EGU24-4453, updated on 08 Mar 2024
https://doi.org/10.5194/egusphere-egu24-4453
EGU General Assembly 2024
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

How do wind shear and gravity waves affect the evolution of optically thin cirrus in the tropical tropopause layer?

Eric Jensen1, Rei Ueyama2, and Leonhard Pfister2
Eric Jensen et al.
  • 1Cooperative Institute for Environmental Research, Boulder, United States of America
  • 2NASA Ames Research Center

Past investigations have shown that gravity waves can affect both when/where cirrus form in the Tropical Tropopause Layer (TTL) and the ice concentrations produced by homogeneous freezing nucleation.  Here, we use high-resolution two-dimensional simulations to investigate the impacts of wind shear and gravity waves on TTL cirrus evolution after the nucleation stage is complete.  We use a bin microphysics model to simulate the physical processes of ice crystal growth/sublimation, advection, and sedimentation.  Gravity wave temperature and wind perturbations are calculated using a Fourier series of wave frequencies with periods ranging from 1 day to near the Brunt Vaisala period, with amplitudes based on aircraft and superpressure balloon measurements.  The simulations are initialized based on high-altitude aircraft measurements of a case just after a homogeneous-freezing ice nucleation event has produced numerous small crystals in a supersaturated environment.  We show that wind shear alone rapidly alters the structure of the cloud, and strong shear can significantly reduce the cloud lifetime.  High-frequency gravity wave temperature oscillations accelerate the reduction of ice concentration as the cloud evolves.  Gravity waves can temporarily increase or decrease cloud optical depth (depending on the initial wave temperature tendencies), but the overall lifetime of the cloud is reduced by the waves.  We will further discuss the relative importance of different wave frequencies on the evolution of TTL cirrus.

How to cite: Jensen, E., Ueyama, R., and Pfister, L.: How do wind shear and gravity waves affect the evolution of optically thin cirrus in the tropical tropopause layer?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4453, https://doi.org/10.5194/egusphere-egu24-4453, 2024.