BeCOOL: A Balloon-Borne Microlidar System Designed for Cirrus and Convective Overshoot Monitoring

A balloon-borne microlidar has been built at LATMOS to monitor cirrus optical properties and convective overshoot topography during long duration flights in the lower tropical stratosphere. Weighting less than 7 kg in a reduced volume and consuming less than 10 W, it will be involved in the CNES-Strateole2 campaign. This instrument paves the way to the use of microlidar technology for planetary missions.

Convective overshoot and macroscopic diffusion in pure-hydrogen-atmosphere white dwarfs

We present a theoretical description of macroscopic diffusion caused by convective overshoot in pure-hydrogen DA white dwarfs using 3D, closed-bottom, radiation hydrodynamics co5bold simulations. We rely on a new grid of deep 3D white dwarf models in the temperature range $11\, 400 \le T_{\mathrm{eff}} \le 18\, 000$ K where tracer particles and a tracer density are used to derive macroscopic diffusion coefficients driven by convective overshoot. These diffusion coefficients are compared to microscopic diffusion coefficients from 1D structures. We find that the mass of the fully mixed region is likely to increase by up to 2.5 orders of magnitude while inferred accretion rates increase by a more moderate order of magnitude. We present evidence that an increase in settling time of up to 2 orders of magnitude is to be expected, which is of significance for time-variability studies of polluted white dwarfs. Our grid also provides the most robust constraint on the onset of convective instabilities in DA white dwarfs to be in the effective temperature range from 18 000 to 18 250 K.

The Mean and Turbulent Properties of a Wildfire Convective Plume

The time-mean and time-varying smoke and velocity structure of a wildfire convective plume is examined using a high-resolution scanning Doppler lidar. The mean plume is shown to exhibit the archetypal form of a bent-over plume in a crosswind, matching the well-established Briggs plume-rise equation. The plume cross section is approximately Gaussian and the plume radius increases linearly with height, consistent with plume-rise theory. The Briggs plume-rise equation is subsequently inverted to estimate the mean fire-generated sensible heat flux, which is found to be 87 kW m−2. The mean radial velocity structure of the plume indicates flow convergence into the plume base and regions of both convective overshoot and sinking flow in the upper plume. The updraft speed in the lower plume is estimated to be 13.5 m s−1 by tracking the leading edge of a convective element ascending through the plume. The lidar data also reveal aspects of entrainment processes during the plume rise. For example, the covariation of the radial velocity and smoke perturbations are shown to dilute the smoke concentration with height.