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.

Impact of ENSO on SST Variability in the North Pacific and North Atlantic: Seasonal Dependence and Role of Extratropical Sea–Air Coupling

Abstract: The influences of El Nino–Southern Oscillation (ENSO) events in the tropical Pacific on interannual variability of the coupled ocean–atmosphere systems in the North Pacific and North Atlantic have been studied using a suite of experiments with a rhomboidal 30-wavenumber, 14-layer general circulation model (GCM). Observed month-to-month fluctuations of the sea surface temperature (SST) in the tropical Pacific during the 1950–95 period were prescribed as the lower boundary condition for the GCM. The SST conditions outside of the tropical Pacific were predicted by a simple ocean mixed layer model with a constant depth. Four independent integrations under this “Tropical Ocean–Global Atmosphere–Mixed Layer (TOGA-ML)” scenario were conducted. Both observational and model results indicate that the imposed ENSO forcing during midwinter is accompanied by prominent atmospheric circulation changes over the North Pacific and Atlantic. These teleconnection patterns in turn alter the heat exchange across the l...

Projected decreases in future marine export production: the role of the carbon flux through the upper ocean ecosystem

Abstract: . Accurate projections of marine particle export production (EP) are crucial for predicting the response of the marine carbon cycle to climate change, yet models show a wide range in both global EP and their responses to climate change. This is, in part, due to EP being the net result of a series of processes, starting with net primary production (NPP) in the sunlit upper ocean, followed by the formation of particulate organic matter and the subsequent sinking and remineralisation of these particles, with each of these processes responding differently to changes in environmental conditions. Here, we compare future projections in EP over the 21st century, generated by four marine ecosystem models under the high emission scenario Representative Concentration Pathways (RCP) 8.5 of the Intergovernmental Panel on Climate Change (IPCC), and determine the processes driving these changes. The models simulate small to modest decreases in global EP between −1 and −12 %. Models differ greatly with regard to the drivers causing these changes. Among them, the formation of particles is the most uncertain process with models not agreeing on either magnitude or the direction of change. The removal of the sinking particles by remineralisation is simulated to increase in the low and intermediate latitudes in three models, driven by either warming-induced increases in remineralisation or slower particle sinking, and show insignificant changes in the remaining model. Changes in ecosystem structure, particularly the relative role of diatoms matters as well, as diatoms produce larger and denser particles that sink faster and are partly protected from remineralisation. Also this controlling factor is afflicted with high uncertainties, particularly since the models differ already substantially with regard to both the initial (present-day) distribution of diatoms (between 11–94 % in the Southern Ocean) and the diatom contribution to particle formation (0.6–3.8 times higher than their contribution to biomass). As a consequence, changes in diatom concentration are a strong driver for EP changes in some models but of low significance in others. Observational and experimental constraints on ecosystem structure and how the fixed carbon is routed through the ecosystem to produce export production are urgently needed in order to improve current generation ecosystem models and their ability to project future changes.

Inherently unstable climate behaviour due to weak thermohaline ocean circulation

Abstract: The oceanic thermohaline circulation (THC) carries light, warm surface water polewards and dense, cold deep water equator-wards, thereby transporting a large amount of heat towards the poles and significantly affecting high latitude climate. The THC has been remarkably stable, and its variability quite low, over the Holocene period (the past 10,000 years). The much greater climate instability and high-frequency variability recorded in ice1 and deep-sea31 cores throughout the preceding 150,000 years has been linked to greater THC variability2,3. Here we argue, using a global coupled ocean–atmosphere–ice general circulation model with realistic geography, that there is a wide range of weak mean states of the THC that cannot be stably sustained by the climate system. When the model THC is forced into a state in the unstable range, the THC may rapidly strengthen, collapse or display strong oscillations. The existence of this unstable regime may account for the greater variability of the THC and climate before the Holocene period.

Impact of ENSO on the Atmospheric Variability over the North Atlantic in Late Winter—Role of Transient Eddies

Abstract: The dynamical mechanism for the late-winter teleconnection between El Nino–Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO) is examined using the output from a 2000-yr integration of a coupled general circulation model (GCM). The coupled model captures many salient features of the observed behavior of both ENSO and NAO, as well as their impact on the surface climate in late winter. Both the observational and model data indicate more occurrences of negative phase of NAO in late winter during El Nino events, and positive NAO in La Nina episodes.The potential role of high-frequency transient eddies in the above teleconnection is diagnosed. During El Nino winters, the intensified transient disturbances along the equatorward-shifted North Pacific storm track extend their influences farther downstream. The eddy-induced negative height tendencies are found to be more coherent and stronger over North Atlantic than that over North Pacific. These negative height tendencies over the North...

Identifying human influences on atmospheric temperature

Abstract: We perform a multimodel detection and attribution study with climate model simulation output and satellite-based measurements of tropospheric and stratospheric temperature change. We use simulation output from 20 climate models participating in phase 5 of the Coupled Model Intercomparison Project. This multimodel archive provides estimates of the signal pattern in response to combined anthropogenic and natural external forcing (the fingerprint) and the noise of internally generated variability. Using these estimates, we calculate signal-to-noise (S/N) ratios to quantify the strength of the fingerprint in the observations relative to fingerprint strength in natural climate noise. For changes in lower stratospheric temperature between 1979 and 2011, S/N ratios vary from 26 to 36, depending on the choice of observational dataset. In the lower troposphere, the fingerprint strength in observations is smaller, but S/N ratios are still significant at the 1% level or better, and range from three to eight. We find no evidence that these ratios are spuriously inflated by model variability errors. After removing all global mean signals, model fingerprints remain identifiable in 70% of the tests involving tropospheric temperature changes. Despite such agreement in the large-scale features of model and observed geographical patterns of atmospheric temperature change, most models do not replicate the size of the observed changes. On average, the models analyzed underestimate the observed cooling of the lower stratosphere and overestimate the warming of the troposphere. Although the precise causes of such differences are unclear, model biases in lower stratospheric temperature trends are likely to be reduced by more realistic treatment of stratospheric ozone depletion and volcanic aerosol forcing.