In this study, I investigated the temporal evolution of cloud streets during Arctic cold air outbreaks (CAOs) and their impact on the atmospheric radiation budget. Cloud streets, which are linear cloud formations, play a significant role in Arctic meteorology, particularly in the context of Arctic amplification. Using data from the HALO-(AC)³ airborne campaign, conducted in the Fram Strait region, I analyzed how these cloud formations evolve and influence the Earth's energy balance.

My research focused on the changes in cloud street structure during a specific CAO event on April 4, 2022. Over a period of approximately two hours, I observed a transition from organized cloud streets to more isotropic cloud patterns. This transition was primarily driven by a decrease in wind speed, which reduced the turbulent kinetic energy necessary to maintain the linear structure of cloud streets. The Richardson number, a measure of the balance between buoyancy and wind shear, indicated that as wind speeds dropped below 11 m/s, the cloud streets began to dissipate, leading to an increase in cloud fraction and cloud top height.

The transition from cloud streets to isotropic clouds also resulted in significant changes in cloud properties. I found that isotropic clouds had a higher cloud fraction and cloud tops, which affected the cloud albedo and the longwave radiation emitted by the clouds. Specifically, the albedo decreased as cloud streets became more isotropic, meaning less solar radiation was reflected, and more was absorbed by the Earth's surface. Additionally, in situ measurements from the Polar 6 aircraft revealed that as the cloud structure became more isotropic, the number concentration of larger ice particles increased, suggesting deeper clouds with more potential for precipitation.

The changes in cloud structure during the CAO event had a measurable impact on the atmospheric radiation budget. The transition to isotropic clouds resulted in a decrease in the net longwave radiation emitted to space and a corresponding increase in the shortwave radiation absorbed by the surface. These findings underscore the importance of accurately modeling cloud processes in climate prediction models, particularly in the rapidly changing Arctic environment.

My research demonstrates that the evolution of cloud streets during Arctic cold air outbreaks significantly influences both cloud microphysical and macrophysical properties and the atmospheric radiation budget. These findings contribute to a better understanding of Arctic amplification and highlight the need for improved climate models to predict the future impacts of these processes on global climate systems.