NON-OROGRAPHIC CONVERGENCE LINES - KEY PARAMETERS

by ZAMG


Typical synoptic environment

Convective lines in advance of frontal cloud bands

09 June 1999/12.00 UTC - Meteosat VIS image; blue: thermal front parameter 700 hPa, red: temperature advection 700 hPa, green: equivalent thickness 700 hPa
The example shows the prefrontal Convergence Lines situated within weak Warm Advection (WA), an equivalent thickness ridge, and in front of the maximum of TFP.

Convective lines in cold air behind Cold Fronts

08 August 1999/12.00 UTC - Meteosat VIS image; red: temperature advection 700 hPa
The Convergence Lines are situated within cold advection.

Pre-frontal Convergence Line

Typical distribution of wind field, divergence and upward motion

09 June 1999/12.00 UTC - Meteosat VIS image; green: wind vectors 925 hPa
Westerly winds to the west, easterly winds to the east of the convergence cloud band result in convergence at lower levels.
09 June 1999/12.00 UTC - Meteosat VIS image; cyan solid: convergence 925 hPa, cyan dashed: divergence 925 hPa
At 925 hPa the image shows strong convergence at the Convergence Lines, whilst at the frontal cloud band, no marked convergence can be found at this height.
09 June 1999/12.00 UTC - Meteosat VIS image; yellow solid: upward motion 925 hPa, yellow dashed: downward motion 925 hPa
The vertical motion at 925 hPa corresponds to the divergence field below. There is strong upward motion at the Convergence Lines, while only weak upward motion or even subsidence is observed in the frontal cloud band.

Post-frontal Convergence Line

13 August 1999/12.00 UTC - Meteosat VIS image; green: wind vectors 925 hPa
The wind vectors show westerly winds decreasing to the east.
13 August 1999/12.00 UTC - Meteosat VIS image; cyan solid: convergence 925 hPa, cyan dashed: divergence 925 hPa
The image shows convergence prevailing at Convergence Lines although the line structure is not reflected in the model field. At higher levels, less convergence and a larger area of divergence is seen.
13 August 1999/12.00 UTC - Meteosat VIS image; yellow solid: vertical motion - upward motion 925 hPa, yellow dashed: vertical motion - downward motion 925 hPa
The field of vertical motion corresponds with the field of divergence. At the lower level there is a large area of upwards motion, whereas there is more downward motions at higher levels.

The post frontal Convergence Lines are not as well marked as pre frontal lines. They also show less convective activity.


SUB-MENU OF NON-OROGRAPHIC CONVERGENCE LINES
METEOROLOGICAL PHYSICAL BACKGROUND
TYPICAL APPEARANCE IN VERTICAL CROSS SECTIONS