A comparison of Loon balloon observations and stratospheric

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TitleA comparison of Loon balloon observations and stratospheric reanalysis productsAbstractLocation information from long-duration super-pressure balloons flying in the Southern Hemisphere lower stratosphere during 2014 as part of X Project Loon are used to assess the quality of a number of different reanalyses including National Centers for Environmental Prediction Climate Forecast System version 2 (NCEP-CFSv2), European Centre for Medium-Range Weather Forecasts (ERA-Interim), NASA Modern Era Retrospective-Analysis for Research and Applications (MERRA), and the recently released MERRA version 2. Balloon GPS location information is used to derive wind speeds which are then compared with values from the reanalyses interpolated to the balloon times and locations. All reanalysis data sets accurately describe the winds, with biases in zonal winds of less than 0.37 ms-1 and meridional biases of less than 0.08 ms-1. The standard deviation on the differences between Loon and reanalyses zonal winds is latitude-dependent, ranging between 2.5 and 3.5 ms-1, increasing equatorward. Comparisons between Loon trajectories and those calculated by applying a trajectory model to reanalysis wind fields show that MERRA-2 wind fields result in the most accurate simulated trajectories with a mean 5-day balloon-reanalysis trajectory separation of 621 km and median separation of 324 km showing significant improvements over MERRA version 1 and slightly outperforming ERA-Interim. The latitudinal structure of the trajectory statistics for all reanalyses displays marginally lower mean separations between 15 and 35 deg S than between 35 and 55 deg S, despite standard deviations in the wind differences increasing toward the equator. This is shown to be related to the distance travelled by the balloon playing a role in the separation statistics. Copyright Author(s) 2017.AcknowledgementsThe work discussed would have been impossible without support from the New Zealand Antarctic Research Institute (NZARI). We also thank the X Project Loon team for the generous supply of the Loon data. We also acknowledge the NCEP reanalysis data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from their website (http://www.esrl.noaa.gov/psd/), the ERA-Interim product provided courtesy of ECMWF (http://apps.ecmwf.int) and the Global Modeling and Assimilation Office (GMAO) and the GES DISC for the dissemination of the MERRA and MERRA-2 products. The author team would like to thank the anonymous reviewers for their valuable input.Funding DetailsNOAA, National Oceanic and Atmospheric Administration; Office of AIDS Research

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1st AuthorFriedrich, L.AuthorFriedrich, L.McDonald, A.Bodeker, G.Cooper, K.Lewis, J.Paterson, A.Year2017JournalAtmospheric Chemistry and PhysicsVolume17Number2Pages855-866DOI10.5194/acp-17-855-2017URLhttps://www.scopus.com/inward/recor.....c3c13b9edb5babd6f5d6247e9Keywordsrank5

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TypeArticleCitationFriedrich, L., McDonald, A., Bodeker, G., Cooper, K., Lewis, J. and Paterson, A. (2017). A comparison of Loon balloon observations and stratospheric reanalysis products. Atmospheric Chemistry and Physics, 17(2): 855-866 IdentifierFriedrich2017Relevancerank5Antarctica NZ supported?YesNZARI?Yes