The Spatiotemporal Structure of Twentieth-Century Climate Variations in Observations and Reanalyses. Part I: Long-Term Trend

Abstract The dominant interannual El Niño–Southern Oscillation (ENSO) phenomenon and the short length of climate observation records make it difficult to study long-term climate variations in the spatiotemporal domain. Based on the fact that the ENSO signal spreads to remote regions and induces delayed climate variation through atmospheric teleconnections, an ENSO-removal method is developed through which the ENSO signal can be approximately removed at the grid box level from the spatiotemporal field of a climate parameter. After this signal is removed, long-term climate variations are isolated at mid- and low latitudes in the climate parameter fields from observed and reanalysis datasets. This paper addresses the long-term global warming trend (GW); a companion paper concentrates on Pacific pan-decadal variability (PDV). The warming that occurs in the Pacific basin (approximately 0.4 K in the twentieth century) is much weaker than in surrounding regions and the other two ocean basins (approximately 0.8 K). The modest warming in the Pacific basin is likely due to its dynamic nature on the interannual and decadal time scales and/or the leakage of upper ocean water through the Indonesian Throughflow. Based on the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) and the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40), a comprehensive atmospheric structure associated with the GW trend is given. Significant discrepancies exist between the two datasets, especially in the tightly coupled dynamics and water vapor fields. The dynamics fields based on NCEP–NCAR, which show a change in the Walker Circulation, are consistent with the GW change in the surface temperature field. However, intensification in the Hadley Circulation is associated with GW trend in ERA-40 instead.

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Isotopic evidence for twentieth-century weakening of the Pacific Walker circulation

Earth and Planetary Science Letters ◽

10.1016/j.epsl.2018.12.002 ◽

2019 ◽

Vol 507 ◽

pp. 85-93

Author(s):

Zhongfang Liu ◽

Zhimin Jian ◽

Christopher J. Poulsen ◽

Liang Zhao

Keyword(s):

Twentieth Century ◽

Walker Circulation ◽

Isotopic Evidence ◽

The Pacific

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Long-term predictability of winter teleconnection indices and their relationship to seasonal temperature extremes in Europe

10.5194/egusphere-egu21-3327 ◽

2021 ◽

Author(s):

Nina Schuhen ◽

Nathalie Schaller ◽

Hannah C. Bloomfield ◽

David J. Brayshaw ◽

Jana Sillmann ◽

...

Keyword(s):

Twentieth Century ◽

Surface Temperature ◽

North Atlantic Oscillation ◽

North Atlantic ◽

Decadal Variability ◽

Environmental Research ◽

Seasonal Temperature ◽

East Atlantic ◽

Teleconnection Patterns

European winter weather is dominated by several low-frequency teleconnection patterns, the main ones being the North Atlantic Oscillation (NAO), East Atlantic, East Atlantic/Western Russia and Scandinavian patterns. Through predicting these patterns, skillful forecasts of weather parameters like surface temperature can be generated, which in turn are used in a variety of applications (e.g., predictions of energy demand). A previous study (Weisheimer et.al., 2017) found that the NAO was subject to decadal variability during the twentieth century, affecting its long-term predictability. During recent decades, predictions for the NAO index have shown considerable skill, but this is likely to change during future periods of reduced predictability.We analyze the century-long ERA-20C reanalysis and ASF-20C seasonal hindcast datasets to find if the other main teleconnection patterns also experience fluctuations in predictability, with potential implications for future skill and development of seasonal forecasting models. By linking the teleconnections to extreme cold and heat wave indices (Russo et al., 2015), we highlight the impact of these large-scale patterns on seasonal surface temperature in Europe during two periods of interest in the middle and end of the century. Our study shows that even though the predictability of the teleconnection patterns themselves fluctuates on a decadal scale, the links to winter surface temperatures are not significantly affected. However, the ability of the seasonal hindcasts to reproduce these patterns is quite limited.&#160;References:Russo, S., Sillmann, J., & Fischer, E. M. (2015). Top ten European heatwaves since 1950 and their occurrence in the coming decades. Environmental Research Letters, 10(12), 124003. doi: 10.1088/1748-9326/10/12/124003Weisheimer, A., Schaller, N., O&#8217;Reilly, C., MacLeod, D. A., & Palmer, T. (2017). Atmospheric seasonal forecasts of the twentieth century:&#160; multi-decadal variability in predictive skill of the winter North Atlantic Oscillation (NAO) and their potential value for extreme event attribution. Quarterly Journal of the Royal Meteorological Society, 143(703), 917-926. doi: 10.1002/qj.29

