Analysis of precipitation from ground observations over the Antarctic coast

Bracci, Alessandro (2018) Analysis of precipitation from ground observations over the Antarctic coast. [Laurea magistrale], Università di Bologna, Corso di Studio in Fisica del sistema terra [LM-DM270]
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The primary mass input of the Antarctic ice sheet is represented by snow precipitation. Despite of their crucial role, the estimates of precipitation over Antarctica are sparse and characterized by large uncertainties. Recently, the Italian Mario Zucchelli station (MZS) at Terra Nova Bay was equipped with instruments for monitoring precipitation. This thesis is part of the APP-PNRA project (Antarctic precipitation properties from ground-based instruments), whose object is to set up an observatory to characterize precipitation at MZS. The present study was focused on the evaluation of the response of solid hydrometeors to the electromagnetic radiation and on the microphysical characterization of precipitation. The former was investigated using a pre-computed discrete dipole approximation (DDA) database for complex-shape snowflakes and a T-Matrix code for soft-spheroids. The backscattering cross sections, calculated at the K-band by the two methods, were compared. In case of aggregate particles the methods show a poor agreement, comparable values were found when pristine crystals were considered. The latter was examined through in-situ observations by a Parsivel disdrometer and Micro Rain Radar. By exploiting the Parsivel data collected during the summer seasons 2016-17 and 2017-18, the particle size distributions (PSD) of hydrometeors were derived, showing a high number of particles with very small diameter. Numerical simulations, driven by DDA and T-Matrix, were also performed by using the PSDs, to obtain the simulated radar reflectivity. The comparative analysis of simulated and actual reflectivity allowed inferring microphysical characterization of precipitation. Based on this methodology, 16 out of 22 snow days were categorized: 6 as having aggregate-like features and 10 as pristine crystal-like. These results will be of practical interest, giving an important contribution toward a more accurate quantification of snow accumulation in Antarctica.

Tipologia del documento
Tesi di laurea (Laurea magistrale)
Autore della tesi
Bracci, Alessandro
Relatore della tesi
Correlatore della tesi
Corso di studio
Ordinamento Cds
Parole chiave
Precipitation,Antarctica,disdrometer,radar,particle size distribution,reflectivity,DDA,T-Matrix
Data di discussione della Tesi
25 Ottobre 2018

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