| NSF Org: |
AGS Division of Atmospheric and Geospace Sciences |
| Recipient: |
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| Initial Amendment Date: | August 25, 2015 |
| Latest Amendment Date: | March 31, 2019 |
| Award Number: | 1540954 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Sylvia Edgerton
sedgerto@nsf.gov (703)292-8522 AGS Division of Atmospheric and Geospace Sciences GEO Directorate for Geosciences |
| Start Date: | September 1, 2015 |
| End Date: | February 28, 2021 (Estimated) |
| Total Intended Award Amount: | $572,578.00 |
| Total Awarded Amount to Date: | $675,710.00 |
| Funds Obligated to Date: |
FY 2019 = $103,132.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
1109 GEDDES AVE STE 3300 ANN ARBOR MI US 48109-1015 (734)763-6438 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
2455 Hayward St Ann Arbor MI US 48109-2143 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): |
Atmospheric Chemistry, Physical & Dynamic Meteorology, Climate & Large-Scale Dynamics |
| Primary Program Source: |
01001920DB NSF RESEARCH & RELATED ACTIVIT |
| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
This research focuses on the use of a global chemistry/climate model to improve the modeling of ice formation in cirrus clouds. This research will better inform climate modelers about the causes of differences in model predictions of the effects of small particles (aerosol) in cirrus clouds. It will also provide a representation of aerosol and ice formation that is based on physical and chemical processes and broadly consistent with the field observations used to evaluate the model.
The researchers hypothesize that a substantial fraction of ice formation in cirrus clouds is associated with secondary organic aerosols (SOA) and/or solid ammonium sulfate (NH4)2SO4 and that changes in these aerosols over time result in a significant climate forcing. The hypothesis will be tested using the Community Atmosphere Model (CAM5) climate model coupled to the IMPACT aerosol model. The IMPACT model ties the formation of SOA to the photochemical oxidation of volatile organic compounds (VOCs) based on a recently extended oxidation scheme. The researchers are in the process of extending the SOA formation framework to allow it to consider how the formation mechanism alters the size distribution of both primary organics and other aerosol species associated with SOA. In this research, they will explore several ways of parameterizing SOA nucleation. They will compare the changes in SOA formation and forcing in cirrus clouds using varying amounts of dust, sulfate, glassy organic aerosols (depending on the glass transition temperature of each SOA), and solid (NH4)2SO4.
The model simulations will be compared with observations from recent measurement campaigns to identify which treatments of SOA formation, ice cloud nucleation, and updraft velocities are best able to reproduce the observations. This research will better inform the climate community of the causes of differences in model predictions of aerosol effects in cirrus clouds. The results of this research will aid in quantifying climate forcing by aerosols and help to inform policy makers of the possible role of aerosols in either heating or cooling climate through their action in nucleating ice crystals.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
As a result of this project, we developed a parameterization for the formation of ice crystals on aerosol particles as a result of the updrafts and downdrafts that result from gravity waves in the upper troposphere and added this parameterization to the coupled NCAR CAM5/CESM climate model and the University of Michigan IMPACT aerosol model. We also improved our formation of secondary organic aerosols (SOA) in order to be able to better represent the formation of ice crystals on these types of aerosols. We examined the radiative forcing associated with different types of aerosol particles and also performed a series of sensitivity tests to quantify how this forcing changes under different assumptions about which aerosol particles might nucleate to ice crystals at lower relative humidities (i.e. through heterogeneous nucleation processes), compared to those that nucleate at higher relative humidities (through homogeneous nucleation). We found that with our best assumptions, the forcing by aircraft soot was relatively strong and negative (-0.14 Wm-2) unless a higher proportion of dust particles are heterogeneous ice nuclei or SOA was able to act as a heterogeneous ice nuclei. To test whether our assumptions about the treatment of soot from aircraft are reasonable, we compared the ice number concentrations from the model to those measured by the CALIPSO satellite. We also examined the observed difference between the April/May 2021 concentrations during the COVID-19 pandemic to those from earlier years. We found that our predicted ice number concentrations were similar to those from CALIPSO, and that the April/May 2021 ice number concentrations were significantly higher than those from previous years for both observations and the model. This is expected if heterogeneous ice nuclei decrease, allowing the much higher homogeneous ice nuclei to form ice crystals. While the treatment of ice nucleation on aircraft soot is controversial, this finding supports the treatment in the CAM5/IMPACT model.
Last Modified: 04/08/2021
Modified by: Joyce E Penner
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