Zonally symmetric adjustment in the presence of artificial relaxation

Abstract Numerical experiments, presented in a companion paper, have been performed in which the zonal-mean state of the stratosphere in a comprehensive, stratosphere-resolving, general circulation model is strongly relaxed (or “nudged”) toward the evolution of a reference sudden warming event in order to investigate its influence on the freely evolving troposphere below. Similar approaches have been used in a number of other studies. This raises the question of whether such an artificial relaxation induces the adiabatic and diabatic adjustments expected below the region of nudging, even in the absence of the stratospheric wave driving responsible for the reference event. Motivated by this question, the zonally symmetric quasigeostrophic diabatic response to zonal forces (representing wave driving) in a system nudged to a time-dependent reference state is studied. In the presence of wave driving in the nudging region that differs from the reference state, the meridional mass circulation of the reference state is reproduced only in the region below the nudging up to a correction that is inversely proportional to the strength of the nudging. The anomalous circulation is confined because of an effective boundary condition at the interface of the nudging layer. The nudging also produces an artificial “sponge-layer feedback” immediately below the region of the nudging in response to differences in the tropospheric wave driving. The strength of this artificial feedback is closely related to the strength of the effective boundary condition; however, the time scale required for the sponge-layer feedback to be established is typically much longer than that required for the confinement.This is the final version. It first appeared at http://journals.ametsoc.org/doi/abs/10.1175/JAS-D-14-0013.1

A Lagrangian perspective of the tropopause and the ventilation of the lowermost stratosphere

Back trajectories driven by large-scale analyzed wind fields are used to investigate troposphere to stratosphere transport (TST) in the Northern Hemisphere tropopause region, as well as the surface sources for such transport, defined in terms of the locations where each trajectory last left the atmospheric boundary layer ( log pressure height z* < 1 km). The proportion chi(BL) of those trajectories arriving in the tropopause region that have visited the boundary layer within the previous fixed time period ( typically 30 days) is determined as a function of each trajectory's final equivalent latitude and potential temperature. For a range of potential temperature surfaces ( similar to 300-380 K), chi(BL) is shown to have a sharp gradient in the extratropics indicative of a partial permeable barrier to transport that can be identified as a "Lagrangian tropopause.'' Variations in chi(BL) with equivalent latitude and potential temperature and on seasonal timescales are shown to provide a novel measure for the relative location and permeability of the tropopause barrier. Details such as the presence of a "ventilated layer'' in the northern summer extratropical lower stratosphere ( similar to 370-410 K) are clearly apparent. Directly below this layer ( 340-370 K) the tropopause barrier to transport is shown to be relatively strong, whereas below 340 K it is again more permeable. A distinction can therefore be made between "extratropical'' TST that primarily ventilates the lowermost stratosphere below 340 K and "tropical'' TST that occurs into the 370-410 K ventilated layer. The boundary layer source regions for extratropical TST are shown to correspond to those regions previously identified as sources for deep frontal uplift in the warm conveyor belt circulations of extratropical cyclones, although elevated regions such as the Himalayan plateau are also seen to be important. Tropical TST has different source regions associated with regions of active deep convection such as the western tropical Pacific and, in the northern summer, the Indian subcontinent. The source regions are, in general, found to be geographically localized, leading to the conclusion that subject to the limitations of the methodology, trace gas emissions in specific regions are substantially more likely to be transported to the lowermost stratosphere than elsewhere. The implications for the assessment of ozone depletion by very short lived halogenated species are mentioned

Decision for reconstructive interventions of the upper limb in individuals with tetraplegia: the effect of treatment characteristics

