scholarly journals Teleconnections and relationship between the El Niño–Southern Oscillation (ENSO) and the Southern Annular Mode (SAM) in reconstructions and models over the past millennium

2020 ◽  
Vol 16 (2) ◽  
pp. 743-756 ◽  
Author(s):  
Christoph Dätwyler ◽  
Martin Grosjean ◽  
Nathan J. Steiger ◽  
Raphael Neukom
Keyword(s):  
Climate Model ◽  
El Nino ◽  
Southern Oscillation ◽  
Southern Annular Mode ◽  
Last Millennium ◽  
Annular Mode ◽  
Model Simulations ◽  
The Past ◽  
Climate Model Simulations ◽  
Past Millennium

Abstract. The climate of the Southern Hemisphere (SH) is strongly influenced by variations in the El Niño–Southern Oscillation (ENSO) and the Southern Annular Mode (SAM). Because of the limited length of instrumental records in most parts of the SH, very little is known about the relationship between these two key modes of variability over time. Using proxy-based reconstructions and last-millennium climate model simulations, we find that ENSO and SAM indices are mostly negatively correlated over the past millennium. Pseudo-proxy experiments indicate that currently available proxy records are able to reliably capture ENSO–SAM relationships back to at least 1600 CE. Palaeoclimate reconstructions show mostly negative correlations back to about 1400 CE. An ensemble of last-millennium climate model simulations confirms this negative correlation, showing a stable correlation of approximately −0.3. Despite this generally negative relationship we do find intermittent periods of positive ENSO–SAM correlations in individual model simulations and in the palaeoclimate reconstructions. We do not find evidence that these relationship fluctuations are caused by exogenous forcing nor by a consistent climate pattern. However, we do find evidence that strong negative correlations are associated with strong positive (negative) anomalies in the Interdecadal Pacific Oscillation and the Amundsen Sea Low during periods when SAM and ENSO indices are of opposite (equal) sign.

scholarly journals Analysis of upper-tropospheric humidity in tropical descent regions using observed and modelled radiances

2013 ◽  
Vol 13 (4) ◽  
pp. 10547-10560
Author(s):  
V. O. John ◽  
D. E. Parker ◽  
S. A. Buehler ◽  
J. Price ◽  
R. W. Saunders
Keyword(s):  
El Niño ◽  
Climate Model ◽  
El Nino ◽  
Southern Oscillation ◽  
Model Simulations ◽  
Multiple Observations ◽  
Major Mode ◽  
Upper Tropospheric Humidity ◽  
Water Vapour Feedback ◽  
Climate Model Simulations

Abstract. We use multiple observations and climate model simulations to study upper tropospheric humidity (UTH) in tropical descent regions. A satellite simulator is used to generate UTH from model fields to ensure a like-to-like comparison. We have shown that HadGEM2 is generally able to reproduce the patterns and magnitude of UTH in these regions. In both models and observations, the major mode of UTH variability in these regions is associated with El Nino and Southern Oscillation (ENSO); a negative UTH anomaly is seen during El Nino years. There is no significant trend in UTH in these regions, where even a small negative trend would lead to an important reduction of the positive water vapour feedback on global warming.

Variability of the Azores High and regional hydroclimate over the past millennium

2020 ◽  
Author(s):  
Caroline Ummenhofer ◽  
Nathaniel Cresswell-Clay ◽  
Diana Thatcher ◽  
Alan Wanamaker ◽  
Rhawn Denniston
Keyword(s):  
Climate Model ◽  
Hadley Circulation ◽  
Meridional Overturning Circulation ◽  
Ice Age ◽  
Last Millennium ◽  
Atlantic Sector ◽  
Model Simulations ◽  
The Past ◽  
Climate Model Simulations ◽  
Azores High