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Coupling Influences of ENSO and PDO on the Inter-Decadal SST Variability of the ACC around the Western South Atlantic

Sustainability ◽

10.3390/su11184853 ◽

2019 ◽

Vol 11 (18) ◽

pp. 4853

Author(s):

You-Lin Wang ◽

Yu-Chen Hsu ◽

Chung-Pan Lee ◽

Chau-Ron Wu

Keyword(s):

Antarctic Circumpolar Current ◽

Water Mass ◽

Southern Oscillation ◽

Drake Passage ◽

South Atlantic ◽

Sst Variability ◽

The Pacific ◽

Circumpolar Current ◽

The Antarctic

The Antarctic Circumpolar Current (ACC) plays an important role in the climate as it balances heat energy and water mass between the Pacific and Atlantic Oceans through the Drake Passage. However, because the historical measurements and observations are extremely limited, the decadal and long-term variations of the ACC around the western South Atlantic Ocean are rarely studied. By analyzing reconstructed sea surface temperatures (SSTs) in a 147-year period (1870–2016), previous studies have shown that SST anomalies (SSTAs) around the Antarctic Peninsula and South America had the same phase change as the El Niño Southern Oscillation (ENSO). This study further showed that changes in SSTAs in the regions mentioned above were enlarged when the Pacific Decadal Oscillation (PDO) and the ENSO were in the same warm or cold phase, implying that changes in the SST of higher latitude oceans could be enhanced when the influence of the ENSO is considered along with the PDO.

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Interannual Modality of Upper-Ocean Temperature: 4D Structure Revealed by Argo Data

Journal of Climate ◽

10.1175/jcli-d-14-00351.1 ◽

2015 ◽

Vol 28 (9) ◽

pp. 3441-3452 ◽

Cited By ~ 2

Author(s):

Ge Chen ◽

Hanou Chen

Keyword(s):

Interannual Variability ◽

Southern Oscillation ◽

Hadley Circulation ◽

Walker Circulation ◽

Upper Ocean ◽

Kelvin Wave ◽

Argo Data ◽

Sea Temperature ◽

Equatorial Undercurrent ◽

The Pacific

Abstract Using the newly available decade-long Argo data for the period 2004–13, a detailed study is carried out on deriving four-dimensional (4D) modality of sea temperature in the upper ocean with emphasis on its interannual variability in terms of amplitude, phase, and periodicity. Three principal modes with central periodicities at 19.2, 33.8, and 50.3 months have been identified, and their relationship with El Niño–Southern Oscillation (ENSO) is investigated, yielding a number of useful results and conclusions: 1) A striking tick-shaped pipe-like feature of interannual variability maxima, which is named the “Niño pipe” in this paper, has been revealed within the 10°S–10°N upper Pacific Ocean. 2) The pipe core extends downward from ~50 m at 130°E to ~250 m near the date line before tilting upward to the sea surface at about 275°E, coinciding nicely with the pathway of the Pacific equatorial undercurrent (EUC). 3) The double-peak zonal modality pattern of the Niño pipe in the upper Pacific is echoed in the subsurface Atlantic and Indian Oceans through Walker circulation, while its single-peak meridional modality pattern is mirrored in the subsurface North and South Pacific through Hadley circulation. 4) A coherent three-peak modal structure implies a strong coupling between sea level variability at the surface and sea temperature variability around the thermocline. Accumulating evidence suggests that Rossby/Kelvin wave dynamics in tandem with EUC-based thermocline dynamics are the main mechanisms of the three-mode Niño pipe in ENSO cycles.

