Transient Eddy Forcing of Blocking Flows

Mullen, Steven L.

doi:10.1175/1520-0469(1987)044<0003:tefobf>2.0.co;2

Cited by 133 publications

(98 citation statements)

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“…Green (1977) first proposed that highfrequency transient eddies within the storm tracks may play a role in maintaining blocking flow. Fol-lowing his proposal, numerous diagnostic, observational and numerical experimental studies have been carried out and have indicated the crucial role of high-frequency transient eddies (e.g., Holopainen et al 1982;Shutts 1986;Mullen 1987;Nakamura and Wallace 1990;Tanaka 1991;. In particular, Shutts (1983) conducted one of the most convincing numerical experiments on the blocking maintenance mechanism by highfrequency transient eddies.…”

Section: Introductionmentioning

confidence: 99%

Relationship between Singular Modes of Blocking Flow and High-frequency Eddies

Maeda¹,

Kobayashi²,

Takano³

et al. 2000

Journal of the Meteorological Society of Japan

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To investigate the maintenance mechanism of the blocking flow, we performed a numerical experiment using a barotropic spectral model on the sphere. The model is linearized about two types of realistic basic flows. One is a blocking flow near Alaska (blocking flow case) and the other is a zonal flow in the North Pacific (zonal flow case).The model is integrated in time with prescribed high-frequency eddies which are generated in the Far East and propagate eastward along the northern flank of the jet stream. After several days of time integration, time mean vorticity flux divergence is calculated. Then, the resulting vorticity flux divergence field is used as the eddy vorticity forcing to compute the second-order flow induced by eddies. It is found that the induced second-order flow intensifies the blocking for the blocking flow case, and that this is not the case for the zonal flow case.To clarify the reason for the difference between the induced second-order flows, we carried out the singular value decomposition (SVD) of the matrix of the barotropic vorticity equation linearized about the basic flows. For the blocking flow case, spatial distributions of the leading singular modes show blocking patterns which are similar to the blocking in the basic flow. It is found that these modes are effectively excited by the eddy vorticity forcing, and enhance the blocking in the basic flow. On the other hand, for the zonal flow case, leading singular modes do not show blocking patterns. These results indicate that blocking flows tend to have easily excited modes that can reinforce the block, and high-frequency eddies could maintain blocking by exciting these modes.The dependency of results of the experiment on the location of high-frequency eddies is also shown. It indicates the limitation of the model to investigate the high-frequency eddies feedback.

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Section: Introductionmentioning

confidence: 99%

Relationship between Singular Modes of Blocking Flow and High-frequency Eddies

Maeda¹,

Kobayashi²,

Takano³

et al. 2000

Journal of the Meteorological Society of Japan

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“…Furthermore, the high sensitivity of the second-order flow to a fine structure in the eddy PV flux divergence field will suggest that the downgradient eddy PV flux divergence structure upstream of the blocking flow does not necessarily imply the enforcement of the blocking flow by the synoptic eddies; observational studies (e.g., Shutts 1986;Mullen 1987) usually insist the enforcement only by indicating such a PV flux divergence field, or the corresponding geopotential tendency field simply obtained with an inverse Laplacian operator. In order to designate a large difference between the second-order flow and the tendency field from the PV flux divergence field, Fig.…”

Section: Discussionmentioning

confidence: 99%

On the Effectiveness of the Eddy Straining Mechanism for the Maintenance of Blocking Flows.

