An Andean ice-core record of a Middle Holocene mega-drought in North Africa and Asia

AbstractAn ice core from the Nevado Huascaran col in the Cordillera Blanca of northern Peru contains high-resolution time series of dust concentrations and size distributions since the end of the last glacial stage. A large dust peak, dated ∼4500 years ago, is contemporaneous with a widespread and prolonged drought that apparently extended from North Africa to eastern China, evidence of which occurs in historical, archeological and paleoclimatic records. This event may have been associated with several centuries of weak Asian/Indian/African monsoons, possibly linked with a protracted cooling in the North Atlantic. During the second half of the 20th century, high austral-summer dust concentrations in the Huascaran record are significantly correlated with atmospheric conditions, such as sea-level pressure and zonal wind velocities that are consistent with El Nino-Southern Oscillation (ENSO) and positive North Atlantic Oscillation (NAO) indices, and with aridity in North Africa, southwest Asia and the Middle East. Therefore, the dominant submicron fraction of the dust may have been transported by more intense northeasterly trade winds from the African dry regions across the tropical Atlantic during a period of frequent and/or intense ENSO activity. The proposed ENSO conditions that may have been linked with drought in the monsoon region may also have contributed to aridity in tropical South America, including the Cordillera Blanca.

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A space–time statistical climate model for hurricane intensification in the North Atlantic basin

Advances in Statistical Climatology Meteorology and Oceanography ◽

10.5194/ascmo-2-105-2016 ◽

2016 ◽

Vol 2 (2) ◽

pp. 105-114 ◽

Cited By ~ 1

Author(s):

Erik Fraza ◽

James B. Elsner ◽

Thomas H. Jagger

Keyword(s):

North Atlantic ◽

Climate Model ◽

Southern Oscillation ◽

Vertical Wind Shear ◽

Credible Interval ◽

Climatic Effects ◽

Trade Winds ◽

The North ◽

Hurricane Intensification ◽

The North Atlantic

Abstract. Climate influences on hurricane intensification are investigated by averaging hourly intensification rates over the period 1975–2014 in 8° × 8° latitude–longitude grid cells. The statistical effects of hurricane intensity and sea-surface temperature (SST), along with the climatic effects of El Niño–Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO) and the Madden–Julian Oscillation (MJO), are quantified using a Bayesian hierarchical model fit to the averaged data. As expected, stronger hurricanes tend to have higher intensification rates, especially over the warmest waters. Of the three climate variables considered, the NAO has the largest effect on intensification rates after controlling for intensity and SST. The model shows an average increase in intensification rates of 0.18 [0.06, 0.31] m s−1 h−1 (95 % credible interval) for every 1 standard deviation decrease in the NAO index. Weak trade winds associated with the negative phase of the NAO might result in less vertical wind shear and thus higher mean intensification rates.

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Non-linearity in the pathway of El Niño-Southern Oscillation to the tropical North Atlantic

10.5194/egusphere-egu21-7483 ◽

2021 ◽

Author(s):

Jake W. Casselman ◽

Andréa S. Taschetto ◽

Daniela I.V. Domeisen

Keyword(s):

North Atlantic ◽

Southern Oscillation ◽

Static Stability ◽

Reanalysis Data ◽

Trade Winds ◽

The North ◽

The Pacific ◽

Tropical North Atlantic ◽

Sst Anomaly ◽

The North Atlantic Oscillation

El Ni&#241;o-Southern Oscillation can influence the Tropical North Atlantic (TNA), leading to anomalous sea surface temperatures (SST) at a lag of several months. Several mechanisms have been proposed to explain this teleconnection. These mechanisms include both tropical and extratropical pathways, contributing to anomalous trade winds and static stability over the TNA region. The TNA SST response to ENSO has been suggested to be nonlinear. Yet the overall linearity of the ENSO-TNA teleconnection via the two pathways remains unclear. Here we use reanalysis data to confirm that the SST anomaly (SSTA) in the TNA is nonlinear with respect to the strength of the SST forcing in the tropical Pacific, as further increases in El Ni&#241;o magnitudes cease to create further increases of the TNA SSTA. We further show that the tropical pathway is more linear than the extratropical pathway by sub-dividing the inter-basin connection into extratropical and tropical pathways. The extratropical pathway is modulated by the North Atlantic Oscillation (NAO) and the location of the SSTA in the Pacific, but this modulation insufficiently explains the nonlinearity in TNA SSTA. As neither extratropical nor tropical pathways can explain the nonlinearity, this suggests that external factors are at play. Further analysis shows that the TNA SSTA is highly influenced by the preconditioning of the tropical Atlantic SST. This preconditioning is found to be associated with the NAO through SST-tripole patterns.

