The life cycle of the intense IOP-14 storm during CASP II. Part II: Sensitivity experiments

Abstract

In this paper, two consecutive (48- and 54-h) predictions of the IOP-14 storm during the Canadian Atlantic Storm Program II (CASP II) with a mesoscale version of the Canadian Regional Finite-Element (RFE) model are used as control runs to investigate the sensitivity of the cyclone development to different initial conditions and various physical and dynamical processes. It is shown that obtaining appropriate initial conditions is crucial in helping to improve the operational predictions of initial cyclogenesis and its subsequent amplification, particularly for travelling disturbances that propagate from upstream data-sparse regions. It is found that at the cyclone's mature stage i) dry dynamics account for more than 70% of the cyclone's total depth; ii) the RFE model predicts the weakest (+32 hPa) and deepest (–12 hPa) storms (with respect to the control-predicted) in the absence of the oceanic surface characteristics and Greenland topography, respectively; iii) concurrent surface sensible and latent heat fluxes have relatively weak positive impacts (–5 hPa) on the explosive deepening of the storm; iv) all experimental storms except for the no-ocean-surface run satisfy the “oceanic bomb” criterion; and v) the observed and predicted non-classical frontal structures, such as the cold frontal “fracture”, the “bent-back” warm front, the “T-bone” thermal pattern and warm core structure, fail to develop in the absence of the oceanic surface characteristics. The results reveal that i) the IOP-14 storm is baroclinically driven in nature and it is only modulated by other physical processes and ii) the explosively deepening nature and the previously documented non-classical frontal structures appear to result from weak surface drag over the ocean. © 1996 Taylor & Francis Group, LLC.