The origin and evolution of low‐level potential vorticity anomalies during a case of Tasman Sea cyclogenesis

• Published in: Tellus. Series A, Dynamic meteorology and oceanography Dynamic meteorology and oceanography, 1995-10, Vol.47 (5), p.779-796
• Main Authors: REVELL, MICHAEL J., RIDLEY, ROGER N.
• Format: Article
• Language: English
• Subjects: Earth, ocean, space; Exact sciences and technology; External geophysics; Marine; Meteorology; Other topics in atmospheric geophysics
• ISSN: 0280-6495; 1600-0870
• DOI: 10.1034/j.1600-0870.1995.00120.x

ABSTRACT The rapid development (15 hPa deepening in 12 hours) of an intense, shallow and small‐scale (∼ 300 km) cyclone off the east coast of Australia was studied, in the context of potential vorticity (PV) thinking. High‐resolution spatial and temporal fields generated by a mesoscale weather prediction model, embedded within ECMWF data were used. This case was well simulated, as verified by the few available observations at neighbouring stations, and by satellite imagery. The PV distribution within this cyclone was computed from the model fields and the origin of its component parts established using backward trajectories. These indicated that at low levels the primary mechanism of PV production was the vertical gradient of latent heat release in a frontal cloud band. Above the level of maximum heating this process reversed sign with corresponding destruction of PV. As the heating became shallow enough and intense enough a low level vortex formed with a vertical scale of 2–3 km and a wave‐CISK like normal mode structure. The length scale and growth rate of this mode agreed well with the observed cyclone, unlike the classical explanation for this type of development (the pure baroclinic instability mechanism of Charney and Eady) which, even including moisture, still predicts length scales of over a 1000 km and doubling times of at least a day.