scholarly journals Two types of North American droughts related to different atmospheric circulation patterns

2019 ◽  
Author(s):  
Angela-Maria Burgdorf ◽  
Stefan Brönnimann ◽  
Jörg Franke
Keyword(s):  
Atmospheric Circulation ◽  
Great Plains ◽  
North Atlantic ◽  
North American ◽  
Wave Train ◽  
Drought Indices ◽  
Dust Bowl ◽  
The North ◽  
The Pacific ◽  
The North Atlantic

Abstract. Proxy-based studies suggest that the southwestern USA is affected by two types of drought, often termed Dust Bowl-type droughts and 1950s type droughts. The spatial drought patterns of the two types are distinct. It has been suggested that they are related to different circulation characteristics, but lack of observation-based data has precluded further studies. In this paper, we analyze multi-annual droughts in North America since 1600 in tree-ring based drought reconstructions and in a global, monthly 3-dimensional reconstruction of the atmosphere. Using cluster analysis of drought indices, we confirm the two main drought types and find a similar catalog of events as previous studies. These two main types of droughts are then analyzed with respect to sea-surface temperatures (SST), sea-level pressure, and 500 hPa geopotential height (GPH) in summer. 1950s-type droughts are related to a stronger wave-train over the Pacific-North American sector than Dust Bowl-type droughts, whereas the latter show the imprint of a poleward shifted jet and establishment of a Great Plains ridge. The 500 hPa GPH patterns of the two types differ significantly not only over the contiguous United States and Canada but also over the North Atlantic and the Pacific. Dust Bowl-type droughts are associated with positive anomalies, while 1950s-type droughts exhibit strong negative anomalies. In comparison with 1950s-type droughts, the Dust Bowl-type droughts are characterized by higher SSTs in the North Atlantic. Results suggest that atmospheric circulation and SST characteristics not only over the Pacific but also over the extratropical North Atlantic affect the spatial pattern of North American droughts.

scholarly journals Two types of North American droughts related to different atmospheric circulation patterns

2019 ◽  
Vol 15 (6) ◽  
pp. 2053-2065 ◽  
Author(s):  
Angela-Maria Burgdorf ◽  
Stefan Brönnimann ◽  
Jörg Franke
Keyword(s):  
Atmospheric Circulation ◽  
Great Plains ◽  
North Atlantic ◽  
North American ◽  
Wave Train ◽  
Boreal Summer ◽  
Drought Indices ◽  
Dust Bowl ◽  
Summer Drought ◽  
The Pacific

Abstract. Proxy-based studies suggest that the southwestern USA is affected by two types of summer drought, often termed Dust Bowl-type droughts and 1950s-type droughts. The spatial drought patterns of the two types are distinct. It has been suggested that they are related to different circulation characteristics, but a lack of observation-based data has precluded further studies. In this paper, we analyze multi-annual summer droughts in North America back to 1600 in tree-ring-based drought reconstructions and in a global, monthly three-dimensional reconstruction of the atmosphere. Using cluster analysis of drought indices, we confirm the two main drought types and find a similar catalog of events as previous studies. These two main types of droughts are then analyzed with respect to 2 m temperatures (T2m), sea-level pressure (SLP), and 500 hPa geopotential height (GPH) in boreal summer. 1950s-type droughts are related to a stronger wave train over the Pacific–North American sector than Dust Bowl-type droughts, whereas the latter show the imprint of a poleward-shifted jet and establishment of a Great Plains ridge. The 500 hPa GPH patterns of the two types differ significantly not only over the contiguous United States and Canada but also over the extratropical North Atlantic and the Pacific. Dust Bowl-type droughts are associated with positive GPH anomalies, while 1950s-type droughts exhibit strong negative GPH anomalies. In comparison with 1950s-type droughts, the Dust Bowl-type droughts are characterized by higher sea-surface temperatures (SSTs) in the northern North Atlantic. Results suggest that atmospheric circulation and SST characteristics not only over the Pacific but also over the extratropical North Atlantic affect the spatial pattern of North American droughts.

