Christelle Barthe

Ensemble Simulation of the Lightning Flash Variability in a 3D Cloud Model with Parameterizations of Cloud Electrification and Lightning Flashes

Abstract A series of ensemble simulations were performed to study the statistics of flash characteristics produced by an electrification and lightning scheme in the cloud-resolving model Meso-NH. Here, the electrical variability of two storms—one supercellular and one multicellular—results from a random triggering location of the flashes and from a branching algorithm that describes the flash path. The study shows that the electrical model is able to generate several estimates of the total flash number for an identical evolution of the dynamics and microphysics of each storm in the 120 ensemble members. The variability of the flash number spans over three standard deviations taken from the ensemble mean. The simulations produce regularly shaped distributions of flash internal parameters (i.e., number of segments and branching levels per flash). The ensemble simulation shows that the model is stable and self-regulatory as suggested by the limited overshoot on the maximum electric field time series. An appl...

Regionalizing rainfall at very high resolution over La Réunion island: a case study for Tropical Cyclone Ando.

Ensemble simulations of Tropical Cyclone (TC) Ando (31 December 2000–9 January 2001) are performed over the southwest Indian Ocean using the nonhydrostatic WRF Model. Nested domains centered over the island of La Reunion allow for the simulation of local rainfall amounts associated with TC Ando at very high resolution (680-m grid spacing). The model is forced by and nudged toward ERA-Interim during the first (1–6) day(s) of the TC’s life cycle. The nudging ends at various dates to constrain either the whole life cycle or only parts of it. As expected, results show weakened member dispersion, as the relaxation lasts longer, with more members producing similar cyclone tracks and intensities. The model shows reasonable skill to simulate local rainfall amounts and distribution, as soon as the simulated TC approaches La Reunion with a realistic distance and azimuth. Strong lower-level wind associated with the TC is forced to ascend over the slopes of the island. The model is able to successfully simulate the extreme daily precipitation amounts (>1200 mm) and their distribution over the highest parts of La Reunion. Nevertheless, smaller-scale features of the rainfall field are less realistic in the simulations. The wind speed and direction upstream of the island are the main drivers of such local uncertainties and errors, and they appear as an important issue to assess the local impacts of the TC over such a complex terrain.