The Diurnal Variation of Atlantic Ocean Tropical Cyclone aoud DistributionInferred from Geostationary Satellite Infrared Measurements

Steranka, J.; Rodgers, E. B.; Gentry, R. Cecil

doi:10.1175/1520-0493(1984)112<2338:tdvoao>2.0.co;2

Cited by 31 publications

(38 citation statements)

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“…This indicates that the boundary layer recovery was often significantly shorter than the diurnal cycle. Both diurnal and semi-diurnal cycles have been found in the areal extent of the upper level cirrus deck of fully developed tropical cyclones (Browner et al, 1977;Muramatsu, 1983;Lajoie and Butterworth, 1984;Steranka et al, 1984;Kossin, 2002). The results presented here for the early stage of a developing system may be relevant to these previous studies, although the existence of substantial convective downdrafts and cold pools in the core of developing tropical cyclones has not yet been established definitively.…”

Section: Discussionmentioning

confidence: 50%

An examination of two pathways to tropical cyclogenesis occurring in idealized simulations with a cloud-resolving numerical model

Nicholls

Montgomery

2013

Atmos. Chem. Phys.

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Simulations are conducted with a cloud-resolving numerical model to examine the transformation of a weak incipient mid-level cyclonic vortex into a tropical cyclone. Results demonstrate that two distinct pathways are possible and that development along a particular pathway is sensitive to model physics and initial conditions. One pathway involves a steady increase of the surface winds to tropical cyclone strength as the radius of maximum winds gradually decreases. A notable feature of this evolution is the creation of small-scale lower tropospheric cyclonic vorticity anomalies by deep convective towers and subsequent merger and convergence by the low-level secondary circulation. The second pathway also begins with a strengthening low-level circulation, but eventually a significantly stronger mid-level circulation develops. Cyclogenesis occurs subsequently when a small-scale surface concentrated vortex forms abruptly near the center of the larger-scale circulation. The small-scale vortex is warm core throughout the troposphere and results in a fall in local surface pressure of a few millibars. It usually develops rapidly, undergoing a modest growth to form a small tropical cyclone. Many of the simulated systems approach or reach tropical cyclone strength prior to development of a prominent mid-level vortex so that the subsequent formation of a strong small-scale surface concentrated vortex in these cases could be considered intensification rather than genesis.

Experiments are performed to investigate the dependence on the inclusion of the ice phase, radiation, the size and strength of the incipient mid-level vortex, the amount of moisture present in the initial vortex, and the sea surface temperature. Notably, as the sea surface temperature is raised, the likelihood of development along the second pathway is increased. This appears to be related to an increased production of ice. The sensitivity of the pathway taken to model physics and initial conditions revealed by these experiments raise the possibility that the solution to this initial value problem is near a bifurcation point. Future improvements to model parameterizations and more accurate observations of the transformation of disturbances to tropical cyclones should clarify the conditions that favor a particular pathway when starting from a mid-level vortex

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Section: Discussionmentioning

confidence: 50%

An examination of two pathways to tropical cyclogenesis occurring in idealized simulations with a cloud-resolving numerical model

Nicholls

Montgomery

2013

Atmos. Chem. Phys.

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“…Numerous studies utilizing IR satellite imagery have shown that there is a significant diurnal cycle of cirrus cloud cover in tropical cyclones (e.g., Browner et al, 1977;Muramatsu, 1983;Lajoie and Butterworth, 1984;Steranka et al, 1984;Kossin, 2002). The maximum areal extent of cloud canopies was found to occur in the early morning and the minimum in the early evening.…”

Section: Introductionmentioning

confidence: 98%

An investigation of how radiation may cause accelerated rates of tropical cyclogenesis and diurnal cycles of convective activity

Nicholls

2015

Atmos. Chem. Phys.

