Is the concept of a zonal mean tropical precipitation change useful?
Abstract
The response of the tropical atmosphere to forcing has been extensively studied through the lens of the energetic theory relating the zonal mean Hadley circulation to atmospheric energy transports across the equator. While this framework is a useful starting point for developing a conceptual understanding of the tropical atmosphere's response to forcing, by construction it averages out the rich zonal nature of atmospheric circulation and rainfall patterns, which reflect the distinct processes that govern large-scale precipitation in different regions of the tropics. We evaluate how meridional shifts in the tropical rain band vary as a function of longitude in response to a wide variety of anthropogenic and paleoclimate forcings. Using a large suite of coupled climate model simulations, we find that the zonal mean framework is generally not useful for characterizing shifts of the rain band at regional scales regardless of the climate perturbation. Under forcings with strong hemispheric asymmetry, the zonal mean shift is robust across models but the direction and magnitude varies strongly as a function of longitude. Under weak hemispheric asymmetry in the forcing, robust zonal mean shifts are small or absent, but large and robust regional shifts that have important dynamical consequences can occur. These findings caution against the practice of inferring large-scale changes in the tropical rain band based on data from a limited spatial domain. In addition, the zonal structure of the precipitation shift in models is found to be highly sensitive to tropical mean state biases, highlighting an important caveat to interpreting regional rainfall changes from model simulations with poor representation of tropical rainfall climatology.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.A31G..02A
- Keywords:
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- 3305 Climate change and variability;
- ATMOSPHERIC PROCESSES;
- 3319 General circulation;
- ATMOSPHERIC PROCESSES;
- 3337 Global climate models;
- ATMOSPHERIC PROCESSES;
- 3373 Tropical dynamics;
- ATMOSPHERIC PROCESSES