Convective Ventilation Research Articles

Boundary Layer Modelling of Flow Acceleration and Energy Transfer Effects in Smart Pavement Design

The integration of remote technology into the construction industry has advanced the emergence of smart, self-learning infrastructure across all levels of land transportation design and development. However, energy harvesting capabilities for smart road ventilation purposes have not yet been fully researched as the world gravitates towards energy sustainability. This study thus presents a mathematical investigation of the self-draining design potentials of road pavements, leveraging on energy absorption and conversion to accelerate conductive and convective ventilation of these pavements during wet conditions, as a means of ensuring the skid resistance and safety of such pavements are not compromised. Applying numerical methods with the aid of commercial software code MATLAB®, the classical physics of fluid-surface interaction was used to model accelerated drainage of microflood off paved surfaces through methodical modification of the thickness of the boundary layer associated with the flow regime over the flat road surface. Results indicate significant influences of energy exchange, thermal, and viscous diffusivity on flow acceleration. Alterations in parameters such as the slip factor, thermally induced Brownian motion or phoretic characteristics of the fluid particles at the boundary induce accelerated flow at the surface of the pavement. The findings contribute to the advancement of smart infrastructure by offering practical insights into the potential benefits of integrating energy-harvesting technologies into road pavement systems. By optimizing flow acceleration mechanisms, smart pavements can play a crucial role in improving road safety and sustainability in urban environments.

The Impact of Internal Courtyard Configuration on Thermal Performance of Long Strip Houses

A courtyard is an essential space for natural lighting and natural convective ventilation of residential buildings in hot-humid climates. This study focuses on the internal courtyard configuration on the thermal performance of long strip houses (LSH) in the hot-climate area of Hainan Island, China. The aim is to identify the best design parameters for the courtyard to improve thermal comfort in modern LSH design. Appropriate strategies, including Mahoney table, field investigation, and CFD simulation, are used to determine thermal performance. As a result, the design guidelines of the courtyard are proposed to optimize the thermal comfort towards energy saving. The study reveals the spatial characteristics and climate regulation of internal courtyards in traditional LSH. In addition, the simulation results show that the enclosure with a shaded cover and a high ratio of H/D is conducive to thermal environment and ventilation, and the section of contracted shape from bottom to top is a preferred option in the internal courtyard configuration. This study should, therefore, be of value in designing practical projects with an interior courtyard for architects.

Experimental study of urban microclimate on scaled street canyons with various aspect ratios

Urban geometry influences urban microclimate by changing both radiation and ventilation processes. Full-scale experiments provide significant information on urban microclimate but usually experience difficulty from complicated urban morphologies. It is challenging to quantify the effect of urban geometry on radiative exchange and convective ventilation under real-world atmospheric conditions. Therefore, this study conducted a scaled outdoor measurement to investigate the surface temperatures, wind velocities, and radiative fluxes in street canyons with various aspect ratios. The velocity ratio of 0.25H to 2H (V0.25H/V2H) was adopted to assess convective ventilation. The urban canyon albedo (UCA) and net all-wave radiation (Q∗) were used to quantify the radiative exchange. An increase in aspect ratio resulted in reduced convective ventilation and increased trapping radiation. The V0.25H/V2H of H/W = 2and 3were 25% and 55% smaller than that of H/W = 1, respectively. The mean midday (11:00–13:00) UCA of H/W = 1, 2, 3, and 6 was 0.11, 0.06, 0.05, and 0.03, respectively. Compared with H/W = 1, the H/W = 2, 3, and 6 increased daily total Q∗ by 11.41%, 14.41%, and 19.40%, respectively. The surface temperature was negatively correlated with aspect ratio during the daytime but positively at night. Such high-quality experimental data are useful for validating and improving the unsteady numerical simulation.

