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  • Open access
  • 8 Reads
Vortex motion state of the dry atmosphere with nonzero velocity divergence

In the present work an analytical model of the vortex motion elementary state of the dry atmosphere with nonzero air velocity divergence is constructed. It is shown that the air parcel moves along the open curve trajectory of spiral geometry. It is found that for the case of nonzero velocity divergence the atmospheric elementary state presents an unlimited sequence of vortex cells transiting from one to another. On the other hand, at zero divergence, the elementary state presents a pair of connected vortices, and the trajectory is a closed curve. If in some cell the air parcel moves upward then in the adjacent cell it will move downward and vice versa. At reaching the cell middle height the parcel reverses the direction of rotation. When parcel moves upward, the motion is of anticyclonic type in the lower part of the vortex cell and of the cyclonic type in the upper part. When parcel moves downward, the motion is of anticyclonic type in the upper part of the vortex cell and of the cyclonic type in the lower part.

  • Open access
  • 10 Reads
Molecular fragmentation of acetylene by VUV double photoionization

Acetylene is a simple molecule of interest for interstellar medium (ISM) and planetary atmospheres. The presence of C2H2 was detected by IR spectroscopic measurements [1]. Acetylene was also found as a minor component in the atmosphere of gas giants like the planet Jupiter, in the atmosphere of Saturn's satellite Titan, and in comets, where photochemical experiments have demonstrated that this simple hydrocarbon is a likely precursor of C2, a widely observed component in such environments [2-4]. It has to be noted that the presence in planetary atmospheres and ISM of Vacuum Ultra Violet (VUV) light’s photons as well as cosmic rays makes highly probable the double photoionization of molecular species with the production of molecular dications producing subsequent dissociation into ionic fragments having a high kinetic energy content of several eV. This translational energy is sufficient in some cases to allow ions escape from the upper atmosphere of some planet of the Solar System, as Venus, Mars and Titan, into space [5-7]. In this contribution we present the experimental study of the microscopic dynamics of the two-body dissociation reactions of the C2H2+2 dication, induced by the double ionization of acetylene molecules by VUV photons in the energy range of 31.9-50.0 eV. The photoionizing agent was a tunable synchrotron radiation beam with a photon energy resolution of about 1.5 meV, while ion products are revealed by coupling photoelectron-photoion-photoion-coincidence and ion imaging techniques [8]. The measured angular distributions and kinetic energy of product ions exhibit significant changes (as the photon energy increases) for the three leading dissociation reactions producing H++C2H+, C++CH2+, and CH+ + CH+, providing detailed information on the fragmentation dynamics of the C2H22+ dication.

[1] O. Witasse et al. 2002, Geophys. Res. Lett., 29, 1263 1-4.

[2] T. Y. Brooke et al., 1996, Nature, 383, 606-608.

[3] J. Cernicharo et al., 2001, Astrophys. J., 546, L123-L126.

[4] P. M. Woods et al., 2002, Astrophys. J., 574, L167-L170.

[5] R. Thissen et al., 2011, Phys. Chem. Chem. Phys., 13, 18264–18287.

[6] S. Falcinelli et al., 2014, Planetary and Space Science, 99, 149-157.

[7] S. Falcinelli et al., 2016, Atmosphere, 7(9), 112.

[8] S. Falcinelli et al., 2017, Acta Physica Polonica A, 131(1), 112-116.

