Evidence of in Situ Cirrus Formation in the Tropical Tropopause Layer over the Southwestern Indian Ocean
- 1LACy, Laboratoire de l’Atmosphère et des Cyclones, UMR8105, CNRS, Université de La Réunion, Météo-France, Saint-Denis, La Réunion, France
- 2Institute for Atmospheric and Climate Science, ETH, Zurich, Switzerland
- 3National Center for Atmospheric Research, Boulder, Colorado, USA
- 4Chemical Sciences Laboratory, NOAA Earth System Research Laboratory, Boulder, Colorado, USA
- 5Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, Colorado, USA
- 6Royal Belgian Institute for Space Aeronomy, Ringlaan 3, 1180 Brussels, Belgium
- 7Department of Chemistry, Ghent University, Krijgslaan 281-S3, 9000 Ghent, Belgium
- 8Deutscher Wetterdienst, Meteorological Observatory Lindenberg, 15848 Lindenberg, Germany
- 10Observatoire des Sciences de l’Univers de La Réunion, UMS3365, CNRS, Université de La Réunion, Météo-France, Saint-Denis, La Réunion, France
A nascent in situ cirrus was observed on 11 January 2019 in the tropical tropopause layer (TTL) over the southwestern Indian Ocean, with the use of balloon-borne instruments. Data from CFH (Cryogenic Frost Point Hygrometer) and COBALD (Compact Optical Backscatter and AerosoL Detector) instruments were used to characterize the cirrus and its environment. Optical modeling was employed to estimate the cirrus microphysical
properties from the COBALD backscatter measurements. Newly-formed ice crystals with radius <1 μm and concentration ∼500 L −1 were reported at the tropopause. The relatively low concentration and CFH ice supersaturation (1.5) suggests a homogeneous freezing event stalled by a high-frequency gravity wave. The observed vertical wind speed and temperature anomalies that triggered the cirrus formation were due to a 1.5-km vertical-
scale wave, as shown by a spectral analysis. This cirrus observation shortly after nucleation is beyond remote sensing capabilities and presents a type of cirrus never reported before.
How to cite: Evan, S., Reinares Martinez, I., Wienhold, F. G., Brioude, J., Jensen, E. J., Thornberry, T. D., Heron, D., Verreyken, B., Korner, S., Vomel, H., Metzger, J.-M., and Posny, F.: Evidence of in Situ Cirrus Formation in the Tropical Tropopause Layer over the Southwestern Indian Ocean , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14156, https://doi.org/10.5194/egusphere-egu21-14156, 2021.
