Journal articles on the topic 'Intense atmospheric vortices'
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Ingel, L. Kh. "On a positive-feedback mechanism in intense atmospheric vortices." Izvestiya, Atmospheric and Oceanic Physics 50, no. 1 (January 2014): 61–65. http://dx.doi.org/10.1134/s000143381401006x.
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Ingel, L. Kh. "On a Positive-Feedback Mechanism in Intense Atmospheric Vortices." Известия Российской академии наук. Физика атмосферы и океана 50, no. 1 (2014): 70–75. http://dx.doi.org/10.7868/s0002351514010064.
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Nerushev, A. F. "Perturbations of the ozone layer induced by intense atmospheric vortices." International Journal of Remote Sensing 29, no. 9 (April 25, 2008): 2705–32. http://dx.doi.org/10.1080/01431160701767526.
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Levina, G. V. "Parameterization of helical turbulence in numerical models of intense atmospheric vortices." Doklady Earth Sciences 411, no. 2 (December 2006): 1417–21. http://dx.doi.org/10.1134/s1028334x06090182.
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Damiani, Rick, and Gabor Vali. "Evidence for Tilted Toroidal Circulations in Cumulus." Journal of the Atmospheric Sciences 64, no. 6 (June 2007): 2045–60. http://dx.doi.org/10.1175/jas3941.1.
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Intense vortical circulations, often organized in counterrotating vortex pairs, were detected in midcontinental cumulus congestus over southeast Wyoming in July 2003. The sampled clouds developed in dry environments and at cold temperatures, and were a few kilometers in depth and width. Observations were obtained with the Wyoming Cloud Radar from aboard the Wyoming King Air research aircraft. Dual-Doppler analyses of the data yielded high-resolution (30–45 m) depictions of the horizontal components of air motions across vigorously growing clouds. The vortices found in the horizontal cross sections are interpreted as components of the toroidal circulations in thermals when those are tilted because of the effect of ambient cross flow. This configuration also leads to a partial stabilization of the vertical trajectory of the updraft, by opposing the drag by the ambient wind. Additionally, dry air intrusions were seen to accompany these features when the vortices developed near the cloud outer boundaries; recirculation of hydrometeors occurred when the vortices were adjacent to in-cloud downdrafts. These features are also evident in the radar reflectivity patterns. In general, gradients of velocities and vorticity values in horizontal planes are comparable to those found in vertical planes.
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Suzuki, Nobuhiro, Tetsu Hara, and Peter P. Sullivan. "Turbulent Airflow at Young Sea States with Frequent Wave Breaking Events: Large-Eddy Simulation." Journal of the Atmospheric Sciences 68, no. 6 (June 1, 2011): 1290–305. http://dx.doi.org/10.1175/2011jas3619.1.
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Abstract A neutrally stratified turbulent airflow over a very young sea surface at a high-wind condition was investigated using large-eddy simulations. In such a state, the dominant drag at the sea surface occurs over breaking waves, and the relationship between the dominant drag and local instantaneous surface wind is highly stochastic and anisotropic. To model such a relationship, a bottom boundary stress parameterization was proposed for the very young sea surface resolving individual breakers. This parameterization was compared to the commonly used parameterization for isotropic surfaces. Over both the young sea and isotropic surfaces, the main near-surface turbulence structure was wall-attached, large-scale, quasi-streamwise vortices. Over the young sea surface, these vortices were more intense, and the near-surface mean velocity gradient was smaller. This is because the isotropic surface weakens the swirling motions of the vortices by spanwise drag. In contrast, the young sea surface exerts little spanwise drag and develops more intense vortices, resulting in greater turbulence and mixing. The vigorous turbulence decreases the mean velocity gradient in the roughness sublayer below the logarithmic layer. Thus, the enhancement of the air–sea momentum flux (drag coefficient) due to breaking waves is caused not only by the streamwise form drag over individual breakers but also by the enhanced vortices. Furthermore, contrary to an assumption used in existing wave boundary layer models, the wave effect may extend as high as 10–20 times the breaking wave height.
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Lewellen, D. C., and W. S. Lewellen. "Near-Surface Intensification of Tornado Vortices." Journal of the Atmospheric Sciences 64, no. 7 (July 1, 2007): 2176–94. http://dx.doi.org/10.1175/jas3965.1.
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Abstract An idealized analytical model and numerical large-eddy simulations are used to explore fluid-dynamic mechanisms by which tornadoes may be intensified near the surface relative to conditions aloft. The analytical model generalizes a simple model of Barcilon and Fiedler and Rotunno for a steady supercritical end-wall vortex to more general vortex corner flows, angular momentum distributions, and time dependence. The model illustrates the role played by the corner flow swirl ratio in determining corner flow structure and intensification; predicts an intensification of near-surface swirl velocities relative to conditions aloft of Iυ ∼ 2 for supercritical end-wall vortices in agreement with earlier analytical, numerical, and laboratory results; and suggests how larger intensification factors might be achieved in some more general corner flows. Examples of the latter are presented using large-eddy simulations. By tuning the lateral inflow boundary conditions near the surface, quasi-steady vortices exhibiting nested inner and outer corner flows and Iυ ∼ 4 are produced. More significantly, these features can be produced without fine tuning, along with an additional doubling (or more) of the intensification, in a broad class of unsteady evolutions producing a dynamic corner flow collapse. These scenarios, triggered purely by changes in the far-field near-surface flow, provide an attractive mechanism for naturally achieving an intense near-surface vortex from a much larger-scale less-intense swirling flow. It is argued that, applied on different scales, this may sometimes play a role in tornadogenesis and/or tornado variability. This phenomenon of corner flow collapse is considered further in a companion paper.
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McRae, D. J., and M. D. Flannigan. "Development of large vortices on prescribed fires." Canadian Journal of Forest Research 20, no. 12 (December 1, 1990): 1878–87. http://dx.doi.org/10.1139/x90-252.
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A detailed set of data has been compiled on large fire whirlwinds occurring on prescribed burns conducted in Ontario. There appear to be two types of such whirlwinds: one occurs in pairs on the leeward side of the convection column and the other is created after the entire convection column begins to rotate. The second type occurs in association with very intense fires that may be described as fire storms. Fire whirlwind occurrence appears to be related principally to meteorological conditions in which wind speeds are less than 10 km/h, to the stability of the atmosphere up to 3000 m altitude, and to conditions where the amount of energy released from the fire is high. The roles of atmospheric stability, rate of energy release from the fire, and ignition pattern in the development of whirlwinds require further study.
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Schielicke, Lisa, Christoph Peter Gatzen, and Patrick Ludwig. "Vortex Identification across Different Scales." Atmosphere 10, no. 9 (September 4, 2019): 518. http://dx.doi.org/10.3390/atmos10090518.
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Vortex identification in atmospheric data remains a challenge. One reason is the general presence of shear throughout the atmosphere that interferes with traditional vortex identification methods based on geopotential height or vorticity. Alternatively, kinematic methods can avoid some of the drawbacks of the traditional methods since they compare the rotational and deformational flow parts. In this work, we apply the kinematic vorticity number method ( W k -method) to atmospheric datasets ranging from the synoptic to the convective scales. The W k -method is tested for winter storm Kyrill, a high-impact extratropical cyclone that affected Germany in January 2007. This case is especially challenging for vortex identification methods since it produced a complex wind occurrence associated with a derecho along a narrow cold-frontal rain band and an area of high winds close to the low pressure center. The W k -method is able to identify vortices in differently-resolved datasets and at different height levels in a consistent manner. Additionally, it is able to determine and visualize the storm characteristics. As a result, we discovered that the total positive circulation of the vortices associated with Kyrill remains of similar order across different data sets though the vorticity magnitude of the most intense vortices increases with increasing resolution.
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Lovell, Levi T., and Matthew D. Parker. "Simulated QLCS Vortices in a High-Shear, Low-CAPE Environment." Weather and Forecasting 37, no. 6 (June 2022): 989–1012. http://dx.doi.org/10.1175/waf-d-21-0133.1.
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Abstract Tornadoes produced by quasi-linear convective systems (QLCSs) in low instability environments present distinctive challenges for forecasters. This study analyzes a population of 56 vortices (all cyclonic) in a full-physics, case study simulation to examine vortex characteristics and their relationships to the pre-line environment. Peak surface vortex intensity correlates with peak vortex depth, peak surface wind speed, and vortex pathlength. The strongest vortices are the deepest and longest lived, implying that they would be most detectable. The modeled surface vortices are primarily associated with gust front cusps and bow echoes, line breaks, and supercell-like features. Strong vortices frequently have sustained, superposed surface vorticity and near-ground updrafts for several minutes. Although weak vortices lack this superposition, they often exhibit impressive midlevel vorticity and midlevel updrafts. The environments of the weak and strong vortices are similar with small, yet statistically significant, differences in several thermodynamic and kinematic fields. The profiles near strong vortices have more low-level CAPE, steeper lapse rates, and stronger deep-layer vertical wind shear. However, the small magnitudes of the differences imply that forecasters might struggle to discriminate well between nontornadic and tornadic environments in high-shear, low-CAPE events. Despite the similarities, the profiles produce distinct reflectivity, updraft, and vertical vorticity distributions in idealized cloud model simulations. The most intense updrafts and vortices in the idealized runs occur when the environmental profiles from the strong vortex cases are combined with a QLCS orientation more normal to the lower-tropospheric vertical wind shear.
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Sippel, Jason A., John W. Nielsen-Gammon, and Stephen E. Allen. "The Multiple-Vortex Nature of Tropical Cyclogenesis." Monthly Weather Review 134, no. 7 (July 1, 2006): 1796–814. http://dx.doi.org/10.1175/mwr3165.1.
