scholarly journals Role of Sea Surface Temperatures in Forcing Circulation Anomalies Driving U.S. Great Plains Pluvial Years

2019 ◽  
Vol 32 (20) ◽  
pp. 7081-7100 ◽  
Author(s):  
Paul X. Flanagan ◽  
Jeffrey B. Basara ◽  
Jason C. Furtado ◽  
Elinor R. Martin ◽  
Xiangming Xiao
Keyword(s):  
Great Plains ◽  
Reanalysis Data ◽  
Tropical Pacific ◽  
Specific Pattern ◽  
Sea Surface ◽  
Northern Great Plains ◽  
The Pacific ◽  
Precipitation Anomalies ◽  
Circulation Anomalies ◽  
Sst Anomalies

Abstract In the U.S. Great Plains (GP), diagnosing precipitation variability is key in developing an understanding of the present and future availability of water in the region. Building on previous work investigating U.S. GP pluvial years, this study uses ERA twentieth century (ERA-20C) reanalysis data to investigate key circulation anomalies driving GP precipitation anomalies during a subset of GP pluvial years (called in this paper Pattern pluvial years). With previous research showing links between tropical Pacific sea surface temperature (SST) anomalies and GP climate variability, this study diagnoses the key circulation anomalies through an analysis of SSTs and their influence on the atmosphere. Results show that during Pattern southern Great Plains (SGP) pluvial years, central tropical Pacific SST anomalies are coincident with key atmospheric anomalies across the Pacific basin and North America. During northern Great Plains (NGP) Pattern pluvial years, no specific pattern of oceanic anomalies emerges that forces the circulation anomaly feature inherent in specific NGP pluvial years. Utilizing the results for SGP pluvial years, a conceptual model is developed detailing the identified pathway for the occurrence of circulation patterns that are favorable for pluvial years over the SGP. Overall, results from this study show the importance of the identified SGP atmospheric anomaly signal and the potential for predictability of such events.

scholarly journals Analysis of variability of tropical Pacific sea surface temperatures

2016 ◽  
Vol 2 (2) ◽  
pp. 155-169
Author(s):  
Georgina Davies ◽  
Noel Cressie
Keyword(s):  
Standard Deviation ◽  
Pacific Ocean ◽  
Climate Models ◽  
Robust Regression ◽  
Southern Oscillation ◽  
Tropical Pacific ◽  
Global Climate Models ◽  
Sea Surface ◽  
The Pacific ◽  
Sst Anomalies

Abstract. Sea surface temperature (SST) in the Pacific Ocean is a key component of many global climate models and the El Niño–Southern Oscillation (ENSO) phenomenon. We shall analyse SST for the period November 1981–December 2014. To study the temporal variability of the ENSO phenomenon, we have selected a subregion of the tropical Pacific Ocean, namely the Niño 3.4 region, as it is thought to be the area where SST anomalies indicate most clearly ENSO's influence on the global atmosphere. SST anomalies, obtained by subtracting the appropriate monthly averages from the data, are the focus of the majority of previous analyses of the Pacific and other oceans' SSTs. Preliminary data analysis showed that not only Niño 3.4 spatial means but also Niño 3.4 spatial variances varied with month of the year. In this article, we conduct an analysis of the raw SST data and introduce diagnostic plots (here, plots of variability vs. central tendency). These plots show strong negative dependence between the spatial standard deviation and the spatial mean. Outliers are present, so we consider robust regression to obtain intercept and slope estimates for the 12 individual months and for all-months-combined. Based on this mean–standard deviation relationship, we define a variance-stabilizing transformation. On the transformed scale, we describe the Niño 3.4 SST time series with a statistical model that is linear, heteroskedastic, and dynamical.

scholarly journals Contribution of Synoptic Transients to the Potential Predictability of PNA Circulation Anomalies: El Niño versus La Niña

2015 ◽  
Vol 28 (21) ◽  
pp. 8347-8362 ◽  
Author(s):  
Muhammad Adnan Abid ◽  
In-Sik Kang ◽  
Mansour Almazroui ◽  
Fred Kucharski
Keyword(s):  
El Niño ◽  
El Nino ◽  
Signal To Noise Ratio ◽  
Tropical Pacific ◽  
La Niña ◽  
Potential Predictability ◽  
La Nina ◽  
The Pacific ◽  
Circulation Anomalies ◽  
Sst Anomalies