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Meridional Tripole Mode of Winter Precipitation over the Arctic and Continental North Africa–Eurasia

Journal of Climate ◽

10.1175/jcli-d-21-0212.1 ◽

2021 ◽

pp. 1

Author(s):

Xiaolin Liu ◽

Jianhua Lu ◽

Yimin Liu ◽

Guoxiong Wu

Keyword(s):

Time Series ◽

North Africa ◽

North Atlantic ◽

Hadley Cell ◽

The Arctic ◽

Positive Phase ◽

The North ◽

Ferrel Cell ◽

The North Atlantic ◽

Westerly Jets

AbstractWintertime precipitation is vital to the growth of glaciers in the northern hemisphere. We find a tripole mode of precipitation (PTM), with each pole of the mode extending zonally over the eastern hemisphere roughly between 30°W and 120°E, and the positive/negative/positive structure for its positive phase extending meridionally from the Arctic to the continental North Africa–Eurasia. The large-scale dynamics associated with the PTM is explored. The positive phase of the PTM is associated with the negative while eastward-shifted phase of the North Atlantic Oscillation (NAO) and a zonal band of positive SST anomaly in the tropics, together with a narrowed Hadley cell and weakened Ferrel cell. While being north-eastward tilted and separated from their North Africa-Eurasia counterpart in the climatological mean, the upper-tropospheric westerly jets over the east Pacific and north Atlantic become extending zonally and shifting southward and hence form a circumpolar subtropical jet as a whole by connecting with the westerly jets over the North Africa-Eurasia. The enhanced zonal winds over the north Atlantic promote more synoptic-scale transient eddies which are waveguided by the jet streams. The polar vortex weakens and cold air dips southward from the North Pole. Further diagnosis of the E-vectors suggests that transient eddies have a positive feedback on the weakening of Ferrel cell. Opposite features are associated with the negative phase of the PTM. The reconstructed time series using multiple linear regression on the NAO index and the tropical SST averaged over 20°S– 20°N, can explain 62.4% of the variance of the original the original precipitation time series.

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A 60 000 year Greenland stratigraphic ice core chronology

Climate of the Past ◽

10.5194/cp-4-47-2008 ◽

2008 ◽

Vol 4 (1) ◽

pp. 47-57 ◽

Cited By ~ 697

Author(s):

A. Svensson ◽

K. K. Andersen ◽

M. Bigler ◽

H. B. Clausen ◽

D. Dahl-Jensen ◽

...

Keyword(s):

North Atlantic ◽

Time Scale ◽

Ice Core ◽

Ice Cores ◽

The North ◽

Annual Layer ◽

Zone Ii ◽

Absolute Age ◽

Age Estimates ◽

New Time

Abstract. The Greenland Ice Core Chronology 2005 (GICC05) is a time scale based on annual layer counting of high-resolution records from Greenland ice cores. Whereas the Holocene part of the time scale is based on various records from the DYE-3, the GRIP, and the NorthGRIP ice cores, the glacial part is solely based on NorthGRIP records. Here we present an 18 ka extension of the time scale such that GICC05 continuously covers the past 60 ka. The new section of the time scale places the onset of Greenland Interstadial 12 (GI-12) at 46.9±1.0 ka b2k (before year AD 2000), the North Atlantic Ash Zone II layer in GI-15 at 55.4±1.2 ka b2k, and the onset of GI-17 at 59.4±1.3 ka b2k. The error estimates are derived from the accumulated number of uncertain annual layers. In the 40–60 ka interval, the new time scale has a discrepancy with the Meese-Sowers GISP2 time scale of up to 2.4 ka. Assuming that the Greenland climatic events are synchronous with those seen in the Chinese Hulu Cave speleothem record, GICC05 compares well to the time scale of that record with absolute age differences of less than 800 years throughout the 60 ka period. The new time scale is generally in close agreement with other independently dated records and reference horizons, such as the Laschamp geomagnetic excursion, the French Villars Cave and the Austrian Kleegruben Cave speleothem records, suggesting high accuracy of both event durations and absolute age estimates.