  • Open access
  • 15 Reads
Wintertime atmospheric blocking events in Western Siberia in the period 2004-2016 and their connection with anomalies of surface temperature

Atmospheric blockings are one of the main causes of many natural disasters (droughts, floods, fires, frosts) that have become more frequent recently. We study wintertime blocking events in 2004 – 2016 over Western Siberia and their influence on the surface temperature. The period 2004 – 2016 is very interesting for study because there has been an increase in the blocking frequency over Western Siberia beginning with 2004. In the work we used data ECMWF ERA Interim (geopotential, surface temperature) and criterion proposed by Tibaldi and Molteni. We investigated blockings events with a duration of 5 days or more for winter intervals (1 November – 31 March). We have chosen 15 blockings events: December 2004, January-February 2005, December 2005, November 2006, January 2008 (two events), December 2008, December- January 2010-2011, January 2011, February 2011, December 2011, January-February 2012, December 2012, February-March 2015, December 2015- January 2016. For each event we calculate surface temperature anomaly in the grid points for two sectors 60 – 90 E; 50 – 60 N (southern part of West Siberia) and 60 – 90 E; 60 – 70 N (northern part of West Siberia). Anomalies were calculated as deviation of daily surface temperature values from 1979 – 2015 mean. To estimate advective transfer for studied 15 events we analyzed the potential temperature on the dynamical tropopause (PV-θ). We showed that wintertime blocking events over the Western Siberia lead to the surface temperature increase in the northern part of West Siberia and to the surface temperature decrease in the southern part of West Siberia. This feature apparently due to warm air masses advection from south-west on the western periphery of the blocking ridge (reinforcing it) and arctic air masses intrusion to the southern part of the Western Siberia on the eastern periphery of this ridge.

This research was supported by the Russian Foundation for Basic Research grants no. 17-05-00119 and no. 17-05-00374

  • Open access
  • 9 Reads
The predictability of Northern Hemispheric blocking events using an ensemble mean forecast system.

Some weather extremes can be the result of atmospheric blocking, which can be responsible for the the stagnation of weather patterns. These large-scale quasi-stationary mid-latitude flow regimes can result in significant temperature and precipitation anomalies in the regions that the blocking event impacts. The ability to predict periods of anomalous weather conditions due to atmospheric blocking is a major problem for medium-range forecasting. Analyzing the NCEP Ensemble 500-mb pressure heights (240 hrs.) ten-day forecasts, and using the University of Missouri blocking archive to identify blocking event, the forecasted duration and intensity of model blocking events are compared to observed blocks. Comparing these differences using four case studies occurring over a one-year period across the Northern Hemisphere has shown the continued need for improvement of the duration and intensity of blocking events. Additionally, a comparison of the block intensity to a diagnostic known as the Integrated Regional Enstrophy (IRE) was performed in order to determine if there is a correlation between these quantities. Having a better understanding of knowing how long each block will last and their associated anomalies can help society prepare for the damage they can cause. Knowing how to correctly identify blocks is important in improving forecast issues.

  • Open access
  • 13 Reads
Monitoring and evaluation of Terni (Central Italy) air quality through spatially resolved analysis

The air quality of Terni was evaluated during a six months monitoring campaign carried out from December 2016 to May 2017. Terni is a city of Central Italy situated in an intramountain depression delimited by the Apennine mountain range. It contains many sources of airborne particulate matter such as vehicular traffic, domestic heating, a power plant for waste treatment and a steel plant. Furthermore, the meteorological conditions of Terni basin limit the dispersion and enhance the accumulation of the atmospheric pollutants. Hence, Terni is an ideal area for the mapping of the spatial variations of PM10 chemical species through innovative analytical methods.

Spatially resolved data were obtained at a monthly temporal resolution by innovative, low flow and self-powered samplers working in parallel at 25 strategic sites. PM10 chemical composition was determined by applying a multiparametric procedure (macro-elements, micro-elements and inorganic ions) previously optimized and validated [1]. This procedure enabled the separation between the water-soluble and the residual fraction of each analyzed element. The application of a chemical fractionation procedure proved to be a valuable approach for the characterization of PM10 and for increasing the selectivity of elements as source tracers [2].

The spatial mapping of the source tracers resulted to be efficient for the individuation of the PM10 chemical source profiles and for the evaluation of the dispersion capacities of PM10 chemical species. In addition silent samplers were utilized to evaluate the air quality of indoor environments (such as dwellings and schools) by calculating the infiltration ratio (indoor/outdoor concentration) of each analyzed source tracer. The information obtained can be used to validate the dispersion models and to improve the evaluation of human exposure to PM.

