Propagating and Nonpropagating MJO Events over Maritime Continent*

Abstract The observed outgoing longwave radiation (OLR) and ERA-Interim data during 1979–2008 (from November to April) were analyzed to reveal fundamental differences between eastward-propagating (EP) and nonpropagating (NP) MJO events across the Maritime Continent (MC). It was found that when the maximum MJO convection arrives near 120°E, a positive moisture tendency lies in a longitudinal zone (10°S–10°N, 130°–170°E) for the EP cases, whereas a negative tendency appears in the same region for the NP cases. In the latter cases, there are clearly detectable westward-propagating Rossby wave–type dry signals over the equatorial central-western Pacific. The dry Rossby-wave signal may hinder the development of new convection to the east of the MJO convective center, preventing the eastward propagation of the MJO. A moisture budget analysis shows that the positive tendency of specific humidity in the EP composite is mainly attributed to the advection of the mean moisture by an intraseasonal ascending motion anomaly, whereas the negative tendency in the NP composite arises from the advection of anomalous dry air by the mean easterly and the advection of the mean moisture by the anomalous easterly. The EP cases were further separated into two groups: a group with, and a group without, a clear suppressed convective phase of OLR to the east of the MJO convection. In the former (latter), the column-integrated moisture anomaly is negative (positive) to the east of the convection. Nevertheless, MJO crosses the MC in both of the groups, in which anomalous moisture tendency is always positive to the east of the MJO convection. Such positive tendencies are caused by different processes. In the former, anomalous horizontal advections associated with eddy moisture transport and mean moisture advection by intraseasonal meridional wind play an important role. In the latter, it is mainly attributed to mean moisture advection by anomalous vertical velocity.

Download Full-text

Impacts of Shallow Convection on MJO Simulation: A Moist Static Energy and Moisture Budget Analysis

Journal of Climate ◽

10.1175/jcli-d-12-00127.1 ◽

2013 ◽

Vol 26 (8) ◽

pp. 2417-2431 ◽

Cited By ~ 34

Author(s):

Qiongqiong Cai ◽

Guang J. Zhang ◽

Tianjun Zhou

Keyword(s):

Boundary Layer ◽

Deep Convection ◽

Lower Troposphere ◽

Longwave Radiation ◽

Reanalysis Data ◽

Specific Humidity ◽

Moist Static Energy ◽

Shallow Convection ◽

Budget Analysis ◽

Static Energy

Abstract The role of shallow convection in Madden–Julian oscillation (MJO) simulation is examined in terms of the moist static energy (MSE) and moisture budgets. Two experiments are carried out using the NCAR Community Atmosphere Model, version 3.0 (CAM3.0): a “CTL” run and an “NSC” run that is the same as the CTL except with shallow convection disabled below 700 hPa between 20°S and 20°N. Although the major features in the mean state of outgoing longwave radiation, 850-hPa winds, and vertical structure of specific humidity are reasonably reproduced in both simulations, moisture and clouds are more confined to the planetary boundary layer in the NSC run. While the CTL run gives a better simulation of the MJO life cycle when compared with the reanalysis data, the NSC shows a substantially weaker MJO signal. Both the reanalysis data and simulations show a recharge–discharge mechanism in the MSE evolution that is dominated by the moisture anomalies. However, in the NSC the development of MSE and moisture anomalies is weaker and confined to a shallow layer at the developing phases, which may prevent further development of deep convection. By conducting the budget analysis on both the MSE and moisture, it is found that the major biases in the NSC run are largely attributed to the vertical and horizontal advection. Without shallow convection, the lack of gradual deepening of upward motion during the developing stage of MJO prevents the lower troposphere above the boundary layer from being preconditioned for deep convection.

Download Full-text

Precursor Signals and Processes Associated with MJO Initiation over the Tropical Indian Ocean*

Journal of Climate ◽

10.1175/jcli-d-12-00113.1 ◽

2013 ◽

Vol 26 (1) ◽

pp. 291-307 ◽

Cited By ~ 98

Author(s):

Chongbo Zhao ◽

Tim Li ◽

Tianjun Zhou

Keyword(s):

