The development of a vertical wind shear model for the lower stratosphere in support of the High Altitude Airship

We present results from an investigation of vertical wind shear in the vicinity of the lower stratosphere. The results of this study will contribute to the preliminary design of the High Altitude Airship (HAA). This large, unmanned airship is required to maintain station at up to 65,000 ft (~20 km) over a fixed point on the earth for up to a year as a military or commercial sensor and telecom platform. Because of weight and power limitations, flight control strategies have to rely on a combination of onboard propulsion and flight level adjustments designed to exploit speed and directional wind shear. Knowledge of the vertical wind shear environment will be critical in the design of trajectory optimization algorithms intended to minimize energy consumption and station keeping error. Statistics were compiled for speed and directional shear, for various vertical separation distances. Suitability of large- and mesoscale model and analysis datasets was evaluated by comparison with very high resolution radiosonde data. Results are presented in the form of several types of probability distribution function plots. The high vertical resolution radiosondes provide the most robust vertical wind shear statistics, while the global NWP data appear to suffer from a lack of vertical resolution. Wind shear statistics from a mesoscale model were directly compared with those from verifying radiosonde data.