SHAKEN, NOT STIRRED: HIGH FREQUENCY PERCUSSIVE VENTILATION AS A SALVAGE THERAPY IN SEVERE ARDS DUE TO COVID-19

TOPIC: Critical Care TYPE: Original Investigations PURPOSE: The Covid-19 pandemic has necessitated alternative strategies to treat severe Acute Respiratory Distress Syndrome (ARDS) and refractory hypoxemia. High frequency percussive ventilation (HFPV) is delivered via a hybrid ventilatory mode merging low-frequency, time cycled and pressure-limited normal volume convective ventilation with high-frequency low-volume pulsatile ventilation. This hybrid mode of ventilation creates a countercurrent flow of air which mobilizes secretions and improves gas exchange. HFPV theoretically achieves alveolar recruitment at lower peak airway pressures compared to conventional ventilation (CV), thus reducing barotrauma and ventilator-induced lung injury. Benefit from HFPV has mainly been shown in burn patients, but it has also been used in ARDS as a rescue therapy. Here, we describe our experience with HFPV in our patients with COVID-19-related ARDS in a Northern California county hospital. METHODS: From January 2020 through March 2021, 18 patients with Covid-19-related ARDS were placed on HFPV at a public tertiary care center. Data regarding demographics, complications during HFPV, ventilation settings, P/F ratios prior to and on HFPV, and hospital outcomes was collected for these patients. RESULTS: 12 men and 6 women ranging from 31-73 years of age (mean age 57 years) with Covid-19-related ARDS utilized HFPV. All patients during their ventilatory course received inhaled nitric oxide. 78% of the patients (n=14) had P/F ratios < 100 prior to being transitioned from CV. Approximately 33% of these patients (n=6) were found to have pneumothorax or pneumo-mediastinum while on HFPV. The mean age of survivors was 51 years old, whereas the mean age of non-survivors was 62 years old. Mean duration on HFPV ventilator among survivors was 15.9 days, versus 11.5 days in non-survivors. Survival rate was 44% in our cohort (n=8), and 7 of these 8 surviving patients underwent tracheostomy. Mean length of total mechanical ventilation (CV plus HFPV) until tracheostomy or extubation in all survivors was 32.3 days. CONCLUSIONS: Our small cohort showed a survival rate of 44% when placing patients with COVID-19-related ARDS on HFPV. Despite the limitations of our study, including small sample size, lack of randomization, and the presence confounding factors effecting outcomes, our study reflects a potential role for HFPV as a therapy for refractory hypoxemia in COVID-19-related ARDS. Future studies are needed to investigate a possible role of HFPV in this population. CLINICAL IMPLICATIONS: Clinical implications of this experience and potential future studies may lead to usage of HFPV as a rescue mode of ventilation for COVID-19-related ARDS. DISCLOSURES: No relevant relationships by Umang Barvalia, source=Web Response No relevant relationships by Weichia Chen, source=Web Response No relevant relationships by Heng Duong, source=Web Response No relevant relationships by Amit Gohil, source=Web Response No relevant relationships by Eric Hsiao, source=Web Response No relevant relationships by Craig Ivie, source=Web Response No relevant relationships by Neharika Khurana, source=Web Response No relevant relationships by Vibha Mohindra, source=Web Response No relevant relationships by Halley Tsai, source=Web Response No relevant relationships by John Wehner, source=Web Response

Ventilation heterogeneity imaged by multibreath wash-ins of hyperpolarized 3 He and 129 Xe in healthy rabbits.

