The precipitating cloud population of the Madden-Julian Oscillation over the Indian and west Pacific Oceans

摘要

The variability of the precipitating cloud population of the Madden-Julian Oscillation (MJO) is represented by statistics of echo features seen by the Tropical Rainfall Measuring Mission's Precipitation Radar over the central Indian and west Pacific Oceans. Echo features include isolated shallow echoes, deep convective cores, wide convective cores, and broad stratiform regions. Isolated shallow echoes are ever present but most numerous during suppressed MJO phases. Broad stratiform regions dominate variability in areal coverage and maximize during active phases. Deep convective and wide convective cores are more common and variable in number than broad stratiform regions. The magnitude of variability is similar in both regions. In the central Indian Ocean, active MJO phases have synchronous maximization of deep convective entities. In the west Pacific, broad stratiform regions maximize prior to wide convective cores. Reanalysis indicates that isolated shallow echoes are most numerous in dry mid-tropospheric conditions and strong low-level (1000-750 hPa) shear. Mid-tropospheric moisture increases before deeper convective features increase in number, maximizes as deep convective features maximize, and decreases as wide convective cores and broad stratiform regions decline in population. Active-stage deep and wide convective cores occur preferentially with moist mid-tropospheric conditions and strong low-level shear. Acute shear may favor downdraft momentum transport and consequently more robust gust-front convective triggering. Broad stratiform regions maximize with a moist mid-troposphere, strong low-level shear, and moderate upper-level (750-500 hPa) shear that is not so strong that the stratiform region disconnects from its convective moisture source. Key Points Stratiform regions dominate the areal variability of the cloud population. Isolated, shallow echoes are most common and variable in terms of number. Population varies with large-scale shear and mid-upper moisture in active stage.