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Abstract This study explores the extent to which potential vorticity (PV) generation and superposition were relevant on a variety of scales during the genesis of Tropical Storm Allison. Allison formed close to shore, and the combination of continuous Doppler radar, satellite, aircraft, and surface observations allows for the examination of tropical cyclogenesis in great detail. Preceding Allison’s genesis, PV superposition on the large scale created an environment where decreased vertical shear and increased instability, surface fluxes, and low-level cyclonic vorticity coexisted. This presented a favorable environment for meso-α-scale PV production by widespread convection and led to the formation of surface-based, meso-β-scale vortices [termed convective burst vortices (CBVs)]. The CBVs seemed to form in association with intense bursts of convection and rotated around each other within the meso-α circulation field. One CBV eventually superposed with a mesoscale convective vortex (MCV), resulting in a more concentrated surface vortex with stronger pressure gradients. The unstable, vorticity-rich environment was also favorable for the development of even smaller, meso-γ-scale vortices that formed within the cores of deep convective cells. Several meso-γ-scale convective vortices were present in the immediate vicinity when a CBV developed, and the smaller vortices may have contributed to the formation of the CBV. The convection associated with the meso-γ vortices also fed PV into existing CBVs. Much of the vortex behavior observed in Allison has been documented or simulated in studies of other tropical cyclones. Multiscale vortex formation and interaction may be a common aspect of many tropical cyclogenesis events.
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Coffer, Brice E., and Matthew D. Parker. "Simulated Supercells in Nontornadic and Tornadic VORTEX2 Environments." Monthly Weather Review 145, no. 1 (December 16, 2016): 149–80. http://dx.doi.org/10.1175/mwr-d-16-0226.1.
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Abstract The composite near-storm environments of nontornadic and tornadic supercells sampled during the second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2) both appear to be generally favorable for supercells and tornadoes. It has not been clear whether small differences between the two environments (e.g., more streamwise horizontal vorticity in the lowest few hundred meters above the ground in the tornadic composite) are actually determinative of storms’ tornadic potential. From the VORTEX2 composite environments, simulations of a nontornadic and a tornadic supercell are used to investigate storm-scale differences that ultimately favor tornadogenesis or tornadogenesis failure. Both environments produce strong supercells with robust midlevel mesocyclones and hook echoes, though the tornadic supercell has a more intense low-level updraft and develops a tornado-like vortex exceeding the EF3 wind speed threshold. In contrast, the nontornadic supercell only produces shallow vortices, which never reach the EF0 wind speed threshold. Even though the nontornadic supercell readily produces subtornadic surface vortices, these vortices fail to be stretched by the low-level updraft. This is due to a disorganized low-level mesocyclone caused by predominately crosswise vorticity in the lowest few hundred meters above ground level within the nontornadic environment. In contrast, the tornadic supercell ingests predominately streamwise horizontal vorticity, which promotes a strong low-level mesocyclone with enhanced dynamic lifting and stretching of surface vertical vorticity. These results support the idea that larger streamwise vorticity leads to a more intense low-level mesocyclone, whereas predominately crosswise vorticity yields a less favorable configuration of the low-level mesocyclone for tornadogenesis.
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Lestrelin, Hugo, Bernard Legras, Aurélien Podglajen, and Mikail Salihoglu. "Smoke-charged vortices in the stratosphere generated by wildfires and their behaviour in both hemispheres: comparing Australia 2020 to Canada 2017." Atmospheric Chemistry and Physics 21, no. 9 (May 10, 2021): 7113–34. http://dx.doi.org/10.5194/acp-21-7113-2021.
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Abstract. The two most intense wildfires of the last decade that took place in Canada in 2017 and Australia in 2019–2020 were followed by large injections of smoke into the stratosphere due to pyro-convection. After the Australian event, Khaykin et al. (2020) and Kablick et al. (2020) discovered that part of this smoke self-organized as anticyclonic confined vortices that rose in the mid-latitude stratosphere up to 35 km. Based on Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) observations and the ERA5 reanalysis, this new study analyses the Canadian case and finds, similarly, that a large plume had penetrated the stratosphere by 12–13 August 2017 and then became trapped within a mesoscale anticyclonic structure that travelled across the Atlantic. It then broke into three offspring that could be followed until mid-October, performing three round-the-world journeys and rising up to 23 km. We analyse the dynamical structure of the vortices produced by these two wildfires and demonstrate how the assimilation of the real temperature and ozone data from instruments measuring the signature of the vortices explains the appearance and maintenance of the vortices in the constructed dynamical fields. We propose that these vortices can be seen as bubbles of small, almost vanishing, potential vorticity and smoke carried vertically across the stratification from the troposphere inside the middle stratosphere by their internal heating, against the descending flux of the Brewer–Dobson circulation.
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Griffiths, R. W., and E. J. Hopfinger. "Coalescing of geostrophic vortices." Journal of Fluid Mechanics 178 (May 1987): 73–97. http://dx.doi.org/10.1017/s0022112087001125.
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Close interactions between pairs of two-dimensional vortices of like sign were investigated in experiments with barotropic vortices and baroclinic vortices. The vortices were generated by sources or sinks in a rotating fluid which, respectively, was homogeneous or contained a two-layer density stratification. For two identical anticyclonic, unstratified vortices there was a critical separation distance beyond which the vortices coalesced to form a single larger anticyclone. The critical distance d*, scaled by the radius R of a core having non-zero relative vorticity, was d*/R = 3.3 ± 0.2. This value is in agreement with results of previous numerical simulations for finite-area vortices in non-rotating flows. The effects on vortex structure of Ekman pumping due to the presence of a rigid boundary caused cyclonic vortices to coalesee from larger distances. Baroclinic vortices in a two-layer stratification were also found to coalesce despite a potential-energy barrier. However, the critical separation distance depended on the internal Rossby radius. When the Rossby radius was large compared with the core radius, vortices coalesced from distances much greater than the critical distance for barotropic vortices. Coalescing of two vortices of equal size and strength led to two symmetric entwined spirals of water, while close interaction of unequal vortices caused the weaker vortex to be wrapped around the outer edge of the stronger. Implications of these results are discussed for ocean eddies and intense atmospheric cyclones.
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Rotunno, Richard, George H. Bryan, David S. Nolan, and Nathan A. Dahl. "Axisymmetric Tornado Simulations at High Reynolds Number." Journal of the Atmospheric Sciences 73, no. 10 (September 15, 2016): 3843–54. http://dx.doi.org/10.1175/jas-d-16-0038.1.
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Abstract This study is the first in a series that investigates the effects of turbulence in the boundary layer of a tornado vortex. In this part, axisymmetric simulations with constant viscosity are used to explore the relationships between vortex structure, intensity, and unsteadiness as functions of diffusion (measured by a Reynolds number Rer) and rotation (measured by a swirl ratio Sr). A deep upper-level damping zone is used to prevent upper-level disturbances from affecting the low-level vortex. The damping zone is most effective when it overlaps with the specified convective forcing, causing a reduction to the effective convective velocity scale We. With this damping in place, the tornado-vortex boundary layer shows no sign of unsteadiness for a wide range of parameters, suggesting that turbulence in the tornado boundary layer is inherently a three-dimensional phenomenon. For high Rer, the most intense vortices have maximum mean tangential winds well in excess of We, and maximum mean vertical velocity exceeds 3 times We. In parameter space, the most intense vortices fall along a line that follows , in agreement with previous analytical predictions by Fiedler and Rotunno. These results are used to inform the design of three-dimensional large-eddy simulations in subsequent papers.
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Steiger, Scott M., Robert Schrom, Alfred Stamm, Daniel Ruth, Keith Jaszka, Timothy Kress, Brett Rathbun, Jeffrey Frame, Joshua Wurman, and Karen Kosiba. "Circulations, Bounded Weak Echo Regions, and Horizontal Vortices Observed within Long-Lake-Axis-Parallel–Lake-Effect Storms by the Doppler on Wheels*." Monthly Weather Review 141, no. 8 (July 25, 2013): 2821–40. http://dx.doi.org/10.1175/mwr-d-12-00226.1.
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Abstract The eastern Great Lakes (Erie and Ontario) are often affected by intense lake-effect snowfalls. Lake-effect storms that form parallel to the major axes of these lakes can strongly impact communities by depositing more than 100 cm of snowfall in less than 24 h. Long-lake-axis-parallel (LLAP) storms are significantly different in structure and dynamics compared to the much more studied wind-parallel roll storms that typically form over the western Great Lakes. A Doppler on Wheels (DOW) mobile radar sampled several of these storms at fine spatial and temporal resolutions (and close to the surface) during the winter of 2010–11 over and downwind of Lake Ontario to document and improve understanding of how these storms develop. Over 1100 observations of vortices were catalogued within the 16 December 2010 and 4–5 January 2011 events. The majority of these vortices were less than 1 km in diameter with a statistical modal difference in Doppler velocity (delta-V) value across the vortex of 11 m s−1. Vortices developed along boundaries, which formed within the bands, suggesting horizontal shear instability was the main cause. Other features noted in the DOW observations included bounded weak echo regions, anvils, and horizontal vortices, typically on the south side of west–east-oriented LLAP bands. The reflectivity and velocity structure of LLAP bands were found to be much more complex than previously thought, which may impact localized precipitation amounts and errors in forecast location/intensity.