Multibreath imaging to estimate regional gas mixing efficiency is superior to intensity-based single-breath ventilation markers, as it is capable of revealing minute but essential measures of ventilation heterogeneity which may be sensitive to subclinical alterations in the early stages of both obstructive and restrictive respiratory disorders. Large-scale convective stratification of ventilation in central-to-peripheral directions is the dominant feature of observed ventilation heterogeneity when imaging a heavy/less diffusive xenon gas mixture; smaller-scale patchiness, probably originating from asymmetric lung function at bronchial airway branching due to the interaction of convective and diffusive flows, is the dominant feature when imaging a lighter/more diffusive helium gas mixture. Since detecting low regional ventilation is crucial for characterizing diseased lungs, our results suggest that dilution with natural abundance helium and imaging at higher lung volumes seem advisable when imaging with hyperpolarized 129 Xe; this will allow the imaging gas to reach slow-filling and/or non-dependent lung regions, which might otherwise be impossible to distinguish from total ventilation shunt regions. The ability to differentiate these regions from those of total shunt is worse with typical single-breath imaging techniques. The mixing of freshly inhaled gas with gas already present in the lung can be directly assessed with heretofore unachievable precision via magnetic resonance imaging of signal build-up resulting from multiple wash-ins of a hyperpolarized (HP) gas. Here, we used normoxic HP 3 He and 129 Xe mixtures to study regional ventilation at different spatial scales in five healthy mechanically ventilated supine rabbits at two different inspired volumes. To decouple the respective effects of density and diffusion rates on ventilation heterogeneity, two additional studies were performed: one in which 3 He was diluted with an equal fraction of natural abundance xenon, and one in which 129 Xe was diluted with an equal fraction of 4 He. We observed systematic differences in the spatial scale of specific ventilation heterogeneity between HP 3 He and 129 Xe. We found that large-scale, central-to-peripheral convective ventilation inhomogeneity is the dominant cause of observed heterogeneity when breathing a normoxic xenon gas mixture. In contrast, small-scale ventilation heterogeneity in the form of patchiness, probably originating from asymmetric lung function at bronchial airway branching due to interactions between convective and diffusive flows, is the dominant feature when breathing a normoxic helium gas mixture, for which the critical zone occurs more proximally and at an imageable spatial scale. We also showed that the existence of particular underventilated non-dependent lung regions when breathing a heavy gas mixture is the result of the density of that mixture - rather than, for example, its diffusion rate or viscosity. Finally, we showed that gravity-dependent ventilation heterogeneity becomes substantially more uniform at higher inspired volumes for xenon gas mixtures compared to helium mixtures.

Cave radon exposure, dose, dynamics and mitigation

Many caves around the world have very high concentrations of naturally occurring 222Rn that may vary dramatically with seasonal and diurnal patterns. For most caves with a variable seasonal or diurnal pattern, 222Rn concentration is driven by bi-directional convective ventilation, which responds to external temperature contrast with cave temperature. Cavers and cave workers exposed to high 222Rn have an increased risk of contracting lung cancer. The International Commission on Radiological Protection (ICRP) has re-evaluated its estimates of lung cancer risk from inhalation of radon progeny (ICRP 115) and for cave workers the risk may now (ICRP 137) be 4–6 times higher than previously recognized. Cave Guides working underground in caves with annual average 222Rn activity &gt; 1,000 Bq/m3 and default ICRP assumptions (2,000 workplace hours per year, equilibrium factor F = 0.4, dose conversion factor DCF = 14 µSv/(kBq h m-3) could now receive a dose of &gt; 20 mSv/y. Using multiple gas tracers (d13 C--CO2, Rn and N2O), linked weather, source gas flux chambers, and convective air flow measurements a previous study unequivocally identified the external soil above Chifley Cave as the source of cave 222Rn. If the source of 222Rn is external to the cave, a strategy to lower cave 222Rn by passively decreasing summer pattern convective ventilation, which draws 222Rn into caves, is possible without harming the cave environment. A small net annual average temperature difference (warmer cave air) due to geothermal heat flux produces a large net annual volumetric air flow bias (2–5:1) favoring a winter ventilation pattern that flushes Rn from caves with ambient air. Rapid anthropogenic climate change over decades may heat the average annual external temperature relative to the cave temperature that is stabilized by the thermal inertia of the large rock mass. Relative external temperature increases due to climate change (Jenolan Caves, 2008–2018, 0.17°C) reduces the winter pattern air flow bias and increases Rn concentration in caves.

A new intermittent regime of convective ventilation threatens the Black Sea oxygenation status

Abstract. The Black Sea is entirely anoxic, except for a thin (∼ 100 m) ventilated surface layer. Since 1955, the oxygen content of this upper layer has decreased by 44 %. The reasons hypothesized for this decrease are, first, a period of eutrophication from the mid-1970s to the early 1990s and, second, a reduction in the ventilation processes, suspected for recent years (post-2005). Here, we show that the Black Sea convective ventilation regime has been drastically altered by atmospheric warming during the last decade. Since 2009, the prevailing regime has been below the range of variability recorded since 1955 and has been characterized by consecutive years during which the usual partial renewal of intermediate water has not occurred. Oxygen records from the last decade are used to detail the relationship between cold-water formation events and oxygenation at different density levels, to highlight the role of convective ventilation in the oxygen budget of the intermediate layers and to emphasize the impact that a persistence in the reduced ventilation regime would bear on the oxygenation structure of the Black Sea and on its biogeochemical balance.

