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William D. Neff
,
Richard J. Lataitis
, and
Guest Editors
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Lisa S. Darby
,
William D. Neff
, and
Robert M. Banta

Abstract

Data from a mesoscale observing network are used to describe the evolution of a complex boundary between a dry air mass near the foothills of the Rocky Mountains and a shallow moist air mass over the eastern plains. Synoptic-scale analyses revealed that the origin of the moist air mass was associated with lee cyclogenesis. Mesoscale analyses provided a detailed picture of a localized anticyclonic circulation that developed within the larger-scale flow. Mixing ratio data from the mesoscale observing network indicated the position of the boundary between the air masses. It is shown that the cooler, moister air on the plains advanced toward and retreated away from the foothills during the evening. Eventually, downslope winds that were opposing the motion of the mesoscale boundary decreased, and the anticyclonic circulation on the plains became more organized. On an even smaller scale, Doppler lidar measurements revealed characteristics of the wind flow associated with the mesofront and the interaction of this flow with the downslope winds near the foothills of the Rocky Mountains. These characteristics included the horizontal variability of the winds near the complex foothills topography; the vertical structure of the winds associated with the mesofront, which indicated density-current-like features; the vertical structure of strong downslope flow opposing the mesofront’s motion; and differences in the aerosol content of the air masses.

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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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Nicholas A. Bond
,
Clifford F. Mass
,
Bradley F. Smull
,
Robert A. Houze
,
Ming-Jen Yang
,
Brian A. Colle
,
Scott A. Braun
,
M. A. Shapiro
,
Bradley R. Colman
,
Paul J. Neiman
,
James E. Overland
,
William D. Neff
, and
James D. Doyle

The Coastal Observation and Simulation with Topography (COAST) program has examined the interaction of both steady-state and transient cool-season synoptic features, such as fronts and cyclones, with the coastal terrain of western North America. Its objectives include better understanding and forecasting of landfalling weather systems and, in particular, the modification and creation of mesoscale structures by coastal orography. In addition, COAST has placed considerable emphasis on the evaluation of mesoscale models in coastal terrain. These goals have been addressed through case studies of storm and frontal landfall along the Pacific Northwest coast using special field observations from a National Oceanic and Atmospheric Administration WP-3D research aircraft and simulations from high-resolution numerical models. The field work was conducted during December 1993 and December 1995. Active weather conditions encompassing a variety of synoptic situations were sampled. This article presents an overview of the program as well as highlights from a sample of completed and ongoing case studies.

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