A Unified Nonlinear Multiscale Interaction Model of Pacific–North American Teleconnection Patterns

2020 ◽  
Vol 77 (4) ◽  
pp. 1387-1414
Author(s):  
Dehai Luo ◽  
Yao Ge ◽  
Wenqi Zhang ◽  
Aiguo Dai
Keyword(s):  
North Atlantic ◽  
North American ◽  
Wave Train ◽  
Interaction Model ◽  
Energy Dispersion ◽  
Pacific North American ◽  
The North ◽  
The North Atlantic ◽  
The Difference ◽  
Multiscale Interaction

Abstract In this paper, reanalysis data are first analyzed to reveal that the individual negative (positive)-phase Pacific–North American pattern (PNA) or PNA− (PNA+) has a lifetime of 10–20 days, is characterized by strong (weak) westerly jet stream meanders, and exhibits clear wave train structures, whereas the PNA− with rapid retrogression tends to have longer lifetime and larger amplitude than the PNA+ with slow retrogression. In contrast, the wave train structure of the North Atlantic Oscillation (NAO) is less distinct, and the positive (negative)-phase NAO shows eastward (westward) movement around a higher latitude than the PNA. Moreover, it is found that the PNA wave train occurs under a larger background meridional potential vorticity gradient (PVy) over the North Pacific than that over the North Atlantic for the NAO. A unified nonlinear multiscale interaction (UNMI) model is then developed to explain why the PNA as a nonlinear wave packet has such characteristics and its large difference from the NAO. The model results reveal that the larger background PVy for the PNA (due to its location at lower latitudes) leads to its larger energy dispersion and weaker nonlinearity than the NAO, thus explaining why the PNA (NAO) is largely a linear (nonlinear) process with a strong (weak) wave train structure, though it is regarded as a nonlinear initial-value problem. The smaller PVy for the PNA− than for the PNA+ leads to lower energy dispersion and stronger nonlinearity for PNA−, which allows it to maintain larger amplitude and have a longer lifetime than the PNA+. Thus, the difference in the background PVy is responsible for the asymmetry between the two phases of PNA and the difference between the PNA and NAO.

Why Does a Colder (Warmer) Winter Tend to Be Followed by a Warmer (Cooler) Summer over Northeast Eurasia?

2020 ◽  
Vol 33 (17) ◽  
pp. 7255-7274
Author(s):  
Shangfeng Chen ◽  
Renguang Wu ◽  
Wen Chen ◽  
Kai Li
Keyword(s):  
Atmospheric Circulation ◽  
North Atlantic ◽  
Wave Train ◽  
The Arctic ◽  
The North ◽  
Atmospheric Wave ◽  
Anomaly Pattern ◽  
Sst Anomaly ◽  
The North Atlantic ◽  
Sst Anomalies

AbstractThis study reveals a pronounced out-of-phase relationship between surface air temperature (SAT) anomalies over northeast Eurasia in boreal winter and the following summer during 1980–2017. A colder (warmer) winter over northeast Eurasia tends to be followed by a warmer (cooler) summer of next year. The processes for the out-of-phase relation of winter and summer SAT involve the Arctic Oscillation (AO), the air–sea interaction in the North Atlantic Ocean, and a Eurasian anomalous atmospheric circulation pattern induced by the North Atlantic sea surface temperature (SST) anomalies. Winter negative AO/North Atlantic Oscillation (NAO)-like atmospheric circulation anomalies lead to continental cooling over Eurasia via anomalous advection and a tripolar SST anomaly pattern in the North Atlantic. The North Atlantic SST anomaly pattern switches to a dipolar pattern in the following summer via air–sea interaction processes and associated surface heat flux changes. The summer North Atlantic dipolar SST anomaly pattern induces a downstream atmospheric wave train, including large-scale positive geopotential height anomalies over northeast Eurasia, which contributes to positive SAT anomalies there via enhancement of downward surface shortwave radiation and anomalous advection. Barotropic model experiments verify the role of the summer North Atlantic SST anomalies in triggering the atmospheric wave train over Eurasia. Through the above processes, a colder winter is followed by a warmer summer over northeast Eurasia. The above processes apply to the years when warmer winters are followed by cooler summers except for opposite signs of SAT, atmospheric circulation, and SST anomalies.

scholarly journals Midlatitude atmospheric circulation responses under 1.5 °C and 2.0 °C warming and implications for regional impacts

