Precessional Forced Zonal Triple-Pole Anomalies in the Tropical Pacific Annual Cycle

2019 ◽  
Vol 32 (21) ◽  
pp. 7369-7402 ◽  
Author(s):  
Yue Wang ◽  
ZhiMin Jian ◽  
Ping Zhao ◽  
Kang Xu ◽  
Haowen Dang ◽  
...  
Keyword(s):  
Annual Cycle ◽  
Walker Circulation ◽  
Bjerknes Feedback ◽  
Central Pacific ◽  
Annual Cycles ◽  
Basin Scale ◽  
Pole Type ◽  
Air Flows ◽  
Winter Insolation ◽  
Sst Anomalies

Abstract Based on a transient simulation of the Community Earth System Model, we identified two anomalous “zonal triple-pole type” annual cycles in the equatorial Pacific sea surface temperature (SST), which were induced by precessional evolution of the summer-minus-winter insolation difference and the autumn-minus-spring insolation difference, respectively. For example, due to the increased summer–winter insolation contrast, a zonal positive–negative–positive pattern of equatorial SST anomalies was detected after subtracting basin-scale summer SST warming. The positive SST anomalies were associated with anomalous upward air flows over the western Pacific and eastern Pacific, whereas the negative SST anomalies in the central Pacific were coupled with anomalous downward air flows, oceanic upwelling, and thermocline cooling. These central Pacific anomalies were due to multiple air–sea interactions, particularly zonal advection feedback and Bjerknes feedback. This anomalous annual cycle also included winter equatorial air–sea coupled anomalies with similar spatial patterns but opposite signs. The annual mean equatorial rainfall was significantly increased west of 135°E but decreased between 135°E and 160°W in response to the moderately intensified Walker circulation west of 160°W. The autumn–spring insolation contrast induced similar seasonal reversed anomalies during autumn and spring, but the annual means were only weakly enhanced for the Walker circulation and the rainfall anomalies had smaller magnitudes east of 160°E. These distinct responses of the annual mean climate indicated different seasonal biases in terms of the equatorial SST and associated Walker circulation anomalies due to forcing by the two seasonal insolation contrasts, and these findings had meaningful implications for paleoceanographic studies.

scholarly journals Indo-Pacific Variability on Seasonal to Multidecadal Time Scales. Part II: Multiscale Atmosphere–Ocean Linkages

2018 ◽  
Vol 31 (2) ◽  
pp. 693-725 ◽  
Author(s):  
Dimitrios Giannakis ◽  
Joanna Slawinska
Keyword(s):  
Time Scales ◽  
El Niño ◽  
El Nino ◽  
Walker Circulation ◽  
La Niña ◽  
Central Pacific ◽  
Australian Monsoon ◽  
La Nina ◽  
Combination Modes ◽  
Sst Anomalies

The coupled atmosphere–ocean variability of the Indo-Pacific domain on seasonal to multidecadal time scales is investigated in CCSM4 and in observations through nonlinear Laplacian spectral analysis (NLSA). It is found that ENSO modes and combination modes of ENSO with the annual cycle exhibit a seasonally synchronized southward shift of equatorial surface zonal winds and thermocline adjustment consistent with terminating El Niño and La Niña events. The surface winds associated with these modes also generate teleconnections between the Pacific and Indian Oceans, leading to SST anomalies characteristic of the Indian Ocean dipole. The family of NLSA ENSO modes is used to study El Niño–La Niña asymmetries, and it is found that a group of secondary ENSO modes with more rapidly decorrelating temporal patterns contributes significantly to positively skewed SST and zonal wind statistics. Besides ENSO, fundamental and combination modes representing the tropospheric biennial oscillation (TBO) are found to be consistent with mechanisms for seasonally synchronized biennial variability of the Asian–Australian monsoon and Walker circulation. On longer time scales, a multidecadal pattern referred to as the west Pacific multidecadal mode (WPMM) is established to significantly modulate ENSO and TBO activity, with periods of negative SST anomalies in the western tropical Pacific favoring stronger ENSO and TBO variability. This behavior is attributed to the fact that cold WPMM phases feature anomalous decadal westerlies in the tropical central Pacific, as well as an anomalously flat zonal thermocline profile in the equatorial Pacific. Moreover, the WPMM is found to correlate significantly with decadal precipitation over Australia.