Indian Ocean ◽

Rossby Wave ◽

Lower Troposphere ◽

Equatorial Indian Ocean ◽

Specific Humidity ◽

Boreal Winter ◽

Mean Flow ◽

Wave Response ◽

The Mean ◽

Convection Initiation

Abstract The precursor signals of convection initiation associated with the Madden–Julian oscillation (MJO) in boreal winter were investigated through the diagnosis of the 40-yr ECMWF Re-Analysis (ERA-40) data for the period 1982–2001. The western equatorial Indian Ocean (WIO) is a key region of the MJO initiation. A marked increase of specific humidity and temperature in the lower troposphere appears 5–10 days prior to the convection initiation. The increased moisture and temperature cause a convectively more unstable stratification, leading to the onset of convection. A diagnosis of lower-tropospheric moisture (heat) budgets shows that the moisture (temperature) increase is caused primarily by the horizontal advection of the mean specific humidity (temperature) by the MJO flow. The anomalous flow is primarily determined by the downstream Rossby wave response to a preceding suppressed-phase MJO over the eastern Indian Ocean, whereas the upstream Kelvin wave response to the previous eastward-propagating convective-phase MJO is not critical. An idealized numerical experiment further supports this claim. The Southern Hemisphere (SH) midlatitude Rossby wave train and associated wave activity flux prior to the MJO initiation were diagnosed. It is found that SH midlatitude Rossby waves may contribute to MJO initiation over the western Indian Ocean through wave energy accumulation. Idealized numerical experiments confirm that SH midlatitude perturbations play an important role in affecting the MJO variance in the tropics. A barotropic energy conversion diagnosis indicates that there is continuous energy transfer from the mean flow to intraseasonal disturbances over the initiation region, which may help trigger MJO development.

Download Full-text

The Role of Background Meridional Moisture Gradient on the Propagation of the MJO over the Maritime Continent

Journal of Climate ◽

10.1175/jcli-d-20-0085.1 ◽

2021 ◽

pp. 1-54

Author(s):

Daehyun Kang ◽

Daehyun Kim ◽

Min-Seop Ahn ◽

Soon-Il An

Keyword(s):

Southern Oscillation ◽

Moisture Gradient ◽

Moisture Distribution ◽

Maritime Continent ◽

Budget Analysis ◽

Sea Surface Temperature Anomalies ◽

The Mean ◽

Strong Control ◽

Meridional Advection

AbstractThis study investigates the role of the background meridional moisture gradient (MMG) on the propagation of the Madden–Julian Oscillation (MJO) across the Maritime Continent (MC) region. It is found that the interannual variability of the seasonal mean MMG over the southern MC area is associated with the meridional expansion and contraction of the moist area in the vicinity of the MC. Sea surface temperature anomalies associated with relatively high and low seasonal mean MMG exhibit patterns that resemble those of the El Niño–Southern Oscillation. By contrasting the years with anomalously low and high MMG, we show that MJO propagation through the MC is enhanced (suppressed) in years with higher (lower) seasonal mean MMG, though the effect is less robust when MMG anomalies are weak. Column-integrated moisture budget analysis further shows that sufficiently large MMG anomalies affects MJO activity by modulating the meridional advection of the mean moisture via MJO wind anomalies. Our results suggest that the background moisture distribution has a strong control over the propagation characteristics of the MJO in the MC region.

Download Full-text

Correlation between the Onset of the East Asian Subtropical Summer Monsoon and the Eastward Propagation of the Madden–Julian Oscillation

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-14-0038.1 ◽

2015 ◽

Vol 72 (3) ◽

pp. 1200-1214 ◽

Cited By ~ 11

Author(s):

Yanzhen Chi ◽

Fuqing Zhang ◽

Wei Li ◽

Jinhai He ◽

Zhaoyong Guan

Keyword(s):

Summer Monsoon ◽

Asian Summer Monsoon ◽

East Asian ◽

Longwave Radiation ◽

Meridional Wind ◽

South Asian High ◽

Madden Julian Oscillation ◽

Asian Summer ◽

The Mean ◽

Climate Prediction Center

Abstract Using the daily outgoing longwave radiation (OLR), the pentad Climate Prediction Center Merged Analysis of Precipitation (CMAP), and the 6-h Climate Forecast System Reanalysis (CFSR) dataset from 1979 to 2010, a composite analysis along with space–time wave filtering is performed to examine the linkage between the Madden–Julian oscillation (MJO) and the onset of the East Asian subtropical summer monsoon (EASSM) (over 20°–30°N, 110°–120°E). The onset of the EASSM is shown to be best characterized by the reversal of the mean meridional wind shear related to the rapid reestablishment of the South Asian high (SAH) over the southern Indochinese Peninsula in the upper troposphere. The mean date of EASMM onset is near the end of April, which is about a month earlier than the typical onset of the East Asian summer monsoon. Further analysis indicates that the onset of the EASSM and the reestablishment of SAH are often associated with the arrival of the wet phase of the tropical MJO over the central and eastern Indian Ocean.

