Possible Influences of Aerosols on Mixed-Phase Clouds in the High Latitudes in the Northern and Southern Hemispheres

In the climate system, anthropogenic aerosols have profound influence. Aerosols and mixed-phase clouds (MPCs) interactions are not well comprehended. There are three aerosol cloud-aerosol interactions in MPCs: the glaciation indirect effect, thermodynamic indirect effect, and riming indirect effect. Polluted conditions were compared to pristine conditions to analyze the three aerosol indirect effects by using in-situ data from the HIAPER Pole-to-Pole Observations (HIPPO) campaign, restricted to the higher latitudes. In the Northern Hemisphere (NH), aerosol number concentrations are higher than that in the Southern Hemisphere (SH).

In the upper-troposphere, evidence of high ice crystal number concentrations (Nice) related to higher aerosol number concentrations (Na) in the polluted conditions in the NH is consistent with the glaciation indirect effect. In the mid-troposphere, observations of lower ice crystal mean diameter (Dice) and lower Nice in the NH compared with the SH is consistent with the thermodynamic indirect effect. In addition, hemispheric differences in cloud liquid properties are also found. That is, SH has higher liquid droplet number concentration, larger liquid droplet mean diameter than the NH, possibly due to Wegener-Bergeron-Findeisen process and riming. To further assess the three indirect effects in MPCs, other conditions are necessary to include, such as meteorological conditions and dynamical processes.