The evolution of deep convective systems and their associated cirrus outflows

Horner, George; Gryspeerdt, Edward

doi:10.5194/acp-2022-755

Cited by 6 publications

(5 citation statements)

References 31 publications

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“…However, both the cloud fraction and the LWP contribute to the higher albedo in the weak-MCAO/high-AOD cases. Previous work has shown that in relatively clean conditions, as the aerosol load increases, less stable conditions typically have a higher LWP than stable conditions (Murray-Watson and Gryspeerdt, 2022), potentially explaining the difference in LWP response between strong and weak events in Fig. 9c.…”

Section: Stability-dependent Aerosol Effectmentioning

confidence: 83%

Investigating the development of clouds within marine cold-air outbreaks

Murray-Watson,

Gryspeerdt,

Goren

2023

Atmos. Chem. Phys.

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Abstract. Marine cold-air outbreaks are important parts of the high-latitude climate system and are characterised by strong surface fluxes generated by the air–sea temperature gradient. These fluxes promote cloud formation, which can be identified in satellite imagery by the distinct transformation of stratiform cloud “streets” into a broken field of cumuliform clouds downwind of the outbreak. This evolution in cloud morphology changes the radiative properties of the cloud and therefore is of importance to the surface energy budget. While the drivers of stratocumulus-to-cumulus transitions, such as aerosols or the sea surface temperature gradient, have been extensively studied for subtropical clouds, the factors influencing transitions at higher latitudes are relatively poorly understood. This work uses reanalysis data to create a set of composite trajectories of cold-air outbreaks moving off the Arctic ice edge and co-locates these trajectories with satellite data to generate a unique view of liquid-dominated cloud development within cold-air outbreaks. The results of this analysis show that clouds embedded in cold-air outbreaks have distinctive properties relative to clouds following other trajectories in the region. The initial strength of the outbreak shows a lasting effect on cloud properties, with differences between clouds in strong and weak events visible over 30 h after the air has left the ice edge. However, while the strength (measured by the magnitude of the marine cold-air outbreak index) of the outbreak affects the magnitude of cloud properties, it does not affect the timing of the transition to cumuliform clouds or the top-of-atmosphere albedo. In contrast, the initial aerosol conditions do not strongly affect the magnitude of the cloud properties but are correlated to cloud break-up, leading to an enhanced cooling effect in clouds moving through high-aerosol conditions due to delayed break-up. Both the aerosol environment and the strength and frequency of marine cold-air outbreaks are expected to change in the future Arctic, and these results provide insight into how these changes will affect the radiative properties of the clouds. These results also highlight the need for information about present-day aerosol sources at the ice edge to correctly model cloud development.

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Section: Stability-dependent Aerosol Effectmentioning

confidence: 83%

Investigating the development of clouds within marine cold-air outbreaks

Murray-Watson,

Gryspeerdt,

Goren

2023

Atmos. Chem. Phys.

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“…This work uses Lagrangian trajectories to study the temporal evolution of the cloud phase in cold air outbreaks. Detailed discussion of the trajectory generation is described in Murray-Watson et al (2023), which in turn is adapted from Horner and Gryspeerdt (2022). In summary, hourly ERA5 (ECMWF Reanalysis v5; Hersbach et al 2020) 1000 hPa wind data are used to advect pixels forward through time.…”

Section: Calculating "Time Since Ice"mentioning

confidence: 99%

Air mass history linked to the development of Arctic mixed-phase clouds

Murray-Watson,

Gryspeerdt

2024

Preprint

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Abstract. Clouds formed during marine cold-air outbreaks (MCAOs) exhibit a distinct transition from stratocumulus decks near the ice edge to broken cumuliform fields further downwind. The mechanisms associated with ice formation are believed to be crucial in driving this transition, yet the factors influencing such formation remain unclear. Through Lagrangian trajectories co-located with satellite data, this study investigates into the development of mixed-phase clouds using these outbreaks. Cloud formed in MCAOs are characterized by a swift shift from liquid to ice-containing states, contrasting with non-MCAO clouds also moving off the ice edge. These mixed-phase clouds are predominantly observed at temperatures below -20 °C near the ice edge. However, further into the outbreak, they become the dominant at temperatures as high as -13 °C. This shift is consistent with the influence of biological ice nucleating particles (INPs), which become more prevalent as the air mass ages over the ocean. The evolution of these clouds is closely linked to the history of the air mass, especially the length of time it spends over snow- and ice-covered surfaces, terrains may that be deficient in INPs. This connection also accounts for the observed seasonal variations in the development of Arctic clouds, both within and outside of MCAO events. The findings highlight the importance of understanding both local marine aerosol sources near the ice edge and the overarching INP distribution in the Arctic for modelling of cloud phase in the region.

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“…Examples of the trajectories generated by this method are shown in Figure 4. The advection procedure is adapted from Horner and Gryspeerdt (2022), which focuses on trajectories starting from points of new convection. Here, a similar method is used, but the initial points are identified as cases where the air has moved from being over sea ice to being over open ocean between time steps of one hour.…”

Section: Trajectory Generationmentioning

confidence: 99%

Investigating the development of clouds within marine cold air outbreaks

Murray-Watson

Gryspeerdt

Goren

2023

Preprint

View full text Add to dashboard Cite

Abstract. Marine cold air outbreaks are important parts of the high-latitude climate system, and are characterised by strong surface fluxes generated by the air-sea temperature gradient. These fluxes promote cloud formation, which can be identified in satellite imagery by the distinct transformation of stratiform cloud 'streets' into a broken field of cumuliform clouds downwind of the outbreak. This evolution in cloud morphology changes the radiative properties of the cloud, and therefore is of importance to the surface energy budget. While the drivers of stratocumulus-to-cumulus transitions, such as aerosols or the sea surface temperature gradient, have been extensively studied for subtropical clouds, the factors influencing transitions at higher latitudes are relatively poorly understood. This work uses reanalysis data to create a set of composite trajectories of cold air outbreaks moving off the Arctic ice edge and co-locates these trajectories with satellite data to generate a unique view of cloud development within cold air outbreaks. The results of this analysis show that clouds embedded in cold-air outbreaks have distinctive properties relative to clouds following other, more stable, trajectories in the region. The initial strength of the outbreak shows a lasting effect on cloud properties, with differences between clouds in strong and weak events visible over 30 hours after the air has left the ice edge. However, while the strength (measured by the magnitude of the marine cold-air outbreak index) of the outbreak affects the magnitude of cloud properties, it does not affect the timing of the transition to cumuliform clouds nor the top-of-atmosphere albedo. In contrast, the initial aerosol concentration does not strongly affect the magnitude of the cloud properties, but aerosol concentration is correlated to cloud break-up, leading to an enhanced cooling effect in clouds moving through high aerosol conditions due to delayed break-up. This evidence of precipitation suppression enhancing cloud lifetime highlights the need for information about aerosol sources at the ice edge to correctly model cloud development. Both the aerosol environment and the strength and frequency of marine cold air outbreaks are expected to change in the future Arctic, and these results provide insight into how these changes will affect the radiative properties of the clouds.

show abstract

The evolution of deep convective systems and their associated cirrus outflows

Cited by 6 publications

References 31 publications

Investigating the development of clouds within marine cold-air outbreaks

Investigating the development of clouds within marine cold-air outbreaks

Air mass history linked to the development of Arctic mixed-phase clouds

Investigating the development of clouds within marine cold air outbreaks

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