The Experts below are selected from a list of 315 Experts worldwide ranked by ideXlab platform
Kerry A. Emanuel - One of the best experts on this subject based on the ideXlab platform.
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Impacts of hemispheric solar geoengineering on Tropical Cyclone frequency
Nature Communications, 2017Co-Authors: Anthony C. Jones, Jim Haywood, Nick Dunstone, Matt Hawcroft, Kevin I. Hodges, Kerry A. Emanuel, Andrew JonesAbstract:Solar geoengineering refers to a range of proposed methods for counteracting global warming by artificially reducing sunlight at Earth’s surface. The most widely known solar geoengineering proposal is stratospheric aerosol injection (SAI), which has impacts analogous to those from volcanic eruptions. Observations following major volcanic eruptions indicate that aerosol enhancements confined to a single hemisphere effectively modulate North Atlantic Tropical Cyclone (TC) activity in the following years. Here we investigate the effects of both single-hemisphere and global SAI scenarios on North Atlantic TC activity using the HadGEM2-ES general circulation model and various TC identification methods. We show that a robust result from all of the methods is that SAI applied to the southern hemisphere would enhance TC frequency relative to a global SAI application, and vice versa for SAI in the northern hemisphere. Our results reemphasise concerns regarding regional geoengineering and should motivate policymakers to regulate large-scale unilateral geoengineering deployments. Solar geoengineering has been proposed as a means of mitigating the warming effects of climate change, yet the consequences of such action remain uncertain. Here, using a general circulation model, the authors evaluate the effect of stratospheric aerosol injection on Tropical Cyclone activity.
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the role of inner core moisture in Tropical Cyclone predictability and practical forecast skill
Journal of the Atmospheric Sciences, 2017Co-Authors: Kerry A. Emanuel, Fuqing ZhangAbstract:AbstractErrors in Tropical Cyclone intensity forecasts are dominated by initial-condition errors out to at least a few days. Initialization errors are usually thought of in terms of position and intensity, but here it is shown that growth of intensity error is at least as sensitive to the specification of inner-core moisture as to that of the wind field. Implications of this finding for Tropical Cyclone observational strategies and for overall predictability of storm intensity are discussed.
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a fast intensity simulator for Tropical Cyclone risk analysis
Natural Hazards, 2017Co-Authors: Kerry A. EmanuelAbstract:Robust estimates of Tropical Cyclone risk can be made using large sets of storm events synthesized from historical data or from physics-based algorithms. While storm tracks can be synthesized very rapidly from statistical algorithms or simple dynamical models (such as the beta-and-advection model), estimation of storm intensity by using full-physics models is generally too expensive to be practical. Although purely statistical intensity algorithms are fast, they may not be general enough to encompass the effects of natural or anthropogenic climate change. Here we present a fast, physically motivated intensity algorithm consisting of two coupled ordinary differential equations predicting the evolution of a wind speed and an inner core moisture variable. The algorithm includes the effects of ocean coupling and environmental wind shear but does not explicitly simulate spatial structure, which must be handled parametrically. We evaluate this algorithm by using it to simulate several historical events and by comparing a risk analysis based on it to an existing method for assessing long-term Tropical Cyclone risk. For simulations based on the recent climate, the two techniques perform comparably well, though the new technique does better with interannual variability in the Atlantic. Compared to the existing method, the new method produces a smaller increase in global Tropical Cyclone frequency in response to global warming, but a comparable increase in power dissipation.
