Japan Geoscience Union Meeting 2024

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[E] Oral

A (Atmospheric and Hydrospheric Sciences ) » A-CG Complex & General

[A-CG33] Multi-scale ocean-atmosphere interaction in the tropics

Mon. May 27, 2024 1:45 PM - 3:15 PM 201A (International Conference Hall, Makuhari Messe)

convener:Ingo Richter(JAMSTEC Japan Agency for Marine-Earth Science and Technology), Yu Kosaka(Research Center for Advanced Science and Technology, University of Tokyo), Michiya Hayashi(National Institute for Environmental Studies), Tomoki Tozuka(Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo), Chairperson:Ingo Richter(JAMSTEC Japan Agency for Marine-Earth Science and Technology), Michiya Hayashi(National Institute for Environmental Studies)

2:45 PM - 3:00 PM

[ACG33-05] Tropical Intraseasonal Variability as a Linear Leading Moisture Dynamic Mode of the Warm-Pool Background State

*Michiya Hayashi1, Fei-Fei Jin2 (1.National Institute for Environmental Studies, 2.University of Hawaii at Manoa)

Keywords:Tropical Intraseasonal Variability, Madden-Julian Oscillation, El Niño-Southern Oscillation, Moist Linear Baroclinic Model

Tropical intraseasonal variability (ISV) is dominated by the Madden–Julian oscillation (MJO) and the boreal summer intraseasonal oscillation (BSISO), and its spatiotemporal characteristics vary with the Indo-Pacific warm-pool background on seasonal and longer timescales. Previous works have aimed to reveal ISV dynamics in various frameworks, whereas a unifying view for the ISV change characteristics remains elusive. Motivated by the recent advance in moisture mode theory for the MJO, we proposed a view for the ISV as a linear moisture mode modulated by varying background states, which was elucidated using a moist linear baroclinic model (mLBM) improved with a simple convective scheme relating convective precipitation to tropospheric and boundary-layer moisture anomalies and simple cloud–radiation feedback representations in atmospheric heating and surface fluxes. Under a boreal winter background state, this improved mLBM yielded a large-scale eastward-propagating mode with a phase speed of 3–5 m/s over the warm-pool region, resembling the MJO. Under a boreal summer background state, the leading mode involved east–northward propagation, resembling the BSISO but with too slow phase speed relative to the observed value. Background lower-tropospheric winds and thermodynamic fields are important in determining the growth rate and periodicity of the leading mode, whose stability strongly depends on cloud–radiation feedback and background state variations. For example, adding El Niño anomalies onto the background state causes eastward displacement of the wintertime MJO-like ISV activity, reminiscent of the observed MJO modulations by El Niño events.