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

Abstract

Abstract. Detailed and accurate vertical distributions of cloud properties (such as cloud fraction, cloud phase, and cloud water content) and their changes are essential to accurately calculate the surface radiative flux and to depict the mean climate state. Surface and space-based active sensors including radar and lidar are ideal to provide this information because of their superior capability to detect clouds and retrieve cloud microphysical properties. In this study, we compare the annual cycles of cloud property vertical distributions from space-based active sensors and surface-based active sensors at two Arctic atmospheric observatories, Barrow and Eureka. Based on the comparisons, we identify the sensors' respective strengths and limitations, and develop a blended cloud property vertical distribution by combining both sets of observations. Results show that surface-based observations offer a more complete cloud property vertical distribution from the surface up to 11 km above mean sea level (a.m.s.l.) with limitations in the middle and high altitudes; the annual mean total cloud fraction from space-based observations shows 25-40 % fewer clouds below 0.5 km than from surface-based observations, and space-based observations also show much fewer ice clouds and mixed-phase clouds, and slightly more liquid clouds, from the surface to 1 km. In general, space-based observations show comparable cloud fractions between 1 and 2 km a.m.s.l., and larger cloud fractions above 2 km a.m.s.l. than from surface-based observations. A blended product combines the strengths of both products to provide a more reliable annual cycle of cloud property vertical distributions from the surface to 11 km a.m.s.l. This information can be valuable for deriving an accurate surface radiative budget in the Arctic and for cloud parameterization evaluation in weather and climate models. Cloud annual cycles show similar evolutions in total cloud fraction and ice cloud fraction, and lower liquidcontaining cloud fraction at Eureka than at Barrow; the differences can be attributed to the generally colder and drier conditions at Eureka relative to Barrow.

A satellite-based estimate of aerosol-cloud microphysical effects over the Arctic Ocean

“…Above 1 km, the 2B-GEOPROF-LIDAR product is similar to or better than ground-based observations, but cloud fraction 10 can be underestimated by up to ~20% below ~1 km (Liu et al, 2017), indicating that cloud detection uncertainties in this study's lowest vertical bin (0.6-1.5 km) are higher there than in other altitude ranges.…”

“…Phase determination has also been validated favorably at high latitudes (Barker et al, 2008), except that in some cases the radar can misclassify small liquid droplets as ice particles (Noh et al, 2011;Van Tricht et al, 2016). CloudSat may also fail to observe some ice and mixed-25 phase clouds below 1 km (Liu et al, 2017), suggesting higher uncertainties in cloud phase as well in the lowest vertical bin of this study. Here, cloud phase certainty values were required to be > 5, indicating a higher confidence in phase classification.…”

“…These were excluded to avoid geographic bias in the analysis, as the few nighttime data that were available during this period tended to occur mainly at the lowest latitudes. Clouds below 0.6 km were not assessed due 30 to near-ground uncertainties in the CloudSat and CALIPSO data (de Boer et al, 2009;Liu et al, 2017 Oceanic areas were determined by ETOPO1 Bedrock GMT4 data (Amante and Eakins, 2009). Oceanic clouds were separated into open ocean and sea ice regions following Zamora et al (2017): for each profile, the corresponding monthly fractional sea ice cover was determined from the NOAA/NSIDC Climate Data Record of Passive Microwave Sea Ice Concentration, version 2 Peng et al, 2013), and samples associated with > 80% or < 20% monthly sea ice fractions were classified as being over sea ice or open ocean, respectively.…”

“…) 5 are discussed for clouds between 0.6-4 km, because clouds at higher altitudes occur mostly in the ice phase (Fig. 3) (Devasthale et al, 2011a;Liu et al, 2017). Over sea ice between 0.6-4 km, all air masses contained a higher relative fraction of ice phase clouds (IPCs) and a lower relative fraction of liquid phase clouds (LPCs) and mixed phase clouds (MPCs) relative to all air masses (Fig.…”

Arctic Clouds Simulated by a Multiscale Modeling Framework and Comparisons With Observations and Conventional GCMs

“…The lower peak near the surface might not be a deficiency of the model, because RL-GeoProf underestimates cloud from surface to 1 km. As shown in Liu et al (2017), RL-GeoProf has 25% to 40% fewer clouds below 0.5 km, when compared with surface-based radar observation at Barrow (71°19′N, 156°37′W) and Eureka (80°80′N, 85°57′W). The amount of underestimate for averages over all locations north of 60°N is expected to be much smaller.…”