Characteristics of gravity waves generated in the jet-front system in a baroclinic instability simulation

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Abstract

An idealized baroclinic instability case is simulated using a ∼10 km resolution global model to investigate the characteristics of gravity waves generated in the baroclinic life cycle. Three groups of gravity waves appear around the high-latitude surface trough at the mature stage of the baroclinic wave. They have horizontal and vertical wavelengths of 40-400 and 2.9-9.8 km, respectively, in the upper troposphere. The two-dimensional phase-velocity spectrum of the waves is arc shaped with a peak at 17 m s-1 eastward. These waves have difficulty in propagating upward through the tropospheric westerly jet. At the breaking stage of the baroclinic wave, a midlatitude surface low is isolated from the higher-latitude trough, and two groups of quasi-stationary gravity waves appear near the surface low. These waves have horizontal and vertical wavelengths of 60-400 and 4.9-14 km, respectively, and are able to propagate vertically for long distances. The simulated gravity waves seem to be generated by surface fronts, given that the structures and speeds of wave phases are coherent with those of the fronts.

Figures

  • Figure 1. Background fields of the pressure (black contour) and horizontal wind speed (shading) at z= 0.25, 2, 5, and 8 km (from bottom to top) on days 4, 5, 6, and 7 at 12:00 UTC (from left to right). The background potential temperature is also plotted at z= 0.25 km (red contour). The contour intervals for the pressure and potential temperature are 8 hPa and 8 K, respectively.
  • Figure 2. Perturbation vertical velocity (w′) at z= 8 km (shading) superimposed on the 250 m background pressure (black) and potential temperature (green) from 12:00 UTC on day 4 to 00:00 UTC on day 8. The figures are shown with 12 h intervals before 00:00 UTC on day 6 and with 6 h intervals afterward. The contour intervals for the pressure and potential temperature are 8 hPa and 8 K, respectively.
  • Figure 3. (a)w′ at z= 8 km when the magnitude ofw′ is largest for each of the five wave groups (W1–W5, see the text) (from top to bottom) and (b) enlargements of the green boxes in (a). (c) Cross sections of w′ along the green lines in (b) with respect to the time relative to the instants in (a) and (b). w′ in (c) is normalized by its maximum, and the normalized w′ for W4 is further divided by 5 for display purposes.
  • Figure 4. Twelve-hour averaged power spectra of w′ at z= 8 km as a function of zonal and meridional wavenumbers calculated in (a) 48– 73◦ N, 20–60◦ E and (b) 21–46◦ N, 20–60◦ E from day 6 to day 8 (from left to right). In (b), the plot for 00:00–12:00 UTC on day 6 is omitted.
  • Figure 5. w′ at z= 8 km (shading) (a) at 00:00 UTC on day 7, reconstructed from the three spectral domains (1–3) indicated in Fig. 4a, and (b) at 12:00 UTC on day 7, from the two spectral domains (4 and 5) in Fig. 4b. The background pressure at 250 m is superimposed (contour) with intervals of 8 hPa. The green lines indicate the axes along which the vertical cross sections are shown in Fig. 11.
  • Figure 6. Horizontal-wavelength power spectra of w′ at z= 8 km averaged over 24 h from 12:00 UTC on day 6 for W1 (red), W2 (yellow), and W3 (green) and from 00:00 UTC on day 7 for W4 (blue) and W5 (black). The spectra for W1–W5 were obtained from the spectral domains 1–5 indicated in Fig. 4, respectively. For W4, the power spectrum is divided by 2.
  • Table 1. Characteristics of the five groups of simulated gravity waves at z= 8 km. The values in bold indicate the primary peaks obtained from the spectra for each characteristic.
  • Figure 7. Power spectra of w′ at z= 8 km as a function of phase speed and propagation direction calculated in (a) 48–73◦ N, 20–60◦ E and (b) 21–46◦ N, 20–60◦ E. The rightmost panels were obtained using all pairs of (k, l), and the other panels are for W1, W2, and W3 in (a) and for W4 and W5 in (b).

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APA

Kim, Y. H., Chun, H. Y., Park, S. H., Song, I. S., & Choi, H. J. (2016). Characteristics of gravity waves generated in the jet-front system in a baroclinic instability simulation. Atmospheric Chemistry and Physics, 16(8), 4799–4815. https://doi.org/10.5194/acp-16-4799-2016

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