Was the North Pacific Wintertime Climate Less Stormy during the Mid-Holocene?

Abstract Model evidence is presented to make the case that the midlatitude North Pacific wintertime transient eddy activity may have been significantly weaker during the mid-Holocene (∼6000 yr BP). A simulation of the mid-Holocene climate in an atmospheric general circulation model coupled to a reduced gravity ocean model showed significant reduction to transient eddy activity, up to 30% in the main storm-track region. The reduced baroclinic eddy activity is associated with basinwide climate changes over the northern and tropical Pacific, including a deepening of the Aleutian low, colder SSTs in the western and central North Pacific, a strengthening and southward shift of the subtropical jet, and a strengthened South Pacific convergence zone. These associated climate changes are consistently simulated across a range of Paleoclimate Modeling Intercomparison Project Phase II (PMIP2) coupled models forced with mid-Holocene climate forcings, suggesting they are a robust response to mid-Holocene orbital forcing. The authors link the mid-Holocene climate changes to two related modern-day analogs: (i) interannual variations in wintertime North Pacific storminess and (ii) the phenomenon of midwinter suppression whereby North Pacific transient eddy activity in today’s climate is reduced in midwinter. In both instances, the associated North Pacific climate conditions resemble those seen in the mid-Holocene simulations. While it remains to be seen which analog is dynamically more appropriate, the latter link—midwinter suppression—offers the simple physical interpretation that the mid-Holocene reduction in storminess is a consequence of a “more winterlike” climate resulting from the mid-Holocene precessional forcing.

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PDO-Related Wintertime Atmospheric Anomalies over the Midlatitude North Pacific: Local versus Remote SST Forcing

Journal of Climate ◽

10.1175/jcli-d-19-0143.1 ◽

2020 ◽

Vol 33 (16) ◽

pp. 6989-7010 ◽

Cited By ~ 2

Author(s):

Lingfeng Tao ◽

Xiu-Qun Yang ◽

Jiabei Fang ◽

Xuguang Sun

Keyword(s):

North Pacific ◽

General Circulation ◽

Large Scale ◽

Circulation Model ◽

Transient Eddy ◽

Atmospheric Variability ◽

Ridge Structure ◽

Sst Gradient ◽

Meridional Sst Gradient ◽

Sst Anomalies

AbstractObserved wintertime atmospheric anomalies over the central North Pacific associated with the Pacific decadal oscillation (PDO) are characterized by a cold/trough (warm/ridge) structure, that is, an anomalous equivalent barotropic low (high) over a negative (positive) sea surface temperature (SST) anomaly. While the midlatitude atmosphere has its own strong internal variabilities, to what degree local SST anomalies can affect the midlatitude atmospheric variability remains unclear. To identify such an impact, three atmospheric general circulation model experiments each having a 63-yr-long simulation are conducted. The control run forced by observed global SST reproduces well the observed PDO-related cold/trough (warm/ridge) structure. However, the removal of the midlatitude North Pacific SST variabilities in the first sensitivity run reduces the atmospheric response by roughly one-third. In the second sensitivity run in which large-scale North Pacific SST variabilities are mostly kept, but their frontal-scale meridional gradients are sharply smoothed, simulated PDO-related cold/trough (warm/ridge) anomalies are also reduced by nearly one-third. Dynamical diagnoses exhibit that such a reduction is primarily due to the weakened transient eddy activities that are induced by weakened meridional SST gradient anomalies, in which the transient eddy vorticity forcing plays a crucial role. Therefore, it is suggested that midlatitude North Pacific SST anomalies make a considerable (approximately one-third) contribution to the observed PDO-related cold/trough (warm/ridge) anomalies in which the frontal-scale meridional SST gradient (oceanic front) is a key player, although most of those atmospheric anomalies are determined by the SST variabilities outside of the midlatitude North Pacific.

