scholarly journals Topographic Effects on the Eastward Propagation and Initiation of the Madden–Julian Oscillation

2005 ◽  
Vol 18 (6) ◽  
pp. 795-809 ◽  
Author(s):  
Huang-Hsiung Hsu ◽  
Ming-Ying Lee
Keyword(s):  
Indian Ocean ◽  
Deep Convection ◽  
Moisture Convergence ◽  
Madden Julian Oscillation ◽  
Near Surface ◽  
Surface Moisture ◽  
Central Indian Ocean ◽  
The Indian Ocean ◽  
The Western Pacific ◽  
Heating Anomaly

Abstract This study investigates the relationship between deep convection (and heating anomaly) in the Madden–Julian oscillation (MJO) and the tropical topography. The eastward propagation of the deep heating anomalies is confined to two regions: the Indian Ocean and the western Pacific warm pool. Superimposed on the eastward propagation is a series of quasi-stationary deep heating anomalies that occur sequentially and discretely downstream in a leapfrog manner in the central Indian Ocean, the Maritime Continent, tropical South America, and tropical Africa. The deep heating anomaly, usually preceded by near-surface moisture convergence and shallow heating anomalies, tends to occur on the windward side of the tropical topography in these regions (except the central Indian Ocean) under the prevailing surface easterly anomaly of the MJO. It is suggested that the lifting and frictional effects of the tropical topography and landmass induce the near-surface moisture convergence anomaly, which in turn triggers the deep heating anomaly. Subsequently, the old heating anomaly located to the west of the tropical topography weakens and the new heating anomaly east of the topography develops because of the eastward shift in the major moisture convergence center to the east of the mountains. Therefore, the deep heating anomaly shifts eastward from one region to another. The equatorial Kelvin wave, which is forced by the tropical heating anomaly and propagates quickly across the ocean basins in the lower troposphere, plays an important role by helping to strengthen the easterly anomaly and lowering the surface pressure. This process is proposed to further our understanding of the shift in the deep convection from the Indian Ocean to the western Pacific, the reappearance of the deep convection in tropical South America, and the initiation of the MJO in the western Indian Ocean. It is suggested that the fast eastward propagation and the slow development of quasi-stationary convection together determine the quasi-periodicity of the MJO.

scholarly journals Impact of the Madden–Julian Oscillation on Summer Rainfall in Southeast China

2009 ◽  
Vol 22 (2) ◽  
pp. 201-216 ◽  
Author(s):  
Lina Zhang ◽  
Bizheng Wang ◽  
Qingcun Zeng
Keyword(s):  
Indian Ocean ◽  
Tropical Indian Ocean ◽  
Summer Rainfall ◽  
Western Pacific ◽  
Madden Julian Oscillation ◽  
Energy Propagation ◽  
Southeast China ◽  
The Indian Ocean ◽  
The Impact ◽  
The Western Pacific

Abstract The impact of the Madden–Julian oscillation (MJO) on summer rainfall in Southeast China is investigated using the Real-time Multivariate MJO (RMM) index and the observational rainfall data. A marked transition of rainfall patterns from being enhanced to being suppressed is found in Southeast China (east of 105°E and south of 35°N) on intraseasonal time scales as the MJO convective center moves from the Indian Ocean to the western Pacific Ocean. The maximum positive and negative anomalies of regional mean rainfall are in excess of 10% relative to the climatological regional mean. Such different rainfall regimes are associated with the corresponding changes in physical fields such as the western Pacific subtropical high (WPSH), moisture, and vertical motions. When the MJO is mainly over the Indian Ocean, the WPSH shifts farther westward, and the moisture and upward motions in Southeast China are increased. In contrast, when the MJO enters the western Pacific, the WPSH retreats eastward, and the moisture and upward motions in Southeast China are decreased. It is suggested that the MJO may influence summer rainfall in Southeast China through remote and local dynamical mechanisms, which correspond to the rainfall enhancement and suppression, respectively. The remote role is the energy propagation of the Rossby wave forced by the MJO-related heating over the Indian Ocean through the low-level westerly waveguide from the tropical Indian Ocean to Southeast China. The local role is the northward shift of the upward branch of the anomalous meridional circulation when the MJO is over the western Pacific, which causes eastward retreat of the WPSH and suppressed moisture transport toward Southeast China.

