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Jin, X, Hanesiak, J, Barber, D (2007). Detecting cloud vertical structures from radiosondes and MODIS over Arctic first-year sea ice. ATMOSPHERIC RESEARCH, 83(1), 64-76.

The cloud vertical structure (CVS) of Arctic clouds is analyzed with data mainly from radiosondes launched between November 2003 and June 2004 during the Canadian Arctic Shelf Exchange Study (CASES). The feasibility of using a radiosonde-based cloud detection method [Minnis, P., Yi, Y. Huang, J., and Ayers, K. 2005: Relationships between radiosonde and RUC-2 meteorological conditions and cloud occurrence determined from ARM data, J. Geophys. Res., 110, D23204, doi: 10. 1029/2005JD006005. MN05 hereafter] is evaluated. At temperatures between - 35 and 5 degrees C, the minimum probability (Pr) calculated from MN05 to detect a cloud layer is 68%. The infeasibility of MN05 in determining Arctic cirrus clouds is speculated to be due to the different freezing, mechanisms at low temperatures (< -40 degrees C) in polluted continental and clean Arctic environments. Based on these facts we present a modified scheme to determine CVS in this paper. 1) for low clouds, 51.6% of all samples are with cloud base height (CBH)< 500 m; 66.5% with cloud top height (CTH) < 1500 m and 80.6% with CTH < 2500 m; 54.7% with cloud vertical thickness (CVT)< 500 m and 73.6% with CVT < 1000 m; 2) for middle clouds, the CBH is almost evenly distributed between 1.8 and 4 km but 68% of all CTHs are at heights between 2000 and 5000 in. 17% of CTHs are above 8000 in and 47% CVTs are thinner than 1000 in and 67% thinner than 2000 in; 3) for high clouds, the frequency distributions of both CBH and CTH decrease with increasing height from 5000 to 8000 in but there are 41% CBHs between 9000 and 11,500 m. The MODIS-derived cloud top pressure (CTP) is compared with data from radiosondes. In general the MODIS CTP agrees well with that from radiosondes between the 400 and 700 hPa layer. MODIS underestimates CTP at heights between 700 and 950 hPa and overestimates CTP at lower layers (> 950 hPa). The underestimate and overestimate of atmospheric temperatures above and under the 950 hPa isobaric layer respectively is thought to be the cause of the differences. (c) 2006 Elsevier B.V. All rights reserved.



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