Climate Dynamics of ENSO Modoki Phenomena

2018 ◽  
Author(s):  
Swadhin Behera ◽  
Toshio Yamagata
Keyword(s):  
El Niño ◽  
El Nino ◽  
Walker Circulation ◽  
The United States ◽  
La Niña ◽  
Central Pacific ◽  
El Niño Modoki ◽  
Enso Modoki ◽  
La Nina ◽  
Sst Anomalies

The El Niño Modoki/La Niña Modoki (ENSO Modoki) is a newly acknowledged face of ocean-atmosphere coupled variability in the tropical Pacific Ocean. The oceanic and atmospheric conditions associated with the El Niño Modoki are different from that of canonical El Niño, which is extensively studied for its dynamics and worldwide impacts. A typical El Niño event is marked by a warm anomaly of sea surface temperature (SST) in the equatorial eastern Pacific. Because of the associated changes in the surface winds and the weakening of coastal upwelling, the coasts of South America suffer from widespread fish mortality during the event. Quite opposite of this characteristic change in the ocean condition, cold SST anomalies prevail in the eastern equatorial Pacific during the El Niño Modoki events, but with the warm anomalies intensified in the central Pacific. The boreal winter condition of 2004 is a typical example of such an event, when a tripole pattern is noticed in the SST anomalies; warm central Pacific flanked by cold eastern and western regions. The SST anomalies are coupled to a double cell in anomalous Walker circulation with rising motion in the central parts and sinking motion on both sides of the basin. This is again a different feature compared to the well-known single-cell anomalous Walker circulation during El Niños. La Niña Modoki is the opposite phase of the El Niño Modoki, when a cold central Pacific is flanked by warm anomalies on both sides.The Modoki events are seen to peak in both boreal summer and winter and hence are not seasonally phase-locked to a single seasonal cycle like El Niño/La Niña events. Because of this distinction in the seasonality, the teleconnection arising from these events will vary between the seasons as teleconnection path will vary depending on the prevailing seasonal mean conditions in the atmosphere. Moreover, the Modoki El Niño/La Niña impacts over regions such as the western coast of the United States, the Far East including Japan, Australia, and southern Africa, etc., are opposite to those of the canonical El Niño/La Niña. For example, the western coasts of the United States suffer from severe droughts during El Niño Modoki, whereas those regions are quite wet during El Niño. The influences of Modoki events are also seen in tropical cyclogenesis, stratosphere warming of the Southern Hemisphere, ocean primary productivity, river discharges, sea level variations, etc. A remarkable feature associated with Modoki events is the decadal flattening of the equatorial thermocline and weakening of zonal thermal gradient. The associated ocean-atmosphere conditions have caused frequent and persistent developments of Modoki events in recent decades.

scholarly journals The Annual-Cycle Modulation of Meridional Asymmetry in ENSO’s Atmospheric Response and Its Dependence on ENSO Zonal Structure

2015 ◽  
Vol 28 (14) ◽  
pp. 5795-5812 ◽  
Author(s):  
Wenjun Zhang ◽  
Haiyan Li ◽  
Fei-Fei Jin ◽  
Malte F. Stuecker ◽  
Andrew G. Turner ◽  
...  
Keyword(s):  
Annual Cycle ◽  
El Niño ◽  
El Nino ◽  
Warm Pool ◽  
Atmospheric Response ◽  
Central Pacific ◽  
Cp El Niño ◽  
El Niño Events ◽  
Sst Anomalies ◽  
El Nino Events

