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Academic literature on the topic 'Hurricane Guillermo'
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Journal articles on the topic "Hurricane Guillermo"
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Reasor, Paul D., and Matthew D. Eastin. "Rapidly Intensifying Hurricane Guillermo (1997). Part II: Resilience in Shear." Monthly Weather Review 140, no. 2 (February 2012): 425–44. http://dx.doi.org/10.1175/mwr-d-11-00080.1.
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This paper examines the structure and evolution of a mature tropical cyclone in vertical wind shear (VWS) using airborne Doppler radar observations of Hurricane Guillermo (1997). In Part I, the modulation of eyewall convection via the rotation of vorticity asymmetries through the downshear-left quadrant was documented during rapid intensification. Here, the focus is on the relationship between VWS, vortex tilt, and associated asymmetry within the tropical cyclone core region during two separate observation periods. A method for estimating local VWS and vortex tilt from radar datasets is further developed, and the resulting vertical structure and its evolution are subjected to statistical confidence tests. Guillermo was a highly resilient vortex, evidenced by its small tilt magnitude relative to the horizontal scale of the vortex core. The deep-layer tilt was statistically significant, oriented on average ~60° left of shear. Large-scale vorticity and thermal asymmetries oriented along the tilt direction support a response of Guillermo to shear forcing that is consistent with balanced dynamics. The time-averaged vertical motion asymmetry within the eyewall exhibited maximum ascent values ~40° left of the deep-layer shear, or in this case, right of the deep-layer tilt. The observation-based analysis of Guillermo’s interaction with VWS confirms findings of recent theoretical and numerical studies, and serves as the basis for a more comprehensive investigation of VWS and tropical cyclone intensity change using a recently constructed multistorm database of Doppler radar analyses.
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Reasor, Paul D., Matthew D. Eastin, and John F. Gamache. "Rapidly Intensifying Hurricane Guillermo (1997). Part I: Low-Wavenumber Structure and Evolution." Monthly Weather Review 137, no. 2 (February 1, 2009): 603–31. http://dx.doi.org/10.1175/2008mwr2487.1.
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Abstract The structure and evolution of rapidly intensifying Hurricane Guillermo (1997) is examined using airborne Doppler radar observations. In this first part, the low-azimuthal-wavenumber component of the vortex is presented. Guillermo’s intensification occurred in an environmental flow with 7–8 m s−1 of deep-layer vertical shear. As a consequence of the persistent vertical shear forcing of the vortex, convection was observed primarily in the downshear left quadrant of the storm. The greatest intensification during the ∼6-h Doppler observation period coincided with the formation and cyclonic rotation of several particularly strong convective bursts through the left-of-shear semicircle of the eyewall. Some of the strongest convective bursts were triggered by azimuthally propagating low-wavenumber vorticity asymmetries. Mesoscale budget analyses of axisymmetric angular momentum and relative vorticity within the eyewall are presented to elucidate the mechanisms contributing to Guillermo’s structural evolution during this period. The observations support a developing conceptual model of the rapidly intensifying, vertically sheared hurricane in which shear-forced mesoscale ascent in the downshear eyewall is modulated by internally generated vorticity asymmetries yielding episodes of anomalous intensification.
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Godinez, Humberto C., Jon M. Reisner, Alexandre O. Fierro, Stephen R. Guimond, and Jim Kao. "Determining Key Model Parameters of Rapidly Intensifying Hurricane Guillermo (1997) Using the Ensemble Kalman Filter." Journal of the Atmospheric Sciences 69, no. 11 (November 1, 2012): 3147–71. http://dx.doi.org/10.1175/jas-d-12-022.1.
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Abstract In this work the authors determine key model parameters for rapidly intensifying Hurricane Guillermo (1997) using the ensemble Kalman filter (EnKF). The approach is to utilize the EnKF as a tool only to estimate the parameter values of the model for a particular dataset. The assimilation is performed using dual-Doppler radar observations obtained during the period of rapid intensification of Hurricane Guillermo. A unique aspect of Guillermo was that during the period of radar observations strong convective bursts, attributable to wind shear, formed primarily within the eastern semicircle of the eyewall. To reproduce this observed structure within a hurricane model, background wind shear of some magnitude must be specified and turbulence and surface parameters appropriately specified so that the impact of the shear on the simulated hurricane vortex can be realized. To identify the complex nonlinear interactions induced by changes in these parameters, an ensemble of model simulations have been conducted in which individual members were formulated by sampling the parameters within a certain range via a Latin hypercube approach. The ensemble and the data, derived latent heat and horizontal winds from the dual-Doppler radar observations, are utilized in the EnKF to obtain varying estimates of the model parameters. The parameters are estimated at each time instance, and a final parameter value is obtained by computing the average over time. Individual simulations were conducted using the estimates, with the simulation using latent heat parameter estimates producing the lowest overall model forecast error.