scholarly journals Effects of Enhanced Front Walker Cell on the Eastward Propagation of the MJO

2018 ◽  
Vol 31 (19) ◽  
pp. 7719-7738 ◽  
Author(s):  
Guosen Chen ◽  
Bin Wang
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
Middle Atmosphere ◽  
Deep Convection ◽  
Madden Julian Oscillation ◽  
Maritime Continent ◽  
Walker Cell ◽  
The Indian Ocean ◽  
Upper Level ◽  
The Western Pacific

Well-organized eastward propagation of the Madden–Julian oscillation (MJO) is found to be accompanied by the leading suppressed convection (LSC) over the Maritime Continent (MC) and the western Pacific (WP) when the MJO convection is in the Indian Ocean (IO). However, it remains unclear how the LSC influences the MJO and what causes the LSC. The present study shows that the LSC is a prevailing precursor for eastward propagation of the MJO across the MC. The LSC enhances the coupling of IO convection and the Walker cell to its east [front Walker cell (FWC)] by increasing the zonal heating gradient. The enhanced FWC strengthens the low-level easterly, which increases boundary layer (BL) convergence and promotes congestus convection to the east of the deep convection; the enhanced congestus convection preconditions the lower to middle atmosphere, which further promotes the transition from congestus to deep convection and leads to eastward propagation of the MJO. The MJO ceases eastward propagation once the FWC decouples from it. Further analysis reveals that LSC has two major origins: one comes from the eastward propagation of the preceding IO dry phase associated with the MJO, and the other develops concurrently with the IO convection. In the latter case, the development of the LSC is brought about by a two-way interaction between the MJO’s tropical heating and the associated tropical–extratropical teleconnection: the preceding IO suppressed convection induces a tropical–extratropical teleconnection, which evolves and forms an anomalous western North Pacific cyclone that generates upper-level convergence and induces significant LSC.

scholarly journals Zonal SST Difference as a Potential Environmental Factor Supporting the Longevity of the Madden–Julian Oscillation

2018 ◽  
Vol 31 (18) ◽  
pp. 7549-7564 ◽  
Author(s):  
Tamaki Suematsu ◽  
Hiroaki Miura
Keyword(s):  
Indian Ocean ◽  
Large Scale ◽  
Low Frequency ◽  
Western Pacific ◽  
Madden Julian Oscillation ◽  
Central Pacific ◽  
The Indian Ocean ◽  
The Difference ◽  
The Western Pacific ◽  
Sst Gradient

An environment favorable for the development of the Madden–Julian oscillation (MJO) was investigated by classifying MJO-like atmospheric patterns as MJO and regionally confined convective (RCC) events. Comparison of MJO and RCC events showed that even when preceded by a major convective suppression event, convective events did not develop into an MJO when large-scale buildup of moist static energy (MSE) was inhibited. The difference in the MSE accumulation between MJO and RCC is related to the contrasting low-frequency basic-state sea surface temperature (SST) pattern; the MJO and RCC events were associated with anomalously warm and cold low-frequency SSTs prevailing over the western to central Pacific, respectively. Differences in the SST anomaly field were absent from the intraseasonal frequency range of 20–60 days. The basic-state SST pattern associated with the MJO was characterized by a positive zonal SST gradient from the Indian Ocean to the western Pacific, which provided a long-standing condition that allowed for sufficient buildup of MSE across the Indian Ocean to the western Pacific via large-scale low-level convergence over intraseasonal and longer time scales. The results of this study suggest the importance of such a basic-state SST, with a long-lasting positive zonal SST gradient, for enhancing convection over a longer than intraseasonal time scale in realizing a complete MJO life cycle.

