Large-scale convective systems identified by hybrid cloud-precipitation
regimes and their modulations by MJO and QBO
Abstract
Tropical convective systems that grow larger than
100,000km2 sizes play a significant role in the water
cycle and energy budget of the Earth system. Previously, we developed
hybrid tropical cloud-precipitation regimes (TCPRs) derived from
Moderate Resolution Imaging Spectroradiometer (MODIS) cloud observations
and Integrated Multi-satellitE Retrievals for GPM (IMERG) precipitation
data at a 1° scale, and demonstrated that TCPRs enabled a simple but
effective identification of convective systems at the synoptic scale.
The Madden-Julian Oscillation (MJO) is the dominant mode of tropical
intraseasonal variability, which is characterized as a planetary-scale
envelop of convective clouds that propagates eastward over the
Indo-Pacific warm pool. Recent studies showed a statistically robust
correlation between the MJO and the quasi-biennial oscillation (QBO);
MJO-related convective activities are enhanced and suppressed during an
easterly and westerly phase of QBO, respectively. While the underlying
mechanism of the MJO-QBO relationship has remained elusive, one of the
most popular hypotheses is that the weakened stability in the upper
troposphere and lower stratosphere during easterly QBO years provides a
preferrable condition for deep convection to develop deeper and persist
longer. To test the stability hypothesis for the QBO control on the MJO,
we examine properties of the convective aggregates of TCPRs in the
southern Maritime Continent region, in which the contrast in MJO
activities between easterly and westerly QBO years is most pronounced.
By taking advantage of TCPRs, we composite the total size, fractions of
stratiform clouds to core area, and top height of core for different
phases of MJO and QBO, and the results are compared to find any
systematic difference in the characteristics of convective aggregates.
Our results show that, as consistent to previous studies, bigger
convective aggregates tend to occur when the stability weakens. Further
insight will be obtained by examining cloud radiative effects and
atmospheric energy budget per convective aggregates.