Publication Date:
2012-10-31
Description:
Polar Stratospheric Clouds (PSCs) play an important role in polar ozone depletion. In particular ice clouds, type PSC-II, with respect to the type PSC-I (nitric acid clouds) produce the most significant effects. Therefore PSC characterization, mainly focused on PSC-II discrimination is needed. The backscattering (R) and volume linear depolarization (δV) ratios are the parameters usually used in lidar measurements for PSC detection and identification. In this work, an improved version of the standard NASA/Micro Pulse Lidar (MPL-4), which includes a built-in depolarization detection module, has been used for PSC observations above the coastal Antarctic Belgrano II station (Argentina, 77.9° S 34.6° W, 256 m a.s.l.) since 2009. Examination of the MPL-4 δV feature as a suitable index for PSC-type discrimination is based on the analysis of the two-channel data, i.e. the parallel (p-) and perpendicular (s-) polarized MPL signals. This study focuses on the comparison of simultaneous δV-profiles as obtained from ground-based MPL-4 measurements during three Antarctic winters with those reported from the space-borne lidar CALIOP aboard the CALIPSO satellite in the same period (48 simultaneous cases are analysed for 2009–2011 austral winter times). Two different variables are considered for the comparison analysis between both lidar datasets in order to test the degree of agreement: the correlation coefficient (CC) and the percentage difference (BIAS). Results indicate a relatively good correlation between the δV-profiles once MPL-4 depolarization calibration parameters are applied. This correlation is based on the linear fitted height-range of the layered structure, obtaining CC values higher than 0.5 for 54% (26 cases) out of all the analysed cases (48 in total). However, less satisfactory results are found when the BIAS test is used in the comparison procedure to test the degree of agreement between the lidar datasets. A predominance of negative BIAS values are observed showing that the MPL-4 δV values are underestimated with respect to CALIOP data; however, differences between the MPL-4 datasets are no greater than an 11% (absolute value) with respect to CALIOP values. Moreover, the agreement appears to be unexpectedly independent of the CALIPSO ground-track overpass distance from the Belgrano II station. Consequently, differences between the δV datasets are not dominated by spatial inhomogeneity of the PSC field.
Electronic ISSN:
1867-8610
Topics:
Geosciences
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