Geophysical Fluid Dynamics Laboratory

About: Geophysical Fluid Dynamics Laboratory is a facility organization based out in Princeton, New Jersey, United States. It is known for research contribution in the topics: Climate model & Climate change. The organization has 525 authors who have published 2432 publications receiving 264545 citations. The organization is also known as: GFDL.

A Numerical Simulation of the Landfall of Tropical Cyclones.

Abstract: A GFDL tropical cyclone model was applied to simulate storm landfall. The numerical model is a three-dimensional, primitive equation model and has 11 vertical levels with four in the planetary boundary layer. The horizontal grid spacing is variable with finest resolution being 20 km near the center. This model was used successfully in the past to investigate the development of tropical cyclones over the ocean. In the present experiments, a simple situation is assumed where a mature tropical cyclone drifts onto flat land. In such a case, the landfall can he simulated by changing the position of the coastline in the computational domain rather than by moving the storm. As the coastline moves with a specified speed, the surface boundary conditions are altered at the shore from those for the ocean to those for the land by increasing the surface roughness length and also by suppressing the evaporation. Despite the simplicity and idealization of the experiments, the cyclone's filing rates are quite rea...

Evaluating the stationarity assumption in statistically downscaled climate projections: is past performance an indicator of future results?

Abstract: Empirical statistical downscaling (ESD) methods seek to refine global climate model (GCM) outputs via processes that glean information from a combination of observations and GCM simulations. They aim to create value-added climate projections by reducing biases and adding finer spatial detail. Analysis techniques, such as cross-validation, allow assessments of how well ESD methods meet these goals during observational periods. However, the extent to which an ESD method’s skill might differ when applied to future climate projections cannot be assessed readily in the same manner. Here we present a “perfect model” experimental design that quantifies aspects of ESD method performance for both historical and late 21st century time periods. The experimental design tests a key stationarity assumption inherent to ESD methods – namely, that ESD performance when applied to future projections is similar to that during the observational training period. Case study results employing a single ESD method (an Asynchronous Regional Regression Model variant) and climate variable (daily maximum temperature) demonstrate that violations of the stationarity assumption can vary geographically, seasonally, and with the amount of projected climate change. For the ESD method tested, the greatest challenges in downscaling daily maximum temperature projections are revealed to occur along coasts, in summer, and under conditions of greater projected warming. We conclude with a discussion of the potential use and expansion of the perfect model experimental design, both to inform the development of improved ESD methods and to provide guidance on the use of ESD products in climate impacts analyses and decision-support applications.

Diel vertical migration: Ecological controls and impacts on the biological pump in a one‐dimensional ocean model

Abstract: [1] Diel vertical migration (DVM) of zooplankton and micronekton is widespread in the ocean and forms a fundamental component of the biological pump, but is generally overlooked in global models of the Earth system. We develop a parameterization of DVM in the ocean and integrate it with a size-structured NPZD model. We assess the model's ability to recreate ecosystem and DVM patterns at three well-observed Pacific sites, ALOHA, K2, and EQPAC, and use it to estimate the impact of DVM on marine ecosystems and biogeochemical dynamics. Our model includes the following: (1) a representation of migration dynamics in response to food availability and light intensity; (2) a representation of the digestive and metabolic processes that decouple zooplankton feeding from excretion, egestion, and respiration; and (3) a light-dependent parameterization of visual predation on zooplankton. The model captures the first-order patterns in plankton biomass and productivity across the biomes, including the biomass of migrating organisms. We estimate that realistic migratory populations sustain active fluxes to the mesopelagic zone equivalent to between 15% and 40% of the particle export and contribute up to half of the total respiration within the layers affected by migration. The localized active transport has important consequences for the cycling of oxygen, nutrients, and carbon. We highlight the importance of decoupling zooplankton feeding and respiration and excretion with depth for capturing the impact of migration on the redistribution of carbon and nutrients in the upper ocean.

Sensitivity of the Aerosol Indirect Effect to Subgrid Variability in the Cloud Parameterization of the GFDL Atmosphere General Circulation Model AM3

Abstract: The recently developed GFDL Atmospheric Model version 3 (AM3), an atmospheric general circulation model (GCM), incorporates a prognostic treatment of cloud drop number to simulate the aerosol indirect effect. Since cloud drop activation depends on cloud-scale vertical velocities, which are not reproduced in present-day GCMs, additional assumptions on the subgrid variability are required to implement a local activation parameterization into a GCM. This paper describes the subgrid activation assumptions in AM3 and explores sensitivities by constructing alternate configurations. These alternate model configurations exhibit only small differences in their presentday climatology. However, the total anthropogenic radiative flux perturbation (RFP) between present-day and preindustrial conditions varies by 650% from the reference, because of a large difference in the magnitude of the aerosol indirect effect. The spread in RFP does not originate directly from the subgrid assumptions but indirectly through the cloud retuning necessary to maintain a realistic radiation balance. In particular, the paper shows a linear correlation between the choice of autoconversion threshold radius and the RFP. Climate sensitivity changes only minimally between the reference and alternate configurations. If implemented in a fully coupled model, these alternate configurations would therefore likely produce substantially different warming from preindustrial to present day.

The mechanisms of summer dryness induced by greenhouse warming

Abstract: To improve understanding of the mechanisms responsible for CO2-induced, midcontinental summer dryness obtained by earlier modeling studies, several integrations were performed using a GCM with idealized geography. The simulated reduction of soil moisture in middle latitudes begins in late spring and is caused by the excess of evaporation over precipitation. The increase of carbon dioxide and the associated increase of atmospheric water vapor enhances the downward flux of terrestrial radiation at the continental surface at all latitudes. However, due mainly to the CO2-induced change in midtropospheric relative humidity, the increase in the downward flux of terrestrial radiation is larger in the equatorward side of the rain belt, making more energy available there for both sensible and latent heat. Since the saturation vapor pressure at the surface increases nonlinearly with surface temperature, a greater fraction of the additional radiative energy is realized as latent heat flux at the expense of ...