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Zou, X., Yonghui Wu, and Peter Sawin Ray. "Verification of a High-Resolution Model Forecast Using Airborne Doppler Radar Analysis during the Rapid Intensification of Hurricane Guillermo." Journal of Applied Meteorology and Climatology 49, no. 4 (April 1, 2010): 807–20. http://dx.doi.org/10.1175/2009jamc2182.1.
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Abstract The NOAA Hurricane Research Division (HRD) P-3 aircraft provided airborne radar observations during the period of rapid intensification of Hurricane Guillermo on 2 August 1997. The inner core structure and evolution of Hurricane Guillermo (1997) over a 120 km by 120 km square area, centered on the storm, was observed by the P-3 aircraft during 10 flight legs at half-hour intervals during a 6-h period from 1800 UTC 2 August to 0000 UTC 3 August 1997. A high-resolution short-term model forecast initialized at 1800 UTC 2 August 1997 was made using the fifth-generation Pennsylvania State University–NCAR nonhydrostatic, two-way interactive, movable, triply nested grid Mesoscale Model (MM5). The weak vortex at the initial time in the NCEP analysis was replaced by a tropical storm–like vortex generated by a 4D variational data assimilation (4D-Var) vortex initialization experiment. The modeled Guillermo followed the observed track with less than a 12-km track error at any time during the 6-h forecast period. The modeled eye is smaller than the observed eye and the modeled vortex is more upright than shown by the radar analysis. The minimum pressure, maximum wind (intensity), and radial profile of tangential winds are close to the radar analysis after 2–3 h of model spinup. A spectral decomposition further reveals that (i) large differences between the model simulation and radar analysis of the asymmetric features are mostly caused by azimuthal phase errors; (ii) the wavenumber 1 component dominates the asymmetric features and remains stationary within the inner core region, as is also observed by airborne Doppler radar; and (iii) although being significantly different from radar analysis, the azimuthal phase of the wavenumber 1 component of modeled reflectivity does not vary greatly with time as the radar data suggest.
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Guimond, Stephen R., and Jon M. Reisner. "A Latent Heat Retrieval and Its Effects on the Intensity and Structure Change of Hurricane Guillermo (1997). Part II: Numerical Simulations." Journal of the Atmospheric Sciences 69, no. 11 (November 1, 2012): 3128–46. http://dx.doi.org/10.1175/jas-d-11-0201.1.
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Abstract In Part I of this study, a new algorithm for retrieving the latent heat field in tropical cyclones from airborne Doppler radar was presented and fields from rapidly intensifying Hurricane Guillermo (1997) were shown. In Part II, the usefulness and relative accuracy of the retrievals is assessed by inserting the heating into realistic numerical simulations at 2-km resolution and comparing the generated wind structure to the radar analyses of Guillermo. Results show that using the latent heat retrievals as forcing produces very low intensity and structure errors (in terms of tangential wind speed errors and explained wind variance) and significantly improves simulations relative to a predictive run that is highly calibrated to the latent heat retrievals by using an ensemble Kalman filter procedure to estimate values of key model parameters. Releasing all the heating/cooling in the latent heat retrieval results in a simulation with a large positive bias in Guillermo’s intensity that motivates the need to determine the saturation state in the hurricane inner-core retrieval through a procedure similar to that described in Part I of this study. The heating retrievals accomplish high-quality structure statistics by forcing asymmetries in the wind field with the generally correct amplitude, placement, and timing. In contrast, the latent heating fields generated in the predictive simulation contain a significant bias toward large values and are concentrated in bands (rather than discrete cells) stretched around the vortex. The Doppler radar–based latent heat retrievals presented in this series of papers should prove useful for convection initialization and data assimilation to reduce errors in numerical simulations of tropical cyclones.