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Climatology of Heavy Orographic Rainfall Induced by Tropical Cyclones over Madagascar: From Synoptic to Mesoscale Perspectives

Earth Science Research ◽

10.5539/esr.v5n2p132 ◽

2016 ◽

Vol 5 (2) ◽

pp. 132 ◽

Cited By ~ 2

Author(s):

Tatiana A. Arivelo ◽

Yuh-Lang Lin

Keyword(s):

Tropical Cyclones ◽

Southern Oscillation Index ◽

Southern Oscillation ◽

Rainfall Variability ◽

Eastern Coast ◽

Quasi Biennial Oscillation ◽

Trade Winds ◽

Southwest Indian Ocean ◽

The North ◽

Orographic Rainfall

Variability of and generation mechanisms for Madagascar rainfall are studied by conducting climatological, synoptic and mesoscale analyses. It is found the rainfall variability is highly sensitive to seasons with high variability in summer (Nov-Apr). The rainfall in summer is controlled by the Intertropical Convergence Zone (ITCZ) and orographic rainfall associated with tropical cyclones (TCs), while the rainfall in winter (May-Oct) is controlled by trade winds and local orographic rainfall along the eastern coast. Synoptic analysis reveals that major climate variations in summer are associated with ITCZ position, which is closely related to TC genesis locations and quasi-biennial oscillation (QBO). Linkages between El-Niño Southern Oscillation Index (ENSO) and Southern Oscillation Index (SOI) are identified as the cause of inconsistent dry or wet summers. Mesoscale analysis depicts the importance of the orographic effects on prevailing wind, which are controlled by the orography in both seasons. In winter, the prevailing trade winds over the Southwest Indian Ocean are from the east and are split to the north and south when it impinges on Malagasy Mountains. On the other hand, in summer the prevailing easterlies are weaker leading to the production of lee vortices, in addition to the flow splitting upstream of the mountain. Thus, the flow is classified into two regimes: (a) flow-over regime with no lee vortices under high Froude number (Fr=1.2-1.8) flow, and (b) flow-around regime with lee vortices under low Fr (=0.88-1.16) flow. A case study of TC Domoina (1984) indicates that the long-lasting heavy rainfall was induced by the strong orographic blocking of Madagascar. The shorter-term (e.g., 2 days) heavy orographic precipitation is characterized by large VH ∙Ñh which is composed by two common ingredients, namely a strong low-level wind normal to the mountain (VH) and a steep mountain slope (∇h).

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Tree-ring radiocarbon reveals reduced solar activity during Younger Dryas cooling

10.5194/egusphere-egu2020-11654 ◽

2020 ◽

Cited By ~ 2

Author(s):

Adam Sookdeo ◽

Bernd Kromer ◽

Florian Adolphi ◽

Jürg Beer ◽

Nicolas Brehm ◽

...

Keyword(s):

Solar Activity ◽

Tree Ring ◽

North Atlantic ◽

Little Ice Age ◽

Ice Core ◽

Younger Dryas ◽

Ice Age ◽

The North ◽

Long Duration ◽

Clear Sign

The Younger Dryas stadial (YD) was a return to glacial-like conditions in the North Atlantic region that interrupted deglacial warming around 12900 cal BP (before 1950 AD). Terrestrial and marine records suggest this event was initiated by the interruption of deep-water formation arising from North American freshwater runoff, but the causes of the millennia-long duration remain unclear. To investigate the solar activity, a possible YD driver, we exploit the cosmic production signals of tree-ring radiocarbon (14C) and ice-core beryllium-10 (10Be). Here we present the highest temporally resolved dataset of 14C measurements (n = 1558) derived from European tree rings that have been accurately extended back to 14226 cal BP (&#177;8, 2-&#963;), allowing precise alignment of ice-core records across this period. We identify a substantial increase in 14C and 10Be production starting at 12780 cal BP is comparable in magnitude to the historic Little Ice Age, being a clear sign of grand solar minima. We hypothesize the timing of the grand solar minima provides a significant amplifying factor leading to the harsh sustained glacial-like conditions seen in the YD.

