The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
Russell L Elsberry - One of the best experts on this subject based on the ideXlab platform.
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Simulations of the Extratropical Transition of Tropical Cyclones: Phasing between the Upper-Level Trough and Tropical Cyclones
Monthly Weather Review, 2007Co-Authors: Elizabeth A. Ritchie, Russell L ElsberryAbstract:Abstract Whether the tropical Cyclone remnants will become a significant Extratropical Cyclone during the reintensification stage of Extratropical transition is a complex problem because of the uncertainty in the tropical Cyclone, the midlatitude circulation, the subtropical antiCyclone, and the nonlinear interactions among these systems. In a previous study, the authors simulated the impact of the strength of the midlatitude circulation trough without changing its phasing with the tropical Cyclone. In this study, the impact of phasing is simulated by fixing the initial position and amplitude of the midlatitude trough and varying the initial position of the tropical Cyclone. The peak intensity of the Extratropical Cyclone following the Extratropical transition is strongly dependent on the phasing, which leads to different degrees of interaction with the midlatitude baroclinic zone. Many aspects of the simulated circulation, temperature, and precipitation fields appear quite realistic for the reintensifyin...
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adjoint sensitivity of an idealized Extratropical Cyclone with moist physical processes
Quarterly Journal of the Royal Meteorological Society, 2006Co-Authors: Rolf H Langland, Russell L Elsberry, Ronald M ErricoAbstract:An adjoint model (MAMS1) that includes parametrizations for convective (subgrid-scale), and non-convective (grid-scale) precipitation, and surface latent-heat flux is used to investigate an idealized Extratropical cyclogenesis. The adjoint sensitivity information demonstrates the effects that perturbations of model variables and parameters at various times during the Cyclone life cycle have on forecast Cyclone intensity. For a nonlinear trajectory that includes precipitation processes and surface latent-heat flux, the accuracy of the tangent-linear and adjoint model is much higher when moist physical processes are included. Inclusion of moist processes in the adjoint model increases sensitivity magnitude compared with sensitivity obtained with a dry adjoint model, but does not alter the primary spatial pattern of sensitivity. The larger Cyclone deepening rates that occur with the inclusion of moisture are related to latent-heat release from condensation of water vapour in areas of the middle and lower troposphere (the warm-front region) that are strongly sensitive to temperature perturbations in both dry and moist Cyclone simulations. The effects of diabatic heating on Cyclone development are interpreted as a reinforcement of dry baroclinic instability, and not a separate development mechanism (which would have a unique non-baroclinic sensitivity signature). The sensitivity patterns explain why favourably positioned latent-heat release is an ingredient that can lead to explosive baroclinic development. Cyclone intensity is very sensitive to the vertical distribution of temperature perturbations, so this feature of diabatic heating is critical to the Cyclone forecast. An increase in the transfer coefficient, CE, for the surface latent-heat flux can intensify the Cyclone by adding moisture to the lower troposphere in the Cyclone warm sector before the release of latent heat by precipitation processes. Perturbations of CE have more effect on Cyclone intensity than perturbations of the transfer coefficients involved in surface sensible-heat flux and surface stress during most of the Cyclone life cycle.
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simulations of the Extratropical transition of tropical Cyclones contributions by the midlatitude upper level trough to reintensification
Monthly Weather Review, 2003Co-Authors: Elizabeth A. Ritchie, Russell L ElsberryAbstract:Abstract The Extratropical Cyclone development processes during the reintensification stage of an Extratropical transition from a tropical Cyclone (TC) are described using numerical simulations. Three control simulations without a tropical Cyclone present examine the Extratropical cyclogenesis associated with upper-level troughs that are characterized as weak, moderate, and strong. When no tropical Cyclone is included in the simulation, the minimum surface pressures attained with the weak, moderate, and strong troughs are 1003, 991, and 977 mb, respectively. In all three cases, the low tilts northwestward with height during intensification, and the rainfall pattern and eventual occlusion are representative of classic Extratropical Cyclone development. The interactions of a tropical Cyclone with each of the three midlatitude circulation patterns are compared with the control simulations to illustrate the contributions to the Extratropical transition of the tropical Cyclone. In the three trough-with-TC case...
