scholarly journals Differences in Atmospheric Circulation between the Development of Weak and Strong Warm Events in the Southern Oscillation

2007 ◽  
Vol 20 (10) ◽  
pp. 2191-2209 ◽  
Author(s):  
David J. Stephens ◽  
Michael J. Meuleners ◽  
Harry van Loon ◽  
Malcolm H. Lamond ◽  
Nicola P. Telcik
Keyword(s):  
High Pressure ◽  
El Niño ◽  
Large Scale ◽  
Rossby Waves ◽  
El Nino ◽  
Southern Oscillation ◽  
Surface Wind ◽  
South Pacific ◽  
The Pacific ◽  
Sst Anomalies

Abstract In this study temporal and spatial aspects of El Niño (warm event) development are explored by comparing composite sequences of sea level pressure (SLP), surface wind, and sea surface temperature (SST) anomalies leading into strong and weak events. El Niño strength is found to be related to the magnitude and spatial extent of large-scale SLP anomalies that move in a low-frequency mode. In association with this, it is also intricately linked to the amplitude and wavelength of the Rossby waves in the southern midlatitudes. The primary signature of the Southern Oscillation is a more pronounced standing wave of pressure anomalies between southeastern Australia and the central South Pacific leading into stronger events. A strong reversal in the strength of the annual cycle between these two regions causes a stronger (weaker) SLP gradient that drives southwesterly (northwesterly) wind stress forcing toward (away from) the western equatorial Pacific in austral winter–spring of year 0 (−1). Thus, pressure variations in the southwest Pacific preconditions the equatorial environment to a particular phase of ENSO and establishes the setting for greater tropical–extratropical interactions to occur in stronger events. Maximum warming in the Niño-3 region occurs between April and July (0) when a strong South Pacific trough most influences the trade winds at both ends of the Pacific. Cool SST anomalies that form to the east of high pressure anomalies over Indo–Australia assist an eastward propogation of high pressure into the Pacific midlatitudes and the demise of El Niño. Strong events have a more pronounced eastward propogation of SST and SLP anomalies and a much more noticeable enhancement of winter hemisphere Rossby waves from May–July (−1) to November–January (+1). Weak events require an enhanced South Pacific trough to develop but have much less support from the North Pacific. They also appear more variable in their development and more difficult to predict with lead time.

scholarly journals Role of the Indo-Pacific Interbasin Coupling in Predicting Asymmetric ENSO Transition and Duration

2012 ◽  
Vol 25 (9) ◽  
pp. 3321-3335 ◽  
Author(s):  
Masamichi Ohba ◽  
Masahiro Watanabe
Keyword(s):  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
Southern Oscillation ◽  
La Niña ◽  
La Nina ◽  
The Pacific ◽  
Enso Asymmetry ◽  
Sst Anomalies

Warm and cold phases of El Niño–Southern Oscillation (ENSO) exhibit a significant asymmetry in their transition/duration such that El Niño tends to shift rapidly to La Niña after the mature phase, whereas La Niña tends to persist for up to 2 yr. The possible role of sea surface temperature (SST) anomalies in the Indian Ocean (IO) in this ENSO asymmetry is investigated using a coupled general circulation model (CGCM). Decoupled-IO experiments are conducted to assess asymmetric IO feedbacks to the ongoing ENSO evolution in the Pacific. Identical-twin forecast experiments show that a coupling of the IO extends the skillful prediction of the ENSO warm phase by about one year, which was about 8 months in the absence of the IO coupling, in which a significant drop of the prediction skill around the boreal spring (known as the spring prediction barrier) is found. The effect of IO coupling on the predictability of the Pacific SST is significantly weaker in the decay phase of La Niña. Warm IO SST anomalies associated with El Niño enhance surface easterlies over the equatorial western Pacific and hence facilitate the El Niño decay. However, this mechanism cannot be applied to cold IO SST anomalies during La Niña. The result of these CGCM experiments estimates that approximately one-half of the ENSO asymmetry arises from the phase-dependent nature of the Indo-Pacific interbasin coupling.

scholarly journals Tropical Cyclone Climatology of the South Pacific Ocean and Its Relationship to El Niño–Southern Oscillation

2012 ◽  
Vol 25 (18) ◽  
pp. 6108-6122 ◽  
Author(s):  
Andrew J. Dowdy ◽  
Lixin Qi ◽  
David Jones ◽  
Hamish Ramsay ◽  
Robert Fawcett ◽  
...  
Keyword(s):  
Tropical Cyclone ◽  
El Niño ◽  
Large Scale ◽  
Critical Line ◽  
El Nino ◽  
Southern Oscillation ◽  
South Pacific ◽  
El Niño Southern Oscillation ◽  
El Nino Southern Oscillation ◽  
The South

