Differences in microphysical properties of cirrus at high and mid latitudes from airborne measurements

Cirrus in mid latitudes (<= 60° N) are often affected by aviation and pollution while cirrus in high latitudes (> 60° N) develop in a more pristine atmosphere. In this study, we compare the microphysical properties of cirrus measured in mid latitudes and cirrus measured in high latitudes. The analyzed properties are: the ice crystal number concentration (N), effective diameter (ED) and ice water content (IWC) of cirrus from in situ measurements during the CIRRUS-HL campaign in June and July 2021. We use a combination of cloud probes covering ice crystals sizes between 2 and 6400 µm. The differences in cirrus properties are investigated with dependence on altitude and latitude and we show that there exist differences between mid-latitude and high-latitude cirrus. An increase in ED and a reduction in N is observed in high-latitude cirrus compared to mid-latitude cirrus.

In order to investigate the cirrus properties in relation to the region of formation, we also combine our measurements with 10-day backward trajectories to identify the location of cirrus formation and the cirrus type: in situ or liquid origin cirrus. According to the latitude of cloud formation and latitude of the measurement, we classify the cirrus in three groups: cirrus formed and measured at mid latitudes (M-M), cirrus formed at mid latitudes and measured at high latitudes (M-H) and cirrus formed and measured at high latitudes (H-H). This analysis shows that part of the cirrus measured at high latitudes are actually formed at mid latitudes and therefore influenced by mid-latitude air masses. We discuss the differences of the cirrus properties under this new classification. Our study helps to advance the understanding of upper-tropospheric cirrus properties at mid and high latitudes in summer and the influence of anthropogenic perturbations.