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The 2005 Atlantic hurricane season was the most active and costly season on record. Recent publications linking an increase in hurricane intensity to increasing tropical sea surface temperatures have fueled the debate on whether or not global warming is causing an increase in hurricane intensity. Because of the substantial implications of the hurricane–global warming issue for society and the immediate policy relevance associated with decision making related to Hurricane Katrina, attacks and rebuttals related to this research are being made in the media and on the World Wide Web without the rigor or accountability expected of scientific discourse. In this paper, we aim to promote a balanced and thoughtful examination of this subject by
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clarifying the debate surrounding the subject as to whether or not global warming is causing an increase in global hurricane intensity,
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illustrating a methodology of hypothesis testing to address multiple criticisms of a complex hypothesis that involves a causal chain, and
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providing a case study of the impact of politics, the media, and the World Wide Web on the scientific process.
The 2005 Atlantic hurricane season was the most active and costly season on record. Recent publications linking an increase in hurricane intensity to increasing tropical sea surface temperatures have fueled the debate on whether or not global warming is causing an increase in hurricane intensity. Because of the substantial implications of the hurricane–global warming issue for society and the immediate policy relevance associated with decision making related to Hurricane Katrina, attacks and rebuttals related to this research are being made in the media and on the World Wide Web without the rigor or accountability expected of scientific discourse. In this paper, we aim to promote a balanced and thoughtful examination of this subject by
-
clarifying the debate surrounding the subject as to whether or not global warming is causing an increase in global hurricane intensity,
-
illustrating a methodology of hypothesis testing to address multiple criticisms of a complex hypothesis that involves a causal chain, and
-
providing a case study of the impact of politics, the media, and the World Wide Web on the scientific process.
The Aerosonde is a small robotic aircraft designed for highly flexible and inexpensive operations. Missions are conducted in a completely robotic mode, with the aircraft under the command of a ground controller who monitors the mission. Here we provide an update on the Aerosonde development and operations and expand on the vision for the future, including instrument pay loads, observational strategies, and platform capabilities. The aircraft was conceived in 1992 and developed to operational status in 1995–98, after a period of early prototyping. Continuing field operations and development since 1998 have led to the Aerosonde Mark 3, with ~2000 flight hours completed. A defined development path through to 2002 will enable the aircraft to become increasingly more robust with increased flexibility in the range and type of operations that can be achieved. An Aerosonde global reconnaissance facility is being developed that consists of launch and recovery sites dispersed around the globe. The use of satellite communications and internet technology enables an operation in which all aircraft around the globe are under the command of a single center. During operation, users will receive data at their home institution in near-real time via the virtual field environment, allowing the user to update the mission through interaction with the global command center. Sophisticated applications of the Aerosonde will be enabled by the development of a variety of interchangeable instrument payloads and the operation of Smart Aerosonde Clusters that allow a cluster of Aerosondes to interact intelligently in response to the data being collected.
The Aerosonde is a small robotic aircraft designed for highly flexible and inexpensive operations. Missions are conducted in a completely robotic mode, with the aircraft under the command of a ground controller who monitors the mission. Here we provide an update on the Aerosonde development and operations and expand on the vision for the future, including instrument pay loads, observational strategies, and platform capabilities. The aircraft was conceived in 1992 and developed to operational status in 1995–98, after a period of early prototyping. Continuing field operations and development since 1998 have led to the Aerosonde Mark 3, with ~2000 flight hours completed. A defined development path through to 2002 will enable the aircraft to become increasingly more robust with increased flexibility in the range and type of operations that can be achieved. An Aerosonde global reconnaissance facility is being developed that consists of launch and recovery sites dispersed around the globe. The use of satellite communications and internet technology enables an operation in which all aircraft around the globe are under the command of a single center. During operation, users will receive data at their home institution in near-real time via the virtual field environment, allowing the user to update the mission through interaction with the global command center. Sophisticated applications of the Aerosonde will be enabled by the development of a variety of interchangeable instrument payloads and the operation of Smart Aerosonde Clusters that allow a cluster of Aerosondes to interact intelligently in response to the data being collected.
