Observational Constraints for Lagrangian COMBLE-MIP Simulations

The Cold-Air Outbreaks in the Marine Boundary Layer Experiment (COMBLE) encountered a range of marine cold-air outbreaks (MCAOs) over the Norwegian Sea. The strongest MCAO case, observed on March 13 2020, is the focus of an ongoing model intercomparison project (MIP). This case showed the formation of cloud rolls off the marginal ice zone near Svalbard (Norway) and the transition towards cloudy cells of growing size with increasing downwind distance approaching the Norwegian continent. The marine boundary layer deepens from a few hundred meters farthest upwind to about 4 km near the continent, where a Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) site collected continuous in-situ and remote sensing measurements. MCAO clouds are expected to sustain a range of cloud microphysical processes that remain poorly understood and that may appear in enhanced form, including primary and secondary ice formation as well as collisional processes between liquid and frozen hydrometeors such as riming. The MIP aims to test the importance of prognostic aerosol and also prognostic primary ice formation in MCAO cloud evolution to reproducing observed MCAO features.

This presentation synthesizes remote sensing observations collected from polar-orbiting satellite platforms that cover a great range of downwind distances and the downwind DOE site. Observations can then be compared against output from a large-eddy simulation (LES) and single column model (SCM), run in Lagrangian mode using a moving domain. Observations that intercept the Lagrangian trajectory provided to simulations can roughly be categorized into three groups:

1. retrievals from multispectral imagers as well as microwave radiometers and their domain mean,
2. analysis of domain-wide visible imagery to determine cloudy cell size and other features by using an object identification algorithm, and
3. vertically resolved signals from active remote sensing that can be compared against signals simulated from LES and SCM output using EMC^2 radiative transfer code.

These observations provide both cloud macro-physical constraints (i.e., cloud-top height and temperature, cloud optical depth, and liquid water path) and micro-physical ones, for example through vertically resolved extinction and doppler velocity profiles collected at the DOE site. MIP LES simulations and their microphysical configurations may also reveal process imprints near the cloud-top region of individual cells that we compare against horizontally resolved imager-based retrievals, further adding constraints that enable refining our understanding of cloud-aerosol-precipitation interactions.