scholarly journals Mechanisms for a remote response to Asian anthropogenic aerosol in boreal winter

2019 ◽  
Vol 19 (14) ◽  
pp. 9081-9095 ◽  
Author(s):  
Laura J. Wilcox ◽  
Nick Dunstone ◽  
Anna Lewinschal ◽  
Massimo Bollasina ◽  
Annica M. L. Ekman ◽  
...  
Keyword(s):  
North Pacific ◽  
Western Europe ◽  
Large Temperature ◽  
Boreal Winter ◽  
Far Field ◽  
Anthropogenic Aerosols ◽  
Local Circulation ◽  
The North ◽  
The North Pacific ◽  
Circulation Changes

Abstract. Asian emissions of anthropogenic aerosols and their precursors have increased rapidly since 1980, with half of the increase since the pre-industrial era occurring in this period. Transient experiments with the HadGEM3-GC2 coupled model were designed to isolate the impact of Asian anthropogenic aerosols on global climate in boreal winter. It is found that this increase has resulted in local circulation changes, which in turn have driven decreases in precipitation over China, alongside an intensification of the offshore monsoon flow. No large temperature changes are seen over China. Over India, the opposite response is found, with decreasing temperatures and increasing precipitation. The dominant feature of the local circulation changes is an increase in low-level convergence, ascent, and precipitation over the Maritime Continent, which forms part of a tropical Pacific-wide La Niña-like response. HadGEM3-GC2 also simulates pronounced far-field responses. A decreased meridional temperature gradient in the North Pacific leads to a positive Pacific–North American circulation pattern, with associated temperature anomalies over the North Pacific and North America. Anomalous northeasterly flow over northeast Europe drives advection of cold air into central and western Europe, causing cooling in this region. An anomalous anticyclonic circulation over the North Atlantic causes drying over western Europe. Using a steady-state primitive equation model, LUMA, we demonstrate that these far-field midlatitude responses arise primarily as a result of Rossby waves generated over China, rather than in the equatorial Pacific.

scholarly journals Mechanisms for a remote response to Asian aerosol emissions in boreal winter

2018 ◽  
Author(s):  
Laura Wilcox ◽  
Nick Dunstone ◽  
Anna Lewinschal ◽  
Massimo Bollasina ◽  
Annica Ekman ◽  
...  
Keyword(s):  
North Pacific ◽  
Boreal Winter ◽  
Far Field ◽  
Anthropogenic Aerosols ◽  
Local Circulation ◽  
The North ◽  
Dominant Feature ◽  
The Impact ◽  
The North Pacific ◽  
Circulation Changes

Abstract. Asian emissions of anthropogenic aerosols have increased rapidly since 1980, with half of the increase since the pre-industrial era occurring in this period. Transient experiments with the HadGEM3-GC2 coupled model were designed to isolate the impact of Asian aerosols on global climate. In boreal winter, it is found that this increase has resulted in local circulation changes, which in turn have driven increases in temperature and decreases in precipitation over China, alongside an intensification of the offshore monsoon flow. Over India, the opposite response is found, with decreasing temperatures and increasing precipitation. The dominant feature of the local circulation changes is an increase in low-level convergence, ascent, and precipitation over the Maritime continent, which forms part of a tropical-Pacific-wide La-Nina-like response. HadGEM3-GC2 also simulates pronounced far-field responses. A decreased meridional temperature gradient in the North Pacific leads to a positive-Pacific-North-American circulation pattern, with associated temperature anomalies over the North Pacific and North America. An anomalous anticyclonic circulation over the North Atlantic, and an anomalous cyclonic circulation over the Mediterranean drive advection of cold air into Europe, causing cooling in this region. Using a steady-state primitive equation model, LUMA, we demonstrate that these far-field midlatitude response arise primarily as a result of Rossby waves generated over China, rather than in the Equatorial Pacific.

scholarly journals Identification of the Eurasian–North Pacific Multidecadal Oscillation and Its Relationship to the AMO