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Bister, Marja, and Kerry A. Emanuel. "The Genesis of Hurricane Guillermo: TEXMEX Analyses and a Modeling Study." Monthly Weather Review 125, no. 10 (October 1997): 2662–82. http://dx.doi.org/10.1175/1520-0493(1997)125<2662:tgohgt>2.0.co;2.
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Eastin, Matthew D., William M. Gray, and Peter G. Black. "Buoyancy of Convective Vertical Motions in the Inner Core of Intense Hurricanes. Part II: Case Studies." Monthly Weather Review 133, no. 1 (January 1, 2005): 209–27. http://dx.doi.org/10.1175/mwr-2849.1.
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Abstract This is the second of two papers on the buoyancy of convective vertical motions in the inner core of intense hurricanes. This paper uses extensive airborne radar, dropwindsonde, and flight-level observations in Hurricanes Guillermo (1997) and Georges (1998) to illustrate typical azimuthal distribution of buoyant convection and demonstrate that the low-level eye can be an important source region for buoyant eyewall convection. In both hurricanes, eyewall vertical velocity and radar reflectivity are asymmetric and exhibit persistent relationships with the direction of the environmental vertical wind shear. Mesoscale vertical motions exhibit a wavenumber-1 structure with maximum ascent downshear and weak descent upshear. The mesoscale reflectivity maxima are located left-of-shear. Buoyant eyewall updraft cores and transient convective-scale reflectivity cells are predominantly downshear and left-of-shear. Most eyewall downdraft cores that transport significant mass downward are located upshear. Negative buoyancy was most common in left-of-shear downdrafts, with positive buoyancy dominant in upshear downdrafts. Inward-spiraling rainbands located outside the eyewall exhibit upband/downband asymmetries. Upband segments contain more convective reflectivity cells and buoyant updraft cores than the more stratiform downband segments. Equal numbers of downdraft cores are found upband and downband, but the majority exhibit negative buoyancy. Several buoyant updraft cores encountered in the midlevel eyewall exhibit equivalent potential temperatures (θe) much higher than the θe observed in the low-level eyewall, but equivalent to the θe observed in the low-level eye. Asymmetric low-wavenumber circulations appear responsible for exporting the high-θe eye air into the relatively low-θe eyewall and generating the locally buoyant updraft cores. Implications of these results upon conceptual models of hurricane structure are discussed. Three mechanisms, whereby an ensemble of asymmetric buoyant convection could contribute to hurricane evolution, are also discussed.
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Sitkowski, Matthew, and Gary M. Barnes. "Low-Level Thermodynamic, Kinematic, and Reflectivity Fields of Hurricane Guillermo (1997) during Rapid Intensification." Monthly Weather Review 137, no. 2 (February 1, 2009): 645–63. http://dx.doi.org/10.1175/2008mwr2531.1.
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Abstract From 0600 UTC 2 August to 1200 UTC 3 August Hurricane Guillermo (1997) deepened by 54 hPa over the eastern North Pacific Ocean, easily exceeding the thresholds that define rapid intensification (RI). The NOAA WP-3Ds observed a portion of this RI with similar two-aircraft missions on consecutive days. The aircraft jettisoned 70 successful global positioning system (GPS) dropwindsondes (or GPS sondes), which reveal how conditions in the lower troposphere on the octant to quadrant scale evolved within 250 km of the eye. Reflectivity fields demonstrate that the deepening is correlated with a spiraling in of the northern eyewall that reduces the eye diameter by 10 km. This behavior contrasts the more uniform contraction witnessed during eyewall replacement cycles. Mixing between the lower eye and eyewall, as detailed by other investigators, appears to have triggered the reduction in the eye diameter. After RI the eyewall remains asymmetrical with the tallest echo tops and heaviest rain rates located on the east or trailing side of the hurricane and to the left of the deep-layer shear vector. Net latent heat release within 60 km of the circulation center increases 21% from 2 to 3 August and is matched by a 30% increase in the inflow below 2 km at the 100-km radius. The GPS sondes, combined with aircraft in situ data for the eyewall region, reveal that the tropical cyclone (TC) establishes an annulus adjacent to and under the eyewall where the tangential wind component and equivalent potential temperature increase substantially. The radial extent of this annulus is constrained by the rainbands that remain robust throughout RI. The results support the argument that RI is controlled by processes within 100 km of the circulation center, and in particular within the eyewall.
