QBO, ENSO, and Solar Cycle Effects in Short-Term Nonmigrating Tidal Variability on Planetary Wave Timescales From SABER-An Information-Theoretic Approach

摘要

Much progress has been made in delineating and understanding the "tidal climate" of the mesosphere and lower thermosphere, that is, tidal variability on seasonal or longer timescales. Short-term tidal variability on timescales of a few days is much less understood, mainly due to observational constraints imposed by satellite local solar time sampling. This paper presents a new approach to study the "tidal weather" in 16 years of SABER temperatures. Our focus is on the eastward-propagating nonmigrating diurnal tide with zonal wave number 3 (DE3) that originates from tropical convection. The statistics of short-term tidal variability derived from "tidal deconvolution" are analyzed using an information-theoretic approach based on Bayesian statistics and time-dependent probability density functions. The paper particularly discusses the statistical characteristics of interannual changes in short-term DE3 variability on a quasi-10-day wave (Q10DW) timescale and relates it to various forcing and propagation conditions such as Quasi-Biennial Oscillation (QBO), El Nino-Southern Oscillation (ENSO), and solar cycle. Understanding the response to these drivers requires a separate treatment of symmetric and antisymmetric DE3 tidal modes. Symmetric DE3 mode variability is enhanced during the easterly phase of the QBO due to enhanced Q10DW activity and during the La Nina phase of ENSO due to enhanced convective forcing but does not show a solar cycle dependence because of stable polar vortex conditions in the southern hemisphere. Antisymmetric DE3 mode variability is enhanced in the westerly phase of the QBO during solar maximum due to Q10DW activity related to a more unstable polar vortex in the northern hemisphere.