Key Parameters

  • Bonner criterion 1 is used to identify the SALLJ events and requires the following:
    • Isotachs at 850 hPa: maximum wind intensity equal to or greater than 12 m/s.
    • Wind shear 850-700 hPa: the wind speed difference between 850 and 700 hPa equal to or greater than 6 m/s in some part enclosed by the 12 m/s isotach.
    • Wind vectors at 850 hPa: the meridional component must be northerly and greater than the zonal component in the entire region enclosed by the 12 m/s isotach.
  • Equivalent thickness 850-500 hPa: maximum gradient in the frontal zone.
  • Thermal front parameter (TFP): maximum values of TFP in the frontal zone.
  • Moisture convergence at 850 hPa: maximum moisture convergence ahead of the front.
  • Streamlines at 200 hPa: well-developed Bolivian High.
  • Isotachs at 250 hPa: upper level jet at the leading side of the mid-latitude trough.

NOTE: These key parameters are shown in the following example only for a Chaco Jet event, where the synoptic pattern is the most favourable for the atmosphere destabilization over Argentina.


Bonner Criterion 1: Wind shear 850-700 hPa, isotachs and wind vectors at 850 hPa.
28 February 2002/06.00 UTC - GOES 13 IR 10.8 image; blue: wind shear 850-700 hPa, red: isotach at 850 hPa, green vector: wind at 850 hPa.

Equivalent Thickness 850-500 hPa and TFP

28 February 2002/06.00 UTC - GOES 13 IR 10.8 image; green: equivalent thickness, blue: TFP.

Moisture convergence and Thetae at 850 hPa
28 February 2002/06.00 UTC - GOES 13 IR 10.8 image; magenta: equivalent potential temperature 850 hPa, yellow: humidity convergence, green vector: wind at 850 hPa.

Streamlines at 200 hPa and isotach at 250 hPa
28 February 2002/06.00 UTC - GOES 13 IR 10.8 image; yellow: isotachs at 250 hPa, green: streamlines at 200 hPa.