In the upper troposphere and lower stratosphere, temperature and vertical velocity (or equivalently cooling rates) fluctuations induced by gravity waves strongly affect chemical and microphysical processes, such as ice nucleation. To model those processes, it is therefore necessary to include realistic wave fluctuations. Yet, observing platforms generally provide Eulerian timeseries, while air parcels and particles undergo Lagrangian disturbances.

In this study, we analyze the spectral and statistical properties of Lagrangian fluctuations using measurements obtained during the Pre-Concordiasi and Concordiasi long-duration balloon flight campaigns, which took place in the tropics and southern high latitudes. With flight durations of several months and 1-minute sampling rates, these observations resolve the full (intrinsic-frequency) spectrum of gravity waves.

First, the characteristics of the observed kinetic and potential energy spectra are analyzed and contrasted between the two locations. The contribution of gravity waves to temperature and vertical-velocity variability is quantified in different frequency ranges and compared to that induced by synoptic-scale motions. We also present results on the distributions of temperature and cooling-rate perturbations. We show that these distributions have symmetric, yet non-gaussian shapes, which are associated with the intermittent nature of gravity waves. Last, we briefly illustrate the impact of gravity-wave fluctuations on Tropical Tropopause Layer cirrus nucleation, and discuss the ability of different wave parameterizations used in Lagrangian models to reproduce observed statistics.

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*email: aurelien.podglajen@lmd.polytechnique.fr
*Preference: Oral