Evaluation of the dispersion coefficient for numerical simulations of tropospheric transport

Data of velocity spectra in wave number and frequency space available in literature are analysed to estimate climatological values of the dissipation rate of kinetic energy ε. In the frame of Kolmogorov (1941) theory, the relationship between diffusion coefficient and spectral window is used to determine the diffusion coefficient as a function of resolved scale. To exploit frequency spectrum data with a limited knowledge of flow conditions, a hypothesis on the relationship between the Eulerian time scale and the sampling temporal window was formulated, and the implied empirical constant was determined. Using the obtained values and some recent similarity relationships for the boundary-layer, a parameterisation of ε was adopted to propose an expression of the horizontal dispersion coefficient for different heights and different scales, which is suitable for use in numerical models with special reference to climate applications

IL-GLOBO (1.0) – integrated Lagrangian particle model and Eulerian general circulation model GLOBO: development of the vertical diffusion module

Abstract. The development and validation of the vertical diffusion module of IL-GLOBO, a Lagrangian transport model coupled online with the Eulerian general circulation model GLOBO, is described. The module simulates the effects of turbulence on particle motion by means of a Lagrangian stochastic model (LSM) consistently with the turbulent diffusion equation used in GLOBO. The implemented LSM integrates particle trajectories, using the native σ-hybrid coordinates of the Eulerian component, and fulfils the well-mixed condition (WMC) in the general case of a variable density profile. The module is validated through a series of 1-D offline numerical experiments by assessing its accuracy in maintaining an initially well-mixed distribution in the vertical. A dynamical time-step selection algorithm with constraints related to the shape of the diffusion coefficient profile is developed and discussed. Finally, the skills of a linear interpolation and a modified Akima spline interpolation method are compared, showing that both satisfy the WMC with significant differences in computational time. A preliminary run of the fully integrated 3-D model confirms the result only for the Akima interpolation scheme while the linear interpolation does not satisfy the WMC with a reasonable choice of the minimum integration time step

A re-evaluation of surface layer turbulence from Antarctic data

A data set of velocity and temperature variances measured in the surface layer over a glacier in Antarctica is analysed in terms of the Monin-Obukhov Similarity Theory. The presence of surface inhomogeneities, flow unsteadiness, and other uncontrolled disturbances affects the shape of the distribution of normalised variances for intervals of the stability parameter. The modal value of the distribution, instead of the mean, is used to estimate the numerical coefficients of the similarity functions to minimize the influence of the (positive) outliers on the estimates. The overall agreement of the present results with previuos investigations is good, and also the spread of the numerical values noted by different authors is confirmed. In particular the investigation points out the need to use a similarity function for the temperature variance which diverges in near neutral conditions, as the heat flux goes to zero, and the occurrence of a large stability region where the variances of velocity and temperature are characterised by a behaviour almost independent of the momentum flux

Thoracic surgery for malignancy and emergency irrespective of COVID-19

until March 24, 2020, a COVID-19 test by nasopharyngeal swab was offered to the patients presenting with symptoms of COVID-19. However, from April 2, 2020, we changed that policy, offering 2 COVID-19 tests by nasopharyngeal swab to everyone undergoing thoracic surgery for malignancies before admission to our general university hospital, even if asymptomatic

A high-volume thoracic surgery division into the storm of the COVID-19 pandemic

Since the coronavirus 2019 (COVID-19) crisis broke out in Italy at the end of February 2020, days before the World Health Organization declared the pandemic,1,2 two crucial issues urgently emerged and needed to be addressed by our institution. First was the containment of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) epidemic together with the restructuring of national public and private health care to face the spread of the new viral disease among the population. Second, central as well, was to maintain the offer of medical and surgical treatments to the patients who still presented with other severe diseases—of these in particular, oncologic patients

Investigations on convective boundary layer turbulence using SODAR data

Acoustic sounding (SODAR) data collected in convective conditions were analysed to estimate high order statistics of the vertical velocity in the lower half of the Convective Boundary Layer (CBL). Limitations of the instrumentation system were assessed and it turned out that spatial and temporal fi ltering have little effect on skewness and kurtosis, and do not prevent a reliable evaluation of these parameters, provided that a suffi ciently long time period is analysed. Vertical profi les of skewness are grouped into two broadly defi ned classes, one which increases almost linearly with height and the other which shows a constant-with-height behaviour. Both behaviours are shown to be consistent with different parameterisations used in literature. Kurtosis profi les are found to be fairly well described adopting a quadratic relationship between skewness and kurtosis, provided that the correct parameterisation of skewness is used

Bronchovascular reconstruction in the era of mini-invasiveness

bronchovascular reconstruction in the era of mininvasivenes

Longitudinal spectra of wind velocity in the atmospheric surface layer perturbed by a small topographic ridge

Turbulence measurements carried out in the near neutral surface layer are presented. The wind velocity components were measured with sonic anemometers at 2 and 10 m height. Three masts are considered, placed about 4 km upwind, on the top and about 6 km downwind of Inexpressible Island, a relief 300 m high and 1 km in cross-section. Spectral features are discussed in detail. Local equilibrium is found in the inertial subrange and in (at least in part of) the intermediate range, characterized by different slopes upwind and downwind (k−1 and k−5/3, respectively) for the components parallel to the terrain

Numerical vs. turbulent diffusion in geophysical flow modelling

Numerical advection schemes induce the spreading of passive tracers from localized sources. The effects of changing resolution and Courant number are investigated using theWAF advection scheme, which leads to a sub-diffusive process. The spreading rate from an instantaneous source is compared with the physical diffusion necessary to simulate unresolved turbulent motions. The time at which the physical diffusion process overpowers the numerical spreading is estimated, and is shown to reduce as the resolution increases, and to increase as the wind velocity increases