Key Parameters

  • Height contours at 1000 hPa
  • Subsidence:
    • Divergence (lower troposphere). For detection of large-scale subsidence.
    • Vertical wind speed
  • Temperature advection:
    Cold advection (lower troposphere). For detection of areas with shallow cold advection.
  • Low-level humidity:
    Moisture in boundary layer is needed for development and maintenance of stratocumulus.
  • Middle-level humidity:
    Low values of humidity in layers above BL indicate subsidence.
  • Temperature inversion height
  • Temperature inversion strength
  • Sea temperature
  • Difference of sea temperature and dew point of air at surface
  • Surface wind (direction/speed)

Absolute topography at 1000 hPa

04 February 2006/12.00 UTC - Meteosat HRVis image; magenta: height contours 1000 hPa

Especially in an extensive area of high pressure (see image: above Ireland and Bay of Biscay) or in a ridge of high pressure (west of coast of Portugal) SC sheets can be found.

Divergence

04 February 2006/12.00 UTC - Meteosat 10.8 image; magenta solid: divergence 850 hPa, magenta dashed: convergence 850 hPa

Divergence at 850 hPa is indicative for subsidence in high pressure area.

Vertical Velocity (850 hPa)

04 February 2006/12.00 UTC - Meteosat 10.8 image; yellow dashed: vertical downwards velocity 850 hPa, yellow solid: vertical upwards velocity 850 hPa

Downward motion at 850 hPa is showing subsidence and is causing an subsidence-inversion beneath moist is trapped and causing Sc clouds.

Temperature Advection

04 February 2006/12.00 UTC - Meteosat 10.8 image; red dashed: temperature advection - CA, red solid: temperature advection - WA

Cold Advection in lower levels is cooling the atmosphere and with moist advection is causing cloud development under an inversion.

Relative Humidity at 850 and 1000 hPa

04 February 2006/12.00 UTC - Meteosat 10.8 image; blue: relative humidity 850 hPa
04 February 2006/12.00 UTC - Meteosat 10.8 image; blue: relative humidity 1000 hPa

Dry air above and moist air below the inversion is indicative for Sc Sheets.

Temperature inversion height and strength

04 February 2006/12.00 UTC - Radio Sounding Camborne

Strong subsidence inversion is shown in the Stüve Sounding diagram of Camborne (SW England) 04 February 2006. Quite clear is seen that moist (SC cloudiness) is trapped under this inversion.

Surface wind (direction and speed)

19 January 2010/12.00 UTC - HRVis Surface winds (flags in green) and surface isobars (black)

Wind speed at the surface under the subsidence inversion is in this case of 19 Jan 2010, and quite often in other situations, about 10-15 kts.