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 Case of Downstream Baroclinic Development over Western North America

Abstract: Numerical simulations have been made of the initiation of a strong ridge-trough system over western North America and the eastern Pacific (the terminus of the Pacific storm track), with the objective of determining the extent to which downstream development contributed to its growth, and the possible influence of topography on the energetics of the storm. While a control simulation demonstrated considerable skill in reproducing the storm, a “simplified” simulation in which topography, surface that fluxes, and latent heating were removed not only reproduced the primary features of the ridge-trough system—permitting a clearer interpretation of the factors contributing to its growth—but actually generated a stronger system, suggesting that these effects as a whole inhibited storm development. Application of an energy budget that distinguishes between energy generation via baroclinic processes and generation via the convergence of geopotential fluxes revealed that early growth of studies that have sh...

The Diffusive Approximation for Eddy Fluxes in Baroclinically Unstable Jets

Abstract: A series of statistically steady states for baroclinically stable jets in a two-layer quasigeostrophic model is examined, in order to evaluate diffusive approximations to the eddy potential vorticity or heat fluxes. The flow is forced by thermal relaxation to an unstable “radiative equilibrium” temperature gradient. The statistically steady states are studied as a function of the width of the radiative equilibrium jet. A local diffusive “theory” for the eddy fluxes is obtained from integrations of a homogeneous, doubly periodic model with prescribed environmental potential vorticity gradients. The flux-gradient relationship generated by the homogeneous model predicts the magnitude and shape of the eddy fluxes in the unstable jet flows remarkably well, as long as the jet is not too narrow. These results confirm the relevance of diffusive closures for eddy potential vorticity and heat fluxes in such flows. For narrow jets that produce eddy fluxes with a half-width of one to two radii of deformation...

Revisiting the evidence of increasing springtime ozone mixing ratios in the free troposphere over western North America

Abstract: We present a 20 year time series of in situ free tropospheric ozone observations above western North America during springtime and interpret results using hindcast simulations (1980–2014) conducted with the Geophysical Fluid Dynamics Laboratory global chemistry-climate model (GFDL AM3). Revisiting the analysis of Cooper et al. (2010), we show that sampling biases can substantially influence calculated trends. AM3 cosampled in space and time with observations reproduces the observed ozone trend (0.65 ± 0.32 ppbv yr−1) over 1995–2008 (in simulations either with or without time-varying emissions), whereas AM3 “true median” with continuous temporal and spatial sampling indicates an insignificant trend (0.25 ± 0.32 ppbv yr−1). Extending this analysis to 1995–2014, we find a weaker ozone trend of 0.31 ± 0.21 ppbv yr−1 from observations and 0.36 ± 0.18 ppbv yr−1 from AM3 “true median.” Rising Asian emissions and global methane contribute to this increase. While interannual variability complicates the attribution of ozone trends, multidecadal hindcasts can aid in the estimation of robust confidence limits for trends based on sparse observational records.

Poleward Deflection of Storm Tracks

Abstract: An analysis of 11 years of European Centre for Medium-Range Weather Forecasts data focuses primarily on the vertically averaged high-frequency transients. The conclusions are discussed in the context of (a) the winter storm track, (b) monthly variability, and (c) interannual variability. (a) Winter storm track: Results show that the pattern of the forcing by the high-frequency eddies along the storm track is highly correlated with the stationary circulation, and the forcing itself is primarily responsible for the location of the trough‐ridge system associated with the stationary flow. The results also clarify the role of wind component covariance terms u9y9 and (y9 2 2 u9 2) in the column-averaged vorticity forcing. The simpler term u9y9 has the well-known effect of intensifying the anticyclonic (cyclonic) tendencies on the southern (northern) side of the jet, thereby producing an increase in the barotropic component of the zonal jet. The (y9 2 2 u9 2) term displays a quadrupole pattern, which is also approximately in phase with the trough‐ridge system associated with the stationary flow. (b) Monthly variability: Eddy activity has been shown to possess a seasonal life cycle, increasing during the early fall and reaching a maximum around the month of November, then decaying for most of the winter months. Month-to-month variations in eddy activity over the Pacific Ocean show that energy levels increase up through November, decreasing thereafter, at the same time the trough‐ridge circulation pattern is intensifying. By December, baroclinicity in the western Pacific has increased substantially, and low-level eddies are found to break by the middle of the ocean. Upper-level eddies start to break well before reaching the west coast of North America, resulting in a displacement of the maximum in (y9 2 2 u9 2) westward from its November position and increasing the trough‐ridge forcing by the high-frequency eddies. (c) Interannual variability: Wintertime eddy kinetic energy is seen to extend further eastward through the Pacific Ocean during the warm phase but displays an abrupt termination during the cold phase. Anomalies in the eddy transient forcing tend to be quite similar to that of the Pacific‐North American pattern itself. The extension of the storm track during the warm phase resembles that of fall conditions and is present in the winter season because the source of low-level baroclinicity

The effect of the dynamic surface bareness on dust source function, emission, and distribution

Abstract: [1] In this study we report the development of a time dependency of global dust source and its impact on dust simulation in the Goddard Chemistry Aerosol Radiation and Transport (GOCART) model. We determine the surface bareness using the 8 km normalized difference vegetation index (NDVI) observed from the advanced very high resolution radiometer satellite. The results are used to analyze the temporal variations of surface bareness in 22 global dust source regions. One half of these regions can be considered permanent dust source regions where NDVI is always less than 0.15, while the other half shows substantial seasonality of NDVI. This NDVI-based surface bareness map is then used, along with the soil and topographic characteristics, to construct a dynamic dust source function for simulating dust emissions with the GOCART model. We divide the 22 dust source regions into three groups of (I) permanent desert, (II) seasonally changing bareness that regulates dust emissions, and (III) seasonally changing bareness that has little effect on dust emission. Compared with the GOCART results with the previously employed static dust source function, the simulation with the new dynamic source function shows significant improvements in category II regions. Even though the global improvement of the aerosol optical depth (AOD) is rather small when compared with satellite and ground-based remote sensing observations, we found a clear and significant effect of the new dust source on seasonal variation of dust emission and dust optical depth near the source regions. Globally, we have found that the permanent bare land contributes to 88% of the total dust emission, whereas the grassland and cultivated crops land contribute to about 12%. Our results suggest the potential of using NDVI over a vegetated area to link the dust emission with land cover and land use change for air quality and climate change studies.