Investigating an indirect aviation effect on mid-latitude cirrus clouds – linking lidar derived optical properties to in-situ measurements
Abstract. Aviation has a large impact on the Earth’s atmosphere and climate by various processes. Line shaped contrails and contrail cirrus clouds lead to changes in the natural cirrus cloud cover, and have a major contribution to the effective radiative forcing from aviation. In addition, aviation emitted aerosols may also change the microphysical properties and, in particular, the optical properties of naturally formed cirrus clouds. Latter aerosol-cloud interactions show large differences in the estimated resulting effective radiative forcing and our understanding on how aviation induced aerosols affect cirrus cloud properties is still poor. Up to now, observations of this aviation induced aerosol effect are rare. In this study, we use combined airborne lidar and in-situ ice cloud measurements to investigate differences in the microphysical and optical properties of naturally formed cirrus clouds, which either formed under influences of aviation induced aerosol emissions or which formed under rather pristine conditions. We relate collocated lidar measurements performed aboard HALO during the ML-CIRRUS mission of the particle linear depolarization ratio with in-situ cloud probe measurements of the number and effective diameter of the ice particles. We find that those clouds, which are more affected by aviation induced aerosol emission, are characterized by larger values of the particle linear depolarization ratio. These aviation-affected cirrus clouds exhibit larger mean effective ice particle diameters connected to decreased ice particle number concentrations, than the cirrus clouds, which evolved in more pristine regions. With this study, we provide new observations of aerosol-cloud interactions, that will help to quantify related changes in the atmospheric energy budget.
Silke Groß et al.
Status: final response (author comments only)
RC1: 'Comment on acp-2022-721', Anonymous Referee #1, 14 Nov 2022
- AC1: 'Reply on RC1', Silke Gross, 19 Mar 2023
RC2: 'Comment on acp-2022-721', Anonymous Referee #2, 30 Nov 2022
- AC2: 'Reply on RC2', Silke Gross, 19 Mar 2023
Silke Groß et al.
Silke Groß et al.
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The authors use a data set of airborne lidar and in-situ measurements to study the effect of aviation on the optical and microphysical properties of natural cirrus clouds. In an earlier study by some of the same authors, lidar measurements of the particle linear depolarization ratio (PLDR) were used together with backward trajectories to identify cirrus clouds that likely formed in regions of high and low air-traffic density. The present work follows up on the previous study by adding the analysis of coinciding in-situ measurements of the ice crystal size distribution and the ice crystal number concentration (ICNC) related to the two PLDR modes to the investigation of an indirect aviation effect on mid-latitude cirrus clouds. The authors conclude that cirrus clouds that are affected by aviation as indicated by higher values of PLDR also show larger effective ice crystal radii and lower ICNC compared to unperturbed, low-PLDR cirrus.
The authors address an interesting topic that is certainly relevant to the readers of ACP. They have a unique set of airborne observations at their disposal. However, the study itself as well as the presentation of the results need considerable improvement before they can be accepted for publication in ACP. Below is a list of major and minor comments to the authors.