A Parameterization of the Roughness Length for the Air-Sea Interface in Free Convection

The response of the upper ocean to the parameterization of the roughness length z ₀ on the air side of the air-sea interface is studied using a one-dimensional mixed-layer model. In particular, it is shown that in the free convection limit when both the wind speed and the friction velocity approach zero, the familiar Charnock formula for the momentum roughness, which relies solely on wind generation, can be modified to account for contributions arising from the thermally generated turbulence. Therefore, a new parameterization is proposed for the momentum roughness length which extends the Charnock formula down to zero friction velocity. The value of a parameter which enters in the new formulation is determined by making use of exsisting free convection surface flux parameterizations. The effect of the new parameterization on the model performance is tested using data from the ocean weathership station Papa (OWS P), and data from the Long-Term Upper-Ocean Study (LOTUS) experiment. Simulations were carried out using a recently developed one-dimensional, second-order, turbulence closure scheme over diurnal as well as seasonal time scales. The findings suggest that the new momentum roughness parameterization improves the overall agreement between the observed and simulated sea-surface temperature (SST).     

Resilience from the ground up: how are local resilience perceptions and global frameworks aligned?

Numerous resilience measurement frameworks for climate programmes have emerged over the past decade to operationalise the concept and aggregate results within and between programmes. Proxies of resilience, including subjective measures using perception data, have been proposed to measure resilience, but there is limited evidence on their validity and use for policy and practice. This article draws on research on the Decentralising Climate Funds project of the Building Resilience and Adaptation to Climate Extremes and Disasters programme, which supports communities in Mali and Senegal to improve climate resilience through locally controlled adaptation funds. It explores attributes of resilience from this bottom‐up perspective to assess its predictors and alignment with food security, as a proxy of well‐being. We find different patterns when comparing resilience and the well‐being proxy, illustrating that the interplay between the two is still unclear. Results also point to the importance of contextualising resilience, raising implications for aggregating results.