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Wu, Liguang, Qingyuan Liu, and Yubin Li. "Tornado-scale vortices in the tropical cyclone boundary layer: numerical simulation with the WRF–LES framework." Atmospheric Chemistry and Physics 19, no. 4 (February 27, 2019): 2477–87. http://dx.doi.org/10.5194/acp-19-2477-2019.
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Abstract. A tornado-scale vortex in the tropical cyclone (TC) boundary layer (TCBL) has been observed in intense hurricanes and the associated intense turbulence poses a severe threat to the manned research aircraft when it penetrates hurricane eyewalls at a lower altitude. In this study, a numerical experiment in which a TC evolves in a large-scale background over the western North Pacific is conducted using the Advanced Weather Research and Forecast (WRF) model by incorporating the large-eddy simulation (LES) technique. The simulated tornado-scale vortex shows features similar to those revealed with limited observational data, including the updraft–downdraft couplet, the sudden jump of wind speeds, the location along the inner edge of the eyewall, and the small horizontal scale. It is suggested that the WRF–LES framework can successfully simulate the tornado-scale vortex with grids at a resolution of 37 m that cover the TC eye and eyewall. The simulated tornado-scale vortex is a cyclonic circulation with a small horizontal scale of ∼1 km in the TCBL. It is accompanied by strong updrafts (more than 15 m s−1) and large vertical components of relative vorticity (larger than 0.2 s−1). The tornado-scale vortex favorably occurs at the inner edge of the enhanced eyewall convection or rainband within the saturated, high-θe layer, mostly below an altitude of 2 km. In nearly all the simulated tornado-scale vortices, the narrow intense updraft is coupled with the relatively broad downdraft, constituting one or two updraft–downdraft couplets, as observed by the research aircraft. The presence of the tornado-scale vortex also leads to significant gradients in the near-surface wind speed and wind gusts.
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GUPTA, AKHILESH, K. J. RAMESH, and U. C. MOHANTY. "Medium range prediction of tropical cyclogenesis of intense vortices over Indian Seas by a Global Spectral Model." MAUSAM 49, no. 3 (December 17, 2021): 331–44. http://dx.doi.org/10.54302/mausam.v49i3.3639.
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The performance of a Global Spectral Model (T-80) operational at the National Centre for Medium Range Weather Forecasting (NCMRWF), New Delhi in predicting the cyclogenesis of six tropical cyclones over Indian Seas formed during 1995-96 has been evaluated. It has been found that the model has the capability to predict cyclogenesis in wind field at least 72 hours in advance although the positions of predicted vortices are seen to be displaced from those of analysed ones in some cases. The quantitative estimates of the atmospheric conditions favourable for cyclogenesis also confirm the conclusions drawn from the qualitative analysis of cyclogenesis predictions of the model in terms of appearance of cyclonic circulation. It also follows from this analysis that the predicted circulations at the cyclogenesis stage are in general more intense and stronger as compared to the corresponding analysis in terms of wind and mass fields. On examining the model systematic errors of prediction it is found that the model has a clear bias for predicting more intense vortex during genesis and weakening stages. On the order hand it predicts relatively less intense vortex during intensification process.
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Doyle, James D., Vanda Grubišić, William O. J. Brown, Stephan F. J. De Wekker, Andreas Dörnbrack, Qingfang Jiang, Shane D. Mayor, and Martin Weissmann. "Observations and Numerical Simulations of Subrotor Vortices during T-REX." Journal of the Atmospheric Sciences 66, no. 5 (May 1, 2009): 1229–49. http://dx.doi.org/10.1175/2008jas2933.1.
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Abstract High-resolution observations from scanning Doppler and aerosol lidars, wind profiler radars, as well as surface and aircraft measurements during the Terrain-induced Rotor Experiment (T-REX) provide the first comprehensive documentation of small-scale intense vortices associated with atmospheric rotors that form in the lee of mountainous terrain. Although rotors are already recognized as potential hazards for aircraft, it is proposed that these small-scale vortices, or subrotors, are the most dangerous features because of strong wind shear and the transient nature of the vortices. A life cycle of a subrotor event is captured by scanning Doppler and aerosol lidars over a 5-min period. The lidars depict an amplifying vortex, with a characteristic length scale of ∼500–1000 m, that overturns and intensifies to a maximum spanwise vorticity greater than 0.2 s−1. Radar wind profiler observations document a series of vortices, characterized by updraft/downdraft couplets and regions of enhanced reversed flow, that are generated in a layer of strong vertical wind shear and subcritical Richardson number. The observations and numerical simulations reveal that turbulent subrotors occur most frequently along the leading edge of an elevated sheet of horizontal vorticity that is a manifestation of boundary layer shear and separation along the lee slopes. As the subrotors break from the vortex sheet, intensification occurs through vortex stretching and in some cases tilting processes related to three-dimensional turbulent mixing. The subrotors and ambient vortex sheet are shown to intensify through a modest increase in the upstream inversion strength, which illustrates the predictability challenges for the turbulent characterization of rotors.
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Mahale, Vivek N., Jerald A. Brotzge, and Howard B. Bluestein. "An Analysis of Vortices Embedded within a Quasi-Linear Convective System Using X-Band Polarimetric Radar." Weather and Forecasting 27, no. 6 (December 1, 2012): 1520–37. http://dx.doi.org/10.1175/waf-d-11-00135.1.
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Abstract On 2 April 2010, a developing quasi-linear convective system (QLCS) moved rapidly northeastward through central Oklahoma spawning at least three intense, mesoscale vortices. At least two of these vortices caused damage rated as category 0 to 1 on the enhanced Fujita scale (EF0–EF1) in and near the town of Rush Springs. Two radar networks—the National Weather Service Weather Surveillance Radar-1988 Doppler network (WSR-88D) and the Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere (CASA) radar network—collected high spatial and temporal resolution data of the event. This study is an in-depth polarimetric analysis of mesovortices within a QLCS. In this case study, the storm development and evolution of the QLCS mesovortices are examined. Significant findings include the following: 1) The damage in Rush Springs was caused by a combination of the fast translation speed and the embedded circulations associated with QLCS vortices. The vortices’ relative winds nearly negated the storm motion to the left of the vortex, but doubled the ground-relative wind to the right of the vortex. 2) A significant differential reflectivity (ZDR) arc developed along the forward flank of the first vortex. The ZDR arc propagated northeastward along the QLCS with the development of each new vortex. 3) A minimum in the copolar correlation coefficient (ρhv) in the center of the strongest vortex was observed, indicating the likely existence of a polarimetric tornado debris signature (TDS). A secondary ρhv minimum also was found just to the right of the vortex center, possibly associated with lofted debris from straight-line winds.
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Kwon, Young C., and William M. Frank. "Dynamic Instabilities of Simulated Hurricane-like Vortices and Their Impacts on the Core Structure of Hurricanes. Part I: Dry Experiments." Journal of the Atmospheric Sciences 62, no. 11 (November 1, 2005): 3955–73. http://dx.doi.org/10.1175/jas3575.1.
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Abstract A series of numerical simulations of dry, axisymmetric hurricane-like vortices is performed to examine the growth of barotropic and baroclinic eddies and their potential impacts on hurricane core structure and intensity. The numerical experiments are performed using the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) with a 6-km horizontal grid. To examine internal effects on the stability of vortices, all external forcings are eliminated. Axisymmetric vortices that resemble observed hurricane structures are constructed on an f plane, and the experiments are performed without moist and boundary layer processes. Three vortices are designed for this study. A balanced control vortex is built based on the results of a full-physics simulation of Hurricane Floyd (1999). Then, two other axisymmetric vortices, EXP-1 and EXP-2, are constructed by modifying the wind and mass fields of the control vortex. The EXP-1 vortex is designed to satisfy the necessary condition of baroclinic instability, while the EXP-2 vortex satisfies the necessary condition of barotropic instability. These modified vortices are thought to lie within the natural range of structural variability of hurricanes. The EXP-1 and EXP-2 vortices are found to be unstable with respect to small imposed perturbations, while the control vortex is stable. Small perturbations added to the EXP-1 and EXP-2 vortices grow exponentially at the expense of available potential energy and kinetic energy of the primary vortex, respectively. The most unstable normal modes of both vortices are obtained via a numerical method. The most unstable mode of the EXP-1 (baroclinically unstable) vortex vertically tilts against shear, and the maximum growth occurs near a height of 14 km and a radius of 20 km. On the other hand, the most unstable normal mode of the EXP-2 (barotropically unstable) vortex has horizontal tilting against the mean angular velocity shear, and the maximum perturbations are located at a lower altitude (around 4 km) and at larger radius (around 100 km). Despite these differences, the normal modes of both vortices have a wavenumber-1 structure. The energy budget analysis shows that the growing baroclinic and barotropic perturbations have opposite effects on the vortex intensity in terms of kinetic energy. Baroclinic eddies strengthen, whereas barotropic eddies weaken, the primary vortex. It is hypothesized that fluctuations in hurricane core structure and intensity can occur due to eddy processes triggered by alternating periods of barotropic and baroclinic eddy growth in the core. Once formed, these eddies may interact with the intense diabatic energy sources in real hurricanes. A similar study of eddy behaviors in a more realistic hurricane, which includes moist and boundary layer processes and uses a finer grid mesh, will be the topic of Part II.
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BOUCHET, F., and J. SOMMERIA. "Emergence of intense jets and Jupiter's Great Red Spot as maximum-entropy structures." Journal of Fluid Mechanics 464 (August 10, 2002): 165–207. http://dx.doi.org/10.1017/s0022112002008789.
