Wednesday, June 28, 2017

Coupling between marine boundary layer clouds and summer-to-summer sea surface temperature variability over the North Atlantic and Pacific

Marine boundary layer clouds play an important role in interannual to interdecadal atmosphere-ocean variability. (Credit: NOAA)

A study published in Climate Dynamics suggests that deficient simulations  of marine boundary layer clouds—which interact with it the ocean—lead to poor simulation of summer-to-summer sea surface temperature variability.

The results of this study highlight the importance of boundary layer clouds for summer climate variability over years and decades.  

Researchers analyzed satellite cloud records and CMIP5 models over the extratropical northern oceans to investigate these ocean-cloud interactions. 

This study was supported by the CPO Climate Variability and Predictability program.

Read the paper:

Myers, T. A., Mechoso, C. R., & DeFlorio, M. J. (2017). Coupling between marine boundary layer clouds and summer-to-summer sea surface temperature variability over the North Atlantic and PacificClimate Dynamics, 1-15. doi:10.1007/s00382-017-3651-8.

Abstract:

Climate modes of variability over the Atlantic and Pacific may be amplified by a positive feedback between sea-surface temperature (SST) and marine boundary layer clouds. However, it is well known that climate models poorly simulate this feedback. Does this deficiency contribute to model-to-model differences in the representation of climate modes of variability? Over both the North Atlantic and Pacific, typical summertime interannual to interdecadal SST variability exhibits horseshoe-like patterns of co-located anomalies of shortwave cloud radiative effect (CRE), low-level cloud fraction, SST, and estimated inversion strength over the subtropics and midlatitudes that are consistent with a positive cloud feedback. During winter over the midlatitudes, this feedback appears to be diminished. Models participating in the Coupled Model Intercomparison Project phase 5 that simulate a weak feedback between subtropical SST and shortwave CRE produce smaller and less realistic amplitudes of summertime SST and CRE variability over the northern oceans compared to models with a stronger feedback. The change in SST amplitude per unit change in CRE amplitude among the models and observations may be understood as the temperature response of the ocean mixed layer to a unit change in radiative flux over the course of a season. These results highlight the importance of boundary layer clouds in interannual to interdecadal atmosphere–ocean variability over the northern oceans during summer. The results also suggest that deficiencies in the simulation of these clouds in coupled climate models contribute to underestimation in their simulation of summer-to-summer SST variability.

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