Variability of Rossby wave propagation in the North Atlantic from TOPEX/POSEIDON altimetry

2002 ◽  
Author(s):  
P. Cipollini ◽  
D. Cromwell ◽  
G.D. Quartly
Keyword(s):  
Wave Propagation ◽  
Rossby Wave ◽  
North Atlantic ◽  
The North ◽  
Rossby Wave Propagation ◽  
The North Atlantic

scholarly journals Interdecadal Variability of the Warm Arctic and Cold Eurasia Pattern and Its North Atlantic Origin

2018 ◽  
Vol 31 (15) ◽  
pp. 5793-5810 ◽  
Author(s):  
Mi-Kyung Sung ◽  
Seon-Hwa Kim ◽  
Baek-Min Kim ◽  
Yong-Sang Choi
Keyword(s):  
Twentieth Century ◽  
Rossby Wave ◽  
North Atlantic ◽  
Storm Track ◽  
Stationary Wave ◽  
Interdecadal Variability ◽  
Temperature Perturbation ◽  
Mean Flow ◽  
The North ◽  
The North Atlantic

This study investigates the origin of the interdecadal variability in the warm Arctic and cold Eurasia (WACE) pattern, which is defined as the second empirical orthogonal function of surface air temperature (SAT) variability over the Eurasian continent in Northern Hemisphere winter, by analyzing the Twentieth Century Reanalysis dataset. While previous studies highlight recent enhancement of the WACE pattern, ascribing it to anthropogenic warming, the authors found that the WACE pattern has experienced a seemingly periodic interdecadal variation over the twentieth century. This long-term variation in the Eurasian SAT is attributable to the altered coupling between the Siberian high (SH) and intraseasonal Rossby wave emanating from the North Atlantic, as the local wave branch interacts with the SH and consequentially enhances the continental temperature perturbation. It is further identified that these atmospheric circulation changes in Eurasia are largely controlled by the decadal amplitude modulation of the climatological stationary waves over the North Atlantic region. The altered decadal mean condition of stationary wave components brings changes in local baroclinicity and storm track activity over the North Atlantic, which jointly change the intraseasonal Rossby wave generation and propagation characteristics as well. With simple stationary wave model experiments, the authors confirm how the altered mean flow condition in the North Atlantic acts as a source for the growth of the Rossby wave that leads to the change in the downstream WACE pattern.

Summer Rainfall Seesaw between Hetao and the Middle and Lower Reaches of the Yangtze River and Its Relationship with the North Atlantic Oscillation

2017 ◽  
Vol 30 (17) ◽  
pp. 6629-6643 ◽  
Author(s):  
Dachao Jin ◽  
Zhaoyong Guan
Keyword(s):  
Rossby Wave ◽  
North Atlantic ◽  
Yangtze River ◽  
Lower Troposphere ◽  
Summer Rainfall ◽  
Northern China ◽  
Upper Troposphere ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Using the NCEP–NCAR reanalysis and other observational datasets, the authors have investigated the relationship of summer rainfall variations between the Hetao region of northern China and the middle and lower reaches of Yangtze River (MLRYR). The results have demonstrated that rainfall in Hetao varies out of phase with that in MLRYR on the interannual time scales. This phenomenon is referred to as the Hetao–Yangtze rainfall seesaw (HYRS). An HYRS index is defined to reveal both spatial and temporal features of HYRS. It is found that the North Atlantic Oscillation (NAO) affects the HYRS. In years when the NAO is in its positive phase, anomalous divergences in the lower troposphere and anomalous convergences in the upper troposphere are observed in regions of the Mediterranean and eastern Europe. The anomalous convergences in the upper troposphere occur as the positive Rossby wave source excites a circumglobal teleconnection (CGT) in the midlatitudes, exhibiting the eastward propagation of Rossby wave energy along the Asian jet. Meanwhile, the Eurasian–Pacific (EUP) teleconnection also affects the HYRS. Influenced mainly by the CGT pattern, the circulations over Hetao and MLRYR are consequently perturbed. The atmosphere over Hetao converges anomalously in the lower troposphere and diverges anomalously in the upper troposphere, facilitating more than normal rainfall there. At the same time, the atmosphere over MLRYR diverges anomalously in the lower troposphere and converges anomalously in the upper troposphere, resulting in more than normal summer rainfall in MLRYR. In this way, the north–south rainfall seesaw is formed. This NAO-induced rainfall seesaw is potentially useful for summer rainfall predictions in both MLRYR and the Hetao region of northern China.

