The use of spatially varying eddy diffusivities is explored with the extended Gent–McWilliams (eGM) closure for both passive tracers and potential vorticity (PV). Numerical experiments are conducted ...with a wind-forced isopycnal channel model. It is shown that, the eGM closure with eddy diffusivities derived from a high-resolution reference solution produces the best results compared to the reference solution in terms of the thickness, PV profiles and volume fluxes. The use of spatially varying eddy diffusivities also removes the unphysical reverse jets near the channel walls shown by the eGM with constant eddy diffusivities.
IntroductionThis study aimed to evaluate the use and dose of loop diuretics (LDs) across the entire ejection fraction (EF) spectrum in a large, ‘real-world’ cohort of chronic heart failure (HF) ...patients.MethodsA total of 10 366 patients with chronic HF from 34 Dutch outpatient HF clinics were analysed regarding diuretic use and diuretic dose. Data regarding daily diuretic dose were stratified by furosemide dose equivalent (FDE)>80 mg or ≤80 mg. Multivariable logistic regression models were used to assess the association between diuretic dose and clinical features.ResultsIn this cohort, 8512 (82.1%) patients used diuretics, of which 8179 (96.1%) used LDs. LD use was highest among HF with reduced EF (HFrEF) patients (81.1%) followed by HF with mild-reduced EF (76.1%) and HF with preserved ejection fraction EF (73.8%, p<0.001). Among all LDs users, the median FDE was 40 mg (IQR: 40–80). The results of the multivariable analysis showed that New York Heart Association classes III and IV and diabetes mellitus were one of the strongest determinants of an FDE >80 mg, across all HF categories. Renal impairment was associated with a higher FDE across the entire EF spectrum.ConclusionIn this large registry of real-world HF patients, LD use was highest among HFrEF patients. Advanced symptoms, diabetes mellitus and worse renal function were significantly associated with a higher diuretic dose regardless of left ventricular ejection fraction.
To provide context for observed sea level rise, the forced response (FR) in dynamic sea level (DSL) during the 20th and 21st centuries is examined in the Community Earth System Model Large Ensemble ...(LE). After accounting for simulation drift, which in the LE is sizable, the DSL FR is found to be complex, both in space and time. Its evolving character is suggested to arise from both the diversity and transient evolution of climate forcing agents and the slow adjustment timescales of the intermediate and deep oceans. Nonetheless, various intervals of spatially coherent change simulated for the recent past and near future are identified, and their characteristics and associated driving mechanisms are identified and discussed. The mid‐ to late‐20th century DSL FR is characterized by an hemispherically asymmetric pattern of change, with depressed rates of rise in the northern oceans. There is also a dipole of change in the Southern Ocean caused by changes in near‐surface zonal winds. Through the late 20th and early 21st centuries, a different pattern of rise emerges with elevated rates in the tropics and depressed rates at high latitudes. Zonal and interbasin variations characterize both intervals and involve the pattern and depth of anomalous ocean heat content storage and spatial contrasts in the expansion coefficient tied mainly to base state temperature, with greater rates of rise in warm regions per unit warming. The relative roles of surface flux and ocean convergence anomalies are examined.
Plain Language Summary
Evolving patterns of sea level rise in the 20th and 21st centuries driven by climate forcings are revealed in climate model simulations and found to affect both our interpretation of past changes and projection of the future.
Key Points
The pattern of the simulated forced response in sea level from 1920 to 2100 is nonuniform in both space and time
The altimeter era is a blend of the 20th C pattern when aerosols are important and 21st C pattern when greenhouse gases start to dominate
Spatial patterns arise chiefly from geographic and depth variations in ocean heat content anomalies and the seawater expansion coefficient
We investigate intraannual to interannual variability in the Antarctic Polar Front (PF) using weekly PF realizations spanning 2002–2014 (found at doi.pangaea.de/10.1594/PANGAEA.855640). While several ...PF studies have used gradient maxima in sea surface temperature (SST) or height to define its location, results from this study are based on a PF defined using SST measurements that avoid cloud contamination and the influence of steric sea level change. With a few regional exceptions, we find that the latitudinal position of the PF does not vary seasonally, yet its temperature exhibits a clear seasonal cycle. Consistent with previous studies, the position and intensity of the PF is largely influenced by bathymetry; generally, over steep topography, we find that the front intensifies and interannual variability in its position is low. We also investigate drivers of PF variability in the context of large‐scale climate variability on various spatial and temporal scales, but find that the major modes of Southern Hemisphere climate variability explain only a tiny fraction of the interannual PF variance. Over the study time period, the PF intensifies at nearly all longitudes while exhibiting no discernible meridional displacement in its zonal mean path.
Key Points:
Zonally averaged frontal temperature and intensity vary seasonally while latitudinal position does not
The zonally averaged front has not shifted meridionally but has intensified
Low congruence between SAM/ENSO and front variability
Multi‐decadal trends in the advection, mixing, and air‐sea flux of natural carbon dioxide (CO2) in the Southern Ocean are investigated using output from a hindcast simulation of a non‐eddy‐resolving ...ocean model. Particular emphasis is placed on the model's improved eddy‐induced advection parameterization. From 1958 to 2007, the model predicts a significant increase in the outgassing of natural CO2 from the Southern Ocean, congruent with a positive trend in the wind speed over this period. The natural CO2 flux trend is largely driven by enhanced Eulerian‐mean advection and diapycnal mixing of dissolved inorganic carbon (DIC) into the Southern Ocean surface. The natural CO2 flux trend would be larger, if not for an increase in the eddy‐induced advection of DIC out of the Southern Ocean surface, caused by the multi‐decadal increase in the model's eddy‐induced advection coefficient.
