The Experts below are selected from a list of 261 Experts worldwide ranked by ideXlab platform
Chris D Thorncroft - One of the best experts on this subject based on the ideXlab platform.
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two contrasting african Easterly Wave behaviors
Journal of the Atmospheric Sciences, 2019Co-Authors: Yuanming Cheng, Chris D Thorncroft, George N KiladisAbstract:AbstractThe dominant structural variability of African Easterly Waves (AEWs) is explored using an empirical orthogonal function (EOF) approach. The structure of AEWs is obtained by projecting the w...
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variability and evolution of african Easterly Wave structures and their relationship with tropical cyclogenesis over the eastern atlantic
Monthly Weather Review, 2015Co-Authors: Alan Brammer, Chris D ThorncroftAbstract:AbstractAfrican Easterly Waves (AEWs) are objectively tracked between West Africa and the tropical Atlantic based on the CFSRv2 data for 1979 to 2012. The characteristics of the troughs of the AEWs at the West African coast are explored and related to whether they favor tropical cyclogenesis over the eastern Atlantic. A logistic regression model was used to determine the optimum combination of predictors that relate AEW characteristics to tropical cyclogenesis. The most skillful model for genesis over the eastern Atlantic consisted of four variables of the AEWs dynamics over the coastal region and the absolute number of days from the peak in the AEW season. Using this diagnostic an equal number of favorable developing and nondeveloping Waves were compared through a composite difference analysis. Favorable developing Waves had significantly higher moisture content in the lower troposphere to the northwest of the trough as they exited the West African coast compared to favorable nondeveloping Waves. Traject...
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the role of convectively coupled atmospheric kelvin Waves on african Easterly Wave activity
Monthly Weather Review, 2013Co-Authors: Michael J Ventrice, Chris D ThorncroftAbstract:AbstractThe role of convectively coupled atmospheric Kelvin Waves (CCKWs) on African Easterly Wave (AEW) activity is explored over tropical Africa during boreal summer. Examination of the pre-Alberto AEW in 2000 highlights the observation that the convective trigger for the initiation of the AEW was generated by a strong CCKW and that the subsequent intensification of the AEW at the West African coast was associated with a second CCKW. Composite analysis shows that, generally, AEW activity increases during and after the passage of the convectively active phase of strong CCKWs. The increase in AEW activity is consistent with convective triggering at the leading edge of the convective phase of the CCKW. This convective triggering occurs in a region where the background low-level Easterly vertical wind shear is increased by the CCKW. As the AEW propagates westward through the convectively active phase of the CCKW, it can develop in an environment favorable for convection. It is also shown that this phase of ...
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the role of convectively coupled atmospheric kelvin Waves on african Easterly Wave activity
Monthly Weather Review, 2013Co-Authors: Michael J Ventrice, Chris D ThorncroftAbstract:The role of convectively coupled atmospheric Kelvin Waves (CCKWs) on African Easterly Wave (AEW) activity is explored over tropical Africa during boreal summer. Examination of the pre-Alberto AEW in 2000 highlights the observation that the convective trigger for the initiation of the AEW was generated by a strong CCKW and that the subsequent intensification of the AEW at the West African coast was associated with a second CCKW. Composite analysis shows that, generally, AEW activity increases during and after the passage of the convectively active phase of strong CCKWs. The increase in AEW activity is consistent with convective triggering at the leading edge of the convective phase of the CCKW. This convective triggering occurs in a region where the background low-level Easterly vertical wind shear is increased by the CCKW. As the AEW propagates westward through the convectively active phase of the CCKW, it can develop in an environment favorable for convection. It is also shown that this phase of the CCKW is characterized by enhancedmeridionalvorticitygradientsin thecore ofthe AfricanEasterlyjet suggesting thatenhancedmixed barotropic‐baroclinic growth may also be responsible for enhanced AEW activity there.
