The vorticity budget of developing typhoon Nuri (2008)

Abstract

Abstract. The formation of west Pacific tropical cyclone Nuri (2008) was observed over four days from easterly wave to typhoon stage by aircraft using scanning Doppler radar and dropsonde data. This disturbance developed rapidly in a significantly sheared environment. In spite of the shear, overlapping closed circulations existed in the frame of reference of the storm in the planetary boundary layer and at 5 km elevation, providing a deep region protected from environmental influences. The rapid spinup of Nuri can be attributed to the strong increase with height at low levels of the vertical mass flux during and after the tropical depression stage, and the correspondingly strong vorticity convergence in the planetary boundary layer. As Nuri developed, convective regions of boundary layer vortex stretching became fewer but more intense, culminating in a single nascent eyewall at the tropical storm stage. A non-developing tropical wave case was also analyzed. This system started with much weaker circulations in the boundary layer and aloft, leaving it unprotected against environmental intrusion. This may explain its failure to develop.

The Pre-Depression Investigation of Cloud-Systems in the Tropics (PREDICT) Experiment: Scientific Basis, New Analysis Tools, and Some First Results

“…The new model finds strong support in the four-season observational survey of the Atlantic and eastern Pacific sectors carried out by DMW09, two recent case studies in the western Pacific sector during the Tropical Cyclone Structure 2008 (TCS08) field experiment (Montgomery et al 2010a;Raymond and López-Carillo 2011), the post-analysis of the 2009 PREDICT Dry Run (Wang et al 2011), and realcase and idealized high-resolution numerical model simulations (Wang et al 2010a,b;Montgomery et al 2010b;Fang andZhang 2010, 2011). Together, these studies point to the pouch center as the preferred location (or "sweet spot") for cyclogenesis, serving as a "focal point" for an upscale vorticity aggregation process while the wave pouch and proto-vortex move together.…”

Tropical low formation during the Australian monsoon: the events of January 2013 (paper updated July 2016)

“…The vorticity tendency equation in pressure coordinates has a particularly concise form in which the local tendency can be written as the horizontal divergence of a horizontal flux (Haynes and McIntyre 1987;Raymond and Lopez-Carillo 2011;Tory et al 2012;Raymond et al 2014). Specifically, the equation for the local tendency of absolute vorticity ζ a may be written as…”

The importance of low-deformation vorticity in tropical cyclone formation

“…The importance of recirculating flow in quasi-closed circulations for the development of tropical cyclones in tropical waves has been the subject of a number of recent studies Montgomery et al, 2010;Raymond and López Carrillo, 2011). The quasi-circulation contains an enhanced vortical environment that provides the background vorticity from which the TC vortex is constructed, and it offers protection from the intrusion of dry air that might disrupt the developing circulation.…”

“…Raymond and López Carrillo (2011) have shown that vertical alignment of the pouch is not critical, but suggests there should be some overlap. This result is consistent with our experience, using data interpolated to a 1 • × 1 • grid, that an overlap which encompasses at least 2 neighbouring grid points is generally required.…”