ESRL/PSD Seminar Series

Orographic Precipitation from Atmospheric Rivers: Exploring the response to microphysics and environmental parameter perturbations

Annareli Morales
Ph.D. Candidate from University of Michigan and Extended Stay Visitor at MMM-NCAR


Atmospheric rivers (ARs) are responsible for 30-50% of the annual precipitation for the U.S. West Coast, mainly through mountain snowfall. When the moist nearly neutral flow associated with these ARs interacts with topography, complex interactions occur between the dynamics, thermodynamics, and cloud microphysics that make it difficult to disentangle the dominant controls on precipitation type, amount, and its location over a mountain. This seminar presents recent work exploring the sensitivity of precipitation to microphysical and environmental parameter perturbations using an idealized modeling framework. We perform standard “one-at-a-time” sensitivity testing and apply the Morris Screening method, a robust statistical algorithm which allows for nonlinear parameter interactions and multiparameter perturbations. Results for the most influential microphysical parameters found in this case (i.e., snow fallspeed coefficient (As), snow particle density (ρs), ice-cloud water collection efficiency (ECI), and rain accretion (WRA)) will be presented. Additionally, experiments are performed to test the impact different environments have on the microphysical parameter sensitivity. In general, perturbations to microphysical parameters affect the location of peak precipitation, while the total amount of precipitation is more sensitive to environmental parameter perturbations. The As parameter is the most influential to precipitation rate, regardless of the environment tested, and displays a strong interaction with other parameters. Overall, these results highlight the complexity of the orographic precipitation response to microphysical parameter changes and suggests that a small subset of the total number of parameters are responsible for most of the microphysics-induced variability in orographic precipitation.

Friday Dec 07, 2018
11:00 am
Seminar Coordinator: Robbie Desen (

SECURITY: If you are coming from outside the NOAA campus, you must stop at the Visitor Center to obtain a vistor badge. Please allow 10 extra minutes for this procedure. If you are a foreign national coming from outside the NOAA campus, please email the seminar coordinator at least 48 hours prior to the seminar to provide information required for security purposes.