The very limited instrumental record makes extensive analyses of the natural variability of global tropical cyclone activities difficult in most of the tropical cyclone basins. However, in the two regions where reasonably reliable records exist (the North Atlantic and the western North Pacific), substantial multidecadal variability (particularly for intense Atlantic hurricanes) is found, but there is no clear evidence of long-term trends. Efforts have been initiated to use geological and geomorphological records and analysis of oxygen isotope ratios in rainfall recorded in cave stalactites to establish a paleoclimate of tropical cyclones, but these have not yet produced definitive results. Recent thermodynamical estimation of the maximum potential intensities (MPI) of tropical cyclones shows good agreement with observations.
Although there are some uncertainties in these MPI approaches, such as their sensitivity to variations in parameters and failure to include some potentially important interactions such as ocean spray feedbacks, the response of upper-oceanic thermal structure, and eye and eyewall dynamics, they do appear to be an objective tool with which to predict present and future maxima of tropical cyclone intensity. Recent studies indicate the MPI of cyclones will remain the same or undergo a modest increase of up to 10%–20%. These predicted changes are small compared with the observed natural variations and fall within the uncertainty range in current studies. Furthermore, the known omissions (ocean spray, momentum restriction, and possibly also surface to 300-hPa lapse rate changes) could all operate to mitigate the predicted intensification.
A strong caveat must be placed on analysis of results from current GCM simulations of the “tropical-cyclone-like” vortices. Their realism, and hence prediction skill (and also that of “embedded” mesoscale models), is greatly limited by the coarse resolution of current GCMs and the failure to capture environmental factors that govern cyclone intensity. Little, therefore, can be said about the potential changes of the distribution of intensities as opposed to maximum achievable intensity. Current knowledge and available techniques are too rudimentary for quantitative indications of potential changes in tropical cyclone frequency.
The broad geographic regions of cyclogenesis and therefore also the regions affected by tropical cyclones are not expected to change significantly. It is emphasized that the popular belief that the region of cyclogenesis will expand with the 26°C SST isotherm is a fallacy. The very modest available evidence points to an expectation of little or no change in global frequency. Regional and local frequencies could change substantially in either direction, because of the dependence of cyclone genesis and track on other phenomena (e.g., ENSO) that are not yet predictable. Greatly improved skills from coupled global ocean–atmosphere models are required before improved predictions are possible.
The very limited instrumental record makes extensive analyses of the natural variability of global tropical cyclone activities difficult in most of the tropical cyclone basins. However, in the two regions where reasonably reliable records exist (the North Atlantic and the western North Pacific), substantial multidecadal variability (particularly for intense Atlantic hurricanes) is found, but there is no clear evidence of long-term trends. Efforts have been initiated to use geological and geomorphological records and analysis of oxygen isotope ratios in rainfall recorded in cave stalactites to establish a paleoclimate of tropical cyclones, but these have not yet produced definitive results. Recent thermodynamical estimation of the maximum potential intensities (MPI) of tropical cyclones shows good agreement with observations.
Although there are some uncertainties in these MPI approaches, such as their sensitivity to variations in parameters and failure to include some potentially important interactions such as ocean spray feedbacks, the response of upper-oceanic thermal structure, and eye and eyewall dynamics, they do appear to be an objective tool with which to predict present and future maxima of tropical cyclone intensity. Recent studies indicate the MPI of cyclones will remain the same or undergo a modest increase of up to 10%–20%. These predicted changes are small compared with the observed natural variations and fall within the uncertainty range in current studies. Furthermore, the known omissions (ocean spray, momentum restriction, and possibly also surface to 300-hPa lapse rate changes) could all operate to mitigate the predicted intensification.
A strong caveat must be placed on analysis of results from current GCM simulations of the “tropical-cyclone-like” vortices. Their realism, and hence prediction skill (and also that of “embedded” mesoscale models), is greatly limited by the coarse resolution of current GCMs and the failure to capture environmental factors that govern cyclone intensity. Little, therefore, can be said about the potential changes of the distribution of intensities as opposed to maximum achievable intensity. Current knowledge and available techniques are too rudimentary for quantitative indications of potential changes in tropical cyclone frequency.
