Addressing the sensitivity of forecast impact to flight path design for targeted observations of extratropical winter storms: A demonstration in anOSSEframework

Few studies have examined the forecast uncertainties brought about from varying aircraft flight track patterns in targeted observations for extratropical winter storms. To examine the degree of uncertainty in downstream forecasts caused by different aircraft flight patterns, a series of observing system simulation experiments (OSSEs) are performed and demonstrated for two extratropical winter storms identified in the European Centre for Medium-Range Weather Forecasts (ECMWF) T511 Nature Run using the National Centers for Environmental Prediction Global Data Assimilation System and Global Forecast System (Q1FY15). Winter storms were chosen to support operational Pacific Ocean targeting strategies using unmanned aircraft. For these two storms, objective and composite flight tracks are generated as they could occur in an operational field mission to sample sensitive areas and meteorologically important regions, and then the changes in downstream forecasts across the various flight tracks are evaluated. The forecast impact downstream is sensitive to flight track orientation and shows case-dependent results, with some flight patterns leading to significant improvements, while others result in neutral to degraded forecasts. The degree of downstream uncertainty in the verification region can vary up to 8% from the different flight paths, depending on the metric used and the atmospheric variables analysed. Although the study is a demonstration of the technique and is limited to only two case studies, it suggests that uncertainty in flight path design should not be neglected in future field missions. Some guidance for mitigating this uncertainty is also discussed.