A186-0002
A Lagrangian perspective on tropical anvil cloud lifecycle in present and future climate

Tuesday, 15 December 2020
Poster
Blaž Gasparini1, Phil Rasch2, Dennis L Hartmann1, Casey Wall3 and Marina Duetsch4, (1)University of Washington, Seattle, WA, United States, (2)Pacific Northwest National Laboratory, Richland, WA, United States, (3)Scripps Institution of Oceanography, La Jolla, CA, United States, (4)University of Washington, Earth and Space Sciences, Seattle, WA, United States
Abstract:
The evolution of tropical anvil clouds from their origin in deep convective cores to their slow decay determines the climatic effects of clouds in tropical convective regions. Despite the relevance of anvil clouds for climate and responses of clouds to global warming, processes dominating their evolution are not well understood. Currently available observational data reveal instantaneous snapshots of anvil cloud properties, but cannot provide a process-based perspective on anvil evolution.

We therefore conduct simulations with the high resolution version of the Exascale Earth System Model in which we track mesoscale convective systems over the Tropical Western Pacific and compute trajectories that follow ice crystals detrained from peaks of convective activity. With this approach we gain new insight into the anvil cloud evolution both in present day and future climate. In particular, the ice crystal tracking offers the following advantages over the standard mean-climate perspective:

  • It gives a direct estimation of cloud lifetimes.
  • It offers an insight on microphysical processes that control anvil evolution and radiative properties. It also allows computing Lagrangian mass budgets.
  • It provides a straightforward and unbiased way of separating cloud responses based on cloud development stage.

Trajectory results indicate that anvil cloud lifetime is about 15 hours with no significant difference in a warmer climate. The anvil cloud ice water content is larger in a warmer climate due to a larger source of ice by detrainment and larger depositional growth leading to a more negative net cloud radiative effect along detrained trajectories. However, the increases in sources are counteracted by increases in sinks of ice, particularly snow formation and sedimentation. Furthermore, we find that the mean anvil cloud feedback along trajectories is positive and consistent with results from more traditional cloud feedback calculation methods in which the positive altitude feedback dominates over a smaller contribution due to the cloud optical depth increase.

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