Mean flow and turbulence statistics over groups of urban-like cubical obstacles

Direct numerical simulations of turbulent flow over regular arrays of urban-like, cubical obstacles are reported. Results are analysed in terms of a formal spatial averaging procedure to enable interpretation of the flow within the arrays as a canopy flow, and of the flow above as a rough wall boundary layer. Spatial averages of the mean velocity, turbulent stresses and pressure drag are computed. The statistics compare very well with data from wind-tunnel experiments. Within the arrays the time-averaged flow structure gives rise to significant 'dispersive stress' whereas above the Reynolds stress dominates. The mean flow structure and turbulence statistics depend significantly on the layout of the cubes. Unsteady effects are important, especially in the lower canopy layer where turbulent fluctuations dominate over the mean flow.

Effects of fluctuating daily surface fluxes on the time-mean oceanic circulation

The effect of fluctuating daily surface fluxes on the time-mean oceanic circulation is studied using an empirical flux model. The model produces fluctuating fluxes resulting from atmospheric variability and includes oceanic feedbacks on the fluxes. Numerical experiments were carried out by driving an ocean general circulation model with three different versions of the empirical model. It is found that fluctuating daily fluxes lead to an increase in the meridional overturning circulation (MOC) of the Atlantic of about 1 Sv and a decrease in the Antarctic circumpolar current (ACC) of about 32 Sv. The changes are approximately 7% of the MOC and 16% of the ACC obtained without fluctuating daily fluxes. The fluctuating fluxes change the intensity and the depth of vertical mixing. This, in turn, changes the density field and thus the circulation. Fluctuating buoyancy fluxes change the vertical mixing in a non-linear way: they tend to increase the convective mixing in mostly stable regions and to decrease the convective mixing in mostly unstable regions. The ACC changes are related to the enhanced mixing in the subtropical and the mid-latitude Southern Ocean and reduced mixing in the high-latitude Southern Ocean. The enhanced mixing is related to an increase in the frequency and the depth of convective events. As these events bring more dense water downward, the mixing changes lead to a reduction in meridional gradient of the depth-integrated density in the Southern Ocean and hence the strength of the ACC. The MOC changes are related to more subtle density changes. It is found that the vertical mixing in a latitudinal strip in the northern North Atlantic is more strongly enhanced due to fluctuating fluxes than the mixing in a latitudinal strip in the South Atlantic. This leads to an increase in the density difference between the two strips, which can be responsible for the increase in the Atlantic MOC.

Iron and zinc status in multiple sclerosis patients with pressure sores

Measurements of weighted dietary intakes and plasma determinations of albumin, iron, zinc, ascorbic acid and TIBC were carried out on twenty female multiple sclerosis patients in a long-stay hospital for disabled people. The group included ten patients with a recent history of pressure sores, closely matched with ten patients without pressure sores. Mean daily intake of carbohydrate was found to be higher in the non-pressure sore group whilst intake of zinc was lower in this group. Intakes of all other nutrients were comparable between the two groups. For both groups, intakes of energy, folate, vitamin D, iron and zinc were less than recommended values. Mean plasma levels of albumin and iron were towards the lower limit of the normal range, whilst that for zinc was considerably less than the normal range. Plasma TIBC was slightly above the normal range. Levels of plasma iron and zinc were significantly lower in the pressure sore group. The data indicate that severely disabled hospitalized patients with multiple sclerosis may be at risk of poor nutritional status. The results suggest that in the presence of pressure sores, there are increased requirements for specific nutrients, notably zinc and iron. Consideration is given to the possible value of supplementation of these individuals.

