27 February 2004: 00 UTC

Potential Vorticity

Isolines of the potential vorticity (green) show a positive anomaly behind the cloud band of the developing cyclone (seen as the higher values of IR and WV grey shades - orange lines). The value of PV equals 1 is considered to be a measure for stratospheric air. In this case, in the region of the developing cyclone there is an intrusion of stratospheric air, i.e. lowering of the tropopause, down to 550 hPa. The fact that dry air is protruding can also be confirmed by rather low values of WV-signal, in the VCS as the orange thick line, in the region of the anomaly. Besides this upper-level anomaly, there are also rather high values of PV near the ground. According to Hoskins theory, positive anomalies of PV are a good indicator for cyclogenesis.

Vorticity Advection

The highest values of Positive Vorticity Advection (PVA) are found in the region very close to the cloud band, with PVA values getting bigger with height. According to the equation of motion, positive change of vorticity advection with height contributes to upward motion, therefore development can be expected in this region. Theoretical background of this concept can be found in Manual of Synoptic Satellite Meteorology in the chapter BASICS. On the other hand there are negative values of vorticity advection further behind the cloud band, indicating sinking in that region. This sinking coincides with the dry air intrusion showed by Potential Vorticity anomaly.

Temperature advection

Temperature advection field shows a typical distribution with the warm advection in the region of the cloud band, especially in the upper levels and very strong cold advection behind. According to the theoretical approach, which can be found in Manual of Synoptic Satellite Meteorology in the chapter BASICS, development is expected in the regions of strong warm advection. The cold advection is, on the other hand, related to sinking motion.