scholarly journals An Observation-Based Assessment of Nonlinear Feedback Processes Associated with the Indian Ocean Dipole

2013 ◽  
Vol 26 (9) ◽  
pp. 2880-2890 ◽  
Author(s):  
Wenju Cai ◽  
Yun Qiu
Keyword(s):  
Indian Ocean ◽  
Indian Ocean Dipole ◽  
Shortwave Radiation ◽  
Heating Process ◽  
Evaporative Heat Loss ◽  
Damping Effect ◽  
Temperature Feedback ◽  
The Indian Ocean ◽  
Sst Anomalies

Abstract A well-known feature of the Indian Ocean dipole (IOD) is its positive skewness, with cold sea surface temperature (SST) anomalies over the east pole (IODE) exhibiting a larger amplitude than warm SST anomalies. Several mechanisms have been proposed for this asymmetry, but because of a lack of observations the role of various processes remains contentious. Using Argo profiles and other newly available data, the authors provide an observation-based assessment of the IOD skewness. First, the role of a nonlinear dynamical heating process is reaffirmed, which reinforces IODE cold anomalies but damps IODE warm anomalies. This reinforcing effect is greater than the damping effect, further contributing to the skewness. Second, the existence of a thermocline–temperature feedback asymmetry, whereby IODE cold anomalies induced by a shoaling thermocline are greater than warm anomalies associated with a deepening thermocline, is the primary forcing of the IOD skewness. This thermocline–temperature feedback asymmetry is a part of the nonlinear Bjerknes-like positive feedback loop involving winds, SST, and the thermocline, all displaying a consistent asymmetry with a stronger response when IODE SST is anomalously cold. The asymmetry is enhanced by a nonlinear barrier layer response, with a greater thinning associated with IODE cold anomalies than a thickening associated with IODE warm anomalies. Finally, in response to IODE cool anomalies, rainfall and evaporative heat loss diminish and incoming shortwave radiation increases, which results in damping the cool SST anomalies. The damping increases with IODE cold anomalies. Thus, the IOD skewness is generated in spite of a greater damping effect of the SST–cloud–radiation feedback process.

scholarly journals Role of the Indian Ocean in the Biennial Transition of the Indian Summer Monsoon

2007 ◽  
Vol 20 (10) ◽  
pp. 2147-2164 ◽  
Author(s):  
Renguang Wu ◽  
Ben P. Kirtman
Keyword(s):  
Indian Ocean ◽  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Indian Monsoon ◽  
Coupled Model ◽  
The Pacific ◽  
The Indian Ocean ◽  
Biennial Variability ◽  
Sst Anomalies

Abstract The biennial variability is a large component of year-to-year variations in the Indian summer monsoon (ISM). Previous studies have shown that El Niño–Southern Oscillation (ENSO) plays an important role in the biennial variability of the ISM. The present study investigates the role of the Indian Ocean in the biennial transition of the ISM when the Pacific ENSO is absent. The influence of the Indian and Pacific Oceans on the biennial transition between the ISM and the Australian summer monsoon (ASM) is also examined. Controlled numerical experiments with a coupled general circulation model (CGCM) are used to address the above two issues. The CGCM captures the in-phase ISM to ASM transition (i.e., a wet ISM followed by a wet ASM or a dry ISM followed by a dry ASM) and the out-of-phase ASM to ISM transition (i.e., a wet ASM followed by a dry ISM or a dry ASM followed by a wet ISM). These transitions are more frequent than the out-of-phase ISM to ASM transition and the in-phase ASM to ISM transition in the coupled model, consistent with observations. The results of controlled coupled model experiments indicate that both the Indian and Pacific Ocean air–sea coupling are important for properly simulating the biennial transition between the ISM and ASM in the CGCM. The biennial transition of the ISM can occur through local air–sea interactions in the north Indian Ocean when the Pacific ENSO is suppressed. The local sea surface temperature (SST) anomalies induce the Indian monsoon transition through low-level moisture convergence. Surface evaporation anomalies, which are largely controlled by surface wind speed changes, play an important role for SST changes. Different from local air–sea interaction mechanisms proposed in previous studies, the atmospheric feedback is not strong enough to reverse the SST anomalies immediately at the end of the monsoon season. Instead, the reversal of the SST anomalies is accomplished in the spring of the following year, which in turn leads to the Indian monsoon transition.

scholarly journals Mechanisms of asymmetry in sea surface temperature anomalies associated with the Indian Ocean Dipole revealed by closed heat budget

