Observed Patterns of Month-to-Month Storm-Track Variability and Their Relationship to the Background Flow*

2010 ◽  
Vol 67 (5) ◽  
pp. 1420-1437 ◽  
Author(s):  
Justin J. Wettstein ◽  
John M. Wallace
Keyword(s):  
Northern Hemisphere ◽  
Geopotential Height ◽  
Storm Track ◽  
Meridional Wind ◽  
Storm Tracks ◽  
Mean Flow ◽  
Annular Mode ◽  
The North ◽  
Jet Variability ◽  
The North Atlantic Oscillation

Abstract Month-to-month storm-track variability is investigated via EOF analyses performed on ERA-40 monthly-averaged high-pass filtered daily 850-hPa meridional heat flux and the variances of 300-hPa meridional wind and 500-hPa height. The analysis is performed both in hemispheric and sectoral domains of the Northern and Southern Hemispheres. Patterns characterized as “pulsing” and “latitudinal shifting” of the climatological-mean storm tracks emerge as the leading sectoral patterns of variability. Based on the analysis presented, storm-track variability on the spatial scale of the two Northern Hemisphere sectors appears to be largely, but perhaps not completely, independent. Pulsing and latitudinally shifting storm tracks are accompanied by zonal wind anomalies consistent with eddy-forced accelerations and geopotential height anomalies that project strongly on the dominant patterns of geopotential height variability. The North Atlantic Oscillation (NAO)–Northern Hemisphere annular mode (NAM) is associated with a pulsing of the Atlantic storm track and a meridional displacement of the upper-tropospheric jet exit region, whereas the eastern Atlantic (EA) pattern is associated with a latitudinally shifting storm track and an extension or retraction of the upper-tropospheric jet. Analogous patterns of storm-track and upper-tropospheric jet variability are associated with the western Pacific (WP) and Pacific–North America (PNA) patterns. Wave–mean flow relationships shown here are more clearly defined than in previous studies and are shown to extend through the depth of the troposphere. The Southern Hemisphere annular mode (SAM) is associated with a latitudinally shifting storm track over the South Atlantic and Indian Oceans and a pulsing South Pacific storm track. The patterns of storm-track variability are shown to be related to simple distortions of the climatological-mean upper-tropospheric jet.

scholarly journals Northern hemisphere winter storm tracks of the Eemian interglacial and the last glacial inception

2007 ◽  
Vol 3 (2) ◽  
pp. 181-192 ◽  
Author(s):  
F. Kaspar ◽  
T. Spangehl ◽  
U. Cubasch
Keyword(s):  
Northern Hemisphere ◽  
North Atlantic ◽  
Storm Track ◽  
Storm Tracks ◽  
Winter Storm ◽  
The North ◽  
The North Atlantic ◽  
Hemisphere Winter ◽  
Eemian Interglacial ◽  
The Last Glacial

Abstract. Climate simulations of the Eemian interglacial and the last glacial inception have been performed by forcing a coupled ocean-atmosphere general circulation model with insolation patterns of these periods. The parameters of the Earth's orbit have been set to conditions of 125 000 and 115 000 years before present (yr BP). Compared to today, these dates represent periods with enhanced and weakened seasonality of insolation in the northern hemisphere. Here we analyse the simulated change in northern hemisphere winter storm tracks. The change in the orbital configuration has a strong impact on the meridional temperature gradients and therefore on strength and location of the storm tracks. The North Atlantic storm track is strengthened, shifted northward and extends further to the east in the simulation for the Eemian at 125 kyr BP. As one consequence, the northern parts of Europe experience an increase in winter precipitation. The frequency of winter storm days increases over large parts of the North Atlantic including the British Isles and the coastal zones of north-western Europe. Opposite but weaker changes in storm track activity are simulated for 115 kyr BP.