The broad geographic regions of cyclogenesis and therefore also the regions affected by tropical cyclones are not expected to change significantly. It is emphasized that the popular belief that the region of cyclogenesis will expand with the 26°C SST isotherm is a fallacy. The very modest available evidence points to an expectation of little or no change in global frequency. Regional and local frequencies could change substantially in either direction, because of the dependence of cyclone genesis and track on other phenomena (e.g., ENSO) that are not yet predictable. Greatly improved skills from coupled global ocean–atmosphere models are required before improved predictions are possible.
A description is given of the Maritime Continent Thunderstorm Experiment held over the Tiwi Islands (12°S, 130°E) during the period November–December 1995. The unique nature of regularly occurring storms over these islands enabled a study principally aimed at investigating the life cycle of island-initiated mesoscale convective systems within the Maritime Continent. The program objectives are first outlined and then selected results from various observationally based and modeling studies are summarized.
These storms are shown to depend typically on island-scale forcing although external mesoscale disturbances can result in significant storm activity as they pass over the heated island. Particular emphasis is given to summarizing the environmental characteristics and the impact this has on the location of storm development and the associated rainfall distribution.
The mean rainfall production from these storms is shown to be about 760 × 105 m3, with considerable variability. The mesoscale evolution is summarized and during the rapid development phase the interaction of storms with preexisting convergence zones is highlighted. In situ microphysical observations show the occurrence of very large rain drops (up to 8-mm diameter) and very large concentrations of ice crystals in the −10° to −60°C temperature range associated with the very intense updrafts. Occurrence of graupel aloft is shown to be strongly linked to cloud to ground lightning. Polarimetric radar-based rainfall estimates using specific differential phase shift are shown to be considerably better than reflectivity based estimates. Studies relating to the structure of anvil cloud and the effect on the radiative heating profile are also summarized. Initial attempts at modeling storm development are also presented. Two different nonhydrostatic models on days with markedly different evolution are employed and indicate that the models show considerable promise in their ability to develop mesoscale systems. However, important differences still remain between observed storm evolution and that modeled.
A description is given of the Maritime Continent Thunderstorm Experiment held over the Tiwi Islands (12°S, 130°E) during the period November–December 1995. The unique nature of regularly occurring storms over these islands enabled a study principally aimed at investigating the life cycle of island-initiated mesoscale convective systems within the Maritime Continent. The program objectives are first outlined and then selected results from various observationally based and modeling studies are summarized.
These storms are shown to depend typically on island-scale forcing although external mesoscale disturbances can result in significant storm activity as they pass over the heated island. Particular emphasis is given to summarizing the environmental characteristics and the impact this has on the location of storm development and the associated rainfall distribution.
The mean rainfall production from these storms is shown to be about 760 × 105 m3, with considerable variability. The mesoscale evolution is summarized and during the rapid development phase the interaction of storms with preexisting convergence zones is highlighted. In situ microphysical observations show the occurrence of very large rain drops (up to 8-mm diameter) and very large concentrations of ice crystals in the −10° to −60°C temperature range associated with the very intense updrafts. Occurrence of graupel aloft is shown to be strongly linked to cloud to ground lightning. Polarimetric radar-based rainfall estimates using specific differential phase shift are shown to be considerably better than reflectivity based estimates. Studies relating to the structure of anvil cloud and the effect on the radiative heating profile are also summarized. Initial attempts at modeling storm development are also presented. Two different nonhydrostatic models on days with markedly different evolution are employed and indicate that the models show considerable promise in their ability to develop mesoscale systems. However, important differences still remain between observed storm evolution and that modeled.