Objective: To determine the effect of treatment characteristics on the\ud decision for reconstructive interventions for the upper extremities (UE) in\ud subjects with tetraplegia. - \ud Setting: Seven specialized spinal cord injury centres in the Netherlands. - \ud Method: Treatment characteristics for UE reconstructive interventions were\ud determined. Conjoint analysis (CA) was used to determine the contribution\ud and the relative importance of the treatment characteristics on the decision\ud for therapy. Therefore, a number of different treatment scenarios using these\ud characteristics were established. Different pairs of scenarios were presented\ud to subjects who were asked to choose the preferred scenario of each set. - \ud Results: forty nine subjects with tetraplegia with a stable C5, C6 or C7\ud lesion were selected. All treatment characteristics significantly influenced\ud the choice for treatment. Relative importance of treatment characteristics\ud were: intervention type (surgery or surgery with FES implant) 13%, number\ud of operations 15%, in patient rehabilitation period 22%, ambulant\ud rehabilitation period 9%, complication rate 15%, improvement of elbow\ud function 10%, improvement of hand function 15%. In deciding for therapy\ud 40% of the subjects focused on one characteristic. - \ud Conclusion: CA is applicable in Spinal Cord Injury medicine to study the\ud effect of health outcomes and non-health outcomes on the decision for\ud treatment. Non-health outcomes which relate to the intensity of treatment\ud are equally important or even more important than functional outcome in the\ud decision for reconstructive UE surgery in subjects with tetraplegia

Stratospheric control of planetary waves

The effects of imposing at various altitudes in the stratosphere zonally symmetric circulation anomalies associated with a stratospheric sudden warming are investigated in a mechanistic circulation model. A shift of the tropospheric jet is found even when the anomalies are imposed only above 2�hPa. Their influence is communicated downward through the planetary wave field via three distinct mechanisms. First, a significant fraction of the amplification of the upward fluxes of wave activity prior to the central date of the warming is due to the coupled evolution of the stratospheric zonal mean state and the wave field throughout the column. Second, a downward propagating region of localized wave, mean-flow interaction is active around the central date but does not penetrate the tropopause. Third, there is deep, vertically synchronous suppression of upward fluxes following the central date. The magnitude of this suppression correlates with that of the tropospheric jet shift.European Research Council ACCI grant project 267760

Spatio-temporal stability analysis applied to monsoon anticyclone flow

© 2020 The Authors. Quarterly Journal of the Royal Meteorological Society published by John Wiley & Sons Ltd on behalf of the Royal Meteorological Society. Flow on a beta-plane driven by a steady localised anticyclonic forcing of potential vorticity (or equivalently a mass source) is considered as a simple model of the Asian monsoon flow in the upper troposphere. Previous authors have noted that the response may be steady, or unsteady, according to the magnitude of the forcing, with the unsteadiness manifested as westward eddy shedding. A detailed study of the transition between steady and eddy-shedding regimes reveals a third regime ('break up'), for intermediate forcing magnitude, where the flow is steady in the neighbourhood of the forcing, but the westward extending plume of low potential vorticity breaks up into isolated anticyclonic vortices some distance away from the forcing region. A related spatio-temporal instability problem for flow on a beta plane is specified and analysed. The flow can be stable, convectively unstable or absolutely unstable. It is argued that these three stability regimes correspond to the steady, break-up and eddy-shedding regimes for the forced flow and good quantitative correspondence between the regimes is demonstrated by explicit solution of the spatio-temporal stability problem.We acknowledge support from the European Commission project StratoClim, 7th Framework Programme, project no. 603557, and the European Research Council, ACCI project no. 267760