Stability of Convective Ventilation after Fan Switching-Off in Mines

The stability of convective air motion in mine shafts after disactivating the draft source is investigated. Based on numerical simulation, it is found that the mine ventilation with natural draft is violated by the formation of air vortices extended along the shaft depth. The transverse profiles of motion velocity and air temperature are determined in approximation of a plane-parallel laminar flow of an incompressible medium with a vertical temperature gradient in the gravity field. Analytical calculations of the stability of the found flow to plane long-wave perturbations are carried out, as a result of which the value of critical Rayleigh parameter is obtained. A correction to the coefficient of air volume expansion allowing taking the hydrostatic compressibility of air into account is simulated. The dependence of the critical value of air temperature vertical gradient in the shaft, the excess of which leads to the formation of convective vortices and violation of through ventilation, is calculated.

Concurrent Flame Spread Over Two-Sided Thick PMMA Slabs in Microgravity

Spacecraft fire safety is an important consideration when designing future exploration missions. Concurrent flow flame spread experiments were carried out aboard the Cygnus spacecraft while in orbit to address current knowledge gaps related to solid fuel combustion in microgravity. The experiments used PMMA (polymethylmethacrylate) samples that were 50 mm wide and 290 mm long with two variations—one sample was a 10 mm thick flat slab, while the other was a 10 mm thick flat sample that had a 4 mm thick grooved center section. The thickness variation had a major impact on the flame shape, and the grooved sample developed a deep inverted-V shaped notch as the thin center section burned through. This notch enhanced heat transfer from the flame to the solid through an effectively wider flame base, which is the part of the flame with the highest temperature. Unlike in normal gravity (and also likely in partial gravity), where buoyant flow promotes acceleratory upward flame growth, the microgravity flames reached a steady size (limiting length) for a fixed forced convective flow in agreement with theory (i.e. there is a zero net heat flux at the flame tip). The limiting length implies that the spread rate of the flame will be controlled by the regression rate (burnout rate) of the material because the flames remains anchored to the upstream end of the fuel samples. This is a significant finding for spacecraft fire safety, and makes the probability of flashover in a spacecraft unlikely as the flame size will be small for low convective ventilation flow environments typical in spacecraft. On the other hand, long-burning flames in small vehicles will generate significant quantities of fuel vapor that may reach the lean flammability limit and cause a backdraft. The rapid extinction of the flame when the flow was turned off also supports the existing fire mitigation strategy on the ISS to deactivate the ventilation system in the event of fire alarm. These findings can be applied to improve the safety of future space exploration missions.

Stability of Convective Ventilation of the Mine after Turning off the Fan

Stability of Convective Ventilation of the Mine after Turning off the Fan

High frequency percussive ventilation increases alveolar recruitment in early acute respiratory distress syndrome: an experimental, physiological and CT scan study