Abstract The potential predictability (PP) of seasonal-mean 200-hPa geopotential height (Z200) anomalies in the Pacific–North American (PNA) region is examined for El Niño and La Niña separately by using 50 ensemble members of twentieth-century AGCM simulations. Observed sea surface temperature (SST) is prescribed for the period 1870–2009, and 14 El Niño and La Niña years after 1900 are selected for the present study. The domain-averaged value of PP for Z200 in the PNA region, as measured by the signal-to-noise ratio, for El Niño is about 60% larger than that of La Niña. Such a large PP is mainly due to a larger signal and partly to less noise during El Niño compared to that during La Niña . The transient eddy feedback to the PNA circulation anomalies is stronger during El Niño events (about 50%) than that during La Niña, and this difference in the transients contributes significantly to the different Z200 signals in the PNA region. The noise variance of the transients during El Niño is about 17% smaller than during La Niña, and thus transients play an important role in the reduction of Z200 noise during El Niño. Idealized experiments with the same spatial pattern but different signs of SST anomalies confirm the results mentioned above. Moreover, these experiments with several different amplitudes of positive and negative phases of tropical Pacific SST anomalies show that signals of Z200 and transients are proportional to precipitation anomalies in the tropical Pacific, and noises of Z200 for El Niño cases are somewhat smaller than the corresponding values of La Niña.

Interannual Tropical Pacific Sea Surface Temperatures and Their Relation to Preceding Sea Level Pressures in the NCAR CCSM2

2006 ◽  
Vol 19 (6) ◽  
pp. 998-1012 ◽  
Author(s):  
Bruce T. Anderson ◽  
Eric Maloney
Keyword(s):  
Sea Level ◽  
Tropical Pacific ◽  
Equatorial Pacific ◽  
Sea Surface ◽  
Boreal Winter ◽  
Atmospheric Variability ◽  
Climate System Model ◽  
Sst Variability ◽  
Ocean Atmosphere ◽  
Sst Anomalies

Abstract This paper describes aspects of tropical interannual ocean/atmosphere variability in the NCAR Community Climate System Model Version 2.0 (CCSM2). The CCSM2 tropical Pacific Ocean/atmosphere system exhibits much stronger biennial variability than is observed. However, a canonical correlation analysis technique decomposes the simulated boreal winter tropical Pacific sea surface temperature (SST) variability into two modes, both of which are related to atmospheric variability during the preceding boreal winter. The first mode of ocean/atmosphere variability is related to the strong biennial oscillation in which La Niña–related sea level pressure (SLP) conditions precede El Niño–like SST conditions the following winter. The second mode of variability indicates that boreal winter tropical Pacific SST anomalies can also be initiated by SLP anomalies over the subtropical central and eastern North Pacific 12 months earlier. The evolution of both modes is characterized by recharge/discharge within the equatorial subsurface temperature field. For the first mode of variability, this recharge/discharge produces a lag between the basin-average equatorial Pacific isotherm depth anomalies and the isotherm–slope anomalies, equatorial SSTs, and wind stress fields. Significant anomalies are present up to a year before the boreal winter SLP variations and two years prior to the boreal winter ENSO-like events. For the second canonical factor pattern, the recharge/discharge mechanism is induced concurrent with the boreal winter SLP pattern approximately one year prior to the ENSO-like events, when isotherms initially deepen and change their slope across the basin. A rapid deepening of the isotherms in the eastern equatorial Pacific and a warming of the overlying SST anomalies then occurs during the subsequent 12 months.

scholarly journals Possible Impact of the Indian Ocean SST on the Northern Hemisphere Circulation during El Niño*

2007 ◽  
Vol 20 (13) ◽  
pp. 3164-3189 ◽  
Author(s):  
H. Annamalai ◽  
H. Okajima ◽  
M. Watanabe
Keyword(s):  
Indian Ocean ◽  
Northern Hemisphere ◽  
El Niño ◽  
El Nino ◽  
Tropical Indian Ocean ◽  
Tropical Pacific ◽  
The Indian Ocean ◽  
Precipitation Anomalies ◽  
Sst Anomalies ◽  
The Tropical Pacific