Download Full-text

Active and weakening MJO events in the Maritime Continent

Climate Dynamics ◽

10.1007/s00382-021-05699-8 ◽

2021 ◽

Author(s):

Bradford S. Barrett ◽

Casey R. Densmore ◽

Pallav Ray ◽

Elizabeth R. Sanabia

Keyword(s):

El Niño ◽

El Nino ◽

Southern Oscillation ◽

Longwave Radiation ◽

Specific Humidity ◽

Atmospheric Moisture ◽

Maritime Continent ◽

Quasi Biennial Oscillation ◽

Westerly Winds ◽

Biennial Oscillation

AbstractTo better understand the Madden–Julian Oscillation (MJO) in the Maritime Continent (MC), events from 1980 to 2019 were classified as active or weakening according to propagation characteristics and amplitude changes in two leading indices, the Real-time Multivariate MJO (RMM) index and Outgoing Longwave Radiation (OLR) MJO Index (OMI). Active MJO events had larger index amplitudes than weakening events, and those amplitude differences appeared at day − 3 in the RMM and day − 8 in the OMI and remained through day + 15 in both indices (day 0 marked the day an event entered the MC). Thus, active events were stronger than weakening events as they approached and crossed the MC. To understand differences in environments between these events, composites of OLR and specific humidity were compared for each. Active MJO events had consistently more negative OLR anomalies and greater specific humidity in both the boundary layer and free troposphere than weakening MJO events. Those differences persisted during both easterly and westerly phases of the Quasi-biennial Oscillation (QBO) and during La Niña and El Niño. Active MJO events during QBO westerly winds had more specific humidity than active events did during QBO easterly winds. Finally, both active and weakening MJO events featured a diurnal cycle of lower-tropospheric specific humidity over land areas of the MC, and the amount of atmospheric moisture available to active events was consistently greater than weakening ones. These results indicate that index amplitude, OLR, and tropospheric specific humidity can all be important tools in identifying active and weakening MJO events in the MC, including for different phases of the QBO and the El Niño-Southern Oscillation (ENSO).

Download Full-text

RESPON CURAH HUJAN DIURNAL TERHADAP MADDEN-JULIAN OSCILLATION AKTIF DI BENUA MARITIM BERBASIS GSMAP GAUGE-CALIBRATED V7

Jurnal Sains & Teknologi Modifikasi Cuaca ◽

10.29122/jstmc.v22i1.4525 ◽

2021 ◽

Vol 22 (1) ◽

pp. 17-24

Author(s):

Achmad Fahruddin Rais ◽

Ahmad Kosasih ◽

Soenardi ◽

Yamin Saleh Saidu ◽

Sanya Gautami ◽

...

Keyword(s):

