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 ENSO with a Global Atmospheric GCM Coupled to a High-Resolution, Tropical Pacific Ocean GCM

Abstract: A global atmospheric general circulation model (GCM) coupled to an oceanic GCM that is dynamically active only in the tropical Pacific simulates variability over a broad spectrum of frequencies even though the forcing, the annual mean incoming solar radiation, is steady. Of special interest is the simulation of a realistically irregular Southern Oscillation between warm El Nino and cold La Nina states. Its time scale is on the order of 5 years. The spatial structure is strikingly different in the eastern and western halves of the ocean basin. Sea surface temperature changes have their largest amplitude in the central and eastern tropical Pacific, but the low-frequency zonal wind fluctuations are displaced westward and are large over the western half of the basin. These zonal wind anomalies are essentially confined to the band of latitudes 10° to 10°S so that they form a jet and have considerable latitudinal shear. During El Nino the associated curl contributes to a pair of pronounced minima in th...

Tracer Conservation with an Explicit Free Surface Method for z-Coordinate Ocean Models

Abstract: This paper details a free surface method using an explicit time stepping scheme for use in z-coordinate ocean models. One key property that makes the method especially suitable for climate simulations is its very stable numerical time stepping scheme, which allows for the use of a long density time step, as commonly employed with coarse-resolution rigid-lid models. Additionally, the effects of the undulating free surface height are directly incorporated into the baroclinic momentum and tracer equations. The novel issues related to local and global tracer conservation when allowing for the top cell to undulate are the focus of this work. The method presented here is quasi-conservative locally and globally of tracer when the baroclinic and tracer time steps are equal. Important issues relevant for using this method in regional as well as large-scale climate models are discussed and illustrated, and examples of scaling achieved on parallel computers provided.

Anticorrelated multidecadal variations between surface and subsurface tropical North Atlantic

Abstract: [1] In this paper for the first time I show that the multidecadal variations of observed tropical North Atlantic (TNA) sea surface temperature (SST) are strongly anticorrelated with those of the observed TNA subsurface ocean temperature, with long-term trends removed. I further show that the anticorrelated change between the TNA surface and subsurface temperature is a distinctive signature of the Atlantic meridional overturning circulation (AMOC) variations, using water-hosing experiments with the GFDL state-of-art coupled climate model (CM2.1). External radiative forced simulations with the same model do not provide a significant relationship between the TNA surface and subsurface temperature variations. The observed detrended multidecadal TNA subsurface temperature anomaly may be taken as a proxy for the AMOC variability. Various mechanisms proposed for the multidecadal TNA SST variations, which are crucial for multidecadal variations of Atlantic hurricane activities, should take into account the observed anticorrelation between the TNA surface and subsurface temperature variations.

Estimates of Ozone Return Dates from Chemistry-Climate Model Initiative Simulations

Abstract: >We analyse simulations performed for the Chemistry-Climate Model Initiative (CCMI) to estimate the return dates of the stratospheric ozone layer from depletion caused by anthropogenic stratospheric chlorine and bromine We consider a total of 155 simulations from 20 models, including a range of sensitivity studies which examine the impact of climate change on ozone recovery For the control simulations (unconstrained by nudging towards analysed meteorology) there is a large spread (±20 DU in the global average) in the predictions of the absolute ozone column Therefore, the model results need to be adjusted for biases against historical data Also, the interannual variability in the model results need to be smoothed in order to provide a reasonably narrow estimate of the range of ozone return dates Consistent with previous studies, but here for a Representative Concentration Pathway (RCP) of 60, these new CCMI simulations project that global total column ozone will return to 1980 values in 2049 (with a 1σ uncertainty of 2043–2055) At Southern Hemisphere mid-latitudes column ozone is projected to return to 1980 values in 2045 (2039–2050), and at Northern Hemisphere mid-latitudes in 2032 (2020–2044) In the polar regions, the return dates are 2060 (2055–2066) in the Antarctic in October and 2034 (2025–2043) in the Arctic in March The earlier return dates in the Northern Hemisphere reflect the larger sensitivity to dynamical changes Our estimates of return dates are later than those presented in the 2014 Ozone Assessment by approximately 5–17 years, depending on the region, with the previous best estimates often falling outside of our uncertainty range In the tropics only around half the models predict a return of ozone to 1980 values, around 2040, while the other half do not reach the 1980 value All models show a negative trend in tropical total column ozone towards the end of the 21st century The CCMI models generally agree in their simulation of the time evolution of stratospheric chlorine and bromine, which are the main drivers of ozone loss and recovery However, there are a few outliers which show that the multi-model mean results for ozone recovery are not as tightly constrained as possible Throughout the stratosphere the spread of ozone return dates to 1980 values between models tends to correlate with the spread of the return of inorganic chlorine to 1980 values In the upper stratosphere, greenhouse gas-induced cooling speeds up the return by about 10–20 years In the lower stratosphere, and for the column, there is a more direct link in the timing of the return dates of ozone and chlorine, especially for the large Antarctic depletion Comparisons of total column ozone between the models is affected by different predictions of the evolution of tropospheric ozone within the same scenario, presumably due to differing treatment of tropospheric chemistry Therefore, for many scenarios, clear conclusions can only be drawn for stratospheric ozone columns rather than the total column As noted by previous studies, the timing of ozone recovery is affected by the evolution of N2O and CH4 However, quantifying the effect in the simulations analysed here is limited by the few realisations available for these experiments compared to internal model variability The large increase in N2O given in RCP 60 extends the ozone return globally by ∼ 15 years relative to N2O fixed at 1960 abundances, mainly because it allows tropical column ozone to be depleted The effect in extratropical latitudes is much smaller The large increase in CH4 given in the RCP 85 scenario compared to RCP 60 also lengthens ozone return by ∼ 15 years, again mainly through its impact in the tropics Overall, our estimates of ozone return dates are uncertain due to both uncertainties in future scenarios, in particular those of greenhouse gases, and uncertainties in models The scenario uncertainty is small in the short term but increases with time, and becomes large by the end of the century There are still some model–model differences related to well-known processes which affect ozone recovery Efforts need to continue to ensure that models used for assessment purposes accurately represent stratospheric chemistry and the prescribed scenarios of ozone-depleting substances, and only those models are used to calculate return dates For future assessments of single forcing or combined effects of CO2, CH4, and N2O on the stratospheric column ozone return dates, this work suggests that it is more important to have multi-member (at least three) ensembles for each scenario from every established participating model, rather than a large number of individual models

A Numerical Study of the Effect of Island Terrain on Tropical Cyclones

Abstract: A triply nested, movable mesh model was used to study the behavior of tropical cyclones encountering island mountain ranges. The integration domain consisted of a 37° wide and 45° long channel, with an innermost mesh resolution of 1/6°. The storms used for this study were embedded in easterly flows of ∼5 and ∼10 m s−1 initially. Realistic distributions of island topography at 1/6° resolution were inserted into the model domain for the region of the Caribbean, including the islands of Cuba, Hispaniola, and Puerto Rico; the island of Taiwan; and the region of Luzon in the northern Philippines. It was found that the islands affected the basic flow as well as the wind field directly associated with the storm system. The combination of these effects caused changes in the track and translational speed of the storm. In particular, in the case of the 5 m s−1 easterly flow, the storm accelerated and veered to the north well before reaching Taiwan. For the other island distributions, the northward deflecti...