scholarly journals Changes in Northern Hemisphere Winter Storm Tracks under the Background of Arctic Amplification

2017 ◽  
Vol 30 (10) ◽  
pp. 3705-3724 ◽  
Author(s):  
Jiabao Wang ◽  
Hye-Mi Kim ◽  
Edmund K. M. Chang
Keyword(s):  
North America ◽  
North Atlantic ◽  
North Pacific ◽  
Storm Track ◽  
Storm Tracks ◽  
Arctic Amplification ◽  
Northeastern North America ◽  
The North ◽  
The North Atlantic ◽  
The North Pacific

Abstract An interdecadal weakening in the North Atlantic storm track (NAST) and a poleward shift of the North Pacific storm track (NPST) are found during October–March for the period 1979–2015. A significant warming of surface air temperature (Ts) over northeastern North America and a La Niña–like change in the North Pacific under the background of Arctic amplification are found to be the contributors to the observed changes in the NAST and the NPST, respectively, via modulation of local baroclinicity. The interdecadal change in baroclinic energy conversion is consistent with changes in storm tracks with an energy loss from eddies to mean flow over the North Atlantic and an energy gain over the North Pacific. The analysis of simulations from the Community Earth System Model Large Ensemble project, although with some biases in storm-track and Ts simulations, supports the observed relationship between the NAST and Ts over northeastern North America, as well as the link between the NPST and El Niño–Southern Oscillation. The near-future projections of Ts and storm tracks are characterized by a warmer planet under the influence of increasing greenhouse gases and a significant weakening of both the NAST and the NPST. The potential role of the NAST in redistributing changes in Ts over the surrounding regions is also examined. The anomalous equatorward moisture flux associated with the weakening trend of the NAST would enhance the warming over its upstream region and hinder the warming over its downstream region via modulation of the downward infrared radiation.

Contributions of Downstream Eddy Development to the Teleconnection between ENSO and the Atmospheric Circulation over the North Atlantic

2012 ◽  
Vol 25 (14) ◽  
pp. 4993-5010 ◽  
Author(s):  
Ying Li ◽  
Ngar-Cheung Lau
Keyword(s):  
North America ◽  
Atmospheric Circulation ◽  
North Atlantic ◽  
El Niño ◽  
North Pacific ◽  
El Nino ◽  
Storm Track ◽  
The North ◽  
The North Atlantic ◽  
The North Pacific

Abstract The spatiotemporal evolution of various meteorological phenomena associated with El Niño–Southern Oscillation (ENSO) in the North Pacific–North American–North Atlantic sector is examined using both NCEP–NCAR reanalyses and output from a 2000-yr integration of a global coupled climate model. Particular attention is devoted to the implications of downstream eddy developments on the relationship between ENSO and the atmospheric circulation over the North Atlantic. The El Niño–related persistent events are characterized by a strengthened Pacific subtropical jet stream and an equatorward-shifted storm track over the North Pacific. The wave packets that populate the storm tracks travel eastward through downstream development. The barotropic forcing of the embedded synoptic-scale eddies is conducive to the formation of a flow that resembles the negative phase of the North Atlantic Oscillation (NAO). The more frequent and higher persistence of those episodes during El Niño winters contribute to the prevalence of negative NAO conditions. The above processes are further delineated by conducting a case study for the 2009/10 winter season, in which both El Niño and negative NAO conditions prevailed. It is illustrated that the frequent and intense surface cyclone development over North America and the western Atlantic throughout that winter are associated with upper-level troughs propagating across North America, which in turn are linked to downstream evolution of wave packets originating from the Pacific storm track.

North Hemispheric winter air temperature variability and its linkage to North Pacific and North Atlantic SST modes?

