22 Jun 2021

22 Jun 2021

Review status: this preprint is currently under review for the journal ACP.

Contrail formation within cirrus: high-resolution simulations using ICON-LEM

Pooja Verma1,a and Ulrike Burkhardt1 Pooja Verma and Ulrike Burkhardt
  • 1Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany
  • aformerly at: Meteorologisches Institut, Ludwig-Maximilians-Universität, Munich, Germany

Abstract. Contrail formation within natural cirrus introduces large perturbations in cirrus ice crystal number concentrations leading to modifications in cirrus microphysical and optical properties. The number of contrail ice crystals formed in an aircraft plume depends on the atmospheric state and aircraft and fuel properties. Our aim is to study the impact of pre-existing cirrus on the contrail formation processes. We analyze contrail ice nucleation within cirrus and the survival of contrail ice crystals within the vortex phase and their change due to the presence of cirrus ice crystals within the high-resolution ICON-LEM at a horizontal resolution of 625 m over Germany.

We have selected two different synoptic situations sampling a large range of cirrus cloud properties from very thick cirrus connected with a frontal system to very thin cirrus within a high-pressure system. We find that contrail formation within cirrus often leads to increases in cirrus ice crystal numbers by a few orders of magnitude. Pre-existing cirrus has an impact on contrail ice crystal number concentrations only if the cirrus is optically thick. In thick cirrus, contrail ice nucleation rates and ice crystal survival rates within the vortex phase are both increased. The sublimation of the cirrus ice crystals sucked into and subsequently sublimated within the aircraft’s engine leads to an increase in the contrail formation threshold by up to 0.7 K which causes an increase in the number of nucleated contrail ice crystals. This increase can be large at lower flight levels where ambient temperatures are close to the contrail formation threshold temperature and when the ice water content of the pre-existing cirrus cloud is large. During the contrail’s vortex phase the aircraft plume is trapped within the descending vortices in which the decrease in plume relative humidity leads to the sublimation of contrail ice crystals. This contrail ice crystal loss can be modified by the cirrus ice crystals that are mixed into the plume before the start of the vortex phase. In particular, high ice crystal number concentrations and large ice water content of the pre-existing cirrus cloud or low contrail ice crystal numbers are associated with significant increases in the contrail ice crystal survival rates.

Pooja Verma and Ulrike Burkhardt

Status: open (until 17 Aug 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on acp-2021-497', Bernd Kärcher, 25 Jun 2021 reply
  • RC1: 'Comment on acp-2021-497', David Lewellen, 27 Jul 2021 reply

Pooja Verma and Ulrike Burkhardt

Data sets

Data_set_for_manuscript_contrail_formation_within_cirrus_Verma_Burkhardt_2021 Pooja Verma, Ulrike Burkhardt

Pooja Verma and Ulrike Burkhardt


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Short summary
This paper investigates contrail ice formation within cirrus and the impact of natural cirrus on the contrail formation in the high-resolution ICON-LEM over Germany. The formation of contrail ice crystals often leads to changes in cirrus ice crystal number concentrations of a few orders of magnitude. Contrail formation is affected by pre-existing cirrus leading to increased ice nucleation rates and larger ice crystal survival rate specifically in optically thick cirrus.