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Mai Nakazato ◽  
Shoichiro Kido ◽  
Tomoki Tozuka
Keyword(s):  
Indian Ocean ◽  
Surface Temperature ◽  
Indian Ocean Dipole ◽  
Heat Budget ◽  
Vertical Mixing ◽  
Sea Surface ◽  
Subsurface Temperature ◽  
Thermocline Feedback ◽  
The Indian Ocean ◽  
Sst Anomalies

AbstractThe Indian Ocean Dipole (IOD) is an interannual climate mode of the tropical Indian Ocean. Although it is known that negative sea surface temperature (SST) anomalies in the eastern pole during the positive IOD are stronger than positive SST anomalies during the negative IOD, no consensus has been reached on the relative importance of various mechanisms that contribute to this asymmetry. Based on a closed mixed layer heat budget analysis using a regional ocean model, here we show for the first time that the vertical mixing plays an important role in causing such asymmetry in SST anomalies in addition to the contributions from the nonlinear advection and the thermocline feedback proposed by previous studies. A decomposition of the vertical mixing term indicates that nonlinearity in the anomalous vertical temperature gradient associated with subsurface temperature anomalies and anomalous vertical mixing coefficients is the main driver of such asymmetry. Such variations in subsurface temperature are induced by the anomalous southeasterly trade winds along the Indonesian coast that modulate the thermocline depth through coastal upwelling/downwelling. Thus, the thermocline feedback contributes to the SST asymmetry not through the vertical advection as previously suggested, but via the vertical mixing.

scholarly journals Factors Affecting the 2019 Atlantic Hurricane Season and the Role of the Indian Ocean Dipole

2020 ◽  
Vol 47 (13) ◽  
Author(s):  
Kimberly M. Wood ◽  
Philip J. Klotzbach ◽  
Jennifer M. Collins ◽  
Louis‐Philippe Caron ◽  
Ryan E. Truchelut ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Indian Ocean Dipole ◽  
Factors Affecting ◽  
Atlantic Hurricane ◽  
Hurricane Season ◽  
The Indian Ocean

scholarly journals Impact of the South China Sea Summer Monsoon on the Indian Ocean Dipole

2018 ◽  
Vol 31 (16) ◽  
pp. 6557-6573 ◽  
Author(s):  
Yazhou Zhang ◽  
Jianping Li ◽  
Jiaqing Xue ◽  
Juan Feng ◽  
Qiuyun Wang ◽  
...  
Keyword(s):  
Indian Ocean ◽  
South China Sea ◽  
Summer Monsoon ◽  
South China ◽  
Indian Ocean Dipole ◽  
The South China Sea ◽  
The South ◽  
China Sea ◽  
The Indian Ocean ◽  
Sst Anomalies

This paper investigates the impact of the South China Sea summer monsoon (SCSSM) on the Indian Ocean dipole (IOD). The results show that the SCSSM has a significant positive relationship with the IOD over the boreal summer [June–August (JJA)] and fall [September–November (SON)]. When the SCSSM is strong, the enhanced southwesterly winds that bring more water vapor to the western North Pacific (WNP) lead to surplus precipitation in the WNP, inducing anomalous ascending there. Consequently, the anomalous descending branch of the SCSSM Hadley circulation (SCSSMHC) develops over the Maritime Continent (MC), favoring deficit precipitation in situ. The precipitation dipole over the WNP and MC as well as the enhanced SCSSMHC leads to intensification of the southeasterly anomalies off Sumatra and Java, which then contributes to the negative sea surface temperature (SST) anomalies through the positive wind–evaporation–SST and wind–thermocline–SST (Bjerknes) feedbacks. Consequently, a positive IOD develops because of the increased zonal gradient of the tropical Indian Ocean SST anomalies and vice versa. The SCSSM has a peak correlation with the IOD when the former leads the latter by three months. This implies that a positive IOD can persist from JJA to SON and reach its mature phase within the frame of the positive Bjerknes feedback in SON. In addition, the local and remote SST anomalies in the tropical Indian and Pacific Oceans have a slight influence on the relationship between the SCSSM and precipitation dipole over the WNP and MC.

scholarly journals Phytoplankton blooms induced/sustained by cyclonic eddies during the Indian Ocean Dipole event of 1997 along the southern coasts of Java and Sumatra

2008 ◽  
Vol 5 (5) ◽  
pp. 3905-3918 ◽  
Author(s):  
P. Rahul Chand Reddy ◽  
P. S. Salvekar
Keyword(s):  
Indian Ocean ◽  
Indian Ocean Dipole ◽  
State Of The Art ◽  
Sea Surface ◽  
Phytoplankton Blooms ◽  
Indian Ocean Dipole Event ◽  
Indonesian Archipelago ◽  
The Indian Ocean ◽  
The Tropics ◽  
Sst Anomalies