2017 ◽  
Author(s):  
Camille Li ◽  
Clio Michel ◽  
Lise Seland Graff ◽  
Ingo Bethke ◽  
Giuseppe Zappa ◽  
...  
Keyword(s):  
Climate Change ◽  
Atmospheric Circulation ◽  
North Atlantic ◽  
North American ◽  
Storm Track ◽  
Internal Variability ◽  
The North ◽  
Regional Impacts ◽  
The North Atlantic ◽  
The Mediterranean

Abstract. This study investigates the global response of the midlatitude atmospheric circulation to 1.5 °C and 2.0 °C of warming using the HAPPI Half a degree Additional warming, Projections, Prognosis and Impacts ensemble, with a focus on the winter season. Characterizing and understanding this response is critical for accurately assessing the near-term regional impacts of climate change and the benefits of limiting warming to the 1.5 °C above pre-industrial levels, as advocated by the Paris Agreement of the United Nations Framework Convention on Climate Change (UNFCCC). The HAPPI experimental design allows an assessment of uncertainty in the circulation response due to model dependence and internal variability. Internal variability is found to dominate the multi-model mean response of the jet streams, storm tracks and stationary waves across most of the midlatitudes; larger signals in these features are mostly consistent with those seen in more strongly forced warming scenarios. Signals that emerge in the 1.5 °C experiment are a weakening of storm activity over North America, an inland shift of the North American stationary ridge, an equatorward shift of the North Pacific jet exit, and an equatorward intensification of the South Pacific jet. Signals that emerge under an additional 0.5 °C of warming include a poleward shift of the North Atlantic jet exit, an eastward extension of the North Atlantic storm track, and an intensification on the flanks of the Southern Hemisphere storm track. Case studies explore the implications of these circulation responses for precipitation impacts in the Mediterranean, western Europe and the North American west coast, paying particular attention to possible outcomes at the tails of the response distributions. For example, the projected weakening of the Mediterranean storm track emerges in the 2.0 °C world, though the ensemble spread still allows for both wetting and drying responses.

scholarly journals A regime view of future atmospheric circulation changes in Northern mid-latitudes

2020 ◽  
Author(s):  
Federico Fabiano ◽  
Virna Meccia ◽  
Paolo Davini ◽  
Paolo Ghinassi ◽  
Susanna Corti
Keyword(s):  
Atmospheric Circulation ◽  
North Atlantic ◽  
The Arctic ◽  
The North ◽  
The Pacific ◽  
General Improvement ◽  
Polar Stratosphere ◽  
The North Atlantic ◽  
Different Levels ◽  
Circulation Changes

Abstract. Future wintertime atmospheric circulation changes in the Euro-Atlantic (EAT) and Pacific-North American (PNA) sectors are studied from a Weather Regimes perspective. The CMIP5 and CMIP6 historical simulations performance in reproducing the observed regimes is first evaluated, showing a general improvement of CMIP6 models, more evident for EAT. The circulation changes projected by CMIP5 and CMIP6 scenario simulations are analyzed in terms of the change in the frequency and persistence of the regimes. In the EAT sector, significant positive trends are found for the frequency and persistence of NAO+ for SSP245, SSP370 and SSP585 scenarios, with a concomitant decrease in the frequency of the Scandinavian Blocking and Atlantic Ridge regimes. For PNA, the Pacific Through regime shows a significant increase, while the Bering Ridge is predicted to decrease in all scenarios analyzed. The spread among the model responses is linked to different levels of warming in the Polar Stratosphere, the North Atlantic and the Arctic.

scholarly journals Enhanced Linkage between Eurasian Winter and Spring Dominant Modes of Atmospheric Interannual Variability since the Early 1990s

2018 ◽  
Vol 31 (9) ◽  
pp. 3575-3595 ◽  
Author(s):  
Shangfeng Chen ◽  
Renguang Wu ◽  
Wen Chen ◽  
Shuailei Yao
Keyword(s):  
Interannual Variability ◽  
Atmospheric Circulation ◽  
North Atlantic ◽  
Wave Train ◽  
Seasonal Prediction ◽  
Dominant Mode ◽  
The North ◽  
Anomaly Pattern ◽  
Sst Anomaly ◽  
The North Atlantic

