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Malcolm J Roberts - One of the best experts on this subject based on the ideXlab platform.
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simulation of the global enso tropical cyclone teleconnection by a high resolution coupled general circulation model
Journal of Climate, 2014Co-Authors: Ray Bell, Kevin I. Hodges, Pier Luigi Vidale, Jane Strachan, Malcolm J RobertsAbstract:AbstractThis study assesses the influence of the El Nino–Southern Oscillation (ENSO) on global tropical cyclone activity using a 150-yr-long integration with a high-resolution coupled atmosphere–ocean general circulation model [High-Resolution Global Environmental Model (HiGEM); with N144 resolution: ~90 km in the atmosphere and ~40 km in the ocean]. Tropical cyclone activity is compared to an atmosphere-only simulation using the atmospheric component of HiGEM (HiGAM). Observations of tropical Cyclones in the International Best Track Archive for Climate Stewardship (IBTrACS) and tropical Cyclones identified in the Interim ECMWF Re-Analysis (ERA-Interim) are used to validate the models. Composite anomalies of tropical cyclone activity in El Nino and La Nina years are used. HiGEM is able to capture the shift in tropical cyclone locations to ENSO in the Pacific and Indian Oceans. However, HiGEM does not capture the expected ENSO–tropical cyclone teleconnection in the North Atlantic. HiGAM shows more skill in...
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response of tropical Cyclones to idealized climate change experiments in a global high resolution coupled general circulation model
Journal of Climate, 2013Co-Authors: Ray Bell, Kevin I. Hodges, Pier Luigi Vidale, Jane Strachan, Malcolm J RobertsAbstract:AbstractThe authors present an assessment of how tropical cyclone activity might change owing to the influence of increased atmospheric carbon dioxide concentrations, using the U.K. High-Resolution Global Environment Model (HiGEM) with N144 resolution (~90 km in the atmosphere and ~40 km in the ocean). Tropical Cyclones are identified using a feature-tracking algorithm applied to model output. Tropical Cyclones from idealized 30-yr 2×CO2 (2CO2) and 4×CO2 (4CO2) simulations are compared to those identified in a 150-yr present-day simulation that is separated into a five-member ensemble of 30-yr integrations. Tropical Cyclones are shown to decrease in frequency globally by 9% in the 2CO2 and 26% in the 4CO2. Tropical Cyclones only become more intense in the 4CO2; however, uncoupled time slice experiments reveal an increase in intensity in the 2CO2. An investigation into the large-scale environmental conditions, known to influence tropical cyclone activity in the main development regions, is used to determin...
Kevin I. Hodges - One of the best experts on this subject based on the ideXlab platform.
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simulation of the global enso tropical cyclone teleconnection by a high resolution coupled general circulation model
Journal of Climate, 2014Co-Authors: Ray Bell, Kevin I. Hodges, Pier Luigi Vidale, Jane Strachan, Malcolm J RobertsAbstract:AbstractThis study assesses the influence of the El Nino–Southern Oscillation (ENSO) on global tropical cyclone activity using a 150-yr-long integration with a high-resolution coupled atmosphere–ocean general circulation model [High-Resolution Global Environmental Model (HiGEM); with N144 resolution: ~90 km in the atmosphere and ~40 km in the ocean]. Tropical cyclone activity is compared to an atmosphere-only simulation using the atmospheric component of HiGEM (HiGAM). Observations of tropical Cyclones in the International Best Track Archive for Climate Stewardship (IBTrACS) and tropical Cyclones identified in the Interim ECMWF Re-Analysis (ERA-Interim) are used to validate the models. Composite anomalies of tropical cyclone activity in El Nino and La Nina years are used. HiGEM is able to capture the shift in tropical cyclone locations to ENSO in the Pacific and Indian Oceans. However, HiGEM does not capture the expected ENSO–tropical cyclone teleconnection in the North Atlantic. HiGAM shows more skill in...
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response of tropical Cyclones to idealized climate change experiments in a global high resolution coupled general circulation model
Journal of Climate, 2013Co-Authors: Ray Bell, Kevin I. Hodges, Pier Luigi Vidale, Jane Strachan, Malcolm J RobertsAbstract:AbstractThe authors present an assessment of how tropical cyclone activity might change owing to the influence of increased atmospheric carbon dioxide concentrations, using the U.K. High-Resolution Global Environment Model (HiGEM) with N144 resolution (~90 km in the atmosphere and ~40 km in the ocean). Tropical Cyclones are identified using a feature-tracking algorithm applied to model output. Tropical Cyclones from idealized 30-yr 2×CO2 (2CO2) and 4×CO2 (4CO2) simulations are compared to those identified in a 150-yr present-day simulation that is separated into a five-member ensemble of 30-yr integrations. Tropical Cyclones are shown to decrease in frequency globally by 9% in the 2CO2 and 26% in the 4CO2. Tropical Cyclones only become more intense in the 4CO2; however, uncoupled time slice experiments reveal an increase in intensity in the 2CO2. An investigation into the large-scale environmental conditions, known to influence tropical cyclone activity in the main development regions, is used to determin...
