New Tamdar Fleets and Their Impact On Rapid Update Cycle (ruc) Forecasts

Abstract

Commercial aircraft now provide more than 160,000 observations per day of wind and temperature aloft over North America. The general term for these data is AMDAR (Aircraft Meteorological Data Reports). These data have been shown to improve both short- and long-term weather forecasts, and have become increasingly important for regional and global numerical weather prediction (Moninger et al. 2003). Two shortfalls of the current AMDAR data set are the absence of data below 25,000 ft between major airline hubs and the almost complete absence of water vapor data at any altitude. To address these deficiencies, a sensor called TAMDAR (Tropospheric AMDAR) was developed by AirDat, LLC, under NASA sponsorship (Daniels et al. 2006). The sensor has been deployed on approximately 50 regional turboprop aircraft flying over the central United States. These turboprops are operated by Mesaba Airlines (doing business as “Northwest Airlink”). Recently, PenAir airlines in Alaska has also begun to provide TAMDAR data. These TAMDAR-equipped aircraft generally cruise at lower altitudes than traditional AMDAR jets, and into regional airports not serviced by AMDAR jets. Like the rest of the AMDAR fleet, TAMDAR measures winds and temperature. But unlike most of the rest of the fleet, TAMDAR also measures humidity, turbulence, and icing. ESRL’s Global Systems Division (GSD) has built an extensive system for evaluating the quality of TAMDAR and AMDAR data, and has applied this system for the three years that TAMDAR has been in operation. Our evaluation system relies primarily on the Rapid Update Cycle (RUC) numerical model and data assimilation system (Benjamin et al. 2004a,b, 2006a) over the contiguous U.S., and the NCEP GFS (Global Forecast System) model elsewhere. Mesaba flies within the RUC domain, and so we are able to evaluate improvements in RUC forecasts due to TAMDAR Mesaba data. We have reported on this impact in the past (Moninger, 2007a,b) and provide an update here. We had expected new TAMDAR fleets to be providing data in the CONUS by January 2008, but this has not occurred. However, PenAir has been reporting TAMDAR data for several months. PenAir flies in southwest Alaska, which is outside of the RUC domain. We therefore report here on the quality of PenAir data by comparing them with 3-h forecasts from the Global Forecast System (GFS).