Abstract Climatological features of tropical cyclones in the South Pacific Ocean have been analyzed based on a new archive for the Southern Hemisphere. A vortex tracking and statistics package is used to examine features such as climatological maps of system intensity and the change in intensity with time, average tropical cyclone system movement, and system density. An examination is presented of the spatial variability of these features, as well as changes in relation to phase changes of the El Niño–Southern Oscillation phenomenon. A critical line is defined in this study based on maps of cyclone intensity to describe the statistical geographic boundary for cyclone intensification. During El Niño events, the critical line shifts equatorward, while during La Niña events the critical line is generally displaced poleward. Regional variability in tropical cyclone activity associated with El Niño–Southern Oscillation phases is examined in relation to the variability of large-scale atmospheric or oceanic variables associated with tropical cyclone activity. Maps of the difference fields between different phases of El Niño–Southern Oscillation are examined for sea surface temperature, vertical wind shear, lower-tropospheric vorticity, and midtropospheric relative humidity. Results are also examined in relation to the South Pacific convergence zone. The common region where each of the large-scale variables showed favorable conditions for cyclogenesis coincided with the location of maximum observed cyclogenesis for El Niño events as well as for La Niña years.

scholarly journals Positive relationship between seasonal Indo-Pacific Ocean wave power and SST

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Sukhwinder Kaur ◽  
Prashant Kumar ◽  
Evan Weller ◽  
Ian R. Young
Keyword(s):  
Pacific Ocean ◽  
El Niño ◽  
Large Scale ◽  
El Nino ◽  
Wave Power ◽  
Tropical Regions ◽  
Positive Indian Ocean Dipole ◽  
The Pacific ◽  
Sst Anomalies

AbstractThe influence of increasing sea surface temperatures (SSTs), in response to greenhouse warming, on wave power (WP) remains uncertain. Here, seasonal relationships between SST anomalies and mean and extreme WP over the Indo-Pacific Ocean are examined. Overall, seasonal WP has significantly increased over much of the Pacific, Indian, and Southern Ocean by 1.21–3.10 kW/m dec−1 over 1979–2019. Contributions from wave characteristics, namely significant wave height (SWH) and peak wave period (PWP), to changes in WP show that SWH contributes most in extra-tropical regions, and PWP most in tropical regions. Further, seasonal relationships between SST anomalies and WP indicate that increases in WP are also seen during strong El Niño years in December–February, and in-phase combinations of El Niño and positive Indian Ocean Dipole (IOD) events during June–August and September–November. Results highlight both long-term increasing SSTs and climate variability roles for inducing large-scale seasonal WP changes throughout the Indo-Pacific.

Large-scale environments of successive atmospheric river events leading to compound precipitation extremes in California

2021 ◽  
pp. 1-66
Keyword(s):  
El Niño ◽  
Large Scale ◽  
El Nino ◽  
Southern Oscillation ◽  
Strong Relationship ◽  
Potential Predictability ◽  
Atmospheric River ◽  
The Pacific ◽  
Average Precipitation ◽  
Compound Events

Abstract Successive atmospheric river (AR) events—known as AR families—can result in prolonged and elevated hydrological impacts relative to single ARs due to the lack of recovery time between periods of precipitation. Despite the outsized societal impacts that often stem from AR families, the large-scale environments and mechanisms associated with these compound events remain poorly understood. In this work, a new reanalysis-based 39-year catalog of 248 AR family events affecting California between 1981 and 2019 is introduced. Nearly all (94%) of the inter-annual variability in AR frequency is driven by AR family versus single events. Using K-means clustering on the 500-hPa geopotential height field, six distinct clusters of large-scale patterns associated with AR families are identified. Two clusters are of particular interest due to their strong relationship with phases of the El Niño/Southern Oscillation (ENSO). One of these clusters is characterized by a strong ridge in the Bering Sea and Rossby wave propagation, most frequently occurs during La Niña and neutral ENSO years and is associated with the highest cluster-average precipitation across California. The other cluster, characterized by a zonal elongation of lower geopotential heights across the Pacific basin and an extended North Pacific Jet, most frequently occurs during El Niño years and is associated with lower cluster-average precipitation across California but a longer duration. In contrast, single AR events do not show obvious clustering of spatial patterns. This difference suggests that the potential predictability of AR families may be enhanced relative to single AR events, especially on sub-seasonal to seasonal timescales.

scholarly journals Volcanic Eruptions, Large-Scale Modes in the Northern Hemisphere, and the El Niño–Southern Oscillation

