The COMBLE Campaign: A Study of Marine Boundary Layer Clouds in Arctic Cold-Air Outbreaks

Abstract

One of the most intense air mass transformations on Earth happens when cold air flows from frozen surfaces to much warmer open water in cold-air outbreaks (CAOs), a process captured beautifully in satellite imagery. Despite the ubiquity of the CAO cloud regime over high-latitude oceans, we have a rather poor understanding of its properties, its role in energy and water cycles, and its treatment in weather and climate models. The Cold-air Outbreaks in the Marine Boundary Layer Experiment (COMBLE) was conducted to better understand this regime and its representation in models. COMBLE aimed to examine the relations between surface fluxes, boundary-layer structure, aerosol, cloud and precipitation properties, and mesoscale circulations in marine CAOs. Processes affecting these properties largely fall in a range of scales where boundary-layer processes, convection, and precipitation are tightly coupled, which makes accurate representation of the CAO cloud regime in numerical weather prediction and global climate models most challenging. COMBLE deployed an Atmospheric Radiation Measurement Mobile Facility at a coastal site in northern Scandinavia (69°N), with additional instruments on Bear Island (75°N), from December 2019 to May 2020. CAO conditions were experienced 19% (21%) of the time at the main site (on Bear Island). A comprehensive suite of continuous in situ and remote sensing observations of atmospheric conditions, clouds, precipitation, and aerosol were collected. Because of the clouds’ well-defined origin, their shallow depth, and the broad range of observed temperature and aerosol concentrations, the COMBLE dataset provides a powerful modeling test bed for improving the representation of mixed-phase cloud processes in large-eddy simulations and large-scale models.

Using Stochastically Perturbed Parameterizations to Represent Model Uncertainty. Part I: Implementation and Parameter Sensitivity

“…In the North Atlantic, northerly flow in the wake of oceanic cyclones (Tilinina et al 2018) and high winds associated with the Greenland tip jet (Doyle and Shapiro 1999) draw Arctic air across the extensive ice edge to create an environment conducive to frequent large-flux events (Papritz and Spengler 2017;Geerts et al 2022). Despite symmetric perturbations to B , the fh_mult ensemble predicts colder screen-level temperatures in this region (Fig.…”

Nudging allows direct evaluation of coupled climate models with in-situ observations: A case study from the MOSAiC expedition

“…We conclude that nudging provides a strong tool to leverage observations, especially from intense, time-limited campaigns, for the evaluation and improvement of coupled climate models. A nudging intercomparison involving more coupled models and using the full MOSAiC dataset, data from the COMBLE campaign (Geerts et al, 2022), YOPPsiteMIP (Uttal et al, 2019) and recent Southern ocean campaigns (McFarquhar et al, 2021) would be an asset for evaluating and improving the representation of crucial processes in climate models.…”

Vertical structure of clouds and precipitation during Arctic cold-air outbreaks and warm-air intrusions: observations from COMBLE

“…The AMF1 deployment included scanning and profiling radars, lidars, passive microwave radiometers, an Atmospheric Emitted Radiance Interferometer (AERI), frequent radiosondes, radiation and surface flux sensors, and an aerosol observing system (Geerts et al, 2022). The most important instrument in this study is the sensitive narrow-beam 35 GHz (Ka-band) profiling radar known as KAZR, providing reflectivity, Doppler velocity, and Doppler spectral width.…”

“…M is a commonly used measure of thermal instability driven by ocean surface heat fluxes, although different upper reference levels have been used in the literature, between 900-700 hPa (e.g., Kolstad & Bracegirdle, 2008;Fletcher et al, 2016;West et al, 2019;Naud et al, 2020;Hu et al, 2022). The convective cloud layer is almost always deeper than the 850 hPa level at Andenes during CAOs (Geerts et al, 2022), so this upper reference level is generally within the mixed layer.…”