Aircraft measurements and numerical simulations of gravity waves in the extratropical UTLS region during the START08 field campaign

Gravity waves are one of the key dynamical processes contributing to the structure and composition of the extratropical upper tropospheric and low-stratospheric (UTLS) region. One of the primary objectives of the START08 (Stratosphere-Troposphere Analyses of Regional Transport Experiment 2008) field experiment is to characterize the source and impacts of these waves with high-resolution aircraft measurements and mesoscale models.

Preliminary analyses have been conducted to examine the GV aircraft (HIAPER) flight-level observations to extract gravity wave information and to explore the spectral distributions of different variables in the lower stratosphere during the START08 mission. We have analyzed one of the research mission flights, RF02, which was dedicated to probing gravity waves associated with strong upper-tropospheric jet-front systems. There are clear signals of significant waves with wavelengths ranging from 10 to 300 km present in almost every leg of the 8-hr flight sampled by the aircraft, mostly in the lower stratosphere. Strong variations of the wave signals are observed over a wide range of background flow conditions covered by this flight including near-jet core, jet over the high mountains and the exist region of the jet. The mesoscale component of the gravity waves measured had some qualitative similarity to those predicted by a realtime mesoscale forecast model with horizontal grid spacing of 15 km and a cloud-resolving hindcast simulation. We will be examining how well does the current generation of mesoscale models predicts the excitation and characteristics of the gravity waves, and how they contribute to understanding the dynamics and impacts of these waves in the UTLS region.