Dynamic versus Thermodynamic Control of Changes in Mean and Extreme Precipitation
Abstract
An outstanding issue in climate change research is to what extent are regional precipitation changes associated with global warming governed mainly by a general increase of atmospheric humidity ("thermodynamic control") or by changes in the statistics of mid-tropospheric vertical velocity ("dynamic control"). Thermodynamic control is stronger and more robust than dynamic control in current climate models. Our investigation of observed precipitation changes since 1979, however, tells a different story. In most regions around the globe, the changes in the mean precipitation and the generally larger changes in extreme (90th percentile) daily precipitation are much more consistent with similar changes in vertical velocity, i.e. with dynamic control. The latter can be quantitatively understood in the framework of the stochastically generated skewed (SGS) theory of atmospheric probability distributions. Also, and with important implications for drought, the observed changes in the probability of dry days are consistent with changes in the probability of days of mid-tropospheric descent. This aspect of the precipitation statistics is consistent with dynamic control, but is totally beyond thermodynamic control.
Uncoupled atmospheric GCM simulations with prescribed observed time-varying SSTs and radiative forcing are reasonably able to capture the observed changes in precipitation and vertical velocity, and hence the dominance of dynamic control. On the other hand, fully coupled climate models, which predict instead of prescribing the SSTs, do not adequately capture these changes, which suggests that the problem lies in their misrepresentation of the SST changes, specifically of the changes in SST gradients.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.A42E..07S
- Keywords:
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- 3305 Climate change and variability;
- ATMOSPHERIC PROCESSES;
- 3354 Precipitation;
- ATMOSPHERIC PROCESSES;
- 1854 Precipitation;
- HYDROLOGY;
- 4313 Extreme events;
- NATURAL HAZARDS