Search

Tropical cyclones (TCs) are complex sources of atmospheric gravity waves (GWs). In this study, the Weather Research and Forecasting Model was used to model TC Soudelor (2015) and the induced elliptical structures of GWs in the upper troposphere (UT) and lower stratosphere (LS) prior to its landfall over Taiwan. Conventional, spectral and wavelet analyses exhibit dominant GWs with horizontal and vertical wavelengths, and periods of 16&ndash, 700 km, 1.5&ndash, 5 km, and 1&ndash, 20 h, respectively. The wave number one (WN1) wind asymmetry generated mesoscale inertia GWs with dominant horizontal wavelengths of 100&ndash, 300 km, vertical wavelengths of 1.5&ndash, 2.5 km (3.5 km) and westward (eastward) propagation at the rear of the TC in the UT (LS). It was also revealed to be an active source of GWs. The two warm anomalies of the TC core induced two quasi-diurnal GWs and an intermediate GW mode with a 10-h period. The time evolution of dominant periods could be indicative of changes in TC dynamics. The FormoSat-3/COSMIC (Formosa Satellite Mission-3/Constellation Observing System for Meteorology, Ionosphere, and Climate) dataset confirmed the presence of GWs with dominant vertical wavelengths of about 3.5 km in the UT and LS.

Ce travail de thèse porte sur l'étude de l'interaction entre l'île et le cyclone DINA qui avait bénéficié pour la première fois d'une couverture radar Doppler lors de son passage en Janvier 2002. Des simulations hautes résolutions ont été menées avec le modèle Méso-NH. Il a été montré que la présence de l'île induit une tendance générale à la stabilisation de la circulation cyclonique naturelle en relation avec un affaiblissement du système. Il a aussi été montré que la circulation des vents et la localisation des précipitations sur l'île en cas cyclonique sont entièrement définies par la topographie. De plus une étude approfondie a montré que l'évolution de la structure du mur de l'oeil en interaction avec le relief découlait de perturbations de l'anneau cyclonique de PV par des bandes de PV anticyclonique générées par l'île.; no abstract

International audience; Communication about The effect of La Réunion island (Indian ocean) on tropical cyclone Dina (2002): a comparative numerical study

Polarimetry improves radar rainfall estimation. It allows a better separation of meteorological and nonmeteorological echoes, a better identification of the type of hydrometeors, and an improved correction of the attenuation due to rain affecting the signal of weather radars working at C- and X-band. The attenuation correction is based on the near-linearity between the specific attenuation at horizontal(vertical) polarization and the specific differential phase shift (on propagation) Kdp. The coefficients of this relationship as well as those of the power law assumed between the specific attenuation and the radar reflectivity depend on the DSD and the dominant microphysical processes. Because raindrop size distribution (DSD) measurements are not available everywhere and all the time, it is difficult to accurately estimate these coefficients. In addition, phase measurements are noisy and can be affected by significant uncertainties, as well as Kdp. Finally, the radar calibration is also important in the process of attenuation correction. In order to investigate and quantify the sensitivity of the classical attenuation correction algorithms to the different parameters involved, a simulation experiment has been conducted. It is based on realistic simulated DSD fields from which all the necessary variables can be derived. The most commonly used algorithms for attenuation correction (namely ZPhi and the self-consistent -SC- version of it) are applied and the obtained corrected reflectivities are compared to the true ones. Uncertainty is added to the main parameters/variables and the respective sensitivities can be quantified. It is shown that ZPhi performs better than SC as long as the parameters are within 30% of their true values. Such accuracy is not easily achievable for all parameters and SC should be preferred if large uncertainties are expected.