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J. B. Nee, C. N. Len, W. N. Chen, and C. I. Lin

Abstract

The authors have detected a cirrus cloud near the tropopause by using a lidar system located at Chung-Li, Taiwan (25°N, 121°E). The cloud usually appeared between the month of May and September. In 1993–95, the cloud was observed almost 50% of the time that the lidar operated.

The cloud was detected in the heights between 15 and 17 km; the region of the atmosphere had a temperature ranging between −70° and −83°C. It was never detected above the tropopause. The cloud was characterized by its very thin structure. The geometrical and optical thicknesses are about 0.6 km and 0.008, respectively, which can be considered as a subvisual cloud. This paper reports more than 20 cloud events observed in the years between 1993 and 1995. Some properties of the clouds are listed and compared with other references.

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Matthew D. Shupe, David D. Turner, Von P. Walden, Ralf Bennartz, Maria P. Cadeddu, Benjamin B. Castellani, Christopher J. Cox, David R. Hudak, Mark S. Kulie, Nathaniel B. Miller, Ryan R. Neely III, William D. Neff, and Penny M. Rowe

Cloud and atmospheric properties strongly influence the mass and energy budgets of the Greenland Ice Sheet (GIS). To address critical gaps in the understanding of these systems, a new suite of cloud- and atmosphere-observing instruments has been installed on the central GIS as part of the Integrated Characterization of Energy, Clouds, Atmospheric State, and Precipitation at Summit (ICECAPS) project. During the first 20 months in operation, this complementary suite of active and passive ground-based sensors and radiosondes has provided new and unique perspectives on important cloud–atmosphere properties.

High atop the GIS, the atmosphere is extremely dry and cold with strong near-surface static stability predominating throughout the year, particularly in winter. This low-level thermodynamic structure, coupled with frequent moisture inversions, conveys the importance of advection for local cloud and precipitation formation. Cloud liquid water is observed in all months of the year, even the particularly cold and dry winter, while annual cycle observations indicate that the largest atmospheric moisture amounts, cloud water contents, and snowfall occur in summer and under southwesterly flow. Many of the basic structural properties of clouds observed at Summit, Greenland, particularly for low-level stratiform clouds, are similar to their counterparts in other Arctic regions.

The ICECAPS observations and accompanying analyses will be used to improve the understanding of key cloud–atmosphere processes and the manner in which they interact with the GIS. Furthermore, they will facilitate model evaluation and development in this data-sparse but environmentally unique region.

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