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We explain the emergence and robustness of intense jets in highly turbulent planetary atmospheres, like that on Jupiter, by a general statistical mechanics approach to potential vorticity patches. The idea is that potential vorticity mixing leads to the formation of a steady organized coarse-grained flow, corresponding to the statistical equilibrium state. Our starting point is the quasi-geostrophic 1-1/2 layer model, and we consider the relevant limit of a small Rossby radius of deformation. Then narrow jets are obtained, in the sense that they scale like the radius of deformation. These jets can be either zonal, or closed into a ring bounding a vortex. Taking into account the beta-effect and a sublayer deep shear flow, we predict organization of the turbulent atmospheric layer into an oval-shaped vortex within a background shear. Such an isolated vortex is centred over an extremum of the equivalent topography, combining the interfacial geostrophic tilt due to the deep shear flow and the planetary beta-effect (the resulting effective beta-effect is locally quadratic). This prediction is in agreement with an analysis of wind data in major Jovian vortices (Great Red Spot and Oval BC).
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Stern, Daniel P., and George H. Bryan. "Using Simulated Dropsondes to Understand Extreme Updrafts and Wind Speeds in Tropical Cyclones." Monthly Weather Review 146, no. 11 (November 1, 2018): 3901–25. http://dx.doi.org/10.1175/mwr-d-18-0041.1.
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Abstract Extreme updrafts (≥10 m s−1) and wind gusts (≥90 m s−1) are ubiquitous within the low-level eyewall of intense tropical cyclones (TCs). Previous studies suggest that both of these features are associated with coherent subkilometer-scale vortices. Here, over 100 000 “virtual” dropsonde trajectories are examined within a large-eddy simulation (31.25-m horizontal grid spacing) of a category 5 hurricane in order to gain insight into the nature of these features and to better understand and interpret dropsonde observations. At such a high resolution, profiles of wind speed and vertical velocity from the virtual sondes are difficult to distinguish from those of real dropsondes. PDFs of the strength of updrafts and wind gusts compare well between the simulated and observed dropsondes, as do the respective range of heights over which these features are found. Individual simulated updrafts can be tracked for periods of up to several minutes, revealing structures that are both coherent and rapidly evolving. It appears that the updrafts are closely associated with vortices and wind speed maxima, consistent with previous studies. The peak instantaneous wind gusts in the simulations (up to 150 m s−1) are substantially stronger than have ever been observed. Using the virtual sondes, it is demonstrated that the probability of sampling such extremes is vanishingly small, and it is argued that actual intense TCs might also be characterized by gusts of these magnitudes.
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Camberlin, Pierre, Marc Kpanou, and Pascal Roucou. "Classification of Intense Rainfall Days in Southern West Africa and Associated Atmospheric Circulation." Atmosphere 11, no. 2 (February 11, 2020): 188. http://dx.doi.org/10.3390/atmos11020188.
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Daily rainfall in southern West Africa (4–8° N, 7° W–3° E) is analyzed with the aim of documenting the intense rainfall events which occur in coastal Ivory Coast, Ghana, Togo, and Benin. The daily 99th percentile (P99) shows that the coastline experiences higher intensity rainfall than inland areas. Using Tropical Rainfall Measuring Mission (TRMM) rainfall data for 1998–2014, a novel way of classifying the intense events is proposed. We consider their space-time structure over a window of 8° latitude-longitude and five days centered on the event. A total 39,680 events (62 at each location) are classified into three major types, mainly found over the oceanic regions south of 5° N, the Bight of Benin, and the inland regions respectively. These types display quite distinct rainfall patterns, propagation features, and seasonal occurrence. Three inland subtypes are also defined. The atmospheric circulation anomalies associated with each type are examined from ERA-interim reanalysis data. Intense rainfall events over the continent are mainly a result of westward propagating disturbances. Over the Gulf of Guinea, many intense events occur as a combination of atmospheric disturbances propagating westward (mid-tropospheric easterly waves or cyclonic vortices) and eastward (lower tropospheric zonal wind and moisture anomalies hypothesized to reflect Kelvin waves). Along the coast, there is a mixture of different types of rainfall events, often associated with interacting eastward- and westward-moving disturbances, which complicates the monitoring of heavy precipitation.
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Lu, Xinyan, Kevin K. W. Cheung, and Yihong Duan. "Numerical Study on the Formation of Typhoon Ketsana (2003). Part I: Roles of the Mesoscale Convective Systems." Monthly Weather Review 140, no. 1 (January 1, 2012): 100–120. http://dx.doi.org/10.1175/2011mwr3649.1.
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Abstract The effects of multiple mesoscale convective systems (MCSs) on the formation of Typhoon Ketsana (2003) are analyzed in this study. Numerical simulations using the Weather Research and Forecasting (WRF) model with assimilation of Quick Scatterometer (QuikSCAT) and Special Sensor Microwave Imager (SSM/I) oceanic winds and total precipitable water are performed. The WRF model simulates well the large-scale features, the convective episodes associated with the MCSs and their periods of development, and the formation time and location of Ketsana. With the successive occurrence of MCSs, midlevel average relative vorticity is strengthened through generation of mesoscale convective vortices (MCVs) mainly via the vertical stretching mechanism. Scale separation shows that the activity of the vortical hot tower (VHT)-type meso-γ-scale vortices correlated well with the development of the MCSs. These VHTs have large values of positive relative vorticity induced by intense low-level convergence, and thus play an important role in the low-level vortex enhancement with aggregation of VHTs as one of the possible mechanisms. Four sensitivity experiments are performed to analyze the possible different roles of the MCSs during the formation of Ketsana by modifying the vertical relative humidity profile in each MCS and consequently the strength of convection within. The results show that the development of an MCS depends substantially on that of the prior ones through remoistening of the midtroposphere, and thus leading to different scenarios of system intensification during the tropical cyclone (TC) formation. The earlier MCSs are responsible for the first stage vortex enhancement, and depending on the location can affect quite largely the simulated formation location. The extreme convection within the last MCS before formation largely determines the formation time.
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Duvel, J. P., S. J. Camargo, and A. H. Sobel. "Role of the Convection Scheme in Modeling Initiation and Intensification of Tropical Depressions over the North Atlantic." Monthly Weather Review 145, no. 4 (March 29, 2017): 1495–509. http://dx.doi.org/10.1175/mwr-d-16-0201.1.
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Abstract The authors analyze how modifications of the convective scheme modify the initiation of tropical depression vortices (TDVs) and their intensification into stronger warm-cored tropical cyclone–like vortices (TCs) in global climate model (GCM) simulations. The model’s original convection scheme has entrainment and cloud-base mass flux closures based on moisture convergence. Two modifications are considered: one in which entrainment is dependent on relative humidity and another in which the closure is based on the convective available potential energy (CAPE). Compared to reanalysis, TDVs are more numerous and intense in all three simulations, probably as a result of excessive parameterized deep convection at the expense of convection detraining at midlevel. The relative humidity–dependent entrainment rate increases both TDV initiation and intensification relative to the control. This is because this entrainment rate is reduced in the moist center of the TDVs, giving more intense convective precipitation, and also because it generates a moister environment that may favor the development of early stage TDVs. The CAPE closure inhibits the parameterized convection in strong TDVs, thus limiting their development despite a slight increase in the resolved convection. However, the maximum intensity reached by TC-like TDVs is similar in the three simulations, showing the statistical character of these tendencies. The simulated TCs develop from TDVs with different dynamical origins than those observed. For instance, too many TDVs and TCs initiate near or over southern West Africa in the GCM, collocated with the maximum in easterly wave activity, whose characteristics are also dependent on the convection scheme considered.
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Singh, Randhir, P. K. Pal, C. M. Kishtawal, and P. C. Joshi. "Impact of Atmospheric Infrared Sounder Data on the Numerical Simulation of a Historical Mumbai Rain Event." Weather and Forecasting 23, no. 5 (October 1, 2008): 891–913. http://dx.doi.org/10.1175/2008waf2007060.1.
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Abstract In this paper, the three-dimensional variational data assimilation scheme (3DVAR) in the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (Penn State–NCAR) Mesoscale Model (MM5) is used to study the impact of assimilating Atmospheric Infrared Sounder (AIRS) retrieved temperature and moisture profiles on board Aqua, a satellite that is part of NASA’s Earth Observing System. A record-breaking heavy rain event that occurred over Mumbai, India, on 26 July 2005 with 24-h rainfall exceeding 94 cm was used for the simulation. By analyzing the data from the NCEP–NCAR reanalysis, possible causes of this heavy rainfall event were investigated. The temporal evolution of meteorological fields clearly indicates the formation of midtropospheric mesoscale vortices over Mumbai that exactly coincides with the duration of the intense rainfall. Analysis also indicated the midlevel dryness with higher temperature and moisture in the lower levels. This midlevel dryness with high temperature and moisture in the lower levels increases the conditional instability, which was conducive for the development of very severe local thunderstorms. The midtropospheric mesoscale vortices existed over Mumbai together with lower-level instability and the active monsoon conditions over the west coast resulted in intense rainfall, on the order of 94 cm in 24 h. Numerical experiments were conducted, with two nested domains (45- and 15-km grid spacing). The assimilation of the AIRS-retrieved temperature and moisture profiles produced significant impacts on the location and intensity of the simulated rainfall. It is seen from the numerical experiments that the assimilation of AIRS data could produce the structure of mesoscale vortices, and lower-level thermodynamics and convergence much more realistically compared with the control simulation. The spatial distribution of the rainfall from the simulation using AIRS data was more realistic than that without AIRS data. To make the quantitative comparison of the predicted rainfall with the observed one, the equitable threat score and bias were calculated for different threshold values of rainfall. Inclusion of AIRS data significantly improved the precipitation as indicated by the equitable threat scores and biases for almost all of the threshold rainfall categories.