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Extratropical transition of western north pacific tropical Cyclones midlatitude and tropical Cyclone contributions to reintensification
Monthly Weather Review, 2002Co-Authors: Peter M Klein, Patrick A Harr, Russell L ElsberryAbstract:Abstract This study of Extratropical transition of western North Pacific tropical Cyclones (TCs) addresses the reintensification stage during which the TC remnants develop as an Extratropical Cyclone. The hypothesis examined here is that reintensification depends on the interaction between the midlatitude circulation contributions from mid- and upper-level dynamic processes, low-level thermal processes from the decaying TC, and upper-level outflow characteristics from the decaying TC. Reintensification occurs when the combination of the dynamic and thermodynamic processes define a region that is favorable for Extratropical Cyclone development. The midlatitude circulation contribution to reintensification is characterized by comparing a control forecast made with an atmosphere-only version of the Coupled Ocean–Atmosphere Mesoscale Prediction System with a simulation in which the TC has been removed (NOTC). The midlatitude contribution is favorable if a significant Extratropical Cyclone forms in the NOTC si...
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Extratropical transition of tropical Cyclones over the western north pacific part i evolution of structural characteristics during the transition process
Monthly Weather Review, 2000Co-Authors: Patrick A Harr, Russell L ElsberryAbstract:Abstract The development of Extratropical Cyclone structural characteristics that resulted from the Extratropical transition of Typhoon (TY) David (1997) and TY Opal (1997) over the western North Pacific is examined. David moved poleward ahead of a midlatitude trough that was moving eastward as the dominant midlatitude circulation feature over the western North Pacific. During the transition, David coupled with the midlatitude trough, which led to the evolution of an intense Cyclone that became the primary circulation over the North Pacific. Although Opal also moved poleward ahead of a midlatitude trough, the principal midlatitude feature over the western North Pacific was a preexisting stationary Cyclone over the Kamchatka peninsula. During transition, Opal weakened and became a secondary Cyclone to the preexisting primary North Pacific Cyclone. The structural characteristics of the evolving Extratropical Cyclone with respect to each case are examined in the context of the interaction between a vortex an...
Ian Simmonds - One of the best experts on this subject based on the ideXlab platform.
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A methodology of tracking transitioning Cyclones
IOP Conference Series: Earth and Environmental Science, 2010Co-Authors: Luke Andrew Garde, Alexandre Bernardes Pezza, Ian Simmonds, N E DavidsonAbstract:"Cyclone transition" is a process in which either a tropical Cyclone or an Extratropical Cyclone undergoes a fundamental dynamic and thermodynamic transformation. A "tropical transition" is a process in which a cold-core Extratropical Cyclone transforms to a warm-core tropical Cyclone, while "Extratropical transition" refers to the opposite mechanism. The transition process is gradual, with no sharp defining threshold representing its commencement or completion. This study develops and explores a methodology of identifying tropical transition and Extratropical transition events. Using the 1.5° ERA-Interim reanalysis dataset over the period from 1989 to present, Cyclone tracks are derived using The Melbourne University Tracking Scheme. The average temperature difference between the Cyclone core and an environmental ring, set at a distance corresponding to the Cyclones size, is then calculated throughout the troposphere during the life cycle of the Cyclone. This difference represents the index or phase of the Cyclone relative to its immediate environment. The lack of a complete Cyclone transition climatology and the uncertainty behind the transition process is the motivation for this research, with the overarching aim of placing these systems in climatic perspective. This methodology seeks to create the foundations for further Cyclone research.
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Effect of tropospheric temperature change on the zonal mean circulation and SH winter Extratropical Cyclones
Climate Dynamics, 2009Co-Authors: Eun-pa Lim, Ian SimmondsAbstract:This study aims to understand the mechanisms which cause an overall reduction of SH Extratropical Cyclone activity with a slight increase in the high latitudes in a warmer climate simulated in general circulation models (GCMs) with increasing CO_2. For this purpose, we conducted idealized model experiments by forcing warm temperature anomalies to the areas where climate change models exhibit local maximum warming—the tropics in the upper troposphere and the polar regions in the lower troposphere—simultaneously and separately. The Melbourne University atmospheric GCM (R21) coupled with prescribed SST was utilized for the experiments. Our results demonstrate that the reduction of SH Extratropical Cyclone frequency and depth in the midlatitudes but the slight increase in the high latitudes suggested in climate change models result essentially from the tropical upper tropospheric warming. With this tropical warming, the enhanced static stability which decreases baroclinicity in the low and midlatitudes turns out to be a major contributor to the decrease of Cyclone activity equatorward of 45°S whereas the increased meridional temperature gradient in the high latitudes seems an important mechanism for the increase of Cyclone activity over 50°–60°S.