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An Extratropical Cyclone Atlas: A Tool for Illustrating Cyclone Structure and Evolution Characteristics
Bulletin of the American Meteorological Society, 2012Co-Authors: Helen F. Dacre, Matt Hawcroft, Marc Stringer, Kevin I. HodgesAbstract:Extratropical cyclone lifecycles have been studied extensively with the aim of understanding the dynamical mechanisms involved in their development. Previous work has often been based on subjective analysis of individual case studies. Such case studies have contributed heavily to the generation of conceptual models of extratropical Cyclones that provide a framework for understanding the dynamical evolution of Cyclones. These conceptual models are widely used in educational meteorology courses throughout the world to illustrate the basic structure and evolution of extratropical Cyclones. This article presents a database of extratropical cyclone composites which highlight the average structure and evolution of 20 years of extratropical Cyclones, as opposed to individual case studies. The composite fields are achieved by combining a database containing cyclone tracks from the ERA-Interim reanalysis (1989-2009, 6 hourly) with the full 3D ERA-Interim reanalysis fields. Vertical and horizontal composites of cyclone structure for Cyclones generated in the Atlantic and Pacific regions identifying features such as the relative positions of cold, warm and occluded fronts and their associated wind and cloud patterns are shown. In addition the evolution of cyclonic flows such as the warm and cold conveyor belts and dry intrusion are illustrated. A webpage containing an archive of the composited data is freely available for educational purposes.
Ray Bell - One of the best experts on this subject based on the ideXlab platform.
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simulation of the global enso tropical cyclone teleconnection by a high resolution coupled general circulation model
Journal of Climate, 2014Co-Authors: Ray Bell, Kevin I. Hodges, Pier Luigi Vidale, Jane Strachan, Malcolm J RobertsAbstract:AbstractThis study assesses the influence of the El Nino–Southern Oscillation (ENSO) on global tropical cyclone activity using a 150-yr-long integration with a high-resolution coupled atmosphere–ocean general circulation model [High-Resolution Global Environmental Model (HiGEM); with N144 resolution: ~90 km in the atmosphere and ~40 km in the ocean]. Tropical cyclone activity is compared to an atmosphere-only simulation using the atmospheric component of HiGEM (HiGAM). Observations of tropical Cyclones in the International Best Track Archive for Climate Stewardship (IBTrACS) and tropical Cyclones identified in the Interim ECMWF Re-Analysis (ERA-Interim) are used to validate the models. Composite anomalies of tropical cyclone activity in El Nino and La Nina years are used. HiGEM is able to capture the shift in tropical cyclone locations to ENSO in the Pacific and Indian Oceans. However, HiGEM does not capture the expected ENSO–tropical cyclone teleconnection in the North Atlantic. HiGAM shows more skill in...
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response of tropical Cyclones to idealized climate change experiments in a global high resolution coupled general circulation model
Journal of Climate, 2013Co-Authors: Ray Bell, Kevin I. Hodges, Pier Luigi Vidale, Jane Strachan, Malcolm J RobertsAbstract:AbstractThe authors present an assessment of how tropical cyclone activity might change owing to the influence of increased atmospheric carbon dioxide concentrations, using the U.K. High-Resolution Global Environment Model (HiGEM) with N144 resolution (~90 km in the atmosphere and ~40 km in the ocean). Tropical Cyclones are identified using a feature-tracking algorithm applied to model output. Tropical Cyclones from idealized 30-yr 2×CO2 (2CO2) and 4×CO2 (4CO2) simulations are compared to those identified in a 150-yr present-day simulation that is separated into a five-member ensemble of 30-yr integrations. Tropical Cyclones are shown to decrease in frequency globally by 9% in the 2CO2 and 26% in the 4CO2. Tropical Cyclones only become more intense in the 4CO2; however, uncoupled time slice experiments reveal an increase in intensity in the 2CO2. An investigation into the large-scale environmental conditions, known to influence tropical cyclone activity in the main development regions, is used to determin...
James P. Kossin - One of the best experts on this subject based on the ideXlab platform.