<p>The subtropical dry zones, including the broader Mediterranean region, are likely to experience considerable changes in hydroclimate in a warming climate. An expansion of the atmosphere’s meridional overturning circulation, the Hadley circulation, over recent decades has been reported, with implications for regional hydroclimate. Yet, there exists considerable disagreement in magnitude and even sign of these trends among different metrics that measure various aspects of the Hadley circulation, as well as discrepancies in trends between different analysis periods and reanalysis products during the 20<sup>th</sup> century. In light of these uncertainties, it is therefore of interest to explore variability and trends in subtropical hydroclimate and its dominant driver, the Hadley Circulation. We focus on the North Atlantic sector and explore variability in the Azores High, the manifestation of the Hadley Circulation’s downward branch, and hydroclimate across the Iberian Peninsula using a combination of observational/reanalysis products, state-of-the-art climate model simulations, and hydroclimatically-sensitive stalagmite records over the past 1200 yr. The Last Millennium Ensemble (LME) with the Community Earth System Model provides thirteen transient simulations covering the period 850 to 2005 A.D. with prescribed external forcing (e.g. greenhouse gas, solar, volcanic, land use, orbital, and aerosol) and smaller subsets with individual forcing only. The LME is shown to accurately simulate the variability and trends in the Azores High when compared to observational records from the 20<sup>th</sup> century. We evaluate variability in the Azores High (e.g., size, intensity, position) in relation to other key metrics that measure different aspects of the Hadley circulation throughout the course of the last millennium, as well as during key periods, such as the Little Ice Age or Medieval Climate Anomaly. The smaller subsets of LME simulations with individual forcing factors (e.g., solar, volcanic) allow for an attribution of past changes in regional hydroclimate to external drivers. Results from the climate model simulations are compared with hydroclimate reconstructed from stalagmites from Portuguese caves.</p>

Variations in Precipitation across the Southern Ocean

2020 ◽  
Vol 33 (24) ◽  
pp. 10653-10670
Author(s):  
M. J. Manton ◽  
Y. Huang ◽  
S. T. Siems
Keyword(s):  
Southern Ocean ◽  
Climate Model ◽  
Southern Oscillation ◽  
Zonal Flow ◽  
Southern Annular Mode ◽  
Accurate Estimate ◽  
Precipitation Anomaly ◽  
Unique Region ◽  
Pressure Anomaly ◽  
Climate Model Simulations

AbstractThe Southern Ocean lies beneath a unique region of the global atmosphere with minimal effects of landmasses on the zonal flow. The absence of landmasses also means that in situ observations of precipitation are limited to a few ocean islands. Two reanalyses and two satellite-based gridded datasets are analyzed to estimate the character of the distribution of precipitation across the region. The latitudinal variation is computed across three longitudinal sectors, representing the Pacific, Atlantic, and Indian Oceans. The most recent ECMWF reanalysis (ERA5) is found to produce the most accurate estimate of the mean profile and seasonal cycle of precipitation. However, there is little consistency in the estimates of trends in monthly anomalies of precipitation. A more consistent description of precipitation trends is found by using linear regression of the precipitation anomaly with the local mean sea level pressure anomaly, the southern annular mode, and the Southern Oscillation index. In broad terms, precipitation is found to be decreasing at lower latitudes and increasing at higher latitudes, which is consistent with earlier climate model simulations on the impacts of anthropogenic climate change.

scholarly journals Evolution of the Southern Annular Mode during the past millennium

2014 ◽  
Vol 4 (7) ◽  
pp. 564-569 ◽  
Author(s):  
Nerilie J. Abram ◽  
Robert Mulvaney ◽  
Françoise Vimeux ◽  
Steven J. Phipps ◽  
John Turner ◽  
...  
Keyword(s):  
Southern Annular Mode ◽  
Annular Mode ◽  
The Past ◽  
Past Millennium

scholarly journals Teleconnections and relationship between ENSO and SAM in reconstructions and models over the past millennium