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Nolan, David S. "Three-dimensional instabilities in tornado-like vortices with secondary circulations." Journal of Fluid Mechanics 711 (September 19, 2012): 61–100. http://dx.doi.org/10.1017/jfm.2012.369.
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AbstractTornadoes and other intense atmospheric vortices are known to occasionally transition to a flow structure with multiple vortices within their larger circulations. This phenomenon has long been ascribed to fluid dynamical instability of the inner-core circulation, and many previous studies have diagnosed low-wavenumber unstable modes in tornado-like vortices that resemble the observed structures. However, relatively few of these studies have incorporated the strong vertical motions of the inner-core circulation into the stability analysis, and no stability analyses have been performed using a complete, frictionally driven secondary circulation with strong radial inflow near the surface. Stability analyses are presented using the complete circulations generated from idealized simulations of tornado-like vortices. Fast-growing unstable modes are found that are consistent with the asymmetric structures present in these simulations. Attempts to correlate the structures and locations of these modes with instability conditions for vortices with axial jets derived by Howard & Gupta and by Leibovich & Stewartson produce only mixed results. Analyses of perturbation energy growth show that interactions between eddy fluxes and the radial shear of the azimuthal wind contribute very little to the growth of the dominant modes. Rather, the radial shear of the vertical wind and the vertical shear of the vertical wind (corresponding to deformation in the axial direction) are the primary energy sources for perturbation growth. Relatively weak axisymmetric instabilities are also identified that have some similarity to symmetric oscillations that have been observed in tornadoes.
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Zhong, Wei, and Da-Lin Zhang. "An Eigenfrequency Analysis of Mixed Rossby–Gravity Waves on Barotropic Vortices." Journal of the Atmospheric Sciences 71, no. 6 (May 30, 2014): 2186–203. http://dx.doi.org/10.1175/jas-d-13-0282.1.
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Abstract In this study, the linearized, f-plane, shallow-water equations are discretized into a matrix eigenvalue problem to examine the full spectrum of free waves on barotropic (monopolar and hollow) vortices. A typical wave spectrum for weak vortices shows a continuous range between zero and an advective frequency associated with vortex Rossby waves (VRWs) and two discrete ranges at both sides associated with inertio-gravity waves (IGWs). However, when the vortex intensity reaches a critical value, higher-frequency waves will be “red shifted” into the continuous spectrum, while low-frequency waves will be “violet shifted” into the discrete spectrum, leading to the emergence of mixed vortex Rossby–inertio-gravity waves (VRIGWs). Results show significant (little) radial wavelike structures of perturbation variables for IGWs (VRWs) with greater (much smaller) divergence than vorticity and the hybrid IGW–VRW radial structures with equal amplitudes of vorticity and divergence for mixed VRIGWs. In addition, VRWs only occur within a critical radius at which the perturbation azimuthal velocity is discontinuous. As the azimuthal wavenumber increases, lower-frequency waves tend to exhibit more mixed-wave characteristics, whereas higher-frequency waves will be more of the IGW type. Two-dimensional wave solutions show rapid outward energy dispersion of IGWs and slower dispersion of VRWs and mixed VRIGWs in the core region. These solutions are shown to resemble the previous analytical solutions, except for certain structural differences caused by the critical radius. It is concluded that mixed VRIGWs should be common in the eyewall and spiral rainbands of intense tropical cyclones. Some different wave behaviors associated with the monopolar and hollow vortices are also discussed.
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Liang, Ju, Jennifer L. Catto, Matthew Hawcroft, Kevin I. Hodges, Mou Leong Tan, and James M. Haywood. "Climatology of Borneo Vortices in the HadGEM3-GC3.1 General Circulation Model." Journal of Climate 34, no. 9 (May 2021): 3401–19. http://dx.doi.org/10.1175/jcli-d-20-0604.1.
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AbstractBorneo vortices (BVs) are intense precipitating winter storms that develop over the equatorial South China Sea and strongly affect the weather and climate over the western Maritime Continent because of their association with deep convection and heavy rainfall. In this study, the ability of the Hadley Centre Global Environment Model 3–Global Coupled, version 3.1 (HadGEM3-GC3.1), global climate model to simulate the climatology of BVs at different horizontal resolutions is examined using an objective feature-tracking algorithm. The HadGEM3-GC3.1 at the N512 (25 km) horizontal resolution simulates BVs with well-represented characteristics, including their frequency, spatial distribution, and lower-tropospheric structures when compared with BVs identified in a climate reanalysis, whereas the BVs in the N96 (~135 km) and N216 (~65 km) simulations are much weaker and less frequent. Also, the N512 simulation better captures the contribution of BVs to the winter precipitation in Borneo and the Malay Peninsula when compared with precipitation from a reanalysis data and from observations, whereas the N96 and N216 simulations underestimate this contribution because of the overly weak low-level convergence of the simulated BVs. The N512 simulation also exhibits an improved ability to reproduce the modulation of BV activity by the occurrence of northeasterly cold surges and active phases of the Madden–Julian oscillation in the region, including increased BV track densities, intensities, and lifetimes. A sufficiently high model resolution is thus found to be important to realistically simulate the present-climate precipitation extremes associated with BVs and to study their possible changes in a warmer climate.
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GRANTS, I., C. ZHANG, S. ECKERT, and G. GERBETH. "Experimental observation of swirl accumulation in a magnetically driven flow." Journal of Fluid Mechanics 616 (December 10, 2008): 135–52. http://dx.doi.org/10.1017/s0022112008003650.
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Independent poloidal and azimuthal body forces are induced in a liquid metal cylinder by travelling and rotating magnetic fields of different frequencies, respectively. The bulk axial and azimuthal velocities are measured by the ultrasound Doppler method. Particle image velocimetry is used to observe the upper free surface velocity distribution. The transition from the poloidal to the azimuthal body force governed regime occurs at a fixed ratio of the respective force magnitude of around 100. This transition is marked by the formation of a concentrated vortex revealing several similarities to intense atmospheric vortices. The vortex structure is controlled by a relatively weak azimuthal force while the maximum speed of the swirl is mainly governed by the poloidal one. Under a certain force ratio the average axial velocity changes its direction in the vortex core, resembling the subsidence in an eye of a tropical cyclone or a large tornado. Multiple moving vortices encircle the vortex core in this regime.
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Sherburn, Keith D., and Matthew D. Parker. "The Development of Severe Vortices within Simulated High-Shear, Low-CAPE Convection." Monthly Weather Review 147, no. 6 (May 24, 2019): 2189–216. http://dx.doi.org/10.1175/mwr-d-18-0246.1.
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Abstract Environments characterized by large values of vertical wind shear and modest convective available potential energy (CAPE) are colloquially referred to as high-shear, low-CAPE (HSLC) environments. Convection within these environments represents a considerable operational forecasting challenge. Generally, it has been determined that large low-level wind shear and steep low-level lapse rates—along with synoptic-scale forcing for ascent—are common ingredients supporting severe HSLC convection. This work studies the specific processes that lead to the development of strong surface vortices in HSLC convection, particularly associated with supercells embedded within a quasi-linear convective system (QLCS), and how these processes are affected by varying low-level shear vector magnitudes and lapse rates. Analysis of a control simulation, conducted with a base state similar to a typical HSLC severe environment, reveals that the key factors in the development of a strong surface vortex in HSLC embedded supercells are (i) a strong low- to midlevel mesocyclone, and (ii) a subsequent strong low-level updraft that results from the intense, upward-pointing dynamic perturbation pressure gradient acceleration. Through a matrix of high-resolution, idealized simulations, it is determined that sufficient low-level shear vector magnitudes are necessary for the development of low- to midlevel vertical vorticity [factor (i)], while steeper low-level lapse rates provide stronger initial low-level updrafts [factor (ii)]. This work shows why increased low-level lapse rates and low-level shear vector magnitudes are important to HSLC convection on the storm scale, while also revealing similarities between surface vortexgenesis in HSLC embedded supercells and higher-CAPE supercells.
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Kosiba, Karen A., Joshua Wurman, Kevin Knupp, Kyle Pennington, and Paul Robinson. "Ontario Winter Lake-effect Systems (OWLeS): Bulk Characteristics and Kinematic Evolution of Misovortices in Long-Lake-Axis-Parallel Snowbands." Monthly Weather Review 148, no. 1 (January 1, 2019): 131–57. http://dx.doi.org/10.1175/mwr-d-19-0182.1.
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Abstract During the Ontario Winter Lake-effect Systems (OWLeS) field campaign, 12 long-lake-axis-parallel (LLAP) snowband events were sampled. Misovortices occurred in 11 of these events, with characteristic diameters of ~800 m, differential velocities of ~11 m s−1, and spacing between vortices of ~3 km. A detailed observational analysis of one such snowband provided further insight on the processes governing misovortex genesis and evolution, adding to the growing body of knowledge of these intense snowband features. On 15–16 December 2013, a misovortex-producing snowband was exceptionally well sampled by ground-based OWLeS instrumentation, which allowed for integrated finescale dual-Doppler and surface thermodynamic analyses. Similar to other studies, horizontal shearing instability (HSI), coupled with stretching, was shown to be the primary genesis mechanism. The HSI location was influenced by snowband-generated boundaries and location of the Arctic front relative to the band. Surface temperature observations, available for the first time, indicated that the misovortices formed along a baroclinic zone. Enhanced mixing, higher radar reflectivity, and increased precipitation rate accompanied the vortices. As the snowband came ashore, OWLeS participants indicated an increase in snowfall and white out conditions with the passage of the snowband. A sharp, small-scale pressure drop, coupled with winds of ~16 m s−1, marked the passage of a misovortex and may be typical of snowband misovortices.