2008 ◽  
Vol 21 (5) ◽  
pp. 910-922 ◽  
Author(s):  
Bo Christiansen
Keyword(s):  
Northern Hemisphere ◽  
El Niño ◽  
Large Scale ◽  
El Nino ◽  
Southern Oscillation ◽  
Volcanic Eruptions ◽  
El Niño Southern Oscillation ◽  
El Nino Southern Oscillation ◽  
The Pacific ◽  
The Impact

Abstract The author analyzes the impact of 13 major stratospheric aerosol producing volcanic eruptions since 1870 on the large-scale variability modes of sea level pressure in the Northern Hemisphere winter. The paper focuses on the Arctic Oscillation (AO) and the North Atlantic Oscillation (NAO) to address the question about the physical nature of these modes. The hypothesis that the phase of the El Niño–Southern Oscillation (ENSO) may control the geographical extent of the dominant mode in the Northern Hemisphere is also investigated, as well as the related possibility that the impact of the eruptions may be different according to the phase of ENSO. The author finds that both the AO and the NAO are excited in the first winter after the eruptions with statistical significance at the 95% level. Both the signal and the significance are larger for the NAO than for the AO. The excitation of the AO and the NAO is connected with the excitation of a secondary mode, which resembles an augmented Pacific–North American pattern. This mode has opposite polarity in the Atlantic and the Pacific and interferes negatively with the AO in the Pacific and positively in the Atlantic in the first winter after the eruptions, giving the superposition a strong NAO resemblance. Some evidence is found that the correlations between the Atlantic and the Pacific are stronger in the negative ENSO phase than in the positive phase, although this difference is not statistically significant when all data since 1870 are considered. The author does not find any evidence that the impact of the volcanic eruptions is more hemispheric in the negative than in the positive ENSO phase.

scholarly journals Multidecadal Changes in the Relationship between ENSO and Wet-Season Precipitation in the Arabian Peninsula

2015 ◽  
Vol 28 (12) ◽  
pp. 4743-4752 ◽  
Author(s):  
In-Sik Kang ◽  
Irfan Ur Rashid ◽  
Fred Kucharski ◽  
Mansour Almazroui ◽  
Abdulrahman K. Alkhalaf
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
Arabian Peninsula ◽  
El Nino ◽  
Southern Oscillation ◽  
Wet Season ◽  
The Pacific ◽  
The Indian Ocean ◽  
The Relationship ◽  
Sst Anomalies

Abstract Multidecadal variations in the relationship between El Niño–Southern Oscillation (ENSO) and the Arabian Peninsula rainfall are investigated using observed data for the last 60 years and various atmospheric general circulation model (AGCM) experiments. The wet season in the Arabian Peninsula from November to April was considered. The 6-month averaged Arabian rainfall was negatively correlated with ENSO for an earlier 30-yr period from 1950 to 1979 and positively correlated to ENSO for a more recent period from 1981 to 2010. The multidecadal variations can be attributed to the variations in Indian Ocean SST anomalies accompanied by ENSO. In the early 30-yr period, ENSO accompanied relatively large SST anomalies in the Indian Ocean, whereas in the recent 30-yr period it accompanied relatively small SST anomalies in the Indian Ocean. The atmospheric anomalies in the Arabian region during ENSO are combined responses to the Pacific and Indian Ocean SST anomalies, which offset each other during ENSO. The recent El Niño events accompanied negative 200-hPa geopotential height (GH) anomalies over the Arabian region, mainly forced by the Pacific SST anomalies, resulting in an increase of precipitation over the region. In contrast, in the early 30-yr period, Indian Ocean SST anomalies played a dominant role in the atmospheric responses over the Arabian region during ENSO, and the negative GH anomalies and more precipitation over the Arabian region were mainly forced by the negative SST anomalies over the Indian Ocean, which appeared during La Niña. These observed findings are confirmed by various AGCM experiments.

scholarly journals Modulation of the Northern Winter Stratospheric El Niño–Southern Oscillation Teleconnection by the PDO

2019 ◽  
Vol 32 (18) ◽  
pp. 5761-5783 ◽  
Author(s):  
Jian Rao ◽  
Chaim I. Garfinkel ◽  
Rongcai Ren
Keyword(s):  
El Niño ◽  
North Pacific ◽  
El Nino ◽  
Southern Oscillation ◽  
La Niña ◽  
El Nino Southern Oscillation ◽  
Atmospheric Response ◽  
La Nina ◽  
The Pacific ◽  
Sst Anomalies