The present study reveals a marked enhancement in the relationship between Eurasian winter and spring atmospheric interannual variability since the early 1990s. Specifically, the dominant mode of winter Eurasian 500-hPa geopotential height anomalies, with same-sign anomalies over southern Europe and East Asia and opposite-sign anomalies over north-central Eurasia, is largely maintained to the following spring after the early 1990s, but not before the early 1990s. The maintenance of the dominant atmospheric circulation anomaly pattern after the early 1990s is associated with a triple sea surface temperature (SST) anomaly pattern in the North Atlantic that is sustained from winter to the subsequent spring. This triple SST anomaly pattern triggers an atmospheric wave train over the North Atlantic through Eurasia during winter through spring. Atmospheric model experiments verify the role of the triple SST anomaly in maintaining the Eurasian atmospheric circulation anomalies. By contrast, before the early 1990s, marked SST anomalies related to the winter dominant mode only occur in the tropical North Atlantic during winter and they disappear during the following spring. The triple SST anomaly pattern after the early 1990s forms in response to a meridional atmospheric dipole over the North Atlantic induced by a La Niña–like cooling over tropical Pacific, and its maintenance into the following spring may be via a positive air–sea interaction process over the North Atlantic. Results of this analysis suggest a potential source for the seasonal prediction of the Eurasian spring climate.

scholarly journals Midlatitude atmospheric circulation responses under 1.5 and 2.0 °C warming and implications for regional impacts

2018 ◽  
Vol 9 (2) ◽  
pp. 359-382 ◽  
Author(s):  
Camille Li ◽  
Clio Michel ◽  
Lise Seland Graff ◽  
Ingo Bethke ◽  
Giuseppe Zappa ◽  
...  
Keyword(s):  
Climate Change ◽  
Atmospheric Circulation ◽  
North Atlantic ◽  
North American ◽  
Storm Track ◽  
Internal Variability ◽  
The North ◽  
Regional Impacts ◽  
The North Atlantic ◽  
The Mediterranean

Abstract. This study investigates the global response of the midlatitude atmospheric circulation to 1.5 and 2.0 °C of warming using the HAPPI (Half a degree Additional warming, Prognosis and Projected Impacts) ensemble, with a focus on the winter season. Characterising and understanding this response is critical for accurately assessing the near-term regional impacts of climate change and the benefits of limiting warming to 1.5 °C above pre-industrial levels, as advocated by the Paris Agreement of the United Nations Framework Convention on Climate Change (UNFCCC). The HAPPI experimental design allows an assessment of uncertainty in the circulation response due to model dependence and internal variability. Internal variability is found to dominate the multi-model mean response of the jet streams, storm tracks, and stationary waves across most of the midlatitudes; larger signals in these features are mostly consistent with those seen in more strongly forced warming scenarios. Signals that emerge in the 1.5 °C experiment are a weakening of storm activity over North America, an inland shift of the North American stationary ridge, an equatorward shift of the North Pacific jet exit, and an equatorward intensification of the South Pacific jet. Signals that emerge under an additional 0.5 °C of warming include a poleward shift of the North Atlantic jet exit, an eastward extension of the North Atlantic storm track, and an intensification on the flanks of the Southern Hemisphere storm track. Case studies explore the implications of these circulation responses for precipitation impacts in the Mediterranean, in western Europe, and on the North American west coast, paying particular attention to possible outcomes at the tails of the response distributions. For example, the projected weakening of the Mediterranean storm track emerges in the 2 °C warmer world, with exceptionally dry decades becoming 5 times more likely.

Changes in Atmospheric Circulation and Ocean Ice Cover over the North Atlantic During the Last 41,000 Years

Science ◽  
1994 ◽  
Vol 263 (5154) ◽  
pp. 1747-1751 ◽  
Author(s):  
P. A. Mayewski ◽  
L. D. Meeker ◽  
S. Whitlow ◽  
M. S. Twickler ◽  
M. C. Morrison ◽  
...  
Keyword(s):  
Atmospheric Circulation ◽  
North Atlantic ◽  
Ice Cover ◽  
The North ◽  
The North Atlantic
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