The Statistics and Structure of Subseasonal Midlatitude Variability in NASA GSFC GCMs

2005 ◽  
Vol 18 (16) ◽  
pp. 3294-3316 ◽  
Author(s):  
Dennis P. Robinson ◽  
Robert X. Black
Keyword(s):  
Three Dimensional ◽  
Storm Track ◽  
Storm Tracks ◽  
Dimensional Structure ◽  
Mean Flow ◽  
Weather Regimes ◽  
Three Dimensional Structure ◽  
Dynamical Characteristics ◽  
The North ◽  
Synoptic Eddies

Abstract A comprehensive analysis of midlatitude intraseasonal variability in extended integrations of NASA GSFC general circulation models (GCMs) is conducted. This is approached by performing detailed intercomparisons of the representation of the storm tracks and anomalous weather regimes occurring during wintertime in the Atmospheric Model Intercomparison Project (AMIP)-type simulations of both the NASA–NCAR and a version of the Aries model used in NASA’s Seasonal-to-Interannual Prediction Project (NSIPP) model. The model-simulated statistics, three-dimensional structure, and dynamical characteristics of these phenomena are diagnosed and directly compared to parallel observational analyses derived from NCEP–NCAR reanalyses. A qualitatively good representation of the vertical structure of intraseasonal eddy kinetic energy (EKE) is provided by both models with maximum values of EKE occurring near 300 hPa. The main model shortcoming is an underestimation of EKE in the upper troposphere, especially for synoptic eddies in the NSIPP model. Nonetheless, both models provide a reasonable representation of the three-dimensional structure and dynamical characteristics of synoptic eddies. Discrepancies in the storm-track structures simulated by the models include an anomalous local minimum over the eastern Pacific basin. However, both GCMs faithfully reproduce the observed Pacific midwinter storm-track suppression. Interestingly, the NSIPP model also produces a midwinter suppression feature over the Atlantic storm track in association with the anomalously strong upper-level jet stream simulated by NSIPP in this region. The regional distribution of anomalous weather regime events is well simulated by the models. However, substantial structural differences exist between observed and simulated events over the North Pacific region. In comparison to observations, model events are horizontally more isotropic, have stronger westward vertical tilts, and are more strongly driven by baroclinic dynamics. The structure and dynamics of anomalous weather regimes occurring over the North Atlantic region are qualitatively better represented by the models. The authors suggest that model deficiencies in representing the zonally asymmetric climatological-mean flow field (particularly the magnitude and structure of the Pacific and Atlantic jet streams) help contribute to model shortcomings in (i) the strength and seasonal variability of the storm tracks and (ii) dynamical distinctions in the maintenance of large-scale weather regimes.

scholarly journals The Annual Cycle of Northern Hemisphere Storm Tracks. Part I: Seasons

2019 ◽  
Vol 32 (6) ◽  
pp. 1743-1760 ◽  
Author(s):  
B. J. Hoskins ◽  
K. I. Hodges
Keyword(s):  
Northern Hemisphere ◽  
Annual Cycle ◽  
Storm Track ◽  
Lower Troposphere ◽  
Meridional Wind ◽  
Diagnostic Techniques ◽  
Storm Tracks ◽  
The Pacific ◽  
Wide Range ◽  
Close Relationship

Abstract In this paper and Part II a comprehensive picture of the annual cycle of the Northern Hemisphere storm tracks is presented and discussed for the first time. It is based on both feature tracking and Eulerian-based diagnostics, applied to vorticity and meridional wind in the upper and lower troposphere. Here, the storm tracks, as diagnosed using both variables and both diagnostic techniques, are presented for the four seasons for each of the two levels. The oceanic storm tracks retain much of their winter mean intensity in spring with only a small change in their latitude. In the summer they are much weaker, particularly in the Pacific and are generally farther poleward. In autumn the intensities are larger again, comparable with those in spring, but the latitude is still nearer to that of summer. However, in the lower troposphere in the eastern ocean basins the tracking metrics show northern and southern tracks that change little with latitude through the year. The Pacific midwinter minimum is seen in upper-troposphere standard deviation diagnostics, but a richer picture is obtained using tracking. In winter there are high intensities over a wide range of latitudes in the central and eastern Pacific, and the western Pacific has high track density but weak intensity. In the lower troposphere all the diagnostics show that the strength of the Pacific and Atlantic storm tracks are generally quite uniform over the autumn–winter–spring period. There is a close relationship between the upper-tropospheric storm track, particularly that based on vorticity, and tropopause-level winds and temperature gradients. In the lower troposphere, in winter the oceanic storm tracks are in the region of the strong meridional SST gradients, but in summer they are located in regions of small or even reversed SST gradients. However, over North America the lower-tropospheric baroclinicity and the upstream portion of the Atlantic storm track stay together throughout the year.

