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Study Investigates Dynamic and Thermodynamic Impacts of Climate Change on Daytime Convection

Climate change intensifies the hydrologic cycle, resulting in an increase and higher frequencies of extreme precipitation events. This occurs due to the impact of climate change on the dynamics and thermodynamics of moist convection. While the dynamical impact concerns an increase of convection strength due to a higher convective available potential energy (CAPE), the thermodynamical impact involves the effects of increased water vapor that the warmer atmosphere can hold and convection can work with.

To better understand the dynamic and thermodynamic impacts of climate change on daytime convective development, the project team led by Dr. Lulin Xue, a third cycle awardee of the UAE Research Program for Rain Enhancement Science (UAEREP) and the Chief Scientist at Hua Xin Chuang Zhi Science and Technology LLC, worked on a pilot study that applied a novel piggybacking modeling methodology to separate both dynamical and thermodynamical impacts.

Small-scale simulations are conducted to separate these two components for daytime development of unorganized convection overland using global climate model (GCM)-predicted changes in atmospheric temperature.

The piggybacking applied two sets of thermodynamic variables in a single cloud field simulation. The first set is associated with the dynamics and drives the simulation, while the second set follows the simulated flow. The driver and piggybacker are then swapped in the second simulation. The modeling setup is based on observations in the Amazon region compiled over a decade ago.

The simulations clearly showed that the simulated impact of climate change on convection is dominated by cloud dynamics, and not by the cloud thermodynamics, indicating that the impact of climate change on precipitation is strongly dependent on the mode of convection.

Differences between driver and piggybacker were found to be relatively small in all simulations. This highlights a relatively small effect of the increased water vapor available for convection on the climate change simulations. However, the study found interesting thermodynamic effects that warrant further investigation, like the reduction of cloud fractions even if the relative humidity is kept constant.

The study also anticipates that the application of the piggybacking simulation method to organized convection simulations in the future will allow improved understanding of dynamical and thermodynamical impacts of climate change on the organized deep convection.

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