Two Perspectives on Arctic Clouds: Blending Observations from the Surface and Space

liu, Y., CIMSS/AOS UW-Madison

Cloud Distributions/Characterizations

High Latitude Processes

Liu Y, M Shupe, Z Wang, and G Mace. 2017. "Cloud vertical distribution from combined surface and space radar–lidar observations at two Arctic atmospheric observatories." Atmospheric Chemistry and Physics, 17(9), 10.5194/acp-17-5973-2017.


Mean vertical distributions of cloud fraction for 2006-2010 from surface observations at Barrow, Alaska (black) and the difference of these measurements relative to multiple space-based products including: 2B—GEOPROF-lidar, CALIPSO 1 km, CALIPSO 5 km, and 2B-GEOPROF.


Mean vertical distributions of cloud fraction for 2006-2010 from surface observations at Barrow, Alaska (black) and the difference of these measurements relative to multiple space-based products including: 2B—GEOPROF-lidar, CALIPSO 1 km, CALIPSO 5 km, and 2B-GEOPROF.

Science

Clouds play a critical role in the Arctic climate system, yet a comprehensive set of cloud observations is lacking due to condition-specific limitations of the available observing systems. These difficulties have in turn led to substantial deficiencies in how models represent Arctic clouds and in particular cloud phase. Observations from ground-based and space-based radar and lidar are compared at two Arctic sites to assess the relative strengths and weaknesses of these observational approaches for characterizing the vertical distribution and phase of Arctic clouds.

Impact

This study increases the value and clarifies the interpretation of both ground-based and space-based observations of clouds, helping the community to better understand the limitations of these observations and ultimately to better understand the role of clouds in the Arctic system. Moreover, a combined cloud product, that draws upon the strengths of both ground- and space-based measurements, is developed to offer a more complete data set for assessing model representations of clouds at these Arctic sites.

Summary

Ground-based remote sensors provide continuous, long-term observations, yet are limited to specific locations. On the other hand, space-based remote sensors cover wide spatial domains, yet cannot resolve diurnal processes at a given location. Both approaches face distinct observational challenges depending on cloud type, microphysical parameters, and the environment. In this study, multiple years of ground-based measurements from zenith-pointing Ka-band cloud radar and depolarization lidar are compared with similar observations from the space-based CloudSat radar and CALIPSO lidar at two sites in the Arctic: the Department of Energy Atmospheric Radiation Measurement Research Facility's North Slope of Alaska site in Barrow and the National Oceanic and Atmospheric Administration/Canadian Network for the Detection of Arctic Change site in Eureka, Canada. In the Arctic, where low clouds are frequent, ground-based sensors observe 25-40% more clouds (primarily ice and mixed-phase clouds) below 1 km than satellite sensors due to CloudSat ground-contamination issues and CALIPSO signal attenuation. The two perspectives show comparable observations between 1-2 km. Space-based sensors observe an annual average of 1-6% more cloudiness at most heights above 2-3 km than surface-based sensors due to diminishing sensitivity of surface sensors with height and lidar attenuation. In summer the space-based measurements observe a higher fraction of liquid-containing clouds at these heights relative to the ground-based observations, while in winter they observe a higher fraction of ice clouds. A blended, monthly average product based on observations from these two perspectives provides the most comprehensive cloud occurrence and phase data set at these Arctic sites to date.