Abstract
While internal climate variability is known to affect climate projections, its influence is often underappreciated and confused with model error. Why? In general, modeling centers contribute a small number of realizations to international climate model assessments [e.g., phase 5 of the Coupled Model Intercomparison Project (CMIP5)]. As a result, model error and internal climate variability are difficult, and at times impossible, to disentangle. In response, the Community Earth System Model (CESM) community designed the CESM Large Ensemble (CESM-LE) with the explicit goal of enabling assessment of climate change in the presence of internal climate variability. All CESM-LE simulations use a single CMIP5 model (CESM with the Community Atmosphere Model, version 5). The core simulations replay the twenty to twenty-first century (1920–2100) 30 times under historical and representative concentration pathway 8.5 external forcing with small initial condition differences. Two companion 1000+-yr-long preindustrial control simulations (fully coupled, prognostic atmosphere and land only) allow assessment of internal climate variability in the absence of climate change. Comprehensive outputs, including many daily fields, are available as single-variable time series on the Earth System Grid for anyone to use. Early results demonstrate the substantial influence of internal climate variability on twentieth- to twenty-first-century climate trajectories. Global warming hiatus decades occur, similar to those recently observed. Internal climate variability alone can produce projection spread comparable to that in CMIP5. Scientists and stakeholders can use CESM-LE outputs to help interpret the observational record, to understand projection spread and to plan for a range of possible futures influenced by both internal climate variability and forced climate change.
Abstract
While internal climate variability is known to affect climate projections, its influence is often underappreciated and confused with model error. Why? In general, modeling centers contribute a small number of realizations to international climate model assessments [e.g., phase 5 of the Coupled Model Intercomparison Project (CMIP5)]. As a result, model error and internal climate variability are difficult, and at times impossible, to disentangle. In response, the Community Earth System Model (CESM) community designed the CESM Large Ensemble (CESM-LE) with the explicit goal of enabling assessment of climate change in the presence of internal climate variability. All CESM-LE simulations use a single CMIP5 model (CESM with the Community Atmosphere Model, version 5). The core simulations replay the twenty to twenty-first century (1920–2100) 30 times under historical and representative concentration pathway 8.5 external forcing with small initial condition differences. Two companion 1000+-yr-long preindustrial control simulations (fully coupled, prognostic atmosphere and land only) allow assessment of internal climate variability in the absence of climate change. Comprehensive outputs, including many daily fields, are available as single-variable time series on the Earth System Grid for anyone to use. Early results demonstrate the substantial influence of internal climate variability on twentieth- to twenty-first-century climate trajectories. Global warming hiatus decades occur, similar to those recently observed. Internal climate variability alone can produce projection spread comparable to that in CMIP5. Scientists and stakeholders can use CESM-LE outputs to help interpret the observational record, to understand projection spread and to plan for a range of possible futures influenced by both internal climate variability and forced climate change.
The Community Earth System Model (CESM) is a flexible and extensible community tool used to investigate a diverse set of Earth system interactions across multiple time and space scales. This global coupled model significantly extends its predecessor, the Community Climate System Model, by incorporating new Earth system simulation capabilities. These comprise the ability to simulate biogeochemical cycles, including those of carbon and nitrogen, a variety of atmospheric chemistry options, the Greenland Ice Sheet, and an atmosphere that extends to the lower thermosphere. These and other new model capabilities are enabling investigations into a wide range of pressing scientific questions, providing new foresight into possible future climates and increasing our collective knowledge about the behavior and interactions of the Earth system. Simulations with numerous configurations of the CESM have been provided to phase 5 of the Coupled Model Intercomparison Project (CMIP5) and are being analyzed by the broad community of scientists. Additionally, the model source code and associated documentation are freely available to the scientific community to use for Earth system studies, making it a true community tool. This article describes this Earth system model and its various possible configurations, and highlights a number of its scientific capabilities.
The Community Earth System Model (CESM) is a flexible and extensible community tool used to investigate a diverse set of Earth system interactions across multiple time and space scales. This global coupled model significantly extends its predecessor, the Community Climate System Model, by incorporating new Earth system simulation capabilities. These comprise the ability to simulate biogeochemical cycles, including those of carbon and nitrogen, a variety of atmospheric chemistry options, the Greenland Ice Sheet, and an atmosphere that extends to the lower thermosphere. These and other new model capabilities are enabling investigations into a wide range of pressing scientific questions, providing new foresight into possible future climates and increasing our collective knowledge about the behavior and interactions of the Earth system. Simulations with numerous configurations of the CESM have been provided to phase 5 of the Coupled Model Intercomparison Project (CMIP5) and are being analyzed by the broad community of scientists. Additionally, the model source code and associated documentation are freely available to the scientific community to use for Earth system studies, making it a true community tool. This article describes this Earth system model and its various possible configurations, and highlights a number of its scientific capabilities.
