Research Article Using Adjoint-Based Forecast Sensitivity Method to Evaluate TAMDAR Data Impacts on Regional Forecasts Xiaoyan Zhang, 1,2 Hongli Wang, 3 Xiang-Yu Huang, 1,4 Feng Gao, 1 and Neil A. Jacobs 5 1 National Center for Atmospheric Research, Boulder, CO 80301, USA 2 Earth System Science Interdisciplinary Center (ESSIC), University of Maryland, College Park, MD 20740, USA 3 Cooperative Institutes for Research in the Atmosphere (CIRA), Colorado State University, Fort Collins, CO 80523, USA 4 Centre for Climate Research Singapore, Meteorological Service Singapore, Singapore 5 Panasonic Avionics Corporation, Morrisville, NC 27560, USA Correspondence should be addressed to Xiaoyan Zhang; xyzucar@gmail.com Received 7 October 2014; Accepted 22 December 2014 Academic Editor: Guijun Han Copyright © Xiaoyan Zhang et al. his is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. his study evaluates the impact of Tropospheric Airborne Meteorological Data Reporting (TAMDAR) observations on regional 24-hour forecast error reduction over the Continental United States (CONUS) domain using adjoint-based forecast sensitivity to observation (FSO) method as the diagnostic tool. he relative impact of TAMDAR observations on reducing the forecast error was assessed by conducting the WRFDA FSO experiments for two two-week-long periods, one in January and one in June 2010. hese experiments assimilated operational TAMDAR data and other conventional observations, as well as GPS refractivity (GPSREF). FSO results show that rawinsonde soundings (SOUND) and TAMDAR exhibit the largest observation impact on 24 h WRF forecast, followed by GeoAMV, aviation routine weather reports (METAR), GPSREF, and synoptic observations (SYNOP). At 0000 and 1200 UTC, TAMDAR has an equivalent impact to SOUND in reducing the 24-hour forecast error. However, at 1800 UTC, TAMDAR has a distinct advantage over SOUND, which has the sparse observation report at these times. In addition, TAMDAR humidity observations at lower levels of the atmosphere (700 and 850 hPa) have a signiicant impact on 24 h forecast error reductions. TAMDAR and SOUND observations present a qualitatively similar observation impact between FSO and Observation System Experiments (OSEs). 1. Introduction Tropospheric Airborne Meteorological Data Reporting (TAMDAR), developed by AirDat (AirDat was acquired by Panasonic Avionics Corporation in 2013), has been providing a continuous operational stream of real-time observations from regional commercial airlines since December 2004. hese observations include temperature, winds, water vapor, pressure, icing, and turbulence. Aircrat equipped with TAMDAR typically ly regional routes and cruise at altitudes generally below 25000 t [1], providing coverage over North America, including Alaska and Mexico, as well as Hawaii, Caribbean, and Europe. TAMDAR was designed to ill in the spatial data voids of traditional Aircrat Meteorological Data Relay (AMDAR) lights, which tend to ly higher altitude routes into major airport hubs with only a small number of planes collecting water vapor, as well as the spatial and temporal data voids of radiosondes, which are launched every 12 h from limited locations. he current TAMDAR-equipped leets make more than 1800 daily lights, providing roughly 3600 radiosonde-like proiles during the ascent and descent phase of light at various regional and major airports across North America and Europe. he time-based horizontal resolution in cruise is 3 min, and the pressure-based vertical resolution during ascent and descent is 10 hPa. he data are transmitted via satellite to a ground-based operation center for quality con- trol and are available for assimilation within 15 s of sampling [1]. hese observations are rapidly becoming a major source of critical data utilized by various assimilation systems for the improvement of mesoscale numerical weather prediction (NWP) and the overall safety of aviation for the future [2]. Hindawi Publishing Corporation Advances in Meteorology Article ID 427616