A140-07
Evidence of in situ cirrus formation in the Tropical Tropopause Layer over the Southwestern Indian Ocean

Monday, 14 December 2020: 04:24
Virtual
Stephanie Evan1,2, Irene Reinares Martinez2, Frank Wienhold3, Jerome F Brioude2, Damien Héron4, Bert Verreyken4, Susanne Korner5, Holger Voemel6, Jean-Marc Metzger4 and Françoise Posny7, (1)CNRS, Paris Cedex 16, France, (2)CNRS / Université de La Réunion / Météo-France, Laboratoire de l'Atmosphere et des Cyclones (LACy), Saint-Denis, Reunion, (3)Swiss Federal Institute of Technology, Zurich, Switzerland, (4)Université de La Réunion, Météo-France, Laboratoire de l'Atmosphere et des Cyclones (LACy), Saint-Denis, Reunion, (5)Deutscher Wetterdienst, Meteorological Observatory Lindenberg, 15848 Lindenberg, Germany;, Lindenberg, Germany, (6)National Center for Atmospheric Research, Earth Observing Laboratory, Boulder, CO, United States, (7)Laboratoire de l'Atmosphère et des Cyclones, UMR8105, Université, Météo‐France, CNRS, La Réunion, France
Recorded Presentation
Abstract:
A nascent cirrus is observed in the tropical tropopause layer (TTL) over the southwestern Indian Ocean using data from a balloon launched from Reunion Island on 11th January 2019 during the field campaign of the CONCIRTO program. The balloon is equipped with COBALD (Compact Optical Backscatter and AerosoL Detector) and CFH (Cryogenic Frost point Hygrometer) sondes.

COBALD retrievals show an increase in the backscatter measured between the ascent and the descent at 16.5 km altitude, the cold point height. Concomitant with the backscatter signal at the ascent, RHi retrieved from the CFH measurements reaches 150%, which indicates that the environment can support ice formation. Furthermore, the estimation of the ice crystals size from the measured backscatter indicate larger particles at the descent (2 μm) compared with the ascent (0.6 μm), suggesting the crystals growth. The analysis suggests that the cloud was observed just after ice nucleation, before the ice has had time to grow, which is quite rare.

According to the Lagrangian dispersion model FLEXPART (FLEXible PARTicle), the air mass sampled by the sondes had remained within the TTL over the southwestern Indian Ocean for the past few days, indicating that the cirrus formed in situ. Furthermore, the observed rise rate increase of 2 - 3 m/s just below the cold point at the ascent is consistent with a strong wave event, which would be very supportive for the high RHi. Wavelet analysis applied to the temperature anomaly and the ascent rate yields a vertical wavelength of 1.5 km. Such wave event can be related to nearby convection around Reunion Island.

<< Previous Abstract | Next Abstract >>