Abstract Previous studies documented that a distinct southward shift of central Pacific low-level wind anomalies occurring during the ENSO decaying phase is caused by an interaction between the western Pacific annual cycle and El Niño–Southern Oscillation (ENSO) variability. The present study finds that the meridional movement of the central Pacific wind anomalies appears only during traditional eastern Pacific El Niño (EP El Niño) events rather than in central Pacific El Niño (CP El Niño) events in which sea surface temperature (SST) anomalies are confined to the central Pacific. The zonal structure of ENSO-related SST anomalies therefore has an important effect on meridional asymmetry in the associated atmospheric response and its modulation by the annual cycle. In contrast to EP El Niño events, the SST anomalies of CP El Niño events extend farther west toward the warm pool region with its climatological warm SSTs. In the warm pool region, relatively small SST anomalies are thus able to excite convection anomalies on both sides of the equator, even with a meridionally asymmetric SST background state. Therefore, almost meridionally symmetric precipitation and wind anomalies are observed over the central Pacific during the decaying phase of CP El Niño events. The SST anomaly pattern of La Niña events is similar to CP El Niño events with a reversed sign. Accordingly, no distinct southward displacement of the atmospheric response occurs over the central Pacific during the La Niña decaying phase. These results have important implications for ENSO climate impacts over East Asia, since the anomalous low-level anticyclone over the western North Pacific is an integral part of the annual cycle–modulated ENSO response.

scholarly journals ENSO Influence on the Atlantic Niño, Revisited: Multi-Year versus Single-Year ENSO Events

2019 ◽  
Vol 32 (14) ◽  
pp. 4585-4600 ◽  
Author(s):  
Hiroki Tokinaga ◽  
Ingo Richter ◽  
Yu Kosaka
Keyword(s):  
Southern Oscillation ◽  
Walker Circulation ◽  
Equatorial Atlantic ◽  
Bjerknes Feedback ◽  
Central Pacific ◽  
Boreal Spring ◽  
Enso Events ◽  
The Past ◽  
Convergence Zones ◽  
Atlantic Niño

Abstract The influence of El Niño–Southern Oscillation (ENSO) on the Atlantic Niño over the past 113 years is investigated by comparing multi-year and single-year ENSO events. Multi-year ENSO events sustain an anomalous zonal gradient of sea surface temperature (SST) in the equatorial western to central Pacific even during boreal spring and summer. This SST gradient is coupled with an anomalous Walker circulation and atmospheric deep convection through the Bjerknes feedback. During multi-year La Niñas, for example, a strengthened Pacific Walker circulation extends into the tropical Atlantic in boreal spring, a season when both the Pacific and Atlantic intertropical convergence zones become more symmetric about the equator. As a result, surface westerly wind anomalies appear over the equatorial Atlantic, triggering an Atlantic Niño. By contrast, such a teleconnection is not found in the spring following the peak of single-year ENSO events. A Pacific pacemaker model experiment reproduces the observed atmospheric response and its impact on the Atlantic Niño, further supporting the importance of prolonged ENSO forcing. The contrasting influence of multi-year and single-year events explains the fragile relationship between ENSO and the Atlantic Niño. An empirical orthogonal function (EOF) analysis shows that the leading EOF mode (EOF-1) for the spring tropical western to central Pacific SST anomalies captures the characteristics of multi-year ENSO events. EOF-1 is highly correlated with the summer Atlantic Niño over the past 113 years while the Niño-3 SST is not. These correlations indicate that ocean–atmosphere coupling in the equatorial western to central Pacific plays a major role in shaping ENSO teleconnections in boreal spring.

scholarly journals Linking Centennial Surface Warming Patterns in the Equatorial Pacific to the Relative Strengths of the Walker and Hadley Circulations