Key Points
GCM predicts Southern Ocean CO2 outgassing trend driven by wind increase
Increased eddy‐induced advection of carbon opposes Eulerian tendency
Eddy‐induced advection of carbon is sensitive to parameterization coefficient
Evidence for the assumptions of the salt-advection feedback in box models is sought by studying the Atlantic meridional overturning circulation (AMOC) internal variability in the long preindustrial ...control runs of two Earth system models. The first assumption is that AMOC strength is proportional to the meridional density difference between the North Atlantic and the Southern Oceans. The model simulations support this assumption, with the caveat that nearly all the long time-scale variability occurs in the North Atlantic density. The second assumption is that the freshwater transport variability by the overturning at the Atlantic southern boundary is controlled by the strength of AMOC. Only one of the models shows some evidence that AMOC variability at 45°N leads variability in the overturning freshwater transport at the southern boundary by about 30 years, but the other model shows no such coherence. In contrast, in both models this freshwater transport variability is dominated by local salinity variations. The third assumption is that changes in the overturning freshwater transport at the Atlantic southern boundary perturb the north–south density difference, and thus feed back on AMOC strength in the north. No evidence for this assumption is found in either model at any time scale, although this does not rule out that the salt-advection feedback may be excited by a strong enough freshwater perturbation.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Interocean waters that are carried northward through South Atlantic surface boundary currents get meridionally split between two large-scale systems when meeting the South American coast at the ...western subtropical portion of the basin. This distribution of the zonal flow along the coast is investigated during the Last Millennium, when natural forcing was key to establish climate variability. Of particular interest are the changes between the contrasting periods of the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). The investigation is conducted with the simulation results from the Community Earth System Model Last Millennium Ensemble (CESM-LME). It is found that the subtropical South Atlantic circulation pattern differs substantially between these natural climatic extremes, especially at the northern boundary of the subtropical gyre, where the westward-flowing southern branch of the South Equatorial Current (sSEC) bifurcates off the South American coast, originating the equatorward-flowing North Brazil Undercurrent (NBUC) and the poleward Brazil Current (BC). It is shown that during the MCA, a weaker anti-cyclonic subtropical gyre circulation took place (inferred from decreased southern sSEC and BC transports), while the equatorward transport of the Meridional Overturning Circulation return flow was increased (intensified northern sSEC and NBUC). The opposite scenario occurs during the LIA: a more vigorous subtropical gyre circulation with decreased northward transport.
The NCAR Climate System Model, version one, is described. The spinup procedure prior to a fully coupled integration is discussed. The fully coupled model has been run for 300 yr with no surface flux ...corrections in momentum, heat, or freshwater. There is virtually no trend in the surface temperatures over the 300 yr, although there are significant trends in other model fields, especially in the deep ocean. The reasons for the successful integration with no surface temperature trend are discussed.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
An accurate diagnosis of ocean heat content (OHC) is essential for interpreting climate variability and change, as evidenced for example by the broad range of hypotheses that exists for explaining ...the recent hiatus in global mean surface warming. Potential insights are explored here by examining relationships between OHC and sea surface height (SSH) in observations and two recently available large ensembles of climate model simulations from the mid-twentieth century to 2100. It is found that in decadal-length observations and a model control simulation with constant forcing, strong ties between OHC and SSH exist, with little temporal or spatial complexity. Agreement is particularly strong on monthly to interannual time scales. In contrast, in forced transient warming simulations, important dependencies in the relationship exist as a function of region and time scale. Near Antarctica, low-frequency SSH variability is driven mainly by changes in the circumpolar current associated with intensified surface winds, leading to correlations between OHC and SSH that are weak and sometimes negative. In subtropical regions, and near other coastal boundaries, negative correlations are also evident on long time scales and are associated with the accumulated effects of changes in the water cycle and ocean dynamics that underlie complexity in the OHC relationship to SSH. Low-frequency variability in observations is found to exhibit similar negative correlations. Combined with altimeter data, these results provide evidence that SSH increases in the Indian and western Pacific Oceans during the hiatus are suggestive of substantial OHC increases. Methods for developing the applicability of altimetry as a constraint on OHC more generally are also discussed.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
It is shown that the effects of mesoscale eddies on tracer transports can be parameterized in a large-scale model by additional advection and diffusion of tracers. Thus, tracers are advected by the ...effective transport velocity, which is the sum of the large-scale velocity and the eddy-induced transport velocity. The density and continuity equations are the familiar equations for adiabatic, Boussinesq, and incompressible flow with the effective transport velocity replacing the large-scale velocity. One of the main points of this paper is to show how simple the parameterization of Gent and McWilliams appears when interpreted in terms of the effective transport velocity. This was not done in their original 1990 paper. It is also shown that, with the Gent and McWilliams parameterization, potential vorticity in the planetary geostrophic model satisfies an equation close to that for tracers. The analogy of this parameterization with vertical mixing of momentum is then described. The effect of the Gent and McWilliams parameterization is illustrated by applying it to a strong, sloping two-dimensional front. The final state is that the front is flat, corresponding to a state of minimum potential energy. However, the amount of water of a given density has not been changed and there has been no flow across isopycnals. These properties are not preserved with horizontal diffusion of tracer. Finally, the Levitus dataset is used to estimate the effects of the Gent and McWilliams parameterization. The zonal mean meridional overturning streamfunction for the eddy-induced transport velocity has a maximum of 18 Sverdrups near the Antarctic Circumpolar Current. The associated poleward heat transport is 0.4 petawatts. The maximum poleward heat transport in the Northern Hemisphere is 0.15 petawatts at 40 degree N. These values are the same order of magnitude as estimates from observations and regional eddy-resolving ocean models.
PDF