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Variability of Southern Hemisphere Extratropical Cyclone behavior, 1958-97
Journal of Climate, 2000Co-Authors: Ian Simmonds, Kevin KeayAbstract:Abstract An analysis of the variability and trends exhibited by many aspects of Southern Hemisphere (SH) mean sea level Extratropical Cyclones during the period 1958–97 is presented. The investigation is undertaken by applying a state-of-the-art Cyclone finding and tracking scheme to the 6-hourly reanalyses produced by the National Centers for Environmental Prediction. The outcome of this is arguably the most reliable analysis of SH Cyclone variability undertaken to date. Across the 40-yr period the annual and seasonal mean Cyclone densities have undergone reductions at most locations south of about 40°S (with the greatest reductions near 60°S), and increases to the north. This pattern of change resembles the “high-latitude mode” identified in many studies of SH circulation features. It is shown that the mean radius of SH Extratropical Cyclones displays almost everywhere a significant positive trend, and there are also increases in annual mean Cyclone “depth” (i.e., the pressure difference between the cen...
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AN ANALYSIS OF ANTARCTIC SEA‐ICE AND Extratropical Cyclone ASSOCIATIONS
International Journal of Climatology, 1996Co-Authors: Christopher R. Godfred‐spenning, Ian SimmondsAbstract:We have examined aspects of the association between Antarctic sea-ice and Southern Hemisphere Extratropical Cyclones for the period 1973–1991, on a seasonal time-scale. It has been found that a sea-ice–Cyclone link is not apparent over the entire sea-ice zone. However, we have found suggestions of interannual connections over certain regimes during particular seasons. Among the connections identified was an association between sea-ice and spatial-system density in the Amundsen Sea in summer. Also, winter cyclogenesis density in the Ross and Bellingshausen Seas appears strongly connected to ice in the same region. By analysing the results obtained through lagging and leading the sea-ice time series by one season, we have concluded that the forcing of sea-ice distribution by atmospheric stresses (either thermally or via wind manipulation) is a more dominant factor than anomalous sea-ice conditions altering Cyclone tracks or spatial density, a finding supported by the more widespread incidence of significant correlation when the sea-ice time series lagged both system density and cyclogenesis by one season. Our results also show that Cyclone density appeared associated more strongly with sea-ice either ‘upstream’ or ‘downstream’, especially for Cyclones in certain sections of the Weddell and Ross Seas during spring. On the other hand, winter cyclogenesis was most strongly linked to local sea-ice.
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an analysis of antarctic sea ice and Extratropical Cyclone associations
International Journal of Climatology, 1996Co-Authors: Christopher R Godfredspenning, Ian SimmondsAbstract:We have examined aspects of the association between Antarctic sea-ice and Southern Hemisphere Extratropical Cyclones for the period 1973–1991, on a seasonal time-scale. It has been found that a sea-ice–Cyclone link is not apparent over the entire sea-ice zone. However, we have found suggestions of interannual connections over certain regimes during particular seasons. Among the connections identified was an association between sea-ice and spatial-system density in the Amundsen Sea in summer. Also, winter cyclogenesis density in the Ross and Bellingshausen Seas appears strongly connected to ice in the same region. By analysing the results obtained through lagging and leading the sea-ice time series by one season, we have concluded that the forcing of sea-ice distribution by atmospheric stresses (either thermally or via wind manipulation) is a more dominant factor than anomalous sea-ice conditions altering Cyclone tracks or spatial density, a finding supported by the more widespread incidence of significant correlation when the sea-ice time series lagged both system density and cyclogenesis by one season. Our results also show that Cyclone density appeared associated more strongly with sea-ice either ‘upstream’ or ‘downstream’, especially for Cyclones in certain sections of the Weddell and Ross Seas during spring. On the other hand, winter cyclogenesis was most strongly linked to local sea-ice.
Geraint Vaughan - One of the best experts on this subject based on the ideXlab platform.
