Climatology and Interannual Variability of Convectively Coupled Equatorial Waves Activity

2011 ◽  
Vol 24 (16) ◽  
pp. 4451-4465 ◽  
Author(s):  
Ping Huang ◽  
Ronghui Huang
Keyword(s):  
Indian Ocean ◽  
Interannual Variability ◽  
El Niño ◽  
El Nino ◽  
Warm Pool ◽  
Eastern Pacific ◽  
Kelvin Wave ◽  
Convectively Coupled Equatorial Waves ◽  
Equatorial Wave ◽  
Sst Anomaly

Abstract Climatology and interannual variability of convectively coupled equatorial wave (CCEW) activity, including the mixed Rossby–gravity (MRG), tropical-depression-type (TD-type), equatorial Rossby (ER), and Kelvin waves, are investigated using the satellite-observed brightness temperature data from the Cloud Archive User Service. The monthly activity of CCEWs is represented by the root mean square of the daily filtered convections in each month based on the Wheeler–Kiladis filtering method. More precise seasonal cycles of CCEW activity are obtained from the meridional and zonal mean climatology. Interannual variance of CCEW activity is further investigated. Kelvin wave activity has maximum interannual variance over the eastern Pacific, while the other three waves are most variable in the intertropical convergence zone. The four active CCEWs all have significant correlation with the background convection and local sea surface temperature (SST) over the central and eastern Pacific, but they are not significantly correlated over other regions. The El Niño events may induce more trapped and active CCEWs over the central and eastern Pacific but weaker MRG and TD-type waves over the warm pool. In contrast, the El Niño Modoki has much weaker correlation with CCEW activity. CCEW activity over the southeastern Indian Ocean is negatively correlated with the Indian Ocean dipole, while that over the western and northern Indian Ocean may be determined by atmospheric internal disturbances. The tropical southern Atlantic mode is the strongest Atlantic SST anomaly mode correlated with the Atlantic CCEW activity.

scholarly journals A Comparative Analysis of the Impacts of Two Types of El Niño on the Central and Eastern Pacific ITCZ

Atmosphere ◽  
2018 ◽  
Vol 9 (7) ◽  
pp. 266
Author(s):  
Jinshuang Zhu ◽  
Yudi Liu ◽  
Ruiqing Xie ◽  
Haijie Chang
Keyword(s):  
Rossby Wave ◽  
El Niño ◽  
El Nino ◽  
Eastern Pacific ◽  
Wave Response ◽  
Mature Period ◽  
Rossby Wave Response ◽  
Sst Anomaly ◽  
Ep El Niño ◽  
Meridional Mode

The precipitation data from the Global Precipitation Climatology Project (GPCP) and CPC Merged Analysis of Precipitation (CMAP) were used to investigate the discrepancy of Centre and Eastern Pacific ITCZ (CEP-ITCZ) during two types of El Niño years. Two models of the heat source distribution during two types of El Niño events were constructed, and the causes of different CEP-ITCZ anomalies for two types of El Niño events were analyzed through the Gill model. The results show that the CEP-ITCZ precipitation is approximately 4.0° southward, and the intensity is enhanced by 3.6 mm/day during the mature period of Eastern Pacific El Niño (EP-El Niño), while during the mature period of Central Pacific El Niño (CP-El Niño), it is only 0.8° southward, and the intensity is enhanced by 3.2 mm/day. The meridional mode of the SST anomaly by means of EOF (Empirical Orthogonal Function) can indirectly affect the CEP-ITCZ by influencing the atmospheric Rossby wave response. In CP-El Niño years, the meridional mode of the SST anomaly is weak, and the atmospheric Rossby wave response enhances the northern and southern trade-wind zones at the same time. The anomaly of cross-equatorial flow is weak and the CEP-ITCZ moves southward a little. At the same time, the wind convergence zone is enhanced, and it is more conducive to the vertical transport of water vapor. In EP-El Niño years, the meridional mode of the SST anomaly is strong, and the atmospheric Rossby wave response strengthens the meridional wind on the northern side of the equator, leading to the southward shift of the CEP-ITCZ. At the same time, the wind convergence zone is weakened and widened, and to a certain extent, it suppresses the vertical transport increase of water vapor caused by the sea surface evaporation.

scholarly journals The Seasonal Development of an SST Anomaly in the Indian Ocean and Its Relationship to ENSO