Roles of Shallow Convective Moistening in the Eastward Propagation of the MJO in MIROC6

2018 ◽  
Vol 31 (8) ◽  
pp. 3033-3047 ◽  
Author(s):  
Nagio Hirota ◽  
Tomoo Ogura ◽  
Hiroaki Tatebe ◽  
Hideo Shiogama ◽  
Masahide Kimoto ◽  
...  
Keyword(s):  
Deep Convection ◽  
Mature Stage ◽  
Free Troposphere ◽  
Madden Julian Oscillation ◽  
Shallow Convection ◽  
Parameter Perturbation ◽  
Convection Scheme ◽  
Initial Stage ◽  
The Indian Ocean ◽  
The Western Pacific

Abstract This study examines the roles of shallow convection in the eastward propagation of the Madden–Julian oscillation (MJO) using new and old versions of the Model for Interdisciplinary Research on Climate, versions 6 and 5 (MIROC6 and MIROC5), respectively. A major modification of MIROC6 from its previous version, MIROC5, is the implementation of the shallow convection scheme following Park and Bretherton. The MJO representation in MIROC6 is improved compared to MIROC5. The MJO convective envelopes that occur over the Indian Ocean, which decay too early over the western Pacific in MIROC5, propagate farther into the eastern Pacific in MIROC6. In the initial stage of the MJO development, the shallow convection transports boundary layer moisture upward forming an important moisture source for the lower free troposphere in MIROC6. In the mature stage of the MJO, the deep convection becomes increasingly active with the large amount of moisture in the free troposphere. Accordingly, the moisture anomalies associated with the MJO show an upward- and westward-tilted structure, as in the observations. Conversely, MIROC5 exhibits a dry bias in the lower free troposphere, suggesting that the shallow convective activity is underestimated. A parameter perturbation experiment, modifying the intensity of shallow convection, confirms that enhanced shallow convection reduces the moisture bias in the lower free troposphere and improves the simulation of the MJO in MIROC6.

Deep-water, offshore, and new records of Schindler’s fishes, Schindleria (Teleostei, Gobiidae), from the Indo-west Pacific collected during the Dana-Expedition, 1928–1930

Zootaxa ◽  
2020 ◽  
Vol 4731 (4) ◽  
pp. 451-470
Author(s):  
HARALD AHNELT ◽  
MICHAEL SAUBERER
Keyword(s):  
Indian Ocean ◽  
Deep Water ◽  
New Records ◽  
The Philippines ◽  
Western Pacific ◽  
Central Indian Ocean ◽  
The Family ◽  
The Indian Ocean ◽  
The Western Pacific ◽  
Southwestern Indian Ocean

Schindleria (Giltay (1934), Schindler’s fishes (or infantfishes), is a genus of small (< 22 mm) paedomorphic species of the family Gobiidae which mature extremely fast. These fishes occur from the eastern Pacific (Cocos Islands off Costa Rica, seamounts Nazca and Sala y Gómez) to the southwestern Indian Ocean (southeast Africa). Nevertheless, there is a large gap in the distributional area between the Philippines (western Pacific) and India/Sri Lanka (Central Indian Ocean) which spans nearly 5000 km. We present the first comprehensive documentation of published records of Schindleria together with samples collected during the Dana-Expedition, between 1928 and 1930 at 44 stations from Polynesia to southeast Africa, with 8 records from the western Pacific to the Central Indian Ocean. We present three first records, 18 new records and the southernmost record for the Indian Ocean. Although Schindler’s fishes were generally documented from or close to islands and reefs, we present 23 offshore records (at least 30 km distant to a shore or reef) and 27 deep-water records (at least 65 m deep). Records between 320 and 360 km offshore are the most extreme offshore records of Schindleria ever documented. The records from about 500- and 1000-m depths are the deepest ever documented for Schindler’s fishes. 

scholarly journals Diagnosing ISO Forecast from GloSea5 Using Dynamic-Oriented ISO Theory

