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- Author or Editor: K. E. Dowell x
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Abstract
An observational study of mesoscale cellular convection occurring over vast regions of the North Atlantic and North Pacific has been done for the period 1 January 1969 through 30 June 1970. Satellite cloud photography from the ESSA 7, ESSA 9 and ATS 3 satellites and conventional rawinsonde data have been analyzed for a total of 38 cases, consisting of 25 open and 13 closed convective patterns. Computations have shown that: 1) the average diameter for open cells is 30 km and for closed cells 32 km; 2) the average convective depth for open cells is 2.3 km, greater than the 1.3 km average for closed cells; 3) the average aspect (diameter-to-depth) ratio for open cells, 15:1, is less than that for closed cells, 28:1; 4) the aspect ratio is inversely proportional to increasing convective depth; 5) sea surface temperature exceeds the air temperature on the average by 2.1C in open cells but is 0.4C less in closed cells; 6) directional and magnitude shear (in the vertical) of the horizontal wind is small, less than 7° km−1 and 2 m sec−1 km−1, respectively, but indicative of backing or cold air advection in open cells and veering or warm air advection in closed cells; 7) a characteristic lapse for the convecting layer of 8.2C km−1; and 8) a strong total heat flux of 218 1y(4 hr) −1 from the sea to the atmosphere in regions of open cell and a weaker total heat flux of 65 1y(4 hr) −1 from the air to the sea in regions of closed cells.
Open cellular patterns which preferably occur in cyclonic synoptic-scale flow portray the oceans as a major energy source for driving the atmosphere's circulation. Closed cellular patterns, on the other hand, usually occurring under conditions of anticyclonic synoptic-scale flow, portray the oceans as a weak sink for the atmosphere's energy.
Abstract
An observational study of mesoscale cellular convection occurring over vast regions of the North Atlantic and North Pacific has been done for the period 1 January 1969 through 30 June 1970. Satellite cloud photography from the ESSA 7, ESSA 9 and ATS 3 satellites and conventional rawinsonde data have been analyzed for a total of 38 cases, consisting of 25 open and 13 closed convective patterns. Computations have shown that: 1) the average diameter for open cells is 30 km and for closed cells 32 km; 2) the average convective depth for open cells is 2.3 km, greater than the 1.3 km average for closed cells; 3) the average aspect (diameter-to-depth) ratio for open cells, 15:1, is less than that for closed cells, 28:1; 4) the aspect ratio is inversely proportional to increasing convective depth; 5) sea surface temperature exceeds the air temperature on the average by 2.1C in open cells but is 0.4C less in closed cells; 6) directional and magnitude shear (in the vertical) of the horizontal wind is small, less than 7° km−1 and 2 m sec−1 km−1, respectively, but indicative of backing or cold air advection in open cells and veering or warm air advection in closed cells; 7) a characteristic lapse for the convecting layer of 8.2C km−1; and 8) a strong total heat flux of 218 1y(4 hr) −1 from the sea to the atmosphere in regions of open cell and a weaker total heat flux of 65 1y(4 hr) −1 from the air to the sea in regions of closed cells.
Open cellular patterns which preferably occur in cyclonic synoptic-scale flow portray the oceans as a major energy source for driving the atmosphere's circulation. Closed cellular patterns, on the other hand, usually occurring under conditions of anticyclonic synoptic-scale flow, portray the oceans as a weak sink for the atmosphere's energy.
A brief review of the classical theory for convective instability is presented, with primary emphasis on the more recent theoretical and experimental findings that pertain to mesoscale cellular convection in the atmosphere. Important physical and geometrical features of three-dimensional patterns of free convection commonly observed over the oceans are discussed, especially those features that point to distinct differences when compared to laboratory convection. Some suggestions for future study are offered with particular reference to the AMTEX program being planned by the Japanese Committee for GARP.
A brief review of the classical theory for convective instability is presented, with primary emphasis on the more recent theoretical and experimental findings that pertain to mesoscale cellular convection in the atmosphere. Important physical and geometrical features of three-dimensional patterns of free convection commonly observed over the oceans are discussed, especially those features that point to distinct differences when compared to laboratory convection. Some suggestions for future study are offered with particular reference to the AMTEX program being planned by the Japanese Committee for GARP.
Abstract
A height-dependent model of the vertical eddy diffusivity for momentum, K(Z), has been formulated for purposes of studying numerically the momentum (and heat) transfer arising from turbulent motions within the planetary boundary layer (PBL). The model possesses those features believed to be characteristic of the PBL: 1) an approximate linear increase in K through the surface boundary layer, 2) a local maximum value of K in the lower portion of the Ekman layer, 3) an exponential decrease in the profile above the level of maximum K, and 4) a K(Z) function that is continuously differentiable. Specifically the model is given aswhere Z represents height, Z T the top of the PBL and the scaling factor, and a, b and c are arbitrarily chosen parameters that specify a unique K profile. The applicability of the model to atmospheric data is shown by fitting curves to the K distributions derived by Pandolfo's study using BOMEX data.
Abstract
A height-dependent model of the vertical eddy diffusivity for momentum, K(Z), has been formulated for purposes of studying numerically the momentum (and heat) transfer arising from turbulent motions within the planetary boundary layer (PBL). The model possesses those features believed to be characteristic of the PBL: 1) an approximate linear increase in K through the surface boundary layer, 2) a local maximum value of K in the lower portion of the Ekman layer, 3) an exponential decrease in the profile above the level of maximum K, and 4) a K(Z) function that is continuously differentiable. Specifically the model is given aswhere Z represents height, Z T the top of the PBL and the scaling factor, and a, b and c are arbitrarily chosen parameters that specify a unique K profile. The applicability of the model to atmospheric data is shown by fitting curves to the K distributions derived by Pandolfo's study using BOMEX data.
