Application of Mesoscale Ensemble-based Sensitivity Analysis to Observation Targeting
In order to determine whether real-time targeting techniques on small scales hold value for a forecast, a set of experiments will be presented for a specific case study to assess the impacts of non-linear relationships between initial conditions and the forecast metric, localization and inflation effects, and the binary nature of convective forecasts. The 4 April 2012 dryline-initiated convective outbreak over Northern Texas will be used to determine impacts that assimilated surface observations from the West Texas Mesonet (WTM) have on forecast error and to validate the usefulness of targeted observing on convective scales. Impacts are determined by running a control simulation that withholds WTM observations, determining which station would have the greatest impact on the forecast metric via variance reduction formulations, and then assimilating that station's surface observations into the model through the EnKF. Expected impacts and actual impacts can then be compared to determine if variance reduction can be accurately predicted under the various assumptions listed above. Lastly, the actual variance reduction from assimilated observations that predict large impacts to those that predict no impact are compared to establish the overall value sensitivity-based targeting might provide with regard to convective forecasts.