Climate Dynamics Group
at the University of California, Santa Cruz

Our research cluster in Tropical Climate Dynamics focuses on the Hadley and Walker circulations, the Intertropical Convergence Zone (ITCZ), and the subtropical deserts—and how they will change in a warmer world. We develop a diagnostic decomposition of the Hadley circulation weakening that accounts for meridional gradients in radiative feedbacks, radiative forcing, and ocean heat uptake; energy transport by atmospheric eddies; and gross moist stability. The picture that emerges is one of complex local and remote interactions, motivating additional, idealized experiments. To that end, we impose systematic variations in the surface albedo feedback in an aquaplanet model to explore how uncertainty in polar feedbacks translates into uncertainty in the tropical circulation response.

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  • Nicole Feldl
  • Simona Bordoni (Caltech)
  • Timothy Merlis (McGill)

The response of atmospheric heat transport to anthropogenic warming is determined by the anomalous meridional energy gradient. Feedback analysis offers a characterization of that gradient and hence reveals how uncertainty in physical processes may translate into uncertainty in the circulation response. However, individual feedbacks do not act in isolation. Anomalies associated with one feedback may be compensated by another, as is the case for the positive water vapor and negative lapse rate feedbacks in the tropics. Here a set of idealized experiments are performed in an aquaplanet model to evaluate the coupling between the surface albedo feedback and other feedbacks, including the impact on atmospheric heat transport. In the tropics, the dynamical response manifests as changes in the intensity and structure of the overturning Hadley... read more →

  • Nicole Feldl
  • Simona Bordoni (Caltech)

The robust weakening of the tropical atmospheric circulation in projections of anthropogenic warming is associated with substantial changes in regional and global climate. The present study focuses on understanding the response of the annual-mean Hadley circulation from a perspective of interactions between climate feedbacks and tropical circulation. Simulations from an ensemble of coupled ocean–atmosphere models are used to quantify changes in Hadley cell strength in terms of feedbacks, radiative forcing, ocean heat uptake, atmospheric eddies, and gross moist stability. Climate feedbacks are calculated for the model integrations from CMIP5 using radiative kernels. Tropical mean circulation is found to be reduced by up to 2.6%/K for an abrupt quadrupling of carbon dioxide concentration. The weakening is characterized by an increase in gross moist stability, by an... read more →