A numerical study of orographic forcing on TC Dina (2002) in South West Indian Ocean

Abstract

Abstract. Using the French non-hydrostatic mesoscale numerical model Méso-NH, intense tropical cyclone (TC) Dina (2002) is simulated to investigate the forcing caused by the steep orography of Réunion island (20.8 • S, 55.5 • E) in the southwest Indian Ocean. The model initialised by a bogus vortex derived from Doppler radar observations reproduces quite well the dynamical characteristics of TC Dina approaching the island and provides some clues on the orographic influence on the structure and the evolution of the TC.The presence of the island is observed to stabilise the cyclonic circulation by damping the natural elliptical eyewall rotation and forcing the flow circulation. Initially, the cyclonic flow is blocked upwind of the orography which induces a convergence associated with upward vertical velocities, intense precipitation and maximum horizontal winds along the upwind slopes of the island. A mountain wave, generated over the highest terrains, is associated with downward motions on the lee side. When the strongest winds reach the island, the flow changes its behaviour from passing around to over the island. Non-dimensional flow parameters in agreement with recent theories are calculated to explain TC track.

The isotopic composition of near‐surface water vapor at the Maïdo observatory (Reunion Island, southwestern Indian Ocean) documents the controls of the humidity of the subtropical troposphere

“…Several MESO‐NH simulations have been successfully performed over Reunion Island at different resolutions to study cyclone formation or pollutant transport [ Tulet and Villeneuve , ; Lesouëf et al ., , ; Jolivet et al ., ; Durand et al ., ; Sivia et al ., ; Vérèmes et al ., ]. The model was set up with four two‐way nested domains having horizontal grid spacing of 16, 8, 2, and 0.5 km and grid size of 200 × 200, 128 × 128, 128 × 128, and 192 × 160 points, respectively.…”

“…Several MESO-NH simulations have been successfully performed over Reunion Island at different resolutions to study cyclone formation or pollutant transport [Tulet and Villeneuve, 2011;Lesouëf et al, 2011Lesouëf et al, , 2013Jolivet et al, 2013;Durand et al, 2014;Sivia et al, 2015;Vérèmes et al, 2016] First, we will use the FLEXPART (FLEXible PARTicle dispersion model) Lagrangian particle dispersion model to assess air masses origin and transport pathways. We will focus on May 2015 to take advantage of the Maïdo ObservatoRy Gaz and Aerosols Ndacc Experiment (MORGANE) field campaign that started in May [Duflot et al, 2017].…”

A New Coupled Ocean‐Waves‐Atmosphere Model Designed for Tropical Storm Studies: Example of Tropical Cyclone Bejisa (2013–2014) in the South‐West Indian Ocean

“…It is a nonhydrostatic anelastic model, able to simulate the motion of the atmosphere, at scales ranging from synoptic (hundreds of kilometers) to microscale (tens of meters). Meso-NH has already been successfully used to simulate storms and tropical cyclones (Barthe et al, 2016;Chane-Ming et al, 2014;Jolivet et al, 2013;Nuissier et al, 2005;Pantillon et al, 2013Pantillon et al, , 2015Pantillon et al, , 2016.…”

Observation and a numerical study of gravity waves during tropical cyclone Ivan (2008)

“…In previous studies, the model proved to be useful for the simulation of cyclones' development. Nuissier et al (2005) Roux et al (2004), was numerically examined in Jolivet et al (2013). In particular, PV estimates revealed that buoyancy waves were generated on the lee side of the island's peak (3070 m) when peripheral cyclonic flow of the TC impacted on the island.…”