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atlantic tropical cyclogenesis a three way interaction between an african Easterly Wave diurnally varying convection and a convectively coupled atmospheric kelvin Wave
Monthly Weather Review, 2012Co-Authors: Michael J Ventrice, Chris D Thorncroft, Matthew A JanigaAbstract:AbstractThis paper explores a three-way interaction between an African Easterly Wave (AEW), the diurnal cycle of convection over the Guinea Highlands (GHs), and a convectively coupled atmospheric equatorial Kelvin Wave (CCKW). These interactions resulted in the genesis of Tropical Storm Debby over the eastern tropical Atlantic during late August 2006. The diurnal cycle of convection downstream of the GHs during the month of August is explored. Convection associated with the coherent diurnal cycle is observed off the coast of West Africa during the morning. Later, convection initiates over and downstream of the GHs during the afternoon. These convective features were pronounced during the passage of the pre-Debby AEW. The superposition between the convectively active phase of a strong CCKW and the pre-Debby AEW occurred shortly after merging with the diurnally varying convection downstream of the GHs. The CCKW–AEW interaction preceded tropical cyclogenesis by 18 h. The CCKW provided a favorable environment...
T J Dunkerton - One of the best experts on this subject based on the ideXlab platform.
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examining the roles of the Easterly Wave critical layer and vorticity accretion during the tropical cyclogenesis of hurricane sandy
Monthly Weather Review, 2015Co-Authors: Louis L Lussier, Michael T Montgomery, Blake Rutherford, Mark A Boothe, T J DunkertonAbstract:AbstractThe tropical cyclogenesis sequence of Hurricane Sandy is examined. It is shown that genesis occurs within a recirculating Kelvin cat’s-eye flow of a westward-propagating tropical Wave. The cat’s-eye flow is able to provide a protective environment for the mesoscale vortex to grow and is characterized by gradual column moistening and increased areal coverage of deep cumulus convection. These findings are generally consistent with a recently proposed tropical cyclogenesis sequence referred to as the “marsupial paradigm.” Sandy’s cyclogenesis provides a useful illustration of the marsupial paradigm within a partially open recirculating region, with the opening located south of the pouch center. It is suggested that the opening acts to enhance the genesis process because it is adjacent to an environment characterized by warm, moist air, conditions favorable for tropical cyclogenesis. From a dynamical perspective, accretion of low-level cyclonic vorticity filaments into the developing vortex from sever...
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supplemental material for examining the roles of the Easterly Wave critical layer and vorticity accretion during the tropical cyclogenesis of hurricane sandy
2014Co-Authors: Louis L Lussier, Michael T Montgomery, Blake Rutherford, Mark A Boothe, T J DunkertonAbstract:Abstract : The tropical cyclogenesis model described in Dunkerton et al. (2009), and tested herein for the case of Hurricane Sandy (2012), provides a comprehensive description of the dynamics and thermodynamics that lead to the formation of a tropical cyclone. The model outlines the relevant physical processes and multi-scale interactions and can be summarized by the following three hypotheses (reproduced from Dunkerton et al. 2009). H1. Proto-vortex cyclonic eddies instrumental in TC formation are intimately associated with the parent Wave s critical latitude in the lower troposphere. The critical layer and Kelvin cat s eye within, formed as a result of the Wave s finite-amplitude interaction with its own critical latitude, contain a region of cyclonic rotation and weak straining/shearing deformation in which synoptic Waves and mesoscale vorticity anomalies, moving westward together, amplify and aggregate on a nearly zero relative mean flow. This multi-scale interaction provides a dynamical pathway to bottom-up development of the proto-vortex from below. H2. The critical-layer cat s eye of the parent Wave provides a set of quasi-closed material contours inside of which air is repeatedly moistened by convection, protected to some degree from lateral intrusion of dry air and impinging vertical shear, and (thanks to its location near the critical latitude) able to keep pace with the parent Wave until the protovortex has strengthened into a self-maintaining entity. H3. The parent Wave is maintained and possibly enhanced by diabatically amplified eddies within the Wave (proto-vortices on the mesoscale), a process favored in regions of small intrinsic phase speed.