2014 ◽  
Vol 71 (9) ◽  
pp. 3454-3464 ◽  
Author(s):  
Jian Ma ◽  
Jin-Yi Yu
Keyword(s):  
El Niño ◽  
El Nino ◽  
Coupled Model ◽  
Walker Circulation ◽  
Equatorial Pacific ◽  
Bjerknes Feedback ◽  
Central Pacific ◽  
Surface Warming ◽  
Temperature Feedback ◽  
Intercomparison Project

Abstract This study analyzes representative concentration pathway 4.5 projections by 18 models from phase 5 of the Coupled Model Intercomparison Project to show that surface warming patterns in the equatorial Pacific during the twenty-first century (centennial warming) are influenced by the relative strengths of the Walker and Hadley circulations. The stronger the Hadley (Walker) circulation is, the greater the surface warming in the central Pacific (CP) [eastern Pacific (EP)]. The EP warming is associated with the Bjerknes feedback, while the CP warming is associated with the wind–evaporation–sea surface temperature feedback. This atmospheric circulation influence on the centennial warming is similar to that found for the EP and CP El Niño. This suggests a methodology to constrain the estimate of the projected surface warming patterns in the equatorial Pacific using recent El Niño activity. The constraint indicates that the “most likely” centennial warming patterns have a maximum in the EP and are 39% weaker than the warming projected by the 18-model mean. The most-likely projection also shows alternating stronger and weaker warming in the subtropical North Pacific, which is not predicted by the 18-model mean projection. Nevertheless, the two projections agree on the minimum warming in the southeastern subtropical Pacific.

scholarly journals Simulation, Precursor Analysis and Targeted Observation Sensitive Area Identification for Two Types of ENSO using ENSO-MC v1.0

2022 ◽  
Author(s):  
Bin Mu ◽  
Yuehan Cui ◽  
Shijin Yuan ◽  
Bo Qin
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Heat Content ◽  
Sensitive Area ◽  
Bjerknes Feedback ◽  
Central Pacific ◽  
Sensitive Areas ◽  
Targeted Observation ◽  
Sst Anomalies

Abstract. The global impact of an El Niño-Southern Oscillation (ENSO) event can differ greatly depending on whether it is an Eastern-Pacific-type (EP-type) event or a Central-Pacific-type (CP-type) event. Reliable predictions of the two types of ENSO are therefore of critical importance. Here we construct a deep neural network with multichannel structure for ENSO (named ENSO-MC) to simulate the spatial evolution of sea surface temperature (SST) anomalies for the two types of events. We select SST, heat content, and wind stress (i.e., three key ingredients of Bjerknes feedback) to represent coupled ocean-atmosphere dynamics that underpins ENSO, achieving skillful forecasts for the spatial patterns of SST anomalies out to one year ahead. Furthermore, it is of great significance to analyze the precursors of EP-type or CP-type events and identify targeted observation sensitive area for the understanding and prediction of ENSO. Precursors analysis is to determine what type of initial perturbations will develop into EP-type or CP-type events. Sensitive area identification is to determine the regions where initial states tend to have greatest impacts on evolution of ENSO. We use saliency map method to investigate the subsurface precursors and identify the sensitive areas of ENSO. The results show that there are pronounced signals in the equatorial subsurface before EP events, while the precursory signals of CP events are located in the North Pacific. It indicates that the subtropical precursors seem to favor the generation of the CP-type El Niño and the EP-type El Niño is more related to the tropical thermocline dynamics. And the saliency maps show that the sensitive areas of the surface and the subsurface are located in the equatorial central Pacific and the equatorial western Pacific, respectively. The sensitivity experiments imply that additional observations in the identified sensitive areas can improve forecasting skills. Our results of precursors and sensitive areas are consistent with the previous theories of ENSO, demonstrating the potential usage and advantages of the ENSO-MC model in improving the simulation, understanding and observations of two ENSO types.

