Atmosphere Ocean Science Colloquium
The coupling of dynamics and water mass in convective clouds
Speaker: Maximilien Bolot, École Normale Supérieure
Location: Warren Weaver Hall 1302
Date: Wednesday, October 9, 2024, 3:30 p.m.
Synopsis:
Turbulence leads to ubiquitous clouds in the Earth's atmosphere, but it is little known that clouds retroact on turbulence too: the atmosphere must perform constant work to maintain its motions against the weight of the water, which directly impacts the kinetic energy flowing in atmospheric motions. In the centers of thunderstorms, the combined load of vapor, liquid water and ice can reach above 150 kg per square meter and the atmosphere must perform thousands of watts of mechanical work to lift that water to the level where it precipitates. This considerable energy cannot be used to accelerate wind and does not contribute to kinetic energy of the storms, showing how water mass has a bearing on dynamics, even if it is also set by it. With the emergence of climate models resolving non-hydrostatic accelerations at kilometer scale--the so-called global storm-resolving models or GSRMs--this coupling between dynamics and water mass can now be revealed globally. I will show some results highlighting the importance of this coupling using recent global warming simulations of the NOAA GFDL's X-SHiELD GSRM. The first result pertains to the intensification of severe storms under warmer conditions. For this, I compute the power dissipated in lifting water globally. I show that the dissipated power increases rapidly under global warming and that the increase is particularly pronounced at the center of storms where the lifting of water exhausts most of the available mechanical power, suggesting that the intensification of severe storms will remain limited under warmer conditions. Another result pertains to the distribution of ice mass in a convection-centric view where the surface is organized by decreasing ice load around the convective center. I show that the ice loading in convective cores exhibits a similar mode of change in global warming simulations of X-SHiELD and with interannual variability in active sensor observations. This mode is modulated by structural changes of the vertical wind field towards an intensification of strong updrafts with warming. The results are conducive to interpretations of the water mass based on the horizontal and vertical momentum of condensed water. Such interpretations will be crucial for incoming space missions aiming at the first-ever global measurements from space of vertical wind from changes in water mass.