Regional Forecast Impacts from GEMS Observations

Technological advancements in MicroElectroMechanical Systems and nanotechnology have inspired a concept for a revolutionary observing system called Global Environmental Micro Sensors (GEMS). The system consists of in situ, buoyant airborne probes that can monitor all regions of the Earth's atmosphere with unprecedented spatial and temporal resolution. The probes will be designed to remain suspended in the atmosphere for days to weeks and take measurements of temperature, humidity, pressure, and wind velocity that are commonly used as dependent variables in numerical weather prediction (NWP) models. While GEMS will likely complement current and even next-generation in situ sensors and ground/space-based remote sensing platforms, the system has the capability to provide a 100-fold increase in the horizontal resolution of in situ synoptic observations especially in the planetary boundary layer. GEMS could provide observing capabilities spanning an extremely broad range of time and space scales from the detailed life cycle of individual clouds through planetary-scale weather.

A set of observing system simulation experiments (OSSEs) has been completed to assess the impact of assimilating GEMS observations on regional weather forecasts. The large-scale OSSEs are run for two 30-day periods in June and December 2001 over a northern hemispheric domain. A nested grid covering the continental U.S. and adjacent waters of the western (eastern) Atlantic (Pacific) Ocean is then used for intermittent data assimilation from day 10-20 of the hemispheric runs to mimic an operational cycle. The model used for the nature run is the Advanced Regional Prediction System (ARPS) coupled with a Lagrangian particle model to simulate dispersion and collection of observations from an ensemble of GEMS probes. The model used for the OSSEs is the Pennsylvania State University/National Center for Atmospheric Research Fifth-generation Mesoscale Model (MM5). Experiments show that the improvements of the primary predicted variables of temperature, dewpoint, and vector wind exceed 50%, in the mid and upper-troposphere, especially for short-range (0-12h) forecasts. A summary of the OSSE methodology, validation/calibration, forecast impact, and several key sensitivity tests will be presented