scholarly journals Role of Indian and Pacific SST in Indian Summer Monsoon Intraseasonal Variability

2011 ◽  
Vol 24 (12) ◽  
pp. 2915-2930 ◽  
Author(s):  
Deepthi Achuthavarier ◽  
V. Krishnamurthy
Keyword(s):  
Indian Ocean ◽  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
General Circulation ◽  
Singular Spectrum Analysis ◽  
Intraseasonal Variability ◽  
Circulation Model ◽  
The Pacific ◽  
The Indian Ocean

Abstract Three regionally coupled experiments are conducted to examine the role of Indian and Pacific sea surface temperature (SST) in Indian summer monsoon intraseasonal variability using the National Centers for Environmental Prediction’s Climate Forecast System, a coupled general circulation model. Regional coupling is employed by prescribing daily mean or climatological SST in either the Indian or the Pacific basin while allowing full coupling elsewhere. The results are compared with a fully coupled control simulation. The intraseasonal modes are isolated by applying multichannel singular spectrum analysis on the daily precipitation anomalies. It is found that the amplitude of the northeastward-propagating mode is weaker when the air–sea interaction is suppressed in the Indian Ocean. The intraseasonal mode is not resolved clearly when the Indian Ocean SST is reduced to daily climatology. Intraseasonal composites of low-level zonal wind, latent heat flux, downward shortwave radiation, and SST provide a picture consistent with the proposed mechanisms of air–sea interaction for the northward propagation. The Pacific SST variability does not seem to be critical for the existence of this mode. The northwestward-propagating mode is obtained in the cases where the Indian Ocean was prescribed by daily mean or daily climatological SST. Intraseasonal SST composites corresponding to this mode are weak.

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 Bomb 14C in the Indian Ocean Measured by Accelerator Mass Spectrometry: Oceanographic Implications

Radiocarbon ◽  
1989 ◽  
Vol 31 (03) ◽  
pp. 510-522 ◽  
Author(s):  
Edouard Bard ◽  
Maurice Arnold ◽  
J R Toggweiler ◽  
Pierre Maurice ◽  
Jean-Claude Duplessy
Keyword(s):  
Mass Spectrometry ◽  
Indian Ocean ◽  
General Circulation ◽  
Circulation Model ◽  
Equatorial Indian Ocean ◽  
Equatorial Zone ◽  
Mode Water ◽  
Indonesian Archipelago ◽  
The Pacific ◽  
The Indian Ocean

AMS 14C measurements on samples collected in the tropical-equatorial Indian Ocean during the INDIGO program (leg II, 1986) are presented and compared with β-counting results obtained under both INDIGO program and GEOSECS expedition in the Indian Ocean (1978). The most significant observation is a doubling of the bomb-14C inventory and mean penetration depth in the equatorial zone. Based on hydrologic considerations, two hypotheses can be proposed: 1) direct influx of Pacific mid-latitude waters through the Indonesian archipelago and 2) advection and/or mixing with Mode Water from the southern gyre of the Indian Ocean. Results obtained with a general circulation model of the ocean suggest that the influx from the Pacific is important in the upper 300m and that below 500m the bomb-14C budget is dominated by Mode Water advection.

scholarly journals Influence of the Pacific–Japan Pattern on Indian Summer Monsoon Rainfall

2018 ◽  
Vol 31 (10) ◽  
pp. 3943-3958 ◽  
Author(s):  
G. Srinivas ◽  
Jasti S. Chowdary ◽  
Yu Kosaka ◽  
C. Gnanaseelan ◽  
Anant Parekh ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
General Circulation ◽  
Rossby Waves ◽  
Function Analysis ◽  
Circulation Model ◽  
Easterly Wind ◽  
Low Level ◽  
The Pacific ◽  
The Impact

Abstract This study discusses the impact of the Pacific–Japan (PJ) pattern on Indian summer monsoon (ISM) rainfall and its possible physical linkages through coupled and uncoupled pathways. Empirical orthogonal function analysis of 850-hPa relative vorticity over the western North Pacific (WNP) is used to extract the PJ pattern as the leading mode of circulation variability. The partial correlation analysis of the leading principal component reveals that the positive PJ pattern, which features anticyclonic and cyclonic low-level circulation anomalies over the tropical WNP and around Japan respectively, enhances the rainfall over the southern and northern parts of India. The northwestward propagating Rossby waves, in response to intensified convection over the Maritime Continent reinforced by low-level convergence in the southern flank of westward extended tropical WNP anticyclone, increase rainfall over southern peninsular India. Meanwhile, the anomalous moisture transport from the warm Bay of Bengal due to anomalous southerlies at the western edge of the low-level anticyclone extending from the tropical WNP helps to enhance the rainfall over northern India. The atmospheric general circulation model forced with climatological sea surface temperature confirms this atmospheric pathway through the westward propagating Rossby waves. Furthermore, the north Indian Ocean (NIO) warming induced by easterly wind anomalies along the southern periphery of the tropical WNP–NIO anticyclone enhances local convection, which in turn feeds back to the WNP convection anomalies. This coupled nature via interbasin feedback between the PJ pattern and NIO is confirmed using coupled model sensitivity experiments. These results are important in identifying new sources of ISM variability/predictability on the interannual time scale.

Two Regimes of the Equatorial Warm Pool. Part II: Hybrid Coupled GCM Experiments

2008 ◽  
Vol 21 (14) ◽  
pp. 3545-3560 ◽  
Author(s):  
Masahiro Watanabe
Keyword(s):  
Simple Model ◽  
Indian Ocean ◽  
General Circulation ◽  
Climate Model ◽  
Climate Modeling ◽  
Circulation Model ◽  
Warm Pool ◽  
Bjerknes Feedback ◽  
The Pacific ◽  
The Indian Ocean

Abstract In this second of a two-part study, the two regimes in a simple tropical climate model identified in Part I are verified using a hybrid coupled general circulation model (HCM) that can reproduce the observed climatology and the interannual variability reasonably well. Defining a ratio of basin width between the Pacific and Indian Oceans, a series of parameter sweep experiments was conducted with idealized tropical land geometry. Consistent with the simple model, the HCM simulates two distinct states: the split warm pool regime with large vacillation between the two ocean basins and the single warm pool regime representing current climate. The former is suddenly switched to the latter as the Pacific becomes wider than the Indian Ocean. Furthermore, the vacillation in the split regime reveals a preferred transition route that the warm phase in the Pacific follows that in the Indian Ocean. This route occurs due to convectively coupled Kelvin waves that accompany precipitation anomalies over land. Additional experiments show that the inclusion of the idealized Eurasian continent stabilizes the split regime by reducing the Bjerknes feedback in the Indian Ocean, suggesting the atmosphere–ocean–land interaction at work in maintaining the observed warm pool. No difference in cloud feedback was found between two regimes; this feature may, however, be model dependent. Both the simple model and the HCM results suggest that the tropical atmosphere–ocean system inherently involves multiple solutions, which may have an implication on climate modeling as well as on the understanding of the observed mean climate.

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.

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