Biological Particles and Aerosol-Cloud Interactions in the Southern Great Plains

Principal Investigator(s):
Allison Steiner, University of Michigan

The United States Southern Great Plains (SGP) is the genesis for much of the warm season precipitation in the central and eastern United States. While atmospheric thermodynamics and large-scale dynamics play an important role in formation of precipitation, precipitation mechanisms are also sensitive to aerosols. Aerosols can suppress precipitation as cloud condensation nuclei (CCN) or act as ice nucleating particles (INP) in deep convective clouds.

The proposed work will evaluate the role of primary biological aerosol particles in the region and its influence on cloud formation. Specifically, we focus on biological aerosol in the form of pollen, one type of primary biological aerosol particle that is emitted in large yet variable quantities from vegetation in the mid latitudes. Field observations provide evidence of pollen in the planetary boundary layer and pollen components in cloud droplets and fine particulate matter. Further, pollen grains can easily rupture when wet, forming smaller, sub pollen particles with sizes less than one micron. This proposal will simulate the emission of pollen and the generation of sub pollen particles, which have been shown to be both cloud condensation nuclei and ice nucleating particles.

In the proposed work, we will address the following questions:

  1. What are the physical and chemical signatures of biological aerosol such as pollen in SGP ARM measurements?
  2. What is the role of pollen-derived particles on deep convection and precipitation in the Central US?

Using measurements from the DoE SGP ARM site and recent airborne campaigns, we will evaluate the signatures of pollen and pollen-derived aerosols on optical properties, cloud properties and precipitation. We will identify pollen-driven events over the past 15 years of observations and use the Weather Research and Forecasting Model with fully coupled chemistry (WRF-Chem) to conduct chemically realistic simulations of aerosols during and summer mesoscale convective events in the Southern Great Plains. This work will improve our understanding of the role of biological aerosol on clouds and precipitation in the Central United States, and place these results in context with anthropogenically-driven processes.