Abstract Two atmospheric general circulation models (AGCMs), differing in numerics and physical parameterizations, are employed to test the hypothesis that El Niño–induced sea surface temperature (SST) anomalies in the tropical Indian Ocean impact considerably the Northern Hemisphere extratropical circulation anomalies during boreal winter [January–March +1 (JFM +1)] of El Niño years. The hypothesis grew out of recent findings that ocean dynamics influence SST variations over the southwest Indian Ocean (SWIO), and these in turn impact local precipitation. A set of ensemble simulations with the AGCMs was carried out to assess the combined and individual effects of tropical Pacific and Indian Ocean SST anomalies on the extratropical circulation. To elucidate the dynamics responsible for the teleconnection, solutions were sought from a linear version of one of the AGCMs. Both AGCMs demonstrate that the observed precipitation anomalies over the SWIO are determined by local SST anomalies. Analysis of the circulation response shows that over the Pacific–North American (PNA) region, the 500-hPa height anomalies, forced by Indian Ocean SST anomalies, oppose and destructively interfere with those forced by tropical Pacific SST anomalies. The model results validated with reanalysis data show that compared to the runs where only the tropical Pacific SST anomalies are specified, the root-mean-square error of the height anomalies over the PNA region is significantly reduced in runs in which the SST anomalies in the Indian Ocean are prescribed in addition to those in the tropical Pacific. Among the ensemble members, both precipitation anomalies over the SWIO and the 500-hPa height over the PNA region show high potential predictability. The solutions from the linear model indicate that the Rossby wave packets involved in setting up the teleconnection between the SWIO and the PNA region have a propagation path that is quite different from the classical El Niño–PNA linkage. The results of idealized experiments indicate that the Northern Hemisphere extratropical response to Indian Ocean SST anomalies is significant and the effect of this response needs to be considered in understanding the PNA pattern during El Niño years. The results presented herein suggest that the tropical Indian Ocean plays an active role in climate variability and that accurate observation of SST there is of urgent need.

Interdecadal Variation of the Relationship between East Asian Water Vapor Transport and Tropical Pacific Sea Surface Temperatures during January and Associated Mechanisms

2019 ◽  
Vol 32 (21) ◽  
pp. 7575-7594 ◽  
Author(s):  
Bo Sun ◽  
Huijun Wang ◽  
Botao Zhou
Keyword(s):  
Water Vapor ◽  
East Asia ◽  
East Asian ◽  
Tropical Pacific ◽  
Vapor Transport ◽  
Sea Surface ◽  
Water Vapor Transport ◽  
The Relationship ◽  
Asian Water ◽  
Sst Anomalies

Abstract This study examined the interdecadal variations in the relationship between the East Asian water vapor transport (WVT) and the central and eastern tropical Pacific (CETP) sea surface temperatures (SSTs) in January during 1951–2018, focusing on the meridional WVT over East Asia, which is critical for the East Asian winter precipitation. The results indicate that before the 1980s, an increased southerly WVT over East Asia was generally associated with warm SST anomalies in the CETP during January, whereas, after the mid-1980s, an increased southerly WVT over East Asia was mostly associated with cold SST anomalies in the central tropical Pacific during January. The underlying mechanisms are discussed based on a comparison on the climate anomalies associated with the East Asian meridional WVT between the periods of 1951–79 and 1986–2018. During 1951–79, the meridional WVT over East Asia was mainly modulated by the Pacific–East Asian (PEA) teleconnection, which would induce an anomalous southerly WVT over East Asia corresponding to warm SST anomalies in the CETP. Whereas, during 1986–2018, the connection between the PEA teleconnection and the East Asian meridional WVT was weakened. The connection among the CETP SSTs, the anomalous zonal circulation over the North Pacific, and the East Asian meridional WVT was enhanced. Additionally, the connection among the CETP SSTs, the circumglobal teleconnection in the Northern Hemisphere, and the East Asian meridional WVT was enhanced. The above two enhanced connections opposed the effect of the PEA teleconnection and would induce an anomalous southerly WVT over East Asia corresponding to cold SST anomalies in the central tropical Pacific.

scholarly journals Interannual to Decadal Variability of Tropical Indian Ocean Sea Surface Temperature: Pacific Influence versus Local Internal Variability

2020 ◽  
pp. 1-50
Author(s):  
Lei Zhang ◽  
Gang Wang ◽  
Matthew Newman ◽  
Weiqing Han
Keyword(s):  
Indian Ocean ◽  
Indian Ocean Dipole ◽  
Tropical Indian Ocean ◽  
Tropical Pacific ◽  
Sea Surface ◽  
External Influence ◽  
Sst Variability ◽  
The Pacific ◽  
The Indian Ocean ◽  
The Tropical Pacific

