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Comprehensive Characterization of the Seasonal Cycles of Ice Nucleating Particles for Studies of Precipitation Drivers in SAIL

Active Dates 9/1/2023-8/31/2026
Program Area Atmospheric System Research
Project Description
Comprehensive Characterization of the Seasonal Cycles of Ice Nucleating Particles for Studies of Precipitation Drivers in SAIL

Principal Investigator:                                            Co-Investigators:

Dr. Russell J. Perkins                                               Prof. Sonia M. Kreidenweis, CSU

Colorado State University (CSU)

In midlatitude regions where mixed phase clouds dominate, abundances and characteristics of cloud condensation nuclei (CCN) and ice nucleating particles (INPs) can exert critical controls on cloud phase, radiative forcing, and precipitation formation. This control can be direct, through cloud droplet formation and freezing, or indirect via processes such as altering air circulations in mountainous terrain, such as found in the study region for the Atmospheric Radiation Measurement (ARM) program’s Surface Atmosphere Integrated field Laboratory (SAIL). In particular, precipitation formation over the Colorado Rockies appears to be sensitive to the abundance of INPs, a motivation for the wintertime orographic cloud seeding programs active in the SAIL study region. Earth System Models (ESMs) have persistently failed in predicting the timing of peak snow depth and snowmelt in winter, and in capturing decadal trends in the timing of summer precipitation. SAIL studies will address the challenge of bridging from local to ESM scales through collecting a comprehensive set of measurements toward understanding and quantifying sub-grid processes, including aerosol-cloud interactions. The goal of the proposed project is to improve the representation of aerosol-cloud interactions in ESMs by extending the aerosol characterizations being done for the SAIL campaign, specifically targeting INP characterizations that will leverage existing samples and measurements. This activity will create the first comprehensive, observationally-based annual cycle of INP types for the Intermountain West.

Specific objectives are to:

(1)      Quantify the annual cycle of INP concentrations (as functions of temperature) by source type and in the context of CCN and total aerosol populations in the SAIL environment, with a special focus on measuring biological particles and biological INPs, and episodes of biomass burning and dust transport influences.

(2)      Distinguish and quantify the contributions of cloud seeding and snowmaking activities to the observed INPs in winter, especially artificial INPs active at small supercooling.

(3)      Determine vertical profiles of total aerosols, CCN, and INPs, to link surface-based observations to those most relevant at cloud base and therefore most relevant to cloud microphysical evolution.

(4)      Synthesize data into new parameterizations describing INP populations and their relationships to ambient aerosols so that the results can be applied to any region, and to transfer these descriptions to collaborators who will incorporate them into numerical models for study of the corresponding aerosol-cloud-precipitation interactions.

Our research tasks and methods are driven by four testable hypotheses: (1) INP concentrations are maximum in summer, driven by biological and episodic organic INP sources; (2) episodic organic INP sources are wildfires and soil dust; (3) surface measurements will be most representative of aerosols reaching cloud levels in summer; (4) the signal of regional cloud seeding efforts will be detectable in INP data during winter storms. Our approach includes greatly supplementing processing of collected filters for “typing” INPs and leveraging other aerosol physical and chemical analyses for interpretation of drivers of cloud-active aerosols. Linking aerosol properties to INPs via parameterization development will support collaborative numerical modeling investigations of aerosol-precipitation interactions in both warm and cold-season clouds, and under seeding scenarios. Thereby we address SAIL science objectives to “establish aerosol regimes, the processes controlling the life cycle of aerosols in those regimes, and quantify the impacts of aerosols in those regimes on the atmospheric and surface radiative budget” and to “quantify the sensitivity of cloud phase and precipitation to cloud condensation nuclei (CCN) and ice-nucleating particle (INP) concentrations.” This work will provide unprecedented interpretation of SAIL ARM data to advance the science of aerosol, cloud, and precipitation interactions, an ASR program goal.
Award Recipient(s)
  • Colorado State University, Fort Collins (PI: Perkins, Russell)