Give


Graduate Exam Abstract


Renzo Bechini

Ph.D. Preliminary

September 11, 2013, 2.30pm

LSC 232

Microphysics and dynamics retrievals from dual-polarization radar for very short-term forecasting


Abstract: Nowcasting is primarily a description of the current atmospheric state and the near-future forecasted state, therefore relying heavily on observations. Besides routine meteorological observations (pressure, temperature, humidity, wind), dual-polarization weather radar provides a large amount of useful information due to the frequent-update (~5 min) and high-resolution (~500 m) three-dimensional sampling of the atmosphere. However, radar remote observations are not directly related to the atmospheric state variables, which implies a complexity in the numerical model data assimilation. This problem is normally dealt with by defining observation operators to simulate the radar variables from the model state vector. The dual-polarization radar observations are analyzed in order to demonstrate their potential for microphysics and dynamics retrievals. Hydrometeor classification algorithms, dual-polarization analyses of signatures in convective storms and in stratiform ice clouds are developed towards this goal. It is found that specific dual-polarization radar signatures can be successfully related to important dynamic properties such as vertical air motions, both in convective precipitation (strong updrafts, several m/s) and in stratiform precipitation (large areas of weak updrafts, tenths of m/s, associated with mid-tropospheric mesoscale forcing). In particular the relevance of a well-known dual-polarization feature ("vertical columns of differential reflectivity") associated with deep convection is shown by including the microphysics (and dynamics-related) information into an analysis of the surface winds. The significance of the results prompts for the development of a novel way to assimilate dual-polarization radar observations in current numerical model variational assimilation schemes.

Adviser: V. Chandrasekar
Co-Adviser: N/A
Non-ECE Member: Paul Mielke, Statistics
Member 3: Branislav Notaros, ECE
Addional Members: Anura Jayasumana, ECE

Publications:
Polarimetric Radar Observations in the Ice Region of Precipitating Clouds at C-Band and X-Band Radar Frequencies R. Bechini, L. Baldini, V. Chandrasekar Journal of Applied Meteorology and Climatology Volume 52, Issue 5 (May 2013) pp. 1147-1169 doi: http://dx.doi.org/10.1175/JAMC-D-12-055.1


Program of Study:
ATS 604
ATS 741
ECE 512
ECE 641
ECE 799
STAT 523
N/A
N/A