2020 ◽  
Author(s):  
Binhe Luo ◽  
Dehai Luo ◽  
Aiguo Dai ◽  
Lixin Wu
Keyword(s):  
North America ◽  
Air Temperature ◽  
North Atlantic ◽  
North Pacific ◽  
Wave Train ◽  
Surface Air Temperature ◽  
Eastern North America ◽  
The North ◽  
The North Atlantic ◽  
The North Pacific

<p>Winter surface air temperature (SAT) over North America exhibits pronounced variability on sub-seasonal-to-interdecadal timescales, but its causes are not fully understood. Here observational and reanalysis data from 1950-2017 are analyzed to investigate these causes. Detrended daily SAT data reveals a known warm-west/cold-east (WWCE) dipole over midlatitude North America and a cold-north/warm-south (CNWS) dipole over eastern North America. It is found that while the North Pacific blocking (PB) is important for the WWCE and CNWS dipoles, they also depend on the phase of the North Atlantic Oscillation (NAO). When a negative-phase NAO (NAO-) concurs with PB, the WWCE dipole is enhanced (compared with the PB alone case) and it also leads to a warm north/cold south dipole anomaly in eastern North America; but when PB occurs with a positive-phase NAO (NAO<sup>+</sup>), the WWCE dipole weakens and the CNWS dipole is enhanced. In particular, the WWCE dipole is favored by a combination of eastward-displaced PB and NAO<sup>-</sup> that form a negative Arctic Oscillation. Furthermore, a WWCE dipole can form over midlatitude North America when PB occurs together with southward-displaced NAO<sup>+</sup>.The PB events concurring with NAO<sup>-</sup> (NAO<sup>+</sup>) and SAT WWCE (CNWS) dipole are favored by the El Nio-like (La Nia-like) SST mode, though related to the North Atlantic warm-cold-warm (cold-warm-cold) SST tripole pattern. It is also found that the North Pacific mode tends to enhance the WWCE SAT dipole through increasing PB-NAO<sup>-</sup> events and producing the WWCE SAT dipole component related to the PB-NAO<sup>+</sup> events because the PB and NAO<sup>+</sup> form a more zonal wave train in this case.</p>

scholarly journals Dynamics of the Northern Annular Mode at Weekly Time Scales

2015 ◽  
Vol 72 (12) ◽  
pp. 4569-4590 ◽  
Author(s):  
Gwendal Rivière ◽  
Marie Drouard
Keyword(s):  
Wave Propagation ◽  
North America ◽  
North Atlantic ◽  
North Pacific ◽  
Low Frequency ◽  
Northern Annular Mode ◽  
The North ◽  
Momentum Fluxes ◽  
The North Atlantic ◽  
The North Pacific

Abstract Rapid onsets of positive and negative tropospheric northern annular mode (NAM) events during boreal winters are studied using ERA-Interim datasets. The NAM anomalies first appear in the North Pacific from low-frequency Rossby wave propagation initiated by anomalous convection in the western tropical Pacific around 2 weeks before the peak of the events. For negative NAM, the enhanced convection leads to a zonal acceleration of the Pacific jet, while for positive NAM, the reduced convection leads to a poleward-deviated jet in its exit region. The North Atlantic anomalies, which correspond to North Atlantic Oscillation (NAO) anomalies, are formed in close connection with the North Pacific anomalies via downstream propagation of low-frequency planetary-scale and high-frequency synoptic waves, the latter playing a major role during the last onset week. Prior to positive NAM, the generation of synoptic waves in the North Pacific and their downstream propagation is strong. The poleward-deviated Pacific jet favors a southeastward propagation of the waves across North America and anticyclonic breaking in the North Atlantic. The associated strong poleward eddy momentum fluxes push the Atlantic jet poleward and form the positive NAO phase. Conversely, prior to negative NAM, synoptic wave propagation across North America is significantly reduced and more zonal because of the more zonally oriented Pacific jet. This, together with a strong eddy generation in the North Atlantic, leads to equatorward eddy momentum fluxes, cyclonic wave breaking, and the formation of the negative NAO phase. Even though the stratosphere may play a role in some individual cases, it is not the main driver of the composited tropospheric NAM events.

