Quantifying the Evolution of Cloud Street Structures During Arctic Marine Cold Air Outbreaks Using Satellite Observations

The clouds associated with Marine Cold Air Outbreaks (MCAOs) exhibit characteristic structures, initially forming as roll clouds or cloud streets parallel to the wind direction, and eventually breaking up into a cellular cloud field.

Here, a novel correlation-based metric, the Correlation clOud Street Index (COSI) is introduced. It is defined as the Pearson correlation coefficient between an image and an optimally oriented and scaled Gabor kernel, providing a quantitative measure of cloud street presence and distinctness. The calculation of this index also extracts cloud street spacing (wavelength) and orientation as structural properties.

Applied to satellite observations with extensive spatial and temporal coverage, we utilise the COSI to get novel insights into the spatio-temporal evolution of cloud street structures in marine cold air outbreaks. By analysing sequences of consecutive satellite images for individual events, we capture the cloud evolution for both the overall MCAO and along quasi-Lagrangian trajectories. We quantify the systematic increase in cloud street wavelength with increasing distance from the ice edge and assess the aspect ratio (wavelength divided by cloud top height) across a larger dataset. The dependence on the MCAO strength is also evaluated. The cases analysed correspond to periods with (AC)³ aircraft campaigns, allowing the aircraft observations to be placed in a broader context and providing more detailed observations of meteorological conditions along flight trajectories.

This work was supported by the DFG funded Transregio-project TRR 172 “Arctic Amplification (AC)³“.