arctic Cloud Microphysical Processes

Principal Investigator(s):
Johannes Verlinde, Pennsylvania State University

The Arctic, where radiant energy lost to space greatly exceeds the energy received from the sun, plays an important role in fueling Earth’s atmospheric general circulation. The Arctic has been observed as warming at a rate faster than the rest of the globe in the last several decades, a phenomenon known as Arctic amplification. Fundamentally, Arctic amplification is the result of various feedback processes resulting from systematic changes in absorption of radiation in Earth’s atmosphere. The most visible manifestation of polar amplification is the loss of Arctic basin sea ice. However, consensus has yet to be attained as to the dominant contributors to this phenomenon, and the urgency for understanding the physical causes of these sea ice losses is great. Multiple oceanic and atmospheric factors relate in complicated ways to changes in sea ice. These factors contribute to several poorly characterized feedback processes that increase the variability in predicted Arctic climate trends over anywhere else on Earth. Our proposed research is on atmospheric processes because of their impact on the sea ice energy budget.

Clouds have a dominant impact on the Arctic radiation budget, with layers of high water vapor content and atmospheric aerosol also playing important (but secondary) roles. Most clouds and aerosols are found in the lower parts of the polar atmosphere where the temperature increases with height, the result of which is to form clouds/aerosols to exist in extensive but shallow layers. Moreover, alternating snow and ice cover on the land and/or ocean produce large horizontal inhomogeneity in surface-atmosphere exchange processes, and hence atmospheric structure. Much recent research has focused on horizontally homogeneous, single-layered, mixed-phase cloud systems and our understanding of the physics of these clouds is advancing. However, beginning with the earliest studies of Arctic clouds, it is clear that multi-layered cloud structures are common in the Arctic. Our research will build on the understanding developed from single-layered cloud systems to address the more general problem of the processes in multiple water vapor, aerosol, and cloud layers in the horizontally inhomogeneous lower troposphere.

We use The Pennsylvania State University Weather Research and Forecasting Model-based Ensemble Data Assimilation system to characterize the North Slope regional flow structure from Doppler velocity and thermodynamic measurements at the two Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) facilities along the coast. This data assimilation approach allows us to understand the impact of horizontal inhomogeneities on Arctic atmospheric processes and cloudy contributions to the surface energy budget. Modeling and observational cloud process studies will utilize this resolved regional flow to investigate the relative roles of local versus long-range transport of moisture and aerosols on the observed atmospheric structure and the surface energy budget. Model simulations will be used in a synergistic fashion with DoE-ARM instrument observations at Oliktok Point and Barrow to evaluate and improve high-resolution simulations of Arctic atmospheric processes.