Nature of the Differences in the Intraseasonal Variability of the Pacific and Atlantic Storm Tracks: A Diagnostic Study

2006 ◽  
Vol 63 (10) ◽  
pp. 2602-2615 ◽  
Author(s):  
Yi Deng ◽  
Mankin Mak
Keyword(s):  
North Atlantic ◽  
North Pacific ◽  
Intraseasonal Variability ◽  
Storm Track ◽  
Late Winter ◽  
The North ◽  
The Pacific ◽  
The North Atlantic ◽  
Early Late ◽  
The North Pacific

Abstract On the basis of an intraseasonal variability index of storm track evaluated for 40 winters (1963–64 through 2003–04) of NCEP–NCAR reanalysis data, it is found that well-defined midwinter minimum [MWMIN; (midwinter maximum MWMAX)] occurs in 21 (8) winters over the North Pacific. In contrast, MWMIN (MWMAX) occurs in 4 (25) of the 40 winters over the North Atlantic. The power spectrum of such an index for the Pacific has a broad peak between 5 and 10 yr, whereas the spectrum of the index for the Atlantic has comparable power in two spectral bands: 2–2.8 and 3.5–8 yr. Over the North Pacific, the increase in the zonal asymmetry of the background baroclinicity as well as in the corresponding horizontal deformation of the time-mean jet from early/late winter to midwinter is distinctly larger in an MWMIN winter. Associated with these changes, there is a distinctly stronger barotropic damping rate in the January of an MWMIN winter. The increase in the net conversion rate of eddy kinetic energy from early/late winter to midwinter is much larger in an MWMAX winter than that in an MWMIN winter. Even though there is a modest increase in the barotropic damping from early/late winter to midwinter over the North Atlantic, it is overcompensated by a larger increase in the baroclinic conversion rate. That would result in MWMAX. These results are empirical evidences in support of a hypothesis that a significant enhancement of the barotropic damping relative to the baroclinic growth from early/late winter to midwinter is a major contributing factor to MWMIN of the Pacific storm track.

scholarly journals Combined Influences on North American Winter Air Temperature Variability from North Pacific Blocking and the North Atlantic Oscillation: Subseasonal and Interannual Time Scales

2020 ◽  
Vol 33 (16) ◽  
pp. 7101-7123 ◽  
Author(s):  
Binhe Luo ◽  
Dehai Luo ◽  
Aiguo Dai ◽  
I. Simmonds ◽  
Lixin Wu
Keyword(s):  
North America ◽  
Air Temperature ◽  
North Atlantic ◽  
North American ◽  
North Pacific ◽  
Eastern North America ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation ◽  
The North Pacific

AbstractWinter surface air temperature (SAT) over North America exhibits pronounced variability on subseasonal, interannual, decadal, and interdecadal time scales. Here, reanalysis data from 1950–2017 are analyzed to investigate the atmospheric and surface ocean conditions associated with its subseasonal to interannual variability. Detrended daily SAT data reveal a known warm west/cold east (WWCE) dipole over midlatitude North America and a cold north/warm south (CNWS) dipole over eastern North America. It is found that while the North Pacific blocking (PB) is important for the WWCE and CNWS dipoles, they also depend on the phase of the North Atlantic Oscillation (NAO). When a negative-phase NAO (NAO−) coincides with PB, the WWCE dipole is enhanced (compared with the PB alone case) and it also leads to a warm north/cold south dipole anomaly in eastern North America; but when PB occurs with a positive-phase NAO (NAO+), the WWCE dipole weakens and the CNWS dipole is enhanced. The PB events concurrent with the NAO− (NAO+) and SAT WWCE (CNWS) dipole are favored by the Pacific El Niño–like (La Niña–like) sea surface temperature mode and the positive (negative) North Pacific mode. The PB-NAO+ has a larger component projecting onto the SAT WWCE dipole during the La Niña winter than during the El Niño winter because a more zonal wave train is formed. Strong North American SAT WWCE dipoles and enhanced projections of PB-NAO+ events onto the SAT WWCE dipole component are also readily seen for the positive North Pacific mode. The North Pacific mode seems to play a bigger role in the North American SAT variability than ENSO.

scholarly journals Further Investigation of the Impact of Idealized Continents and SST Distributions on the Northern Hemisphere Storm Tracks

