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 multi-model study of the hemispheric transport and deposition of oxidised nitrogen

Abstract: Fifteen chemistry-transport models are used to quantify, for the first time, the export of oxidised nitrogen (NOy) to and from four regions (Europe, North America, South Asia, and East Asia), and to estimate the uncertainty in the results. Between 12 and 24% of the NOx emitted is exported from each region annually. The strongest impact of each source region on a foreign region is: Europe on East Asia, North America on Europe, South Asia on East Asia, and East Asia on North America. Europe exports the most NOy, and East Asia the least. East Asia receives the most NOy from the other regions. Between 8 and 15% of NOx emitted in each region is transported over distances larger than 1000 km, with 3–10% ultimately deposited over the foreign regions.

The Termination of the 1997-98 El Niño. Part II: Mechanisms of Atmospheric Change

Abstract: The mechanisms that drove zonal wind stress ( x ) changes in the near-equatorial Pacific at the end of the extreme 1997–98 El Nino event are explored using a global atmospheric general circulation model. The analysis focuses on three features of the x evolution between October 1997 and May 1998 that were fundamental in driving the oceanic changes at the end of this El Nino event: (i) the southward shift of near-date-line surface zonal wind stress ( x ) anomalies beginning November 1997, (ii) the disappearance of the easterly x from the eastern equatorial Pacific (EEqP) in February 1998, and (iii) the reappearance of easterly x in the EEqP in May 1998. It is shown that these wind changes represent the deterministic response of the atmosphere to the observed sea surface temperature (SST) field, resulting from changes in the meridional structure of atmospheric convective anomalies in response to the seasonally phase-locked meridional movement of the warmest SST. The southward shift of the near-date-line x anomalies at the end of this El Nino event was controlled by the seasonal movement of the warmest SST south of the equator, which—both directly and through its influence on the atmospheric response to changes in SST anomaly—brought the convective anomalies from being centered about the equator to being centered south of the equator. The disappearance (reappearance) of easterly EEqP x has only been evident in extreme El Nino events and has been associated with the development (northward retreat) of an equatorial intertropical convergence zone (ITCZ). The disappearance/return of EEqP easterly x arises in the AGCM as the deterministic response to changes in the SST field, tied principally to the changes in climatological SST (given time-invariant extreme El Nino SSTA) and not to changes in the underlying SSTA field. The disappearance (return) of EEqP easterly x in late boreal winter (late boreal spring) is a characteristic atmospheric response to idealized extreme El Nino SST anomalies; this suggests that the distinctive termination of the 1997–98 El Nino event is that to be expected for extreme El Nino events.

The atlantic meridional heat transport at 26.5°N and its relationship with the MOC in the RAPID array and the GFDL and NCAR coupled models

Abstract: The link at 26.58N between the Atlantic meridional heat transport (MHT) and the Atlantic meridional overturning circulation (MOC) is investigated in two climate models, the GFDL Climate Model version 2.1 (CM2.1) and the NCAR Community Climate System Model version 4 (CCSM4), and compared with the recent observational estimates from the Rapid Climate Change‐Meridional Overturning Circulation and Heatflux Array (RAPID‐MOCHA) array. Despite a stronger-than-observed MOC magnitude, both models underestimate the mean MHT at 26.58N because of an overly diffuse thermocline.Biases result from errors in both overturning and gyre components of the MHT. The observed linear relationship between MHT and MOC at 26.58N is realistically simulatedbythe twomodelsandis mainlyduetotheoverturningcomponent of the MHT. Fluctuations in overturning MHT are dominated by Ekman transport variability in CM2.1 and CCSM4, whereas baroclinic geostrophic transport variability plays a larger role in RAPID. CCSM4, which has a parameterization of Nordic Sea overflows and thus a more realistic North Atlantic Deep Water (NADW) penetration, shows smaller biases in the overturning heat transport than CM2.1 owing to deeper NADW at colder temperatures. The horizontal gyre heat transport and its sensitivity to the MOC are poorly represented in both models. The wind-driven gyre heat transport is northward in observations at 26.58N, whereas it is weakly southward in both models, reducing the total MHT. This study emphasizes model biases that are responsible for the too-weak MHT, particularly at the western boundary. The use of direct MHT observations through RAPID allows for identification of the source of the too-weak MHT in the two models, a bias shared by a number of Coupled Model Intercomparison Project phase 5 (CMIP5) coupled models.

Sea Ice–Albedo Feedback and Nonlinear Arctic Climate Change

Abstract: The potential for sea ice―albedo feedback to give rise to nonlinear climate change in the Arctic Ocean region, defined as a nonlinear relationship between polar and global temperature change or, equivalently, a time-varying polar amplification, is explored in the Intergovernmental Panel on Climate Change climate models. Five models supplying Special Report on Emissions Scenario A1B ensembles for the 21st century are examined, and very linear relationships are found between polar and global temperatures (indicating linear polar region climate change) and between polar temperature and albedo (the potential source of nonlinearity). Two of the climate models have Arctic Ocean simulations that become annually sea ice―free under the stronger CO 2 increase to quadrupling forcing. Both of these runs show increases in polar amplification at polar temperatures above -5°C, and one exhibits heat budget changes that are consistent with the small ice cap instability of simple energy balance models. Both models show linear warming up to a polar temperature of ―5°C, well above the disappearance of their September ice covers at about ―9°C. Below ―5°C, effective annual surface albedo decreases smoothly as reductions move, progressively, to earlier parts of the sunlit period. Atmospheric heat transport exerts a strong cooling effect during the transition to annually ice-free conditions, counteracting the albedo change. Specialized experiments with atmosphere-only and coupled models show that the main damping mechanism for sea ice region surface temperature is reduced upward heat flux through the adjacent ice-free oceans resulting in reduced atmospheric heat transport into the region.