2013 ◽  
Vol 26 (20) ◽  
pp. 8139-8153 ◽  
Author(s):  
Ming-Ying Lee ◽  
Huang-Hsiung Hsu
Keyword(s):  
North Pacific ◽  
Geopotential Height ◽  
Western Europe ◽  
Atlantic Multidecadal Oscillation ◽  
Warming Trend ◽  
Multidecadal Variability ◽  
Upper Troposphere ◽  
The North ◽  
The Tropics ◽  
The North Pacific

Abstract A multidecadal geopotential height pattern in the upper troposphere of the extratropical Northern Hemisphere (NH) is identified in this study. This pattern is characterized by the nearly zonal symmetry of geopotential height and temperature between 35° and 65°N and the equivalent barotropic vertical structure with the largest amplitude in the upper troposphere. This pattern is named the Eurasian–Pacific multidecadal oscillation (EAPMO) to describe its multidecadal time scale and the largest amplitudes over Eurasia and the North Pacific. Although nearly extending over the entire extratropics, the EAPMO exhibits larger amplitudes over western Europe, East Asia, and the North Pacific with a zonal scale equivalent to zonal wavenumbers 4 and 5. The zonally asymmetric perturbation tends to amplify over the major mountain ranges in the region, suggesting a significant topographic influence. The EAPMO has fluctuated concurrently with the Atlantic multidecadal oscillation (AMO) at least since the beginning of the twentieth century. The numerical simulation results suggest that the EAPMO could be induced by the AMO-like sea surface temperature anomaly and strengthened regionally by topography, especially over the Asian highland region, although the amplitude was undersimulated. This study found that the multidecadal variability of the upper-tropospheric geopotential height in the extratropical NH is much more complicated than in the tropics and the Southern Hemisphere (SH). It takes both first (warming trend) and second (multidecadal) EOFs to explain the multidecadal variability in the extratropical NH, while only the first EOF, which exhibited a warming trend, is sufficient for the tropics and SH.

scholarly journals Winter Extreme Flux Events in the Kuroshio and Gulf Stream Extension Regions and Relationship with Modes of North Pacific and Atlantic Variability

2015 ◽  
Vol 28 (12) ◽  
pp. 4950-4970 ◽  
Author(s):  
Xiaohui Ma ◽  
Ping Chang ◽  
R. Saravanan ◽  
Dexing Wu ◽  
Xiaopei Lin ◽  
...  
Keyword(s):  
North Pacific ◽  
Gulf Stream ◽  
Kuroshio Extension ◽  
Storm Track ◽  
Propagation Path ◽  
Northwestern Pacific ◽  
Boreal Winter ◽  
The North ◽  
The Kuroshio ◽  
The North Pacific

Abstract Boreal winter (November–March) extreme flux events in the Kuroshio Extension region (KER) of the northwestern Pacific and the Gulf Stream region (GSR) of the northwestern Atlantic are analyzed and compared, based on NCEP Climate Forecast System Reanalysis (CFSR), NCEP–NCAR reanalysis, and NOAA Twentieth Century Reanalysis data, as well as the observationally derived OAFlux dataset. These extreme flux events, most of which last less than 3 days, are characterized by cold air outbreaks (CAOs) with an anomalous northerly wind that brings cold and dry air from the Eurasian and North American continents to the KER and GSR, respectively. A close relationship between the extreme flux events over KER (GSR) and the Aleutian low pattern (ALP) [east Atlantic pattern (EAP)] is found with more frequent occurrence of the extreme flux events during a positive ALP (EAP) phase and vice versa. A further lag-composite analysis suggests that the ALP (EAP) is associated with accumulated effects of the synoptic winter storms accompanied by the extreme flux events and shows that the event-day storms tend to have a preferred southeastward propagation path over the North Pacific (Atlantic), potentially contributing to the southward shift of the storm track over the eastern North Pacific (Atlantic) basin during the ALP (EAP) positive phase. Finally, lag-regression analyses indicate a potential positive influence of sea surface temperature (SST) anomalies along the KER (GSR) on the development of the extreme flux events in the North Pacific (Atlantic).

