Tropical cyclogenesis

About: Tropical cyclogenesis is a research topic. Over the lifetime, 1195 publications have been published within this topic receiving 44011 citations.

Global view of the origin of tropical disturbances and storms

Abstract: A global observational study of atmospheric conditions associated with tropical disturbance and storm development is presented. This study primarily uses upper air observations which have become available over the tropical oceans in the last decade. Climatological values of vertical stability, low level wind, tropospheric vertical wind shear and other parameters relative to the location and seasons of tropical disturbance and storm development are discussed. Individual storm data are also presented in summary form for over 300 development cases (with over 1,500 individual observation times) for four tropical storm genesis areas. Results show that most tropical disturbances and storms form in regions equatorward of 20° lat. on the poleward side of doldrum Equatorial Troughs where the tropospheric vertical shear of horizontal wind (i.e., baroclinicity) is a minimum or zero. Storm development occurring on the poleward side of 20° lat. in the Northwest Atlantic and North-west Pacific takes place unde...

An Air-Sea Interaction Theory for Tropical Cyclones. Part I: Steady-State Maintenance

Abstract: Observations and numerical simulators of tropical cyclones show that evaporation from the sea surface is essential to the development of reasonably intense storms. On the other hand, the CISK hypothesis, in the form originally advanced by Charney and Eliassen, holds that initial development results from the organized release of preexisting conditional instability. In this series of papers, we explore the relative importance of ambient conditional instability and air-sea latent and sensible heat transfer in both the development and maintenance of tropical cyclones using highly idealized models. In particular, we advance the hypothesis that the intensification and maintenance of tropical cyclones depend exclusively on self-induced heat transfer from the ocean. In this sense, these storms may be regarded as resulting from a finite amplitude air-sea interaction instability rather than from a linear instability involving ambient potential buoyancy. In the present paper, we attempt to show that reasona...

The increasing intensity of the strongest tropical cyclones

Abstract: Atlantic tropical cyclones are getting stronger on average, with a 30-year trend that has been related to an increase in ocean temperatures over the Atlantic Ocean and elsewhere. Over the rest of the tropics, however, possible trends in tropical cyclone intensity are less obvious, owing to the unreliability and incompleteness of the observational record and to a restricted focus, in previous trend analyses, on changes in average intensity. Here we overcome these two limitations by examining trends in the upper quantiles of per-cyclone maximum wind speeds (that is, the maximum intensities that cyclones achieve during their lifetimes), estimated from homogeneous data derived from an archive of satellite records. We find significant upward trends for wind speed quantiles above the 70th percentile, with trends as high as 0.3 +/- 0.09 m s(-1) yr(-1) (s.e.) for the strongest cyclones. We note separate upward trends in the estimated lifetime-maximum wind speeds of the very strongest tropical cyclones (99th percentile) over each ocean basin, with the largest increase at this quantile occurring over the North Atlantic, although not all basins show statistically significant increases. Our results are qualitatively consistent with the hypothesis that as the seas warm, the ocean has more energy to convert to tropical cyclone wind.

On the Growth of the Hurricane Depression

Abstract: Why do cyclones form in a conditionally unstable tropical atmosphere whose vertical thermal structure is apparently more favorable to small-scale cumulus convection than to convective circulations of tropical cyclone scale? It is proposed that the cyclone develops by a kind of secondary instability in which existing cumulus convection is augmented in regions of low-level horizontal convergence and quenched in regions of low-level divergence. The cumulus- and cyclone-scale motions are thus to be regarded as cooperating rather than as competing–the clouds supplying latent heat energy to the cyclone, and the cyclone supplying the fuel, in the form of moisture, to the clouds. A scale-analysis indicates that it is appropriate to use the balance equations of Eliassen for the macro-motion; in this case the effect of friction in the boundary-layer may be incorporated as a condition on the vertical velocity at the top of the boundary layer. It is argued that the mean humidity in a system of convecting cum...

A Vortical Hot Tower Route to Tropical Cyclogenesis.

Abstract: A nonhydrostatic cloud model is used to examine the thermomechanics of tropical cyclogenesis under realistic meteorological conditions. Observations motivate the focus on the problem of how a midtropospheric cyclonic vortex, a frequent by-product of mesoscale convective systems during summertime conditions over tropical oceans, may be transformed into a surface-concentrated (warm core) tropical depression. As a first step, the vortex transformation is studied in the absence of vertical wind shear or zonal flow. Within the cyclonic vorticity-rich environment of the mesoscale convective vortex (MCV) embryo, the simulations demonstrate that small-scale cumulonimbus towers possessing intense cyclonic vorticity in their cores [vortical hot towers (VHTs)] emerge as the preferred coherent structures. The VHTs acquire their vertical vorticity through a combination of tilting of MCV horizontal vorticity and stretching of MCV and VHT-generated vertical vorticity. Horizontally localized and exhibiting conve...