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James, Eric P., and Richard H. Johnson. "Patterns of Precipitation and Mesolow Evolution in Midlatitude Mesoscale Convective Vortices." Monthly Weather Review 138, no. 3 (March 1, 2010): 909–31. http://dx.doi.org/10.1175/2009mwr3076.1.
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Abstract Surface pressure manifestations of mesoscale convective vortices (MCVs) that traversed Oklahoma during the periods May–August 2002–05 are studied using the Weather Surveillance Radar-1988 Doppler (WSR-88D), the Oklahoma Mesonet, and the NOAA Profiler Network data. Forty-five MCVs that developed from mesoscale convective systems (MCSs) have been investigated, 28 (62%) of which exhibit mesolows detectable at the surface. Within this group, three distinct patterns of precipitation organization and associated mesolow evolution have been identified. The remaining 17 (38%) of the cases do not contain a surface mesolow. Two repeating patterns of precipitation organization are identified for the latter group. The three categories of MCVs possessing a surface mesolow are as follows. Nineteen are classified as “rear-inflow-jet MCVs,” and tend to form within large and intense asymmetric MCSs. Rear inflow into the MCS, enhanced by the development of an MCV on the left-hand side relative to system motion, produces a rear-inflow notch and a distinct surface wake low at the back edge of the stratiform region. Hence, the surface mesolow and MCV are displaced from one another. Eight are classified as “collapsing-stratiform-region MCVs.” These MCVs arise from small asymmetric MCSs. As the stratiform region of the MCS weakens, a large mesolow appears beneath its dissipating remnants due to broad subsidence warming, and at the same time the midlevel vortex spins up due to column stretching. One case, called a “vertically coherent MCV,” contains a well-defined surface mesolow and associated cyclonic circulation, apparently due to the strength of the midlevel warm core and the weakness of the low-level cold pool. In these latter two cases, the surface mesolow and MCV are approximately collocated. Within the group of MCVs without a surface mesolow, 14 are classified as “remnant-circulation MCVs” containing no significant precipitation or surface pressure effects. Finally, three are classified as “cold-pool-dominated MCVs;” these cases contain significant precipitation but no discernible surface mesolow. This study represents the first systematic analysis of the surface mesolows associated with MCVs. The pattern of surface pressure and winds accompanying MCVs can affect subsequent convective development in such systems. Extension of the findings herein to tropical oceans may have implications regarding tropical cyclogenesis.
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Doyle, James D., and Dale R. Durran. "Rotor and Subrotor Dynamics in the Lee of Three-Dimensional Terrain." Journal of the Atmospheric Sciences 64, no. 12 (December 1, 2007): 4202–21. http://dx.doi.org/10.1175/2007jas2352.1.
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Abstract The internal structure and dynamics of rotors that form in the lee of topographic ridges are explored using a series of high-resolution eddy-resolving numerical simulations. Surface friction generates a sheet of horizontal vorticity along the lee slope that is lifted aloft by the mountain lee wave at the boundary layer separation point. Parallel-shear instability breaks this vortex sheet into small intense vortices or subrotors. The strength and evolution of the subrotors and the internal structure of the main large-scale rotor are substantially different in 2D and 3D simulations. In 2D, the subrotors are less intense and are ultimately entrained into the larger-scale rotor circulation, where they dissipate and contribute their vorticity toward the maintenance of the main rotor. In 3D, even for flow over a uniform infinitely long barrier, the subrotors are more intense, and primarily are simply swept downstream past the main rotor along the interface between that rotor and the surrounding lee wave. The average vorticity within the interior of the main rotor is much weaker and the flow is more chaotic. When an isolated peak is added to a 3D ridge, systematic along-ridge velocity perturbations create regions of preferential vortex stretching at the leading edge of the rotor. Subrotors passing through such regions are intensified by stretching and may develop values of the ridge-parallel vorticity component well in excess of those in the parent, shear-generated vortex sheet. Because of their intensity, such subrotor circulations likely pose the greatest hazard to aviation.
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Menelaou, Konstantinos, David A. Schecter, and M. K. Yau. "On the Relative Contribution of Inertia–Gravity Wave Radiation to Asymmetric Instabilities in Tropical Cyclone–like Vortices." Journal of the Atmospheric Sciences 73, no. 9 (August 4, 2016): 3345–70. http://dx.doi.org/10.1175/jas-d-15-0360.1.
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Abstract Intense atmospheric vortices such as tropical cyclones experience various asymmetric instabilities during their life cycles. This study investigates how vortex properties and ambient conditions determine the relative importance of different mechanisms that can simultaneously influence the growth of an asymmetric perturbation. The focus is on three-dimensional disturbances of barotropic vortices with nonmonotonic radial distributions of potential vorticity. The primary modes of instability are examined for Rossby numbers between 10 and 100 and Froude numbers in the broad neighborhood of unity. This parameter regime is deemed appropriate for tropical cyclone perturbations with vertical length scales ranging from the depth of the vortex to moderately smaller scales. At relatively small Froude numbers, the main cause of instability inferred from analysis typically involves the interaction of vortex Rossby waves with each other and/or critical-layer potential vorticity perturbations. As the Froude number increases from its lower bound, the main cause of instability transitions to inertia–gravity wave radiation. In some cases, the transition occurs abruptly at a critical point where a mode whose growth is driven almost entirely by radiation suddenly becomes dominant. In other cases, the transition is gradual and less direct as the fastest-growing mode continuously changes its structure. Examination of the angular pseudomomentum budget helps quantify the impact of radiation. The radiation-driven instabilities examined herein are shown to be quite fast and potentially relevant to real-world tropical cyclones. Their sensitivities to parameterized moisture and outer vorticity skirts are briefly addressed.
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Nielsen, Erik R., and Russ S. Schumacher. "Observations of Extreme Short-Term Precipitation Associated with Supercells and Mesovortices." Monthly Weather Review 148, no. 1 (December 17, 2019): 159–82. http://dx.doi.org/10.1175/mwr-d-19-0146.1.
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Abstract Extreme hourly rainfall accumulations (e.g., exceeding 75 mm h−1) in several noteworthy flash flood events have suggested that the most intense accumulations were attendant with discrete mesoscale rotation or rotation embedded within larger organized systems. This research aims to explore how often extreme short-term rain rates in the United States are associated with storm-scale or mesoscale vortices. Five years of METAR observations and three years of Stage-IV analyses were obtained and filtered for hourly accumulations over 75 and 100 mm, respectively, clustered into events, and subjectively identified for rotation. The distribution of the short-term, locally extreme events shows the majority of the events were located along the Atlantic and Gulf of Mexico coastlines with additional events occurring in the central plains and into the Midwest. Nearly 50% of the cases were associated with low-level rotation in high-precipitation supercells or mesoscale vortices embedded in organized storm modes. Rotation events occurred more clearly in the warm sector, while nonrotation events tended to occur along a surface boundary. The rotation events tended to produce higher hourly accumulations over a larger region, but were associated with somewhat stronger synoptic-to-mesoscale forcing for ascent and more total column moisture. These results support recent modeling results suggesting that rotationally induced dynamic vertical pressure perturbations should not be ignored when it comes to extreme precipitation and can potentially enhance the short-term rain rates.
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SENGUPTA, S. "Localized floods in Rajasthan owing to exceedingly heavy rains: Case study of small scale accentuations in the summer monsoon field associated with intense upper anticyclonic shear zones." MAUSAM 37, no. 3 (July 1, 1986): 385–90. http://dx.doi.org/10.54302/mausam.v37i3.2466.
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Most of Rajasthan, being an area of less annual rainfall, soil and topography adhered to the condition, sudden, rapid and exceedingly heavy rains for even a day or two, in a localized area can cause severe floods with natural calamity of very high order: Study of some of these situations in the Indian summer monsoon field reveals, that, fractional superimposition and therefore fractional accentuation of pre-existing lower troposphere cyclonic vortices by upper anticyclonic shear zones formed out of propagation and amplification of an upper westerly and an easterly wave, in close proximity is actually responsible for such exceeding heavy falls in meso or small areas.
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Wurman, Joshua, and Karen Kosiba. "The Role of Small-Scale Vortices in Enhancing Surface Winds and Damage in Hurricane Harvey (2017)." Monthly Weather Review 146, no. 3 (March 2018): 713–22. http://dx.doi.org/10.1175/mwr-d-17-0327.1.
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Strong hurricanes cause severe, but highly variable, wind damage to homes and community infrastructure. It has been speculated, but not previously shown, that damage variability is caused by tornadoes or other small-scale phenomena. Here, the authors present the first mapping and tracking of persistent tornado-scale vortices (TSVs) in the eyewall and the first documentation of the likely role of eyewall mesovortices (MVs) and TSVs in enhancing surface winds and damage. Unprecedented finescale observations in the eyewall of Hurricane Harvey (2017) were obtained by a Doppler on Wheels (DOW) radar deployed inside the eye. These observations reveal several persistent eyewall MVs revolving about the eye, as well as superimposed subkilometer-scale TSVs. Wind field perturbations associated with TSVs and MVs are less than those typical in supercell tornadoes, but since they are embedded in strong background eyewall flow, they are likely responsible for the enhancement of surface wind gusts and significant damage, including destroyed buildings and lofted vehicles. Potential climate change may result in more frequent intense and/or rapidly intensifying hurricanes; thus, understanding and forecasting the causes of hurricane wind damage is a high priority.
