QBO/Solar Influences on the Tropical Madden‐Julian Oscillation: A Mechanism Based on Extratropical Wave Forcing in Late Fall and Early Winter

Possible sources of the observed modulation tropical Madden-Julian oscillation (MJO) by stratospheric quasi-biennial (QBO) and 11-year solar cycle are investigated using 41 years reanalysis data archived climate model data. Larger upward fluxes extratropical planetary-scale waves, leading in some cases to sudden warmings (SSWs), late fall early winter during easterly phase QBO than westerly (the “Holton-Tan effect”). A similar but smaller increase occurs, on average, minima relative maxima. In addition warming at high latitudes, wave forcing events produce cooling reduced static stability lower stratosphere. Here, it is found that if SSWs occur (before ∼mid-January), produces, a statistically significant, lagged strengthening MJO. This therefore represents possible mechanism for producing, or least enhancing, modulations MJO boreal winter. An initial analysis shows one version with realistic 4 CO2 forcings partly simulates both these characteristics (QBO/solar following SSWs). However, modeled insufficiently sensitive QBO-induced reductions, precluding simulation QBO-MJO connection.