The mechanisms leading to a stratospheric hydration by overshooting convection

AbstractOvershoots are convective air parcels that rise beyond their level of neutral buoyancy. A giga-large-eddy simulation (100-m cubic resolution) of “Hector the Convector,” a deep convective system that regularly forms in northern Australia, is analyzed to identify overshoots and quantify the effect of hydration of the stratosphere. In the simulation, 1507 individual overshoots were identified, and 46 of them were tracked over more than 10 min. Hydration of the stratosphere occurs through a sequence of mechanisms: overshoot penetration into the stratosphere, followed by entrainment of stratospheric air and then by efficient turbulent mixing between the air in the overshoot and the entrained warmer air, leaving the subsequent mixed air at about the maximum overshooting altitude. The time scale of these mechanisms is about 1 min. Two categories of overshoots are distinguished: those that significantly hydrate the stratosphere and those that have little direct hydration effect. The former reach higher altitudes and hence entrain and mix with air that has higher potential temperatures. The resulting mixed air has higher temperatures and higher saturation mixing ratios. Therefore, a greater amount of the hydrometeors carried by the original overshoot sublimates to form a persistent vapor-enriched layer. This makes the maximum overshooting altitude the key prognostic for the parameterization of deep convection to represent the correct overshoot transport. One common convection parameterization is tested, and the results suggest that the overshoot downward acceleration due to negative buoyancy is too large relative to that predicted by the numerical simulations and needs to be reduced.This research was supported by the StratoClim project funded by the European Union Seventh Framework Programme under Grant Agree- ment 603557 and the Idex Teasao project. Todd Lane is supported by the Australian Research Council’s Centres of Excellence scheme (CE170100023). Computer re- sources were allocated by GENCI through Projects 90569 and 100231 (Grand Challenge Turing)

Exploring the equity of GP practice prescribing rates for selected coronary heart disease drugs: a multiple regression analysis with proxies of healthcare need

Background There is a small, but growing body of literature highlighting inequities in GP practice prescribing rates for many drug therapies. The aim of this paper is to further explore the equity of prescribing for five major CHD drug groups and to explain the amount of variation in GP practice prescribing rates that can be explained by a range of healthcare needs indicators (HCNIs). Methods The study involved a cross-sectional secondary analysis in four primary care trusts (PCTs 1–4) in the North West of England, including 132 GP practices. Prescribing rates (average daily quantities per registered patient aged over 35 years) and HCNIs were developed for all GP practices. Analysis was undertaken using multiple linear regression. Results Between 22–25% of the variation in prescribing rates for statins, beta-blockers and bendrofluazide was explained in the multiple regression models. Slightly more variation was explained for ACE inhibitors (31.6%) and considerably more for aspirin (51.2%). Prescribing rates were positively associated with CHD hospital diagnoses and procedures for all drug groups other than ACE inhibitors. The proportion of patients aged 55–74 years was positively related to all prescribing rates other than aspirin, where they were positively related to the proportion of patients aged >75 years. However, prescribing rates for statins and ACE inhibitors were negatively associated with the proportion of patients aged >75 years in addition to the proportion of patients from minority ethnic groups. Prescribing rates for aspirin, bendrofluazide and all CHD drugs combined were negatively associated with deprivation. Conclusion Although around 25–50% of the variation in prescribing rates was explained by HCNIs, this varied markedly between PCTs and drug groups. Prescribing rates were generally characterised by both positive and negative associations with HCNIs, suggesting possible inequities in prescribing rates on the basis of ethnicity, deprivation and the proportion of patients aged over 75 years (for statins and ACE inhibitors, but not for aspirin)

Sensitivity of stratospheric water vapour to variability in tropical tropopause temperatures and large-scale transport