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Harasti, Paul R., and Roland List. "Principal Component Analysis of Doppler Radar Data. Part I: Geometric Connections between Eigenvectors and the Core Region of Atmospheric Vortices." Journal of the Atmospheric Sciences 62, no. 11 (November 1, 2005): 4027–42. http://dx.doi.org/10.1175/jas3613.1.
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Abstract This is the first in a three-part series of papers that present the first applications of principal component analysis (PCA) to Doppler radar data. Although this novel approach has potential applications to many types of atmospheric phenomena, the specific goal of this series is to describe and verify a methodology that establishes the position and radial extent of the core region of atmospheric vortices. The underlying assumption in the current application is that the streamlines of the nondivergent component of the horizontal wind are predominantly circular, which is a characteristic often observed in intense vortices such as tropical cyclones. The method employs an S2-mode PCA on the Doppler velocity data taken from a single surveillance scan and arranged sequentially in a matrix according to the range and azimuth coordinates. Part I begins the series by examining the eigenvectors obtained from such a PCA applied to a Doppler velocity model for a modified, Rankine-combined vortex, where the ratio of the radius of maximum wind to the range from the radar to the circulation center is varied over a wide range of values typically encountered in the field. Results show that the first two eigenvectors within the eigenspace of range coordinates represent over 99% of the total variance in the data. It is also demonstrated that the coordinates of particular cusps in the curves of the eigenvector coefficients plotted against their indices are geometrically related to both the position of circulation center and the radius of maximum wind.
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Trier, Stanley B., and Christopher A. Davis. "Mesoscale Convective Vortices Observed during BAMEX. Part II: Influences on Secondary Deep Convection." Monthly Weather Review 135, no. 6 (June 1, 2007): 2051–75. http://dx.doi.org/10.1175/mwr3399.1.
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Abstract Observations from the Bow Echo and Mesoscale Convective Vortex (MCV) Experiment are used to examine the role of the five mesoscale convective vortices described in Part I on heavy precipitation during the daytime heating cycle. Persistent widespread stratiform rain without deep convection occurs for two strong MCVs in conditionally stable environments with strong vertical shear. Two other MCVs in moderate-to-strong vertical shear have localized redevelopment of deep convection (termed secondary convection) on their downshear side, where conditional instability exists. The strongest of the five MCVs occurs in weak vertical shear and has widespread secondary convection, which is most intense on its conditionally unstable southeast periphery. The two MCVs with only localized secondary convection have well-defined mesoscale vertical motion couplets with downshear ascent and upshear descent above the planetary boundary layer (PBL). Although the amplitude is significantly greater, the kinematically derived vertical motion dipole resembles that implied by steady, vortex-relative isentropic flow, consistent with previous idealized (dry) simulations and diagnoses based on operational model analyses. In the other three cases with either widespread precipitation or weak environmental vertical shear, the kinematic and isentropic vertical motion patterns are poorly correlated. Vertical motions above the PBL provide a focus for secondary convection through adiabatic cooling downshear and adiabatic warming upshear of the MCV center. The MCVs occur within surface frontal zones with large temperature and moisture gradients across the environmental vertical shear vector (Part I). Thus, the effect of vertical motions on conditional instability is reinforced by horizontal advections of high equivalent potential temperature air downshear, and low equivalent potential temperature air upshear within the PBL. On average, the quadrant immediately right of downshear (typically southeast of the MCV center) best supports deep convection because of the juxtaposition of greatest mesoscale ascent, high equivalent potential temperature PBL air, and MCV-induced enhancement of the vertical shear.
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O’Neill, Morgan E., Kerry A. Emanuel, and Glenn R. Flierl. "Weak Jets and Strong Cyclones: Shallow-Water Modeling of Giant Planet Polar Caps." Journal of the Atmospheric Sciences 73, no. 4 (April 1, 2016): 1841–55. http://dx.doi.org/10.1175/jas-d-15-0314.1.
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Abstract Giant planet tropospheres lack a solid, frictional bottom boundary. The troposphere instead smoothly transitions to a denser fluid interior below. However, Saturn exhibits a hot, symmetric cyclone centered directly on each pole, bearing many similarities to terrestrial hurricanes. Transient cyclonic features are observed at Neptune’s South Pole as well. The wind-induced surface heat exchange mechanism for tropical cyclones on Earth requires energy flux from a surface, so another mechanism must be responsible for the polar accumulation of cyclonic vorticity on giant planets. Here it is argued that the vortical hot tower mechanism, claimed by Montgomery et al. and others to be essential for tropical cyclone formation, is the key ingredient responsible for Saturn’s polar vortices. A 2.5-layer polar shallow-water model, introduced by O’Neill et al., is employed and described in detail. The authors first explore freely evolving behavior and then forced-dissipative behavior. It is demonstrated that local, intense vertical mass fluxes, representing baroclinic moist convective thunderstorms, can become vertically aligned and accumulate cyclonic vorticity at the pole. A scaling is found for the energy density of the model as a function of control parameters. Here it is shown that, for a fixed planetary radius and deformation radius, total energy density is the primary predictor of whether a strong polar vortex forms. Further, multiple very weak jets are formed in simulations that are not conducive to polar cyclones.
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Menelaou, Konstantinos, M. K. Yau, and Yosvany Martinez. "Impact of Asymmetric Dynamical Processes on the Structure and Intensity Change of Two-Dimensional Hurricane-Like Annular Vortices." Journal of the Atmospheric Sciences 70, no. 2 (February 1, 2013): 559–82. http://dx.doi.org/10.1175/jas-d-12-0192.1.
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Abstract In this study, a simple two-dimensional (2D) unforced barotropic model is used to study the asymmetric dynamics of the hurricane inner-core region and to assess their impact on the structure and intensity change. Two sets of experiments are conducted, starting with stable and unstable annular vortices, to mimic intense mature hurricane-like vortices. The theory of empirical normal modes (ENM) and the Eliassen–Palm flux theorem are then applied to extract the dominant wave modes from the dataset and diagnose their kinematics, structure, and impact on the primary vortex. From the first experiment, it is found that the evolution and the lifetime of an elliptical eyewall, described by a stable annular vortex perturbed by an external wavenumber-2 impulse, may be controlled by the inviscid damping of sheared vortex Rossby waves (VRWs) or the decay of an excited quasimode. The critical radius and structure of the quasimode obtained by the ENM analysis are shown to be consistent with the predictions of a linear eigenmode analysis of small perturbations. From the second experiment, it is found that the outward-propagating VRWs that arise due to barotropic instability and the inward mixing of high vorticity in the unstable annular vortex affect the primary circulation and create a secondary ring of enhanced vorticity that contains a secondary wind maximum. Sensitivity tests performed on the spatial extent of the initial external impulse verifies the robustness of the results. That the secondary eyewall occurs close to the critical radius of some of the dominant modes emphasizes the important role played by the VRWs.
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Zhu, Lin, Da-Lin Zhang, Stefan F. Cecelski, and Xinyong Shen. "Genesis of Tropical Storm Debby (2006) within an African Easterly Wave: Roles of the Bottom-Up and Midlevel Pouch Processes." Journal of the Atmospheric Sciences 72, no. 6 (May 27, 2015): 2267–85. http://dx.doi.org/10.1175/jas-d-14-0217.1.
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Abstract The “bottom up” generation of low-level vortices (LVs) and midlevel vortices (MVs) during the genesis of Tropical Storm Debby (2006) and the roles of a midlevel “marsupial pouch” associated with an African easterly wave (AEW) are examined using an 84-h simulation with the finest grid size of 1.33 km. Results show that several MVs are generated in leading convective bands and then advected rearward into stratiform regions by front-to-rear ascending flows. Because of different Lagrangian storm-scale circulations, MVs and LVs are displaced along different paths during the early genesis stages. MVs propagate cyclonically inward within the AEW pouch while experiencing slow intensification and merging under the influence of converging flows. The MVs’ merging into a mesovortex is accelerated as they come closer to each other in the core region. In contrast, the low-level Lagrangian circulation is opened as a wave trough prior to tropical depression (TD) stage, so the LVs tend to “escape” from the pouch region. Only after the low-level flows become closed do some LVs congregate and contribute directly to Debby’s genesis. The TD stage is reached when the midlevel mesovortex and an LV are collocated with a convective zone having intense low-level convergence. Results also show the roles of upper-level warming in hydrostatically maintaining the midlevel pouch and producing mesoscale surface pressure falls. It is found that the vertically tilted AEW with a cold dome below is transformed to a deep warm-core TD vortex by subsiding motion. A conceptual model describing the key elements in the genesis of Debby is also provided.
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Nielsen, Erik R., and Russ S. Schumacher. "Dynamical Insights into Extreme Short-Term Precipitation Associated with Supercells and Mesovortices." Journal of the Atmospheric Sciences 75, no. 9 (August 15, 2018): 2983–3009. http://dx.doi.org/10.1175/jas-d-17-0385.1.
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Abstract In some prominent extreme precipitation and flash flood events, radar and rain gauge observations have suggested that the heaviest short-term rainfall accumulations (up to 177 mm h−1) were associated with supercells or mesovortices embedded within larger convective systems. In this research, we aim to identify the influence that rotation has on the storm-scale processes associated with heavy precipitation. Numerical model simulations conducted herein were inspired by a rainfall event that occurred in central Texas in October 2015 where the most extreme rainfall accumulations were collocated with meso-β-scale vortices. Five total simulations were performed to test the sensitivity of precipitation processes to rotation. A control simulation, based on a wind profile from the aforementioned event, was compared with two experiments with successively weaker low-level shear. With greater environmental low-level shear, more precipitation fell, in both a point-maximum and an area-averaged sense. Intense, rotationally induced low-level vertical accelerations associated with the dynamic nonlinear perturbation vertical pressure gradient force were found to enhance the low- to midlevel updraft strength and total vertical mass flux and allowed access to otherwise inhibited sources of moisture and CAPE in the higher-shear simulations. The dynamical accelerations, which increased with the intensity of the low-level shear, dominated over buoyant accelerations in the low levels and were responsible for inducing more intense low-level updrafts that were sustained despite a stable boundary layer.