References

[1] S. Canepari, E. Cardarelli, A. Giuliano, A. Pietrodangelo, Talanta 69 (2006) 581–587.

[2] S. Canepari, A. Pietrodangelo, C. Perrino, M.L. Astolfi , M.L. Marzo, Atmospheric Environment 43 (2009) 4754–4765.

  • Open access
  • 10 Reads
Dynamical downscaling of future climate change scenarios in urban heat island and its neighborhood in a Brazilian subtropical area

The impact of climate change on cities is an important, relevant and a difficult theme to study, since there are many uncertainties about the real consequences of climate change in urban areas. According to IPCC reports, a greater frequency, intensity and duration of heat waves in urban areas are expected. This is related to the dynamical evolution of the cities, since the changes of the natural surface modifies the roughness pattern, reduce the wind intensity, changes the available humidity in the soil and the radiative properties. All these changes characterize an effect in the local microclimate, known as Urban Heat Island (UHI). Given the importance of UHI in the impact of extreme temperatures, this work proposes to investigate the physical processes of the future projections on the urban heat island formation and intensity, as well as their effects over neighborhoods crop areas. A dynamical downscaling of A2 and B1 future scenarios for Londrina, a medium-size city of Southern Brazil, using Weather Research Forecasting model is used. A2 is described as a pessimistic scenario, while B1 is considered the most sustainable scenario. Simulations for 20 to 24 July for 2015 were done using CCSM4 scenarios and GFS as input data. This period is considered as a prediction for the scenarios. An evaluation of the simulations was done to investigate the current trends. The results show a tendency of following the worst proposed scenarios (A2), and a drier rural area for both projection, which has direct influence on the urban heat island intensity and formation, and in the agriculture of the region

  • Open access
  • 9 Reads
Oxidative potential of selected PM components

Particulate matter (PM) is a complex mixture of suspended solid and liquid particles characterized by toxicological properties (1). Oxidative stress is considered as one of the most important mechanism of PM toxicity on living organisms. Reactive oxygen species (ROS) may in fact damage lipids in biological membranes, enzymatic proteins and DNA. ROS content in PM samples is frequently evaluated in the literature in terms of oxidative potential (OP). However, the relations between the obtained results and the chemical and physical characteristic of particles are still largely unknown.In this work we report the results obtained by three different assays for measuring oxidative potential (OP) on selected components of PM having a very different chemical composition (road dust, soil dust, brake dust, desert dust, pellet ash and coke and certified material NIST1648a – urban dust). The first two methods are based on the decrease of reducing species concentration (respectively Dithiothreitol - DTT and Ascorbic Acid - AA) due to ROS (2); the third one is based on the formation of a fluorescent compound (dichlorofluorescein - DCF) from oxidation of 2′,7′-dichlorofluorescein (DCFH ) in the presence of horseradish peroxidase (HRP) (3). The results show that the three methods respond very differently to each dust and that, accordingly to the results of a previous study of the oxidative stress on simple in vivo organism model (4), the un-soluble chemical components of dusts have an OP much higher than that of the soluble species.

1-Canepari et al. 2013, Aerosol and Air Quality Research 13, 1619-1629.

2-Fang et al. 2015, Atmospheric Chemistry and Physics 15, 30609–30644.

3-Huang et al. 2016, Water, Air, & Soil Pollution 227-164.

4-Marcoccia et al. 2017, Chemosphere 173, 124-134.

  • Open access
  • 7 Reads
An overview of statistical methods for studying the extreme rainfalls in Mediterranean.