Atmospheric conservation properties in ERA-Interim

We study the global atmospheric budgets of mass, moisture, energy and angular momentum in the latest reanalysis from the European Centre for Medium-Range Weather Forecasts (ECMWF), ERA-Interim, for the period 1989–2008 and compare with ERA-40. Most of the measures we use indicate that the ERA-Interim reanalysis is superior in quality to ERA-40. In ERA-Interim the standard deviation of the monthly mean global dry mass of 0.7 kg m−2 (0.007%) is slightly worse than in ERA-40, and long time-scale variations in dry mass originate predominately in the surface pressure field. The divergent winds are improved in ERA-Interim: the global standard deviation of the time-averaged dry mass budget residual is 10 kg m−2 day−1 and the quality of the cross-equatorial mass fluxes is improved. The temporal variations in the global evaporation minus precipitation (E − P) are too large but the global moisture budget residual is 0.003 kg m−2 day−1 with a spatial standard deviation of 0.3 kg m−2 day−1. Both the E − P over ocean and P − E over land are about 15% larger than the 1.1 Tg s−1 transport of water from ocean to land. The top of atmosphere (TOA) net energy losses are improved, with a value of 1 W m−2, but the meridional gradient of the TOA net energy flux is smaller than that from the Clouds and the Earth's Radiant Energy System (CERES) data. At the surface the global energy losses are worse, with a value of 7 W m−2. Over land however, the energy loss is only 0.5 W m−2. The downwelling thermal radiation at the surface in ERA-Interim of 341 W m−2 is towards the higher end of previous estimates. The global mass-adjusted energy budget residual is 8 W m−2 with a spatial standard deviation of 11 W m−2, and the mass-adjusted atmospheric energy transport from low to high latitudes (the sum for the two hemispheres) is 9.5 PW

Cloud-resolving model simulations with one- and two-way couplings via the weak temperature gradient approximation

A cloud-resolving model is modified to implement the weak temperature gradient approximation in order to simulate the interactions between tropical convection and the large-scale tropical circulation. The instantaneous domain-mean potential temperature is relaxed toward a reference profile obtained from a radiative–convective equilibrium simulation of the cloud-resolving model. For homogeneous surface conditions, the model state at equilibrium is a large-scale circulation with its descending branch in the simulated column. This is similar to the equilibrium state found in some other studies, but not all. For this model, the development of such a circulation is insensitive to the relaxation profile and the initial conditions. Two columns of the cloud-resolving model are fully coupled by relaxing the instantaneous domain-mean potential temperature in both columns toward each other. This configuration is energetically closed in contrast to the reference-column configuration. No mean large-scale circulation develops over homogeneous surface conditions, regardless of the relative area of the two columns. The sensitivity to nonuniform surface conditions is similar to that obtained in the reference-column configuration if the two simulated columns have very different areas, but it is markedly weaker for columns of comparable area. The weaker sensitivity can be understood as being a consequence of a formulation for which the energy budget is closed. The reference-column configuration has been used to study the convection in a local region under the influence of a large-scale circulation. The extension to a two-column configuration is proposed as a methodology for studying the influence on local convection of changes in remote convection.

Does dairy food intake predict arterial stiffness and blood pressure in men? Evidence from the Caerphilly prospective study

Arterial stiffness is an independent predictor of cardiovascular disease events and mortality, and like blood pressure, may be influenced by dairy food intake. Few studies have investigated the effects of consumption of these foods on prospective measures of arterial stiffness. The present analysis aimed to investigate the prospective relationship between milk, cheese, cream, and butter consumption and aortic pulse wave velocity, augmentation index, systolic and diastolic blood pressure, as well as cross-sectional relationships between these foods and systolic and diastolic blood pressure and metabolic markers using data from the Caerphilly Prospective Study. Included in this cohort were 2512 men, aged 45 to 59 years, who were followed up at 5-year intervals for a mean of 22.8 years (number follow-up 787). Augmentation index was 1.8% lower in subjects in the highest quartiles of dairy product intake compared with the lowest (P trend=0.021), whereas in the highest group of milk consumption systolic blood pressure was 10.4 mm Hg lower (P trend=0.033) than in nonmilk consumers after a 22.8-year follow-up. Cross-sectional analyses indicated that across increasing quartiles of butter intake, insulin (P trend=0.011), triacylglycerol (P trend=0.023), total cholesterol (P trend=0.002), and diastolic blood pressure (P trend=0.027) were higher. Across increasing groups of milk intake and quartiles of dairy product intake, glucose (P trend=0.032) and triglyceride concentrations (P trend=0.031) were lower, respectively. The present results confirm that consumption of milk predicts prospective blood pressure, whereas dairy product consumption, excluding butter, is not detrimental to arterial stiffness and metabolic markers. Further research is needed to better understand the mechanisms that underpin these relationships.

