Numerical Modeling of Multiscale Atmospheric Flows: From Cloud Microscale to Climate

Wojciech W. Grabowski

National Center for Atmospheric Research
Boulder, Colorado

Abstract

An outstanding feature of atmospheric flows is the range of spatial and temporal scales involved. Development of rain through gravitational collisions of small cloud droplets concerns processes at sub-centimeter scales. Size distribution of cloud droplets within turbulent cumulus and stratocumulus clouds in the tropics and subtropics, where the solar insolation is at its peak, has a critical impact on the amount of radiation reflected back to space, and thus on the planetary albedo. Tropical deep convective clouds, often organized into mesoscale convective systems with horizontal scales of tens to hundreds of kilometers, drive planetary-scale Hadley circulation, which plays an essential role in the Earth energy and water budgets. For all these scales, numerical modeling---either for scientific research or for practical purposes, like the numerical weather prediction---plays an important role. The multiscale nature of these flows, often involving variable physics (e.g., hydrostatic large-scale flow and nonhydrostatic convective dynamics for the climate problem) needs to be carefully addressed. In this lecture, I will present examples of multiscale modeling approaches to selected problems in atmospheric fluid dynamics. These will include collision/coalescence of cloud droplets, turbulent entrainment into convective clouds, and representation of cloud processes in climate models.