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The Arctic Atmospheric Boundary-Layer Structure and Its Interactions with the Free Troposphere and Surface

Active Dates 8/1/2022-7/31/2025
Program Area Atmospheric System Research
Project Description
The Arctic Atmospheric Boundary-Layer Structure and Its Interactions with the Free Troposphere and Surface

              Ola Persson, CIRES/University of Colorado, Boulder, CO USA (Principal Investigator)

              Ian Brooks and Gillian Young McCusker (formerly Gillian Young), University of Leeds, Leeds, United Kingdom (co-Investigators)

              Matthew Shupe and Amy Solomon, CIRES/Univ. of Colorado, Boulder, CO (co-investigators)

Recent studies have suggested that the atmospheric boundary layer over Arctic sea ice can conceptually be described as an ubiquitous Arctic inversion (AI) separating the free troposphere above from the sea-ice boundary below and extending to heights of 1000-1500 m. This typically stable AI inhibits vertical mixing, but is modified by the Arctic boundary layer (ABL) nearest the surface through local frictional or buoyant processes and the cloud-forced mixed layer (CML) aloft forced by cloud-top radiative cooling. When the forcing of the ABL is sufficiently strong, the ABL becomes a surface-based mixed layer (SML). While the cloud-forced and surface-based mixed layers are generally distinct, they can at times appear to couple with each other producing a layer from the surface to cloud top that has a near-neutral lapse rate throughout. Hence, during these periods, significant transport of heat, moisture, momentum, aerosols, and even trace gases can occur. The formation of low-level wind jets (LLJs) within the Arctic inversion also modifies the turbulent structure within the Arctic inversion, possibly enhancing the vertical transport.

The proposed project aims to evaluate, explore, and advance this conceptual model using the recently acquired MOSAiC data set and selected numerical modeling experiments. The specific objectives of the project are to:

1) Evaluate and further develop the Arctic inversion/dual mixing layer paradigm for cloudy and clear-sky states by exploring the generality of the concept of an independent Arctic inversion with distinct ABL(surface-based mixed layer) and cloud-forced mixed layer substructures, determining if there is a seasonal variability for the dual mixed-layer concept, determining if the paradigm holds true for clear skies with just the removal of the cloud-forced mixed layer, understanding how the LLJ fits into this structural paradigm, and addressing how larger-scale forcings, such as from low-pressure systems and fronts, and cloud depth/type impact the concept?

2) Identify the forcing and characteristics of dual mixed-layer coupling processes by exploring a) the relative impacts of synoptic forcing, cloud-top height, and microphysical forcing/radiational cooling on the penetration depth of the CML and the coupling with the SML.

3) Identify the roles of low-level jets in the Arctic inversion paradigm, especially for vertical mixing, by identifying their locations and temporal occurrence relative to other Arctic inversion structures, characterizing their associated turbulence structure, and quantifying their turbulence characteristics, impacts on vertical mixing, and mixing efficiency.

4) Characterize the turbulent structures and their relationships with mixing layers, cloudy-sky coupling modes, and the clear-sky structural paradigm. This will include characterizing the vertical structure of turbulent mixing, exploring the characteristic length scales of turbulent eddies forced by different mechanisms, and exploring the eddy length-scale implications for the efficiency of vertical mixing and transport.

The above objectives will be addressed with analysis of the numerous measurements obtained by the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) campaign in the Central Arctic from Oct 2019 to Oct 2020, including data from 6-h rawinsondes, the Univ. of Colorado meteorological flux tower and distributed ASFS stations, and numerous remote sensing instruments deployed by ARM/AMF2 and the U. Leeds/U. Trier. Some of the objectives will be addressed with directed numerical simulations using the NOAA Coupled Arctic Forecast System (CAFS), the UK Met Office/NERC Cloud Model (MONC), and the MetOffice Unified Model (MetUM). The project will advance our understanding of key structures and interactive processes in the Arctic boundary layer, including how and when vertical mixing can occur through the generally stable Arctic inversion, and provide a stronger and clearer conceptual paradigm for use in future observational and modeling studies.
Award Recipient(s)
  • University of Colorado Boulder (PI: Persson, Ola)