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How Predictable Are the Arctic and North Atlantic Oscillations? Exploring the Variability and Predictability of the Northern Hemisphere

Journal of Climate ◽

10.1175/jcli-d-17-0226.1 ◽

2018 ◽

Vol 31 (3) ◽

pp. 997-1014 ◽

Cited By ~ 19

Author(s):

Daniela I. V. Domeisen ◽

Gualtiero Badin ◽

Inga M. Koszalka

Keyword(s):

Time Scales ◽

Northern Hemisphere ◽

North Atlantic ◽

Prediction Models ◽

The Arctic ◽

Ensemble Prediction ◽

Atmospheric Conditions ◽

Short Term ◽

The North ◽

The North Atlantic Oscillation

ABSTRACT The North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO) describe the dominant part of the variability in the Northern Hemisphere extratropical troposphere. Because of the strong connection of these patterns with surface climate, recent years have shown an increased interest and an increasing skill in forecasting them. However, it is unclear what the intrinsic limits of short-term predictability for the NAO and AO patterns are. This study compares the variability and predictability of both patterns, using a range of data and index computation methods for the daily NAO and AO indices. Small deviations from Gaussianity are found along with characteristic decorrelation time scales of around one week. In the analysis of the Lyapunov spectrum it is found that predictability is not significantly different between the AO and NAO or between reanalysis products. Differences exist, however, between the indices based on EOF analysis, which exhibit predictability time scales around 12–16 days, and the station-based indices, exhibiting a longer predictability of 18–20 days. Both of these time scales indicate predictability beyond that currently obtained in ensemble prediction models for short-term predictability. Additional longer-term predictability for these patterns may be gained through local feedbacks and remote forcing mechanisms for particular atmospheric conditions.

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Understanding the Interdecadal Variability of East Asian Summer Monsoon Precipitation: Joint Influence of Three Oceanic Signals

Journal of Climate ◽

10.1175/jcli-d-17-0657.1 ◽

2018 ◽

Vol 31 (14) ◽

pp. 5485-5506 ◽

Cited By ~ 21

Author(s):

Zhiqi Zhang ◽

Xuguang Sun ◽

Xiu-Qun Yang

Keyword(s):

Summer Monsoon ◽

North Atlantic ◽

Asian Summer Monsoon ◽

Wave Train ◽

Eastern China ◽

Monsoon Precipitation ◽

The North ◽

Joint Influence ◽

Asian Summer ◽

Precipitation Anomalies

Abstract East Asian summer monsoon precipitation (EASMP) features complicated interdecadal variability with multiple time periods and spatial patterns. Using century-long datasets of HadISST, CRU precipitation, and the ECMWF twentieth-century reanalysis (ERA-20C), this study examines the joint influence of three oceanic interdecadal signals [i.e., Pacific decadal oscillation (PDO), Atlantic multidecadal oscillation (AMO), and Indian Ocean Basin mode (IOBM)] on the EASMP, which, however, is found not to be simply a linear combination of their individual effects. When PDO and AMO are out of phase, the same-sign SST anomalies occur in the North Pacific and North Atlantic, and a zonally orientated teleconnection wave train appears across the Eurasian mid-to-high latitudes, propagating from the North Atlantic to northern East Asia along the Asian westerly jet waveguide. Correspondingly, the interdecadal precipitation anomalies are characterized by a meridional tripole mode over eastern China. When PDO and AMO are in phase, with opposite sign SST anomalies in the North Pacific and North Atlantic, the sandwich pattern of anomalous stationary Rossby wavenumber tends to reduce the effect of the waveguide in the eastern Mediterranean region, and the teleconnection wave train from the North Atlantic travels only to western central Asia along a great circle route, causing Indian summer monsoon precipitation (ISMP) anomalies. The ISMP anomalies, in turn, interact with the teleconnection wave train induced by the PDO and AMO, leading to a meridional dipole mode of interdecadal precipitation anomalies over eastern China. Through the impact on the ISMP, the IOBM exerts significantly linear modulation on the combined impacts of PDO and AMO, especially over northern East Asia.

