Understanding the natural sources of aerosols and their impacts on cloud formation and climate across hemispheres

It is widely recognized that many of the limitations in the predictive ability of state-of-the-science regional and global climate models stem from incomplete representations of cloud processes, including aerosol-cloud interactions.

aerosol-cloud interaction

The interaction of airborne particles (aerosols) with clouds. Scientists study how aerosols affect clouds and how these interactions can impact the Earth's climate.

Source: DOE Source

A notable example is the failure of models to capture the frequency of supercooled liquid water in Southern Ocean clouds, possibly due to lower than predicted levels of ice nucleating particles

ice nucleating particles

Tiny specks of material suspended in the air that act as starting points for the formation of ice crystals in clouds.

Source: Pacific Northwest National Laboratory Source

(INPs) that are required for first ice formation at temperatures above -38ºC. Deep convective clouds

deep convective cloud

Deep convective clouds (e.g., cumulonimbus clouds) are associated with severe storms, which can transport ice and supercooled large droplets into the higher levels of the atmosphere, frequently reaching an altitude of 10 km (33,000 feet), and sometimes much higher.

Source: NOAA Source

over continental regions are influenced by the abundance of cloud condensation nuclei

cloud condensation nuclei

Tiny airborne particles suspended in the atmosphere that serve as the seeds around which cloud droplets form.

Source: Source

(CCN) and INPs, and their cloud microphysical impacts that affect precipitation, updraft strength, anvils, and cold pools. The goal of the proposed project is to improve the representation of aerosol-cloud interactions in global climate models by leveraging a broad range of observations from DOE Atmospheric Radiation Measurement (ARM) campaigns across the world. This work exploits recent DOE-funded Southern Ocean (Measurements of Aerosols

aerosols

Small particles or droplets, such as wildfire smoke, volcanic gases, or salty sea spray, that float in the air. They are emitted by both natural events and human activities.

Source: NASA Global Climate Change Source

Radiation and Clouds over the Southern Ocean, MARCUS; Macquarie Island Cloud and Radiation Experiment, MICRE), Arctic (Cold-air Outbreaks in the Marine Boundary Layer Experiment, COMBLE; Multidisciplinary Drifting Observatory for the Study of Arctic Climate, MOSAiC), and continental mid-latitude North American (SGP Ice Nuclei Characterization Experiment, SINCE; Aerosol Ice Formation Closure Pilot Study, AEROICESTUDY) and South American (Cloud, Aerosol, and Complex Terrain Interactions--CACTI) ARM data

ARM data

Continuous field measurements of atmospheric data collected with Atmospheric Radiation Measurement (ARM) instruments at fixed and varying locations worldwide.

Source: Argonne National Laboratory Source

sets, and leverages existing collaborations funded by the Atmospheric System Research (ASR) program and other agencies. These studies together provide a unique opportunity to test whether parameterizations fail because models cannot adequately predict aerosol fields, or if they fail because the proposed links between aerosols and CCN or INP are incorrect. By comparing observations and model outputs in climate-critical land and ocean regions in both hemispheres, we expect the greatest progress to be made. Our specific objectives are:
Provide new information on the abundance, types, and roles of biologically-sourced particles as key cloud-active particles, currently not adequately represented in models for these varied environments.
Develop parameterizations that correctly represent the intrinsic differences between the sources and aerosol impacts of these populations in the Northern and Southern Hemispheres, and between marine and continental sites.
Work with national and international observational and modeling partners to improve model aerosol representation and prediction of CCN and INP from modeled aerosols.
Work with collaborators conducting case study analyses/simulations to apply our findings to develop further understanding of aerosol-cloud interactions in the context of each field study’s objectives.

We will utilize a range of analyses to evaluate hypotheses regarding the similarities and differences of aerosols over Northern versus Southern Hemispheric marine and continental regions, including: aerosol size distribution and composition information to normalize CCN and INP data; INP typing analyses of archived data; selected new laboratory analyses of INP sizes and compositions; modeled fields of aerosols and predicted INPs; satellite-derived and in-situ ocean chlorophyll-a; wind and wave height reanalyses; trajectory analyses; and supplemental data from international collaborators in the high latitude Arctic studies.

This work will provide unprecedented interpretation of ARM data to advance the science of interactions of aerosols, clouds and precipitation, a key Atmospheric System Research (ASR) programmatic goal. We will validate and improve regional scale and climate model predictions of global aerosol fields, demonstrating their use for driving predictions of the cloud-active particle subsets, and capturing the physical reasons for variability. This project will benefit studies of climate-sensitive high-latitude regions where incomplete understanding of aerosol impacts affects predictability of cloud formation, phase, and radiation budgets; and studies of midlatitude regions where models are challenged to represent aerosol effects on convective clouds and severe weather.