6.5
Vertically propagating stratospheric waves associated with the Madden-Julian Oscillation
George N. Kiladis, NOAA/ERL/AL, Boulder, CO; and K. A. Harris and G. C. Reid
Spectra of lower stratospheric temperature over the "warm pool " region of the equatorial western Pacific in radiosonde data exhibit strong spectral peaks at frequencies corresponding to periods of around 45-50 days. These fluctuations are also manifested in the height and temperature of the tropopause over that region. We show that these perturbations are associated with vertically propagating waves forced by the convective heating envelope of the Madden-Julian Oscillation (MJO) in the troposphere, which propagates eastward across the warm pool at around 5-10 m/s. These waves lead to temperature perturbations with downward phase propagation of large amplitude from around 50 hPa (20 km) down to around 250 hPa (11 km). Below that level phase propagation is upward, implying an upper tropospheric energy source region. The three dimensional structure of the waves is examined using NCEP and ECMWF reanalysis data. Radiosonde data are used as "reality check" anchor points to define the tropopause and stratospheric temperature signal. The association with the large scale diabatic heating signal is isolated by utilizing Outgoing Longwave Radiation (OLR) as a proxy for tropical convection. The maximum amplitudes of the stratospheric temperature and tropopause perturbations are not associated locally with the MJO convection, but lead it by several days, and propagate horizontally at a similar phase speed as the convective envelope. The propagation and three dimensional structure of the stratospheric and tropopause signals are consistent with the forcing of the planetary scale basic state by the slowly evolving convective field associated with the MJO.
Session 6, Continued
Thursday, 13 January 2000, 1:30 PM-3:15 PM
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