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Connections between wintertime jet stream variability, oceanic surface heating, and transient eddy activity in the North Pacific

Journal of Geophysical Research Atmospheres ◽

10.1029/2007jd009464 ◽

2008 ◽

Vol 113 (D21) ◽

Cited By ~ 29

Author(s):

Xuejuan Ren ◽

Yaocun Zhang ◽

Yang Xiang

Keyword(s):

North Pacific ◽

Surface Heating ◽

Jet Stream ◽

Transient Eddy ◽

Eddy Activity ◽

The North ◽

Oceanic Surface ◽

The North Pacific

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Warming of Western North Pacific Ocean and Energetics of Transient Eddy Activity

Monthly Weather Review ◽

10.1175/mwr-d-11-00256.1 ◽

2012 ◽

Vol 140 (9) ◽

pp. 2860-2873 ◽

Cited By ~ 7

Author(s):

Ki-Young Heo ◽

Kyung-Ja Ha ◽

Sun-Seon Lee

Keyword(s):

Pacific Ocean ◽

Potential Energy ◽

North Pacific ◽

Western North Pacific ◽

North Pacific Ocean ◽

Storm Track ◽

Transient Eddy ◽

Western North Pacific Ocean ◽

Eddy Activity ◽

The Pacific

Abstract This study examines the increase in the sea surface temperature (SST) in the western North Pacific Ocean (WNPO) during December–February for the period 1959–2008. The relationship of this SST increase with significant interdecadal changes in the baroclinicity and the energetics of transient eddy activity is also examined. These results show that the interannual variations of the WNPO SST and atmospheric conditions including baroclinicity and turbulent heat flux are responses to the upstream atmospheric forcings associated with the East Asian winter monsoon (EAWM). For the interdecadal variations, the intensified baroclinicity downstream of the Pacific storm-track activity is responsible for an increase in the baroclinic energy conversion (BCEC) from the mean available potential energy (MAPE) to the eddy available potential energy (EAPE) to the east of 180°. This in turn increases the BCEC from the EAPE to the eddy kinetic energy (EKE) over this region. The BCEC and generation of EAPE by diabatic heating are enhanced to the east of 180° as a result of the intensified baroclinicity. This could be responsible for the development of transient eddy activity downstream of the Pacific storm track over the North Pacific.

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Baroclinic Development in Observations and NASA GSFC General Circulation Models

Monthly Weather Review ◽

10.1175/mwr3110.1 ◽

2006 ◽

Vol 134 (4) ◽

pp. 1161-1173 ◽

Cited By ~ 3

Author(s):

Dennis P. Robinson ◽

Robert X. Black

Keyword(s):

North Atlantic ◽

North Pacific ◽

General Circulation ◽

Storm Track ◽

Model Simulations ◽

The North ◽

The Pacific ◽

The North Atlantic ◽

The North Pacific ◽

Midwinter Suppression

Abstract Comparative diagnostic analyses of developing synoptic-scale baroclinic disturbances in NCEP–NCAR reanalyses and the NASA–NCAR (NASCAR) and Aries [NASA’s Seasonal-to-Interannual Prediction Project (NSIPP)] general circulation model simulations are performed. In particular, lag composite analyses of wintertime cyclonic and anticyclonic events occurring in the North Pacific and North Atlantic storm tracks are constructed to pursue a synoptic and dynamic characterization of eddy development. The data are also seasonally stratified to study aspects of the North Pacific midwinter suppression phenomenon. Winter-averaged results indicate that the model-simulated events are generally too weak in amplitude, particularly in the upper troposphere. For the North Pacific storm track, model-simulated events are also anomalously distended in the meridional direction. The existing model biases in eddy structure and magnitude lead to anomalously weak baroclinic energy conversions for both cyclonic and anticyclonic events over the North Pacific. For the North Atlantic storm track the NASCAR model provides a very good representation of the structure of developing cyclonic events. However, growing North Atlantic cyclones in the NSIPP model are anomalously weak and horizontally too isotropic (meridionally retracted). These latter two characteristics are also observed in both models for developing anticyclonic flow anomalies over the North Atlantic. The relative weakness of NSIPP synoptic events over the North Atlantic region is largely responsible for the 50% deficiency in areal-averaged baroclinic energy conversions. Conversely, the NASCAR model climatology features anomalously strong temperature gradients over the western North Atlantic that provide local enhancements to the baroclinic energy conversion field. A seasonally stratified diagnostic analysis reveals that the simulated climatological storm tracks over the North Pacific undergo larger spatial migrations during the cool season compared to observations. It is further determined that the suppression of synoptic eddy activity observed in the Pacific storm track is associated with a relative midwinter weakness in the magnitude of the growing cyclonic anomalies. Specifically, during midwinter the cyclonic perturbations entering the Pacific storm track are deficient in magnitude compared to their early and late winter counterparts. It is also discovered that the midwinter suppression pattern over the North Pacific region has a clear organized extension upstream into Siberia, the region from which incipient upper-tropospheric short-wave features emanate. This behavior is found in both observations and the model simulations. The results herein support the idea that the North Pacific midwinter suppression phenomenon is linked to a midwinter weakness in the upstream formation of upper-level short waves, leading to anomalously weak “seeding” of baroclinic disturbances in the Pacific storm track.