Phase Shift ◽

Outgoing Longwave Radiation ◽

Longwave Radiation ◽

Madden Julian Oscillation ◽

Maritime Continent ◽

June July August ◽

Diurnal Rainfall ◽

The Mean ◽

June July ◽

Peak Phase

Intisari Keberadaan pergeseran puncak curah hujan diurnal (DR) terhadap Madden-Julian Oscillation (MJO) aktif di Maritime Continent (MC) masih diperdebatkan sehingga studi ini bertujuan untuk menginvestigasi perubahan tersebut. Selain itu, intensitas rata-rata dan amplitudo DR juga dikaji dalam penelitian ini berbasis GSMaP Gauge-Calibrated V7. Komposit anomali intensitas rata-rata (Ra), amplitudo (Rax) DR MJO aktif dan perbandingan fase puncak DR MJO aktif terhadap klimatologinya (Pax-Pm) pada periode Desember-Januari-Februari (DJF), Maret-April-Mei (MAM), Juni-Juli-Agustus (JJA) dan September-Oktober-November (SON) digunakan dalam tulisan ini dengan uji-z 80%. MJO aktif berbasis rekonstruksi outgoing longwave radiation (OLR) dari kedua indeks realtime multivariate MJO (RMM). Hasil memperlihatkan bahwa MJO aktif memodulasi peningkatan intensitas rata-rata dan amplitudo DR di lautan dan mempengaruhi pergeseran puncak DR menjadi lebih cepat 1 jam dari klimatologi musimannya. Abstract The occurrence of peak phase shift of diurnal rainfall (DR) to active Madden-Jullian Oscillation (MJO) has been debatable, so this study is aimed to investigate the change. Moreover, the mean and amplitude intensity of DR were also analyzed in this study based on GSMaP Gauge-Calibrated V7. The composite of the mean (Ra) and amplitude (Rax) intensity anomaly of DR, and the comparison of DR peak phase during the active MJO to its climatology (Pax-Pm) in the period December-January-February (DJF), March-April-May (MAM), June-July-August (JJA), and September-October-November (SON) were used in the study with the z-test of 80%. The active MJO was based on reconstructed outgoing longwave radiation (OLR) of two real-time multivariate MJO (RMM) indexes. The results showed that active MJO modulated the increased mean and amplitude intensity of DR over the ocean and influenced the DR peak phase shift to be faster than its seasonal climatology by one hour.

Download Full-text

The MJO on the equatorial beta-plane: an eastward propagating Rossby wave induced by meridional moisture advection

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-21-0071.1 ◽

2021 ◽

Author(s):

Fiaz Ahmed

Keyword(s):

Rossby Wave ◽

Phase Speed ◽

Moisture Gradient ◽

Slow Phase ◽

Horizontal Structure ◽

Low Level ◽

Budget Analysis ◽

Moisture Advection ◽

Beta Plane ◽

Equatorial Rossby Wave

AbstractLinearized wave solutions on the equatorial beta-plane are examined in the presence of a background meridional moisture gradient. Of interest is a slow, eastward propagating n = 1 mode that is unstable at planetary scales and only exists for a small range of zonal wavenumbers (≲ 6). The mode dispersion curve appears as an eastward extension of the westward propagating equatorial Rossby wave solution. This mode is therefore termed the eastward propagating equatorial Rossby wave (ERW). The zonal wavenumber 2 ERW horizontal structure consists of a low-level equatorial convergence center flanked by quadrupole off-equatorial gyres, and resembles the horizontal structure of the observed MJO. An analytic, leading order dispersion relationship for the ERW shows that meridional moisture advection imparts eastward propagation, and that the smallness of a gross moist stability like parameter contributes to the slow phase speed. The ERW is unstable near planetary scales when low-level easterlies moisten the column. This moistening could come from either zonal moisture advection or surface fluxes or a combination thereof. When westerlies instead moisten the column, the ERW is damped and the westward propagating long Rossby wave is unstable. The ERW does not exist when the meridional moisture gradient is too weak. A moist static energy budget analysis shows that the ERW scale selection is partly due to finite timescale convective adjustment and less effective zonal wind-induced moistening at smaller scales. Similarities in the phase speed, preferred scale and horizontal structure suggest that the ERW is a beta-plane analog of the MJO.

Download Full-text

Characteristics of Large-Scale Circulation Affecting the Inter-Annual Precipitation Variability in Northern Sumatra Island during Boreal Summer

Atmosphere ◽

10.3390/atmos12020136 ◽

2021 ◽

Vol 12 (2) ◽

pp. 136

Author(s):

Yahya Darmawan ◽

Huang-Hsiung Hsu ◽

Jia-Yuh Yu

Keyword(s):

