scholarly journals Northern Hemisphere atmospheric pattern enhancing Eastern Mediterranean Transient-type events during the past 1000 years 

2021 ◽  
Author(s):  
Aleix Cortina-Guerra ◽  
Juan José Gomez-Navarro ◽  
Belen Martrat ◽  
Juan Pedro Montávez ◽  
Alessandro Incarbona ◽  
...  
Keyword(s):  
Northern Hemisphere ◽  
Climate Model ◽  
Eastern Mediterranean ◽  
Aegean Sea ◽  
Sea Surface ◽  
The West ◽  
The Past ◽  
Main Driver ◽  
Climate Model Simulations ◽  
Past 1000 Years

Abstract. High resolution climate model simulations for the last millennium were used to elucidate the main winter Northern Hemisphere atmospheric pattern during enhanced Eastern Mediterranean Transient (EMT-type) events, a situation in which an additional overturning cell is detected in the Mediterranean at the Aegean Sea. The differential upward heat flux between the Aegean Basin and the Gulf of Lions was taken as a proxy of EMT-type events and correlated with winter mean geopotential height at 500 mb in the Northern Hemisphere (200 N-900 N and 1000 W-800 E). Correlations revealed a pattern similar to the Eastern Atlantic/Western Russian (EA/WR) mode as the main driver of EMT-type events, with the past 1000 yr of EA/WR-like mode simulations being enhanced during insolation minima. Our model results are consistent with alkenone Sea Surface Temperature (SST) reconstructions that documented an increase in the west-east basin gradients during EMT-type events.

scholarly journals Northern Hemisphere atmospheric pattern enhancing Eastern Mediterranean Transient-type events during the past 1000 years

2021 ◽  
Vol 17 (4) ◽  
pp. 1523-1532
Author(s):  
Aleix Cortina-Guerra ◽  
Juan José Gomez-Navarro ◽  
Belen Martrat ◽  
Juan Pedro Montávez ◽  
Alessandro Incarbona ◽  
...  
Keyword(s):  
Northern Hemisphere ◽  
Climate Model ◽  
Eastern Mediterranean ◽  
Aegean Sea ◽  
East Atlantic ◽  
The Past ◽  
Gulf Of Lion ◽  
Main Driver ◽  
Climate Model Simulations ◽  
Past 1000 Years

Abstract. High-resolution climate model simulations for the last millennium were used to elucidate the main winter Northern Hemisphere atmospheric pattern during enhanced Eastern Mediterranean Transient (EMT-type) events, a situation in which an additional overturning cell is detected in the Mediterranean at the Aegean Sea. The differential upward heat flux between the Aegean Basin and the Gulf of Lion was taken as a proxy of EMT-type events and correlated with winter mean geopotential height at 500 mbar in the Northern Hemisphere (20–90∘ N and 100∘ W–80∘ E). Correlations revealed a pattern similar to the East Atlantic/Western Russian (EA/WR) mode as the main driver of EMT-type events, with the past 1000 years of EA/WR-like mode simulations being enhanced during insolation minima. Our model results are consistent with alkenone sea surface temperature (SST) reconstructions that documented an increase in the west–east basin gradients during EMT-type events.

scholarly journals Causes for increased flood frequency in central Europe in the 19th century

2019 ◽  
Author(s):  
Stefan Brönnimann ◽  
Luca Frigerio ◽  
Mikhaël Schwander ◽  
Marco Rohrer ◽  
Peter Stucki ◽  
...  
Keyword(s):  
19Th Century ◽  
Climate Model ◽  
Warm Season ◽  
Flood Frequency ◽  
Sea Surface ◽  
Weather Types ◽  
Annual Series ◽  
Climate Model Simulations ◽  
Post War ◽  
The 19Th Century