Extreme rainfall is one of the most devastating natural events. The frequency and intensity of these events has increased. This trend will likely continue as the effects of climate change become more pronounced. As a consequence, it is necessary to evaluate the different statistical methods that assess the occurrence of the extreme rainfalls. This research evaluates some of the most important statistical methods that are used for the analysis of the extreme precipitation events. Extreme Value Theory is applied on ten station data located in the Mediterranean region. Furthermore, its two main fundamental approaches (Block-Maxima and POT) and three commonly used methods for the calculation of the extreme distributions parameters (Maximum Likelihood, L-Moments, and Bayesian) are analyzed and compared. The results showed that the Generalized Pareto Distribution provides better theoretical justification to predict extreme precipitation compared to Generalized Extreme Value (GEV) distribution while in the majority of stations the most accurate parameters for the highest precipitation levels are estimated with the Bayesian method. Extreme precipitation for return period of 50, 150 and 300 years were finally obtained which indicated that Generalized Extreme Value Distribution with Bayesian estimator presents the highest return levels for western stations, while for the eastern Mediterranean stations the Generalized Pareto Distribution with Bayesian estimator presents the highest ones.

  • Open access
  • 6 Reads
Evaluation of the sensitivity of the updated RegCM4 model to physics parameterizations over the Mediterranean region: Precipitation and temperature simulations

During the last years, a great effort is being made from the scientific community to study the sensitivity of regional climate models to specific parameterizations. Numerous studies have been made regarding that field of research; however, it has not been widely applied in Europe. Thus, it was essential to study the sensitivity of regional climate models to the different physics parameterization schemes in the Mediterranean region. The examined regional climate model used in this study is RegCM4.4.5.1. Its spatial resolution is 25x25km. Different simulations were performed with changes in the model’s physics parameterization schemes for the time period 1981-1990. In order to “run” RegCM4, ERA-Interim data for initial and boundary conditions (ICBC) and sea surface temperature (SST) were utilized. For the examination of the sensitivity of the regional climate model to the different physics configurations of the model, the different simulated data of temperature and precipitation were processed on a seasonal basis and the differences between the simulations were calculated, mapped and compared. The statistical significance of the differences is calculated with Student’s t-test. Aiming a more detailed simulation of the changes that occur, a division of the area of study in five sub-regions was performed according to the common EURO-CORDEX analysis domain and the Taylor diagrams for the examined parameters were calculated. This study is a first attempt to find the best combination of parameterizations to “run” RegCM4 for the domain of interest and finally to perform a dynamical downscaling of the regional climate model in order to produce the best possible projections for future climate in the Greek area.

  • Open access
  • 11 Reads
Observing actual evapotranspiration within a heterogeneous watershed: The case study of the Kamech site, Cap Bon Peninsula, Tunisia

There is a strong need for continuous long term observations of land surface fluxes, especially the latent heat flux, or actual evapotranspiration (ETa), a key component of both the surface energy balance and the hydrological cycle. The eddy covariance (EC) method is widely used to provide continuous measurements of land surface fluxes. However, missing data are inherent to EC measurements and several gap-filling methods have been proposed. Nevertheless, observing ETa by EC and testing gap-filling methods in heterogeneous and hilly watersheds have received little attention.

The main objective of this study was to obtain complete ETa chronicles from EC measurements collected within a small hilly watershed. This implied to adapt and test gap-filling techniques in the particular conditions of a hilly and heterogeneous watershed.

The experiment was conducted within the agricultural watershed Kamech, Northeast Tunisia. Kamech, one of the experimental sites of the OMERE environmental observatory, has a 2.45 km2 area and is typified by spatial heterogeneities related to topography, pedology and crops. A 9.6-meter-high EC flux tower, located close to the center of the watershed, has been operating since 2010. Sensible and latent heat fluxes data collected from 2010 to 2013 were instrumentally corrected and quality controlled.         

The software REddyProc was used to fill gap of the chronicles of latent and sensible heat fluxes at hourly timescale. In order to account for the combine effects of wind direction, topography and heterogeneity, the gap filling was applied after discriminating between the two dominant wind directions, which slightly improved the estimation of the sensible and latent heat fluxes. Aggregating the hourly ETa estimates at daily and monthly timescales allows analyzing the temporal variability of ETa over the seasons and between years.

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