Annual, Interannual, and Intraseasonal Variability of Tropical Tropopause Transition Layer Cirrus

2010 ◽  
Vol 67 (10) ◽  
pp. 3097-3112 ◽  
Author(s):  
Katrina S. Virts ◽  
John M. Wallace
Keyword(s):  
Annual Cycle ◽  
El Niño ◽  
Transition Layer ◽  
El Nino ◽  
Southern Oscillation ◽  
Cirrus Clouds ◽  
Boreal Winter ◽  
Central Pacific ◽  
Tropical Tropopause ◽  
The Pacific

Abstract Cloud fields based on the first three years of data from the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) mission are used to investigate the relationship between cirrus within the tropical tropopause transition layer (TTL) and the Madden–Julian oscillation (MJO), the annual cycle, and El Niño–Southern Oscillation (ENSO). The TTL cirrus signature observed in association with the MJO resembles convectively induced, mixed Kelvin–Rossby wave solutions above the Pacific warm pool region. This signature is centered to the east of the peak convection and propagates eastward more rapidly than the convection; it exhibits a pronounced eastward tilt with height, suggestive of downward phase propagation and upward energy dispersion. A cirrus maximum is observed over equatorial Africa and South America when the enhanced MJO-related convection enters the western Pacific. Tropical-mean TTL cirrus is modulated by the MJO, with more than twice as much TTL cirrus fractional coverage equatorward of 10° latitude when the enhanced convection enters the Pacific than a few weeks earlier, when the convection is over the Indian Ocean. The annual cycle in cirrus clouds around the base of the TTL is equatorially asymmetric, with more cirrus observed in the summer hemisphere. Higher in the TTL, the annual cycle in cirrus clouds is more equatorially symmetric, with a maximum in the boreal winter throughout most of the tropics. The ENSO signature in TTL cirrus is marked by a zonal shift of the peak cloudiness toward the central Pacific during El Niño and toward the Maritime Continent during La Niña.

Changes in the Amplitude of the Temperature Annual Cycle in China and Their Implication for Climate Change Research

2011 ◽  
Vol 24 (20) ◽  
pp. 5292-5302 ◽  
Author(s):  
Cheng Qian ◽  
Congbin Fu ◽  
Zhaohua Wu
Keyword(s):  
Climate Change ◽  
Annual Cycle ◽  
Linear Trend ◽  
Surface Air Temperature ◽  
Mean Amplitude ◽  
Warming Trend ◽  
Ensemble Empirical Mode Decomposition ◽  
Surface Solar Radiation ◽  
Climate Change Research ◽  
Annual Cycles

Abstract Climate change is not only reflected in the changes in annual means of climate variables but also in the changes in their annual cycles (seasonality), especially in the regions outside the tropics. In this study, the ensemble empirical mode decomposition (EEMD) method is applied to investigate the nonlinear trend in the amplitude of the annual cycle (which contributes 96% of the total variance) of China’s daily mean surface air temperature for the period 1961–2007. The results show that the variation and change in the amplitude are significant, with a peak-to-peak annual amplitude variation of 13% (1.8°C) of its mean amplitude and a significant linear decrease in amplitude by 4.6% (0.63°C) for this period. Also identified is a multidecadal change in amplitude from significant decreasing (−1.7% decade−1 or −0.23°C decade−1) to significant increasing (2.2% decade−1 or 0.29°C decade−1) occurring around 1993 that overlaps the systematic linear trend. This multidecadal change can be mainly attributed to the change in surface solar radiation, from dimming to brightening, rather than to a warming trend or an enhanced greenhouse effect. The study further proposes that the combined effect of the global dimming–brightening transition and a gradual increase in greenhouse warming has led to a perceived warming trend that is much larger in winter than in summer and to a perceived accelerated warming in the annual mean since the early 1990s in China. It also notes that the deseasonalization method (considering either the conventional repetitive climatological annual cycle or the time-varying annual cycle) can also affect trend estimation.

