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.

Comparing Ocean Surface Boundary Vertical Mixing Schemes Including Langmuir Turbulence

Abstract: Six recent Langmuir turbulence parameterization schemes and five traditional schemes are implemented in a common single‐column modeling framework and consistently compared. These schemes are tested in scenarios versus matched large eddy simulations, across the globe with realistic forcing (JRA55‐do, WAVEWATCH‐III simulated waves) and initial conditions (Argo), and under realistic conditions as observed at ocean moorings. Traditional non‐Langmuir schemes systematically underpredict large eddy simulation vertical mixing under weak convective forcing, while Langmuir schemes vary in accuracy. Under global, realistic forcing Langmuir schemes produce 6% (−1% to 14% for 90% confidence) or 5.2 m (−0.2 m to 17.4 m for 90% confidence) deeper monthly mean mixed layer depths than their non‐Langmuir counterparts, with the greatest differences in extratropical regions, especially the Southern Ocean in austral summer. Discrepancies among Langmuir schemes are large (15% in mixed layer depth standard deviation over the mean): largest under wave‐driven turbulence with stabilizing buoyancy forcing, next largest under strongly wave‐driven conditions with weak buoyancy forcing, and agreeing during strong convective forcing. Non‐Langmuir schemes disagree with each other to a lesser extent, with a similar ordering. Langmuir discrepancies obscure a cross‐scheme estimate of the Langmuir effect magnitude under realistic forcing, highlighting limited understanding and numerical deficiencies. Maps of the regions and seasons where the greatest discrepancies occur are provided to guide further studies and observations.

A measured look at ocean chlorophyll trends

Abstract: Arising from D. G. Boyce, M. R. Lewis & B. Worm , 591–596 (2010)10.1038/nature09268 ; Boyce et al. reply Identifying major changes in global ecosystem properties is essential to improve our understanding of biological responses to climate forcing and exploitation. Recently, Boyce et al.1 reported an alarming, century-long decline in marine phytoplankton biomass of 1% per year, which would imply major changes in ocean circulation, ecosystem processes and biogeochemical cycling over the period and have significant implications for management of marine fisheries. Closer examination reveals that time-dependent changes in sampling methodology combined with a consistent bias in the relationship between in situ and transparency-derived chlorophyll (Chl) measurements generate a spurious trend in the synthesis of phytoplankton estimates used by Boyce et al.1. Our results indicate that much, if not all, of the century-long decline reported by Boyce et al.1 is attributable to this temporal sampling bias and not to a global decrease in phytoplankton biomass.

Land-surface controls on afternoon precipitation diagnosed from observational data : uncertainties and confounding factors

Abstract: . The feedback between soil moisture and precipitation has long been a topic of interest due to its potential for improving weather and seasonal forecasts. The generally proposed mechanism assumes a control of soil moisture on precipitation via the partitioning of the surface turbulent heat fluxes, as assessed via the evaporative fraction (EF), i.e., the ratio of latent heat to the sum of latent and sensible heat, in particular under convective conditions. Our study investigates the poorly understood link between EF and precipitation by relating the before-noon EF to the frequency of afternoon precipitation over the contiguous US, through statistical analyses of multiple EF and precipitation data sets. We analyze remote-sensing data products (Global Land Evaporation: the Amsterdam Methodology (GLEAM) for EF, and radar precipitation from the NEXt generation weather RADar system (NEXRAD)), FLUXNET station data, and the North American Regional Reanalysis (NARR). Data sets agree on a region of positive relationship between EF and precipitation occurrence in the southwestern US. However, a region of strong positive relationship over the eastern US in NARR cannot be confirmed with observation-derived estimates (GLEAM, NEXRAD and FLUXNET). The GLEAM–NEXRAD data set combination indicates a region of positive EF–precipitation relationship in the central US. These disagreements emphasize large uncertainties in the EF data. Further analyses highlight that much of these EF–precipitation relationships could be explained by precipitation persistence alone, and it is unclear whether EF has an additional role in triggering afternoon precipitation. This also highlights the difficulties in isolating a land impact on precipitation. Regional analyses point to contrasting mechanisms over different regions. Over the eastern US, our analyses suggest that the EF–precipitation relationship in NARR is either atmospherically controlled (from precipitation persistence and potential evaporation) or driven by vegetation interception rather than soil moisture. Although this aligns well with the high forest cover and the wet regime of that region, the role of interception evaporation is likely overestimated because of low nighttime evaporation in NARR. Over the central and southwestern US, the EF–precipitation relationship is additionally linked to soil moisture variations, owing to the soil-moisture-limited climate regime.

The Effects of Mesoscale Eddies on the Stratification and Transport of an Ocean with a Circumpolar Channel

Abstract: The effects of eddies in a primitive equation ocean model configured in a single hemisphere domain with circumpolar channels at their poleward ends are investigated; in particular, two regimes for the mass balance in the channel are investigated. With small overlying winds, the channel stratification is largely set by diffusion operating in the gyre portion of the domain: the depth scale varies with a fractional power of the diffusivity but has little dependence on the wind stress. As the winds are increased, the depth becomes increasingly controlled by a tendency toward small residual circulation. In this limit, a scaling theory is derived for the stratification in the channel that predicts the overall depth of the thermocline as a power of the wind stress and that allows the eddy length scale to differ from the channel length scale. The predicted depth depends on the details of the closure chosen for the eddy buoyancy flux, but in general it varies as some fractional power of the wind stress, a...

The Observed Annual Cycle in the Meridional Transport of Atmospheric Energy

Abstract: The annual cycles in the atmospheric storage and in the meridional transport of energy are discussed. The calculations are based on a five-year sample from more than 500 radiosonde stations mainly located in the Northern Hemisphere. All statistics represent values integrated vertically between the earth's surface and 75 mb and horizontally along a latitude circle. Several new and interesting features of the eddy and mean transports of potential energy, sensible heat, latent heat and kinetic energy become apparent by the breakdown according to calendar month. In December through February more than half of the sensible heat is transported poleward by the standing eddies. The transient eddy heat flux does not peak in winter but in April and November. The strong annual cycle in the tropical Hadley circulation does not contribute to the poleward transfer of energy for the year as a whole.