BackgroundHigh frequency percussive ventilation (HFPV) combines diffusive (high frequency mini-bursts) and convective ventilation patterns. Benefits include enhanced oxygenation and hemodynamics, and alveolar recruitment, while providing hypothetic lung-protective ventilation. No study has investigated HFPV-induced changes in lung aeration in patients with early acute respiratory distress syndrome (ARDS).MethodsEight patients with early non-focal ARDS were enrolled and five swine with early non-focal ARDS were studied in prospective computed tomography (CT) scan and animal studies, in a university-hospital tertiary ICU and an animal laboratory. Patients were optimized under conventional “open-lung” ventilation. Lung CT was performed using an end-expiratory hold (Conv) to assess lung morphology. HFPV was applied for 1 hour to all patients before new CT scans were performed with end-expiratory (HFPV EE) and end-inspiratory (HFPV EI) holds. Lung volumes were determined after software analysis. At specified time points, blood gases and hemodynamic data were collected. Recruitment was defined as a change in non-aerated lung volumes between Conv, HFPV EE and HFPV EI. The main objective was to verify whether HFPV increases alveolar recruitment without lung hyperinflation. Correlation between pleural, upper airways and HFPV-derived pressures was assessed in an ARDS swine-based model.ResultsOne-hour HFPV significantly improved oxygenation and hemodynamics. Lung recruitment significantly rose by 12.0% (8.5–18.0%), P = 0.05 (Conv-HFPV EE) and 12.5% (9.3–16.8%), P = 0.003 (Conv-HFPV EI). Hyperinflation tended to increase by 2.0% (0.5–2.5%), P = 0.89 (Conv-HFPV EE) and 3.0% (2.5–4.0%), P = 0.27 (Conv-HFPV EI). HFPV hyperinflation correlated with hyperinflated and normally-aerated lung volumes at baseline: r = 0.79, P = 0.05 and r = 0.79, P = 0.05, respectively (Conv-HFPV EE); and only hyperinflated lung volumes at baseline: r = 0.88, P = 0.01 (Conv-HFPV EI). HFPV CT-determined tidal volumes reached 5.7 (1.1–8.1) mL.kg-1 of ideal body weight (IBW). Correlations between pleural and HFPV-monitored pressures were acceptable and end-inspiratory pleural pressures remained below 25cmH20.ConclusionsHFPV improves alveolar recruitment, gas exchanges and hemodynamics of patients with early non-focal ARDS without relevant hyperinflation. HFPV-derived pressures correlate with corresponding pleural or upper airways pressures.Trial registrationClinicalTrials.gov, NCT02510105. Registered on 1 June 2015. The trial was retrospectively registered.

Similar burrow architecture of three arid-zone scorpion species implies similar ecological function.

Many animals reside in burrows that may serve as refuges from predators and adverse environmental conditions. Burrow design varies widely among and within taxa, and these structures are adaptive, fulfilling physiological (and other) functions. We examined the burrow architecture of three scorpion species of the family Scorpionidae: Scorpio palmatus from the Negev desert, Israel; Opistophthalmus setifrons, from the Central Highlands, Namibia; and Opistophthalmus wahlbergii from the Kalahari desert, Namibia. We hypothesized that burrow structure maintains temperature and soil moisture conditions optimal for the behavior and physiology of the scorpion. Casts of burrows, poured in situ with molten aluminum, were scanned in 3D to quantify burrow structure. Three architectural features were common to the burrows of all species: (1) a horizontal platform near the ground surface, long enough to accommodate the scorpion, located just below the entrance, 2-5cm under the surface, which may provide a safe place where the scorpion can monitor the presence of potential prey, predators, and mates and where the scorpion warms up before foraging; (2) at least two bends that might deter incursion by predators and may reduce convective ventilation, thereby maintaining relatively high humidity and low temperature; and (3) an enlarged terminal chamber to a depth at which temperatures are almost constant (±2-4°C). These common features among the burrows of three different species suggest that they are important for regulating the physical environment of their inhabitants and that burrows are part of scorpions' "extended physiology" (sensu Turner, Physiol Biochem Zool 74:798-822, 2000).

Influence of the ventilation of a karst show cave on the surrounding vadose CO2 reservoir (Nerja, South Spain)

This study continues previous work done in a karst area—the Nerja Cave research site to characterize the vadose CO2 reservoir. The Nerja Cave is an important show cave, receiving nearly 500,000 visitors per year. The results of a new monitoring point in the vadose zone are presented: the Pintada Cave man-made shaft. An approximate, semi-quantitative balance of CO2 inside the Nerja Cave has also been carried out. Finally, data from the network of vadose research boreholes near the cavity have been analyzed. This study suggests that vadose CO2 is exhaled through the cave into the outside atmosphere during the “winter” period (from October to June), when a relatively strong convective ventilation regime affects the cavity. The net gas flux into the Nerja Cave during this period averages 24 mmol m−2 day−1. In summer, the cavity ventilation is practically inhibited. The CO2 concentration measured in boreholes in the relatively less karstified vadose environment around the cavity confirms this, showing a significant increase in the average gas contents: from 15,000 ppmv in “winter” to 27,000 ppmv in summer. The preliminary data in the Pintada Cave shaft show the occurrence of short-term increases of CO2 levels from the vadose reservoir, although masked by the effect of the significant ventilation affecting this new monitoring point due to its nature: a large, open conduit seemingly connected with the Nerja Cave.

