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Physics Colloquium - Dr. Sisi Chen

This is a past event.

Thursday, February 27, 2020, 4 pm– 5 pm

This is a past event.

of National Center for Atmospheric Research [NCAR] will give a talk on "Formation of clouds and rain: the role of turbulence and aerosols" on Thursday, February 27 at 4:00pm in Fisher Hall 139.

A social with refreshments will be held 30 minutes prior to the talk in the Fisher Hall lobby.

Abstract:  Shallow clouds, such as the cumulus clouds, often have a vertical extension below the freezing level in the atmosphere. Therefore, they are also named warm clouds. Gentle as they appear, warm clouds contribute 31% of the total rainfall on the planet and are responsible for some disasters, such as floods and aircraft carburetor icing. In numerical modeling, an accurate prediction of clouds and rain is challenging due to a poor understanding of cloud processes at microscales (cloud microphysics).

In this talk, Dr. Sisi Chen will discuss the key microphysical processes in the formation of clouds and rain. Clouds are turbulent in nature, and aerosol particles are the major condensation nuclei on which water vapor condenses to form cloud droplets. Her research explores the effect of turbulence and aerosols on cloud droplet growth. With the advancing computer power, we are able to numerically resolve the finest structure of turbulent flows at millimeter scales using direct numerical simulation (DNS). The DNS model is also the only numerical approach capable of explicitly simulating the interactions and growth of millions of individual droplets in a turbulent cloud. Dr. Chen’s work uses and improves the DNS to identify and quantify the contribution of processes key to the rain formation. With the integration of measurements from laboratory experiments and field studies to constrain its initial conditions, the model is able to qualitatively reconstruct the microphysical processes that are difficult to measure, for example, droplet collisions, Langrangian trajectory of cloud particles, and fluctuations of supersaturation (moisture) in 3D space.

The knowledge gained in microphysics modeling will help to understand clouds and rain at larger scales and provide insights to improve the fidelity of weather and climate prediction.


Bio:  Dr. Sisi Chen is a postdoctoral fellow in the Advanced Study Program (ASP) at the National Center for Atmospheric Research (NCAR), Boulder, Colorado. Her research interest is to understand cloud-aerosol-turbulence interactions using high-resolution cloud models. Her current research projects look at the mechanisms of rain formation and the effect of cloud seeding. She received her Ph.D. in Atmospheric Sciences from McGill University, Montreal, Canada and BS in Applied Meteorology from Sun Yat-Sen University, Guangzhou, China.

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