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genesis of pre hurricane felix 2007 part i the role of the Easterly Wave critical layer
Journal of the Atmospheric Sciences, 2010Co-Authors: Zhuo Wang, Michael T Montgomery, T J DunkertonAbstract:Abstract The formation of pre–Hurricane Felix (2007) in a tropical Easterly Wave is examined in a two-part study using the Weather Research and Forecasting (WRF) model with a high-resolution nested grid configuration that permits the representation of cloud system processes. The simulation commences during the Wave stage of the precursor African Easterly-Wave disturbance. Here the simulated and observed developments are compared, while in Part II of the study various large-scale analyses, physical parameterizations, and initialization times are explored to document model sensitivities. In this first part the authors focus on the Wave/vortex morphology, its interaction with the adjacent intertropical convergence zone complex, and the vorticity balance in the neighborhood of the developing storm. Analysis of the model simulation points to a bottom-up development process within the Wave critical layer and supports the three new hypotheses of tropical cyclone formation proposed recently by Dunkerton, Montgome...
Michael T Montgomery - One of the best experts on this subject based on the ideXlab platform.
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examining the roles of the Easterly Wave critical layer and vorticity accretion during the tropical cyclogenesis of hurricane sandy
Monthly Weather Review, 2015Co-Authors: Louis L Lussier, Michael T Montgomery, Blake Rutherford, Mark A Boothe, T J DunkertonAbstract:AbstractThe tropical cyclogenesis sequence of Hurricane Sandy is examined. It is shown that genesis occurs within a recirculating Kelvin cat’s-eye flow of a westward-propagating tropical Wave. The cat’s-eye flow is able to provide a protective environment for the mesoscale vortex to grow and is characterized by gradual column moistening and increased areal coverage of deep cumulus convection. These findings are generally consistent with a recently proposed tropical cyclogenesis sequence referred to as the “marsupial paradigm.” Sandy’s cyclogenesis provides a useful illustration of the marsupial paradigm within a partially open recirculating region, with the opening located south of the pouch center. It is suggested that the opening acts to enhance the genesis process because it is adjacent to an environment characterized by warm, moist air, conditions favorable for tropical cyclogenesis. From a dynamical perspective, accretion of low-level cyclonic vorticity filaments into the developing vortex from sever...
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supplemental material for examining the roles of the Easterly Wave critical layer and vorticity accretion during the tropical cyclogenesis of hurricane sandy
2014Co-Authors: Louis L Lussier, Michael T Montgomery, Blake Rutherford, Mark A Boothe, T J DunkertonAbstract:Abstract : The tropical cyclogenesis model described in Dunkerton et al. (2009), and tested herein for the case of Hurricane Sandy (2012), provides a comprehensive description of the dynamics and thermodynamics that lead to the formation of a tropical cyclone. The model outlines the relevant physical processes and multi-scale interactions and can be summarized by the following three hypotheses (reproduced from Dunkerton et al. 2009). H1. Proto-vortex cyclonic eddies instrumental in TC formation are intimately associated with the parent Wave s critical latitude in the lower troposphere. The critical layer and Kelvin cat s eye within, formed as a result of the Wave s finite-amplitude interaction with its own critical latitude, contain a region of cyclonic rotation and weak straining/shearing deformation in which synoptic Waves and mesoscale vorticity anomalies, moving westward together, amplify and aggregate on a nearly zero relative mean flow. This multi-scale interaction provides a dynamical pathway to bottom-up development of the proto-vortex from below. H2. The critical-layer cat s eye of the parent Wave provides a set of quasi-closed material contours inside of which air is repeatedly moistened by convection, protected to some degree from lateral intrusion of dry air and impinging vertical shear, and (thanks to its location near the critical latitude) able to keep pace with the parent Wave until the protovortex has strengthened into a self-maintaining entity. H3. The parent Wave is maintained and possibly enhanced by diabatically amplified eddies within the Wave (proto-vortices on the mesoscale), a process favored in regions of small intrinsic phase speed.
