Regional Simulations of Summer Arctic Boundary Layers

Abstract:

Profound changes have been occurring in the Arctic. The most significant change is the rapid decline of sea ice coverage and thickness over past several decades. The observed reduction in Arctic sea ice is a consequence of both thermodynamic and dynamic processes, including such factors as preconditioning of the ice cover, changes in cloud coverage, ice export, advection of ocean heat, and ice-albedo feedback. Many crucially interactive physical processes occur in the Arctic boundary layers, where energy exchange at the interface is critical for sea ice evolution and clouds strongly interact with sea ice through radiation and turbulence. Our ability of understanding the Arctic boundary layer and modeling its temporal evolution and spatial distribution is essential to understanding the Arctic climate change.

This study presents a regional simulation study of summer Arctic boundary layers. The analysis includes an evaluation of the simulations during the ASCOS (Arctic Summer Cloud Ocean Study) field campaign; it also examines the model ability to simulate some key boundary layer structures observed during ASCOS. COAMPS (Coupled Ocean-Atmosphere Mesoscale Prediction System) is used in this study. ACNFS (Arctic Cap Nowcast/Forecast System) is used to provide sea ice conditions, including sea ice temperature and concentration, to COAMPS. An advanced surface layer parameterization based on SHEBA data is implemented to provide turbulent fluxes at the surface. The simulation domain is configured to contain four grid meshes (45 km, 15 km, 5km and 1.67 km) with 60 levels in the vertical. The model provides 24 h twice daily simulations between August 1 and September 6. Observations from ASCOS are used to evaluate simulations results with a focus on the turbulent and cloud structure of boundary layer. Compared with observations, the boundary layer (BL) warming/cooling and moistening/drying periods are generally well simulated. The model simulations can represent the basic features such as well-mixed and decoupled BL structures. The observed moisture inversion is, however, poorly represented. Simple single column COAMPS simulations suggest that the moisture inversion may contribute to the development of the BL decoupled structure. Detailed analyses will be presented in the AGU fall meeting.