| NSF Org: |
AGS Division of Atmospheric and Geospace Sciences |
| Recipient: |
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| Initial Amendment Date: | August 21, 2017 |
| Latest Amendment Date: | August 21, 2017 |
| Award Number: | 1701526 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Nicholas Anderson
nanderso@nsf.gov (703)292-4715 AGS Division of Atmospheric and Geospace Sciences GEO Directorate for Geosciences |
| Start Date: | September 1, 2017 |
| End Date: | August 31, 2019 (Estimated) |
| Total Intended Award Amount: | $279,999.00 |
| Total Awarded Amount to Date: | $279,999.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
10889 WILSHIRE BLVD STE 700 LOS ANGELES CA US 90024-4200 (310)794-0102 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
607 Charles E Young Drive, East Los Angeles CA US 90095-7228 |
| 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: |
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| 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 project will make use of satellite data to improve the understanding of how pollution affects ice clouds. A significant fraction of the globe is covered by cirrus and related ice clouds and these clouds have an important impact on the radiation budget of Earth. Pollution can impact clouds by changing the size and density of the ice particles that make up the cloud. However, there are still significant uncertainties related to the kinds of pollution that affect clouds and how that translates to changes in the radiative balance and climate. The long-term impact of the project will be to improve global climate models by addressing ice clouds, which are one of the key remaining uncertainties. The project also includes training for an early-career scientist.
The research team will improve understanding of the ice nucleation process associated with anthropogenic aerosols. The focus of the project will be on black carbon, biomass burning aerosols, organic matter and solid ammonium sulfate with a goal to provide a comprehensive assessment of the contribution of anthropogenic aerosols to ice nucleation, ice cloud properties, and the consequent regional radiative forcing. Data from the A-train constellation of satellites, including CloudSat, CALIPSO, and Aqua will be used to: 1) investigate the correlation between aerosol loading and ice cloud microphysical and macro-physical properties, 2) evaluate the impacts of various meteorological parameters on the observed aerosol-cloud relationship to extract the effect of aerosols, and 3) perform a comprehensive analysis of observations of collocated aerosols and ice clouds to quantify the radiative forcing exerted by aerosols interacting with ice clouds.
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.
Impact of Anthropogenic Air Pollution on Ice Clouds and Regional Radiative Forcing
Impact of anthropogenic pollution on ice formation. Ice formation process determines cloud hydrometeor number and size and alters cloud fraction and lifetime and the radiative balance. Atmospheric ice formation also plays an important role in the global hydrological cycle, since most precipitation initiates through ice-phase processes over land. While mineral dust is known to be an effective ice nucleating particle, the role of aerosols from anthropogenic pollution in ice nucleation is still a subject of uncertainty. We demonstrate that aerosols from anthropogenic pollution contain a considerable fraction of ice nucleating particles (INP, an important factor in the formation of ice clouds) using a novel top-down approach that combines 11-year observations from multiple satellites and cloud-resolving model simulations, and provide a valuable constraint on estimates of the anthropogenic INP budget in modelling studies. Furthermore, our finding has important implications for global and regional climate studies. By acting as INPs, anthropogenic aerosols could have profound impacts on cloud lifetime and radiative effect as well as precipitation efficiency. To date, only a few studies have considered the heterogeneous ice nucleation by certain aerosol species from anthropogenic pollution in climate models. Incorporation of this process could change cloud glaciation rate and result in a different anthropogenic radiative forcing from preindustrial times to the present. It also benefits the assessment of changes in the Earth's hydrology cycle and the distribution of water resources.
Type-dependent responses of ice cloud properties to aerosols. Ice clouds in the Earth's atmosphere have profound impacts on weather and climate. The physical properties of ice clouds, including their thickness, optical depth, and fraction, determine their infrared greenhouse (warming) effect and solar albedo (cooling) effect, as well as the balance between the two. We demonstrate that ice cloud properties respond significantly to aerosol loadings. The response is especially strong at relatively small AOD range (column AOD < 0.25). The occurrence frequency of this AOD range is about 53%, and the related clouds account for about 45% of the total cloud cover. More importantly, we illustrate the first evidence that these responses of ice clouds differ significantly in both sign and magnitude, according to the types of ice clouds and aerosols. These findings appear to be important for understanding and reconciling the conflicting observational results concerning the aerosol effects on ice cloud properties. Moreover, the cloud/aerosol type dependent relationships derived in this study can be used to evaluate and constrain atmospheric models to resolve the causes for different model estimates of aerosol-ice cloud radiative forcing [-0.67 to 0.70 W m2] and help to improve the model assessment of aerosol-ice cloud interactions.
Impact of various aerosol types on ice crystal effective radius. Aerosols have strong and intricate effects on ice cloud effective size through their indirect effect. We provide the first and direct evidence that the competition between the "Twomey effect" and "anti-Twomey effect" is controlled by certain meteorological parameters, primarily water vapor amount. Consequently, the first aerosol indirect forcing, defined as the radiative forcing due to aerosol-induced changes in ice crystal size under a constant ice water content, would change from negative (-0.46 W/m2, 95% confidence interval [-0.49, -0.43 W/m2]) to positive (0.10 W/m2, [0.08, 0.13 W/m2]) between highest third and lowest third relative humidity ranges, implying that the water vapor modulation could play an important role in determining the sign, magnitude, and seasonal and regional variations of aerosol-ice cloud radiative forcings. These radiative effects are very significant given that the best estimate of global aerosol indirect forcing by all cloud types is -0.45 W m-2 (90% confidence interval [-1.2, 0 W/m2]) according to IPCC. It is also evident from our study that the aerosol-induced variability in ice crystal size is affected by nonlinear interplays between microphysical and dynamical processes. An adequate and accurate representation of this modulation in climate models will induce changes in the magnitude and sign of the current estimate of aerosol-ice cloud radiative forcing.
Last Modified: 10/11/2019
Modified by: Yu Gu
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