Simulating the Seasonal Cycle of the Northern Hemisphere Storm Tracks Using Idealized Nonlinear Storm-Track Models

2007 ◽  
Vol 64 (7) ◽  
pp. 2309-2331 ◽  
Author(s):  
Edmund K. M. Chang ◽  
Pablo Zurita-Gotor
Keyword(s):  
Northern Hemisphere ◽  
Nonlinear Model ◽  
Seasonal Cycle ◽  
Storm Track ◽  
Stationary Wave ◽  
Storm Tracks ◽  
Stationary Waves ◽  
Mean Flow ◽  
Seasonal Evolution ◽  
Wave Development

Abstract In this study, an idealized nonlinear model is used to investigate whether dry dynamical factors alone are sufficient for explaining the observed seasonal modulation of the Northern Hemisphere storm tracks during the cool season. By construction, the model does an excellent job simulating the seasonal evolution of the climatological stationary waves. Yet even under this realistic mean flow, the seasonal modulation in storm-track amplitude predicted by the model is deficient over both ocean basins. The model exhibits a stronger sensitivity to the mean flow baroclinicity than observed, producing too-large midwinter eddy amplitudes compared to fall and spring. This is the case not only over the Pacific, where the observed midwinter minimum is barely apparent in the model simulations, but also over the Atlantic, where the October/April eddy amplitudes are also too weak when the January amplitude is tuned to be about right. The nonlinear model generally produces stronger eddy amplitude with stronger baroclinicity, even in the presence of concomitant stronger deformation due to the enhanced stationary wave. The same was found to be the case in a simpler quasigeostrophic model, in which the eddy amplitude nearly always increases with baroclinicity, and deformation only limits the maximum eddy amplitude when the baroclinicity is unrealistically weak. Overall, these results suggest that it is unlikely that dry dynamical effects alone, such as deformation, can fully explain the observed Pacific midwinter minimum in eddy amplitude. It is argued that one should take into account the seasonal evolution of the impacts of diabatic heating on baroclinic wave development in order to fully explain the seasonal cycle of the storm tracks. A set of highly idealized experiments that attempts to represent some of the impacts of moist heating is presented in an appendix to suggest that deficiencies in the model-simulated seasonal cycle of both storm tracks may be corrected when these effects, together with observed seasonal changes in mean flow structure, are taken into account.

scholarly journals The Annual Cycle of Northern Hemisphere Storm Tracks. Part II: Regional Detail

2019 ◽  
Vol 32 (6) ◽  
pp. 1761-1775 ◽  
Author(s):  
B. J. Hoskins ◽  
K. I. Hodges
Keyword(s):  
North Atlantic ◽  
Annual Cycle ◽  
North Pacific ◽  
East Asian ◽  
Storm Track ◽  
Meridional Wind ◽  
Storm Tracks ◽  
Annual Cycles ◽  
The North ◽  
The North Pacific

Abstract In Part I of this study, the annual cycle of the Northern Hemisphere storm tracks was investigated using feature tracking and Eulerian variance-based diagnostics applied to both the vorticity and meridional wind fields. Results were presented and discussed for the four seasons at both upper- (250 hPa) and lower- (850 hPa) tropospheric levels. Here, using the meridional wind diagnostics, the annual cycles of the North Pacific and North Atlantic storm tracks are examined in detail. This is done using monthly and 20° longitudinal sector averages. Many sectors have been considered, but the focus is on sectors equally spaced in the two main oceanic storm tracks situated at their western, central, and eastern regions, with the western ones being mainly over the upstream continents. The annual cycles of the upper- and lower-tropospheric storm tracks in the central and eastern Pacific, as well as in the western and central Atlantic sectors, all have rather similar structures. In amplitude, each sector at both levels has a summer minimum and a relatively uniform strength from October to April, despite the strong winter maxima in the westerly jets. However, high-intensity storms occur over a much wider latitudinal band in winter. The storm track in each sector moves poleward from May to August and returns equatorward from October to December, and there is a marked asymmetry between spring and autumn. There are many differences between the North Pacific and North Atlantic storm tracks, and some of these seem to have their origin in the behavior over the upstream East Asian and North American continents, suggesting the importance of seeding from these regions. The East Asian storm track near 48°N has marked spring and autumn maxima and weak amplitude in winter and summer. The 33°N track is strong only in the first half of the year. In contrast, the eastern North American storm track is well organized throughout the year, around the baroclinicity that moves latitudinally with the seasons. The signatures associated with these features are found to gradually decrease downstream in each case. In particular, there is very little latitudinal movement in the storm track in the eastern Atlantic.