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Marks, Frank D., Peter G. Black, Michael T. Montgomery, and Robert W. Burpee. "Structure of the Eye and Eyewall of Hurricane Hugo (1989)." Monthly Weather Review 136, no. 4 (April 1, 2008): 1237–59. http://dx.doi.org/10.1175/2007mwr2073.1.
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Abstract On 15 September 1989, one of NOAA’s WP-3D research aircraft, N42RF [lower aircraft (LA)], penetrated the eyewall of Hurricane Hugo. The aircraft had an engine fail in severe turbulence while passing the radius of maximum wind and before entering the eye at 450-m altitude. After the aircraft returned to controlled flight within the 7-km radius eye, it gained altitude gradually as it orbited in the eye. Observations taken during this period provide an updated model of the inner-core structure of an intense hurricane and suggest that LA penetrated an intense cyclonic vorticity maximum adjacent to the strongest convection in the eyewall [eyewall vorticity maximum (EVM)]. This EVM was distinct from the vortex-scale cyclonic circulation observed to orbit within the eye three times during the 1 h that LA circled in the eye. At the time, Hugo had been deepening rapidly for 12 h. The maximum flight-level tangential wind was 89 m s−1 at a radius of 12.5 km; however, the primary vortex peak tangential wind, derived from a 100-s filter of the flight-level data, was estimated to be 70 m s−1, also at 12.5-km radius. The primary vortex tangential wind was in approximate gradient wind balance, was characterized by a peak in angular velocity just inside the radius of maximum wind, and had an annular vorticity structure slightly interior to the angular velocity maximum. The EVM along the aircraft’s track was roughly 1 km in diameter with a peak cyclonic vorticity of 1.25 × 10−1 s−1. The larger circulation center, with a diameter >15 km, was observed within the eye and exhibited an average orbital period of 19 min. This period is about the same as that of the angular velocity maximum of the axisymmetric mean vortex and is in reasonable agreement with recent theoretical and model predictions of a persistent trochoidal “wobble” of circulation centers in mature hurricane-like vortices. This study is the first with in situ documentation of these vortical entities, which were recently hypothesized to be elements of a lower-tropospheric eye/eyewall mixing mechanism that supports strong storms.
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RAO, P. SANJEEVA. "Arabian Sea monsoon experiment: An overview." MAUSAM 56, no. 1 (January 19, 2022): 1–6. http://dx.doi.org/10.54302/mausam.v56i1.849.
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The Arabian Sea Monsoon Experiment (ARMEX) is one of the land-ocean-atmosphere field experiments implemented in June-July 2002 and March-June 2003 under the Indian Climate Research Programme. The broad scientific objectives of the ARMEX are (i) to study the offshore trough embedded mesoscale vortices (Arabian Sea convection) associated with intense rainfall events on the west coast of India during monsoon period, and (ii) to study the evolution, maintenance and the collapse of the Arabian Sea warm pool and onset phase of the monsoon. Conventional weather monitoring systems, weather satellite observational systems, ships, met-ocean buoys, automatic weather stations, surface layer meteorological towers and aircraft were deployed with state-of-the-art instrumentation for this experiment. This paper attempts to provide an overview of the ARMEX scientific objectives, implementation strategy, resource mobilization, infrastructure deployed, observational data collation, archival and initial analysis by the participating scientists.
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Guimond, Stephen R., Jun A. Zhang, Joseph W. Sapp, and Stephen J. Frasier. "Coherent Turbulence in the Boundary Layer of Hurricane Rita (2005) during an Eyewall Replacement Cycle." Journal of the Atmospheric Sciences 75, no. 9 (August 17, 2018): 3071–93. http://dx.doi.org/10.1175/jas-d-17-0347.1.
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Abstract The structure of coherent turbulence in an eyewall replacement cycle in Hurricane Rita (2005) is presented from novel airborne Doppler radar observations using the Imaging Wind and Rain Airborne Profiler (IWRAP). The IWRAP measurements and three-dimensional (3D) wind vector calculations at a grid spacing of 250 m in the horizontal and 30 m in the vertical reveal the ubiquitous presence of organized turbulent eddies in the lower levels of the storm. The data presented here, and the larger collection of IWRAP measurements, currently are the highest-resolution Doppler radar 3D wind vectors ever obtained in a hurricane over the open ocean. Coincident data from NOAA airborne radars, the Stepped Frequency Microwave Radiometer, and flight-level data help to place the IWRAP observations into context and provide independent validation. The typical characteristics of the turbulent eddies are the following: radial wavelengths of ~1–3 km (mean value is ~2 km), depths from the ocean surface up to flight level (~1.5 km), aspect ratio of ~1.3, and horizontal wind speed perturbations of 10–20 m s−1. The most intense eddy activity is located on the inner edge of the outer eyewall during the concentric eyewall stage with a shift to the inner eyewall during the merging stage. The evolving structure of the vertical wind shear is connected to this shift and together these characteristics have several similarities to boundary layer roll vortices. However, eddy momentum flux analysis reveals that high-momentum air is being transported upward, in contrast with roll vortices, with large positive values (~150 m2 s−2) found in the turbulent filaments. In the decaying inner eyewall, elevated tangential momentum is also being transported radially outward to the intensifying outer eyewall. These results indicate that the eddies may have connections to potential vorticity waves with possible modifications due to boundary layer shear instabilities.
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Markowski, Paul M., and Yvette P. Richardson. "The Influence of Environmental Low-Level Shear and Cold Pools on Tornadogenesis: Insights from Idealized Simulations." Journal of the Atmospheric Sciences 71, no. 1 (December 27, 2013): 243–75. http://dx.doi.org/10.1175/jas-d-13-0159.1.
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Abstract Idealized, dry simulations are used to investigate the roles of environmental vertical wind shear and baroclinic vorticity generation in the development of near-surface vortices in supercell-like “pseudostorms.” A cyclonically rotating updraft is produced by a stationary, cylindrical heat source imposed within a horizontally homogeneous environment containing streamwise vorticity. Once a nearly steady state is achieved, a heat sink, which emulates the effects of latent cooling associated with precipitation, is activated on the northeastern flank of the updraft at low levels. Cool outflow emanating from the heat sink spreads beneath the updraft and leads to the development of near-surface vertical vorticity via the “baroclinic mechanism,” as has been diagnosed or inferred in actual supercells that have been simulated and observed. An intense cyclonic vortex forms in the simulations in which the environmental low-level wind shear is strong and the heat sink is of intermediate strength relative to the other heat sinks tested. Intermediate heat sinks result in the development (baroclinically) of substantial near-surface circulation, yet the cold pools are not excessively strong. Moreover, the strong environmental low-level shear lowers the base of the midlevel mesocyclone, which promotes strong dynamic lifting of near-surface air that previously resided in the heat sink. The superpositioning of the dynamic lifting and circulation-rich, near-surface air having only weak negative buoyancy facilitates near-surface vorticity stretching and vortex genesis. An intense cyclonic vortex fails to form in simulations in which the heat sink is excessively strong or weak or if the low-level environmental shear is weak.
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Dawson, Daniel T., Ming Xue, Alan Shapiro, Jason A. Milbrandt, and Alexander D. Schenkman. "Sensitivity of Real-Data Simulations of the 3 May 1999 Oklahoma City Tornadic Supercell and Associated Tornadoes to Multimoment Microphysics. Part II: Analysis of Buoyancy and Dynamic Pressure Forces in Simulated Tornado-Like Vortices." Journal of the Atmospheric Sciences 73, no. 3 (February 9, 2016): 1039–61. http://dx.doi.org/10.1175/jas-d-15-0114.1.
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Abstract Vortex stretching by intense upward accelerations is a critical process for tornadogenesis and maintenance. Two high-resolution (250-m grid spacing) real-data simulations of the 3 May 1999 Oklahoma City, Oklahoma, supercell and associated tornadoes, using single- and triple-moment microphysics parameterization schemes, respectively, are examined. Microphysical, thermodynamic, and dynamic impacts on the vertical accelerations near and within simulated tornado-like vortices (TLVs) are analyzed. Systematic differences in behavior of the TLVS between the two experiments are found; the TLV in the triple-moment simulation is substantially more intense and longer lived than in the single-moment case. The triple-moment scheme in this case produces less rain and hail mass in the low levels and drop size distributions of rain shifted toward larger drops, relative to the single-moment scheme, leading to less latent cooling and warmer outflow. Trajectory analyses reveal that more parcels entering the TLV in the triple-moment simulation have a history of dynamically induced descent, whereas buoyantly driven descent is more prevalent in the single-moment experiment. It is found that the intensity and longevity of the TLV are tied to weaker negative or neutral thermal buoyancy in the air flowing into the TLV in the triple-moment case, consistent with previous observational and modeling studies. Finally, the contribution to buoyancy from pressure perturbations is found to be of prime importance within the TLV, where strong negative pressure perturbations lead to substantial positive buoyancy. This contribution compensates for the slight negative thermal buoyancy and negative dynamic pressure gradient acceleration in the triple-moment case.