Is fatty acid intake a predictor of arterial stiffness and blood pressure in men? Evidence from the Caerphilly Prospective Study

Background and aims: Arterial stiffness is an independent predictor of cardiovascular disease (CVD) events and all-cause mortality and may be differentially affected by dietary fatty acid (FA) intake. The aim of this study was to investigate the relationship between FA consumption and arterial stiffness and blood pressure in a community-based population. Methods and results: The Caerphilly Prospective Study recruited 2398 men, aged 45-59 years, who were followed up at 5-year intervals for a mean of 17.8-years (n 787). A semi-quantitative food frequency questionnaire estimated intakes of total, saturated, mono- and poly-unsaturated fatty acids (SFA, MUFA, PUFA). Multiple regression models investigated associations between intakes of FA at baseline with aortic pulse wave velocity (aPWV), augmentation index (AIx), systolic and diastolic blood pressure (SBP, DBP) and pulse pressure after a 17.8-year follow-up - as well as cross-sectional relationships with metabolic markers. After adjustment, higher SFA consumption at baseline was associated with higher SBP (P = 0.043) and DBP (P = 0.002) and after a 17.8-year follow-up was associated with a 0.51 m/s higher aPWV (P = 0.006). After adjustment, higher PUFA consumption at baseline was associated with lower SBP (P = 0.022) and DBP (P = 0.036) and after a 17.8-year follow-up was associated with a 0.63 m/s lower aPWV (P = 0.007). Conclusion: This study suggests that consumption of SFA and PUFA have opposing effects on arterial stiffness and blood pressure. Importantly, this study suggests that consumption of FA is an important risk factor for arterial stiffness and CVD.

The importance of surface pressure changes in the response of the atmosphere to zonally-symmetric thermal and mechanical forcing

he classical problem of the response of a balanced, axisymmetric vortex to thermal and mechanical forcing is re-examined, paying special attention to the lower boundary condition. The correct condition is DΦ/Dt = 0, where Φ is the geopotential and D/Dt the material derivative, which explicitly accounts for a mass redistribution as part of the mean-flow response. This redistribution is neglected when using the boundary condition Dp/Dt = 0, which has conventionally been applied in this problem. It is shown that applying the incorrect boundary condition, and thereby ignoring the surface pressure change, leads to a zonal wind acceleration δū/δt that is too strong, especially near the surface. The effect is significant for planetary-scale forcing even when applied at tropopause level. A comparison is made between the mean-flow evolution in a baroclinic life-cycle, as simulated in a fully nonlinear, primitive-equation model, and that predicted by using the simulated eddy fluxes in the zonally-symmetric response problem. Use of the correct lower boundary condition is shown to lead to improved agreement.

Ocean heat transport and water vapor greenhouse in a warm equable climate: a new look at the low gradient paradox

The authors study the role of ocean heat transport (OHT) in the maintenance of a warm, equable, ice-free climate. An ensemble of idealized aquaplanet GCM calculations is used to assess the equilibrium sensitivity of global mean surface temperature and its equator-to-pole gradient (ΔT) to variations in OHT, prescribed through a simple analytical formula representing export out of the tropics and poleward convergence. Low-latitude OHT warms the mid- to high latitudes without cooling the tropics; increases by 1°C and ΔT decreases by 2.6°C for every 0.5-PW increase in OHT across 30° latitude. This warming is relatively insensitive to the detailed meridional structure of OHT. It occurs in spite of near-perfect atmospheric compensation of large imposed variations in OHT: the total poleward heat transport is nearly fixed. The warming results from a convective adjustment of the extratropical troposphere. Increased OHT drives a shift from large-scale to convective precipitation in the midlatitude storm tracks. Warming arises primarily from enhanced greenhouse trapping associated with convective moistening of the upper troposphere. Warming extends to the poles by atmospheric processes even in the absence of high-latitude OHT. A new conceptual model for equable climates is proposed, in which OHT plays a key role by driving enhanced deep convection in the midlatitude storm tracks. In this view, the climatic impact of OHT depends on its effects on the greenhouse properties of the atmosphere, rather than its ability to increase the total poleward energy transport.

On the generalized eigenvalue problem for the Rossby wave vertical velocity in the presence of mean flow and topography

In a series of papers, Killworth and Blundell have proposed to study the effects of a background mean flow and topography on Rossby wave propagation by means of a generalized eigenvalue problem formulated in terms of the vertical velocity, obtained from a linearization of the primitive equations of motion. However, it has been known for a number of years that this eigenvalue problem contains an error, which Killworth was prevented from correcting himself by his unfortunate passing and whose correction is therefore taken up in this note. Here, the author shows in the context of quasigeostrophic (QG) theory that the error can ulti- mately be traced to the fact that the eigenvalue problem for the vertical velocity is fundamentally a non- linear one (the eigenvalue appears both in the numerator and denominator), unlike that for the pressure. The reason that this nonlinear term is lacking in the Killworth and Blundell theory comes from neglecting the depth dependence of a depth-dependent term. This nonlinear term is shown on idealized examples to alter significantly the Rossby wave dispersion relation in the high-wavenumber regime but is otherwise irrelevant in the long-wave limit, in which case the eigenvalue problems for the vertical velocity and pressure are both linear. In the general dispersive case, however, one should first solve the generalized eigenvalue problem for the pressure vertical structure and, if needed, diagnose the vertical velocity vertical structure from the latter.