2007 ◽  
Vol 20 (1) ◽  
pp. 38-52 ◽  
Author(s):  
Motoki Nagura ◽  
Masanori Konda
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
El Nino ◽  
Surface Wind ◽  
La Niña ◽  
Seasonal Development ◽  
La Nina ◽  
The Indian Ocean ◽  
Dipole Pattern ◽  
Sst Anomaly

Abstract The seasonal development of the sea surface temperature (SST) anomaly in the Indian Ocean is investigated in relation to El Niño–Southern Oscillation (ENSO), using NOAA optimally interpolated SST and NCEP reanalysis data. The result shows that the onset season of El Niño affects the seasonal development of surface wind anomalies over the equatorial eastern Indian Ocean (EEIO); these surface wind anomalies, in turn, determine whether the SST anomaly in the EEIO evolves into the eastern pole of the dipole pattern. In years when the dipole pattern develops, surface zonal wind anomalies over the EEIO switch from westerly to easterly in spring as La Niña switches to El Niño. The seasonal zonal wind over the EEIO also switches from westerly to easterly in spring, and the anomalous wind strengthens seasonal wind from winter to summer. Stronger winds and resultant thermal forcings produce the negative SST anomaly in the EEIO in winter, and its amplitude increases in summer. The SST anomaly becomes the eastern pole of the dipole pattern in fall. In contrast, if the change from La Niña to El Niño is delayed until late summer/fall or if La Niña persists throughout the year, a westerly anomaly persists from winter to summer over the EEIO. The persistent westerly anomaly strengthens the wintertime climatological westerlies and weakens the summertime easterlies. Therefore, negative SST anomalies are produced in the EEIO in winter, but the amplitude decreases in summer, and the eastern pole is not present in fall. The above explanation also applies to onset years of La Niña if the signs of the anomalies are reversed.

Two Types of El Niño Events: Cold Tongue El Niño and Warm Pool El Niño

2009 ◽  
Vol 22 (6) ◽  
pp. 1499-1515 ◽  
Author(s):  
Jong-Seong Kug ◽  
Fei-Fei Jin ◽  
Soon-Il An
Keyword(s):  
Spatial Patterns ◽  
El Niño ◽  
El Nino ◽  
Warm Pool ◽  
Discharge Process ◽  
Cold Tongue ◽  
El Niño Events ◽  
Sst Anomaly ◽  
Sst Anomalies ◽  
El Nino Events

Abstract In this study, two types of El Niño events are classified based on spatial patterns of the sea surface temperature (SST) anomaly. One is the cold tongue (CT) El Niño, which can be regarded as the conventional El Niño, and the other the warm pool (WP) El Niño. The CT El Niño is characterized by relatively large SST anomalies in the Niño-3 region (5°S–5°N, 150°–90°W), while the WP El Niño is associated with SST anomalies mostly confined to the Niño-4 region (5°S–5°N, 160°E–150°W). In addition, spatial patterns of many atmospheric and oceanic variables are also distinctively different for the two types of El Niño events. Furthermore, the difference in the transition mechanism between the two types of El Niño is clearly identified. That is, the discharge process of the equatorial heat content associated with the WP El Niño is not efficient owing to the spatial structure of SST anomaly; as a result, it cannot trigger a cold event. It is also demonstrated that zonal advective feedback (i.e., zonal advection of mean SST by anomalous zonal currents) plays a crucial role in the development of a decaying SST anomaly associated with the WP El Niño, while thermocline feedback is a key process during the CT El Niño.

Mechanisms for the Interannual Variability in the Tropical Indian Ocean. Part II: Regional Processes

2007 ◽  
Vol 20 (13) ◽  
pp. 2937-2960 ◽  
Author(s):  
Bohua Huang ◽  
J. Shukla
Keyword(s):  
Indian Ocean ◽  
Interannual Variability ◽  
El Niño ◽  
El Nino ◽  
Tropical Indian Ocean ◽  
Global Ocean ◽  
Trade Wind ◽  
Tropical Ocean ◽  
The Indian Ocean ◽  
Sst Anomalies

