The sporadic nature of meridional heat transport in the atmosphere

The present study analyses meridional atmospheric heat transport, due to transient eddies, in the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data. Probability density functions of the transport highlight the dominant role played by extreme events. In both hemispheres, events in the top 5 percentiles typically account for over half of the net poleward transport. As a result of this sensitivity to extremes, a large fraction of the heat transport by transient eddies, at a given location and season, is realised through randomly spaced bursts (a few per season), rather than through a continuum of events. Abstract Fast growing atmospheric modes are associated with a large heat transport, suggesting a link between these bursts and growing baroclinic systems (defined here as motions in the 2.5–6 day band). However, wavelet power spectra of the transport extremes suggest that they are driven by very precise phase and coherence relationships, between meridional velocity and moist static energy anomalies, acting over a broad range of frequencies (2-32 days). Motions with periods beyond 6 days play a key role in this framework. Moreover, these longer periods are found to be mainly driven by planetary-scale motions. Notwithstanding this, the heat transport bursts can be matched to specific synoptic-scale patterns. The bursts are therefore interpreted as the signatures of travelling synoptic systems superimposed on larger scale motions. The dominant role of extreme events can be reproduced in highly idealised simulations. Both a statistical model, where atmospheric motions are assumed to be linear superpositions of sinusoidal curves, and a two-layer model, representing heat transport as a quantised process effected by point vorticity anomalies, are successful in simulating the transport bursts. The fact that two very different idealised models both reproduce the transport's sporadic nature suggests that this must be an intrinsic property of waves in the atmosphere.Open Acces

Spherical convolution and other forms of informed machine learning for deep neural network based weather forecasts

Recently, there has been a surge of research on data-driven weather forecasting systems, especially applications based on convolutional neural networks (CNNs). These are usually trained on atmospheric data represented as regular latitude-longitude grids, neglecting the curvature of the Earth. We asses the benefit of replacing the convolution operations with a spherical convolution operation, which takes into account the geometry of the underlying data, including correct representations near the poles. Additionally, we assess the effect of including the information that the two hemispheres of the Earth have "flipped" properties - for example cyclones circulating in opposite directions - into the structure of the network. Both approaches are examples of informed machine learning. The methods are tested on the Weatherbench dataset, at a high resolution of ~ 1.4$^{\circ}$ which is higher than in previous studies on CNNs for weather forecasting. We find that including hemisphere-specific information improves forecast skill globally. Using spherical convolution leads to an additional improvement in forecast skill, especially close to the poles in the first days of the forecast. Combining the two methods gives the highest forecast skill, with roughly equal contributions from each. The spherical convolution is implemented flexibly and scales well to high resolution datasets, but is still significantly more expensive than a standard convolution operation. Finally, we analyze cases with high forecast error. These occur mainly in winter, and are relatively consistent across different training realizations of the networks, pointing to connections with intrinsic atmospheric predictability

A work for the future. The union's gaze on the topic of sustainable work, in the Padua area: a socio-anthropological approach

openIl prossimo futuro pone una serie di interrogativi a proposito del mondo del lavoro, riguardanti in particolar modo la sua sostenibilità. In un contesto in cui il lavoro è sempre più assimilato ad una merce, è necessario interrogarsi sulle possibili vie di cambiamento verso la sostenibilità del lavoro. In questo lavoro, si analizza il ruolo dei sindacati come possibili attori di cambiamento nel mondo del lavoro, analizzandone le prospettive secondo un approccio socio-antropologico

Impacts of dust reduction on the northward expansion of the African monsoon during the Green Sahara period

AbstractThe West African Monsoon (WAM) is crucial for the socio-economic stability of millions of people living in the Sahel. Severe droughts have ravaged the region in the last three decades of the 20th century, highlighting the need for a better understanding of the WAM dynamics. One of the most dramatic changes in the West African Monsoon (WAM) occurred between 15000–5000 yr BP, when increased summer rainfall led to the so-called “Green Sahara” and to a reduction in dust emissions from the region. However, model experiments are unable to fully reproduce the intensification and geographical expansion of the WAM during this period, even when vegetation over the Sahara is considered. Here, we use a fully coupled simulation for 6000 yr BP (Mid-Holocene) in which prescribed Saharan vegetation and dust concentrations are changed in turn. A closer agreement with proxy records is obtained only when both the Saharan vegetation changes and dust decrease are taken into account. The dust reduction strengthens the vegetation–albedo feedback, extending the monsoon's northern limit approximately 500 km further than the vegetation-change case only. We therefore conclude that accounting for changes in Saharan dust loadings is essential for improving model simulations of the WAM during the Mid-Holocene

The global atmospheric energy transport analysed by a wavelength-based scale separation

Source at https://www.weather-climate-dynamics.net/.The global atmospheric circulation is fundamental for the local weather and climate by redistributing energy and moisture. To the present day, there is a knowledge gap at which spatial scales the energy and its components are transported. Therefore, we separate the meridional atmospheric energy transport in the ERA5 reanalysis by the spatial scales, the quasi-stationary and transient flow patterns, and the latent and dry-static component. We focus on the annual and seasonal mean in the transport components as well as their inter-annual variability. Motivated by similarities across latitudes in the atmospheric transport spectra when displayed as function of wavelength, we refine the existing scale separation method to be based on wavelength instead of wavenumber. This reveals advantageous, as the following conclusions can be drawn, which are fairly similar in the two hemispheres. Transport by synoptic waves, defined at wavelengths between 2,000 and 8,000 km, is the largest contributor to extra-tropical energy and moisture transport, is mainly of transient character, and is little influenced by seasonality. In contrast, the transport by planetary waves, larger than 8,000 km, highly depends on the season and has two distinct characteristics. (1) In the extra-tropical winter, planetary waves are of major importance due to transport of dry-static energy. This planetary transport feature the largest inter-annual variability, and is mainly quasi-stationary in the Northern Hemisphere, but transient in its southern counterpart. (2) In the subtropical summer, quasi-stationary planetary waves are the most important transport component mainly due to advection of moisture, which is associated with monsoons. In contrast to transport by planetary and synoptic waves, only a negligible amount of energy is transported by mesoscale eddies (< 2,000 km)

Special Resins for Stereolithography: In Situ Generation of Silver Nanoparticles

The limited availability of materials with special properties represents one of the main limitations to a wider application of polymer-based additive manufacturing technologies. Filled resins are usually not suitable for vat photo-polymerization techniques such as stereolithography (SLA) or digital light processing (DLP) due to a strong increment of viscosity derived from the presence of rigid particles within the reactive suspension. In the present paper, the possibility to in situ generate silver nanoparticles (AgNPs) starting from a homogeneous liquid system containing a well dispersed silver salt, which is subsequently reduced to metallic silver during stereolithographic process, is reported. The simultaneous photo-induced cross-linking of the acrylic resin produces a filled thermoset resin with thermal-mechanical properties significantly enhanced with respect to the unfilled resin, even at very low AgNPs concentrations. With this approach, the use of silver salts having carbon-carbon double bonds, such as silver acrylate and silver methacrylate, allows the formation of a nanocomposite structure in which the release of by-products is minimized due to the active role of all the reactive components in the three dimensional (3D)-printing processes. The synergy, between this nano-technology and the geometrical freedom offered by SLA, could open up a wide spectrum of potential applications for such a material, for example in the field of food packaging and medical and healthcare sectors, considering the well-known antimicrobial effects of silver nanoparticles