scholarly journals Spatial Pattern and Zonal Shift of the North Atlantic Oscillation. Part I: A Dynamical Interpretation

2010 ◽  
Vol 67 (9) ◽  
pp. 2805-2826 ◽  
Author(s):  
Dehai Luo ◽  
Zhihui Zhu ◽  
Rongcai Ren ◽  
Linhao Zhong ◽  
Chunzai Wang
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Function Analysis ◽  
Storm Track ◽  
Phase Speed ◽  
Mean Flow ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation ◽  
Nao Pattern

Abstract This paper presents a possible dynamical explanation for why the North Atlantic Oscillation (NAO) pattern exhibits an eastward shift from the period 1958–77 (P1) to the period 1978–97 (P2) or 1998–2007 (P3). First, the empirical orthogonal function analysis of winter mean geopotential heights during P1, P2, and P3 reveals that the NAO dipole anomaly exhibits a northwest–southeast (NW–SE) tilting during P1 but a northeast–southwest (NE–SW) tilting during P2 and P3. The NAO pattern, especially its northern center, undergoes a more pronounced eastward shift from P1 to P2. The composite calculation of NAO events during P1 and P2 also indicates that the negative (positive) NAO phase dipole anomaly can indeed exhibit such a NW–SE (NE–SW) tilting. Second, a linear Rossby wave formula derived in a slowly varying basic flow with a meridional shear is used to qualitatively show that the zonal phase speed of the NAO dipole anomaly is larger (smaller) in higher latitudes and smaller (larger) in lower latitudes during the life cycle of the positive (negative) NAO phases because the core of the Atlantic jet is shifted to the north (south). Such a phase speed distribution tends to cause the different movement speeds of the NAO dipole anomaly at different latitudes, thus resulting in the different spatial tilting of the NAO dipole anomaly depending on the phase of the NAO. The zonal displacement of the northern center of the NAO pattern appears to be more pronounced because the change of the mean flow between two phases of the NAO is more distinct in higher latitudes than in lower latitudes. In addition, a weakly nonlinear analytical solution, based on the assumption of the scale separation between the NAO anomaly and transient synoptic-scale waves, is used to demonstrate that an eastward shift of the Atlantic storm-track eddy activity that is associated with the eastward extension of the Atlantic jet stream is a possible cause of the whole eastward shift of the center of action of the NAO pattern during P2/P3.

scholarly journals An Energetics Study of Wintertime Northern Hemisphere Storm Tracks under 4 × CO2 Conditions in Two Ocean–Atmosphere Coupled Models

2009 ◽  
Vol 22 (3) ◽  
pp. 819-839 ◽  
Author(s):  
Alexandre Laîné ◽  
Masa Kageyama ◽  
David Salas-Mélia ◽  
Gilles Ramstein ◽  
Serge Planton ◽  
...  
Keyword(s):  
Latent Heat ◽  
Northern Hemisphere ◽  
Storm Track ◽  
Coupled Model ◽  
Storm Tracks ◽  
Latent Heating ◽  
Mean Flow ◽  
Coupled Models ◽  
Intergovernmental Panel ◽  
Ocean Atmosphere

Abstract Different possible behaviors of winter Northern Hemisphere storm tracks under 4 × CO2 forcing are considered by analyzing the response of two of the ocean–atmosphere coupled models that were run for the fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC-AR4), namely the Institut Pierre Simon Laplace’s global coupled model (IPSL-CM4) and the Centre National de Recherches Meteorologiques’s coupled ocean–atmosphere model (CNRM-CM3). It is interesting to compare these models due to their very different responses, especially concerning the North Atlantic storm track. A local energetics study of the synoptic variability in both models is performed, derived from the eddy energy equations, including diabatic terms. The ability of both models to simulate the present-day eddy energetics is considered, indicating no major discrepancies. Both models indicate that the primary cause for synoptic activity changes at the western end of the storm tracks is related to the baroclinic conversion process, due to mean temperature gradient changes in some localized regions of the western oceanic basins, but also resulting from changes in the eddy efficiency to convert energy from the mean flow. Farther downstream, latent heat release during the developing and mature stages of eddies becomes an important eddy energy source especially in terms of changes between 4 × CO2 and preindustrial conditions. This diabatic process amplifies the upstream synoptic (hence usually baroclinic) changes, with more and/or stronger storms implying more latent heat being released (and the converse being true for weaker synoptic activity). This amplification is asymmetrical for the models considered under the simulated 4 × CO2 conditions, due to a greater amount of water vapor contained in warmer air and hence the potential for more condensation for a given synoptic activity. The magnitude of the reduced latent heating is attenuated, whereas increased latent heating is strengthened. Ageostrophic geopotential fluxes are also important in relocating eddy kinetic energy, especially in the vertical.

