Contrasting characteristics of open- and closed-cellular stratocumulus cloud in the eastern North Atlantic

Abstract

Abstract. Extensive regions of marine boundary layer cloud impact the radiative balance through their significant shortwave albedo while having little impact on outgoing longwave radiation. Despite this importance, these cloud systems remain poorly represented in large-scale models due to difficulty in representing the processes that drive their life cycle and coverage. In particular, the mesoscale organization and cellular structure of marine boundary clouds have important implications for the subsequent cloud feedbacks. In this study, we use long-term (2013–2018) observations from the Atmospheric Radiation Measurement (ARM) Facility's Eastern North Atlantic (ENA) site on Graciosa Island, Azores, Portugal, to identify cloud cases with open- or closed-cellular organization. More than 500 h of each organization type are identified. The ARM observations are combined with reanalysis and satellite products to quantify the cloud, precipitation, aerosol, thermodynamic, and large-scale synoptic characteristics associated with these cloud types. Our analysis shows that both cloud organization populations occur during similar sea surface temperature conditions, but the open-cell cases are distinguished by stronger cold-air advection and large-scale subsidence compared to the closed-cell cases, consistent with their formation during cold-air outbreaks. We also find that the open-cell cases were associated with deeper boundary layers, stronger low-level winds, and higher rain rates compared to their closed-cell counterparts. Finally, raindrops with diameters larger than 1 mm were routinely recorded at the surface during both populations, with a higher number of large drops during the open-cellular cases. The similarities and differences noted herein provide important insights into the environmental and cloud characteristics during varying marine boundary layer cloud mesoscale organization and will be useful for the evaluation of model simulations for ENA marine clouds.

Exploring relations between cloud morphology, cloud phase, and cloud radiative properties in Southern Ocean's stratocumulus clouds

“…The mean CTHs between open and closed MCC clouds are similar during austral summer, whereas during austral winter, at least for MPCs, we see higher CTHs in open cells. Many studies show that there are CTH differences between the two morphological regimes with higher CTHs in open MCC clouds (Muhlbauer et al, 2014;Glassmeier and Feingold, 2017;Jensen et al, 2021).…”

“…A study using ground-based and satellite observations in the eastern North Atlantic shows that closed MCC clouds have a lower mean CTH (Jensen et al, 2021). Moreover, Glassmeier and Feingold (2017) Deeper boundary layers associated with higher CTHs are often decoupled and favor conditional instabilities associated with stronger vertical updrafts, which in turn favor ice growth and potentially ice formation through secondary ice processes.…”

Exploring Relations between Cloud Morphology, Cloud Phase, and Cloud Radiative Properties in Southern Ocean Stratocumulus Clouds

“…The mean CTHs between open and closed MCC clouds are similar during austral summer, whereas during austral winter at least for MPCs we see higher CTHs in open cells. Many studies show that there are CTH differences between the two morphological regimes with higher CTHs in open MCC clouds (Muhlbauer et al, 2014;Glassmeier and Feingold, 2017;Jensen et al, 2021). A study using ground-based and satellite observations in the Eastern North Atlantic shows that closed MCC clouds have a lower mean CTH (Jensen et al, 2021).…”

“…Many studies show that there are CTH differences between the two morphological regimes with higher CTHs in open MCC clouds (Muhlbauer et al, 2014;Glassmeier and Feingold, 2017;Jensen et al, 2021). A study using ground-based and satellite observations in the Eastern North Atlantic shows that closed MCC clouds have a lower mean CTH (Jensen et al, 2021). Further, Glassmeier and Feingold (2017) demonstrate in a large-eddy simulation that open cells favor deeper boundary layer heights and thus also higher CTHs.…”

Observed Relationships Between Cloud Droplet Effective Radius and Biogenic Gas Concentrations in Summertime Marine Stratocumulus Over the Eastern North Atlantic

“…A vast MBL cloud system exists over the Eastern North Atlantic (ENA). This cloud system exhibits seasonal variability in cloud morphology, coverage, precipitation, and microphysical structure (Ghate & Cadeddu, 2019; Ghate et al., 2020; Giagrande et al., 2019; Jensen et al., 2021; Lamer et al., 2020; and others). The northern latitudes of the ENA are characterized by relatively solid MBL overcast often characterized by a single cloud layer that evolves into a complex mixture of layer and convective clouds in the southern ENA.…”