Wave–mean flow interactions associated with the Holton–Tan effect (HTE), whereby the tropical quasi-biennial oscillation (QBO) modulates the Northern Hemisphere wintertime stratospheric polar vortex, are studied using the ERA-Interim dataset. Significant evidence of the HTE in isentropic coordinates is found, with a weaker and warmer polar vortex present when the lower-stratospheric QBO is in its easterly phase (QBOe). For the first time, the authors quantify the QBO modulation of wave propagation, wave–mean flow interaction, and wave decay/growth via a calculation of potential vorticity (PV)-based measures, the zonal-mean momentum budget, and up-/downgradient eddy PV fluxes. The effect of the tropospheric subtropical jet on QBO modulation of the wave activity is also investigated. In the subtropical-to-midlatitude lower stratosphere, QBOe is associated with an enhanced upward flux of wave activity, and corresponding wave convergence and wave growth, which leads to a stronger poleward zonal-mean meridional circulation and consequently a warmer polar region. In the middle stratosphere, QBOe is associated with increased poleward wave propagation, leading to enhanced wave convergence and in situ wave growth at high latitudes and contributing to the weaker polar vortex. In agreement with recent studies, the results suggest that the critical-line effect cannot fully account for these wave anomalies associated with the HTE. Instead, it is suggestive of a new, additional mechanism that hinges on the QBO-induced meridional circulation effect on the latitudinal positioning of the subtropical jet. Under QBOe, the QBO-induced meridional circulation causes a poleward shift of the subtropical jet, encouraging more waves to propagate into the stratosphere at midlatitudes.
Photo: Photo: Leonardo Share this article Leonardo’s TH-119 single-engine helicopter, which is being pitched for the US Navy’s new helicopter trainer program, now benefits from the new Genesys Aerosystems avionics, the company has announced.The new avionics and cockpit allowing IFR operations is being integrated at Leonardo’s Philadelphia facility, home to the AW119 single engine final assembly line for the US and global market.The TH-119 is expected to perform its maiden flight in autumn and to achieve FAA certification in the 1Q2019.The TH-119 is a dedicated variant of the AW119 specifically designed for military training customers, primarily to meet the US Navy requirements.The US Navy is looking to acquire commercial aircraft to replace its TH-57 helicopter trainer currently in service. The service expects to procure 105 aircraft with acquisition starting in fiscal year 2020.The new TH-119 features distinctive capabilities and unique features differentiating it from the AW119 commercial helicopter while keeping certification advantages, the company says.“This event marks a major step forward in the integration of the all new avionics into the only IFR operations-capable single engine helicopter, as we get close to more extensive ground and flight testing activities towards FAA certification early next year,” William Hunt, CEO, AgustaWestland Philadelphia Corporation said. “I congratulate the whole team and partners for this achievement aimed at offering US naval aviators the best, most cost-effective US-made solution for their future basic and operational training.”The TH-119 maintains redundancies on several key systems for maximum safety, high power margin thanks to its popular and highly reliable Pratt & Whitney Canada PT6-B engine while featuring a Genesys Aerosystems cockpit that gives flexibility to instruct from either seat.Other contenders in the competition are Bell Helicopter with its 407GX single-engine helicopter and Airbus with a helicopter based on the commercial H135. View post tag: Leonardo View post tag: US Navy View post tag: helicopter training