Research Article

Atmospheric blocking as a traffic jam in the jet stream

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Science  06 Jul 2018:
Vol. 361, Issue 6397, pp. 42-47
DOI: 10.1126/science.aat0721
  • Fig. 1 A blocked jet stream disrupts wave propagation.

    (A) Z500 (500-hPa geopotential height) (contours every 50 m) and horizontal wind speed (color) in the Northern Hemisphere extratropics for 7 January 2005 (18 UTC). The star identifies the center of a block. (B) As in (A) but for 26 January 2005 (06 UTC). (C) Z500 at 49.5°N as a function of longitude and time (1 December 2004 to 31 March 2005). The contour interval is 50 m. (D) As in (C) but for column LWA. In all panels, the zero longitude corresponds to the International Reference Meridian. Data were obtained by using the ERA-Interim reanalysis product (8).

  • Fig. 2 LWA and eastward wind covary negatively.

    (A) Color indicates the covariance between Embedded Image and Embedded Image in the boreal winter, and contours indicate DJF climatology of Embedded Image expressed in meters per second. The locations of peak covariance are labeled A (9°W, 45°N) and B (147°W, 42°N). Data were obtained by using the ERA-Interim reanalysis product for 1979 to 2016 (8). (B) Scatter diagram of 4-day average Embedded Image versus 4-day average Embedded Image for the same period at location B. The cyan box represents the DJF climatological mean. The red diamonds represent periods in which Embedded Image and Embedded Image are simultaneously in the top and bottom 5 percentiles, respectively, of all 858 sampled values (listed in tables S1 and S2). The orange line is a least-squares fit whose slope is indicated. (C) Same as (B) but for location A.

  • Fig. 3 LWA in climatology and blocked states.

    (A) DJF climatology of Embedded Image (color) and Z500 (contours, in meters) in the Northern Hemisphere extratropics. (B) Same as (A) but a composite of 24 anomalous Atlantic events. (C) Same as (A) but a composite of 22 anomalous Pacific events. The analysis locations (A and B) are the same as those in Fig. 2.

  • Fig. 4 LWA and its zonal flux at the jet exit.

    Relationships between Embedded Image (abscissa) and the flux terms on the RHS of Eq. 3 (ordinate). (A and B) 9°W, 45°N (location A). (C and D) 147°W, 42°N (location B). [(A) and (C)] Four-day averages of F1 + F3 (orange) and Embedded Image (blue) against the 4-day average of column LWA, sampled during DJF of 1979 to 2016. The red diamonds correspond to those in Fig. 2, B and C. [(B) and (D)] Diagrams simplifying (A) and (C) with a least-squares fit (orange), a chi-square fit with a parabolic curve (blue), and quartile plots. The quartile plots show maximum, minimum, and median values, together with the upper and lower quartiles of Embedded Image, for 10-ms−1 intervals of Embedded Image. Boxes and bars were not drawn if the interval contains fewer than five data points. The cyan squares in (A) and (C) and blue squares in (B) and (D) indicate the DJF climatological mean values.

  • Fig. 5 Composite life cycle of Atlantic blocks.

    (A) Composite longitude-time diagram of Embedded Image along 45°N for the 24 Atlantic events listed in table S1 in supplementary materials. The black contour indicates 60 ms−1. Day 0 corresponds to the peak of blocking. (B) Same as (A) but for Embedded Image. The white contour indicates 0. (C) Same as (A) but for Embedded Image. The gray and black contours indicate 0 and 600 m2 s−2, respectively.

  • Fig. 6 Blocking life cycle simulated by Eq. 4.

    (A) Longitude-time diagram of A = A0 + Â for a 1D experiment. The black contour indicates 52 ms−1. Day 0 corresponds to the peak of the wave event. (B) Same as (A) but for u. The white contour indicates 11 ms−1. (C) Same as (A) but for F. The contours indicate 608, 656, and 704 m2 s−2. In all panels, only a part of the computational domain is shown. See movie S1 for more details.

Supplementary Materials

  • Atmospheric blocking as a traffic jam in the jet stream

    Noboru Nakamura and Clare S. Y. Huang

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

    Download Supplement
    • Materials and Methods
    • Figs. S1 to S5
    • Tables S1 to S4
    • Caption for Movie S1
    • References

    Images, Video, and Other Media

    Movie S1
    1D experiment of blocking lifecycle
    This video shows the result of the 1D experiment of blocking lifecycle described in the main text. The horizontal axis is longitude (periodic, shifted in such a way as to map approximately the same range as Figs. 1a, 1b, and 2a). The stationary red curve is A0(x) (stationary wave component of LWA); the black curve is A = A0 + Â (total LWA). This curve represents the envelope of wave crests and does not include the phase structure of the waves. The blue curve is Ŝ (forcing; arbitrary unit). The experiment was initialized at Day –290 but shown only for Days –22 through +28. See Materials and Methods for the parameters used in the model
    Correction (22 June 2018): In a previous version of the supplementary materials, time t in eq. S14 was not defined relative to the beginning of the numerical integration. The timing of forcing was also displayed incorrectly in fig. S3 and movie S1. In the materials and methods, the list of symbols did not include a definition for cg. The supplementary materials have been corrected since First Release.
    The original PDF is accessible here and the movie here.

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