High Latitude Aerosol-Cloud Interaction during MARCUS, MICRE, and AWARE: The role of CCN variability on Marine Cloud Brightening and links to Precipitation

Abstract

Our research objective is to investigate the coupling among aerosols, clouds, and precipitation over the Southern Ocean (SO) and other high latitude regions recently documented by DOE ARM facility field campaigns.  The Southern Ocean is unique on Earth as it is largely isolated from anthropogenic influences while  Circumpolar oceanic currents (ACC) and upwelling tend to isolate the Southern Ocean from the amplified warming observed in the Northern Hemisphere Arctic.   

We have laid the foundation for this work in our ongoing ASR-funded research.  We have analyzed a unique data set collected from ships during the summer of 2018 that significantly constrains the properties and relationships among aerosols, clouds, and precipitation over a longitude domain between Hobart, Tasmania and East Antarctica.  To build upon this foundation, we ask very specific questions regarding how aerosol composition over the Southern Ocean, relates to seasonally varying biological productivity to modulate the properties of clouds in the presence of precipitation of both liquid and ice phases. 

Using analysis methodologies specifically tailored to the data sets we seek to analyze, we propose to address the following science questions: 

1. What are the determining processes that control cloud condensation nuclei (CCN) in the high latitude Southern Ocean and the ACC region to the north? 
2. What is the process-level association between surface observed cloud condensation nuclei and marine boundary-layer cloud and radiative properties – in particular the cloud droplet number concentration of boundary layer clouds?  
3. What is the role of cloud and precipitation processes in the cloud-aerosol interaction in this pristine region?  

To address these questions, we will expand our data analysis methodology that combines aerosol size and compositional time series with active and passive remote sensing collected by lidars, radars, and radiometers from several recent measurement campaigns.  Uniquely, we will use radar Doppler spectra to isolate the cloud droplet radar reflectivity combined with lidar-derived cloud extinction to derive cloud droplet number concentrations in the presence of light precipitation.  Precipitation properties will be derived from combinations of radar and lidar as well using established methodologies tailored to the data sets we analyze. 

A unique aspect of our approach is to place the ARM data into context provided by:

1. A suite of NASA satellites that largely replicate the ARM measurements in less detail but with greater spatial coverage over all seasons
2.  Backwards airmass trajectories.  Uniquely, to better constrain the air mass history, we will document the aerosol, cloud, and precipitation properties along those back trajectories using satellite data. 
3. Collaborate with several domestic and international modeling groups to determine the extent to which the models are able to replicate the processes that are documented in the ARM data within the unique air masses that the ARM data observed.

In addition, we will expand our analysis methodology to other high latitude data sets collected by ARM in both hemispheres.