24 Feb 2022
24 Feb 2022
Status: a revised version of this preprint is currently under review for the journal ACP.

The effect of ice supersaturation and thin cirrus on lapse rates in the upper troposphere

Klaus Gierens1, Lena Wilhelm1, Sina Hofer1, and Susanne Rohs2 Klaus Gierens et al.
  • 1Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany
  • 2Forschungszentrum Jülich, IEK-8, Jülich, Germany

Abstract. In this paper, the effects of ice-supersaturated regions and thin, subvisual cirrus clouds on lapse rates are examined. For that, probability distribution and density functions of ten years of measurement data from the MOZAIC/IAGOS project and ERA-5 reanalysis data were produced, and an analysis of an example case of an ice supersaturated region with a large vertical extent is performed. For the study of the probability distribution and density functions, a distinction is made between ice-subsaturated, ice-supersaturated air masses and so-called Big Hits, which are situations of particularly high ice-supersaturation that allow the formation of optically thick and strongly warming contrails. The distribution functions show much higher lapse rates, which correspond to almost neutral stratification, for ice-supersaturated regions and Big Hits than for subsaturated air masses. The highest lapse rates are found for Big Hit situations, because of the strong interaction between radiation and high ice-supersaturation.

For the examination of an example case, ERA-5 data and forecasts from ICON-EU (DWD) are compared. ERA-5 data, in particular, shows a large ice-supersaturated region below the tropopause, that was pushed up by uplifting air, while the data of ICON-EU indicates areas of saturation. The lapse rate in this ice-supersaturated region (ISSR), which is large, is associated with clouds and high relative humidity. Supersaturation and cloud formation result from uplifting of air layers. The temperature gradient within an uplifting layer steepens, both for dry and moist air, but for moist air there is an additional mechanism: it is the emission and absorption of radiation within the moist air: The upper part of this region emits longwave infrared radiation to space, while the bottom absorbs infrared radiation from lower and warmer layers, which consequently increases the lapse rate. This effect becomes even stronger, if ice crystals are involved (clouds).

Klaus Gierens et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-117', Philipp Reutter, 16 Mar 2022
    • AC2: 'Reply on RC1', Klaus Gierens, 25 May 2022
  • RC2: 'Comment on acp-2022-117', RUBEN RODRIGUEZ DE LEON, 25 Mar 2022
    • AC3: 'Reply on RC2', Klaus Gierens, 25 May 2022
  • AC1: 'Comment on acp-2022-117', Klaus Gierens, 25 May 2022

Klaus Gierens et al.

Klaus Gierens et al.


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Short summary
We are interested in the prediction of condensation trails, in particular strong ones. For this we need a good forecast of temperature and humidty in the levels where aircraft cruise. Unfortunately, the humidity forecast is quite difficult for these levels, in particular the ice supersaturation, that is needed for long-lasting contrails. We are thus seeking proxy variables that help distinguish situations where strong contrails can form, for instance the lapse rate.