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Challenges for Diadromous Fishes in a Dynamic Global Environment

Challenges for Diadromous Fishes in a Dynamic Global Environment ◽

10.47886/9781934874080.ch15 ◽

2009 ◽

Keyword(s):

El Niño ◽

El Nino ◽

Southern Oscillation ◽

Sargasso Sea ◽

Atmospheric Conditions ◽

Feeding Success ◽

The North ◽

Spawning Areas ◽

Silver Eels ◽

Ocean Conditions

Abstract.-Declines in recruitment of temperate anguillid eels have occurred in the past 30 years in many areas of their species ranges. The cumulative effects of anthropogenic changes to their freshwater growth habitats are likely contributors to reductions in population sizes, but changes in ocean-atmospheric conditions in the ocean also appear to be contributing to the declines. This paper reviews how changes in the ocean may contribute to recruitment declines by affecting the spawning location of silver eels, larval feeding success, or the transport of their leptocephalus larvae by ocean currents. Recruitment of European eels Anguilla anguillla has shown correlations with the North Atlantic Oscillation and specific changes in ocean conditions in the Sargasso Sea where spawning and development occurs. The American eel A. rostrata spawns in an area that overlaps with the European eel and so could also be affected by these types of changes. Recruitment of Japanese eels A. japonica appears to be correlated to the El Niño Southern Oscillation index and latitudinal changes in salinity fronts in the western North Pacific. The general spawning and recruitment patterns of the temperate Australasian shortfin eels A. australis and New Zealand longfin eels A. dieffenbachii in the western South Pacific are similar to those of the northern temperate anguillids and also may be affected by El Niño-related factors. The changes in ocean conditions associated with atmospheric forcing or a warming of the ocean could alter the biological characteristics of the surface layer where leptocephali feed, due to changes in productivity or community structure, in addition to having possible effects on larval transport and location of the spawning areas by silver eels. Changes in ocean-atmospheric conditions could result in lower feeding success and survival of leptocephali, or increased retention in offshore areas due to changes in the location of spawning areas, resulting in reductions in recruitment.

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Impacts of large-scale atmospheric circulation changes due to winter sea-ice retreat on Black Carbon transport and deposition to the Arctic

10.5194/acp-2016-1007 ◽

2016 ◽

Author(s):

Luca Pozzoli ◽

Srdan Dobricic ◽

Simone Russo ◽

Elisabetta Vignati

Keyword(s):

Sea Ice ◽

Atmospheric Circulation ◽

North Atlantic ◽

Large Scale ◽

Southern Oscillation ◽

The Arctic ◽

The North ◽

Ice Retreat ◽

The North Atlantic Oscillation ◽

Sea Ice Retreat

Abstract. Winter warming and sea ice retreat observed in the Arctic in the last decades determine changes of large scale atmospheric circulation pattern that may impact as well the transport of black carbon (BC) to the Arctic and its deposition on the sea ice, with possible feedbacks on the regional and global climate forcing. In this study we developed and applied a new statistical algorithm, based on the Maximum Likelihood Estimate approach, to determine how the changes of three large scale weather patterns (the North Atlantic Oscillation, the Scandinavian Blocking, and the El Nino-Southern Oscillation), associated with winter increasing temperatures and sea ice retreat in the Arctic, impact the transport of BC to the Arctic and its deposition. We found that the three atmospheric patterns together determine a decreasing winter deposition trend of BC between 1980 and 2015 in the Eastern Arctic while they increase BC deposition in the Western Arctic. The increasing trend is mainly due to the more frequent occurrences of stable high pressure systems (atmospheric blocking) near Scandinavia favouring the transport in the lower troposphere of BC from Europe and North Atlantic directly into to the Arctic. The North Atlantic Oscillation has a smaller impact on BC deposition in the Arctic, but determines an increasing BC atmospheric load over the entire Arctic Ocean with increasing BC concentrations in the upper troposphere. The El Nino-Southern Oscillation does not influence significantly the transport and deposition of BC to the Arctic. The results show that changes in atmospheric circulation due to polar atmospheric warming and reduced winter sea ice significantly impacted BC transport and deposition. The anthropogenic emission reductions applied in the last decades were, therefore, crucial to counterbalance the most likely trend of increasing BC pollution in the Arctic.

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