Key Parameters

  • Isotachs (at 300 hPa, 250 and 200 hPa can all be considered)
    • Indications of jet intensity and the location of entrance and exit regions
    • Jet Fibres form very near to the jet maximum
  • Shear vorticity (zero-line of shear vorticity at 300 hPa)
    • Indication of jet axis
    • Zero-line of shear vorticity is parallel to both Jet Fibre and the WV Dark Stripe

In cases where Fibres are associated with the Warm Front, they appear mostly in the leading part of the jet streak. In cases of the Cold Front, Fibres usually lie within the wind maximum or in the entrance region of the jet streak.

When compared to jet axes, Fibres can in most cases be found along the zero-line of shear vorticity or slightly shifted to the anticyclonic side of the jet. Some exceptions occur in Warm Front cases (see Meteorological Physical Background ).

06 November 2003/ 06.00 UTC - Meteosat IR image, yellow: isotachs, violet: zero line of shear vorticity 300 hPa

The diagrams above show the location of wind maximum and zero-line of shear vorticity behind Ana and Kata Cold Fronts. Fibres form in the entrance region or adjacent to the jet streak.

17 June 2003/12.00 UTC - Meteosat IR image; yellow: isotachs, violet: zero line of shear vorticity 300 hPa

In the Warm Front case, the jet axis follows the cloud band along the cyclonic side. Fibres mostly form in the leading part of the jet streak and mostly on the anticyclonic side, but there are some exceptions (see Meteorological Physical Background ).

Supporting Parameters

  • Relative humidity - necessary condition for the formation of clouds
    Distribution of humidity in the model fields is governed by the synoptic scale features with which Fibres are associated.
  • Warm conveyor belt - the Jet Fibre coincides with the limiting streamline.

06 November 2003/06.00 UTC - Meteosat IR image, blue: relative humidity 300hPa
17 June 2003/12.00 UTC - Meteosat IR image, blue: relative humidity 300hPa
05 November 2003/06.00 UTC - Meteosat IR image; magenta: relative streams 304K - system velocity 216° 12 m/s; yellow: isobars 304K