Intraseasonal Modulation of the North Pacific Storm Track by Tropical Convection in Boreal Winter

2011 ◽  
Vol 24 (4) ◽  
pp. 1122-1137 ◽  
Author(s):  
Yi Deng ◽  
Tianyu Jiang
Keyword(s):  
North Pacific ◽  
Storm Track ◽  
Tropical Convection ◽  
Boreal Winter ◽  
Mean Flow ◽  
Central Pacific ◽  
Synoptic Eddy ◽  
The North ◽  
The North Pacific ◽  
North Pacific Storm Track

Abstract The modulation of the North Pacific storm track by tropical convection on intraseasonal time scales (30–90 days) in boreal winter (December–March) is investigated using the NCEP–NCAR reanalysis and NOAA satellite outgoing longwave radiation (OLR) data. Multivariate empirical orthogonal function (MEOF) analysis and case compositing based upon the principal components (PCs) of the EOFs reveal substantial changes in the structure and intensity of the Pacific storm track quantified by vertically (925–200 mb) averaged synoptic eddy kinetic energy (SEKE) during the course of a typical Madden–Julian oscillation (MJO) event. The storm-track response is characterized by an amplitude-varying dipole propagating northeastward as the center of the anomalous tropical convection moves eastward across the eastern Indian Ocean and the western-central Pacific. A diagnosis of the SEKE budget indicates that the storm-track anomaly is induced primarily by changes in the convergence of energy flux, baroclinic conversion, and energy generation due to the interaction between synoptic eddies and intraseasonal flow anomalies. This demonstrates the important roles played by eddy–mean flow interaction and eddy–eddy interaction in the development of the extratropical response to MJO variability. The feedback of synoptic eddy to intraseasonal flow anomalies is pronounced: when the center of the enhanced tropical convection is located over the Maritime Continent (western Pacific), the anomalous synoptic eddy forcing partly drives an upper-tropospheric anticyclonic (cyclonic) and, to its south, a cyclonic (anticyclonic) circulation anomaly over the North Pacific. Associated with the storm-track anomaly, a three-band (dry–wet–dry) anomaly in both precipitable water and surface precipitation propagates poleward over the eastern North Pacific and induces intraseasonal variations in the winter hydroclimate over western North America.

Influence of Atmospheric Blocking on Storm Track Activity Over the North Pacific During Boreal Winter

2021 ◽  
Vol 48 (17) ◽  
Author(s):  
Minghao Yang ◽  
Dehai Luo ◽  
Chongyin Li ◽  
Yao Yao ◽  
Xin Li ◽  
...  
Keyword(s):  
North Pacific ◽  
Storm Track ◽  
Boreal Winter ◽  
Atmospheric Blocking ◽  
The North ◽  
Storm Track Activity ◽  
The North Pacific

Changes in the characteristics of North Pacific Jet as a Conduit for U. S. surface air temperature in boreal winter across the late 1990s

2021 ◽  
pp. 1-43
Author(s):  
Se-Yong Song ◽  
Sang-Wook Yeh ◽  
Hyun-Su Jo
Keyword(s):  
Air Temperature ◽  
North Pacific ◽  
Surface Air Temperature ◽  
The United States ◽  
Cyclonic Circulation ◽  
Boreal Winter ◽  
The North ◽  
Anomalous Surface ◽  
Intensity Changes ◽  
The North Pacific

AbstractThe leading modes of the North Pacific Jet (NPJ) variability include intensity changes and meridional shifts in jet position on the low frequency timescales. These leading modes of NPJ variability are closely associated with weather and climate conditions spanning from Asia to the United States (US). In this study, we investigated changes in the NPJ’s role as a conduit for US surface air temperature (SAT) anomalies during the boreal winter across the late 1990s. We found that the leading mode of NPJ variability changed from the NPJ intensity changes to meridional shifts in NPJ position across the late 1990s. It leads to the change in the role of NPJ as a conduit for US SAT anomalies. Before the late 1990s, the variability of NPJ’s intensity significantly impacted western US SAT anomalies related to the anomalous surface cyclonic circulation over the North Pacific. After the late 1990s, however, the variability of NPJ’s meridional shift significantly influenced on the eastern US SAT anomalies in association with the anomalous surface cyclonic circulation over the northern North Pacific. Further analysis and model experiments revealed that the western to central North Pacific Ocean has been warming since the late 1990s and modulates atmospheric baroclinicity. This phenomenon mainly leads to a northward NPJ shift and implies that the eddy driven mechanism on the NPJ’s formation, which acts to enhance the meridional variability of NPJ position, becomes dominant. We conclude that this northward shift of NPJ could have contributed to enhancing the NPJ’s meridional shift variability, significantly influencing the eastern US SAT anomalies since the late 1990s.