Abstract. Historians and historical climatologists have long pointed to an increased flood frequency in Central Europe in the mid and late 19th century. However, the causes have remained unclear. Here, we investigate the changes in flood frequency in Switzerland based on long time series of discharge and lake levels, of precipitation and weather types, and based on climate model simulations, focusing on the warm season. Annual series of peak discharge or maximum lake level, in agreement with previous studies, display increased frequency of floods in the mid 19th century and decreased frequency after the Second World War. Annual series of warm-season mean precipitation and high percentiles of 3-day precipitation totals (partly) reflect these changes. A daily weather type classification since 1763 is used to construct flood probability indices for the catchments of the Rhine in Basel and the outflow of Lake Lugano, Ponte Tresa. The indices indicate an increased frequency of flood-prone weather types in the mid 19th century and a decreased frequency in the post-war period, consistent with a climate reconstruction that shows increased (decreased) cyclonic flow over Western Europe in the former (latter) period. To assess the driving factors of the detected circulation changes, we analyse weather types and precipitation in a large ensemble of climate model simulations forced with observed sea-surface temperatures. In the simulations, we do not find an increase in flood-prone weather types in the Rhine catchment in the 19th century, but a decrease in the post-war period related to the sea-surface temperature anomalies.

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 Implication of methodological uncertainties for mid-Holocene sea surface temperature reconstructions

2014 ◽  
Vol 10 (6) ◽  
pp. 2237-2252 ◽  
Author(s):  
I. Hessler ◽  
S. P. Harrison ◽  
M. Kucera ◽  
C. Waelbroeck ◽  
M.-T. Chen ◽  
...  
Keyword(s):  
Climate Model ◽  
Time Window ◽  
Planktonic Foraminifera ◽  
Regional Scale ◽  
Time Frame ◽  
Sea Surface ◽  
Model Simulations ◽  
Climate Model Simulations ◽  
Analytical Approaches ◽  
Baseline Climate

Abstract. We present and examine a multi-sensor global compilation of mid-Holocene (MH) sea surface temperatures (SST), based on Mg/Ca and alkenone palaeothermometry and reconstructions obtained using planktonic foraminifera and organic-walled dinoflagellate cyst census counts. We assess the uncertainties originating from using different methodologies and evaluate the potential of MH SST reconstructions as a benchmark for climate-model simulations. The comparison between different analytical approaches (time frame, baseline climate) shows the choice of time window for the MH has a negligible effect on the reconstructed SST pattern, but the choice of baseline climate affects both the magnitude and spatial pattern of the reconstructed SSTs. Comparison of the SST reconstructions made using different sensors shows significant discrepancies at a regional scale, with uncertainties often exceeding the reconstructed SST anomaly. Apparent patterns in SST may largely be a reflection of the use of different sensors in different regions. Overall, the uncertainties associated with the SST reconstructions are generally larger than the MH anomalies. Thus, the SST data currently available cannot serve as a target for benchmarking model simulations. Further evaluations of potential subsurface and/or seasonal artifacts that may contribute to obscure the MH SST reconstructions are urgently needed to provide reliable benchmarks for model evaluations.

scholarly journals Episodic Neoglacial expansion and rapid 20th century retreat of a small ice cap on Baffin Island, Arctic Canada, and modeled temperature change

2017 ◽  
Vol 13 (11) ◽  
pp. 1527-1537 ◽  
Author(s):  
Simon L. Pendleton ◽  
Gifford H. Miller ◽  
Robert A. Anderson ◽  
Sarah E. Crump ◽  
Yafang Zhong ◽  
...  
Keyword(s):  
Temperature Change ◽  
Climate Model ◽  
Ice Age ◽  
The Arctic ◽  
Baffin Island ◽  
Radiocarbon Dates ◽  
The Past ◽  
Ice Cap ◽  
Climate Model Simulations ◽  
Glacier Advance