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a global slowdown of tropical cyclone translation speed
Nature, 2018Co-Authors: James P. KossinAbstract:As the Earth’s atmosphere warms, the atmospheric circulation changes. These changes vary by region and time of year, but there is evidence that anthropogenic warming causes a general weakening of summertime tropical circulation1–8. Because tropical Cyclones are carried along within their ambient environmental wind, there is a plausible a priori expectation that the translation speed of tropical Cyclones has slowed with warming. In addition to circulation changes, anthropogenic warming causes increases in atmospheric water-vapour capacity, which are generally expected to increase precipitation rates 9 . Rain rates near the centres of tropical Cyclones are also expected to increase with increasing global temperatures10–12. The amount of tropical-cyclone-related rainfall that any given local area will experience is proportional to the rain rates and inversely proportional to the translation speeds of tropical Cyclones. Here I show that tropical-cyclone translation speed has decreased globally by 10 per cent over the period 1949–2016, which is very likely to have compounded, and possibly dominated, any increases in local rainfall totals that may have occurred as a result of increased tropical-cyclone rain rates. The magnitude of the slowdown varies substantially by region and by latitude, but is generally consistent with expected changes in atmospheric circulation forced by anthropogenic emissions. Of particular importance is the slowdown of 30 per cent and 20 per cent over land areas affected by western North Pacific and North Atlantic tropical Cyclones, respectively, and the slowdown of 19 per cent over land areas in the Australian region. The unprecedented rainfall totals associated with the ‘stall’ of Hurricane Harvey13–15 over Texas in 2017 provide a notable example of the relationship between regional rainfall amounts and tropical-cyclone translation speed. Any systematic past or future change in the translation speed of tropical Cyclones, particularly over land, is therefore highly relevant when considering potential changes in local rainfall totals.
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arabian sea tropical Cyclones intensified by emissions of black carbon and other aerosols
Nature, 2011Co-Authors: Amato T Evan, James P. Kossin, Chul Eddy Chung, V RamanathanAbstract:Strong vertical wind shear can prevent the formation of tropical Cyclones, even when ocean temperatures are otherwise warm enough to brew them up. Amato Evan et al. now show that increased emissions of black carbon, sulphates and other aerosols have altered the atmospheric circulation in the pre-monsoon season over the Arabian Sea, leading to decreased vertical wind shear. As a result, these anthropogenic emissions seem to have caused an increase in the intensity of tropical Cyclones in the pre-monsoon season. Throughout the year, average sea surface temperatures in the Arabian Sea are warm enough to support the development of tropical Cyclones1, but the atmospheric monsoon circulation and associated strong vertical wind shear limits cyclone development and intensification, only permitting a pre-monsoon and post-monsoon period for cyclogenesis1,2,3,4. Thus a recent increase in the intensity of tropical Cyclones over the northern Indian Ocean5 is thought to be related to the weakening of the climatological vertical wind shear3,4. At the same time, anthropogenic emissions of aerosols have increased sixfold since the 1930s, leading to a weakening of the southwesterly lower-level and easterly upper-level winds that define the monsoonal circulation over the Arabian Sea6,7,8,9. In principle, this aerosol-driven circulation modification could affect tropical cyclone intensity over the Arabian Sea, but so far no such linkage has been shown. Here we report an increase in the intensity of pre-monsoon Arabian Sea tropical Cyclones during the period 1979–2010, and show that this change in storm strength is a consequence of a simultaneous upward trend in anthropogenic black carbon and sulphate emissions. We use a combination of observational, reanalysis and model data to demonstrate that the anomalous circulation, which is radiatively forced by these anthropogenic aerosols, reduces the basin-wide vertical wind shear, creating an environment more favourable for tropical cyclone intensification. Because most Arabian Sea tropical Cyclones make landfall1, our results suggest an additional impact on human health from regional air pollution.