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analysis of an ex tropical Cyclone after its reintensification as a warm core Extratropical Cyclone
Quarterly Journal of the Royal Meteorological Society, 1998Co-Authors: Keith A. Browning, P. Panagi, Geraint VaughanAbstract:Ex-hurricane Lili reintensified as an Extratropical Cyclone before travelling across the data-rich region of the British Isles on 28 October 1996. The Cyclone centre passed close to a Mesosphere-Stratosphere-Troposphere (MST) radar, providing continuous profiles of wind etc. which were used to evaluate diagnostics from the mesoscale version of the operational UK Meteorological Office Unified Model. The paper presents a mesoanalysis of the mature Extratropical Cyclone using model output together with radar and satellite observations. The combined analysis reveals a vertically extensive warm core three-quarters surrounded by a low-level jet reaching over 40 m s−1. There was an associated eye, relatively free of cloud and partly surrounded by a hook cloud producing extensive heavy rain, which was itself encircled by cooler dry-intrusion air. The stratospheric part of the dry intrusion (and its potential-vorticity (PV) anomaly) descended within a tropopause fold around the cloud hook generally to below 400 hPa, with small pockets penetrating significantly lower. The Cyclone's reintensification as an Extratropical Cyclone was related to its interaction with the stratospheric PV anomaly. This interaction commenced immediately after the decay of the strong moist ascent and associated deep column of diabatically generated positive PV that had characterized the earlier tropical-Cyclone phase. Following reintensification, the dry-intrusion air entered the eye region of the Extratropical Cyclone over a deep layer. The mesoscale model represented many aspects of the Cyclone structure well but it underestimated the dryness of the dry-intrusion air entering the eye. The MST radar vividly depicted the region of moist boundary-layer air responsible for the hook cloud rising up into the region of the lowered tropopause.
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Analysis of an ex‐tropical Cyclone after its reintensification as a warm‐core Extratropical Cyclone
Quarterly Journal of the Royal Meteorological Society, 1998Co-Authors: Keith A. Browning, P. Panagi, Geraint VaughanAbstract:Ex-hurricane Lili reintensified as an Extratropical Cyclone before travelling across the data-rich region of the British Isles on 28 October 1996. The Cyclone centre passed close to a Mesosphere-Stratosphere-Troposphere (MST) radar, providing continuous profiles of wind etc. which were used to evaluate diagnostics from the mesoscale version of the operational UK Meteorological Office Unified Model. The paper presents a mesoanalysis of the mature Extratropical Cyclone using model output together with radar and satellite observations. The combined analysis reveals a vertically extensive warm core three-quarters surrounded by a low-level jet reaching over 40 m s−1. There was an associated eye, relatively free of cloud and partly surrounded by a hook cloud producing extensive heavy rain, which was itself encircled by cooler dry-intrusion air. The stratospheric part of the dry intrusion (and its potential-vorticity (PV) anomaly) descended within a tropopause fold around the cloud hook generally to below 400 hPa, with small pockets penetrating significantly lower. The Cyclone's reintensification as an Extratropical Cyclone was related to its interaction with the stratospheric PV anomaly. This interaction commenced immediately after the decay of the strong moist ascent and associated deep column of diabatically generated positive PV that had characterized the earlier tropical-Cyclone phase. Following reintensification, the dry-intrusion air entered the eye region of the Extratropical Cyclone over a deep layer. The mesoscale model represented many aspects of the Cyclone structure well but it underestimated the dryness of the dry-intrusion air entering the eye. The MST radar vividly depicted the region of moist boundary-layer air responsible for the hook cloud rising up into the region of the lowered tropopause.
Elizabeth A. Ritchie - One of the best experts on this subject based on the ideXlab platform.
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Simulations of the Extratropical Transition of Tropical Cyclones: Phasing between the Upper-Level Trough and Tropical Cyclones
Monthly Weather Review, 2007Co-Authors: Elizabeth A. Ritchie, Russell L ElsberryAbstract:Abstract Whether the tropical Cyclone remnants will become a significant Extratropical Cyclone during the reintensification stage of Extratropical transition is a complex problem because of the uncertainty in the tropical Cyclone, the midlatitude circulation, the subtropical antiCyclone, and the nonlinear interactions among these systems. In a previous study, the authors simulated the impact of the strength of the midlatitude circulation trough without changing its phasing with the tropical Cyclone. In this study, the impact of phasing is simulated by fixing the initial position and amplitude of the midlatitude trough and varying the initial position of the tropical Cyclone. The peak intensity of the Extratropical Cyclone following the Extratropical transition is strongly dependent on the phasing, which leads to different degrees of interaction with the midlatitude baroclinic zone. Many aspects of the simulated circulation, temperature, and precipitation fields appear quite realistic for the reintensifyin...
