Colorado State University Tropical Weather and Climate Research


Multi-scale interaction

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How the wave pouch and vertical wind shear interactions play important roles in cyclongenesis in multi-scales?


Group Members: C. Chelsea Nam , Michael Bell

Tropical cyclogenesis of pre-depression Hagupit was delayed while it interacted with upper-level trough, experiencing strong VWS. For the downscale cascade from the synoptic to meso-alpha scale, our analysis showed that pre-depression Hagupit was significantly affected by the strong northwesterly vertical wind shear. However, Hagupit survived through the hostile, strongly sheared environment, and eventually developed into a tropical cyclone after it escaped from the influence of upper-level trough. The upscale cascade from the persistent deep convection and its vorticity amplification through vortex tube stretching was a key process that enabled the pouch to persist even under 20 m/s VWS. We highlight the roles of localized low-level shear and cumulus congestus clouds inside the wave pouch as the localized vertical vorticity generated from the convective cells is aggregated through a vortex merger process inside the marsupial pouch.

How do the precursor waves develop prior to Tropical Cyclogenesis?


Group Members: C. Chelsea Nam , Michael M. Bell

PISTON 2018 saw enhanced seasonal vorticity anomaly over western North Pacific that supports easterly wave propagation. Invest98 was an interesting cast that the disturbance was intensifying after spinning up from Super Typhoon Jebi's rainband. Invest98 produced more than 200mm rain over our shipborne Sea-Pol radar. Convective systems ranging from isolated to linearly organized MCS. With this case study, we aim to learn more about the multi-scale TC genesis problem, bridging the gap between large-scale wave mode and meso-scale convection.