Aerosol Effect on the Cloud Phase of Low‐Level Clouds Over the Arctic

Abstract

Three years of nighttime Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation data was used in synergy with CloudSat measurements to quantify how strongly aerosol type and aerosol load affect the cloud phase in low‐level clouds over the Arctic. Supercooled liquid layers were present in the majority of observed low‐level clouds (0.75 ≤ z ≤ 3.5 km) between −10 and −25 °C. Furthermore, based on the subset (6%) of data with high quality assurance for aerosol typing, ice formation is more common in the presence of dust or continental aerosols as opposed to marine or elevated smoke aerosols. With the first aerosol group, glaciated clouds were found at cloud top temperatures of 2 to 4 °C warmer than with the latter aerosol types. Further association of the aerosol concentration with the cloud phase showed that the aerosol concentration outweighs the aerosol type effect. Depending on the aerosol load, the temperature at which a cloud completely glaciates can vary by up to 6–10 °C. However, this behavior was most pronounced in stable atmospheric conditions and absent over open ocean with lower tropospheric stability values and probably less stratified clouds. Finally, more mixed‐phase clouds were associated with high aerosol load, suggesting that mixed‐phase clouds have an extended lifetime in the Arctic under high cloud condensation nuclei concentrations. This implies that in a pristine environment, with few or no local aerosol sources, and under the investigated conditions the amount of aerosol particles affects the cloud phase more than the aerosol type does.

Space‐Based Analysis of the Cloud Thermodynamic Phase Transition for Varying Microphysical and Meteorological Regimes

“…It is possible that Antarctic clouds glaciate at lower temperature than other clouds because Antarctic clouds are in contact with lower concentrations of aerosols that may serve as potential ice nuclei and facilitate phase transitions. Coopman et al (2018) studied the phase transition of Arctic clouds for different regimes of pollution from fossil fuel combustion and retrieved a glaciation temperature of about −20 • C; the presence of pollution increases the glaciation temperature up to 4 • C. Similarly, Filioglou et al (2019) have shown from CALIPSO and CloudSat measurements that high aerosol loadings increase the glaciation temperature by 10 • C in presence of dust and continental aerosols in the Arctic. We suggest that larger liquid cloud droplets are associated with higher glaciation temperatures because they aid secondary ice nucleation (Rosenfeld et al, 2011).…”

Modelling mixed-phase clouds with the large-eddy model UCLALES–SALSA

“…where r n is the radius of the insoluble portion of the droplet, k is Boltzmann's constant and T is temperature. The pre-exponential factor (kinetic coefficient) is 10 26 (cm −2 )r 2 n (Fletcher, 1962). Here, the case-dependent activation energy F act is set to zero (Khvorostyanov and Curry, 2000).…”

Effect of Dust Load on the Cloud Top Ice‐Water Partitioning Over Northern Middle to High Latitudes With CALIPSO Products

“…Biomass burning was suggested as the possible origin of this phenomenon, as it strongly influenced the aerosol composition during the season, injecting biological material, soil dust, and 10.1029/2020GL088030 ash particles into the atmosphere. Filioglou et al (2019) also addressed the effect of aerosol type (classified as marine, continental, dust, and elevated smoke) and aerosol load on the cloud phase (water, mixed-phase, and ice) of Arctic low-level clouds. Although they introduced a quantitative parameter, aerosol optical depth, to estimate the role of the aerosol load on freezing, their discussion was limited to two categories: high and low aerosol optical depths.…”