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The Hadley Circulation Regime Change: Combined Effect of the Western Pacific Warming and Increased ENSO Amplitude

Journal of Climate ◽

10.1175/jcli-d-18-0306.1 ◽

2018 ◽

Vol 31 (23) ◽

pp. 9739-9751 ◽

Cited By ~ 2

Author(s):

Yi-Peng Guo ◽

Zhe-Min Tan

Keyword(s):

Regime Change ◽

Southern Oscillation ◽

Hadley Circulation ◽

Warming Trend ◽

Combined Effect ◽

Western Pacific ◽

South Pacific Convergence Zone ◽

Boreal Winter ◽

Enso Events

The variation in the interannual relationship between the boreal winter Hadley circulation (HC) and El Niño–Southern Oscillation (ENSO) during 1948–2014 is investigated. The interannual variability of the HC is dominated by two principal modes: the equatorial asymmetric mode (AM) and the equatorial symmetric mode (SM). The AM of the HC during ENSO events mainly results from a combined effect of the ENSO sea surface temperature (SST) anomalies and the climatological background SST over the South Pacific convergence zone. Comparatively, the SM shows a steady and statistically significant relationship with ENSO; however, the interannual relationship between the AM and ENSO is strengthened during the mid-1970s, which leads to a HC regime change—that is, the interannual pulse of the HC intensity and its response to ENSO are stronger after the mid-1970s than before. The long-term warming trend of the tropical western Pacific since the 1950s and the increased ENSO amplitude play vital roles in the HC regime change. Although the tropical eastern Pacific also experienced a long-term warming trend, it has little influence on the HC regime change due to the climatologically cold background SST over the cold tongue region.

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Half-precessional cycle of thermocline temperature in the western equatorial Pacific and its bihemispheric dynamics

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1915510117 ◽

2020 ◽

Vol 117 (13) ◽

pp. 7044-7051

Author(s):

Zhimin Jian ◽

Yue Wang ◽

Haowen Dang ◽

David W. Lea ◽

Zhengyu Liu ◽

...

Keyword(s):

Climate Change ◽

Southern Oscillation ◽

Decisive Role ◽

Equatorial Pacific ◽

The Pacific ◽

Equatorial Thermocline ◽

Western Equatorial Pacific ◽

Tightly Coupled ◽

Interannual Climate Variability

The El Niño−Southern Oscillation (ENSO), which is tightly coupled to the equatorial thermocline in the Pacific, is the dominant source of interannual climate variability, but its long-term evolution in response to climate change remains highly uncertain. This study uses Mg/Ca in planktonic foraminiferal shells to reconstruct sea surface and thermocline water temperatures (SST and TWT) for the past 142 ky in a western equatorial Pacific (WEP) core MD01-2386. Unlike the dominant 100-ky glacial−interglacial cycle recorded by SST and δ18O, which echoes the pattern seen in other WEP sites, the upper ocean thermal gradient shows a clear half-precessional (9.4 ky or 12.7 ky) cycle as indicated by the reconstructed and simulated temperature (ΔT) and δ18O differences between the surface and thermocline waters. This phenomenon is attributed to the interplay of subtropical-to-tropical thermocline anomalies forced by the antiphased meridional insolation gradients in the two hemispheres at the precessional band. In particular, the TWT shows greater variability than SST, and dominates the ΔT changes which couple with the west−east SST difference in the equatorial Pacific at the half-precessional band, implying a decisive role of the tropical thermocline in orbital-scale climate change.

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Decadal Variability of the ENSO Teleconnection to the High-Latitude South Pacific Governed by Coupling with the Southern Annular Mode*

Journal of Climate ◽

10.1175/jcli3671.1 ◽

2006 ◽

Vol 19 (6) ◽

pp. 979-997 ◽

Cited By ~ 250

Author(s):

Ryan L. Fogt ◽

David H. Bromwich

Keyword(s):