scholarly journals Change In The Variability In The Western Pacific Pattern During Boreal Winter: Roles of Tropical Pacific Sea Surface Temperature Anomalies And North Pacific Storm Track Activity

2021 ◽  
Author(s):  
Hasi Aru ◽  
Shangfeng Chen ◽  
Wen Chen
Keyword(s):  
Surface Temperature ◽  
North Pacific ◽  
Storm Track ◽  
High Variability ◽  
Sea Surface ◽  
Boreal Winter ◽  
The North ◽  
The Western Pacific ◽  
The North Pacific ◽  
North Pacific Storm Track

Abstract Using multiple reanalysis datasets, this study reveals that the variability in the Western Pacific pattern (WP) in boreal winter has shown notable changes during recent decades. The variability in the winter WP exhibited a marked weakening trend before the early 2000s and increased slightly thereafter. Two epochs with the highest and lowest WP variabilities are selected for a comparative analysis. Winter WP-related meridional dipole atmospheric anomalies over the North Pacific were stronger and had a broader range during the high-variability epoch than during the low-variability epoch. Correspondingly, the winter WP had larger impacts on surface temperature variations over Eurasia and North America during the high-variability epoch than during the low-variability epoch. We find that the shift in the winter WP variability is closely related to changes in the connection between the winter WP and the El Niño-Southern Oscillation (ENSO) and to changes in the amplitude of the North Pacific storm track. Specifically, ENSO had a closer connection with the WP during the high-variability epoch, at which time the amplitude of the North Pacific storm track was also stronger. During the high-variability epoch, the extratropical atmospheric anomalies generated by the tropical ENSO shifted westward and projected more on the WP-related atmospheric anomalies, thus contributing to an increase in WP variability. In addition, the larger amplitude of the North Pacific storm track that occurred during the high-variability epoch led to the stronger feedback of synoptic-scale eddies to the mean flow and contributed to stronger WP variability. Further analysis indicates that the change in the connection of ENSO with the WP may be partly related to the zonal shift of the sea surface temperature anomaly in the tropical Pacific associated with ENSO.

scholarly journals A Model Investigation of Aerosol-Induced Changes in Boreal Winter Extratropical Circulation

2011 ◽  
Vol 24 (23) ◽  
pp. 6077-6091 ◽  
Author(s):  
Y. Ming ◽  
V. Ramaswamy ◽  
Gang Chen
Keyword(s):  
North Atlantic ◽  
General Circulation ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Boreal Winter ◽  
Anthropogenic Aerosols ◽  
The North ◽  
The North Atlantic ◽  
Extratropical Circulation ◽  
Circulation Changes

Abstract The authors examine the key characteristics of the boreal winter extratropical circulation changes in response to anthropogenic aerosols, simulated with a coupled atmosphere–slab ocean general circulation model. The zonal-mean response features a pronounced equatorward shift of the Northern Hemisphere subtropical jet owing to the midlatitude aerosol cooling. The circulation changes also show strong zonal asymmetry. In particular, the cooling is more concentrated over the North Pacific than over the North Atlantic despite similar regional forcings. With the help of an idealized model, the authors demonstrate that the zonally asymmetrical response is linked tightly to the stationary Rossby waves excited by the anomalous diabatic heating over the tropical east Pacific. The altered wave pattern leads to a southeastward shift of the Aleutian low (and associated changes in winds and precipitation), while leaving the North Atlantic circulation relatively unchanged. Despite the rich circulation changes, the variations in the extratropical meridional latent heat transport are controlled strongly by the dependence of atmospheric moisture content on temperature. This suggests that one can project reliably the changes in extratropical zonal-mean precipitation solely from the global-mean temperature change, even without a good knowledge of the detailed circulation changes caused by aerosols. On the other hand, such knowledge is indispensable for understanding zonally asymmetrical (regional) precipitation changes.

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