The Gly482Ser genotype at the PPARGC1A gene and elevated blood pressure: a meta-analysis involving 13,949 individuals.

The protein encoded by the PPARGC1A gene is expressed at high levels in metabolically active tissues and is involved in the control of oxidative stress via reactive oxygen species detoxification. Several recent reports suggest that the PPARGC1A Gly482Ser (rs8192678) missense polymorphism may relate inversely with blood pressure. We used conventional meta-analysis methods to assess the association between Gly482Ser and systolic (SBP) or diastolic blood pressures (DBP) or hypertension in 13,949 individuals from 17 studies, of which 6,042 were previously unpublished observations. The studies comprised cohorts of white European, Asian, and American Indian adults, and adolescents from South America. Stratified analyses were conducted to control for population stratification. Pooled genotype frequencies were 0.47 (Gly482Gly), 0.42 (Gly482Ser), and 0.11 (Ser482Ser). We found no evidence of association between Gly482Ser and SBP [Gly482Gly: mean = 131.0 mmHg, 95% confidence interval (CI) = 130.5-131.5 mmHg; Gly482Ser mean = 133.1 mmHg, 95% CI = 132.6-133.6 mmHg; Ser482Ser: mean = 133.5 mmHg, 95% CI = 132.5-134.5 mmHg; P = 0.409] or DBP (Gly482Gly: mean = 80.3 mmHg, 95% CI = 80.0-80.6 mmHg; Gly482Ser mean = 81.5 mmHg, 95% CI = 81.2-81.8 mmHg; Ser482Ser: mean = 82.1 mmHg, 95% CI = 81.5-82.7 mmHg; P = 0.651). Contrary to previous reports, we did not observe significant effect modification by sex (SBP, P = 0.966; DBP, P = 0.715). We were also unable to confirm the previously reported association between the Ser482 allele and hypertension [odds ratio: 0.97, 95% CI = 0.87-1.08, P = 0.585]. These results were materially unchanged when analyses were focused on whites only. However, statistical evidence of gene-age interaction was apparent for DBP [Gly482Gly: 73.5 (72.8, 74.2), Gly482Ser: 77.0 (76.2, 77.8), Ser482Ser: 79.1 (77.4, 80.9), P = 4.20 x 10(-12)] and SBP [Gly482Gly: 121.4 (120.4, 122.5), Gly482Ser: 125.9 (124.6, 127.1), Ser482Ser: 129.2 (126.5, 131.9), P = 7.20 x 10(-12)] in individuals <50 yr (n = 2,511); these genetic effects were absent in those older than 50 yr (n = 5,088) (SBP, P = 0.41; DBP, P = 0.51). Our findings suggest that the PPARGC1A Ser482 allele may be associated with higher blood pressure, but this is only apparent in younger adults.

Up-gradient eddy fluxes of potential vorticity near the subtropical jet

The role of eddy fluxes in the general circulation is often approached by treating eddies as (macro)turbulence. In this approach, the eddies act to diffuse certain quasiconservative quantities, such as potential vorticity (PV), along isentropic surfaces in the free atmosphere. The eddy fluxes are determined primarily by the eddy diffusivities and are necessarily down-gradient of the basic state PV field. Support for the (macro)turbulence approach stems from the fact that the eddy fluxes of PV in the free atmosphere are generally down-gradient in the long-term mean. Here we call attention to a pronounced and significant region of upgradient eddy PV fluxes on the poleward flank of the jet core in both hemispheres. The region of up-gradient (i.e., notionally “antidiffusive”) eddy PV fluxes is most pronounced during the winter and spring seasons and partially contradicts the turbulence approach described above. Analyses of the PV variance (potential enstrophy) budget suggest that the up-gradient PV fluxes represent local wave decay and are maintained by poleward fluxes of PV variance. Finite-amplitude effects thus represent leading order contributions to the PV variance budget, whereas dissipation is only of secondary importance locally. The appearance of up-gradient PV fluxes in the long-term mean is associated with the poleward shift of the jet—and thus the region of wave decay relative to wave growth—following wave-breaking events.