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midlevel ventilation s constraint on Tropical Cyclone intensity
Journal of the Atmospheric Sciences, 2010Co-Authors: Brian H Tang, Kerry A. EmanuelAbstract:Abstract Midlevel ventilation, or the flux of low-entropy air into the inner core of a Tropical Cyclone (TC), is a hypothesized mechanism by which environmental vertical wind shear can constrain a Tropical Cyclone’s intensity. An idealized framework based on steadiness, axisymmetry, and slantwise neutrality is developed to assess how ventilation affects Tropical Cyclone intensity via two possible pathways: the first through downdrafts outside the eyewall and the second through eddy fluxes directly into the eyewall. For both pathways, ventilation has a detrimental effect on Tropical Cyclone intensity by decreasing the maximum steady-state intensity significantly below the potential intensity, imposing a minimum intensity below which a TC will unconditionally decay, and providing an upper-ventilation bound beyond which no steady Tropical Cyclone can exist. Ventilation also decreases the thermodynamic efficiency as the eyewall becomes less buoyant relative to the environment, which compounds the effects of v...
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Tropical Cyclone activity downscaled from noaa cires reanalysis 1908 1958
Journal of Advances in Modeling Earth Systems, 2010Co-Authors: Kerry A. EmanuelAbstract:[1] A recently developed technique for deducing Tropical Cyclone activity from global reanalyses and climate models is applied to a reanalysis of the global atmosphere during the period 1908–1958. This reanalysis assimilates only sea surface temperature, sea ice, and surface pressure observations, which are relatively homogeneous over the period. The downscaling technique has been shown to produce results in good agreement with observations of Tropical Cyclones when driven by reanalyses over the period 1980–2006, a period when global Tropical Cyclone frequency was robustly observed. When applied to the 1908–1958 reanalysis, the derived global frequency of Tropical Cyclones shows no significant trend over the period, while the frequency of events in the southern hemisphere shows a statistically significant decline and that of the northern hemisphere shows a marginally significant increase. There are statistically significant increases in frequency over the period in the North Atlantic, eastern North Pacific, and northern Indian Oceans, while frequency declines in the western North Pacific. Power dissipation estimates from best-track data are highly correlated with the power dissipation of downscaled events in the Atlantic, though the amplitude of the variability and trends of the downscaled power dissipation are smaller than those of the best-track estimates by about a factor of two. A recently developed genesis index applied to the reanalysis data is highly correlated with downscaled event frequency on regional spatial scales, but is largely uncorrelated at the scale of the globe and even on the scale of large Tropical Cyclone-producing regions such as the western North Pacific. Finally, while it is tempting to believe that specification of sea surface temperature is sufficient for capturing most aspects of the general state of the atmosphere relevant to Tropical Cyclones, we show, using simple arguments, that failure to account for changing radiative properties of the atmosphere can distort the response of Tropical Cyclone activity to changing distributions of sea surface temperature; moreover, models appear to systematically underestimate the response of near-tropopause temperatures to changing surface temperature, and this too can affect the response of potential intensity.
Jeffrey D. Kepert - One of the best experts on this subject based on the ideXlab platform.
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the dynamics of boundary layer jets within the Tropical Cyclone core part i linear theory
Journal of the Atmospheric Sciences, 2001Co-Authors: Jeffrey D. KepertAbstract:Abstract Observations of wind profiles within the Tropical Cyclone boundary layer have until recently been quite rare. The recent massive increase in observations due to the operational implementation of the global positioning system dropwindsonde has emphasised that a low-level wind speed maximum is a common feature of the Tropical Cyclone boundary layer. Here is proposed a mechanism for producing such a maximum, whereby strong inward advection of angular momentum generates the supergradient flow. The processes that maintain the necessary inflow against the outward acceleration resulting from gradient wind imbalance are identified as being (i) vertical diffusion, (ii) vertical advection, and (iii) horizontal advection. Two complementary tools are used to diagnose the properties and dynamics of the jet. The first, presented here, is a linear analytical model of the boundary layer flow in a translating Tropical Cyclone. It is an extension of the classical Ekman boundary layer model, as well as of earlier w...