Stability of natural ventilation mode after main fan stoppage

Results of seasonal experimental investigations of natural draft in the potash mines after main fan stoppage are presented and analyzed. Underground mines with equal top elevations are considered. Three modes of natural ventilation depending on the season are determined: flow-through, local and convective ventilation modes. The mathematical model of unsteady heat exchange between mine air, shaft support and rock mass is proposed. This model allows prediction of natural draft intensity for flow-through ventilation mode. Also using system of linear convection equations we formulate natural ventilation stability criterion in case of convective natural ventilation mode for mine shafts after main fan stoppage. Formulated criterion based on Rayleigh number allows prediction of convective ventilation mode formation in shafts.

S45 Specific ventilation inequality and dead space components of lung clearance index in patients with asthma and cystic fibrosis

BackgroundLung clearance index (LCI) is a widely reported marker of gas mixing inefficiency within the airways that is derived using the multiple breath inert gas washout (MBW) technique. We developed...

Acinar and conductive ventilation heterogeneity in severe CF lung disease: Back to the model

Severe convective ventilation heterogeneity occurring in CF lung disease requires a modified method to determine acinar and conductive components of ventilation heterogeneity from normalized phase III slope (Sn) curves. Modified Sacin* and Scond* (as opposed to standard Sacin and Scond) are proposed and interpreted on the basis of 2 conceptual mechanisms: (a) flow asynchrony between two convection-dependent units with a different specific ventilation, but with an identical acinus inside each unit (generating an identical diffusion-convection-dependent portion of Sn); (b) different specific ventilation (without any flow asynchrony) between two convection-dependent units with the worst ventilated unit containing an abnormal acinus generating the greatest diffusion-convection-dependent portion of Sn. In CF patients with an abnormal lung clearance index (LCI), Scond* (but not Scond) and Sacin* were significant contributors to LCI (β(Scond*)=0.70; β(Sacin*)=0.49; P<0.001 for both). Mechanism (a) can entirely account for experimental Scond* values, while mechanism (b) implies that experimental Sacin* values are likely dominated by peripheral ventilation heterogeneity in the best ventilated portions of the lung.

Lung clearance index in adult cystic fibrosis patients: the role of convection-dependent lung units

We investigated the extent of convective ventilation heterogeneity contributing to the observed lung clearance index values in adult cystic fibrosis patients, as the result of two simulated scenarios, either 1) a fixed part of the lungs becoming increasingly less compliant, or 2) an increasingly greater part of the lung being less compliant. In 25 cystic fibrosis patients and 25 matched controls, we computed the lung clearance index and also quantified curvilinearity of the washout concentration curve, where curvilinearity is equal to 0 (linear in semilog plot) reflects homogeneous ventilation and curvilinearity equal to 1 corresponds to the presence of an infinitesimally slowly emptying lung unit. In the cystic fibrosis group (forced expiratory volume in 1 s 27-100% predicted), lung clearance index and curvilinearity average±sd values were 10.3±2.3 and 0.57±0.13, respectively, and were significantly different from control values (6.2±0.4 and 0.18±0.07; both p<0.001); lung clearance index and curvilinearity were also correlated (R = 0.67; p<0.001). The average curvilinearity value in the cystic fibrosis group was found to be compatible with a cumulative volume of underventilated lung of 40-50%, depending on the simulation scenario considered. The degree of washout curvilinearity observed here indicates that a major determinant of the abnormal lung clearance index values observed in adult cystic fibrosis patients is ventilation heterogeneity generated between convection-dependent lung units, while the remainder of lung clearance index abnormality with respect to normal controls potentially represents the small airways within these lung zones.

