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.

Simulation of Atmospheric Variability

Abstract: A spectral atmospheric circulation model is time-integrated for approximately 18 years. The model has a global computational domain and realistic geography and topography. The model undergoes an annual cycle as daily values of seasonally varying insolation and sea surface temperature are prescribed without any interannual variation. It has a relatively low computational resolution with 15 spectral components retained in both zonal and meridional directions. Analysis of the results from the last 15 years of the time integration indicates that, in middle and high latitudes, the model approximately reproduces the observed geographical distribution of the variability (i.e., standard deviation) of daily, monthly and yearly mean surface pressure and temperature. In the tropics, the model tends to underestimate the variability of surface pressure, particularly at longer time scales. This result suggests the importance of processes with long time scales such as ocean–atmosphere interaction, in maintainin...

Inconsistent strategies to spin up models in CMIP5: implications for ocean biogeochemical model performance assessment

Abstract: . During the fifth phase of the Coupled Model Intercomparison Project (CMIP5) substantial efforts were made to systematically assess the skill of Earth system models. One goal was to check how realistically representative marine biogeochemical tracer distributions could be reproduced by models. In routine assessments model historical hindcasts were compared with available modern biogeochemical observations. However, these assessments considered neither how close modeled biogeochemical reservoirs were to equilibrium nor the sensitivity of model performance to initial conditions or to the spin-up protocols. Here, we explore how the large diversity in spin-up protocols used for marine biogeochemistry in CMIP5 Earth system models (ESMs) contributes to model-to-model differences in the simulated fields. We take advantage of a 500-year spin-up simulation of IPSL-CM5A-LR to quantify the influence of the spin-up protocol on model ability to reproduce relevant data fields. Amplification of biases in selected biogeochemical fields (O2, NO3, Alk-DIC) is assessed as a function of spin-up duration. We demonstrate that a relationship between spin-up duration and assessment metrics emerges from our model results and holds when confronted with a larger ensemble of CMIP5 models. This shows that drift has implications for performance assessment in addition to possibly aliasing estimates of climate change impact. Our study suggests that differences in spin-up protocols could explain a substantial part of model disparities, constituting a source of model-to-model uncertainty. This requires more attention in future model intercomparison exercises in order to provide quantitatively more correct ESM results on marine biogeochemistry and carbon cycle feedbacks.

Effect of latitude on the persistence of eddy-driven jets

Abstract: [1] An asymmetry in the persistence of the eddy-driven jet is demonstrated, whereby the equatorward-shifted (low-phase) jet is more persistent than the poleward-shifted (high-phase) jet. The asymmetry is investigated by stirring the non-divergent vorticity equation on the sphere and is shown to arise due to the sphericity of the earth, which inhibits poleward wave breaking when the jet is at high latitudes. This spherical effect becomes increasingly important as the mean jet is positioned at higher latitudes. The persistence of the annular mode decreases as the mean jet moves closer to the pole due to the decreased persistence of the high-phase state, while the low-phase state exhibits similar persistence regardless of the jet position. These results suggest that with the expected poleward shift of the jet due to increasing greenhouse gases, the annular mode's total persistence will decrease due to a decrease in the persistence of the high-phase.

Effects of patchy ocean fertilization on atmospheric carbon dioxide and biological production

Abstract: [1] Increasing oceanic productivity by fertilizing nutrient-rich regions with iron has been proposed as a mechanism to offset anthropogenic emissions of carbon dioxide. Earlier studies examined the impact of large-scale fertilization of vast reaches of the ocean for long periods of time. We use an ocean general circulation model to consider more realistic scenarios involving fertilizing small regions (a few hundred kilometers on a side) for limited periods of time (of order 1 month). A century after such a fertilization event, the reduction of atmospheric carbon dioxide is between 2% and 44% of the initial pulse of organic carbon export to the abyssal ocean. The fraction depends on how rapidly the surface nutrient and carbon fields recover from the fertilization event. The modeled recovery is very sensitive to the representation of biological productivity and remineralization. Direct verification of the uptake would be nearly impossible since changes in the air-sea flux due to fertilization would be much smaller than those resulting from natural spatial variability. Because of the sensitivity of the uptake to the long-term fate of the iron and organic matter, indirect verification by measurement of the organic matter flux would require high vertical resolution and long-term monitoring. Finally, the downward displacement of the nutrient profile resulting from an iron-induced productivity spurt may paradoxically lead to a long-term reduction in biological productivity. In the worst-case scenario, removing 1 ton of carbon from the atmosphere for a century is associated with a 30-ton reduction in biological export of carbon.

The Effect of Salinity on the Wind-Driven Circulation and the Thermal Structure of the Upper Ocean

Abstract: Studies of the effect of a freshening of the surface waters in high latitudes on the oceanic circulation have thus far focused almost entirely on the deep thermohaline circulation and its poleward heat transport. Here it is demonstrated, by means of an idealized general circulation model, that a similar freshening can also affect the shallow, wind-driven circulation of the ventilated thermocline and its heat transport from regions of gain (mainly in the upwelling zones of low latitudes) to regions of loss in higher latitudes. A freshening that decreases the surface density gradient between low and high latitudes reduces this poleward heat transport, thus forcing the ocean to gain less heat in order to maintain a balanced heat budget. The result is a deepening of the equatorial thermocline. (The deeper the thermocline in equatorial upwelling zones is, the less heat the ocean gains.) For a sufficiently strong freshwater forcing, the poleward heat transport all but vanishes, and permanently warm conditions prevail in the Tropics. The approach to warm oceanic conditions is shown to introduce a bifurcation mechanism for the north‐south asymmetry of the thermal and salinity structure of the upper ocean.