AbstractThe Indian Ocean has received increasing attention for its large impacts on regional and global climate. However, sea surface temperature (SST) variability arising from Indian Ocean internal processes has not been well understood particularly on decadal and longer timescales, and the external influence from the Tropical Pacific has not been quantified. This paper analyzes the interannual-to-decadal SST variability in the Tropical Indian Ocean in observations and explores the external influence from the Pacific versus internal processes within the Indian Ocean using a Linear Inverse Model (LIM). Coupling between Indian Ocean and tropical Pacific SST anomalies (SSTAs) is assessed both within the LIM dynamical operator and the unpredictable stochastic noise that forces the system. Results show that the observed Indian Ocean Basin (IOB)-wide SSTA pattern is largely a response to the Pacific ENSO forcing, although it in turn has a damping effect on ENSO especially on annual and decadal timescales. On the other hand, the Indian Ocean Dipole (IOD) is an Indian Ocean internal mode that can actively affect ENSO; ENSO also has a returning effect on the IOD, which is rather weak on decadal timescale. The third mode is partly associated with the Subtropical Indian Ocean Dipole (SIOD), and it is primarily generated by Indian Ocean internal processes, although a small component of it is coupled with ENSO. Overall, the amplitude of Indian Ocean internally generated SST variability is comparable to that forced by ENSO, and the Indian Ocean tends to actively influence the tropical Pacific. These results suggest that the Indian-Pacific Ocean interaction is a two-way process.

scholarly journals Influence of the Tropics on the Southern Annular Mode

2012 ◽  
Vol 25 (18) ◽  
pp. 6330-6348 ◽  
Author(s):  
Qinghua Ding ◽  
Eric J. Steig ◽  
David S. Battisti ◽  
John M. Wallace
Keyword(s):  
Indian Ocean ◽  
Rossby Wave ◽  
High Latitude ◽  
Southern Annular Mode ◽  
Tropical Pacific ◽  
The Pacific ◽  
Indian Ocean Sector ◽  
The Indian Ocean ◽  
Ocean Sector ◽  
Sst Anomalies

Abstract Perturbations in the southern annular mode (SAM) are shown to be significantly correlated with SST anomalies in the central tropical Pacific during austral winter and SST anomalies in the eastern tropical Pacific during austral summer. The SAM signature in the Pacific sector resembles a tropically forced Rossby wave train, the so-called Pacific–South American pattern, while the signature in the Indian Ocean sector is a zonally elongated meridional dipole. Thus, the SAM contains strong zonally asymmetric variability and tends to behave differently in the Eastern and Western Hemispheres, with internal dynamics prevailing in the Indian Ocean sector and the forced response to tropical SST anomalies exerting a strong influence in the Pacific sector. The tropically forced component of the SAM in the Pacific sector is related to a geographically fixed active Rossby wave source to the east of Australia within the core of the subtropical jet. In addition to the well-documented positive trend in summer, the SAM also exhibits a negative wintertime trend since 1979, characterized by prominent geopotential height increases over the high latitudes. In both seasons, SAM trends are closely linked to long-term trends in tropical Pacific SST that are independent of the canonical eastern Pacific ENSO variability. Although the SAM is an intrinsic pattern of high-latitude variability, the SAM index reflects the superposition of both high-latitude and tropically forced variability.

scholarly journals The Obduction of Equatorial 13°C Water in the Pacific Identified by a Simulated Passive Tracer*

2010 ◽  
Vol 40 (10) ◽  
pp. 2282-2297 ◽  
Author(s):  
Tangdong Qu ◽  
Shan Gao ◽  
Ichiro Fukumori ◽  
Rana A. Fine ◽  
Eric J. Lindstrom
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Mixed Layer ◽  
Tropical Pacific ◽  
Sea Surface ◽  
Surface Mixed Layer ◽  
Passive Tracer ◽  
Eastern Tropical Pacific ◽  
Easterly Wind ◽  
The Pacific

Abstract The obduction of equatorial 13°C Water in the Pacific is investigated using a simulated passive tracer of the Consortium for Estimating the Circulation and Climate of the Ocean (ECCO). The result shows that the 13°C Water initialized in the region 8°N–8°S, 130°–90°W enters the surface mixed layer in the eastern tropical Pacific, mainly through upwelling near the equator, in the Costa Rica Dome, and along the coast of Peru. Approximately two-thirds of this obduction occurs within 10 years after the 13°C Water being initialized, with the upper portion of the water mass reaching the surface mixed layer in only about a month. The obduction of the 13°C Water helps to maintain a cool sea surface temperature year-round, equivalent to a surface heat flux of about −6.0 W m−2 averaged over the eastern tropical Pacific (15°S–15°N, 130°W–eastern boundary) for the period of integration (1993–2006). During El Niño years, when the thermocline deepens as a consequence of the easterly wind weakening, the obduction of the 13°C Water is suppressed, and the reduced vertical entrainment generates a warming anomaly of up to 10 W m−2 in the eastern tropical Pacific and in particular along the coast of Peru, providing explanations for the warming of sea surface temperature that cannot be accounted for by local winds alone. The situation is reversed during La Niña years.

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