The wave-generated vertical displacements near the anvil base may aid band formation in the layer above.īands of anvil cirrus extending radially outward from regions of deep convection ( Fig. High-frequency gravity waves emanating from the parent deep convection are trapped in a layer of strong static stability and vertical wind shear beneath the near-neutral anvil and, consistent with satellite studies, are oriented approximately normal to the developing radial bands. The vertical shear in the MCS outflow is important not only in influencing the orientation of the radial bands but also for its role, through differential temperature advection, in helping to thermodynamically destabilize the environment in which they originate. The weak stratification of the anvil, the ratio of band horizontal wavelength to the depth of the near-neutral anvil layer (5:1 to 10:1), and band orientation approximately parallel to the vertical shear within the same layer are similar to corresponding aspects of horizontal convective rolls in the atmospheric boundary layer, which result from thermal instability. The simulated bands result from shallow convection in the near-neutral to weakly unstable MCS outer anvil. The 10–20-km horizontal spacing between the bands is also similar to typical spacing found in a recent satellite-based climatology of MCS-induced radial outflow bands. The timing, location, and orientation of these simulated bands are similar to those in satellite imagery for this case. A high-resolution convection permitting model is used to simulate bands of this type observed on 17 June 2005. Turbulence affecting aircraft is frequently reported within bands of cirrus anvil cloud extending radially outward from upstream deep convection in mesoscale convective systems (MCSs). The k −5/3 spectral density dependence on wavenumber line is shown for reference. (d) 1D power spectra of brightness temperature averaged in the y direction for the 90 km × 60 km regions of (a) and (b) at 0845 UTC (solid) and 0945 UTC (dashed). (c) Total cloud condensate (shaded) and meridional component of relative vorticity (contoured in intervals 2 × 10 −3 s −1, solid red contours positive, dashed blue contours negative) in a vertical cross section, oriented along line WE in (a), and averaged for 3 km in both directions across this line. The brightness temperature displayed in these panels is at full horizontal resolution. Simulated brightness temperature (shaded), moist static stability (blue contours with intervals of 2 × 10 −5 s −1 with negative values, N m 2 < 0, dashed), and 13–11.5-km MSL vertical wind difference vectors (red wind barb symbols) with a full barb = 10 m s −1 and a half barb = 5 m s −1 at (a) 0845 UTC and (b) 0945 UTC over the red dashed rectangular regions in Figs.
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