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The effect of sea spray evaporation on Tropical Cyclone boundary layer structure and intensity
Monthly Weather Review, 2001Co-Authors: Yu-qiao Wang, Jeffrey D. Kepert, Richard H. Johnson, Matthew D Parker, G J HollandAbstract:Strong winds in a Tropical Cyclone over the ocean can produce high seas with substantial amounts of spray in the lower part of the atmospheric boundary layer. The effects that the evaporation of this sea spray may have on the transfer of energy between the ocean and the atmosphere, and consequent effects on the boundary layer structure, cumulus convection, and the evolution of the Tropical Cyclone, are largely unknown. In this study, a high-resolution Tropical Cyclone model with explicit cloud microphysics, developed by Y. Wang, has been used to study these potential effects. The sea spray evaporation is incorporated into the model by two bulk parameterization schemes with quite different properties. The numerical results show that inclusion of the Fairall et at. sea spray parameterization increases the direct sensible heat flux from the ocean by about 70%, but has little effect on the direct latent heat flux. Sea spray itself causes a sensible heat flux of only about 6% of the direct sensible heat flux, while it contributes a latent heat flux by evaporation of sea spray droplets by 60%-70% of the direct latent heat flux. As a result, the total enthalpy flux with sea spray evaporation increases by about 20%, while the net contribution by sea spray is only about 1.5% of the total enthalpy flux. Consistent with this, the intensity of the model Tropical Cyclone is moderately increased by 8% in the maximum wind speed by the introduction of sea spray. The lower atmosphere becomes cooler and moister due to the evaporation of sea spray, which is supported by the available observations. The cooling in the surface layer further modifies the boundary layer structure and the activity of convection, especially in the near-core region where the highest concentration of sea spray exists. On the other hand, with the Andreas and DeCosmo parameterization scheme, the intensity of the model Tropical Cyclone is increased by 25% in maximum wind speed. This dramatic increase in the model Tropical Cyclone intensity is due to both the large net sensible heat flux and the latent heat flux associated with the effect of sea spray by this parameterization scheme. The net upward sensible heat flux warms the air near the surface and results in a near-isotherm al surface layer in the near-core environment under the Tropical Cyclone. Such a structure, however, is not supported by the available observations, which the authors argue is not physically realistic. The radically different results with this scheme are due to the unusual way that the feedbacks between direct and spray-mediated fluxes are handled within the parameterization.
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The impact of sea spray evaporation on Tropical Cyclone intensification
23rd Conference on Hurricanes and Tropical Meteorology 10-15 January 1999 Dallas Texas, 1999Co-Authors: Yu-qiao Wang, Jeffrey D. Kepert, G J HollandAbstract:Strong winds in a Tropical Cyclone over the ocean can generate substantial amounts of spray in the lowest few metres of the atmosphere by both bursting air bubbles in whitecaps and whipping spume from the tips of waves. Since the energy source of a Tropical Cyclone is the sensible and latent heat fluxes from the ocean, the question remains as to whether the presence of sea spray can affect the Tropical Cyclone intensification and intensity. If so, how and to what degree can the sea spray evaporation affect both the boundary layer structure and the intensity and intensification of a Tropical Cyclone by modifying the heat fluxes at the sea surface? In this study, a very high resolution Tropical Cyclone model with explicit cloud microphysics developed in the Bureau of Meteorology Research Centre (BMRC) by Wang (1998) is used to show such a potential effect. We will show that the presence of sea spray evaporation generally reduces the intensification rate of a model Tropical Cyclone but little affects the final intensity of a Cyclone. The next section describes the numerical model. Design of numerical experiments along with a brief summary of the bulk parameterisation of sea spray evaporation in the model are presented in Section 3. The numerical results are discussed in Section 4. Our major findings are summarised in the last section.
G J Holland - One of the best experts on this subject based on the ideXlab platform.