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simulations of the Extratropical transition of tropical Cyclones contributions by the midlatitude upper level trough to reintensification
Monthly Weather Review, 2003Co-Authors: Elizabeth A. Ritchie, Russell L ElsberryAbstract:Abstract The Extratropical Cyclone development processes during the reintensification stage of an Extratropical transition from a tropical Cyclone (TC) are described using numerical simulations. Three control simulations without a tropical Cyclone present examine the Extratropical cyclogenesis associated with upper-level troughs that are characterized as weak, moderate, and strong. When no tropical Cyclone is included in the simulation, the minimum surface pressures attained with the weak, moderate, and strong troughs are 1003, 991, and 977 mb, respectively. In all three cases, the low tilts northwestward with height during intensification, and the rainfall pattern and eventual occlusion are representative of classic Extratropical Cyclone development. The interactions of a tropical Cyclone with each of the three midlatitude circulation patterns are compared with the control simulations to illustrate the contributions to the Extratropical transition of the tropical Cyclone. In the three trough-with-TC case...
Keith A. Browning - One of the best experts on this subject based on the ideXlab platform.
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analysis of an ex tropical Cyclone after its reintensification as a warm core Extratropical Cyclone
Quarterly Journal of the Royal Meteorological Society, 1998Co-Authors: Keith A. Browning, P. Panagi, Geraint VaughanAbstract:Ex-hurricane Lili reintensified as an Extratropical Cyclone before travelling across the data-rich region of the British Isles on 28 October 1996. The Cyclone centre passed close to a Mesosphere-Stratosphere-Troposphere (MST) radar, providing continuous profiles of wind etc. which were used to evaluate diagnostics from the mesoscale version of the operational UK Meteorological Office Unified Model. The paper presents a mesoanalysis of the mature Extratropical Cyclone using model output together with radar and satellite observations. The combined analysis reveals a vertically extensive warm core three-quarters surrounded by a low-level jet reaching over 40 m s−1. There was an associated eye, relatively free of cloud and partly surrounded by a hook cloud producing extensive heavy rain, which was itself encircled by cooler dry-intrusion air. The stratospheric part of the dry intrusion (and its potential-vorticity (PV) anomaly) descended within a tropopause fold around the cloud hook generally to below 400 hPa, with small pockets penetrating significantly lower. The Cyclone's reintensification as an Extratropical Cyclone was related to its interaction with the stratospheric PV anomaly. This interaction commenced immediately after the decay of the strong moist ascent and associated deep column of diabatically generated positive PV that had characterized the earlier tropical-Cyclone phase. Following reintensification, the dry-intrusion air entered the eye region of the Extratropical Cyclone over a deep layer. The mesoscale model represented many aspects of the Cyclone structure well but it underestimated the dryness of the dry-intrusion air entering the eye. The MST radar vividly depicted the region of moist boundary-layer air responsible for the hook cloud rising up into the region of the lowered tropopause.
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Analysis of an ex‐tropical Cyclone after its reintensification as a warm‐core Extratropical Cyclone
Quarterly Journal of the Royal Meteorological Society, 1998Co-Authors: Keith A. Browning, P. Panagi, Geraint VaughanAbstract:Ex-hurricane Lili reintensified as an Extratropical Cyclone before travelling across the data-rich region of the British Isles on 28 October 1996. The Cyclone centre passed close to a Mesosphere-Stratosphere-Troposphere (MST) radar, providing continuous profiles of wind etc. which were used to evaluate diagnostics from the mesoscale version of the operational UK Meteorological Office Unified Model. The paper presents a mesoanalysis of the mature Extratropical Cyclone using model output together with radar and satellite observations. The combined analysis reveals a vertically extensive warm core three-quarters surrounded by a low-level jet reaching over 40 m s−1. There was an associated eye, relatively free of cloud and partly surrounded by a hook cloud producing extensive heavy rain, which was itself encircled by cooler dry-intrusion air. The stratospheric part of the dry intrusion (and its potential-vorticity (PV) anomaly) descended within a tropopause fold around the cloud hook generally to below 400 hPa, with small pockets penetrating significantly lower. The Cyclone's reintensification as an Extratropical Cyclone was related to its interaction with the stratospheric PV anomaly. This interaction commenced immediately after the decay of the strong moist ascent and associated deep column of diabatically generated positive PV that had characterized the earlier tropical-Cyclone phase. Following reintensification, the dry-intrusion air entered the eye region of the Extratropical Cyclone over a deep layer. The mesoscale model represented many aspects of the Cyclone structure well but it underestimated the dryness of the dry-intrusion air entering the eye. The MST radar vividly depicted the region of moist boundary-layer air responsible for the hook cloud rising up into the region of the lowered tropopause.