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the increasing intensity of the strongest tropical Cyclones
Nature, 2008Co-Authors: James B Elsner, James P. Kossin, Thomas H JaggerAbstract:Although Cyclones in the tropical Atlantic appear, on average, to be getting stronger in response to increasing ocean temperatures, no clear trends of this sort have been discerned in other tropical regions. A new analysis of cyclone intensity, using 25 years' worth of satellite data, suggests that there is a global trend, but that it is quite subtle. The main changes appear not in an upward trend of average cyclone intensity, but rather in the maximum speeds attained by Cyclones during their lifetimes — and the stronger the cyclone, the greater the change. A possible pattern of increasing maximum speeds for the strongest Cyclones is detected in each ocean basin, but is most pronounced in the tropical North Atlantic. Although Cyclones in the tropical Atlantic seem to be getting stronger in response to increasing ocean temperatures, no clear trends of this sort have been discerned in other tropical regions. A new analysis of cyclone intensity using satellite data suggests that there is a global trend, but that it is quite subtle. The main changes appear not in an upward trend of average cyclone intensity, but rather in the maximum speeds attained by Cyclones during their lifetimes, the stronger the cyclone, the greater the change. Atlantic tropical Cyclones are getting stronger on average, with a 30-year trend that has been related to an increase in ocean temperatures over the Atlantic Ocean and elsewhere1,2,3,4. Over the rest of the tropics, however, possible trends in tropical cyclone intensity are less obvious, owing to the unreliability and incompleteness of the observational record and to a restricted focus, in previous trend analyses, on changes in average intensity. Here we overcome these two limitations by examining trends in the upper quantiles of per-cyclone maximum wind speeds (that is, the maximum intensities that Cyclones achieve during their lifetimes), estimated from homogeneous data derived from an archive of satellite records. We find significant upward trends for wind speed quantiles above the 70th percentile, with trends as high as 0.3 ± 0.09 m s-1 yr-1 (s.e.) for the strongest Cyclones. We note separate upward trends in the estimated lifetime-maximum wind speeds of the very strongest tropical Cyclones (99th percentile) over each ocean basin, with the largest increase at this quantile occurring over the North Atlantic, although not all basins show statistically significant increases. Our results are qualitatively consistent with the hypothesis that as the seas warm, the ocean has more energy to convert to tropical cyclone wind.
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the increasing intensity of the strongest tropical Cyclones
Nature, 2008Co-Authors: James B Elsner, James P. Kossin, Thomas H JaggerAbstract:Atlantic tropical Cyclones are getting stronger on average, with a 30-year trend that has been related to an increase in ocean temperatures over the Atlantic Ocean and elsewhere. Over the rest of the tropics, however, possible trends in tropical cyclone intensity are less obvious, owing to the unreliability and incompleteness of the observational record and to a restricted focus, in previous trend analyses, on changes in average intensity. Here we overcome these two limitations by examining trends in the upper quantiles of per-cyclone maximum wind speeds (that is, the maximum intensities that Cyclones achieve during their lifetimes), estimated from homogeneous data derived from an archive of satellite records. We find significant upward trends for wind speed quantiles above the 70th percentile, with trends as high as 0.3 +/- 0.09 m s(-1) yr(-1) (s.e.) for the strongest Cyclones. We note separate upward trends in the estimated lifetime-maximum wind speeds of the very strongest tropical Cyclones (99th percentile) over each ocean basin, with the largest increase at this quantile occurring over the North Atlantic, although not all basins show statistically significant increases. Our results are qualitatively consistent with the hypothesis that as the seas warm, the ocean has more energy to convert to tropical cyclone wind.
Helen F. Dacre - One of the best experts on this subject based on the ideXlab platform.
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The role of secondary Cyclones and cyclone families for the North Atlantic storm track and clustering over western Europe
Quarterly Journal of the Royal Meteorological Society, 2020Co-Authors: Matthew D. K. Priestley, Helen F. Dacre, Len Shaffrey, Sebastian Schemm, Joaquim G. PintoAbstract:Secondary Cyclones are those that form in association with a pre‐existing primary cyclone, typically along a trailing cold front. In previously studied cases they have been shown to cause extreme damage across Europe, particularly when multiple Cyclones track over the same location in rapid succession (known as cyclone clustering). To determine the dynamical relationship between primary and secondary Cyclones over the North Atlantic, a frontal identification algorithm is partnered with a cyclone identification method to objectively identify secondary Cyclones in 35 extended winter periods using reanalysis data. Cyclones are grouped into “cyclone families” consisting of a single primary cyclone and one or more secondary Cyclones. This paper aims to quantify the differences between secondary and primary Cyclones over the North Atlantic, and how cyclone families contribute to episodes of cyclone clustering across western Europe. Secondary Cyclones are shown to occur most frequently in the central and eastern North Atlantic, whereas primary Cyclones are commonly found over the western North Atlantic. Cyclone families have their strongest presence over the North Atlantic Ocean and contribute more than 50% of Cyclones over the main North Atlantic storm track. A final category, solo Cyclones, which are not associated with cyclogenesis on any connected fronts, are most commonly identified over continental regions as well as the Mediterranean Sea. Primary Cyclones are associated with the development of an environment that is favourable for secondary cyclone growth. Enhanced Rossby wave breaking following primary cyclone development leads to an increase in the upper‐level jet speed and a decrease in low‐level stability. Secondary cyclogenesis commonly occurs in this region of anomalously low stability, close to the European continent. During periods of cyclone clustering, secondary Cyclones are responsible for approximately 50% of the total number of Cyclones. The increase in jet speed and decrease in static stability initiated by the primary Cyclones acts to concentrate the genesis region of secondary Cyclones and direct the Cyclones that form along a similar track. While there is an increase in the secondary cyclogenesis rate near western Europe during periods of European clustering, the basin‐wide secondary cyclogenesis rate decreases during these periods. Thus the large‐scale environment redistributes secondary Cyclones during periods of clustering rather than increasing the total number of secondary Cyclones.