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Effects of the Mean Flow on Martian Transient Eddy Activity: Studies with an Idealized General Circulation Model

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-18-0247.1 ◽

2019 ◽

Vol 76 (8) ◽

pp. 2375-2397

Author(s):

Todd A. Mooring ◽

Isaac M. Held ◽

R. John Wilson

Keyword(s):

General Circulation Model ◽

Spatial Patterns ◽

General Circulation ◽

Circulation Model ◽

Transient Eddy ◽

Mean Flow ◽

Eddy Activity ◽

Idealized Model ◽

Zonal Wavenumber ◽

The Mean

Abstract The extent to which the eddy statistics of the Martian atmosphere can be inferred from the mean state and highly simplified assumptions about diabatic and frictional processes is investigated using an idealized general circulation model (GCM) with Newtonian relaxation thermal forcing. An iterative technique, adapted from previous terrestrial studies, is used to generate radiative equilibrium temperatures such that the three-dimensional time-mean temperature fields of the idealized model match means computed from the Mars Analysis Correction Data Assimilation (MACDA). Focusing on a period of strong Northern Hemisphere eddy activity prior to winter solstice, it is found that the idealized model reproduces some key features of the spatial patterns of the MACDA eddy temperature variance and kinetic energy fields. The idealized model can also simulate aspects of MACDA’s seasonal cycle of spatial patterns of low-level eddy meridional wind and temperature variances. The most notable weakness of the model is its eddy amplitudes—both their absolute values and seasonal variations are quite unrealistic, for reasons unclear. The idealized model was also run with a mean flow based on output from the Geophysical Fluid Dynamics Laboratory (GFDL) full-physics Mars GCM. The idealized model captures the difference in mean flows between MACDA and the GFDL Mars GCM and reproduces a bias in the more complex model’s eddy zonal wavenumber distribution. This implies that the mean flow is an important influence on transient eddy wavenumbers and that improving the GFDL Mars GCM’s mean flow would make its eddy scales more realistic.

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Downstream Suppression of Baroclinic Waves

Journal of Climate ◽

10.1175/jcli-d-20-0483.1 ◽

2021 ◽

Vol 34 (3) ◽

pp. 919-930

Author(s):

Lina Boljka ◽

David W. J. Thompson ◽

Ying Li

Keyword(s):

North Atlantic ◽

North Pacific ◽

General Circulation ◽

Wave Packets ◽

Storm Track ◽

Eddy Activity ◽

Baroclinic Waves ◽

The North ◽

The North Pacific ◽

Downstream Development

AbstractBaroclinic waves drive both regional variations in weather and large-scale variability in the extratropical general circulation. They generally do not exist in isolation, but rather often form into coherent wave packets that propagate to the east via a mechanism called downstream development. Downstream development has been widely documented and explored. Here we document a novel but also key aspect of baroclinic waves: the downstream suppression of baroclinic activity that occurs in the wake of eastward propagating disturbances. Downstream suppression is apparent not only in the Southern Hemisphere storm track as shown in previous work, but also in the North Pacific and North Atlantic storm tracks. It plays an essential role in driving subseasonal periodicity in extratropical eddy activity in both hemispheres, and gives rise to the observed quiescence of the North Atlantic storm track 1–2 weeks following pronounced eddy activity in the North Pacific sector. It is argued that downstream suppression results from the anomalously low baroclinicity that arises as eastward propagating wave packets convert potential to kinetic energy. In contrast to baroclinic wave packets, which propagate to the east at roughly the group velocity in the upper troposphere, the suppression of baroclinic activity propagates eastward at a slower rate that is comparable to that of the lower to midtropospheric flow. The results have implications for understanding subseasonal variability in the extratropical troposphere of both hemispheres.