scholarly journals Dynamical Evolution of North Atlantic Ridges and Poleward Jet Stream Displacements

2011 ◽  
Vol 68 (5) ◽  
pp. 954-963 ◽  
Author(s):  
Tim Woollings ◽  
Joaquim G. Pinto ◽  
João A. Santos
Keyword(s):  
Rossby Wave ◽  
North Atlantic ◽  
Wave Breaking ◽  
Large Scale ◽  
Wave Train ◽  
Jet Stream ◽  
Rossby Wave Breaking ◽  
The North ◽  
The North Atlantic ◽  
Circulation Anomalies

Abstract The development of a particular wintertime atmospheric circulation regime over the North Atlantic, comprising a northward shift of the North Atlantic eddy-driven jet stream and an associated strong and persistent ridge in the subtropics, is investigated. Several different methods of analysis are combined to describe the temporal evolution of the events and relate it to shifts in the phase of the North Atlantic Oscillation and East Atlantic pattern. First, the authors identify a close relationship between northward shifts of the eddy-driven jet, the establishment and maintenance of strong and persistent ridges in the subtropics, and the occurrence of upper-tropospheric anticyclonic Rossby wave breaking over Iberia. Clear tropospheric precursors are evident prior to the development of the regime, suggesting a preconditioning of the Atlantic jet stream and an upstream influence via a large-scale Rossby wave train from the North Pacific. Transient (2–6 days) eddy forcing plays a dual role, contributing to both the initiation and then the maintenance of the circulation anomalies. During the regime there is enhanced occurrence of anticyclonic Rossby wave breaking, which may be described as low-latitude blocking-like events over the southeastern North Atlantic. A strong ridge is already established at the time of wave-breaking onset, suggesting that the role of wave-breaking events is to amplify the circulation anomalies rather than to initiate them. Wave breaking also seems to enhance the persistence, since it is unlikely that a persistent ridge event occurs without being also accompanied by wave breaking.

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.

scholarly journals Longitude-dependent decadal ozone changes and ozone trends in boreal winter months during 1960–2000

2008 ◽  
Vol 26 (5) ◽  
pp. 1275-1286 ◽  
Author(s):  
D. H. W. Peters ◽  
A. Gabriel ◽  
G. Entzian
Keyword(s):  
Rossby Wave ◽  
North Atlantic ◽  
Total Ozone ◽  
Planetary Wave ◽  
Wave Structure ◽  
Boreal Winter ◽  
The North ◽  
The North Atlantic ◽  
Eastern North Atlantic ◽  
The 1960S

Abstract. This study examines the longitude-dependent decadal changes and trends of ozone for the boreal winter months during the period of 1960–2000. These changes are caused primarily by changes in the planetary wave structure in the upper troposphere and lower stratosphere. The decadal changes and trends over 4 decades of geopotential perturbations, defined as a deviation from the zonal mean, are estimated by linear regression with time. The decadal changes in longitude-dependent ozone were calculated with a simple transport model of ozone based on the known planetary wave structure changes and prescribed zonal mean ozone gradients. For December of the 1960s and 1980s a statistically significant Rossby wave track appeared over the North Atlantic and Europe with an anticyclonic disturbance over the Eastern North Atlantic and Western Europe, flanked by cyclonic disturbances. In the 1970s and 1990s statistically significant cyclonic disturbances appeared over the Eastern North Atlantic and Europe, surrounded by anticyclonic anomalies over Northern Africa, Central Asia and Greenland. Similar patterns have been found for January. The Rossby wave track over the North Atlantic and Europe is stronger in the 1980s than in the 1960s. For February, the variability of the regression patterns is higher. For January we found a strong alteration in the modelled decadal changes in total ozone over Central and Northern Europe, showing a decrease of about 15 DU in the 1960s and 1980s and an increase of about 10 DU in the 1970s and 1990s. Over Central Europe the positive geopotential height trend (increase of 2.3 m/yr) over 40 years is of the same order (about 100 m) as the increase in the 1980s alone. This is important to recognize because it implies a total ozone decrease over Europe of the order of 14 DU for the 1960–2000 period, for January, if we use the standard change regression relation that about a 10-m geopotential height increase at 300 hPa is related to about a 1.4-DU total ozone decrease.

