The Role of Air–Sea Interaction for Prediction of Australian Summer Monsoon Rainfall

Abstract Forecast skill for seasonal mean rainfall across northern Australia is lower during the summer monsoon than in the premonsoon transition season based on 25 years of hindcasts using the Predictive Ocean Atmosphere Model for Australia (POAMA) coupled model seasonal forecast system. The authors argue that this partly reflects an intrinsic property of the monsoonal system, whereby seasonally varying air–sea interaction in the seas around northern Australia promotes predictability in the premonsoon season and demotes predictability after monsoon onset. Trade easterlies during the premonsoon season support a positive feedback between surface winds, SST, and rainfall, which results in stronger and more persistent SST anomalies to the north of Australia that compliment the remote forcing of Australian rainfall from El Niño in the Pacific. After onset of the Australian summer monsoon, this local feedback is not supported in the monsoonal westerly regime, resulting in weaker SST anomalies to the north of Australia and with lower persistence than in the premonsoon season. Importantly, the seasonality of this air–sea interaction is captured in the POAMA forecast model. Furthermore, analysis of perfect model forecasts and forecasts generated by prescribing observed SST results in largely the same conclusion (i.e., significantly lower actual and potential forecast skill during the monsoon), thereby supporting the notion that air–sea interaction contributes to intrinsically lower predictability of rainfall during the monsoon.

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Roles of the Indian Ocean in the Australian Summer Monsoon–ENSO Relationship

Journal of Climate ◽

10.1175/jcli4281.1 ◽

2007 ◽

Vol 20 (18) ◽

pp. 4768-4788 ◽

Cited By ~ 18

Author(s):

Renguang Wu ◽

Ben P. Kirtman

Keyword(s):

Indian Ocean ◽

Summer Monsoon ◽

Negative Correlation ◽

Coupled Model ◽

Term Change ◽

Australian Summer Monsoon ◽

The Indian Ocean ◽

Sst Anomalies ◽

Australian Summer

Abstract A negative correlation is observed between interannual variations of the Australian summer monsoon (ASM) and El Niño–Southern Oscillation (ENSO). This negative relationship is well simulated in the Center for Ocean–Land–Atmosphere (COLA) interactive ensemble coupled general circulation model (CGCM). The present study investigates roles of the Indian Ocean in the ASM–ENSO relationship through controlled numerical experiments with the COLA CGCM. It is found that air–sea coupling in the Indian Ocean plays an important role in maintaining the negative ASM–ENSO relationship. When the Indian Ocean is decoupled from the atmosphere, the ASM–ENSO relationship is significantly weakened or even masked by the internal atmospheric variability. This change in the ASM–ENSO relationship is related to complementary roles of Indian Ocean sea surface temperature (SST) anomalies in the ASM variability and feedbacks from the Indian Ocean on ENSO. Without a coupled Indian Ocean, the ENSO amplitude is reduced, leading to a decrease in the ENSO-induced ASM variability, and the constructive impacts of the Indian Ocean SST anomalies on the ASM variability are substantially reduced. This reduces the ASM variability related to ENSO. Consistent with the change in the ASM–ENSO relationship, the local air–sea relationship in the ASM region displays important differences with and without a coupled Indian Ocean. The long-term change in the ASM–ENSO relationship is related to that in ENSO amplitude in the interactive ensemble coupled model. A relatively higher (lower) negative correlation occurs in periods of larger (smaller) ENSO amplitude. This relationship, however, is not clear in the anomaly coupled model with only one atmospheric realization. This difference is attributed to changes in the signal-to-noise ratio in the ASM variability. A comparison is made with observations and the long-term change in the Indian summer monsoon (ISM)–ENSO relationship in the model.

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Possible Role of the Indian Ocean in the In-Phase Transition of the Indian-to-Australian Summer Monsoon

Journal of Climate ◽

10.1175/2008jcli2354.1 ◽

2008 ◽

Vol 21 (21) ◽

pp. 5727-5741 ◽

Cited By ~ 10

Author(s):

Renguang Wu

Keyword(s):

Indian Ocean ◽

Summer Monsoon ◽

Southern Oscillation ◽

Tropical Indian Ocean ◽

Australian Summer Monsoon ◽

The Indian Ocean ◽

Numerical Model Experiments ◽

Sst Anomalies ◽

Australian Summer

Abstract Analysis of observations shows that in-phase transitions from the Indian summer monsoon (ISM) to the Australian summer monsoon (ASM) have occurred both in El Niño–Southern Oscillation (ENSO) and non-ENSO years. The present study investigates possible roles of the Indian Ocean in the in-phase ISM-to-ASM transitions. It is shown that an anomalous ISM leads to sea surface temperature (SST) anomalies in the tropical Indian Ocean through wind–evaporation effects. The resultant Indian Ocean SST anomalies induce an anomalous ASM of the same sign as the ISM through an anomalous east–west circulation over the eastern Indian Ocean and the Maritime Continent–northern Australia. The results indicate that the in-phase ISM-to-ASM transitions in non-ENSO years can be accomplished through monsoon–Indian Ocean interactions. The results of observational analysis are confirmed with numerical model experiments.