Formulation and implementation of a residual-mean ocean circulation model

A parameterization of mesoscale eddies in coarse-resolution ocean general circulation models (GCM) is formulated and implemented using a residual-mean formalism. In that framework, mean buoyancy is advected by the residual velocity (the sum of the Eulerian and eddy-induced velocities) and modified by a residual flux which accounts for the diabatic effects of mesoscale eddies. The residual velocity is obtained by stepping forward a residual-mean momentum equation in which eddy stresses appear as forcing terms. Study of the spatial distribution of eddy stresses, derived by using them as control parameters to ‘‘fit’’ the residual-mean model to observations, supports the idea that eddy stresses can be likened to a vertical down-gradient flux of momentum with a coefficient which is constant in the vertical. The residual eddy flux is set to zero in the ocean interior, where mesoscale eddies are assumed to be quasi-adiabatic, but is parameterized by a horizontal down-gradient diffusivity near the surface where eddies develop a diabatic component as they stir properties horizontally across steep isopycnals. The residual-mean model is implemented and tested in the MIT general circulation model. It is shown that the resulting model (1) has a climatology that is superior to that obtained using the Gent and McWilliams parameterization scheme with a spatially uniform diffusivity and (2) allows one to significantly reduce the (spurious) horizontal viscosity used in coarse resolution GCMs.

The ionospheric signatures of flux transfer events and solar wind dynamic pressure changes

The generation of flow and current vortices in the dayside auroral ionosphere has been predicted for two processes ocurring at the dayside magnetopause. The first of these mechanisms is time-dependent magnetic reconnection, in “flux transfer events” (FTEs); the second is the action of solar wind dynamic pressure changes. The ionospheric flow signature of an FTE should be a twin vortex, with the mean flow velocity in the central region of the pattern equal to the velocity of the pattern as a whole. On the other hand, a pulse of enhanced or reduced dynamic pressure is also expected to produce a twin vortex, but with the central plasma flow being generally different in speed from, and almost orthogonal to, the motion of the whole pattern. In this paper, we make use of this distinction to discuss recent observations of vortical flow patterns in the dayside auroral ionosphere in terms of one or other of the proposed mechanisms. We conclude that some of the observations reported are consistent only with the predicted signature of FTEs. We then evaluate the dimensions of the open flux tubes required to explain some recent simultaneous radar and auroral observations and infer that they are typically 300 km in north–south extent but up to 2000 km in longitudinal extent (i.e., roughly 5 hours of MLT). Hence these observations suggest that recent theories of FTEs which invoke time-varying reconnection at an elongated neutral line may be correct. We also present some simultaneous observations of the interplanetary magnetic field (IMF) and solar wind dynamic pressure (observed using the IMP8 satellite) and the ionospheric flow (observed using the EISCAT radar) which are also only consistent with the FTE model. We estimate that for continuously southward IMF ( ≈ 5 nT) these FTEs contribute about 30 kV to the mean total transpolar voltage (∼30%).

Transition from suppressed to active convection modulated by a weak-temperature gradient derived large-scale circulation

Numerical simulations are performed to assess the influence of the large-scale circulation on the transition from suppressed to active convection. As a model tool, we used a coupled-column model. It consists of two cloud-resolving models which are fully coupled via a large-scale circulation which is derived from the requirement that the instantaneous domain-mean potential temperature profiles of the two columns remain close to each other. This is known as the weak-temperature gradient approach. The simulations of the transition are initialized from coupled-column simulations over non-uniform surface forcing and the transition is forced within the dry column by changing the local and/or remote surface forcings to uniform surface forcing across the columns. As the strength of the circulation is reduced to zero, moisture is recharged into the dry column and a transition to active convection occurs once the column is sufficiently moistened to sustain deep convection. Direct effects of changing surface forcing occur over the first few days only. Afterward, it is the evolution of the large-scale circulation which systematically modulates the transition. Its contributions are approximately equally divided between the heating and moistening effects. A transition time is defined to summarize the evolution from suppressed to active convection. It is the time when the rain rate within the dry column is halfway to the mean value obtained at equilibrium over uniform surface forcing. The transition time is around twice as long for a transition that is forced remotely compared to a transition that is forced locally. Simulations in which both local and remote surface forcings are changed produce intermediate transition times.