Andrea Cappelletti

An investigation of thermohaline circulation in Terra Nova Bay polynya

This paper addresses the study of the thermohaline circulation and convective processes induced by the presence of a coastal polynya in Terra Nova Bay (Ross Sea, Antarctica). These processes are analysed by means of oceanographic observations and numerical simulations. Time series of hydrological parameters and currents show the High Salinity Shelf Water (HSSW) formation with the mixing of the water column down to great depths, and a seasonal cycle of kinetic energy. A two-dimensional time dependent model for the numerical simulation of the effects of polynya on the circulation has been implemented. This model allows estimation of the contribution of thermohaline forcing on the circulation pattern, the amount of ice production consistent with the observed salinity distribution and annual cycle of currents and the amount of HSSW exported. The thermohaline forcing due to the polynya is able to induce strong horizontal currents up to 40 cm s−1 near the polynya area, as well as vertical movements of the order of 1 cm s−1. An annual ice production, ranging from 45 m to 90 m, mixes the water column at great depths, up to 750 m, and increases the salinity of the surface incoming waters up to 34.82. The estimated net north-eastward transport of HSSW ranges from 0.34 Sv to 1.23 Sv, depending on ice production.

Upper ocean layer dynamics and response to atmospheric forcing in the Terra Nova Bay polynya, Antarctica

Abstract A one-year time series of Acoustic Doppler Current Profiler (ADCP) data was collected in Terra Nova Bay (TNB) polynya (Ross Sea, Antarctica) during 2000. Together with Automatic Weather Station (AWS) Eneide meteorological data and Special Sensor Microwave Imager (SSM/I) ice concentration data, ADCP data were analysed to investigate upper layer dynamics and variability due to atmospheric forcing. Empirical Orthogonal Function (EOF) analysis was performed to separate the surface variability caused by local forcing from the large-scale circulation component. In particular, the first mode represented the barotropic circulation while the second the stronger surface currents. The decrease in shelf water density from melting sea ice resulted in an off-shore density gradient producing a southern shift in the circulation. This result proved to be consistent with the in situ data acquired during February–April at 120 m depth. The observed variability of the surface currents was assessed with respect to the thermal wind equation and the steady Ekman model. Strong katabatic winds shifted the surface currents eastward with respect to the general north-eastern circulation. The wind stress acted as a relevant forcing for the surface large-scale circulation in TNB, but had negligible effects on the vertically integrated transport.

Modeling Air Quality over Italy with MINNI Atmospheric Modeling System: From Regional to Local Scale

This study shows part of the results obtained during the operational evaluation of MINNI atmospheric modeling system over Italy. MINNI is the Italian Integrated Assessment Modelling System for supporting the International Negotiation Process on Air Pollution and assessing Air Quality Policies at national/local level sponsored by the Italian Ministry of the Environment. The evaluation was carried out for both meteorology and air quality for the years 1999 and 2005. Changes of meteorological variables and of ozone concentrations in relation to the change of horizontal grid resolution were also investigated. The results show the capability of the modelling system to reconstruct the meteorological and ozone fields over Italy.

Modeled deposition of nitrogen and sulfur in Europe estimated by 14 air quality model systems: evaluation, effects of changes in emissions and implications for habitat protection

