Although the spatial resolution of the global ECMWF model is not very high, an indication of a Stau process can be seen in vertical cross sections. The edge of the Stau 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 Stau 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 Stau 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.

Relative humidity

Divergence

Vertical motion