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GFDL Research Highlights

September 29th, 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? If the latter, what were the relative contributions of anthropogenic greenhouse gases and aerosols? Answering these questions poses a challenging test on our fundamental knowledge of the changes to the Earth’s hydrological cycle, and on our ability to understand and project future regional climate change. Read More…

September 12th, 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. Using 20 years of radiosonde observations, and simulations from two state-of-the-art climate models, this study examines the spatial and temporal variability of three SBI characteristics – frequency of occurrence, depth (from the surface to the inversion top), and intensity (temperature difference over the SBI depth) – and relationships among them. Read More…

July 3rd, 2011 - Different magnitudes of projected subsurface ocean warming around Greenland and Antarctica

Recent acceleration of Greenland and Antarctic outlet glaciers and ice flows is closely linked to ocean warming, especially in the subsurface layer. This land ice melt will cause sea level rise.

We find that in response to an increase in atmospheric greenhouse-gas concentrations, the subsurface oceans (200-500 m) surrounding the two polar ice sheets both warm substantially more than has been observed thus far. Model projections suggest that the maximum ocean warming around Greenland will be double the global mean, whereas ocean warming around Antarctica will be only half the global mean. Read More…

July 1st, 2011 - The GFDL CM3 model

Earlier generations of climate models at GFDL have specified cloud properties to be independent of atmospheric aerosol composition, despite fairly well-understood (at least for liquid clouds) dependence of cloud droplet number on aerosol composition and size distribution. Cloud drop number in turn exerts a major control on cloud radiation, notably albedo, and microphysics and macrophysics, notably cloud structure and lifetimes. Aerosol-cloud interactions are likely to be important in anthropogenic climate change. They have been difficult to incorporate in climate models because they occur at scales much smaller than resolved by climate models. CM3 parameterizes these smaller scales using probability distribution functions for motions smaller than those it explicitly resolves. Read More…

July 1st, 2011 - Sensitivity of the aerosol indirect effect to subgrid variability in the cloud parameterization of the GFDL Atmosphere General Circulation Model AM3

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. Read More…

June 5th, 2011 - Raining from the Ground Up

Though it is obvious that rainfall moistens the land surface, our scientific understanding of how land surface moisture may interact with the atmosphere to encourage or suppress subsequent rainfall is limited. Using data from the North American Regional Reanalysis (NARR, Mesinger et al., 2006), this study shows that the likelihood of afternoon rainfall in the eastern United States and Mexico is strongly linked to evaporation from the land surface earlier in the day. Read More…

April 2nd, 2011 - Downward shortwave surface flux in the GFDL CM2.1 General Circulation Model

The downward solar flux at the surface is an important component of the earth’s climate system, being a major factor governing the surface temperature and hydrologic cycle. The availability of derived flux climatologies from both ground-based measurements and satellite-based estimates provide a reference for properly assessing general circulation model biases, not only in the surface irradiance, but in the atmospheric factors (aerosols, clouds, and water vapor) affecting it. Read More…

February 2nd, 2011 - North American isoprene influence on intercontinental ozone pollution

Changing land-use and climate may increase biogenic isoprene emissions, which could offset the benefits from North American air pollution controls for both domestic and European air quality (surface ozone). Both anthropogenic and biogenic emission changes are reflected in peroxy acetyl nitrate (PAN), which may serve as a more effective indicator of intercontinental emission changes than ozone itself. Read More…

February 1st, 2011 - The meteorological nature of variable soluble iron transport and deposition within the North Atlantic Ocean basin

Biological productivity in vast regions of the oceans is known to be limited by the supply of iron, an essential nutrient to marine organisms, impacting carbon export to the ocean floor. The atmospheric source of iron originates from desert mineral dust aerosols and is converted to a bio-available form of soluble iron during transport. Little is known of the magnitude and variability of soluble iron deposition (SFeD) and the character of its transport. We have used the GFDL Global Chemical Transport Model to examine the emission of mineral dust (~3.5% Fe) during Saharan desert dust storms; the chemical processing of iron to a soluble form during transport; and the subsequent dry surface deposition and precipitation scavenging deposition to the North Atlantic Ocean. Read More…

October 1st, 2010 - Sensitivity of the NOy budget over the United States to anthropogenic and lightning NOx in summer

The study by Fang et al. [2010] examines the implications of new estimates of the anthropogenic and lightning nitrogen oxide (NOx) sources for the budget of oxidized nitrogen (NOy) over the United States in summer using a 3-D global chemical transport model (MOZART-4). NOy export and burden response less than linearly to either NOx emission changes due to the NOy partitioning change and the corresponding lifetime change. Lightning NOxcontributes 24%−43% of the free tropospheric (FT) NOy export from the U.S. to the North Atlantic and 28%−34% to the NOy wet deposition over the United States. Increasing lightning NOx decreases the fractional contribution of PAN to total NOy export and decreases the FT ozone (O3) production efficiency. Therefore, a model with biased low lightning NOx would lead to biased high downwind O3 responses due to anthropogenic NOx emission regulations. Better constraints on the lightning NOx source are required to more confidently assess the impacts of anthropogenic emission regulations on air quality over downwind regions. Read More…

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