Differences in the Tropical Convective Activities at the Opposite Phases of the Quasi-Biennial Oscillation
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Differences in convective activities in the tropical region (30°S–30°N, 180°E–180°W) during different phases of the quasi-biennial oscillation (QBO) are investigated over 32 years (1979–2010) using five metrics representing tropical convection: (i) precipitation and (ii) outgoing longwave radiation from observations and (iii) convective available potential energy (CAPE), (iv) deep convective heating rate, and (v) convective cloud top pressure from reanalysis data. The easterly (QBOE) and westerly (QBOW) phases of the QBO are defined using the zonal wind anomaly from the monthly climatology at 50 hPa. During the QBOE (QBOW), the convective activities are intensified (weakened) over the Maritime Continent and weakened (intensified) over the equatorial eastern and central Pacific. Therefore, the zonal mean values of the five metrics averaged over chronically convective regions show stronger convective activities during the QBOE than during the QBOW, while the opposite is true for the whole tropical region. Composite analyses are also performed during the neutral, El Niño, and La Niña periods. In the neutral period, the convective activities during QBOE are stronger than during QBOW except in the equatorial region (10°S–10°N). The convective activities over the Maritime Continent (central and eastern Pacific) are enhanced when La Niña and the QBOE (El Niño and the QBOW) occur simultaneously. All metrics show similar pattern to one another, implying that the metrics from reanalysis data represent the variations in the convective activities with respect to the QBO reasonably well. Among the five metrics, the CAPE is most sensitive to the QBO phase, likely because the virtual temperature in the upper troposphere is modulated by anomalous meridional circulations induced by different QBO phases.
KeywordsQuasi-biennial oscillation Tropical deep convection Convective activity ENSO
This work was funded by the Korea Meteorological Administration Research and Development Program under Grant KMIPA 2015-6160.
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