Atmosphere ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 114
Author(s):  
Young-Min Yang ◽  
Taehyoun Shim ◽  
Ja-Yeon Moon ◽  
Ki-Young Kim ◽  
Yu-Kyung Hyun
Keyword(s):  
Indian Ocean ◽  
Deep Convection ◽  
Intraseasonal Oscillation ◽  
Lower Troposphere ◽  
Moisture Convergence ◽  
Lower Atmosphere ◽  
Vertical Shear ◽  
Boreal Summer ◽  
Kelvin Wave ◽  
The Indian Ocean

A Madden–Jillian oscillation (MJO) and boreal summer intraseasonal oscillation (BSISO) are important climate variabilities, which affect a forecast of weather and climate. In this study, the MJO and the BSISO hindcasts from the Global Seasonal Forecast System, version 5 (GS5) were diagnosed using dynamic-oriented theories. We additionally analyzed the GS5 climatological run to identify whether the weakness of the GS5 hindcast results from the model physics or initialization processes. The GS5 hindcast captures three-dimensional dynamics and thermodynamics structure of MJO eastward propagation well in the Indian Ocean. The model produces the boundary layer (BL) moisture convergence anomalies to the east of the MJO deep precipitation with easterly anomalies associated with the Kelvin wave. The enhanced BL moisture convergence increases upward transport of moisture from the surface to the lower troposphere, inducing the moist lower troposphere and the positive convective instability by destabilization of the lower atmosphere and, thus, generating the next convection to the east of MJO deep convection and promoting MJO eastward propagation. However, the signal for eastward propagation is relatively weak in the Maritime Continent (MC) and the Western Pacific (WP). To improve the MJO eastward propagation in the MC and WP, improved heating induced by shallow (or congestus) clouds interacting with enhanced BL dynamics may be required. On the other hand, the GS5 hindcast reproduces the BSISO northward propagation reasonably well in the Indian Ocean, which is attributed to positive vorticity anomalies induced by strong vertical shear.

scholarly journals Convective Characteristics of the Madden–Julian Oscillation over the Central Indian Ocean Observed by Shipborne Radar during DYNAMO

2014 ◽  
Vol 71 (8) ◽  
pp. 2859-2877 ◽  
Author(s):  
Weixin Xu ◽  
Steven A. Rutledge
Keyword(s):  
Time Series ◽  
Indian Ocean ◽  
Phase 1 ◽  
Deep Convection ◽  
Tropical Rainfall Measuring Mission ◽  
Heavy Precipitation ◽  
Upper Troposphere ◽  
Central Indian Ocean ◽  
Radar Echo ◽  
Two Phases

Abstract This study investigates the convective population and environmental conditions during three MJO events over the central Indian Ocean in late 2011 using measurements collected from the Research Vessel (R/V) Roger Revelle deployed in Dynamics of the MJO (DYNAMO). Radar-based rainfall estimates from the Revelle C-band radar are first placed in the context of larger-scale Tropical Rainfall Measuring Mission (TRMM) rainfall data to demonstrate that the reduced Revelle radar range captured the MJO convective evolution. Time series analysis and MJO phase-based composites of Revelle measurements both support the “recharge–discharge” MJO theory. Time series of echo-top heights indicate that convective deepening during the MJO onset occurs over a 12–16-day period. Composite statistics show evident recharging–discharging features in convection and the environment. Population of shallow/isolated convective cells, SST, CAPE, and the lower-tropospheric moisture increase (recharge) substantially approximately two to three phases prior to the MJO onset. Deep and intense convection and lightning peak in phase 1 when the sea surface temperature and CAPE are near maximum values. However, cells in this phase are not well organized and produce little stratiform rain, possibly owing to reduced shear and a relatively dry upper troposphere. The presence of deep convection leads the mid- to upper-tropospheric humidity by one to two phases, suggesting its role in moistening these levels. During the MJO onset (i.e., phase 2), the mid- to upper troposphere becomes very moist, and precipitation, radar echo-top heights, and the mesoscale extent of precipitation all increase and obtain peak values. Persistent heavy precipitation in these active periods helps reduce the SST and dry/stabilize (or discharge) the atmosphere.

