Giampietro Casasanta

Observed and Modelled Convective Mixing-Layer Height at Dome C, Antarctica

The mixing-layer height is estimated using measurements from a high resolution surface-layer sodar run at the French-Italian station of Concordia at Dome C, Antarctica during the summer 2011–2012. The temporal and spatial resolution of the sodar allows the monitoring of the mixing-layer evolution during the whole diurnal cycle, i.e. a very shallow nocturnal boundary layer followed by a typical daytime growth. The behaviour of the summer mixing-layer height, variable between about 10- and 300 m, is analyzed as a function of the mean and turbulent structure of the boundary layer. Focusing on convective cases only, the retrieved values are compared with those calculated using a one-dimensional prognostic equation. The role of subsidence is examined and discussed. We show that the agreement between modelled and experimental values significantly increases if the subsidence is not kept fixed during the day. A simple diagnostic equation, which depends on the time-averaged integral of the near-surface turbulent heat flux, the background static stability and the buoyancy parameter, is proposed and evaluated. The diagnostic relation performance is comparable to that of the more sophisticated prognostic model.

Observed influence of liquid cloud microphysical properties on ultraviolet surface radiation

Measurements of different UV quantities (UV index, ozone photolysis rates, global and diffuse irradiances, and actinic flux spectra) and cloud properties were collected during a field campaign carried out in Southern Italy in May–June 2010. Independent measurements of cloud liquid water path and optical depth allowed retrieving the cloud effective radius. The cloud modification factor (CMF) is used to investigate the influence of liquid cloud properties on the UV radiation under overcast conditions. CMF was also simulated using a 1-D radiative transfer model. Experimental and simulated CMF values for UV index (under overcast conditions) show a normalized root-mean-square error around 11%. Clouds with small effective radius determine a higher UV radiation attenuation than clouds formed by large particles. The CMFs for the UV index and the global spectral irradiance show a very weak dependence on the solar zenith angle (SZA), while the CMFs for actinic flux (both integrated and spectral) and diffuse spectral irradiance show a variation with SZA. The irradiance is more effectively attenuated at low SZA, while the actinic flux at high SZA. These effects are due to the different weight given to the direct and the diffuse components.

Wavelike Structures in the Turbulent Layer During the Morning Development of Convection at Dome C, Antarctica

In the period January–February 2014, observations were made at the Concordia station, Dome C, Antarctica to study atmospheric turbulence in the boundary layer using a high-resolution sodar. The turbulence structure was observed beginning from the lowest height of about 2 m, with a vertical resolution of less than 2 m. Typical patterns of the diurnal evolution of the spatio-temporal structure of turbulence detected by the sodar are analyzed. Here, we focus on the wavelike processes observed within the transition period from stable to unstable stratification occurring in the morning hours. Thanks to the high-resolution sodar measurements during the development of the convection near the surface, clear undulations were detected in the overlying turbulent layer for a significant part of the time. The wavelike pattern exhibits a regular braid structure, with undulations associated with internal gravity waves attributed to Kelvin–Helmholtz shear instability. The main spatial and temporal scales of the wavelike structures were determined, with predominant periodicity of the observed wavy patterns estimated to be 40–50 s. The horizontal scales roughly estimated using Taylor’s frozen turbulence hypothesis are about 250–350 m.

New Atmospheric Pollution Indicators and Tools to Support Policy for Environmental Sustainable Development

Air pollution, in particular high air pollution events, increase the effects of climate change on human health. It is necessary to undertake actions to prevent and minimize these adverse events with the aim of supporting a policy for environmental sustainable development.

Erratum to: Observed and Modelled Convective Mixing-Layer Height at Dome C, Antarctica

We have discovered a calculation error in the evaluation of the history scale Q represented by Eq. 3 (Sect. 4.2). We apologise for any confusion or inconvenience that may have arisen. The miscalculation does not affect the general performance of the diagnostic relation proposed in the same section, so that the conclusions remain almost unchanged. After the correction, the values of α (Eq. 4) and of the determination coefficient (R2) retrieved by the linear regression showed in Fig. 8 become 11.20±0.30 and 0.86, respectively. The corrected values of the parameters listed in the last column (Diagnost relation) of Table 2 are mae = 33, rmse = 47, F B = 0.19, and I oA = 0.76. Figures7 and 8 with the correct calculation of Q are shown below.