Typical Appearance In Vertical Cross Sections

Although the spatial resolution of the global ECMWF model is not very high, an indication of a Barrage process can be seen in vertical cross sections. The edge of the Barrage Cloud towards the lee side is displayed in a satellite image as a sharp decrease of IR values, indicating the position of the main mountain chain.

  • Isentropes:
    • Flat minimum of equivalent potential temperature on the windward side of the mountain ridge
  • Relative humidity:
    • A maximum of relative humidity on the windward side indicates the position of the Barrage cloud and the area of confluence
    • A maximum towards higher levels indicates the ascent of humid air during the flow over the barrier
  • Divergence:
    • A distinct maximum of convergence at low levels confirms confluence in the windward Barrage area
    • At higher levels on the windward side a minimum can be seen which is in accordance with the concept of compensation of convergence at upper levels.
    • The opposite process takes place on the lee side with a maximum of convergence at upper levels and a minimum below.
  • Vertical motion:
    • A maximum of upward motion can be seen directly over the wind ward mountain slopes
    • On the lee side the maximum of upward vertical motion is positioned at higher levels with sinking air below.

12 January 2007/12.00 UTC - Meteosat 8 IR10.8 image; position of vertical cross section indicated

Relative humidity
12 January 2007/12.00 UTC - Vertical cross section; black: isentropes (ThetaE); blue: relative humidity; orange thin: IR pixel values;

Divergence
12 January 2007/12.00 UTC - Vertical cross section; black: isentropes (ThetaE); magenta: divergence, thick: convergence; orange thin: IR pixel values;

Vertical motion
12 January 2007/12.00 UTC - Vertical cross section; black: isentropes (ThetaE); cyan thick: vertical motion (omega) - upward motion, cyan thin: vertical motion (omega) - downward motion; orange thin: IR pixel values;