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Deciphering Atmospheric Ice Nucleation using Molecular-Scale Microscopy

Thurmer, Konrad T.; Friddle, Raymond W.; Wheeler, Lauren B.; Bartelt, Norman C.; Roesler, Erika L.; Kolasinski, Robert K.

Atmospheric ice affects Earth's radiative properties and initiates most precipitation. Growing ice typically requires a particle, often airborne mineral dust, e.g., to catalyze freezing of supercooled cloud droplets. How chemistry, structure and morphology determine the ice - nucleating ability of minerals remains elusive. Not surprisingly, poor understanding of a erosol - cloud interactions is a major source of uncertainty in climate models. In this project, we combine d optical microscopy with atomic force microscopy t o explore the mechanisms of initial ice formation on alkali feldspar, a mineral proposed to dominate ice nucleation in Earth's atmosphere. When cold air becomes supersaturated with respect to water, we discovered that supercooled liquid water condenses at steps without having to overcome a nucleation barrier, and subsequently freezes quickly. Our results imply that steps, common even on macroscopically flat feldspar surfaces, can accelerate water condensation followed by freezing, thus promoting glaciation and dehydration of mixed - phase clouds. Motivated by the fact that current climate simulations do not properly account for feldspar's extreme efficiency to nucleate ice, we modified DOE's climate model, the Energy Exascale Earth System Model (E3SM), to i ncrease the activation of ice nucleation on feldspar dust. This included add ing a new aerosol tracer into the model and updat ing the ice nucleation parameterization, based on Classical Nucleation Theory, for multiple mineral dust tracers. Although t he se m odifications have little impact on global averages , predictions of regional averages can be strongly affected .

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TYPE SAND Report YEAR 2019
OSTIDOI

Building and Running TDAAPS Models: WRF Postdictions

Poppeliers, Christian P.; Aur, Katherine A.; Wheeler, Lauren B.; Poppeliers, Christian P.; Preston, Leiph A.

This document serves to guide a researcher through the process of running the Weather Research and Forecasting (WRF) model and incorporating observations into coarse resolution reanalysis products to model atmospheric conditions at high (50 m) resolution. This documentation is specific to WRF and the WRF Preprocessing System (WPS) version 3.8.1 and the Objective Analysis (OBSGRID) code released on April 8, 2016. Output from WRF serves as an input into the Time-Domain Atmospheric Acoustic Propagation Suite (TDAAPS) which performs staggered-grid finite difference modeling of the acoustic velocity pressure system to produce Green's functions through these atmospheric models.

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TYPE SAND Report YEAR 2018
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19 Results
19 Results