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the genesis of typhoon nuri as observed during the tropical cyclone structure 2008 tcs 08 field experiment part 1 the role of the Easterly Wave critical layer
Atmospheric Chemistry and Physics, 2010Co-Authors: Michael T Montgomery, Louis L Lussier, Richard W Moore, Zhuo WangAbstract:Abstract. An observational and real-time model forecast study of the genesis of Typhoon Nuri during the Tropical Cyclone Structure 2008 (TCS-08) field campaign in the western North Pacific sector is presented. Analysis and observational data show that the surrounding base state is an Easterly trade wind flow and the precursor disturbance to Typhoon Nuri is an Easterly Wave that originates in the ITCZ in the Central Pacific. This disturbance can be tracked more than 10 days prior to tropical storm formation. An overview of the field data is presented here using a newly proposed dynamical framework for tropical cyclone formation within the critical layer of an Easterly Wave. Despite propagating through a hostile environment ripe with strong vertical wind shear and relatively dry air, the Easterly Wave critical layer protects the proto-vortex and allows it to gestate until it reaches a more favorable environment. Within this protective "Kelvin cat's eye flow" located within the Wave's critical layer existed a sweet spot, defined as the intersection between the Wave trough and critical latitude, which is the preferred location for tropical cyclogenesis. Global Forecast System Final Analyses and IR satellite imagery, which shows convective bands wrapping around the sweet spot as genesis nears, confirm that this sweet spot is the location where Typhoon Nuri's dominant low-level circulation emerges. United States Air Force C130 and Naval Research Laboratory P3 research flights on 16 and 17 August collected flight-level, dropwindsonde, and Doppler radar data that allowed an evaluation of the dynamic and thermodynamic processes within the cat's eye circulation. The dropwindsonde analyses identifies the precursor Easterly Wave disturbance on 16 August and identifies an area of weak low-level cyclonic circulation on 17 August. Real-time forecasts were produced using operational global prediction model data to support scientific missions during TCS-08. These forecasts were found to be useful in flight planning discussions and predicted Typhoon Nuri's eventual genesis latitude within 1.5 degrees 72 h in advance.
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genesis of pre hurricane felix 2007 part i the role of the Easterly Wave critical layer
Journal of the Atmospheric Sciences, 2010Co-Authors: Zhuo Wang, Michael T Montgomery, T J DunkertonAbstract:Abstract The formation of pre–Hurricane Felix (2007) in a tropical Easterly Wave is examined in a two-part study using the Weather Research and Forecasting (WRF) model with a high-resolution nested grid configuration that permits the representation of cloud system processes. The simulation commences during the Wave stage of the precursor African Easterly-Wave disturbance. Here the simulated and observed developments are compared, while in Part II of the study various large-scale analyses, physical parameterizations, and initialization times are explored to document model sensitivities. In this first part the authors focus on the Wave/vortex morphology, its interaction with the adjacent intertropical convergence zone complex, and the vorticity balance in the neighborhood of the developing storm. Analysis of the model simulation points to a bottom-up development process within the Wave critical layer and supports the three new hypotheses of tropical cyclone formation proposed recently by Dunkerton, Montgome...
Zhuo Wang - One of the best experts on this subject based on the ideXlab platform.
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characteristics of tropical Easterly Wave pouches during tropical cyclone formation
Monthly Weather Review, 2014Co-Authors: Zhuo Wang, Isaac HankesAbstract:AbstractThe pregenesis evolution of Wave pouches was examined for 164 named tropical cyclones that originated from zonally propagating tropical Easterly Waves over the Atlantic during July–October 1989–2010 using the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Re-Analysis (ERA-Interim) and the Climate Prediction Center (CPC) morphing technique (CMORPH) precipitation. East of 60°W, most Wave pouches (~80%) form at 700 hPa first, often extending down to 850 or 925 hPa off the coast of West Africa. By contrast, the majority of the Wave pouches (~68%) over the west Atlantic (west of 60°W) form at 850 or 925 hPa first. Wave pouches become more vertically aligned approaching genesis. It was also found that vorticity at 925 hPa intensifies faster than that at 600 hPa. A warm-core structure forms at the meso-β scale near the pouch center prior to genesis but is less well defined at the meso-α pouch scale. The evolution of precipitation and the low-level convergence suggests that convection ...
