Tropical cyclogenesis in a tropical wave critical layer: easterly waves

摘要: Abstract. The development of tropical depressions within waves over the Atlantic and eastern Pacific is usually preceded by a "surface low along wave" as if to suggest hybrid wave-vortex structure in which flow streamlines not only undulate with waves, but form closed circulation lower troposphere surrounding low. This structure, equatorward easterly jet axis, identified herein familiar critical layer shear flow, configuration arguably provides simplest conceptual framework for cyclogenesis resulting from their interaction mean diabatic processes associated deep moist convection. recirculating Kelvin cat's eye represents sweet spot proto-vortex may grow its parent wave. A common location storm given intersection wave's latitude trough axis at center eye, analyzed vorticity centroid nearby. wave vortex live together time, initially propagate approximately same speed. In most cases this coupled propagation continues few days after depression identified. For name suggests, westward. It shown that order visualize optimally Lagrangian motions, one should view streamlines, or stream function, frame reference translating horizontally phase co-moving frame, are equivalent particle trajectories. quasi-stationary, dividing streamline separates air outside. important because (i) region cyclonic weak deformation resolved (ii) containment moisture entrained developing gyre and/or lofted convection therein, (iii) confinement mesoscale aggregation, (iv) predominantly convective type heating profile, (v) maintenance enhancement until becomes self-sustaining entity emerges depression. entire sequence likened marsupial infant mother's pouch. These ideas formulated three new hypotheses describing kinematics dynamics, thermodynamics wave/vortex interactions comprising "marsupial paradigm". survey 55 named storms 1998–2001 reveals actual layers sometimes resemble ideal east-west train eyes, less regular, more recirculation regions frame. isolated proto-vortices carried also can be visualized near speed proper translation speeds vary height owing vertical interaction. Some implications entrainment/containment discussed perspective, based on observational survey.