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quantifying the climatological relationship between extratropical cyclone intensity and atmospheric precursors
Geophysical Research Letters, 2013Co-Authors: Helen F. Dacre, Suzanne L GrayAbstract:[1] We introduce a novel technique in which linear regression analysis is applied to clusters of tracked Cyclones to statistically assess the factors controlling cyclone development. We illustrate this technique by evaluating the differences between Cyclones forming in the west and east North Atlantic (herein termed west and east Atlantic Cyclones). Enhanced cyclone intensity 2 days after genesis is found to be associated with deeper upper-level troughs upstream of the cyclone center at the genesis time in both west and east Atlantic Cyclones. However, whilst west Atlantic Cyclones are also enhanced by the presence of strong fronts, east Atlantic Cyclones are not. Instead, east Atlantic Cyclones exhibit an enhancement when diabatically generated midlevel potential vorticity is present (with the enhancement being of approximately equal magnitude to that associated with the potential vorticity in the upper-level trough). This is consistent with the paradigm of latent heat release in the warm conveyor belt region playing an important role in the development of east Atlantic Cyclones.
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An Extratropical Cyclone Atlas: A Tool for Illustrating Cyclone Structure and Evolution Characteristics
Bulletin of the American Meteorological Society, 2012Co-Authors: Helen F. Dacre, Matt Hawcroft, Marc Stringer, Kevin I. HodgesAbstract:Extratropical cyclone lifecycles have been studied extensively with the aim of understanding the dynamical mechanisms involved in their development. Previous work has often been based on subjective analysis of individual case studies. Such case studies have contributed heavily to the generation of conceptual models of extratropical Cyclones that provide a framework for understanding the dynamical evolution of Cyclones. These conceptual models are widely used in educational meteorology courses throughout the world to illustrate the basic structure and evolution of extratropical Cyclones. This article presents a database of extratropical cyclone composites which highlight the average structure and evolution of 20 years of extratropical Cyclones, as opposed to individual case studies. The composite fields are achieved by combining a database containing cyclone tracks from the ERA-Interim reanalysis (1989-2009, 6 hourly) with the full 3D ERA-Interim reanalysis fields. Vertical and horizontal composites of cyclone structure for Cyclones generated in the Atlantic and Pacific regions identifying features such as the relative positions of cold, warm and occluded fronts and their associated wind and cloud patterns are shown. In addition the evolution of cyclonic flows such as the warm and cold conveyor belts and dry intrusion are illustrated. A webpage containing an archive of the composited data is freely available for educational purposes.
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the spatial distribution and evolution characteristics of north atlantic Cyclones
Monthly Weather Review, 2009Co-Authors: Helen F. Dacre, Suzanne L GrayAbstract:A climatology of extratropical Cyclones is produced using an objective method of identifying Cyclones based on gradients of 1-km height wet-bulb potential temperature. Cyclone track and genesis density statistics are analyzed and this method is found to compare well with other cyclone identification methods. The North Atlantic storm track is reproduced along with the major regions of genesis. Cyclones are grouped according to their genesis location and the corresponding lysis regions are identified. Most of the Cyclones that cross western Europe originate in the east Atlantic where the baroclinicity and the sea surface temperature gradients are weak compared to the west Atlantic. East Atlantic Cyclones also have higher 1-km height relative vorticity and lower mean sea level pressure at their genesis point than west Atlantic Cyclones. This is consistent with the hypothesis that they are secondary Cyclones developing on the trailing fronts of preexisting “parent” Cyclones. The evolution characteristics of composite west and east Atlantic Cyclones have been compared. The ratio of their upper- to lower-level forcing indicates that type B Cyclones are predominant in both the west and east Atlantic, with strong upper- and lower-level features. Among the remaining Cyclones, there is a higher proportion of type C Cyclones in the east Atlantic, whereas types A and C are equally frequent in the west Atlantic.
