Research Highlights / Atmospheric Physics Chemistry and Climate
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March 29, 2013
Sensitivity of tropospheric oxidants to biomass burning emissions: implications for radiative forcing
Biomass burning is one of the largest sources of trace gases and aerosols in the atmosphere, and has profound influence on tropospheric oxidants and radiative forcing. Using a fully coupled chemistry-climate model (GFDL AM3), the authors found that co-emission of trace gases and aerosol from present-day biomass burning increases the global tropospheric ozone burden by 5.1%, and decreases global mean OH, a major sink for methane, by 6.3%.
March 4, 2013
Cloud tuning in a coupled climate model: impact on 20th century warming
Clouds remain one of the largest sources of uncertainty in predictions from climate models. Globally, clouds cool the Earth through the net effect of two opposing contributions: cooling from reflection of incoming solar radiation and warming from trapping of infrared radiation emitted by the Earth. By comparison, the cooling effect of clouds is estimated to be about six times larger than the warming effect resulting from the increase in anthropogenic greenhouse gases since 1750. This is why uncertainties in the representation of clouds can have considerable impact on the simulated climate.
January 21, 2013
Springtime high surface ozone events over the western United States: Quantifying the role of stratospheric intrusions
Stratosphere-to-troposphere transport of ozone is a common occurrence at mid- and high latitudes, but its influence on tropospheric ozone levels remains a long-standing question, despite decades of research. GFDL scientists and colleagues analyzed balloon soundings, lidar, surface and satellite measurements using GFDL’s new global high-resolution chemistry-climate model, to look at the extent to which naturally occurring stratospheric ozone intrusions reach the surface and affect air quality.
August 24, 2012
Mixing of dust and NH3 observed globally over anthropogenic dust sources
Dust is one of the most abundant aerosols in the atmosphere, and by scattering and absorbing solar radiation, it affects climate. Anthropogenic dust is largely ignored in most current climate studies. We show how pervasive it is throughout the world, and that it is mostly associated with croplands.
August 17, 2012
Global scale attribution of anthropogenic and natural dust sources and their emission rates based on MODIS Deep Blue aerosol products
Dust is one of the most abundant aerosols in the atmosphere, and by scattering and absorbing solar radiation, it affects climate. In particular, anthropogenic dust is a significant source of radiative forcing on the climate system. Increasing numerical resolution of climate models provides an opportunity to create a realistic, high-resolution dust-source inventory.
July 23, 2012
Evaluation of cloud and water vapor simulations in CMIP5 climate models using NASA "A-Train" satellite observations
Clouds and water vapor are among the difficult features of the atmosphere for global climate models to simulate because they are affected by physical processes that operate over very small areas compared to the weather patterns that the models explicitly calculate. The authors used satellite data to assess the representation of clouds and water vapor simulated by several climate models that will participate in the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5).
July 16, 2012
Nonlinear climate response to regional brightening of tropical marine stratocumulus
To combat global warming, there have been suggestions to increase the albedo of (i.e. brighten) low-level marine clouds by deliberately injecting them with aerosols. Though such cloud seeding could mitigate global-mean temperature rise through the aerosol indirect effects, the full climate response to this geoengineering scheme is poorly understood. For example, one prior simulation of cloud seeding exhibited catastrophic rainfall decrease over the Amazon, while another showed moderate rainfall increase there.
June 1, 2012
Model Precipitation Bias over the Southwestern Equatorial Indian Ocean
This study investigated the spatio-temporal features of the serious positive precipitation bias over the southwestern equatorial Indian Ocean which is found in most current coupled and uncoupled general circulation models, and its links with the large scale monsoon circulation. The study attempted to answer two questions: Is there a common identifiable mechanism forcing the local bias? Does the local bias have an influence on the continental simulated monsoon precipitation?
May 4, 2012
Tropical Tropospheric-Only Responses to Absorbing Aerosols
An ongoing challenge in quantifying aerosols’ impact on the climate is determining an optimal way of calculating aerosols’ radiative forcing. For absorbing aerosols, in particular, studies have shown that a forcing calculation that does not include the tropospheric response to absorbing aerosol (instantaneous forcing) is a poor proxy for the change in global mean surface temperature caused by the aerosol.
April 27, 2012
Comparing Global Atmospheric Model Simulations of Tropical Convection
An intercomparison of global atmospheric model simulations of tropical convection has been presented and evaluated with available observations collected during the TWP-ICE field experiment. Short simulations initialized from the ECMWF analysis have been used to constrain model large-scale states and thus isolate model systematic biases originating from various physical parameterizations. With realistic thermodynamic and kinematic fields captured in various weather regimes (wet, dry, and break), model precipitation, cloud properties (LWC, IWC, cloud fraction), radiation, and vertical heating profiles respond accordingly in these regimes. Despite somewhat realistically simulated precipitation, there are substantial cloud property discrepancies among the models, which are mainly influenced by cloud and convective parameterizations.
March 29, 2012
Reducing Uncertainty in Understanding Ocean Oxygen and Nitrogen Cycles
Oxygen minimum zones (OMZs) exclude many classes of the biological community and are major sites of fixed nitrogen removal from the open ocean. Previous estimates of rate of fixed nitrogen loss through denitrification in the pelagic ocean and in sediments have been unable to match estimates of the supply of fixed nitrogen via N2 fixation, rivers, and atmospheric deposition. This has led some scientists to the conclusion that the global ocean nitrogen cycle is out of balance, and the oceans are accumulating fixed nitrogen.
February 24, 2012
Transport of Asian ozone pollution into surface air over the western United States in spring
As Asian countries develop, they are emitting more ozone precursors that pollute surface level air. Many studies have documented this pollution being carried by air currents to the western United States. To determine the extent to which this pollution is affecting air quality in the western U.S., We analyzed balloon soundings, aircraft, surface and satellite measurements from May through June 2010 using a new global high-resolution chemistry-climate model. Our findings indicate that Asian pollution contributes as much as 20 percent of total ozone during springtime pollution episodes in western U.S. surface air.
September 29, 2011
Anthropogenic Aerosols and the Weakening of the South Asian Summer Monsoon
An important part of the global water cycle, the South Asian summer monsoon provides about 80% of the region’s annual precipitation, and touches the lives of more than 20% of the world’s population. Using the NOAA/GFDL state-of-the-art global climate model that accounts for all the known natural and anthropogenic forcings, we have investigated what caused the observed decrease in the South Asian summer monsoon rainfall over the second half of the 20th century. Was the widespread drying due to natural factors or human activities?
September 12, 2011
Climatological characteristics of Arctic and Antarctic surface-based inversions
Surface-based inversions (SBI) are frequent features of the Arctic and Antarctic atmospheric boundary layer and influence important climate processes. However, prior to this study, climatological polar SBI properties had not been fully characterized, nor had climate model simulations of SBIs been compared comprehensively to observations.
July 1, 2011
Sensitivity of the aerosol indirect effect to subgrid variability in the cloud parame
The recently developed GFDL AM3 model (Donner et. al 2011) incorporates a prognostic treatment of cloud drop number to simulate the aerosol indirect effect. The present work explores formulation sensitivities by constructing three alternate model configurations (S1, S2, S3). These alternate configurations exhibit only small differences in their present day climatology.