Teleconnections between Tropical Pacific SST Anomalies and Extratropical Southern Hemisphere Climate

2014 ◽  
Vol 28 (1) ◽  
pp. 56-65 ◽  
Author(s):  
Laura M. Ciasto ◽  
Graham R. Simpkins ◽  
Matthew H. England
Keyword(s):  
Sea Ice ◽  
Atmospheric Circulation ◽  
Southern Hemisphere ◽  
Rossby Wave ◽  
Wave Train ◽  
Cold Season ◽  
Tropical Pacific ◽  
Central Pacific ◽  
Sst Variability ◽  
Sst Anomalies

Abstract Teleconnections from tropical Pacific sea surface temperature (SST) anomalies to the high-latitude Southern Hemisphere (SH) are examined using observations and reanalysis. Analysis of tropical Pacific SST anomalies is conducted separately for the central Pacific (CP) and eastern Pacific (EP) regions. During the austral cold season, extratropical SH atmospheric Rossby wave train patterns are observed in association with both EP and CP SST variability. The primary difference between the patterns is the westward displacement of the CP-related atmospheric anomalies, consistent with the westward elongation of CP-related convective SST required for upper-level divergence and Rossby wave generation. Consequently, CP-related patterns of SH SST, Antarctic sea ice, and temperature anomalies also exhibit a westward displacement, but otherwise, the cold season extratropical SH teleconnections are largely similar. During the warm season, however, extratropical SH teleconnections associated with tropical CP and EP SST anomalies differ substantially. EP SST variability is linked to largely zonally symmetric structures in the extratropical atmospheric circulation, which projects onto the southern annular mode (SAM), and is strongly related to the SH temperature and sea ice fields. In contrast, CP SST variability is only weakly related to the SH atmospheric circulation, temperature, or sea ice fields and no longer exhibits any clear association with the SAM. One hypothesized mechanism suggests that the relatively weak CP-related SST anomalies are not able to substantially impact the background flow of the subtropical jet and its subsequent interaction with equatorward-propagating waves associated with variability in the SAM. However, there is currently no widely established mechanism that links tropical Pacific SST anomalies to the SAM.

scholarly journals Using Self-Organizing Maps to Identify Coherent CONUS Precipitation Regions

2019 ◽  
Vol 32 (22) ◽  
pp. 7747-7761 ◽  
Author(s):  
Leif M. Swenson ◽  
Richard Grotjahn
Keyword(s):  
Extreme Events ◽  
Annual Cycle ◽  
Large Scale ◽  
Robust Statistics ◽  
Grid Point ◽  
Future Application ◽  
Self Organizing Maps ◽  
Annual Cycles ◽  
Extreme Precipitation Events ◽  
Self Organizing

Abstract Extreme precipitation events have major societal impacts. These events are rare and can have small spatial scale, making statistical analysis difficult; both factors are mitigated by combining events over a region. A methodology is presented to objectively define “coherent” regions wherein data points have matching annual cycles. Regions are found by training self-organizing maps (SOMs) on the annual cycle of precipitation for each grid point across the contiguous United States (CONUS). Using the annual cycle for our intended application minimizes problems caused by consecutive dry periods and localized extreme events. Multiple criteria are applied to identify useful numbers of regions for our future application. Criteria assess these properties for each region: having many more events than experienced by a single grid point, good connectedness and compactness, and robustness to changing the number of regions. Our methodology is applicable across datasets and is tested here on both reanalysis and gridded observational data. Precipitation regions obtained align with large-scale geographical features and are readily interpretable. Useful numbers of regions balance two conflicting preferences: larger regions contain more events and thereby have more robust statistics, but more compact regions allow weather patterns associated with extreme events to be aggregated with confidence. For 6-h precipitation, 12–15 regions over the CONUS optimize our metrics. The regions obtained are compared against two existing region archetypes. For example, a popular set of regions, based on nine groups of states, has less coherent regions than defining the same number of regions with our SOM methodology.

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