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Yuntao Wei and Zhaoxia Pu

Abstract

Despite the great importance of interactions between moisture, clouds, radiation, and convection in the Madden-Julian Oscillation, their role in the boreal summer intraseasonal oscillation (BSISO) has not been well established. This study investigates the moisture variation of a BSISO during its rapid redevelopment over the eastern Maritime Continent through a cloud-permitting-scale numerical simulation. It is found that moisture variation depends closely on the evolution of clouds and precipitation. Total moisture budget analysis reveals that the deepening and strengthening (lessening) of humidity before (after) the BSISO deep convection are attributed largely to zonal advection. In addition, the column moistening/drying is mostly in phase with the humidity and is related to the maintenance of BSISO.

An objective cloud-type classification method and a weak temperature gradient approximation are used to further understand the column moistening/drying. Results indicate that elevated stratiform clouds play a significant role in moistening the lower troposphere through cloud water evaporation. Decreases in deep convection condensation and re-evaporation of deep stratiform precipitation induce moistening during the development and after the decay of BSISO deep convection, respectively. Meanwhile, anomalous longwave radiative heating appears first in the lower troposphere during the developing stage of BSISO, further strengthens via the increase of deep stratiform clouds, and eventually deepens with elevated stratiform clouds. Accordingly, anomalous moistening largely in phase with the humidity of BSISO toward its suppressed stage is induced via compensated ascent. Owing to the anomalous decrease in the ratio of vertical moisture and potential temperature gradients, the cloud-radiation effect is further enhanced in the convective phase of BSISO.

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Lei Zhou, Ruomei Ruan, and Raghu Murtugudde

Abstract

Madden-Julian Oscillations (MJOs) are a major component of tropical intraseasonal variabilities. There are two paths for MJOs across the Maritime Continent; one is a detoured route into the Southern Hemisphere and the other one is around the equator across the Maritime Continent. Here, it is shown that the detoured and non-detoured MJOs have significantly different impacts on the South Pacific convergence zone (SPCZ). The detoured MJOs trigger strong cross-equatorial meridional winds from the Northern Hemisphere into the Southern Hemisphere. The associated meridional moisture and energy transports due to the background states carried by the intraseasonal meridional winds are favorable for reinforcing the SPCZ. In contrast, the influences of non-detoured MJOs on either hemisphere or the meridional transports across the equator are much weaker. The detoured MJOs can extend their impacts to the surrounding regions by shedding Rossby waves. Due to different background vorticity during detoured MJOs in boreal winter, more ray paths of Rossby waves traverse the Maritime Continent connecting the southern Pacific Ocean and the eastern Indian Ocean, but far fewer Rossby wave paths traverse Australia. Further studies on such processes are expected to contribute to a better understanding of extreme climate and natural disasters on the rim of the southern Pacific and Indian Oceans.

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Arun Kumar, Jieshun Zhu, and Wanqiu Wang

potentially predictable. In addition, as compared with predictability studies that are based on model forecasts or reforecasts, our observational approach provides a much more objective measure of predictability that is independent of model biases (and their influence on skill). In future, we will follow the analysis strategy for other variables: for example, vertical wind shear and tropospheric moisture content. Using lead–lag analysis, it may be possible to quantify the propagation characteristics of

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Jieshun Zhu, Arun Kumar, and Wanqiu Wang

simulated the intraseasonal wind variability resulting in significant biases in latent heat flux and in SST variability. Unrealistic SST variations, in turn, degraded the MJO simulation by affecting SST-modulated heat fluxes and the boundary layer moisture convergence or surface moist static energy (e.g., Flatau et al. 1997 ; Maloney and Sobel 2004 ). Given the critical role of convective parameterization in MJO simulations, it is possible that the large uncertainties in current estimates for MJO

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Marvin Xiang Ce Seow, Yushi Morioka, and Tomoki Tozuka

, 2008 : An enhanced moisture convergence–evaporation feedback mechanism for MJO air–sea interaction . J. Atmos. Sci. , 65 , 970 – 986 , https://doi.org/10.1175/2007JAS2313.1 . 10.1175/2007JAS2313.1 Masson , S. , P. Terray , G. Madec , J.-J. Luo , T. Yamagata , and K. Takahashi , 2012 : Impact of intra-daily SST variability on ENSO characteristics in a coupled model . Climate Dyn . , 39 , 681 – 707 , https://doi.org/10.1007/s00382-011-1247-2 . 10.1007/s00382

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Chu-Chun Chen, Min-Hui Lo, Eun-Soon Im, Jin-Yi Yu, Yu-Chiao Liang, Wei-Ting Chen, Iping Tang, Chia-Wei Lan, Ren-Jie Wu, and Rong-You Chien

4, we use the radiative transfer scheme of the modified NCAR Community Climate Model version 3 (CCM3), the nonlocal planetary boundary layer scheme of Holtslag ( Holtslag et al. 1990 ), the ocean flux scheme of Zeng ( Zeng et al. 1998 ), and the Subgrid Explicit Moisture (SUBEX) scheme for the resolved scale precipitation, which are default schemes of RegCM4 ( Giorgi et al. 2012 ) or applied schemes for RegCM4 simulations of the Southeast Asia domain ( Chung et al. 2018 ). We also performed

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Ching-Shu Hung and Chung-Hsiung Sui

; Neelin et al. 1987 ), cloud–radiative feedback ( Hu and Randall 1994 ; Andersen and Kuang 2012 ), and moisture mode theory ( Raymond 2001 ; Sobel and Maloney 2012 , 2013 ; Adames and Kim 2016 ). Several observational studies have shown that the development and propagation of the MJO are closely related to atmospheric moisture, radiation, and surface turbulent fluxes ( Sobel et al. 2014 ; Johnson et al. 2015 ; Tseng et al. 2015 ). Moreover, the MJO simulations in some GCMs are also improved when

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Wan-Ling Tseng, Huang-Hsiung Hsu, Noel Keenlyside, Chiung-Wen June Chang, Ben-Jei Tsuang, Chia-Ying Tu, and Li-Chiang Jiang

weakening the MJO in model simulation ( Bladé and Hartmann 1993 ; Oh et al. 2012 , 2013 ; Hagos et al. 2016 ). By contrast, a local strengthening effect has also been reported. Some studies (e.g., Hsu et al. 2004 ; Hsu and Lee 2005 ; Wu and Hsu 2009 ) argue that the lifting and frictional effects caused by orography and the land–sea contrast in the MC might enhance the near-surface moisture convergence east of the topography, thus developing a new deep convection region. A sudden shift in the deep

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Claire L. Vincent and Todd P. Lane

1. Introduction The Maritime Continent (MC) plays an important role as a heat and moisture source that can impact global circulation and modulate planetary-scale variability ( Neale and Slingo 2003 ). However, despite its importance, large errors are commonly found in the MC region in global and regional climate and weather models (e.g., Gianotti et al. 2012 ; Holloway et al. 2012 ; Nguyen et al. 2015 ; Dirmeyer et al. 2012 ; and others). One likely source of these errors arises from the

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Chidong Zhang and Jian Ling

model capability of subseasonal prediction. Several possible reasons for the MC barrier effect on MJO propagation have been suggested. If surface fluxes, especially latent heat flux, are important to the MJO ( Maloney and Sobel 2004 ; Sobel et al. 2008 ), then the MJO would be weakened or diminished by the reduction in surface fluxes in the MC region because of its many islands. If moisture convergence of the low-level circulation is essential to the MJO ( Wang 1988 ; 2005 ), then its distortion

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