Abstract
The 2016–18 NOAA Hazardous Weather Testbed (HWT) Spring Forecasting Experiments (SFE) featured the Community Leveraged Unified Ensemble (CLUE), a coordinated convection-allowing model (CAM) ensemble framework designed to provide empirical guidance for development of operational CAM systems. The 2017 CLUE included 81 members that all used 3-km horizontal grid spacing over the CONUS, enabling direct comparison of forecasts generated using different dynamical cores, physics schemes, and initialization procedures. This study uses forecasts from several of the 2017 CLUE members and one operational model to evaluate and compare CAM representation and next-day prediction of thunderstorms. The analysis utilizes existing techniques and novel, object-based techniques that distill important information about modeled and observed storms from many cases. The National Severe Storms Laboratory Multi-Radar Multi-Sensor product suite is used to verify model forecasts and climatologies of observed variables. Unobserved model fields are also examined to further illuminate important intermodel differences in storms and near-storm environments. No single model performed better than the others in all respects. However, there were many systematic intermodel and intercore differences in specific forecast metrics and model fields. Some of these differences can be confidently attributed to particular differences in model design. Model intercomparison studies similar to the one presented here are important to better understand the impacts of model and ensemble configurations on storm forecasts and to help optimize future operational CAM systems.
Abstract
The 2016–18 NOAA Hazardous Weather Testbed (HWT) Spring Forecasting Experiments (SFE) featured the Community Leveraged Unified Ensemble (CLUE), a coordinated convection-allowing model (CAM) ensemble framework designed to provide empirical guidance for development of operational CAM systems. The 2017 CLUE included 81 members that all used 3-km horizontal grid spacing over the CONUS, enabling direct comparison of forecasts generated using different dynamical cores, physics schemes, and initialization procedures. This study uses forecasts from several of the 2017 CLUE members and one operational model to evaluate and compare CAM representation and next-day prediction of thunderstorms. The analysis utilizes existing techniques and novel, object-based techniques that distill important information about modeled and observed storms from many cases. The National Severe Storms Laboratory Multi-Radar Multi-Sensor product suite is used to verify model forecasts and climatologies of observed variables. Unobserved model fields are also examined to further illuminate important intermodel differences in storms and near-storm environments. No single model performed better than the others in all respects. However, there were many systematic intermodel and intercore differences in specific forecast metrics and model fields. Some of these differences can be confidently attributed to particular differences in model design. Model intercomparison studies similar to the one presented here are important to better understand the impacts of model and ensemble configurations on storm forecasts and to help optimize future operational CAM systems.
Abstract
Under the Paris Agreement (PA), progress of emission reduction efforts is tracked on the basis of regular updates to national greenhouse gas (GHG) inventories, referred to as bottom-up estimates. However, only top-down atmospheric measurements can provide observation-based evidence of emission trends. Today, there is no internationally agreed, operational capacity to monitor anthropogenic GHG emission trends using atmospheric measurements to complement national bottom-up inventories. The European Commission (EC), the European Space Agency, the European Centre for Medium-Range Weather Forecasts, the European Organisation for the Exploitation of Meteorological Satellites, and international experts are joining forces to develop such an operational capacity for monitoring anthropogenic CO2 emissions as a new CO2 service under the EC’s Copernicus program. Design studies have been used to translate identified needs into defined requirements and functionalities of this anthropogenic CO2 emissions Monitoring and Verification Support (CO2MVS) capacity. It adopts a holistic view and includes components such as atmospheric spaceborne and in situ measurements, bottom-up CO2 emission maps, improved modeling of the carbon cycle, an operational data-assimilation system integrating top-down and bottom-up information, and a policy-relevant decision support tool. The CO2MVS capacity with operational capabilities by 2026 is expected to visualize regular updates of global CO2 emissions, likely at 0.05° x 0.05°. This will complement the PA’s enhanced transparency framework, providing actionable information on anthropogenic CO2 emissions that are the main driver of climate change. This information will be available to all stakeholders, including governments and citizens, allowing them to reflect on trends and effectiveness of reduction measures. The new EC gave the green light to pass the CO2MVS from exploratory to implementing phase.
Abstract
Under the Paris Agreement (PA), progress of emission reduction efforts is tracked on the basis of regular updates to national greenhouse gas (GHG) inventories, referred to as bottom-up estimates. However, only top-down atmospheric measurements can provide observation-based evidence of emission trends. Today, there is no internationally agreed, operational capacity to monitor anthropogenic GHG emission trends using atmospheric measurements to complement national bottom-up inventories. The European Commission (EC), the European Space Agency, the European Centre for Medium-Range Weather Forecasts, the European Organisation for the Exploitation of Meteorological Satellites, and international experts are joining forces to develop such an operational capacity for monitoring anthropogenic CO2 emissions as a new CO2 service under the EC’s Copernicus program. Design studies have been used to translate identified needs into defined requirements and functionalities of this anthropogenic CO2 emissions Monitoring and Verification Support (CO2MVS) capacity. It adopts a holistic view and includes components such as atmospheric spaceborne and in situ measurements, bottom-up CO2 emission maps, improved modeling of the carbon cycle, an operational data-assimilation system integrating top-down and bottom-up information, and a policy-relevant decision support tool. The CO2MVS capacity with operational capabilities by 2026 is expected to visualize regular updates of global CO2 emissions, likely at 0.05° x 0.05°. This will complement the PA’s enhanced transparency framework, providing actionable information on anthropogenic CO2 emissions that are the main driver of climate change. This information will be available to all stakeholders, including governments and citizens, allowing them to reflect on trends and effectiveness of reduction measures. The new EC gave the green light to pass the CO2MVS from exploratory to implementing phase.