2019 ◽  
Author(s):  
Christoph Dätwyler ◽  
Martin Grosjean ◽  
Nathan J. Steiger ◽  
Raphael Neukom
Keyword(s):  
Climate Model ◽  
Southern Oscillation ◽  
Negative Temperature ◽  
Internal Variability ◽  
Southern Annular Mode ◽  
Teleconnection Patterns ◽  
Modes Of Variability ◽  
Proxy Records ◽  
Climate Model Simulations ◽  
Instrumental Records

Abstract. The climate of the Southern Hemisphere (SH) is strongly influenced by variations in the El Niño-Southern Oscillation (ENSO) and the Southern Annular Mode (SAM). Due to the temporally very limited instrumental records in most parts of the SH, very little is known about the relationship between these two key modes of variability and its stability over time. Here, we use proxy-based reconstructions and climate model simulations to quantify changes in tropical-extratropical SH teleconnections as represented by the correlation between the ENSO and SAM indices. Reconstructions indicate mostly negative correlations back to around 1400 CE confirming the pattern seen in the instrumental record over the last few decades. An ensemble of last millennium simulations of the model CESM1 confirms this pattern with very stable ensemble mean correlations around −0.3. Individual forced simulations, the pre-industrial control run and the proxy-based reconstructions indicate intermittent periods of positive correlations and particularly strong negative correlations. The fluctuations of the ENSO-SAM correlations are not significantly related to solar nor volcanic forcing in both proxy and model data, indicating that they are driven by internal variability in the climate system. Pseudoproxy experiments indicate that the currently available proxy records are able to reproduce the tropical-extratropical teleconnection patterns back to around 1600 CE. We analyse the spatial temperature and sea level pressure patterns during periods of positive and particularly strong negative teleconnections in the CESM model. Results indicate no consistent pattern during periods where the ENSO-SAM teleconnection changes its sign. However, periods of very strong negative SH teleconnections are associated with negative temperature anomalies across large fractions of the extra-tropical Pacific and a strengthening of the Aleutian Low.

scholarly journals Diagnosing ENSO and Global Warming Tropical Precipitation Shifts Using Surface Relative Humidity and Temperature

2018 ◽  
Vol 31 (4) ◽  
pp. 1413-1433 ◽  
Author(s):  
Alexander Todd ◽  
Matthew Collins ◽  
F. Hugo Lambert ◽  
Robin Chadwick
Keyword(s):  
Global Warming ◽  
Relative Humidity ◽  
Climate Model ◽  
Southern Oscillation ◽  
Precipitation Change ◽  
Method Performance ◽  
Model Simulations ◽  
Tropical Precipitation ◽  
Climate Model Simulations ◽  
Precipitation Changes

Large uncertainty remains in future projections of tropical precipitation change under global warming. A simplified method for diagnosing tropical precipitation change is tested here on present-day El Niño–Southern Oscillation (ENSO) precipitation shifts. This method, based on the weak temperature gradient approximation, assumes precipitation is associated with local surface relative humidity (RH) and surface air temperature (SAT), relative to the tropical mean. Observed and simulated changes in RH and SAT are subsequently used to diagnose changes in precipitation. Present-day ENSO precipitation shifts are successfully diagnosed using observations (correlation r = 0.69) and an ensemble of atmosphere-only (0.51 ≤ r ≤ 0.8) and coupled (0.5 ≤ r ≤ 0.87) climate model simulations. RH ( r = 0.56) is much more influential than SAT ( r = 0.27) in determining ENSO precipitation shifts for observations and climate model simulations over both land and ocean. Using intermodel differences, a significant relationship is demonstrated between method performance over ocean for present-day ENSO and projected global warming ( r = 0.68). As a caveat, the authors note that mechanisms leading to ENSO-related precipitation changes are not a direct analog for global warming–related precipitation changes. The diagnosis method presented here demonstrates plausible mechanisms that relate changes in precipitation, RH, and SAT under different climate perturbations. Therefore, uncertainty in future tropical precipitation changes may be linked with uncertainty in future RH and SAT changes.

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