2012 ◽  
Vol 69 (3) ◽  
pp. 840-856 ◽  
Author(s):  
Jérôme Saulière ◽  
David James Brayshaw ◽  
Brian Hoskins ◽  
Michael Blackburn
Keyword(s):  
Boundary Conditions ◽  
North Atlantic ◽  
North Pacific ◽  
Rossby Waves ◽  
Storm Track ◽  
Storm Tracks ◽  
The North ◽  
The Pacific ◽  
The North Atlantic ◽  
The Impact

Abstract Building on previous studies of the basic ingredients of the North Atlantic storm track (examining land–sea contrast, orography, and SST), this article investigates the impact of Eurasian topography and Pacific SST anomalies on North Pacific and Atlantic storm tracks through a hierarchy of atmospheric GCM simulations using idealized boundary conditions in the Hadley Centre HadGAM1 atmospheric circulation model. The Himalaya–Tibet mountain complex is found to play a crucial role in shaping the North Pacific storm track. The northward deflection of the westerly flow around northern Tibet generates an extensive pool of very cold air in the northeastern tip of the Asian continent, which strengthens the meridional temperature gradient and favors baroclinic growth in the western Pacific. The Kuroshio SST front is also instrumental in strengthening the Pacific storm track through its impact on near-surface baroclinicity, while the warm waters around Indonesia tend to weaken it through the impact on baroclinicity of stationary Rossby waves propagating poleward from the convective heating regions. Three mechanisms by which the Atlantic storm track may be affected by changes in the boundary conditions upstream of the Rockies are discussed. In the model configuration used here, stationary Rossby waves emanating from Tibet appear to weaken the North Atlantic storm track substantially, whereas those generated over the cold waters off Peru appear to strengthen it. Changes in eddy-driven surface winds over the Pacific generally appear to modify the flow over the Rocky Mountains, leading to consistent modifications in the Atlantic storm track. The evidence for each of these mechanisms is, however, ultimately equivocal in these simulations.

Comparing Cyclone Life Cycle Characteristics and Their Interannual Variability in Different Reanalyses

2013 ◽  
Vol 26 (17) ◽  
pp. 6419-6438 ◽  
Author(s):  
Natalia Tilinina ◽  
Sergey K. Gulev ◽  
Irina Rudeva ◽  
Peter Koltermann
Keyword(s):  
Interannual Variability ◽  
North Atlantic ◽  
North Pacific ◽  
Storm Track ◽  
Department Of Energy ◽  
The North ◽  
Decadal Scale ◽  
The North Atlantic ◽  
Highly Correlated ◽  
The North Pacific

Abstract Characteristics of Northern Hemisphere extratropical cyclone activity were compared for five concurrent reanalyses: the NCEP–U.S. Department of Energy (DOE) reanalysis (herein NCEP–DOE), the Japanese 25-year Reanalysis Project (JRA-25), the ECMWF Interim Re-Analysis (ERA-Interim), the National Aeronautics and Space Administration's Modern-Era Retrospective Analysis for Research and Applications (NASA-MERRA), and the NCEP Climate Forecast System Reanalysis (NCEP-CFSR), for the period 1979–2010 using a single cyclone tracking algorithm. The total number of cyclones, ranging from 1400 to more than 1800 yr−1, was found to depend strongly on the spatial resolution of the respective reanalysis. The largest cyclone population was identified using NASA-MERRA data, which also showed the highest occurrence of very deep cyclones. Of the reanalyses, two (NCEP–DOE and ERA-Interim) are associated with statistically significant positive trends in the total number of cyclones from 1% to 2% decade−1. These trends result from moderate and shallow cyclones contributing to approximately 90% of the total cyclone count on average. The number of very deep cyclones (<960 hPa) in the North Atlantic increased in most reanalyses until 1990 and then declined during the last decade. In the North Pacific, the number of these events reached a peak in 2000 and then decreased during the last decade. The winter pattern is characterized by robust trends in cyclone numbers, with an enhancement of the North Atlantic storm track and a weakening of the North Pacific subtropical storm track. In the summer, there is a robust intensification of the Mediterranean storm track and a decrease in counts over the North Atlantic. Interannual variability and decadal-scale variations of the cyclone counts are highly correlated among the reanalyses, with the greatest agreement in moderate and deep cyclones.

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