Large Scale ◽

Precipitation Variability ◽

Specific Humidity ◽

Boreal Summer ◽

Moisture Budget ◽

Large Scale Circulation ◽

Budget Analysis ◽

Sumatra Island ◽

Precipitation Anomalies ◽

The Impact

This study aims to explore the contrasting characteristics of large-scale circulation that led to the precipitation anomalies over the northern parts of Sumatra Island. Further, the impact of varying the Asian–Australian Monsoon (AAM) was investigated for triggering the precipitation variability over the study area. The moisture budget analysis was applied to quantify the most dominant component that induces precipitation variability during the JJA (June, July, and August) period. Then, the composite analysis and statistical approach were applied to confirm the result of the moisture budget. Using the European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Anaysis Interim (ERA-Interim) from 1981 to 2016, we identified 9 (nine) dry and 6 (six) wet years based on precipitation anomalies, respectively. The dry years (wet years) anomalies over the study area were mostly supported by downward (upward) vertical velocity anomaly instead of other variables such as specific humidity, horizontal velocity, and evaporation. In the dry years (wet years), there is a strengthening (weakening) of the descent motion, which triggers a reduction (increase) of convection over the study area. The overall downward (upward) motion of westerly (easterly) winds appears to suppress (support) the convection and lead to negative (positive) precipitation anomaly in the whole region but with the largest anomaly over northern parts of Sumatra. The AAM variability proven has a significant role in the precipitation variability over the study area. A teleconnection between the AAM and other global circulations implies the precipitation variability over the northern part of Sumatra Island as a regional phenomenon. The large-scale tropical circulation is possibly related to the PWC modulation (Pacific Walker Circulation).

Download Full-text

Human Contribution to the Increasing Summer Precipitation in Central Asia from 1961 to 2013

Journal of Climate ◽

10.1175/jcli-d-17-0843.1 ◽

2018 ◽

Vol 31 (19) ◽

pp. 8005-8021 ◽

Cited By ~ 15

Author(s):

Dongdong Peng ◽

Tianjun Zhou ◽

Lixia Zhang ◽

Bo Wu

Keyword(s):

Central Asia ◽

Vertical Motion ◽

Summer Precipitation ◽

Specific Humidity ◽

Moisture Budget ◽

Anthropogenic Forcing ◽

Radiative Forcings ◽

Budget Analysis ◽

Community Atmosphere Model ◽

Advection Term

The ecosystem and societal development over arid Central Asia, the core connecting region of the Silk Road Economic Belt, are highly sensitive to climate change. The results derived from multiobservational datasets show that summer precipitation over Central Asia has significantly increased by 20.78% from 1961 to 2013. It remains unclear whether anthropogenic forcing has contributed to the summer wetting trend or not. In this study, the corresponding physical processes and contributions of anthropogenic forcing are investigated by comparing reanalysis and experiments of the Community Atmosphere Model, version 5.1 (CAM5.1), from the CLIVAR Climate of the Twentieth Century Plus (C20C+) Project. The observed wetting trend is well reproduced in the simulation driven by all radiative forcings (CAM5-All), but poorly reproduced in the simulation with natural forcings only (CAM5-Nat), confirming the important role of human contribution in the observed wetting trend. Moisture budget analysis shows that the observed wetting trend is dominated by the increasing vertical moisture advection term and results from enhanced vertical motion over nearly all of Central Asia. The observed contributions of moisture budget components to the wetting trend are only captured by CAM5-All experiments. The dynamic contribution is determined by the warm advection anomalies in association with a human-induced meridional uneven warm pattern. Human-induced warming increases the specific humidity over all of Central Asia, increasing (decreasing) the precipitation over the climatological ascent (descent) region in eastern (western) Central Asia.

Download Full-text

Local Finite-Amplitude Wave Activity as a Diagnostic for Rossby Wave Packets

Monthly Weather Review ◽

10.1175/mwr-d-18-0068.1 ◽

2018 ◽

Vol 146 (12) ◽

pp. 4099-4114 ◽

Cited By ~ 4

Author(s):

Paolo Ghinassi ◽

Georgios Fragkoulidis ◽

Volkmar Wirth

Keyword(s):

Rossby Wave ◽

Model Simulation ◽

Wave Packets ◽

Meridional Wind ◽

Finite Amplitude ◽

Wave Activity ◽

Amplitude Wave ◽

High Impact Weather ◽

Finite Amplitude Wave Activity ◽

Isentropic Coordinates

AbstractUpper-tropospheric Rossby wave packets (RWPs) are important dynamical features, because they are often associated with weather systems and sometimes act as precursors to high-impact weather. The present work introduces a novel diagnostic to identify RWPs and to quantify their amplitude. It is based on the local finite-amplitude wave activity (LWA) of Huang and Nakamura, which is generalized to the primitive equations in isentropic coordinates. The new diagnostic is applied to a specific episode containing large-amplitude RWPs and compared with a more traditional diagnostic based on the envelope of the meridional wind. In this case, LWA provides a more coherent picture of the RWPs and their zonal propagation. This difference in performance is demonstrated more explicitly in the framework of an idealized barotropic model simulation, where LWA is able to follow an RWP into its fully nonlinear stage, including cutoff formation and wave breaking, while the envelope diagnostic yields reduced amplitudes in such situations.

Download Full-text