| NSF Org: |
AGS Division of Atmospheric and Geospace Sciences |
| Recipient: |
|
| Initial Amendment Date: | June 8, 2015 |
| Latest Amendment Date: | June 8, 2015 |
| Award Number: | 1455682 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Eric DeWeaver
edeweave@nsf.gov (703)292-8527 AGS Division of Atmospheric and Geospace Sciences GEO Directorate for Geosciences |
| Start Date: | June 15, 2015 |
| End Date: | December 31, 2019 (Estimated) |
| Total Intended Award Amount: | $325,735.00 |
| Total Awarded Amount to Date: | $325,735.00 |
| Funds Obligated to Date: |
|
| History of Investigator: |
|
| Recipient Sponsored Research Office: |
200 UNIVERSTY OFC BUILDING RIVERSIDE CA US 92521-0001 (951)827-5535 |
| Sponsor Congressional District: |
|
| Primary Place of Performance: |
900 University Ave Riverside CA US 92521-0001 |
| Primary Place of
Performance Congressional District: |
|
| Unique Entity Identifier (UEI): |
|
| Parent UEI: |
|
| NSF Program(s): | Climate & Large-Scale Dynamics |
| Primary Program Source: |
|
| Program Reference Code(s): |
|
| Program Element Code(s): |
|
| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
The solar heating of the Earth is affected by aerosols emitted from human activites including agriculture (for instance the burning of crop residue after the harvest), power generation (including both sulfate aerosol which reflects solar radiation and black carbon aerosol that absorbs it), and transportation. The radiative effects of these anthropogenic aerosols are hard to quantify, and their climatic effect is among the largest uncertainties in projections of future climate change. The goal of this project is to develop observationally-based estimates of the radiative forcing due to anthropogenic aerosols using the best available satellite and surface-based datasets. More specifically, the research seeks to produce estimates of the effective radiative forcing from aerosol-radiation interactions (ERFari), which includes both the radiative effects of the aerosols and the changes in radiative forcing due to changes in clouds brought about by aerosol radiative heating. For example, the heating due to absorption of solar radiation by black carbon aerosols (soot) can lead to the "burn off" of clouds, resulting in more sunlight reaching the ground. Data used to determine aerosol amounts, vertical profiles, and radiative parameters comes from several satellite missions ( (MODIS, the CALIPSO/CALIOP lidar, MISR, CERES) and from the ground-based AERONET network. The aerosol amounts and properties are used in combination with a radiative transfer model (MACR) to determine the aerosol radiative forcing. The radiative forcing is then used as an input to global climate models, from which estimates of the further impact of aerosols on cloud radiative forcing are determined. Model-derived estimates of the cloud radiative properties are then compared to further satellite cloud observations. A key assumption of the project is that fine-mode aerosols can be used as a proxy for anthropogenic aerosols, provided that known natural sources of fine-mode aerosol (dust, marine sulfate, sea salt) can be factored out.
The work has broader impacts due to the potential importance of anthropogenic aerosol as a regional and global climate forcing. Work to reduce the large uncertainty in this climate forcing could lead to better projections of future climate change and its impacts on human activities. In addition, the project would support a graduate student and provide a research opportunity for an undergraduate student at an ethnically diverse university. One of the PIs also performs outreach to local K-12 students through a local nonprofit organization.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
Note:
When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external
site maintained by the publisher. Some full text articles may not yet be available without a
charge during the embargo (administrative interval).
Some links on this page may take you to non-federal websites. Their policies may differ from
this site.
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.
Project Outcomes Report for the General Public
Collaborative Research: Observationally-Constrained Estimates of Effective Radiative Forcing from Aerosol Radiation Interactions
NSF award AGS-1455682
Much of our current uncertainty in recent and future climate change stems from aerosol-radiation and aerosol-cloud interactions. This includes aerosol impacts on surface temperature and precipitation, as well as their impacts on large-scale atmospheric circulations and weather systems. This project addressed both aerosol-radiation interactions and aerosol-cloud interactions via rapid adjustments (previously called "semi-direct" effects), as well as aerosol impacts on the tropical atmospheric circulation, including the Hadley and Walker circulations.
Using satellite observations, surface networks and modeling, we developed an observationally constrained estimate of aerosol direct radiative effects. Our global annual value of -0.11 (-0.28 to +0.05) W m-2 suggests that global direct anthropogenic aerosol radiative forcing is less negative than prior estimates of -0.35-0.5 W m-2. Using this observationally-constrained aerosol radiative effect dataset and a suite of climate models, we then constrained the aerosol-cloud rapid adjustment to be positive, likely on the order of a few tenths of a W m-2. This is in contrast to past estimates, which range between -0.44 and +0.1 W m-2. Thus, our estimate suggests a larger positive aerosol-cloud rapid adjustment, and further suggests absorbing aerosol not only warms the climate system through absorption of solar radiation, but also by burning off low and mid-level cloud.
We also identified reasons why prior aerosol-cloud rapid adjustment estimates are likely negatively biased. This includes excessive absorbing aerosol in the upper-troposphere, which leads to high cloud reductions, increasing outgoing longwave radiation and cooling. These results emphasize a need for model improvement of the vertical aerosol profile, which is likely related to better representation of wet removal processes.
Finally, this project investigated how aerosols can impact the large-scale atmospheric circulation. Since ~1979, the tropical belt and its associated subtropical dry zones have been expanding. Although such expansion is an expected response to increasing greenhouse gases, aerosols may also contribute. However, the role of aerosols remains controversial. We show that absorbing (scattering) aerosol drives widening (contraction) of the tropical belt. These responses are consistent with changes in subtropical static stability, a key parameter controlling tropical belt width. Moreover, black carbon (the main absorbing aerosol) is more efficient (per unit forcing) than are greenhouse gases in driving tropical expansion, particularly in the Northern Hemisphere.
We also show that aerosols--most notably biomass burning aerosols from Africa--can excite an atmospheric teleconnection to the tropical Pacific. This response involves strengthening of the tropical Pacific Walker Circulation, and a La Nina-like response in the tropical Pacific. Observations also support a relationship between south African biomass burning emissions and La Nina, with La Nina events preceding strong south African biomass burning in boreal fall. Our simulations suggest a possible two-way feedback between La Nina and south African biomass burning, with La Nina promoting more biomass burning emissions, which may then strengthen the developing La Nina. This is a novel finding, which we plan to explore in more detail.
Last Modified: 03/03/2020
Modified by: Robert J Allen
Please report errors in award information by writing to: awardsearch@nsf.gov.
