Typical Appearance In Vertical Cross Sections
- Equivalent potential temperature: maximum gradient tilted downward in the frontal zone.
- Frontal slope: depends on the temperature contrast of air masses on both sides of the cold front. A higher/lower thermal contrast means lower/higher slope.
- Relative humidity: high on the front slope and low behind it.
- Temperature advection: maximum warm advection on top of the frontal zone, cold advection behind and below the frontal zone.
- Divergence: maximum surface convergence ahead of the front.
- Upward movement: maximum vertical motion on top of the frontal zone, these being higher in summer than winter. Downward motion below the frontal zone.
- Brightness temperature (IR images): minimum values (below -20°C) related to cloudiness in the frontal zone. In the region of deep convection the values are below -60°C. In the stratiform cloudiness values range between -30 and -40°C.
The following examples show two situations associated with the presence of cold fronts in central Argentina. The main difference is the steepness of the frontal zone slope, which is determined by the thermal contrast between both air masses (Margules, 1906). The slope of the cold fronts in winter/summer could be shallow/steep because of the high/low thermal contrast.
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6 February 2014/00.00 UTC - GOES 13 IR 10.7 image
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10 September 2015/00.00 UTC - GOES 13 IR 10.7 image
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Isentropes and Relative humidity
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Lon: 63°W. Equivalent potential temperature (K) in black, relative humidity (%) in blue and brightness temperature (°C) in yellow. 6 Feb 2014/00.00 UTC.
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Lon: 63°W. Equivalent potential temperature (K) in black, relative humidity (%) in blue and brightness temperature (°C) in yellow. 10 Sep 2015/00.00 UTC.
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Temperature advection
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Lon: 63°W. Equivalent potential temperature (K) in black, temperature advection (10 -4 °C/s) in red and brightness temperature (°C) in yellow . 6 Feb 2014/00.00 UTC.
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Lon: 63°W. Equivalent potential temperature (K) in black, temperature advection (10 -4 °C/s) in red and brightness temperature (°C) in yellow . 10 Sep 2015/00.00 UTC.
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Divergence
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Lon: 63°W. Equivalent potential temperature (K) in black, divergence (10-5 s-1) in magenta and brightness temperature (°C) in yellow. 6 Feb 2014/00.00 UTC.
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Lon: 63°W. Equivalent potential temperature (K) in black, divergence (10-5 s-1) in magenta and brightness temperature (°C) in yellow. 10 Sep 2015/00.00 UTC.
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Vertical motion
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Lon: 63°W. Equivalent potential temperature (K) in black, omega (Pa/s) shaded and brightness temperature (°C) in yellow. 6 Feb 2014/00.00 UTC.
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Lon: 63°W. Equivalent potential temperature (K) in black, omega (Pa/s) shaded and brightness temperature (°C) in yellow. 10 Sep 2015/00.00 UTC.
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