Abstract. The Indonesian archipelago is the gateway in the tropics connecting two oceans (Pacific and the Indian Ocean) and two continents (Asia and Australia). During the Indian Ocean Dipole 1997, record anomalous and unanticipated upwelling had occurred along the southern coasts of Java and Sumatra causing massive phytoplankton blooms. But the method/mode/process for such anomalous upwelling was not known. Using monthly SeaWifs chlorophyll-a anomalies, TOPEX Sea Surface Height (SSH) anomalies, Sea Surface Temperatures (SST) and currents from a state-of-the-art OGCM, we report the presence of a series of cyclonic eddies along southern coasts of Sumatra and Java during November, December 1997 and January 1998. Upwelling caused by these cyclonic eddies, as also supported by the SSH and SST anomalies, has been responsible for the phytoplankton blooms to persist and dissipate during the 3 months (November, December 1997 and January 1998).

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

2008 ◽  
Vol 21 (21) ◽  
pp. 5727-5741 ◽  
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.

scholarly journals Possible Role of the Indian Ocean in the Out-of-Phase Transition of the Australian to Indian Summer Monsoon

2009 ◽  
Vol 22 (7) ◽  
pp. 1834-1849 ◽  
Author(s):  
Renguang Wu
Keyword(s):  
Indian Ocean ◽  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Tropical Indian Ocean ◽  
North Indian Ocean ◽  
The North ◽  
The Indian Ocean ◽  
Sst Anomalies ◽  
Type Of Transition

Abstract The present study investigates processes for out-of-phase transitions from the Australian summer monsoon (ASM) to the Indian summer monsoon (ISM). Two types of out-of-phase ASM-to-ISM transitions have been identified, depending on the evolution of the Pacific El Niño–Southern Oscillation (ENSO) events. The first type of transition is accompanied by a phase switch of ENSO in boreal spring to early summer. In the second type of transition, ENSO maintains its phase through boreal summer. The direct ENSO forcing plays a primary role for the first type of out-of-phase ASM-to-ISM transition, with complementary roles from the north Indian Ocean sea surface temperature (SST) anomalies that are partly induced by ENSO. The second type of out-of-phase ASM-to-ISM transition involves air–sea interaction processes in the tropical Indian Ocean that generate the north Indian Ocean SST anomalies and contribute to the monsoon transition. The initiation of tropical Indian Ocean air–sea interaction is closely related to ENSO in observations, but could also occur without ENSO according to a coupled general circulation model simulation. Results of numerical simulations substantiate the role of the Indian Ocean air–sea interaction in the out-of-phase ASM-to-ISM transition.

Impact of the South China Sea summer monsoon on the Indian Ocean dipole in CMIP5 models

2020 ◽  
pp. 1
Author(s):  
Yazhou Zhang ◽  
Jianping Li ◽  
Fei Zheng ◽  
Miao Yu ◽  
Juan Feng ◽  
...  
Keyword(s):  
Indian Ocean ◽  
South China Sea ◽  
Summer Monsoon ◽  
South China ◽  
Indian Ocean Dipole ◽  
Cmip5 Models ◽  
Physical Processes ◽  
Low Level ◽  
The Indian Ocean ◽  
Sst Anomalies

AbstractThe impact of the South China Sea summer monsoon (SCSSM) on the Indian Ocean dipole (IOD) has been systematically investigated in observations. This study focuses on the ability of climate models participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5) to reproduce the observed relationship between the SCSSM and IOD, and the relevant physical mechanisms. All 23 models reproduce significant correlations between the SCSSM and IOD during boreal summer (June–July–August, JJA), whereas the influence of the SCSSM on the IOD varies considerably across the CMIP5 models. To explore the causes, all models are divided into two groups. Models that successfully simulated both the correlations between the SCSSM and JJA IOD and of the SCSSM and JJA IOD with precipitation over the western North Pacific and Maritime Continent are classified as Type-I, and these produce stronger low-level wind anomalies over the tropical southeastern Indian Ocean. The stronger low-level wind anomalies enhance local sea surface temperature (SST) anomalies via positive wind–evaporation–SST (WES) and wind–thermocline–SST (Bjerknes) feedbacks. This corresponds to a strengthening of IOD events due to the increased zonal gradient of SST anomalies over the tropical Indian Ocean. In contrast, Type-II models perform poorly in representing the relationship between the SCSSM and JJA IOD or relevant physical processes, corresponding to weaker WES and Bjerknes feedbacks, and produce weaker IOD events. These results demonstrate that the better the model simulation of the critical physical processes, the larger contribution of the SCSSM to the IOD.

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