author_facet Spichtinger, P.
Krämer, M.
Spichtinger, P.
Krämer, M.
author Spichtinger, P.
Krämer, M.
spellingShingle Spichtinger, P.
Krämer, M.
Atmospheric Chemistry and Physics
Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers
Atmospheric Science
author_sort spichtinger, p.
spelling Spichtinger, P. Krämer, M. 1680-7324 Copernicus GmbH Atmospheric Science http://dx.doi.org/10.5194/acp-13-9801-2013 <jats:p>Abstract. The occurrence of high, persistent ice supersaturation inside and outside cold cirrus in the tropical tropopause layer (TTL) remains an enigma that is intensely debated as the "ice supersaturation puzzle". However, it was recently confirmed that observed supersaturations are consistent with very low ice crystal concentrations, which is incompatible with the idea that homogeneous freezing is the major method of ice formation in the TTL. Thus, the tropical tropopause "ice supersaturation puzzle" has become an "ice nucleation puzzle". To explain the low ice crystal concentrations, a number of mainly heterogeneous freezing methods have been proposed. Here, we reproduce in situ measurements of frequencies of occurrence of ice crystal concentrations by extensive model simulations, driven by the special dynamic conditions in the TTL, namely the superposition of slow large-scale updraughts with high-frequency short waves. From the simulations, it follows that the full range of observed ice crystal concentrations can be explained when the model results are composed from scenarios with consecutive heterogeneous and homogeneous ice formation and scenarios with pure homogeneous ice formation occurring in very slow (&lt; 1 cm s−1) and faster (&gt; 1 cm s−1) large-scale updraughts, respectively. This statistical analysis shows that about 80% of TTL cirrus can be explained by "classical" homogeneous ice nucleation, while the remaining 20% stem from heterogeneous and homogeneous freezing occurring within the same environment. The mechanism limiting ice crystal production via homogeneous freezing in an environment full of gravity waves is the shortness of the gravity waves, which stalls freezing events before a higher ice crystal concentration can be formed. </jats:p> Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers Atmospheric Chemistry and Physics
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title Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers
title_unstemmed Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers
title_full Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers
title_fullStr Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers
title_full_unstemmed Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers
title_short Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers
title_sort tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers
topic Atmospheric Science
url http://dx.doi.org/10.5194/acp-13-9801-2013
publishDate 2013
physical 9801-9818
description <jats:p>Abstract. The occurrence of high, persistent ice supersaturation inside and outside cold cirrus in the tropical tropopause layer (TTL) remains an enigma that is intensely debated as the "ice supersaturation puzzle". However, it was recently confirmed that observed supersaturations are consistent with very low ice crystal concentrations, which is incompatible with the idea that homogeneous freezing is the major method of ice formation in the TTL. Thus, the tropical tropopause "ice supersaturation puzzle" has become an "ice nucleation puzzle". To explain the low ice crystal concentrations, a number of mainly heterogeneous freezing methods have been proposed. Here, we reproduce in situ measurements of frequencies of occurrence of ice crystal concentrations by extensive model simulations, driven by the special dynamic conditions in the TTL, namely the superposition of slow large-scale updraughts with high-frequency short waves. From the simulations, it follows that the full range of observed ice crystal concentrations can be explained when the model results are composed from scenarios with consecutive heterogeneous and homogeneous ice formation and scenarios with pure homogeneous ice formation occurring in very slow (&lt; 1 cm s−1) and faster (&gt; 1 cm s−1) large-scale updraughts, respectively. This statistical analysis shows that about 80% of TTL cirrus can be explained by "classical" homogeneous ice nucleation, while the remaining 20% stem from heterogeneous and homogeneous freezing occurring within the same environment. The mechanism limiting ice crystal production via homogeneous freezing in an environment full of gravity waves is the shortness of the gravity waves, which stalls freezing events before a higher ice crystal concentration can be formed. </jats:p>
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author Spichtinger, P., Krämer, M.
