Data assimilation Team leader:  Sim Aberson (HRD) Team members: Kathryn Sellwood (UM/CIMAS) Sharanya Majumdar (UM/RSMAS) Brian Etherton (UNCC) Fuqing Zhang (PSU) Altug Aksoy (UM/CIMAS) Sundararaman Gopalakrishnan (HRD) Carlisle Thacker (PhOD) Mark Powell (HRD) Bachir Annane (UM/CIMAS) Shirley Murillo (HRD) Robert Rogers (HRD) Kevin Yeh (UM/CIMAS) Tom Hamill (ESRL) Jeff Whitaker (ESRL) John McGinley (ESRL) Nikki Prive (ESRL) Yuanfu Xie (ESRL) Objective: Improvement of tropical cyclone forecasts through improvement of initial conditions for numerical weather prediction models by: improving the assimilation of observations, especially core observations from aircraft, into numerical models providing improved data sets for other research projects. Methods: This will be accomplished by, in all available basins by: Testing various techniques for data assimilation (eg. LAPS, STMAS, 3DVAR, 4DVAR, EnKF) for convective-scale tropical cyclone core data assimilation.