Aerosol hygroscopic growth, mixing state, and cloud condensation nuclei activity during Tracking Aerosol Convection Interactions ExpeRiment (TRACER)

Convective clouds play a critical role in the Earth’s climate system. Recent research has shown that realistic representation of convective processes is critical to constraining climate sensitivity in global climate models. Theoretical and modeling studies showed that 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

could have a strong dynamic feedback to convection

convection

The rising of warm air and the sinking of cool air. Convection can cause local breezes, winds, and thunderstorms.

Source: NASA earth observatory Source

in warm and humid environments through enhancing ice-related processes and condensational growth. A few observation-based studies also suggested influence of aerosols on convective cloud and precipitation properties. However, robust observational quantification of an aerosol effect on convective clouds isolated from other factors remains elusive.

Understanding the impact of aerosol on convective clouds requires the knowledge 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

spectrum, which represents the number of particles that uptake water and form cloud droplets as a function of supersaturation. The water uptake by aerosol is also of critical importance for the direct interaction of aerosol with radiation (i.e., aerosol direct effect) due to light scattering and absorption

absorption

The mechanism through which energy (e.g., solar or infrared) is converted into heat and contributes to the overall warming of the Earth's atmosphere and surface.

Source: NOAA Source

by aerosol. While both droplet activation under supersaturated conditions (i.e., relative humidity > 100%) and the hygroscopic growth under sub-saturated conditions (i.e., relative humidity < 100%) are strongly influenced by particle hygroscopicity,

hygroscopicity

The ability of a particle to take up moisture from the environment and is important for understanding the ability of particles to act as cloud condensation nuclei (CCN).

Source: ARM Source

 the thermodynamic regimes and measurement methods are very different. Aerosol particles, especially organic particles, can exhibit elevated hygroscopicity for droplet activation than that for hygroscopic growth. In the subsaturated regime, the hygroscopicity of organic particles can also vary strongly with relative humidity. However, global climate models usually treat organic species in aerosols with a constant hygroscopicity, potentially introducing substantial uncertainties in the quantification of aerosol radiative effects. 

We propose to deploy two advanced instruments, a size-resolved cloud condensation nuclei system and a Relative Humidity controlled Fast Integrated Mobility Spectrometer, during the Intensive Operation Period of the Tracking Aerosol Convection interactions ExpeRiment (TRACER).  The TRACER campaign focuses on the measurements of detailed convective cloud properties and the environment, including thermodynamic and aerosol properties. This proposed project has two main objectives: (1) to provide high quality and comprehensive characterization of aerosol microphysics including hygroscopic growth, mixing state, and cloud condensation nuclei activity that are necessary to address key objectives of the TRACER campaign, and (2) to quantify and understand the difference in hygroscopicity between subsaturated and supersaturated regimes and the variation of hygroscopicity with the relative humidity for aerosols of representative compositions and sources. This project helps maximize the scientific impact of TRACER campaign through deployment of advanced instruments that complements and leverages observations provided by the Atmospheric Radiation Measurement Climate Research Facility. The proposed research also helps improve the understanding and representation of aerosol hygroscopicity in global climate models such as Department of Energy’s Energy Exascale Earth System Model.

Energy Exascale Earth System Model (E3SM)

The Energy Exascale Earth System Model (E3SM) project includes Earth System Models, simulations, and predictions to investigate energy-relevant science using code optimized for DOE's advanced supercomputers.

Source: NVCL Web Page Source