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the genesis of typhoon nuri as observed during the tropical cyclone structure 2008 tcs 08 field experiment part 1 the role of the Easterly Wave critical layer
Atmospheric Chemistry and Physics, 2010Co-Authors: Michael T Montgomery, Louis L Lussier, Richard W Moore, Zhuo WangAbstract:Abstract. An observational and real-time model forecast study of the genesis of Typhoon Nuri during the Tropical Cyclone Structure 2008 (TCS-08) field campaign in the western North Pacific sector is presented. Analysis and observational data show that the surrounding base state is an Easterly trade wind flow and the precursor disturbance to Typhoon Nuri is an Easterly Wave that originates in the ITCZ in the Central Pacific. This disturbance can be tracked more than 10 days prior to tropical storm formation. An overview of the field data is presented here using a newly proposed dynamical framework for tropical cyclone formation within the critical layer of an Easterly Wave. Despite propagating through a hostile environment ripe with strong vertical wind shear and relatively dry air, the Easterly Wave critical layer protects the proto-vortex and allows it to gestate until it reaches a more favorable environment. Within this protective "Kelvin cat's eye flow" located within the Wave's critical layer existed a sweet spot, defined as the intersection between the Wave trough and critical latitude, which is the preferred location for tropical cyclogenesis. Global Forecast System Final Analyses and IR satellite imagery, which shows convective bands wrapping around the sweet spot as genesis nears, confirm that this sweet spot is the location where Typhoon Nuri's dominant low-level circulation emerges. United States Air Force C130 and Naval Research Laboratory P3 research flights on 16 and 17 August collected flight-level, dropwindsonde, and Doppler radar data that allowed an evaluation of the dynamic and thermodynamic processes within the cat's eye circulation. The dropwindsonde analyses identifies the precursor Easterly Wave disturbance on 16 August and identifies an area of weak low-level cyclonic circulation on 17 August. Real-time forecasts were produced using operational global prediction model data to support scientific missions during TCS-08. These forecasts were found to be useful in flight planning discussions and predicted Typhoon Nuri's eventual genesis latitude within 1.5 degrees 72 h in advance.
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genesis of pre hurricane felix 2007 part i the role of the Easterly Wave critical layer
Journal of the Atmospheric Sciences, 2010Co-Authors: Zhuo Wang, Michael T Montgomery, T J DunkertonAbstract:Abstract The formation of pre–Hurricane Felix (2007) in a tropical Easterly Wave is examined in a two-part study using the Weather Research and Forecasting (WRF) model with a high-resolution nested grid configuration that permits the representation of cloud system processes. The simulation commences during the Wave stage of the precursor African Easterly-Wave disturbance. Here the simulated and observed developments are compared, while in Part II of the study various large-scale analyses, physical parameterizations, and initialization times are explored to document model sensitivities. In this first part the authors focus on the Wave/vortex morphology, its interaction with the adjacent intertropical convergence zone complex, and the vorticity balance in the neighborhood of the developing storm. Analysis of the model simulation points to a bottom-up development process within the Wave critical layer and supports the three new hypotheses of tropical cyclone formation proposed recently by Dunkerton, Montgome...
Da-lin Zhang - One of the best experts on this subject based on the ideXlab platform.
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genesis of hurricane julia 2010 within an african Easterly Wave sensitivity to ice microphysics
Journal of Applied Meteorology and Climatology, 2016Co-Authors: Stefan F. Cecelski, Da-lin ZhangAbstract:AbstractWhile much attention has been given to investigating the dynamics of tropical cyclogenesis (TCG), little work explores the thermodynamical evolution and related cloud microphysical processes occurring during TCG. This study elaborates on previous research by examining the impact of ice microphysics on the genesis of Hurricane Julia during the 2010 North Atlantic Ocean hurricane season. As compared with a control simulation, two sensitivity experiments are conducted in which the latent heat of fusion owing to depositional growth is removed in one experiment and homogeneous freezing is not allowed to occur in the other. Results show that removing the latent heat of fusion substantially reduces the warming of the upper troposphere during TCG. This results in a lack of meso-α-scale hydrostatic surface pressure falls and no tropical depression (TD)-scale mean sea level pressure (MSLP) disturbance. In contrast, removing homogeneous freezing has little impact on the structure and magnitude of the upper-t...