Arai

Mukougawa

2002

Journal of the Meteorological Society of Japan

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In connection with the maintenance of blocking flows by the migrating synoptic disturbances, we examine the effectiveness of the eddy straining mechanism proposed by Shutts (1983) in an equivalent barotropic b-channel model. The model used here is identical to that in Haines and Marshall (1987) (hereafter referred to as HM) except with a channel twice as wide.This model possesses two stationary solutions accompanying isolated structures in prescribed uniform westerlies when a vorticity forcing associated with the analytical modon solution is assumed: ''blocking solution'' similar to the modon solution and ''zonal flow solution'' characterized by dominant zonal flows. The infinitesimal transient eddies which mimic synoptic disturbances are generated by a wavemaker forcing located far upstream of the diffluence associated with the basic flow prescribed by stable stationary solutions. The effectiveness of the eddy straining mechanism is evaluated from the resemblance between the basic flow and the second-order flow induced by the time-averaged eddy potential vorticity (PV) flux divergence.The distribution of the time-averaged PV divergence for the blocking solution in our model is the same as in HM in a sense that there is a PV north/south, divergence/convergence dipole upstream of the diffluence of the basic flow. However, the computed second-order flow has a quadruple structure which tends to shift the blocking dipole downstream instead of the dipole structure enforcing the blocking as shown in HM. On the other hand, the second-order flow tends to maintain a weak diffluence associated with the zonal solution. Thus, the effectiveness of the eddy straining mechanism depends on the basic flow. The second-order flow for the blocking solution is also drastically deformed by a negligible distortion of the PV divergence field associated with a small change in the property of imposed eddies. The effectiveness of the eddy straining mechanism depends also on the property of synoptic eddies.Finally, this study suggests that the PV north/south, divergence/convergence dipole pattern does not necessarily maintain the blocking dipole. This remark is especially important for the observational study to assess the role of synoptic disturbances in the maintenance of blocking flows.

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“…5), the anomalous divergence leads to the amplification and westward expansion of positive Z300 anomalies in the eastern North Pacific by the following month ( Figs. 3c and 3d; Hoskins et al 1983;Mullen 1987). The detailed change from Fig.…”

Section: Precursors and The Development Of Eof1 And Eof2mentioning

confidence: 95%

“…4) were amplified westward with the guided activation of TEs in the west like the development of blocking with TEs (Hoskins et al 1983;Mullen 1987). To verify this hypothesis, we evaluated the baroclinic instability in the lower troposphere (850−700 hPa) (BI) through the Eady growth rate maximum (Lindzen and Farrell 1980;Hoskins and Vales 1990), which is expressed as follows:…”

Section: Precursors and The Development Of Eof1 And Eof2mentioning

confidence: 99%

A Precursor of the Monthly-Mean Large-Scale Atmospheric Circulation Anomalies over the North Pacific

Tomita

Yamaura

2017

SOLA

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The North Pacific shows dominant monthly-mean largescale atmospheric circulation anomalies, even after removing the variabilities of the Northern Hemisphere annular mode and the El Niño/Southern Oscillation. This work examines the precursors and their development for these residual anomalous circulations by applying objective reanalysis data to empirical orthogonal function (EOF) analysis. The first EOF mode (EOF1) features a monopole, while a dipole characterizes the second EOF mode (EOF2) over the North Pacific. Transient eddies (TEs) interactively induce the two EOF modes.The precursors of EOF1 and EOF2 are detected in the anomalies of one month earlier; these are the systematic zonal bands detected in surface temperature and baroclinic instability (BI) in the lower troposphere over Eurasia and North America. The BI anomalies further extend into the central North Pacific at different latitudes between EOF1 and EOF2. Coherent zonal bands also appear in the geopotential height anomalies of upper troposphere. Such zonal bands reflect the ovalization of Arctic circumpolar circulation with different continent-ward shifts of the longer axis. The direction of this shift determines which EOF mode develops by the following month through the guided activation of TEs at a designated latitude over the North Pacific.(Citation: Tomita, T., and T. Yamaura, 2017: A precursor of the monthly-mean large-scale atmospheric circulation anomalies over the North Pacific. SOLA, 13, 85−89,

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Transient Eddy Forcing of Blocking Flows

Cited by 133 publications

References 0 publications

Relationship between Singular Modes of Blocking Flow and High-frequency Eddies

Relationship between Singular Modes of Blocking Flow and High-frequency Eddies

On the Effectiveness of the Eddy Straining Mechanism for the Maintenance of Blocking Flows.

A Precursor of the Monthly-Mean Large-Scale Atmospheric Circulation Anomalies over the North Pacific

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