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The effect of sea spray evaporation on Tropical Cyclone boundary layer structure and intensity
Monthly Weather Review, 2001Co-Authors: Yu-qiao Wang, Jeffrey D. Kepert, Richard H. Johnson, Matthew D Parker, G J HollandAbstract:Strong winds in a Tropical Cyclone over the ocean can produce high seas with substantial amounts of spray in the lower part of the atmospheric boundary layer. The effects that the evaporation of this sea spray may have on the transfer of energy between the ocean and the atmosphere, and consequent effects on the boundary layer structure, cumulus convection, and the evolution of the Tropical Cyclone, are largely unknown. In this study, a high-resolution Tropical Cyclone model with explicit cloud microphysics, developed by Y. Wang, has been used to study these potential effects. The sea spray evaporation is incorporated into the model by two bulk parameterization schemes with quite different properties. The numerical results show that inclusion of the Fairall et at. sea spray parameterization increases the direct sensible heat flux from the ocean by about 70%, but has little effect on the direct latent heat flux. Sea spray itself causes a sensible heat flux of only about 6% of the direct sensible heat flux, while it contributes a latent heat flux by evaporation of sea spray droplets by 60%-70% of the direct latent heat flux. As a result, the total enthalpy flux with sea spray evaporation increases by about 20%, while the net contribution by sea spray is only about 1.5% of the total enthalpy flux. Consistent with this, the intensity of the model Tropical Cyclone is moderately increased by 8% in the maximum wind speed by the introduction of sea spray. The lower atmosphere becomes cooler and moister due to the evaporation of sea spray, which is supported by the available observations. The cooling in the surface layer further modifies the boundary layer structure and the activity of convection, especially in the near-core region where the highest concentration of sea spray exists. On the other hand, with the Andreas and DeCosmo parameterization scheme, the intensity of the model Tropical Cyclone is increased by 25% in maximum wind speed. This dramatic increase in the model Tropical Cyclone intensity is due to both the large net sensible heat flux and the latent heat flux associated with the effect of sea spray by this parameterization scheme. The net upward sensible heat flux warms the air near the surface and results in a near-isotherm al surface layer in the near-core environment under the Tropical Cyclone. Such a structure, however, is not supported by the available observations, which the authors argue is not physically realistic. The radically different results with this scheme are due to the unusual way that the feedbacks between direct and spray-mediated fluxes are handled within the parameterization.
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The impact of sea spray evaporation on Tropical Cyclone intensification
23rd Conference on Hurricanes and Tropical Meteorology 10-15 January 1999 Dallas Texas, 1999Co-Authors: Yu-qiao Wang, Jeffrey D. Kepert, G J HollandAbstract:Strong winds in a Tropical Cyclone over the ocean can generate substantial amounts of spray in the lowest few metres of the atmosphere by both bursting air bubbles in whitecaps and whipping spume from the tips of waves. Since the energy source of a Tropical Cyclone is the sensible and latent heat fluxes from the ocean, the question remains as to whether the presence of sea spray can affect the Tropical Cyclone intensification and intensity. If so, how and to what degree can the sea spray evaporation affect both the boundary layer structure and the intensity and intensification of a Tropical Cyclone by modifying the heat fluxes at the sea surface? In this study, a very high resolution Tropical Cyclone model with explicit cloud microphysics developed in the Bureau of Meteorology Research Centre (BMRC) by Wang (1998) is used to show such a potential effect. We will show that the presence of sea spray evaporation generally reduces the intensification rate of a model Tropical Cyclone but little affects the final intensity of a Cyclone. The next section describes the numerical model. Design of numerical experiments along with a brief summary of the bulk parameterisation of sea spray evaporation in the model are presented in Section 3. The numerical results are discussed in Section 4. Our major findings are summarised in the last section.
Yu-qiao Wang - One of the best experts on this subject based on the ideXlab platform.