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Interdecadal changes in synoptic transient eddy activity over the Northeast Pacific and their role in tropospheric Arctic amplification

Climate Dynamics ◽

10.1007/s00382-021-05752-6 ◽

2021 ◽

Author(s):

Dong Xiao ◽

Hongli Ren

Keyword(s):

Heat Flux ◽

North Pacific ◽

The Arctic ◽

Transient Eddy ◽

Arctic Amplification ◽

Eddy Activity ◽

The North ◽

Eddy Heat Flux ◽

Subtropical Jet ◽

The North Pacific

AbstractArctic amplification refers to the greater surface warming of the Arctic than of other regions during recent decades. A similar phenomenon occurs in the troposphere and is termed “tropospheric Arctic amplification” (TAA). The poleward eddy heat flux and eddy moisture flux are critical to Arctic warming. In this study, we investigate the synoptic transient eddy activity over the North Pacific associated with TAA and its relationship with the subtropical jet stream, and propose the following mechanism. A poleward shift of the subtropical jet axis results in anomalies of the meridional gradient of zonal wind over the North Pacific, which drive a meridional dipole pattern of synoptic transient wave intensity over the North Pacific, referred to as the North Pacific Synoptic Transient wave intensity Dipole (NPSTD). The NPSTD index underwent an interdecadal shift in the late 1990s accompanying that of the subtropical jet stream. During the positive phase of the NPSTD index, synoptic eddy heat flux transports more heat to the Arctic Circle, and the eddy heat flux diverges, increasing Arctic temperature. This mechanism highlights the need to consider synoptic transient eddy activity over the North Pacific as the link between the mean state of the North Pacific subtropical upper jet and TAA.

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Multimodel Ensemble Projections of Wave Climate in the Western North Pacific Using CMIP6 Marine Surface Winds

Journal of Marine Science and Engineering ◽

10.3390/jmse9080835 ◽

2021 ◽

Vol 9 (8) ◽

pp. 835

Author(s):

Mochamad Riam Badriana ◽

Han Soo Lee

Keyword(s):

North Pacific ◽

General Circulation ◽

Western North Pacific ◽

Wave Climate ◽

Coastal Development ◽

Climate Projections ◽

Surface Winds ◽

Time Step ◽

Wave Characteristics ◽

Marine Surface

For decades, the western North Pacific (WNP) has been commonly indicated as a region with high vulnerability to oceanic and atmospheric hazards. This phenomenon can be observed through general circulation model (GCM) output from the Coupled Model Intercomparison Project (CMIP). The CMIP consists of a collection of ensemble data as well as marine surface winds for the projection of the wave climate. Wave climate projections based on the CMIP dataset are necessary for ocean studies, marine forecasts, and coastal development over the WNP region. Numerous studies with earlier phases of CMIP are abundant, but studies using CMIP6 as the recent dataset for wave projection is still limited. Thus, in this study, wave climate projections with WAVEWATCH III are conducted to investigate how wave characteristics in the WNP will have changed in 2050 and 2100 compared to those in 2000 with atmospheric forcings from CMIP6 marine surface winds. The wave model runs with a 0.5° × 0.5° spatial resolution in spherical coordinates and a 10-min time step. A total of eight GCMs from the CMIP6 dataset are used for the marine surface winds modelled over 3 hours for 2050 and 2100. The simulated average wave characteristics for 2000 are validated with the ERA5 Reanalysis wave data showing good consistency. The wave characteristics in 2050 and 2100 show that significant decreases in wave height, a clockwise shift in wave direction, and the mean wave period becomes shorter relative to those in 2000.

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