The evaluation and intercomparison of air quality models is key to reducing model errors and uncertainty. The projects AQMEII3 and EURODELTA-Trends, in the framework of the Task Force on Hemispheric Transport of Air Pollutants and the Task Force on Measurements and Modelling, respectively (both task forces under the UNECE Convention on the Long Range Transport of Air Pollution, LTRAP), have brought together various regional air quality models to analyze their performance in terms of air concentrations and wet deposition, as well as to address other specific objectives. This paper jointly examines the results from both project communities by intercomparing and evaluating the deposition estimates of reduced and oxidized nitrogen (N) and sulfur (S) in Europe simulated by 14 air quality model systems for the year 2010. An accurate estimate of deposition is key to an accurate simulation of atmospheric concentrations. In addition, deposition fluxes are increasingly being used to estimate ecological impacts. It is therefore important to know by how much model results differ and how well they agree with observed values, at least when comparison with observations is possible, such as in the case of wet deposition. This study reveals a large variability between the wet deposition estimates of the models, with some performing acceptably (according to previously defined criteria) and others underestimating wet deposition rates. For dry deposition, there are also considerable differences between the model estimates. An ensemble of the models with the best performance for N wet deposition was made and used to explore the implications of N deposition in the conservation of protected European habitats. Exceedances of empirical critical loads were calculated for the most common habitats at a resolution of 100 × 100 m2 within the Natura 2000 network, and the habitats with the largest areas showing exceedances are determined. Moreover, simulations with reduced emissions in selected source areas indicated a fairly linear relationship between reductions in emissions and changes in the deposition rates of N and S. An approximate 20 % reduction in N and S deposition in Europe is found when emissions at a global scale are reduced by the same amount. European emissions are by far the main contributor to deposition in Europe, whereas the reduction in deposition due to a decrease in emissions in North America is very small and confined to the western part of the domain. Reductions in European emissions led to substantial decreases in the protected habitat areas with critical load exceedances (halving the exceeded area for certain habitats), whereas no change was found, on average, when reducing North American emissions in terms of average values per habitat.

Study of the Impact of Low vs. High Resolution Meteorology on Air Quality Simulations Using the MINNI Model Over Italy

Modelling air quality requires the description of a large number of processes interacting each other. In order to properly model concentrations of atmospheric pollutants it is crucial to have a realistic reproduction of meteorological parameters, which can be critical in areas presenting a complex orography like the Italian peninsula. This work shows an analysis of the results obtained with the national model MINNI at two different horizontal resolutions (20 and 4 km), for a whole year over Italy. Comparisons between modelled and observed temperature and pollutants concentrations are carried out. The prediction of temperature is improved with the increase of model spatial resolution, as it is for pollutants like NO2 and CO, while the improvement is not always evident for O3 concentrations. Results are discussed providing an interpretation of the observed features.

Air quality modeling and inhalation health risk assessment for a new generation coal-fired power plant in Central Italy

An assessment of potential carcinogenic and toxic health outcomes related to atmospheric emissions from the new-generation coal fired power plant of Torrevaldaliga Nord, in Central Italy, has been conducted. A chemical-transport model was applied on the reference year 2010 in the area of the plant, in order to calculate airborne concentrations of a set of 17 emitted pollutants of health concern. Inhalation cancer risks and hazard quotients, for each pollutant and for each target organ impacted via the inhalation pathway, were calculated and mapped on the study domain for the overall ambient concentrations and for the sole contribution of the plant to airborne concentrations, allowing to assess the relative contribution of the power plant to the risk from all sources. Cancer risks, cumulated on all pollutants, resulted around 5 × 10-5 for the concentrations from all sources and below 3 × 10-7 for the plant contribution, mainly targeting the respiratory system. On each part of the study domain, the plant contributed for less than 6% to the overall cancer risk. Hazard quotients from all sources, cumulated on all pollutants, reached values of 2.5 for the respiratory and 1.5 for the cardiovascular systems. Hazard quotients of non-carcinogenic risks from the plant, cumulated on all pollutants, resulted below 0.03 for the respiratory system and 0.02 for the cardiovascular system. On each part of the study domain, the plant contributed for less than 5% to the respiratory and cardiovascular risks. Both cancer risks and hazard quotients related to the plant are far below international thresholds for human health protection, while the values from all sources require consideration. The proposed method provides an instrument for prospective health risk assessment of large industrial sources, with some limitations presented and discussed.

On the Ekman Equations for Ocean Currents Driven by a Stochastic Wind

The basic assumptions for the depth-dependent Ekman equations are presented. An analysis of three wind stress time series, from different geographical locations, is performed: The results lead to interpret the wind stress as a stochastic process, with components fluctuating with deterministic frequencies. The stochastic equations coupling wind stress and ocean currents are formulated; their solutions are stochastically bounded. Results of numerical simulations are given to show the main behaviors of the system.