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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, 2015Co-Authors: Lin Zhu, Stefan F. Cecelski, Da-lin Zhang, Xinyong ShenAbstract:AbstractThe “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 r...
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genesis of hurricane julia 2010 within an african Easterly Wave sensitivity analyses of wrf letkf ensemble forecasts
Journal of the Atmospheric Sciences, 2014Co-Authors: Stefan F. Cecelski, Da-lin ZhangAbstract:AbstractIn this study, the predictability of tropical cyclogenesis (TCG) is explored by conducting ensemble sensitivity analyses on the TCG of Hurricane Julia (2010). Using empirical orthogonal functions (EOFs), the dominant patterns of ensemble disagreements are revealed for various meteorological parameters such as mean sea level pressure (MSLP) and upper-tropospheric temperature. Using the principal components of the EOF patterns, ensemble sensitivities are generated to elucidate which mechanisms drive the parametric ensemble differences.The dominant pattern of MSLP ensemble spread is associated with the intensity of the pre–tropical depression (pre-TD), explaining nearly half of the total variance at each respective time. Similar modes of variance are found for the low-level absolute vorticity, though the patterns explain substantially less variance. Additionally, the largest modes of variability associated with upper-level temperature anomalies closely resemble the patterns of MSLP variance, suggesti...
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genesis of hurricane julia 2010 within an african Easterly Wave developing and nondeveloping members from wrf letkf ensemble forecasts
Journal of the Atmospheric Sciences, 2014Co-Authors: Stefan F. Cecelski, Da-lin Zhang, Takemasa MiyoshiAbstract:AbstractIn this study, the predictability of and parametric differences in the genesis of Hurricane Julia (2010) are investigated using 20 mesoscale ensemble forecasts with the finest resolution of 1 km. Results show that the genesis of Julia is highly predictable, with all but two members undergoing genesis. Despite the high predictability, substantial parametric differences exist between the stronger and weaker members. Notably, the strongest-developing member exhibits large upper-tropospheric warming within a storm-scale outflow during genesis. In contrast, the nondeveloping member has weak and more localized warming due to inhibited convective development and a lack of a storm-scale outflow. A reduction in the Rossby radius of deformation in the strongest member aids in the accumulation of the warmth, while little contraction takes place in the nondeveloping member. The warming in the upper troposphere is responsible for the development of meso-α-scale surface pressure falls and a meso-β surface low i...
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Genesis of Hurricane Julia (2010) within an African Easterly Wave: Low-Level Vortices and Upper-Level Warming
Journal of the Atmospheric Sciences, 2013Co-Authors: Stefan F. Cecelski, Da-lin ZhangAbstract:AbstractWhile a robust theoretical framework for tropical cyclogenesis (TCG) within African Easterly Waves (AEWs) has recently been developed, little work explores the development of low-level meso-β-scale vortices (LLVs) and a meso-α-scale surface low in relation to deep convection and upper-tropospheric warming. In this study, the development of an LLV into Hurricane Julia (2010) is shown through a high-resolution model simulation with the finest grid size of 1 km. The results presented expand upon the connections between LLVs and the AEW presented in previous studies while demonstrating the importance of upper-tropospheric warming for TCG.It is found that the significant intensification phase of Hurricane Julia is triggered by the pronounced upper-tropospheric warming associated with organized deep convection. The warming is able to intensify and expand during TCG owing to formation of a storm-scale outflow beyond the Rossby radius of deformation. Results confirm previous ideas by demonstrating that th...