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The intraseasonal atmospheric angular momentum associated with MJO convective initiations
Author(s) -
Sakaeda Naoko,
Roundy Paul E.
Publication year - 2016
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.2740
Subject(s) - madden–julian oscillation , convection , climatology , eddy , atmospheric sciences , troposphere , geology , anomaly (physics) , momentum (technical analysis) , subtropics , wind shear , physics , wind speed , meteorology , oceanography , turbulence , finance , condensed matter physics , fishery , economics , biology
The first part of this study examines the driving mechanisms of the equatorial intraseasonal relative atmospheric angular momentum ( AAM ) and its dynamical relationship to the upper‐tropospheric zonal wind over the W estern H emisphere ( WH ) during the convective initiation of the M adden– J ulian O scillation ( MJO) over the I ndian O cean. The budget analysis shows that the main driver of the equatorial intraseasonal AAM anomaly is the meridional transport of momentum induced by the modulation of the background subtropical eddies by the intraseasonal eddies. While the subtropical eddies over the central P acific basin partly drive the equatorial AAM by meridionally transporting the momentum, the equatorial zonal wind associated with the same subtropical eddies is zonally advected and locally amplified over the east P acific and A tlantic basins. The common source phenomena that transport momentum result in simultaneous evolution of the WH upper‐tropospheric zonal wind and the AAM on intraseasonal time‐scales, but their main driving mechanisms are different. The second part of the study investigates the influence of the equatorial intraseasonal AAM state on the subsequent development of initiating MJO convection over the I ndian O cean. In the presence of the WH upper‐tropospheric easterly wind, MJO convection tends to develop a stronger enhanced convective envelope when the initiation occurs during the negative intraseasonal AAM state, which strengthens and extends the upper‐tropospheric easterly wind in the WH . When the AAM anomaly is positive, it tends to induce stronger mid‐tropospheric convergence above the region of convective initiation, thereby suppressing the lower‐tropospheric updraught and suppressing the further growth of convection. The results show that the combined effects of the WH circumnavigating circulation and the AAM can influence the subsequent development of MJO convection over the I ndian O cean.