Decadal and multi-decadal variability of Labrador Sea Water in the north-western North Atlantic Ocean derived from tracer distributions: Heat budget, ventilation, and advection

Time series of profiles of potential temperature, salinity, dissolved oxygen, and planetary potential vorticity at intermediate depths in the Labrador Sea, the Irminger Sea, and the Iceland Basin have been constructed by combining the hydrographic sections crossing the sub-arctic gyre of the North Atlantic Ocean from the coast of Labrador to Europe, occupied nearly annually since 1990, and historic hydrographic data from the preceding years since 1950. The temperature data of the last 60 years mainly reflect a multi-decadal variability, with a characteristic time scale of about 50 years. With the use of a highly simplified heat budget model it was shown that this long-term temperature variability in the Labrador Sea mainly reflects the long-term variation of the net heat flux to the atmosphere. However, the analysis of the data on dissolved oxygen and planetary potential vorticity show that convective ventilation events, during which successive classes of Labrador Sea Water (LSW) are formed, occurring on decadal or shorter time scales. These convective ventilation events have performed the role of vertical mixing in the heat budget model, homogenising the properties of the intermediate layers (e.g. temperature) for significant periods of time. Both the long-term and the near-decadal temperature signals at a pressure of 1500 dbar are connected with successive deep LSW classes, emphasising the leading role of Labrador Sea convection in running the variability of the intermediate depth layers of the North Atlantic. These signals are advected to the neighbouring Irminger Sea and Iceland Basin. Advection time scales, estimated from the 60 year time series, are slightly shorter or of the same order as most earlier estimates, which were mainly based on the feature tracking of the spreading of the LSW 94 class formed in the period 1989–1994 in the Labrador Sea.

Moisture transport in midlatitude cyclones

AbstractWe discuss how synoptic‐scale variability controls the transport of atmospheric water vapour by midlatitude cyclones. Idealized simulations are used to investigate quantitatively which factors determine the magnitude of cyclone moisture transport. It is demonstrated that large‐scale ascent on the warm conveyor belt and shallow cumulus convection are equally important for ventilating moisture from the boundary layer into the free troposphere, and that ventilated moisture can be transported large distances eastwards and polewards by the cyclone, before being returned to the surface as precipitation.The initial relative humidity is shown to have little effect on the ability of the cyclone to transport moisture, whilst the absolute temperature and meridional temperature gradient provide much stronger controls. Scaling arguments are presented to quantify the dependence of moisture transport on large‐scale and boundary‐layer parameters. It is shown that ventilation by shallow convection and warm‐conveyor‐belt advection vary in the same way with changes to large‐scale parameters. However, shallow convective ventilation has a much stronger dependence on boundary‐layer parameters than warm‐conveyor‐belt ventilation. Copyright © 2011 Royal Meteorological Society

Reasons for the presence or absence of convective (pressurized) ventilation in the genus Equisetum

• The very high rates of convective ventilation reported recently in Equisetum telmateia (up to 120 cm(3) min(-1); internal wind speed, 10 cm s(-1)) prompted this study of a further eight species for the presence or absence of convection and the possible reasons for this. • Convection rates were examined in relation to anatomical pathways, internal resistance to applied pressurized gas flow and stomata. • Only species with interconnecting cortical aerenchyma in branches (when present), shoots and rhizomes induced convection. Rapid humidity-induced convection (HIC) occurred in E. palustre (up to 13 cm(3) min(-1)), with slower rates in E. × schaffneri and E. ramosissimum (≤ 6 and 3 cm(3) min(-1), respectively). Excised shoots of E. hyemale and E. fluviatile showed the potential for HIC (≤ 0.5 and 0.15 cm(3) min(-1), respectively), but not into the rhizomes. High rates were linked to low internal gas flow resistance. No convection was detected in E. scirpoides, E. sylvaticum or E. arvense due to the extremely high resistance to pressure flow, for example, from intercalary meristems and, in the last two, to nonaerenchymatous branches. • Of the nine Equisetum species studied so far, four showed through-flow convection; the other species must rely solely on diffusion for underground aeration in wet soils.