Using the CMIP5 multimodel ensemble (MME) historical experiments, the modulation of the stratospheric El Niño–Southern Oscillation (ENSO) teleconnection by the Pacific decadal oscillation (PDO) is investigated in this study. El Niño (La Niña) significantly impacts the extratropical stratosphere mainly during the positive (negative) PDO in the MME. Although the composite tropical ENSO SST intensities are similar during the positive and negative PDO in models, the Pacific–North American (PNA) responses are only significant when the PDO and ENSO are in phase. The local SST anomalies in the North Pacific can constructively (destructively) interfere with the tropical ENSO forcing to influence the extratropical eddy height anomalies when the PDO and ENSO are in (out of) phase. The difference between the positive and negative PDO in El Niño or La Niña winters filters out the tropical SST forcing, permitting the deduction of the extratropical SST contribution to the atmospheric response. The composite shows that the cold (warm) SST anomalies in the central North Pacific associated with the positive (negative) PDO have a similar impact to that of the warm (cold) SST anomalies in the tropical Pacific, exhibiting a positive (negative) PNA-like response, enhancing (weakening) the upward propagation of waves over the western coast of North America. The composite difference between the positive and negative PDO in El Niño or La Niña winters, as well as in eastern Pacific ENSO or central Pacific ENSO winters, presents a highly consistent atmospheric response pattern, which may imply a linear interference of the PDO’s impact with ENSO’s.

scholarly journals The Varied Impacts of El Niño–Southern Oscillation on Pacific Island Climates

2014 ◽  
Vol 27 (11) ◽  
pp. 4015-4036 ◽  
Author(s):  
Bradley F. Murphy ◽  
Scott B. Power ◽  
Simon McGree
Keyword(s):  
El Niño ◽  
Large Scale ◽  
El Nino ◽  
Southern Oscillation ◽  
El Nino Southern Oscillation ◽  
Convergence Zone ◽  
Pacific Island ◽  
Pacific Island Countries ◽  
Convergence Zones ◽  
Sst Anomalies

Abstract El Niño–Southern Oscillation (ENSO) drives interannual climate variability in many tropical Pacific island countries, but different El Niño events might be expected to produce varying rainfall impacts. To investigate these possible variations, El Niño events were divided into three categories based on where the largest September–February sea surface temperature (SST) anomalies occur: warm pool El Niño (WPE), cold tongue El Niño (CTE), and mixed El Niño (ME), between the other two. Large-scale SST and wind patterns for each type of El Niño show distinct and significant differences, as well as shifts in rainfall patterns in the main convergence zones. As a result, November to April rainfall in many Pacific island countries is significantly different among the El Niño types. In western equatorial Pacific islands, CTE events are associated with drier than normal conditions whereas ME and WPE events are associated with significantly wetter than normal conditions. This is due to the South Pacific convergence zone and intertropical convergence zone moving equatorward and merging in CTE events. Rainfall in the convergence zones is enhanced during ME and WPE and the displacement is smaller. La Niña events also show robust impacts that most closely mirror those of ME events. In the northwest and southwest Pacific strong CTE events have much larger impacts on rainfall than ME and WPE, as SST anomalies and correspondingly large-scale surface wind and rainfall changes are largest in CTE. While variations in rainfall exist between different types of El Niño and the significant impacts on Pacific countries of each event are different, the two extreme CTE events have produced the most atypical impacts.

scholarly journals Determination of a New Coastal ENSO Oceanic Index for Northern Peru

Climate ◽  
2021 ◽  
Vol 9 (5) ◽  
pp. 71
Author(s):  
Edgard Gonzales ◽  
Eusebio Ingol
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Extreme Rainfall ◽  
Polynomial Equation ◽  
Extreme Rainfall Events ◽  
Emergency Operations Center ◽  
The Pacific ◽  
Northern Portion ◽  
Sequential Generation

In 2017, extreme rainfall events occurred in the northern portion of Peru, causing nearly 100,000 victims, according to the National Emergency Operations Center (COEN). This climatic event was attributed to the occurrence of the El Niño Southern Oscillation (ENSO). Therefore, the main objective of this study was to determine and differentiate between the occurrence of canonical ENSO, with a new type of ENSO called “El Niño Costero” (Coastal El Niño). The polynomial equation method was used to analyze the data from the different types of existing ocean indices to determine the occurrence of ENSO. It was observed that the anomalies of sea surface temperature (SST) 2.5 °C (January 2016) generated the “Modoki El Niño” and that the anomaly of SST −0.3 °C (January 2017) generated the “Modoki La Niña”; this sequential generation generated El Niño Costero. This new knowledge about the sui generis origin of El Niño Costero, based on the observations of this analysis, will allow us to identify and obtain important information regarding the occurrence of this event. A new oceanic index called the Pacific Regional Equatorial Index (PREI) was proposed to follow the periodic evolution and forecast with greater precision a new catastrophic event related to the occurrence of El Niño Costero and to implement prevention programs.

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.

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