scholarly journals The Classification of Synoptic-Scale Eddies at 850 hPa over the North Pacific in Wintertime

2016 ◽  
Vol 2016 ◽  
pp. 1-8
Author(s):  
Linlin Xia ◽  
Yanke Tan ◽  
Chongyin Li ◽  
Cheng Cheng
Keyword(s):  
North Pacific ◽  
Geopotential Height ◽  
Wave Train ◽  
Storm Track ◽  
Meridional Wind ◽  
Synoptic Scale ◽  
The North ◽  
The North Pacific ◽  
Midwinter Suppression ◽  
Developing Pattern

Empirical orthogonal function (EOF) is applied to the study of the synoptic-scale eddies at 850 hPa over the North Pacific in winter from 1948 to 2010. The western developing pattern synoptic-scale eddies (WSE) and the eastern developing pattern synoptic-scale eddies (ESE) are extracted from the first four leading modes of EOF analysis of high-pass filtered geopotential height. The results show the following: (1) The WSE and the ESE both take the form of a wave train propagating eastward. The WSE reach their largest amplitude around the dateline in the North Pacific, while the largest amplitude of ESE occurs in the northeast Pacific. (2) The WSE and ESE are the most important modes of the synoptic-scale eddies at 850 hPa over the North Pacific, which correspond to the two max value centers of the storm track. (3) In addition to geopotential height, the WSE and the ESE also leave their wave-like footprints in the temperature, meridional wind, and vertical velocity fields, which assume typical baroclinic wave features. (4) The WSE and the ESE have an intrinsic time scale of four days and experience a “midwinter suppression” corresponding to the midwinter suppression of storm tracks.

scholarly journals Spatial Patterns and Intensity of the Surface Storm Tracks in CMIP5 Models

2017 ◽  
Vol 30 (13) ◽  
pp. 4965-4981 ◽  
Author(s):  
James F. Booth ◽  
Young-Oh Kwon ◽  
Stanley Ko ◽  
R. Justin Small ◽  
Rym Msadek
Keyword(s):  
Storm Track ◽  
Storm Tracks ◽  
Cmip5 Models ◽  
Western Boundary ◽  
Spatial Correlations ◽  
Boundary Current ◽  
Near Surface ◽  
Surface Stability ◽  
The North ◽  
Basin Scale

To improve the understanding of storm tracks and western boundary current (WBC) interactions, surface storm tracks in 12 CMIP5 models are examined against ERA-Interim. All models capture an equatorward displacement toward the WBCs in the locations of the surface storm tracks’ maxima relative to those at 850 hPa. An estimated storm-track metric is developed to analyze the location of the surface storm track. It shows that the equatorward shift is influenced by both the lower-tropospheric instability and the baroclinicity. Basin-scale spatial correlations between models and ERA-Interim for the storm tracks, near-surface stability, SST gradient, and baroclinicity are calculated to test the ability of the GCMs’ match reanalysis. An intermodel comparison of the spatial correlations suggests that differences (relative to ERA-Interim) in the position of the storm track aloft have the strongest influence on differences in the surface storm-track position. However, in the North Atlantic, biases in the surface storm track north of the Gulf Stream are related to biases in the SST. An analysis of the strength of the storm tracks shows that most models generate a weaker storm track at the surface than 850 hPa, consistent with observations, although some outliers are found. A linear relationship exists among the models between storm-track amplitudes at 500 and 850 hPa, but not between 850 hPa and the surface. In total, the work reveals a dual role in forcing the surface storm track from aloft and from the ocean surface in CMIP5 models, with the atmosphere having the larger relative influence.

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