Example: 16 December 2011

Kelvin-Helmholtz waves also exist in lower atmospheric levels as shown in the example below from Birmingham, Alabama in December 2011 (figure 7). The wind blows over a cold near-surface cloud layer. On top of the cloud layer, at the level of the temperature inversion, vertical wind shear generates waves.

Figure 7: Kelvin-Helmholtz waves over Birmingham, Alabama on 16 December 2011. ©ABC 33/40-TV.

Figure 8 shows the corresponding sounding (17 December 2011 at 00 UTC) from the nearby Shelby County Airport. A low level inversion can be detected at around 900 hPa with a vertical wind shear of about 15 knots (5 knots below and 20 knots above the inversion). This is approximately the height of the wave base observed in figure 7.

Figure 8: Sounding from 17 December 2011 at 00 UTC at Shelby County Airport (Alabama)