High Latitude ◽

Decadal Variability ◽

Southern Oscillation ◽

Phase Relationship ◽

South Pacific ◽

Southern Annular Mode ◽

Height Anomaly ◽

Austral Spring ◽

Annular Mode ◽

The Pacific

Abstract Decadal variability of the El Niño–Southern Oscillation (ENSO) teleconnection to the high-latitude South Pacific is examined by correlating the European Centre for Medium-Range Weather Forecasts (ECMWF) 40-yr Re-Analysis (ERA-40) and observations with the Southern Oscillation index (SOI) over the last two decades. There is a distinct annual contrast between the 1980s and the 1990s, with the strong teleconnection in the 1990s being explained by an enhanced response during austral spring. Geopotential height anomaly composites constructed during the peak ENSO seasons also demonstrate the decadal variability. Empirical orthogonal function (EOF) analysis reveals that the 1980s September–November (SON) teleconnection is weak due to the interference between the Pacific–South American (PSA) pattern associated with ENSO and the Southern Annular Mode (SAM). An in-phase relationship between these two modes during SON in the 1990s amplifies the height and pressure anomalies in the South Pacific, producing the strong teleconnections seen in the correlation and composite analyses. The in-phase relationship between the tropical and high-latitude forcing also exists in December–February (DJF) during the 1980s and 1990s. These results suggest that natural climate variability plays an important role in the variability of SAM, in agreement with a growing body of literature. Additionally, the significantly positive correlation between ENSO and SAM only during times of strong teleconnection suggests that both the Tropics and the high latitudes need to work together in order for ENSO to strongly influence Antarctic climate.

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Unraveling Causes for the Changing Behavior of the Tropical Indian Ocean in the Past Few Decades

Journal of Climate ◽

10.1175/jcli-d-17-0445.1 ◽

2018 ◽

Vol 31 (6) ◽

pp. 2377-2388 ◽

Cited By ~ 23

Author(s):

Lei Zhang ◽

Weiqing Han ◽

Frank Sienz

Keyword(s):

Indian Ocean ◽

Time Scales ◽

Climate Models ◽

Decadal Variability ◽

Global Climate ◽

Tropical Indian Ocean ◽

Volcanic Eruptions ◽

Warming Trend ◽

External Forcing ◽

The Pacific

Observations show that decadal (10–20 yr) to interdecadal (>20 yr) variability of the tropical Indian Ocean (TIO) sea surface temperature (SST) closely follows that of the Pacific until the 1960s. Since then, the TIO SST exhibits a persistent warming trend, whereas the Pacific SST shows large-amplitude fluctuations associated with the interdecadal Pacific oscillation (IPO), and the decadal variability of the TIO SST is out of phase with that of the Pacific after around 1980. Here causes for the changing behavior of the TIO SST are explored, by analyzing multiple observational datasets and the recently available large-ensemble simulations from two climate models. It is found that on interdecadal time scales, the persistent TIO warming trend is caused by emergence of anthropogenic warming overcoming internal variability, while the time of emergence occurs much later in the Pacific. On decadal time scales, two major tropical volcanic eruptions occurred in the 1980s and 1990s causing decadal SST cooling over the TIO during which the IPO was in warm phase, yielding the out-of-phase relation. The more evident fingerprints of external forcing in the TIO compared to the Pacific result from the much weaker TIO internal decadal–interdecadal variability, making the TIO prone to the external forcing. These results imply that the ongoing warming and natural external forcing may make the Indian Ocean more active, playing an increasingly important role in affecting regional and global climate.

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What Caused the Observed Twentieth-Century Weakening of the Walker Circulation?

Journal of Climate ◽

10.1175/2011jcli4101.1 ◽

2011 ◽

Vol 24 (24) ◽

pp. 6501-6514 ◽

Cited By ~ 44

Author(s):

Scott B. Power ◽

Greg Kociuba

Keyword(s):