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The Onset of the Indonesian–Australian Summer Monsoon Triggered by the First-Branch Eastward-Propagating Madden–Julian Oscillation

Journal of Climate ◽

10.1175/jcli-d-18-0513.1 ◽

2019 ◽

Vol 32 (17) ◽

pp. 5453-5470 ◽

Cited By ~ 4

Author(s):

Yongliang Duan ◽

Hongwei Liu ◽

Weidong Yu ◽

Lin Liu ◽

Guang Yang ◽

...

Keyword(s):

Summer Monsoon ◽

Heat Budget ◽

Sea Surface ◽

Specific Humidity ◽

Surface Mixed Layer ◽

Madden Julian Oscillation ◽

Northern Australia ◽

Surface Warming ◽

Australian Summer Monsoon ◽

Australian Summer

Abstract The Madden–Julian oscillation (MJO) often causes the onset of the Indonesian–Australian summer monsoon (IASM) over Indonesia and northern Australia. In the present study, a composite analysis is conducted to reveal the detailed IASM onset process and its air–sea interactions associated with the first-branch eastward-propagating MJO (FEMJO) based on 30-yr ERA-Interim data, satellite-derived sea surface temperature (SST), outgoing longwave radiation (OLR), and SODA3 ocean reanalysis. The results distinctly illustrate the phase-locked relationships among the persistent sea surface warming north of Australia, the FEMJO, and the established westerlies. It is found that the SST to the north of Australia reaches its annual maximum just before the onset of the summer monsoon. The oceanic surface mixed layer heat budget discloses that this rapid warming is primarily produced by the enhanced surface heat flux. In addition, this premonsoon sea surface warming increases the air specific humidity in the low-level troposphere and then establishes zonal moisture asymmetry relative to the FEMJO convection. This creates a more unstable atmospheric stratification southeast of the FEMJO and favors convection throughout the vicinity of northern Australia, which ultimately triggers the onset of the IASM. The results in this study thus may potentially be applicable to seasonal monsoon climate monitoring and prediction.

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Possible roles of regional SST anomalies in long-term changes in the relationship between the Indian and Australian summer monsoon rainfall

Theoretical and Applied Climatology ◽

10.1007/s00704-015-1443-9 ◽

2015 ◽

Vol 124 (3-4) ◽

pp. 663-677 ◽

Cited By ~ 7

Author(s):

Renguang Wu

Keyword(s):

Summer Monsoon ◽

Monsoon Rainfall ◽

Summer Monsoon Rainfall ◽

Long Term Changes ◽

Australian Summer Monsoon ◽

The Relationship ◽

Sst Anomalies ◽

Australian Summer

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Changes in the in-phase relationship between the Indian and subsequent Australian summer monsoons during the past five decades

Annales Geophysicae ◽

10.5194/angeo-25-1929-2007 ◽

2007 ◽

Vol 25 (9) ◽

pp. 1929-1933 ◽

Cited By ~ 1

Author(s):

J.-Y. Yu ◽

M. A. Janiga

Keyword(s):

Summer Monsoon ◽

Indian Summer Monsoon ◽

Phase Relationship ◽

Austral Summer ◽

Australian Monsoon ◽

The Past ◽

The Pacific ◽

Australian Summer Monsoon ◽

Sst Anomalies ◽

Australian Summer

Abstract. This study examines the decadal changes in the in-phase relationship between Indian summer monsoon and the subsequent Australian summer monsoon using observational data from 1950–2005. The in-phase relationship is the tendency for a strong Indian summer monsoon to be followed by a strong Australian summer monsoon and vice versa. It is found that the in-phase relationship was weak during the late 1950s and early 1960s, strengthened to a maximum in the early 1970s just before the 1976/77 Pacific climate shift, then declined until the late 1990s. Pacific SST anomalies are noticed to have strong persistence from boreal to austral summer, providing the memory to connect the Indian and subsequent Australian summer monsoon. The simultaneous correlation between the Pacific SST anomalies and the Indian summer monsoon is always strong. It is the weakening and strengthening of the simultaneous correlation between the Australian summer monsoon and the Pacific SST anomalies that contributes to the decadal variations of the in-phase monsoon relation. This study suggests that the interaction between the Australian monsoon and the Pacific Ocean is crucial to tropical climate variability and has experienced significant changes over the past five decades.

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