Model study of intermediate-scale tropical inertia gravity waves and comparison to TWP-ICE campaign observations

A 2-day inertia gravity wave (IGW) was observed in high-resolution radiosonde soundings of horizontal wind and temperature taken during the TWP-ICE experiment in Darwin area. The wave presented vertical and horizontal wavelengths of around 6 km and 7220 km respectively. The wave was observed to propagate southeastward during the end of the easterly phase of the QBO. The total vertical momentum flux associated with the wave is estimated to be 1 to 2.2x10^-3 m2 s-2. This is of the same order of magnitude as previous observations of 4-10 day Kelvin waves in the lower stratosphere.

A comparison between the characteristics of the IGW derived with the ECMWF analyses to the properties of the wave derived with the radiosonde data shows that the ECMWF model captures similar structure for this 2-day wave event.

The Advanced Research Weather Research and Forecasting (WRF) modeling system is used to study the wave generation mechanisms and propagation dynamics. The model domain configured as a tropical channel encompasses the evolution of the 2-day IGW. The ECMWF analyses provide the north/south boundaries and initial conditions. The model is run from January 18 to February 12 2006 to cover the wave lifecycle. To minimize wave reflection effects the model top is placed at 1hPa with a 15km damping layer depth. Different simulations have been performed to determine the sensitivity of the wave structure to increased vertical resolution, cumulus schemes and initial conditions. The main focus of this study is to address WRF ability to resolve the 2-day tropical IGW in the stratosphere. The wave characteristics inferred from WRF simulations will be presented, including the generation, propagation and morphology. In addition model results will be compared to ECMWF analyses and MERRA reanalyses.