Twentieth Century ◽

Climate Models ◽

Southern Oscillation ◽

Walker Circulation ◽

Natural Variability ◽

First Century ◽

External Forcing ◽

Wide Range ◽

Twenty First Century ◽

The Walker Circulation

Abstract The Walker circulation (WC) is one of the world’s most prominent and important atmospheric systems. The WC weakened during the twentieth century, reaching record low levels in recent decades. This weakening is thought to be partly due to global warming and partly due to internally generated natural variability. There is, however, no consensus in the literature on the relative contribution of external forcing and natural variability to the observed weakening of the WC. This paper examines changes in the strength of the WC using an index called BoxΔP, which is equal to the difference in mean sea level pressure across the equatorial Pacific. Change in both the observations and in World Climate Research Programme (WCRP) Coupled Model Intercomparison Project phase 3 (CMIP3) climate models are examined. The annual average BoxΔP declines in the observations and in 15 out of 23 models during the twentieth century (results that are significant at or above the 95% level), consistent with earlier work. However, the magnitude of the multimodel ensemble mean (MMEM) 1901–99 trend (−0.10 Pa yr−1) is much smaller than the magnitude of the observed trend (−0.52 Pa yr−1). While a wide range of trends is evident in the models with approximately 90% of the model trends in the range (−0.25 to +0.1 Pa yr−1), even this range is too narrow to encompass the magnitude of the observed trend. Twenty-first-century changes in BoxΔP under the Special Report on Emissions Scenarios (SRES) A1B and A2 are also examined. Negative trends (i.e., weaker WCs) are evident in all seasons. However, the MMEM trends for the A1B and A2 scenarios are smaller in magnitude than the magnitude of the observed trend. Given that external forcing linked to greenhouse gases is much larger in the twenty-first-century scenarios than twentieth-century forcing, this, together with the twentieth-century results mentioned above, would seem to suggest that external forcing has not been the primary driver of the observed weakening of the WC. However, 9 of the 23 models are unable to account for the observed change unless the internally generated component of the trend is very large. But indicators of observed variability linked to El Niño–Southern Oscillation (ENSO) and the Interdecadal Pacific Oscillation have modest trends, suggesting that internally variability has been modest. Furthermore, many of the nine “inconsistent” models tend to have poorer simulations of climatic features linked to ENSO. In addition, the externally forced component of the trend tends to be larger in magnitude and more closely matches the observed trend in the models that are better able to reproduce ENSO-related variability. The “best” four models, for example, have a MMEM of −0.2 Pa yr−1 (i.e., approximately 40% of the observed change), suggesting a greater role for external forcing in driving the observed trend. These and other considerations outlined below lead the authors to conclude that (i) both external forcing and internally generated variability contributed to the observed weakening of the WC over the twentieth century and (ii) external forcing accounts for approximately 30%–70% of the observed weakening with internally generated climate variability making up the rest.

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Climatology and Variability of Warm and Cold Fronts over North America from 1979 to 2018

Journal of Climate ◽

10.1175/jcli-d-19-0680.1 ◽

2020 ◽

Vol 33 (15) ◽

pp. 6531-6554

Author(s):

Ryan Lagerquist ◽

John T. Allen ◽

Amy McGovern

Keyword(s):

North America ◽

El Niño ◽

El Nino ◽

Southern Oscillation ◽

Specific Humidity ◽

Regional Patterns ◽

Cold Fronts ◽

The Pacific ◽

Cyclone Tracks

AbstractThis paper describes the development and analysis of an objective climatology of warm and cold fronts over North America from 1979 to 2018. Fronts are detected by a convolutional neural network (CNN), trained to emulate fronts drawn by human meteorologists. Predictors for the CNN are surface and 850-hPa fields of temperature, specific humidity, and vector wind from the ERA5 reanalysis. Gridded probabilities from the CNN are converted to 2D frontal regions, which are used to create the climatology. Overall, warm and cold fronts are most common in the Pacific and Atlantic cyclone tracks and the lee of the Rockies. In contrast with prior research, we find that the activity of warm and cold fronts is significantly modulated by the phase and intensity of El Niño–Southern Oscillation. The influence of El Niño is significant for winter warm fronts, winter cold fronts, and spring cold fronts, with activity decreasing over the continental United States and shifting northward with the Pacific and Atlantic cyclone tracks. Long-term trends are generally not significant, although we find a poleward shift in frontal activity during the winter and spring, consistent with prior research. We also identify a number of regional patterns, such as a significant long-term increase in warm fronts in the eastern tropical Pacific Ocean, which are characterized almost entirely by moisture gradients rather than temperature gradients.

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