The Life Cycle of an Undular Bore and Its Interaction with a Shallow, Intense Cold Front

Hartung, Daniel C.; Otkin, Jason A.; Martin, Jonathan E.; Turner, David D.

doi:10.1175/2009mwr3028.1

Cited by 19 publications

(21 citation statements)

References 49 publications

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“…' Clarke (1986) also indicated the possibility that the cold front itself can transform into an undular bore. A recent study by Hartung et al (2010) investigates the evolution of an undular bore generated by a cold front over the southern plains of the United States using both observational data and the Weather Research and Forecasting Model (WRF). These waves were shown to develop in a prefrontal trough ahead of the cold front itself, and were located about 300 km ahead of the front.…”

Section: Introductionmentioning

confidence: 66%

“…In cases where the wave amplitude is relatively large, nonlinear waves may lift air above the level of free convection and trigger deep convection and thunderstorms if the environment is conditionally unstable (Smith et al 1982). Hartung et al (2010) provides a comprehensive description of gravity currents, undular bores, and solitary waves, and so only a brief discussion will be given here to describe the features addressed in this study. This is particularly important in southeastern Australia in summer when forecasts of wind changes are often crucial in deciding strategies to combat wildfires (Smith et al 1982).…”

Section: Introductionmentioning

confidence: 99%

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Nonlinear Waves ahead of Fronts in the Great Australian Bight

Schmidt¹,

Goler²

2010

Monthly Weather Review

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This study investigates nonlinear waves ahead of cold fronts in the Great Australian Bight, south of the Australian continent. These waves often form a series of roll clouds on their crests analogous to the ''morning glory,'' which is observed around the Gulf of Carpentaria in northeastern Australia. High-resolution visible satellite imagery from NASA's polar-orbiting Aqua and Terra satellites between 23 October 2004 and 29 February 2008 is used to determine how frequently these cloud lines occur ahead of cold fronts. A total of 14 cases are identified with the most cases occurring in summer and none occurring in winter. The authors hypothesize that the summer maximum is due to a combination of lower cloud amounts associated with summertime cold fronts, and a stronger maritime stable layer, which is produced as hot continental air, is advected offshore.Three cloud line events are modeled using the fifth-generation Pennsylvania State University-National Center for Atmospheric Research (PSU-NCAR) Mesoscale Model (MM5, version 3.6). In each case the lowlevel divergence field reveals convergence lines, which coincide with the cloud lines as identified on the satellite images. In two cases vertical cross sections of virtual potential temperature and horizontal and vertical velocity through the disturbances show a cold front advancing into a stratified environment leading to wave production at the leading edge of the cold air mass. Modeled maximal upward velocities range between 0.8 and 2.5 m s 21 . Surface pressure jumps of about 1 hPa associated with the propagating waves occur in each case, which coincides with that predicted by simple bore theory. In two cases the front moves at supercritical speed (i.e., the frontal speed is larger than the speed of the fastest mode of small-amplitude long waves). In the third case the front does not propagate and the nonlinear waves produced become stationary as well.

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Section: Introductionmentioning

confidence: 66%

Section: Introductionmentioning

confidence: 99%

Nonlinear Waves ahead of Fronts in the Great Australian Bight

Schmidt¹,

Goler²

2010

Monthly Weather Review

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“…Atmospheric bores may form when a density current, often produced by convection, or a cold front, impinges on a stable layer such as the nocturnal boundary layer (NBL; e.g., Crook 1988;Rottman and Simpson 1989;Hartung et al 2010). It has been shown that atmospheric bores may destabilize the boundary layer through mixing or permanent upward displacements (e.g., Koch et al 2008a;Koch et al 1991), and the lifting may also aide in convective initiation (e.g., Koch et al 2008a;Locatelli et al 2002;Koch and Clark 1999;Karyampudi et al 1995).…”

Section: Introductionmentioning

confidence: 72%

Radiometer and Profiler Analysis of the Effects of a Bore and a Solitary Wave on the Stability of the Nocturnal Boundary Layer

Coleman

Knupp

2011

Monthly Weather Review

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This study uses data from a microwave profiling radiometer (MPR), along with 915-MHz wind profiler, Doppler radar, and surface data to quantify the kinematic and thermodynamic effects of two wave features, an undular bore and a soliton, on the nocturnal boundary layer (NBL) at high temporal resolution. Both wave features passed directly over the MPR and the wind profiler, allowing for detailed analyses. The effects of the wave features on the convective environment are examined, and convective initiation (CI) associated with the wave features is discussed.The undular bore was illustrated well in Doppler velocity data, and profiler measurements indicated that it produced four wavelengths of upward and downward motion. MPR-derived time-height sections of potential temperature and mixing ratio showed an increase in the depth of the stable boundary layer, along with a decrease in stability, partially associated with mixing of the NBL. The soliton produced a temporary decrease in the depth of the NBL, and also produced destabilization. Trajectory analyses were performed assuming the wave features were two-dimensional, allowing a time-to-space conversion of profiler data. Trajectory analyses, in addition to propagation speed, confirm that the wave features were indeed a bore and a soliton, and that there was vertical divergence in the NBL, likely associated with the decrease in static stability.MPR data were also used to produce time series of convective parameters, including CAPE, convective inhibition (CIN), and the level of free convection (LFC). The CIN was initially too large for free convection despite sufficient CAPE, but MPR data showed that the CIN decreased by more than 50% upon passage of the bore, and again with the soliton. The waves also decreased the LFC due to cooling above the NBL and slight warming near the surface in the bore. Both the reduction in CIN and the lowering of the LFC made convection more likely. Convective initiation occurred behind both wave features, and the vertical motion provided by the waves may have also aided in this CI.

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“…An atmospheric bore is a propagating hydraulic jump, typically associated with a sudden increase in the depth of a stable boundary layer and a sudden rise in pressure, and it may form when a density current impinges on a stable layer (e.g., Christie et al 1978;Crook 1986;Rottman and Simpson 1989;Koch et al 2008;Hartung et al 2010). There is typically an energy imbalance across the bore.…”

Section: Introductionmentioning

confidence: 99%

An Undular Bore and Gravity Waves Illustrated by Dramatic Time-Lapse Photography

Coleman

Knupp

Herzmann

2010

Journal of Atmospheric and Oceanic Technology

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On 6 May 2007, an intense atmospheric undular bore moved over eastern Iowa. A ''Webcam'' in Tama, Iowa, captured dramatic images of the effects of the bore and associated gravity waves on cloud features, because its viewing angle was almost normal to the propagation direction of the waves. The time lapse of these images has become a well-known illustration of atmospheric gravity waves. The environment was favorable for bore formation, with a wave-reflecting unstable layer above a low-level stable layer. Surface pressure and wind data are correlated for the waves in the bore, and horizontal wind oscillations are also shown by Doppler radar data. Quantitative analysis of the time-lapse photography shows that the sky brightens in wave troughs because of subsidence and darkens in wave ridges because of ascent.

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The Life Cycle of an Undular Bore and Its Interaction with a Shallow, Intense Cold Front

Cited by 19 publications

References 49 publications

Nonlinear Waves ahead of Fronts in the Great Australian Bight

Nonlinear Waves ahead of Fronts in the Great Australian Bight

Radiometer and Profiler Analysis of the Effects of a Bore and a Solitary Wave on the Stability of the Nocturnal Boundary Layer

An Undular Bore and Gravity Waves Illustrated by Dramatic Time-Lapse Photography

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