The AMV phase-dependence of the connection between February NAO and March surface air temperature over the Tibetan Plateau

2021 ◽  
Author(s):  
Jingyi Li ◽  
Fei Li ◽  
Shengping He ◽  
Huijun Wang ◽  
Yvan J Orsolini
Keyword(s):  
Tibetan Plateau ◽  
Air Temperature ◽  
Rossby Wave ◽  
North Atlantic ◽  
Wave Train ◽  
Surface Air Temperature ◽  
The Tibetan Plateau ◽  
The North ◽  
Rossby Wave Train ◽  
The North Atlantic

<p>The Tibetan Plateau (TP), referred to as the “Asian water tower”, contains one of the largest land ice masses on Earth. The local glacier shrinkage and frozen-water storage are strongly affected by variations in surface air temperature over the TP (TPSAT), especially in springtime. This study reveals a distinct out-of-phase connection between the February North Atlantic Oscillation (NAO) and March TPSAT, which is non-stationary and regulated by the warm phase of the Atlantic Multidecadal Variability (AMV+). The results show that during the AMV+, the negative phase of the NAO persists from February to March, and is accompanied by a quasi-stationary Rossby wave train trapped along a northward-shifted subtropical westerly jet stream across Eurasia, inducing an anomalous adiabatic descent that warms the TP. However, during the cold phase of the AMV, the negative NAO does not persist into March. The Rossby wave train propagates along the well-separated polar and subtropical westerly jets, and the NAO−TPSAT connection is broken. Further investigation suggests that the enhanced synoptic eddy and low-frequency flow (SELF) interaction over the North Atlantic in February and March during the AMV+, caused by the enhanced and southward-shifted storm track, help maintain the NAO anomaly pattern via positive eddy feedback. This study provides a new detailed perspective on the decadal variability of the North Atlantic−TP connections in late winter−early spring.</p>

Source locations of microseisms in the North Atlantic from Matched Field Processing using full Green's Functions.

2021 ◽  
Author(s):  
Sven Schippkus ◽  
Céline Hadziioannou
Keyword(s):  
Wave Propagation ◽  
Travel Time ◽  
North Atlantic ◽  
Seismic Noise ◽  
Green's Functions ◽  
Green’S Functions ◽  
Regional Scale ◽  
Matched Field Processing ◽  
The North ◽  
The North Atlantic

<p>Precise knowledge of the sources of seismic noise is fundamental to our understanding of the ambient seismic field and its generation mechanisms. Two approaches to locating such sources exist currently. One is based on minimizing the misfit between estimated Green's functions from cross-correlation of seismic noise and synthetically computed correlation functions. This approach is computationally expensive and not yet widely adopted. The other, more common approach is Beamforming, where a beam is computed by shifting waveforms in time corresponding to the slowness of a potentially arriving wave front. Beamforming allows fast computations, but is limited to the plane-wave assumption and sources outside of the array.</p><p>Matched Field Processing (MFP) is Beamforming in the spatial domain. By probing potential source locations directly, it allows for arbitrary wave propagation in the medium as well as sources inside of arrays. MFP has been successfully applied at local scale using a constant velocity for travel-time estimation, sufficient at that scale. At regional scale, travel times can be estimated from phase velocity maps, which are not yet available globally at microseism frequencies.</p><p>To expand MFP’s applicability to new regions and larger scales, we replace the replica vectors that contain only travel-time information with full synthetic Green's functions. This allows to capture the full complexity of wave propagation by including relative amplitude information between receivers and multiple phases. We apply the method to continuous recordings of stations surrounding the North Atlantic and locate seismic sources in the primary and secondary microseism band, using pre-computed databases of Green's functions for computational efficiency. The framework we introduce here can easily be adapted to a laterally homogeneous Earth once such Green’s function databases become available, hopefully in the near future.</p>