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Abstract. Recent cloud-resolving numerical modeling results suggest that radiative forcing causes accelerated rates of tropical cyclogenesis and early intensification. Furthermore, observational studies of tropical cyclones have found that oscillations of the cloud canopy areal extent often occur that are clearly related to the solar diurnal cycle. A theory is put forward to explain these findings. The primary mechanism that seems responsible can be considered a refinement of the mechanism proposed by Gray and Jacobson (1977) to explain diurnal variations of oceanic tropical deep cumulus convection. It is hypothesized that differential radiative cooling or heating between a relatively cloud-free environment and a developing tropical disturbance generates circulations that can have very significant influences on convective activity in the core of the system. It is further suggested that there are benefits to understanding this mechanism by viewing it in terms of the lateral propagation of thermally driven gravity wave circulations, also known as buoyancy bores. Numerical model experiments indicate that mean environmental radiative cooling outside the cloud system is playing an important role in causing a significant horizontal differential radiative forcing and accelerating the rate of tropical cyclogenesis. As an expansive stratiform cloud layer forms aloft within a developing system the mean low-level radiative cooling is reduced, while at mid levels small warming occurs. During the daytime there is not a very large differential radiative forcing between the environment and the cloud system, but at nighttime when there is strong radiative clear-sky cooling of the environment it becomes significant. Thermally driven circulations develop, characterized by relatively weak subsidence in the environment but much stronger upward motion in the cloud system. This upward motion leads to a cooling tendency and increased relative humidity. The increased relative humidity at night appears to be a major factor in enhancing convective activity, thereby leading in the mean to an increased rate of genesis. It is postulated that the increased upward motion and relative humidity that occur throughout a deep layer aid both in the triggering of convection and in providing a more favorable local environment at mid levels for maintenance of buoyancy in convective cells due to a reduction of the detrimental effects of dry air entrainment. Additionally, the day/night modulations of the environmental radiative forcing appear to play a major role in the diurnal cycles of convective activity in the cloud system. It is shown that the upward velocity tendencies in the system core produced by the radiative forcing are extremely weak when compared to those produced by latent heat release in convective towers, but nevertheless over the course of a night they appear capable of significantly influencing convective activity.

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“…An observational study of hurricanes and tropical cyclones by Steranka et al (1984) found significant diurnal and semidiurnal cloud cycles in observations of satellite derived cloud-top temperatures. Kossin (2002) confirmed the diurnal oscillations and hypothesized that radiative cooling induced subsidence at night in the region of the hurricane canopy reduces the spatial coverage of high cirrus clouds producing the observed reduction in cloudtop heights.…”

Section: Introductionmentioning

confidence: 99%

Diurnal Radiation Cycle Impact on the Pregenesis Environment of Hurricane Karl (2010)

Melhauser

Zhang

2014

Journal of the Atmospheric Sciences

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Through convection-permitting ensemble and sensitivity experiments, this study examines the impact of the diurnal radiation cycle on the pregenesis environment of Hurricane Karl (2010). It is found that the pregenesis environmental stability and the intensity of deep moist convection can be considerably modulated by the diurnal extremes in radiation. Nighttime destabilization of the local and large-scale environment through radiative cooling may promote deep moist convection and increase the genesis potential, likely enhancing the intensity of the resultant tropical cyclones. Modified longwave and shortwave radiation experiments found tropical cyclone development to be highly sensitive to the periodic cycle of heating and cooling, with suppressed formation in the daytime-only and no-radiation experiments and quicker intensification compared with the control for nighttime-only experiments.

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The Diurnal Variation of Atlantic Ocean Tropical Cyclone aoud DistributionInferred from Geostationary Satellite Infrared Measurements

Cited by 31 publications

References 0 publications

An examination of two pathways to tropical cyclogenesis occurring in idealized simulations with a cloud-resolving numerical model

An examination of two pathways to tropical cyclogenesis occurring in idealized simulations with a cloud-resolving numerical model

An investigation of how radiation may cause accelerated rates of tropical cyclogenesis and diurnal cycles of convective activity

Diurnal Radiation Cycle Impact on the Pregenesis Environment of Hurricane Karl (2010)

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