author_facet Spichtinger, P., Krämer, M., Spichtinger, P., Krämer, M.
author_sort spichtinger, p.
container_issue 19
container_start_page 9801
container_title Atmospheric Chemistry and Physics
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description <jats:p>Abstract. The occurrence of high, persistent ice supersaturation inside and outside cold cirrus in the tropical tropopause layer (TTL) remains an enigma that is intensely debated as the "ice supersaturation puzzle". However, it was recently confirmed that observed supersaturations are consistent with very low ice crystal concentrations, which is incompatible with the idea that homogeneous freezing is the major method of ice formation in the TTL. Thus, the tropical tropopause "ice supersaturation puzzle" has become an "ice nucleation puzzle". To explain the low ice crystal concentrations, a number of mainly heterogeneous freezing methods have been proposed. Here, we reproduce in situ measurements of frequencies of occurrence of ice crystal concentrations by extensive model simulations, driven by the special dynamic conditions in the TTL, namely the superposition of slow large-scale updraughts with high-frequency short waves. From the simulations, it follows that the full range of observed ice crystal concentrations can be explained when the model results are composed from scenarios with consecutive heterogeneous and homogeneous ice formation and scenarios with pure homogeneous ice formation occurring in very slow (&lt; 1 cm s−1) and faster (&gt; 1 cm s−1) large-scale updraughts, respectively. This statistical analysis shows that about 80% of TTL cirrus can be explained by "classical" homogeneous ice nucleation, while the remaining 20% stem from heterogeneous and homogeneous freezing occurring within the same environment. The mechanism limiting ice crystal production via homogeneous freezing in an environment full of gravity waves is the shortness of the gravity waves, which stalls freezing events before a higher ice crystal concentration can be formed. </jats:p>
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spelling Spichtinger, P. Krämer, M. 1680-7324 Copernicus GmbH Atmospheric Science http://dx.doi.org/10.5194/acp-13-9801-2013 <jats:p>Abstract. The occurrence of high, persistent ice supersaturation inside and outside cold cirrus in the tropical tropopause layer (TTL) remains an enigma that is intensely debated as the "ice supersaturation puzzle". However, it was recently confirmed that observed supersaturations are consistent with very low ice crystal concentrations, which is incompatible with the idea that homogeneous freezing is the major method of ice formation in the TTL. Thus, the tropical tropopause "ice supersaturation puzzle" has become an "ice nucleation puzzle". To explain the low ice crystal concentrations, a number of mainly heterogeneous freezing methods have been proposed. Here, we reproduce in situ measurements of frequencies of occurrence of ice crystal concentrations by extensive model simulations, driven by the special dynamic conditions in the TTL, namely the superposition of slow large-scale updraughts with high-frequency short waves. From the simulations, it follows that the full range of observed ice crystal concentrations can be explained when the model results are composed from scenarios with consecutive heterogeneous and homogeneous ice formation and scenarios with pure homogeneous ice formation occurring in very slow (&lt; 1 cm s−1) and faster (&gt; 1 cm s−1) large-scale updraughts, respectively. This statistical analysis shows that about 80% of TTL cirrus can be explained by "classical" homogeneous ice nucleation, while the remaining 20% stem from heterogeneous and homogeneous freezing occurring within the same environment. The mechanism limiting ice crystal production via homogeneous freezing in an environment full of gravity waves is the shortness of the gravity waves, which stalls freezing events before a higher ice crystal concentration can be formed. </jats:p> Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers Atmospheric Chemistry and Physics
spellingShingle Spichtinger, P., Krämer, M., Atmospheric Chemistry and Physics, Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers, Atmospheric Science
title Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers
title_full Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers
title_fullStr Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers
title_full_unstemmed Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers
title_short Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers
title_sort tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers
title_unstemmed Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers
topic Atmospheric Science
url http://dx.doi.org/10.5194/acp-13-9801-2013