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| Titel |
Comparison of CALIPSO aerosol optical depth retrievals to AERONET measurements, and a climatology for the lidar ratio of dust |
| VerfasserIn |
G. L. Schuster, M. Vaughan, D. MacDonnell, W. Su, D. Winker, O. Dubovik, T. Lapyonok, C. Trepte |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 12, no. 16 ; Nr. 12, no. 16 (2012-08-17), S.7431-7452 |
| Datensatznummer |
250011395
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| Publikation (Nr.) |
 copernicus.org/acp-12-7431-2012.pdf |
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| Zusammenfassung |
| We compared CALIPSO column aerosol optical depths at
0.532 μm to measurements at 147 AERONET sites, synchronized
to within 30 min of satellite overpass times during a 3-yr
period. We found 677 suitable overpasses, and a CALIPSO bias of
−13% relative to AERONET for the entire data set; the
corresponding absolute bias is −0.029, and the standard deviation of
the mean (SDOM) is 0.014. Consequently, the null hypothesis is
rejected at the 97% confidence level, indicating
a statistically significant difference between the datasets. However,
if we omit CALIPSO columns that contain dust from our analysis, the
relative and absolute biases are reduced to −3% and −0.005
with a standard error of 0.016 for 449 overpasses, and the statistical
confidence level for the null hypothesis rejection is reduced to
27%. We also analyzed the results according to the six
CALIPSO aerosol subtypes and found relative and absolute biases of
−29% and −0.1 for atmospheric columns that contain the dust
subtype exclusively, but with a relatively high correlation
coefficient of R = 0.58; this indicates the possibility that the
assumed lidar ratio (40 sr) for the CALIPSO dust retrievals is
too low. Hence, we used the AERONET size distributions, refractive
indices, percent spheres, and forward optics code for spheres and
spheroids to compute a lidar ratio climatology for AERONET sites
located in the dust belt. The highest lidar ratios of our analysis
occur in the non-Sahel regions of Northern Africa, where the median
lidar ratio at 0.532 μm is 55.4 sr for 229
retrievals. Lidar ratios are somewhat lower in the African Sahel
(49.7 sr for 929 retrievals), the Middle East (42.6 sr
for 489 retrievals), and Kanpur, India (43.8 sr for 67
retrievals). We attribute this regional variability in the lidar ratio
to the regional variability of the real refractive index of dust, as
these two parameters are highly anti-correlated (correlation
coefficients range from −0.51 to −0.85 for the various regions). The
AERONET refractive index variability is consistent with the
variability of illite concentration in dust across the dust belt. |
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