Abstract. Records of Neoglacial glacier activity in the Arctic constructed from moraines are often incomplete due to a preservation bias toward the most extensive advance, often the Little Ice Age. Recent warming in the Arctic has caused extensive retreat of glaciers over the past several decades, exposing preserved landscapes complete with in situ tundra plants previously entombed by ice. The radiocarbon ages of these plants define the timing of snowline depression and glacier advance across the site, in response to local summer cooling. Erosion rapidly removes most dead plants that have been recently exposed by ice retreat, but where erosive processes are unusually weak, dead plants may remain preserved on the landscape for decades. In such settings, a transect of plant radiocarbon ages can be used to construct a near-continuous chronology of past ice margin advance. Here we present radiocarbon dates from the first such transect on Baffin Island, which directly dates the advance of a small ice cap over the past two millennia. The nature of ice expansion between 20 BCE and ∼ 1000 CE is still uncertain, but episodic advances at ∼ 1000 CE, ∼ 1200, and  ∼ 1500 led to the maximum Neoglacial dimensions ~ 1900 CE. We employ a two-dimensional numerical glacier model calibrated using the plant radiocarbon ages ice margin chronology to assess the sensitivity of the ice cap to temperature change. Model experiments show that at least ∼ 0.44 °C of cooling over the past 2 kyr is required for the ice cap to reach its 1900 CE margin, and that the period from ∼ 1000 to 1900 CE must have been at least 0.25° C cooler than the previous millennium, results that agree with regional temperature reconstructions and climate model simulations. However, significant warming since 1900 CE is required to explain retreat to its present position, and, at the same rate of warming, the ice cap will disappear before 2100 CE.

Extra-tropical Northern Hemisphere land temperature variability over the past 1000 years

2004 ◽  
Vol 23 (20-22) ◽  
pp. 2063-2074 ◽  
Author(s):  
Edward R. Cook ◽  
Jan Esper ◽  
Rosanne D. D’Arrigo
Keyword(s):  
Northern Hemisphere ◽  
Temperature Variability ◽  
The Past ◽  
Past 1000 Years

Evolution of Water Vapor Concentrations and Stratospheric Age of Air in Coupled Chemistry-Climate Model Simulations

2007 ◽  
Vol 64 (3) ◽  
pp. 905-921 ◽  
Author(s):  
John Austin ◽  
John Wilson ◽  
Feng Li ◽  
Holger Vömel
Keyword(s):  
Water Vapor ◽  
Greenhouse Gas ◽  
Climate Model ◽  
Sea Surface ◽  
Time Slice ◽  
Sea Surface Temperatures ◽  
Model Simulations ◽  
Stratospheric Water Vapor ◽  
Surface Temperatures ◽  
Climate Model Simulations

Abstract Stratospheric water vapor concentrations and age of air are investigated in an ensemble of coupled chemistry-climate model simulations covering the period from 1960 to 2005. Observed greenhouse gas concentrations, halogen concentrations, aerosol amounts, and sea surface temperatures are all specified in the model as time-varying fields. The results are compared with two experiments (time-slice runs) with constant forcings for the years 1960 and 2000, in which the sea surface temperatures are set to the same climatological values, aerosol concentrations are fixed at background levels, while greenhouse gas and halogen concentrations are set to the values for the relevant years. The time-slice runs indicate an increase in stratospheric water vapor from 1960 to 2000 due primarily to methane oxidation. The age of air is found to be significantly less in the year 2000 run than the 1960 run. The transient runs from 1960 to 2005 indicate broadly similar results: an increase in water vapor and a decrease in age of air. However, the results do not change gradually. The age of air decreases significantly only after about 1975, corresponding to the period of ozone reduction. The age of air is related to tropical upwelling, which determines the transport of methane into the stratosphere. Oxidation of increased methane from enhanced tropical upwelling results in higher water vapor amounts. In the model simulations, the rate of increase of stratospheric water vapor during the period of enhanced upwelling is up to twice the long-term mean. The concentration of stratospheric water vapor also increases following volcanic eruptions during the simulations.

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