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Farfán, Luis M., and Joseph A. Zehnder. "Orographic Influence on the Synoptic-Scale Circulations Associated with the Genesis of Hurricane Guillermo (1991)." Monthly Weather Review 125, no. 10 (October 1997): 2683–98. http://dx.doi.org/10.1175/1520-0493(1997)125<2683:oiotss>2.0.co;2.
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Reasor, Paul D., Michael T. Montgomery, and Lance F. Bosart. "Mesoscale Observations of the Genesis of Hurricane Dolly (1996)." Journal of the Atmospheric Sciences 62, no. 9 (September 1, 2005): 3151–71. http://dx.doi.org/10.1175/jas3540.1.
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Abstract Recent numerical studies of tropical cyclone genesis suggest a new paradigm for how the surface vortex is established based on a highly nonaxisymmetric mechanism involving the interaction of low-level cyclonic circulations generated by deep cumulonimbus convection. A reexamination of mesoscale observations during the genesis of Hurricane Guillermo (1991) confirms the presence of multiple cyclonic circulations. More recently, airborne Doppler radar wind observations during the genesis of Atlantic Hurricane Dolly (1996) also reveal multiple lower-to-middle-tropospheric mesoscale cyclonic circulations during sequential 15–20-min compositing periods. A particularly well-organized, but initially weak (mean tangential wind of 7 m s−1), low-level cyclonic vortex embedded within the pre-Dolly tropical disturbance is observed coincident with deep, vertically penetrating cumulonimbus convection. The earliest observations of this vortex show the peak circulation near 2-km height with a mean diameter of 30–40 km. The circulation undergoes a slight intensification over a 2-h period, with the maximum tangential winds ultimately peaking below 1-km height. Approximately 18 h after these observations Dolly is classified as a hurricane by the National Hurricane Center. A synthesis of observations during the early development of Dolly supports a stochastic view of tropical cyclone genesis in which multiple lower-to-middle-tropospheric mesoscale cyclonic circulations are involved in building the surface cyclonic circulation. It is suggested that, in particular, the interaction of low-level circulations generated by a series of deep cumulonimbus convective events, like the one documented here, within an environment of elevated cyclonic vorticity was instrumental to the formation of the Dolly surface vortex.
Dissertations / Theses on the topic "Hurricane Guillermo"
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Farfan, Molina Luis Manuel. "An analysis of the genesis of Hurricane Guillermo (1991)." Diss., The University of Arizona, 1996. http://hdl.handle.net/10150/187480.
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A case study of tropical cyclogenesis in the eastern Pacific Ocean is investigated. The tropical cyclone developed in 1991 during the Tropical Experiment in Mexico (TEXMEX) project. In this case study, the initial circulation originated west of Central America and after a period of intensification this circulation became Hurricane Guillermo. The purpose of this research is to identify the physical mechanisms that are active in the formation of the initial circulation and the role that the topography plays in this formation. A documentation of the characteristics of the large scale-flow present prior to the detection of the initial circulation is performed. The observations used include data derived from upper-air soundings and satellite imagery. These observations show that a synoptic-scale easterly wave moved over the Caribbean Sea and while the wave approached the topography of Central America, a low-level, mesoscale circulation developed over the eastern Pacific. It is observed that the modification of the easterly flow by the mountains is an important element in organizing the initial circulation. In order to investigate the dynamics involved in the formation of the circulation model simulations are performed. The objective of these simulations is to reproduce the formation of the circulation and analyze the contribution from the topographic modification of the flow in the formation of the vortex. This objective is accomplished by performing numerical simulations with a mesoscale model. The model fields indicate that the initiation of the circulation occurred while the easterly wave axis moved close to the mountains of Central America. The changes in the direction of the upstream easterly flow, induced by the wave, and the deflection of the winds by the mountains generated a pair of easterly jets in the eastern Pacific. These two elements, along with the Intertropical Convergence Zone (ITCZ), provided a mesoscale area of enhanced vorticity that defined the formation of a closed circulation. A further intensification of the circulation occurred and the storm evolved into a stronger system.
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Sitkowski, Matthew. "Low-level thermodynamic, kinematic and reflectivity fields of hurricane Guillermo (1997) during rapid intensification." Thesis, 2007. http://hdl.handle.net/10125/20710.
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