Abstract To understand the mechanisms of the interannual variability in the tropical Indian Ocean, two long-term simulations are conducted using a coupled ocean–atmosphere GCM—one with active air–sea coupling over the global ocean and the other with regional coupling restricted within the Indian Ocean to the north of 30°S while the climatological monthly sea surface temperatures (SSTs) are prescribed in the uncoupled oceans to drive the atmospheric circulation. The major spatial patterns of the observed upper-ocean heat content and SST anomalies can be reproduced realistically by both simulations, suggesting that they are determined by intrinsic coupled processes within the Indian Ocean. In both simulations, the interannual variability in the Indian Ocean is dominated by a tropical mode and a subtropical mode. The tropical mode is characterized by a coupled feedback among thermocline depth, zonal SST gradient, and wind anomalies over the equatorial and southern tropical Indian Ocean, which is strongest in boreal fall and winter. The tropical mode simulated by the global coupled model reproduces the main observational features, including a seasonal connection to the model El Niño–Southern Oscillation (ENSO). The ENSO influence, however, is weaker than that in a set of ensemble simulations described in Part I of this study, where the observed SST anomalies for 1950–98 are prescribed outside the Indian Ocean. Combining with the results from Part I of this study, it is concluded that ENSO can modulate the temporal variability of the tropical mode through atmospheric teleconnection. Its influence depends on the ENSO strength and duration. The stronger and more persistent El Niño events in the observations extend the life span of the anomalous events in the tropical Indian Ocean significantly. In the regional coupled simulation, the tropical mode is still active, but its dominant period is shifted away from that of ENSO. In the absence of ENSO forcing, the tropical mode is mainly stimulated by an anomalous atmospheric direct thermal cell forced by the fluctuations of the northwestern Pacific monsoon. The subtropical mode is characterized by an east–west dipole pattern of the SST anomalies in the southern subtropical Indian Ocean, which is strongest in austral fall. The SST anomalies are initially forced by surface heat flux anomalies caused by the anomalous southeast trade wind in the subtropical ocean during austral summer. The trade wind anomalies are in turn associated with extratropical variations from the southern annular mode. A thermodynamic air–sea feedback strengthens these subtropical anomalies quickly in austral fall and extends their remnants into the tropical ocean in austral winter. In the simulations, this subtropical variability is independent of ENSO.

Indian Ocean Variability in the GFDL Coupled Climate Model

2007 ◽  
Vol 20 (13) ◽  
pp. 2895-2916 ◽  
Author(s):  
Qian Song ◽  
Gabriel A. Vecchi ◽  
Anthony J. Rosati
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
El Nino ◽  
Deep Convection ◽  
Warm Pool ◽  
Surface Winds ◽  
Pacific Warm Pool ◽  
El Niño Events ◽  
The Indian Ocean ◽  
El Nino Events

Abstract The interannual variability of the Indian Ocean, with particular focus on the Indian Ocean dipole/zonal mode (IODZM), is investigated in a 250-yr simulation of the GFDL coupled global general circulation model (CGCM). The CGCM successfully reproduces many fundamental characteristics of the climate system of the Indian Ocean. The character of the IODZM is explored, as are relationships between positive IODZM and El Niño events, through a composite analysis. The IODZM events in the CGCM grow through feedbacks between heat-content anomalies and SST-related atmospheric anomalies, particularly in the eastern tropical Indian Ocean. The composite IODZM events that co-occur with El Niño have stronger anomalies and a sharper east–west SSTA contrast than those that occur without El Niño. IODZM events, whether or not they occur with El Niño, are preceded by distinctive Indo-Pacific warm pool anomaly patterns in boreal spring: in the central Indian Ocean easterly surface winds, and in the western equatorial Pacific an eastward shift of deep convection, westerly surface winds, and warm sea surface temperature. However, delayed onsets of the anomaly patterns (e.g., boreal summer) are often not followed by IODZM events. The same anomaly patterns often precede El Niño, suggesting that the warm pool conditions favorable for both IODZM and El Niño are similar. Given that IODZM events can occur without El Niño, it is proposed that the observed IODZM–El Niño relation arises because the IODZM and El Niño are both large-scale phenomena in which variations of the Indo-Pacific warm pool deep convection plays a central role. Yet each phenomenon has its own dynamics and life cycle, allowing each to develop without the other. The CGCM integration also shows substantial decadal modulation of the occurrence of IODZM events, which is found to be not in phase with that of El Niño events. There is a weak, though significant, negative correlation between the two. Moreover, the statistical relationship between the IODZM and El Niño displays strong decadal variability.

scholarly journals Indian Ocean Feedback to the ENSO Transition in a Multimodel Ensemble

