Possible contribution of the inter-annual Tibetan Plateau snow cover variation to the Madden-Julian oscillation convection variability

The Madden-Julian oscillation (MJO) is the major mode of intra-seasonal variability in the Tropics, yet researches about factors related to this oscillation have not been well understood, particularly on an inter-annual timescale. As a crucial index of the thermal condition of the plateau, the Tibetan Plateau snow cover (TPSC) has attracted great attention with its potential climatic effects. In this paper, observational evidences present that the inter-annual variation in the wintertime TPSC can exert influence on the convection variability associated with the MJO. For the excessive TPSC winters, the MJO convection tends to be stronger in the Indian Ocean (phases 2-3), while it is more vigorous over the western Pacific (phases 6-7) during the reduced TPSC winters. Furthermore, the South Asia High (SAH) is found to be the key system in the potential physical mechanism. A reduced (excessive) TPSC can excite upper-level anomalous anticyclone (cyclone) over the Tibetan Plateau and eastern China, which is in favour of westwards extension (eastwards withdrawal) and enhancing (weakening) of the SAH over tropical oceans. Through an anomalous tropical zonal-vertical circulation, the intensified ascending (descending) motions over the tropical western Pacific may subsequently depress (enhances) the convection over the Indian Ocean. Over the Indian Ocean (phases 2-3) and the western Pacific (phases 6-7), the zonal-vertical circulation associated with the MJO is exactly superposed with the inter-annual anomalous vertical circulation linked with the TPSC, so the according changes of MJO convection are most significant in these two categorized phases.