Mesoscale Data Assimilation and Prediction with Commercial Aircraft (TAMDAR) Observations Yubao Liu* 1 , Mark Anderson 2 , Scott Swerdlin 1 , Ming Ge 1 , Laurie Carson 1 , Wei Yu 1 and Tom Warner 1 1 National Center For Atmospheric Research, Boulder, Colorado 2 AirDat LLC, Evergreen, Colorado * Corresponding author address: Yubao Liu, NCAR/RAP, P.O. Box 3000, Boulder, CO 80307-3000; email: yliu@ucar.edu . NCAR is sponsored by NSF. 1. INTRODUCTION Mesoscale (10 - 2000 km) meteorological data assimilation and prediction are challenging due to the sparseness of observations, especially in the upper-air atmosphere. In the past 15 years, a number of instruments, e.g. wind profilers, commercial aircraft reports, satellite measurements, and others, have been developed to enhance the upper-air observations. Despite these advances, the present systems are still not sufficient for mesoscale data assimilation and prediction. In this paper, a new source of sensor data, called TAMDAR (Tropospheric Airborne Meteorological Data Reporting), is described. The impact of TAMDAR data on mesoscale weather analysis and short-term forecast are explored using the NCAR/ATEC (National Center for Atmospheric Research and Army Test and Evaluation Command) real-time multiscale, rapid- cycling, four-dimensional data assimilation and forecast (RTFDDA) system during the Great Lakes Field Experiments (GLFE) when the first TAMDAR fleet became operational. 2. TAMDAR DATA AND GLFE TAMDAR sensors, recently developed by AirDat LLC, which is sponsored by NASA, are specially designed to instrument smaller commercial aircrafts that fly in the lower troposphere over the CONUS and other parts of the world. These sensors provide a full suite of meteorological measurements, including temperature, winds, humidity, icing, turbulence, et al., with very high time/space density. The measurement precisions of the meteorological variables are comparable to those of standard radiosondes, with 0.5 C for temperature, 5% for relative humidity, 4 knots for wind speeds and 5 degrees for wind directions. More details about the TAMDAR and calibration results can be found in Daniels et al. (2005). Starting in late 2004, AirDat worked with Mesaba Airlines to equip and operate Mesaba Airlines' fleet of turboprop regional aircrafts with TAMDAR sensors. By mid-January 2005, with 63 Saab 340s equipped with TAMDAR, a six-month Great Lakes Fleet Experiment (GLFE) was launched by NASA, NOAA, FAA and AirDat, to demonstrate and evaluate the value of this pilot TAMDAR system (Moninger et al., 2005). The operational flights of the equipped Mesaba Saab 340 aircrafts provide about 800 soundings a day and ~20,000 meteorological reports. The GLFE experiment initially spun six months, from January 15 to July Fig. 1 Picture of the TAMDAR sensor developed by AirDat LLc 15, 2005. It has been extended through the