Deriving Arctic Cloud Microphysics at Barrow, Alaska: Algorithms, Results, and Radiative Closure

Abstract

26Cloud phase and microphysical properties control the radiative effects of clouds in the climate 27 system and are therefore crucial to characterize in a variety of conditions and locations. An 28 Arctic-specific, ground-based, multi-sensor cloud retrieval system is described here and applied 29 to two years of observations from Barrow, Alaska. Over these two years, clouds occurred 75% 30 of the time, with cloud ice and liquid each occurring nearly 60% of the time. Liquid water 31 occurred at least 25% of the time even in winter, and existed up to heights of 8 km. The 32 vertically integrated mass of liquid was typically larger than that of ice. While it is generally 33 difficult to evaluate the overall uncertainty of a comprehensive cloud retrieval system of this 34 type, radiative flux closure analyses were performed where flux calculations using the derived 35 microphysical properties were compared to measurements at the surface and top-of-atmosphere. 36 Radiative closure biases were generally smaller for cloudy scenes relative to clear skies, while 37 the variability of flux closure results was only moderately larger than under clear skies. The best 38 closure at the surface was obtained for liquid-containing clouds. Radiative closure results were 39 compared to those based on a similar, yet simpler, cloud retrieval system. These comparisons 40 demonstrated the importance of accurate cloud phase and type classification, and specifically the 41 identification of liquid water, for determining radiative fluxes. Enhanced retrievals of liquid 42 water path for thin clouds were also shown to improve radiative flux calculations.43 44 45 3

Cloud vertical distribution from combined surface and space radar–lidar observations at two Arctic atmospheric observatories

“…The combined radar-lidar cloud fraction best estimation, cloud fraction vertical profiles, cloud phase vertical profiles, and cloud water content vertical profiles, from surface observations at these two sites, are described in detail in Shupe et al (2011Shupe et al ( , 2015 and Shupe (2011). These products are based on coincident measurements from the Ka-band cloud radar, depolarization lidars including the micropulse lidar (MPL) at Barrow, and the high-spectral-resolution lidar (HSRL) at Eureka, microwave radiometer, and radiosondes, which are combined to determine cloud phase (Shupe, 2007) and microphysical properties at 1 min temporal and 100 m vertical resolutions.…”

“…Details of the collection and processing of the data can be found in Shupe (2011) and Shupe et al (2011Shupe et al ( , 2015. Surface observations of good quality are available at Eureka for most of this time period and at Barrow from mid-February 2008 to December 2010.…”

Recent Advances in Arctic Cloud and Climate Research

“…Constraining radiative transfer calculations over the Arctic is challenging with the limited cloud and atmospheric temperature and humidity profiles that are available. One particular [36], who used the R04 version of the CloudSat fluxes and heating rates product challenge is measuring cloud liquid water path, which is known to have a large influence on surface radiative fluxes [34,36,55]. At present, no spaceborne satellite is able to directly measure liquid water path in polar regions.…”

Thin ice clouds in the Arctic: cloud optical depth and particle size retrieved from ground-based thermal infrared radiometry

“…As cloud altitudes (temperatures) can lead to large uncertainties in this latter technique, Platt (1973) proposed using lidar backscatter profiles along with IR radiometry to estimate cloud altitudes and accordingly improve the retrieval accuracy of cloud emissivity. This active/passive technique (called LIRAD for lidar/radiometer method by Platt) has evolved over the years with improvements such as the availability of high-resolution spectrometers (Smith et al, 1993;Lubin, 1994). The LI-RAD technique is based on spectral radiance/brightness temperature comparisons between measurements and radiative transfer calculations.…”

“…It performs better in the presence of high thermal contrast and is thus well suited for cloud retrievals (Lubin, 1994). In more recent applications, cloud optical depth, effective radius and ice fraction were retrieved from AERI (Atmospheric Emitted Radiance Interferometer; Knuteson et al, 2004a, b) spectral downwelling radiance observations in Antarctic, during the surface heat budget of the Arctic Ocean (SHEBA) campaign and the ARM (Atmospheric Radiation Measurement) Alaska North Slope site Shupe et al, 2015;Mahesh et al, 2001, respectively). The Turner (2005) method was also employed at Eureka (Nunavut, Canada) to retrieve cloud optical depth and cloud microphysical parameters from AERI spectra acquired between (Cox et al, 2014.…”