Climate feedbacks of subtropical stratocumulus remain uncertain despite their importance and decades of intense research. Order-of-one uncertainties remain both the radiative feedback and in the role that stratocumulus play in teleconnections that determine global climate feedbacks as recently demonstrated by Kang et al. (2023). The key question at stake is “How resilient are maritime stratocumulus decks to rising CO₂ concentration?”

We want to explore whether the influence mesoscale dynamics on stratocumulus cloud regimes is the missing link to advance our understanding of processes like cloud break up and finally of their impact on the climate system. HALO has proven during the EUREC⁴A campaign to be the ideal tool to observe cloud-circulation interaction at the mesoscale. We intend to transfer this approach to the stratocumulus regime to test climate feedback hypothesis on a statistical basis as Vogel et al. (2023) have demonstrated it for the trade wind cumulus regime. As an extension, we will aim to measure the mesoscale dynamical state and shallow mesoscale overturning circulations (SMOCs) at multiple scales form 200 km – like during EUREC⁴A – down to about 50 km.

Stratocumulus decks are ubiquitous in the oceanic upwelling region in the South East Atlantic next to the African coast. From September to November closed cells structures are most frequent and this time period is ideal to study stratocumulus evolution and transition to different regimes like open cell structures. HALO may be stationed e.g. at Walvis Bay (Namibia) or Cape Town (South Africa) and will sample stratocumulus clouds and its mesoscale embedding by dropsonde circles at varying scales (50-200 km).

HALO observations of the mesoscale environment like inversion and subsidence strength will be used as boundary condition to constrain high resolution simulations (down to DNS resolution) of the stratocumulus dynamics. Complementing cloud remote sensing observations ranging from cloud radiative fluxes to microphysical retrievals of cloud droplet size distribution will both help to verify the simulation and to prescribe microphysical conditions. The ability to sense the vertical profile of the precipitation flux will be used to analyze the role of evaporating precipitation in the transition to organized open cell convection.

STACCATO – like the preceding missions – is expected to be again a nucleus for accompanying related science activities and we aim at teaming up with international groups providing additional aircrafts or research vessels. The core flight strategy might be expanded to cover an additional topic. We envision e.g. studies on the triggering of inland precipitation by oceanic moisture transport or the interaction of stratocumulus with the Southerly storm tracks as potential extensions.