scholarly journals A Central Indian Ocean Mode and Heavy Precipitation during the Indian Summer Monsoon

2017 ◽  
Vol 30 (6) ◽  
pp. 2055-2067 ◽  
Author(s):  
Lei Zhou ◽  
Raghu Murtugudde ◽  
Dake Chen ◽  
Youmin Tang
Keyword(s):  
Indian Ocean ◽  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Critical Role ◽  
Western Indian Ocean ◽  
Heavy Precipitation ◽  
Central Indian Ocean ◽  
Monsoonal Precipitation ◽  
Monsoon System ◽  
The Indian Ocean

A central Indian Ocean (CIO) mode is found to play a critical role in driving the heavy precipitation during the Indian summer monsoon (ISM). It is typically denoted with a combination of intraseasonal sea surface temperature (SST) anomalies and intraseasonal wind anomalies over the central Indian Ocean, and it preserves the mechanistic links among various dynamic and thermodynamic fields. Like a T junction, it controls the propagation direction of the intraseasonal variabilities (ISVs) originating in the western Indian Ocean. During the ISM, the CIO mode creates an environment favorable for the northward-propagating mesoscale variabilities. These results unveil the relation between the subseasonal monsoonal precipitation and the CIO mode in the ocean–atmosphere system in the Indian Ocean. The identification of the CIO mode deepens our understanding of the coupled monsoon system and brightens the prospects for better simulation and prediction of monsoonal precipitation in the affected countries.

scholarly journals Simulation of the Madden–Julian Oscillation in the NCAR CCM3 Using a Revised Zhang–McFarlane Convection Parameterization Scheme

2005 ◽  
Vol 18 (19) ◽  
pp. 4046-4064 ◽  
Author(s):  
Guang J. Zhang ◽  
Mingquan Mu
Keyword(s):  
Relative Humidity ◽  
Indian Ocean ◽  
Zonal Wind ◽  
Lower Troposphere ◽  
Parameterization Scheme ◽  
Madden Julian Oscillation ◽  
Shallow Convection ◽  
Time Period ◽  
The Indian Ocean ◽  
Convection Parameterization

Abstract This study presents the simulation of the Madden–Julian oscillation (MJO) in the NCAR CCM3 using a modified Zhang–McFarlane convection parameterization scheme. It is shown that, with the modified scheme, the intraseasonal (20–80 day) variability in precipitation, zonal wind, and outgoing longwave radiation (OLR) is enhanced substantially compared to the standard CCM3 simulation. Using a composite technique based on the empirical orthogonal function (EOF) analysis, the paper demonstrates that the simulated MJOs are in better agreement with the observations than the standard model in many important aspects. The amplitudes of the MJOs in 850-mb zonal wind, precipitation, and OLR are comparable to those of the observations, and the MJOs show clearly eastward propagation from the Indian Ocean to the Pacific. In contrast, the simulated MJOs in the standard CCM3 simulation are weak and have a tendency to propagate westward in the Indian Ocean. Nevertheless, there remain several deficiencies that are yet to be addressed. The time period of the MJOs is shorter, about 30 days, compared to the observed time period of 40 days. The spatial scale of the precipitation signal is smaller than observed. Examination of convective heating from both deep and shallow convection and its relationship with moisture anomalies indicates that near the mature phase of the MJO, regions of shallow convection developing ahead of the deep convection coincide with regions of positive moisture anomalies in the lower troposphere. This is consistent with the recent observations and theoretical development that shallow convection helps to precondition the atmosphere for MJO by moistening the lower troposphere. Sensitivity tests are performed on the individual changes in the modified convection scheme. They show that both change of closure and use of a relative humidity threshold for the convection trigger play important roles in improving the MJO simulation. Use of the new closure leads to the eastward propagation of the MJO and increases the intensity of the MJO signal in the wind field, while imposing a relative humidity threshold enhances the MJO variability in precipitation.

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