Tracking Aerosol Convection interactions Experiment (TRACER): An Upcoming Field Campaign

Convective clouds play an important role in the Earth’s climate system as a driver of large-scale circulations and a primary mechanism for the transport of heat, moisture, aerosols, and momentum through the troposphere. Despite their climatic importance, multi-scale models continue to have persistent biases produced by insufficient representation of convective clouds. This is the result of an incomplete understanding of key processes such as convective initiation, updraft and downdraft dynamics, cloud and precipitation microphysics, and aerosol-convection interactions.

To improve our understanding of convective clouds processes, particularly the impacts of aerosols on convective dynamics, microphysics and precipitation, the DOE Atmospheric Radiation Measurement (ARM) Facility’s TRacking Aerosol Convection Interactions ExpeRiment (TRACER) campaign, will take place from April 2021-April 2022 in the Houston, TX metropolitan region. The city of Houston lies within a humid subtropical climate regime, where onshore flow and associated sea-breeze generated convection interact with a variety of aerosol conditions from Houston’s urban and industrial emissions. A series of pilot studies through the Aerosol-Cloud-Precipitation and Climate initiative (acpcintitative.org) have suggested that Houston is an optimal location for observing the interaction of aerosols and deep convective clouds.

Currently, the TRACER campaign involves the year-long deployment of the First ARM Mobile Facility (AMF1), designed for detailed, continuous in situ and remote sensing observations of cloud, aerosol, precipitation and atmospheric state, and the 2^nd generation C-band ARM Scanning Precipitation Radar. An additional site will be deployed during an intensive operational period (IOP) from June -September 2021 with more aerosol and thermodynamic measurements. During the IOP period, on forecast convective days, the C-SAPR2 will focus on the tracking of isolated convective cells through their lifecycle. In addition, radiosondes will be launched at higher frequency to capture the quickly evolving thermodynamics and kinematic conditions near convective cells. TRACER will also leverage existing measurement networks within the Houston area including surface meteorology and air quality networks operated by the Texas Commission on Environmental Quality, and the Houston-area Lightning Mapping Array operated by Texas A&M University. Evolving interagency and international partnerships will aim to further quantify the temporal and spatial variability in atmospheric thermodynamics and aerosol properties, in addition to coastal and urban impacts on cloud, aerosol, and precipitation characteristics.

The measurements collected during the TRACER campaign will enable:

1) The characterization and linking of convective cloud kinematic and microphysical lifecycles, 2) the quantification of environmental thermodynamic and kinematic controls on convective lifecycle properties, and 3) the isolation and quantification of the impacts of aerosol properties on convective cloud kinematic and microphysical evolution.

This unique combination of cloud, precipitation, lightning, aerosol, and atmospheric state measurements associated with tracked convective cells will ultimately improve our understanding of the convective cloud lifecycle and its interaction with individual environmental factors such that improved, next generation cumulus, microphysics, turbulence, and aerosol parameterizations can be designed.