2012 ◽  
Vol 25 (20) ◽  
pp. 6942-6957 ◽  
Author(s):  
Jong-Seong Kug ◽  
Yoo-Geun Ham
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
Climate Models ◽  
El Nino ◽  
Coupled Model ◽  
Warm Pool ◽  
Multimodel Ensemble ◽  
Phase 3 ◽  
Intercomparison Project ◽  
The Western Pacific

Abstract Observational studies hypothesized that Indian Ocean (IO) feedback plays a role in leading to a fast transition of El Niño. When El Niño accompanies IO warming, IO warming induces the equatorial easterlies over the western Pacific (WP), leading to a rapid termination of El Niño via an oceanic adjust process. In this study, this IO feedback is reinvestigated using the Coupled Model Intercomparison Project phase 3 (CMIP3) coupled GCM simulations. It is found that most of the climate models mimic this IO feedback reasonably, supporting the observational hypothesis. However, most climate models tend to underestimate the strength of the IO feedback, which means the phase transition of ENSO due to the IO feedback is less effective than the observed one. Furthermore, there is great intermodel diversity in simulating the strength of the IO feedback. It is shown that the strength of the IO feedback is related to the precipitation responses to El Niño and IO SST forcings over the warm-pool regions. Moreover, the authors suggest that the distribution of climatological precipitation is one important component in controlling the strength of the IO feedback.

scholarly journals Tropical Indian Ocean Influence on Northwest Pacific Tropical Cyclones in Summer following Strong El Niño*

2011 ◽  
Vol 24 (1) ◽  
pp. 315-322 ◽  
Author(s):  
Yan Du ◽  
Lei Yang ◽  
Shang-Ping Xie
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
El Nino ◽  
Tropical Indian Ocean ◽  
Vertical Shear ◽  
Northwest Pacific ◽  
Kelvin Wave ◽  
Anomalous Anticyclone ◽  
The Western Pacific ◽  
Inducing Surface

Abstract In the summer following a strong El Niño, tropical cyclone (TC) number decreases over the Northwest (NW) Pacific despite little change in local sea surface temperature. The authors’ analysis suggests El Niño–induced tropical Indian Ocean (TIO) warming as the cause. The TIO warming forces a warm tropospheric Kelvin wave that propagates into the western Pacific. Inducing surface divergence off the equator, the tropospheric Kelvin wave suppresses convection and induces an anomalous anticyclone over the NW Pacific, both anomalies unfavorable for TCs. The westerly vertical shear associated with the warm Kelvin wave reduces the magnitude of vertical shear in the South China Sea and strengthens it in the NW Pacific, an east–west variation that causes TC activity to increase and decrease in respective regions. These results help improve seasonal TC prediction.

scholarly journals Indian Ocean Variability in the CMIP5 Multimodel Ensemble: The Basin Mode

2013 ◽  
Vol 26 (18) ◽  
pp. 7240-7266 ◽  
Author(s):  
Yan Du ◽  
Shang-Ping Xie ◽  
Ya-Li Yang ◽  
Xiao-Tong Zheng ◽  
Lin Liu ◽  
...  
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Tropical Indian Ocean ◽  
Ocean Basin ◽  
North Indian Ocean ◽  
Cmip5 Models ◽  
Northwest Pacific ◽  
Kelvin Wave

Abstract This study evaluates the simulation of the Indian Ocean Basin (IOB) mode and relevant physical processes in models from phase 5 of the Coupled Model Intercomparison Project (CMIP5). Historical runs from 20 CMIP5 models are available for the analysis. They reproduce the IOB mode and its close relationship to El Niño–Southern Oscillation (ENSO). Half of the models capture key IOB processes: a downwelling oceanic Rossby wave in the southern tropical Indian Ocean (TIO) precedes the IOB development in boreal fall and triggers an antisymmetric wind anomaly pattern across the equator in the following spring. The anomalous wind pattern induces a second warming in the north Indian Ocean (NIO) through summer and sustains anticyclonic wind anomalies in the northwest Pacific by radiating a warm tropospheric Kelvin wave. The second warming in the NIO is indicative of ocean–atmosphere interaction in the interior TIO. More than half of the models display a double peak in NIO warming, as observed following El Niño, while the rest show only one winter peak. The intermodel diversity in the characteristics of the IOB mode seems related to the thermocline adjustment in the south TIO to ENSO-induced wind variations. Almost all the models show multidecadal variations in IOB variance, possibly modulated by ENSO.

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