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The existence and production of reduced upper-tropospheric potential vorticity (RUPV) by heating is considered. An objective technique is used that identifies anomalies of PV arising from a particular physical process (here latent heat release). The evolution of two RUPV anomalies and a related diabatically increased lower-tropospheric PV (ILPV) anomaly occurring during Intensive Observing Period One of the cyclones from the Fronts and Atlantic Storm Track Experiment (FASTEX) is examined using model analyses, sounding data, and trajectory calculations. Three distinct airflows are identified emanating from the ILPV anomaly each with a different evolution. Results show that RUPV anomalies exist in the atmosphere and, in a weaker form, in numerical models. The dynamical role of RUPV anomalies is examined using a nonlinear balance PV inversion and reruns of the U.K. Meteorological Office Limited Area Model. This shows that instantaneously the flow and temperature perturbations associated with RUPV anomalies are of at least comparable magnitude and extent to those induced by a similar positive anomaly. Over time one RUPV anomaly is seen to have a significant effect upon the development of its parent low. This low is more compact and more rapidly developing in the absence of the anomaly. The effect of the positive anomaly is also significant, but removing it has only a short-term effect as the anomaly quickly reforms. These results show that it is important to consider the role of RUPV in the PV model of a midlatitude cyclone.
Pomroy et al. (Thu,) studied this question.