Observed Ambient Conditions in Winter Storm Cloud Sandwiches

Winter storms often contain “cloud sandwiches”, sets of layers that appear more transparent to the human eye between layers that are more opaque. The middle, more transparent layer of the cloud sandwich is usually subsaturated with respect to water. Precipitation-size ice (> 0.2 mm diameter) falling through the more transparent layer is observed as radar echo. Hence, regions with cloud sandwiches often appear as vertically continuous radar echo.

We examine ambient conditions and evidence for microphysical processes that occur in cloud sandwiches, particularly ice crystal growth and sublimation. We use data from the NASA IMPACTS (Investigation of Microphysics and Precipitation for Atlantic-Coast Threatening Snowstorms) research campaign over three winter seasons. Data sets include flight camera videos to determine the visual presence of cloud sandwiches in storms, in situ ambient condition measurements from the NASA P-3 research aircraft to determine temperature, relative humidity, and particle concentrations, and airborne radar data from the NASA ER-2 research aircraft to look at the radar signatures of these cloud sandwiches. We also analyze high-resolution ice particle images taken by the PHIPS (Particle Habit Imaging and Polar Scattering) probe on the NASA P-3 to characterize ice shapes, degree of riming, and evidence of sublimation.

Figure 1: An image of a cloud sandwich from the NASA IMPACTS P-3 flight on 17 January 2022 at 1415 UTC. The plane is flying through a more transparent layer with cloudy layers both above and below. Snow was falling at the surface.