Intraseasonal to interannual variability of Kelvin wave momentum fluxes as derived from high-resolution radiosonde data
Jeremiah P. Sjoberg1,a, Thomas Birner1, and Richard H. Johnson11Department of Atmospheric Science, Colorado State University, Fort Collins, CO 80521 anow at: COSMIC Project Office, University Corporation for Atmospheric Research, Boulder, Colorado
Received: 02 Dec 2016 – Accepted for review: 09 Jan 2017 – Discussion started: 13 Jan 2017
Abstract. Observational estimates of Kelvin wave momentum fluxes in the tropical lower stratosphere remains challenging. Here we extend a method based on linear wave theory to estimate time series of these momentum fluxes from high-resolution radiosonde data. Testing the sensitivity to vertical resolution, our estimated momentum fluxes are found to be most sensitive to vertical resolution greater than 1 km, largely due to overestimation of the vertical wavelength. Estimates of momentum fluxes derived from reanalyses and coarse-resolution satellite data are notably larger. Daily time series are produced for sounding sites operated by the U.S. Department of Energy (DOE) and from the recent Dynamics of the Madden-Julian Oscillation (DYNAMO) field campaign. Our momentum flux estimates are found to be robust to different data sources and processing, and in quantitative agreement with estimates from prior studies. Climatological analysis is performed over the selected 11 year span of data from the ARM sites. Analyses for the available 11-year span of data reveal the expected seasonal cycle of momentum flux maxima in boreal winter and minima in boreal summer and variability associated with the quasi-biennial oscillation (QBO) of maxima during easterly phase and minima during westerly phase. Analysis of Madden-Julian Oscillation (MJO) active periods suggests that the MJO provides a nontrivial increase in lowermost stratospheric momentum fluxes, though statistical significance is not found due to the small number of events observed in the available time series.
Sjoberg, J. P., Birner, T., and Johnson, R. H.: Intraseasonal to interannual variability of Kelvin wave momentum fluxes as derived from high-resolution radiosonde data, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-1088, in review, 2017.