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The effect of sea spray evaporation on Tropical Cyclone boundary layer structure and intensity
Monthly Weather Review, 2001Co-Authors: Yu-qiao Wang, Jeffrey D. Kepert, Richard H. Johnson, Matthew D Parker, G J HollandAbstract:Strong winds in a Tropical Cyclone over the ocean can produce high seas with substantial amounts of spray in the lower part of the atmospheric boundary layer. The effects that the evaporation of this sea spray may have on the transfer of energy between the ocean and the atmosphere, and consequent effects on the boundary layer structure, cumulus convection, and the evolution of the Tropical Cyclone, are largely unknown. In this study, a high-resolution Tropical Cyclone model with explicit cloud microphysics, developed by Y. Wang, has been used to study these potential effects. The sea spray evaporation is incorporated into the model by two bulk parameterization schemes with quite different properties. The numerical results show that inclusion of the Fairall et at. sea spray parameterization increases the direct sensible heat flux from the ocean by about 70%, but has little effect on the direct latent heat flux. Sea spray itself causes a sensible heat flux of only about 6% of the direct sensible heat flux, while it contributes a latent heat flux by evaporation of sea spray droplets by 60%-70% of the direct latent heat flux. As a result, the total enthalpy flux with sea spray evaporation increases by about 20%, while the net contribution by sea spray is only about 1.5% of the total enthalpy flux. Consistent with this, the intensity of the model Tropical Cyclone is moderately increased by 8% in the maximum wind speed by the introduction of sea spray. The lower atmosphere becomes cooler and moister due to the evaporation of sea spray, which is supported by the available observations. The cooling in the surface layer further modifies the boundary layer structure and the activity of convection, especially in the near-core region where the highest concentration of sea spray exists. On the other hand, with the Andreas and DeCosmo parameterization scheme, the intensity of the model Tropical Cyclone is increased by 25% in maximum wind speed. This dramatic increase in the model Tropical Cyclone intensity is due to both the large net sensible heat flux and the latent heat flux associated with the effect of sea spray by this parameterization scheme. The net upward sensible heat flux warms the air near the surface and results in a near-isotherm al surface layer in the near-core environment under the Tropical Cyclone. Such a structure, however, is not supported by the available observations, which the authors argue is not physically realistic. The radically different results with this scheme are due to the unusual way that the feedbacks between direct and spray-mediated fluxes are handled within the parameterization.
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The impact of sea spray evaporation on Tropical Cyclone intensification
23rd Conference on Hurricanes and Tropical Meteorology 10-15 January 1999 Dallas Texas, 1999Co-Authors: Yu-qiao Wang, Jeffrey D. Kepert, G J HollandAbstract:Strong winds in a Tropical Cyclone over the ocean can generate substantial amounts of spray in the lowest few metres of the atmosphere by both bursting air bubbles in whitecaps and whipping spume from the tips of waves. Since the energy source of a Tropical Cyclone is the sensible and latent heat fluxes from the ocean, the question remains as to whether the presence of sea spray can affect the Tropical Cyclone intensification and intensity. If so, how and to what degree can the sea spray evaporation affect both the boundary layer structure and the intensity and intensification of a Tropical Cyclone by modifying the heat fluxes at the sea surface? In this study, a very high resolution Tropical Cyclone model with explicit cloud microphysics developed in the Bureau of Meteorology Research Centre (BMRC) by Wang (1998) is used to show such a potential effect. We will show that the presence of sea spray evaporation generally reduces the intensification rate of a model Tropical Cyclone but little affects the final intensity of a Cyclone. The next section describes the numerical model. Design of numerical experiments along with a brief summary of the bulk parameterisation of sea spray evaporation in the model are presented in Section 3. The numerical results are discussed in Section 4. Our major findings are summarised in the last section.
Pascal Peduzzi - One of the best experts on this subject based on the ideXlab platform.
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global trends in Tropical Cyclone risk
Nature Climate Change, 2012Co-Authors: Pascal Peduzzi, Bruno Chatenoux, A De Bono, Christian Herold, James P Kossin, Frederic MoutonAbstract:Assessments of Tropical Cyclone risk trends are typically based on reported losses, which are biased by improvements in information access. Now research based on thousands of physically observed events and contextual factors shows that, despite projected reductions in Tropical Cyclone frequency, projected increases in demographic pressure and Tropical Cyclone intensity can be expected to exacerbate disaster risk.