Extratropical Atmospheric Response to Equatorial Atlantic Cold Tongue Anomalies

2007 ◽  
Vol 20 (10) ◽  
pp. 2076-2091 ◽  
Author(s):  
Reindert J. Haarsma ◽  
Wilco Hazeleger
Keyword(s):  
Rossby Wave ◽  
North Atlantic ◽  
Maximum Amplitude ◽  
Vertical Shear ◽  
Boreal Summer ◽  
Atmospheric Response ◽  
Cold Tongue ◽  
The North ◽  
Subtropical Jet ◽  
The North Atlantic

Abstract The extratropical atmospheric response to the equatorial cold tongue mode in the Atlantic Ocean has been investigated with the coupled ocean–atmosphere model, Speedy Ocean (SPEEDO). Similar to the observations, the model simulates a lagged covariability between the equatorial cold tongue mode during late boreal summer and the east Atlantic pattern a few months later in early winter. The equatorial cold tongue mode attains its maximum amplitude during late boreal summer. However, only a few months later, when the ITCZ has moved southward, it is able to induce a significant upper-tropospheric divergence that is able to force a Rossby wave response. The lagged covariability is therefore the result of the persistence of the cold tongue anomaly and a favorable tropical atmospheric circulation a few months later. The Rossby wave energy is trapped in the South Asian subtropical jet and propagates circumglobally before it reaches the North Atlantic. Due to the local increase of the Hadley circulation, forced by the cold tongue anomaly, the subtropical jet over the North Atlantic is enhanced. The resulting increase in the vertical shear of the zonal wind increases the baroclinicity over the North Atlantic. This causes the nonlinear growth of the anomalies due to transient eddy feedbacks to be largest over the North Atlantic, resulting in an enhanced response over that region.

scholarly journals The Development of a Statistical Forecast Model for Changma

2013 ◽  
Vol 28 (6) ◽  
pp. 1304-1321 ◽  
Author(s):  
Seung-Eon Lee ◽  
Kyong-Hwan Seo
Keyword(s):  
Wave Propagation ◽  
North Atlantic ◽  
North Pacific ◽  
Forecast Model ◽  
Tropical Pacific ◽  
The North ◽  
Sst Anomaly ◽  
The North Atlantic ◽  
The North Pacific ◽  
The Tropical Pacific

Abstract Forecasting year-to-year variations in East Asian summer monsoon (EASM) precipitation is one of the most challenging tasks in climate prediction because the predictors are not sufficiently well known and the forecast skill of the numerical models is poor. In this paper, a statistical forecast model for changma (the Korean portion of the EASM system) precipitation is proposed that was constructed with three physically based predictors. A forward-stepwise regression was used to select the predictors that included sea surface temperature (SST) anomalies over the North Pacific, the North Atlantic, and the tropical Pacific Ocean. Seasonal predictions with this model showed high forecasting capabilities that had a Gerrity skill score of ~0.82. The dynamical processes associated with the predictors were examined prior to their use in the prediction scheme. All predictors tended to induce an anticyclonic anomaly to the east or southeast of Japan, which was responsible for transporting a large amount of moisture to the southern Korean Peninsula. The predictor in the North Pacific formed an SST front to the east of Japan during the summertime, which maintained a lower-tropospheric baroclinicity. The North Atlantic SST anomaly induced downstream wave propagation in the upper troposphere, developing anticyclonic activity east of Japan. Forcing from the tropical Pacific SST anomaly triggered a cyclonic anomaly over the South China Sea, which was maintained by atmosphere–ocean interactions and induced an anticyclonic anomaly via northward Rossby wave propagation. Overall, the model used for forecasting changma precipitation performed well (R = 0.85) and correctly predicted information for 16 out of 19 yr of observational data.

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