Abstract. Concentrations of water vapour entering the tropical lower stratosphere are primarily determined by conditions that air parcels encounter as they are transported through the tropical tropopause layer (TTL). Here we quantify the relative roles of variations in TTL temperatures and transport in determining seasonal and interannual variations of stratospheric water vapour. Following previous studies, we use trajectory calculations with the water vapour concentration set by the Lagrangian dry point (LDP) along trajectories. To assess the separate roles of transport and temperatures, the LDP calculations are modified by replacing either the winds or the temperatures with those from different years to investigate the wind or temperature sensitivity of water vapour to interannual variations and, correspondingly, with those from different months to investigate the wind or temperature sensitivity to seasonal variations. Both ERA-Interim reanalysis data for the 1999–2009 period and data generated by a chemistry–climate model (UM-UKCA) are investigated. Variations in temperatures, rather than transport, dominate interannual variability, typically explaining more than 70 % of variability, including individual events such as the 2000 stratospheric water vapour drop. Similarly seasonal variation of temperatures, rather than transport, is shown to be the dominant driver of the annual cycle in lower stratospheric water vapour concentrations in both the model and reanalysis, but it is also shown that seasonal variation of transport plays an important role in reducing the seasonal cycle maximum (reducing the annual range by about 30 %). The quantitative role in dehydration of sub-seasonal and sub-monthly Eulerian temperature variability is also examined by using time-filtered temperature fields in the trajectory calculations. Sub-monthly temperature variability reduces annual mean water vapour concentrations by 40 % in the reanalysis calculation and 30 % in the model calculation. As with other aspects of dehydration, simple Eulerian measures of variability are not sufficient to quantify the implications for dehydration, and the Lagrangian sampling of the variability must be taken into account. These results indicate that, whilst capturing seasonal and interannual variation of temperature is a major factor in modelling realistic stratospheric water vapour concentrations, simulation of seasonal variation of transport and of sub-seasonal and sub-monthly temperature variability are also important and cannot be ignored. </jats:p

QUBIC: The QU Bolometric Interferometer for Cosmology

One of the major challenges of modern cosmology is the detection of B-mode polarization anisotropies in the CMB. These originate from tensor fluctuations of the metric produced during the inflationary phase. Their detection would therefore constitute a major step towards understanding the primordial Universe. The expected level of these anisotropies is however so small that it requires a new generation of instruments with high sensitivity and extremely good control of systematic effects. We propose the QUBIC instrument based on the novel concept of bolometric interferometry, bringing together the sensitivity advantages of bolometric detectors with the systematics effects advantages of interferometry. Methods: The instrument will directly observe the sky through an array of entry horns whose signals will be combined together using an optical combiner. The whole set-up is located inside a cryostat. Polarization modulation will be achieved using a rotating half-wave plate and interference fringes will be imaged on two focal planes (separated by a polarizing grid) tiled with bolometers. We show that QUBIC can be considered as a synthetic imager, exactly similar to a usual imager but with a synthesized beam formed by the array of entry horns. Scanning the sky provides an additional modulation of the signal and improve the sky coverage shape. The usual techniques of map-making and power spectrum estimation can then be applied. We show that the sensitivity of such an instrument is comparable with that of an imager with the same number of horns. We anticipate a low level of beam-related systematics thanks to the fact that the synthesized beam is determined by the location of the primary horns. Other systematics should be under good control thanks to an autocalibration technique, specific to our concept, that will permit the accurate determination of most of the systematics parameters.Comment: 12 pages, 10 figures, submitted to Astronomy and Astrophysic

A SIMPLE-MODEL OF ROSSBY-WAVE HYDRAULIC BEHAVIOR

This paper considers hydraulic control and upstream influence in systems where the only wave propagation mechanism arises from the variation of vorticity or potential vorticity. These systems include two-dimensional shear flows as well as many simple paradigms for large-scale geophysical flows. The simplest is a flow in which the vorticity or potential vorticity is piecewise constant. We consider such a flow confined to a rotating channel and disturbed by a topographic perturbation. We analyse the behaviour of the system using steady nonlinear long-wave theory and demonstrate that it exhibits behaviour analogous to open-channel hydraulics, with the possibility of different upstream and downstream states. The manner by which the system achieves such states is examined using time-dependent long-wave theory via integration along characteristics and using full numerical solution via the contour-dynamics technique.The full integrations agree well with the hydraulic interpretation of the steady-state theory. One aspect of the behaviour of the system that is not seen in open-channel hydraulics is that for strong subcritical flows there is a critical topographic amplitude beyond which information from the control cannot propagate far upstream. Instead flow upstream of the topographic perturbation adjusts until the long-wave speed is zero, the control moves to the leading edge of the obstacle and flow downstream of the control is supercritical, with a transition from one supercritical branch to another on the downstream slope of the obstacle