QBO-ENSO Connections and Influence on the Tropical Cold Point Tropopause

We have used both high vertical-resolution and conventional radiosonde data to investigate two aspects of the quasi-biennial oscillation in the equatorial lower stratosphere. Taguchi (2010) used monthly mean wind information from three radiosonde stations in the Western Pacific region to show that QBO periods are generally shorter during El Nino than during La Nina conditions and that QBO amplitudes are generally greater during La Nina conditions. We show that these results are valid for all longitudes in equatorial regions. We also show that QBO modulations of the cold-point-tropopause, on the average, are greater during La Nina conditions, although this result is variable for different stations at different latitudes and longitudes. We believe that this variability is likely due to local influences of convection significantly affecting the cold-point tropopause. Our strategy for investigating both of these aspects of ENSO influences on the QBO was to show that spline-fitting of conventional radiosonde observations gave similar results for both ENSO and QBO variations of winds and temperatures to those derived using high vertical-resolution radiosonde data over a nine year period (as suggested by the results of Bell and Geller, 2008), but that this was too short a period to properly separate ENSO from QBO effects. Given that these similar results were obtained using spline-fits to conventional radiosonde data to those obtained using high vertical-resolution radiosonde data, we then analyzed much longer time series of conventional radiosonde data for several stations, where such data were available over several decades. References Bell, S. W., and M. A. Geller (2008), Tropopause inversion layer: Seasonal and latitudinal variations and representation in standard radiosonde data and global models, J. Geophys. Res., 113, D05109, doi:10.1029/2007JD009022. Taguchi, M. (2010), Observed connection of the stratospheric quasi-biennial oscillation with El Niño-Southern Oscillation in radiosonde data, J. Geophys. Res., 115, D18120, doi:10.1029/2010JD014325.