Search Results
You are looking at 21 - 30 of 46 items for
- Author or Editor: Greg J. Holland x
- Refine by Access: All Content x
Abstract
No abstract available
Abstract
No abstract available
Considerable interest in the use of autonomous aircraft for atmospheric measurements in remote and hazardous areas worldwide has arisen over recent years. Their application in tropical cyclone reconnaissance is under study by the World Meteorological Organization and the International Council for Scientific Unions under the United Nations International Decade for Natural Disaster Reduction. More diverse experiments, particularly for stratospheric operations, are being planned by agencies in the United States.
The aerosonde can provide an economical and flexible element in these international initiatives. The concept is for a small aircraft (weighing less than 20 kg) with on-board meteorological sensors to provide radiosonde-quality observations at any location on the globe. Individual missions could span several thousand kilometers and several days' duration, using the Global Positioning System for autonomous navigation, and satellite relay for data return and flight-plan updates. With a supercharged engine, the aerosonde could make soundings from sea level to 100 hPa and back in a cycle of about 4 h. Aerosondes flying such profiles in routine wide-scale use are expected to achieve a per-sounding cost competitive with that of balloon-borne radiosondes, but with much greater flexibility of operation.
Considerable interest in the use of autonomous aircraft for atmospheric measurements in remote and hazardous areas worldwide has arisen over recent years. Their application in tropical cyclone reconnaissance is under study by the World Meteorological Organization and the International Council for Scientific Unions under the United Nations International Decade for Natural Disaster Reduction. More diverse experiments, particularly for stratospheric operations, are being planned by agencies in the United States.
The aerosonde can provide an economical and flexible element in these international initiatives. The concept is for a small aircraft (weighing less than 20 kg) with on-board meteorological sensors to provide radiosonde-quality observations at any location on the globe. Individual missions could span several thousand kilometers and several days' duration, using the Global Positioning System for autonomous navigation, and satellite relay for data return and flight-plan updates. With a supercharged engine, the aerosonde could make soundings from sea level to 100 hPa and back in a cycle of about 4 h. Aerosondes flying such profiles in routine wide-scale use are expected to achieve a per-sounding cost competitive with that of balloon-borne radiosondes, but with much greater flexibility of operation.
Abstract
North Australian Clouds Lines are distinctive, squall-line phenomena that occur in easterly flow across northern Australia. Three basic types have been identified, ranging from a long, narrow line of convective clouds (Type 1) to a severe squall line (Type 3). In this paper we examine a group of Type 1 lines, which occurred during the first phase of the Australian Monsoon Experiment (AMEX). The lines occurred in an ambient easterly flow with a distinct maximum near 850 hPa. Most of the lines developed on the western side of deep convective cells along the sea-breeze front in a manner that had substantial similarities to the African squall-line development described by Bolton. The resolvable structure resembled a shallow version of the Moncrieff–Miller squall line.
Abstract
North Australian Clouds Lines are distinctive, squall-line phenomena that occur in easterly flow across northern Australia. Three basic types have been identified, ranging from a long, narrow line of convective clouds (Type 1) to a severe squall line (Type 3). In this paper we examine a group of Type 1 lines, which occurred during the first phase of the Australian Monsoon Experiment (AMEX). The lines occurred in an ambient easterly flow with a distinct maximum near 850 hPa. Most of the lines developed on the western side of deep convective cells along the sea-breeze front in a manner that had substantial similarities to the African squall-line development described by Bolton. The resolvable structure resembled a shallow version of the Moncrieff–Miller squall line.
Abstract
The meteorological conditions for the development of Australian east-coast cyclones are described. The main synoptic precursor is a trough (or “dip”) in the easterly wind regime over eastern Australia. The cyclones are a mesoscale development which occurs on the coast in this synoptic environment. They form preferentially at night, in the vicinity of a marked low-level baroclinic zone, and just equatorward of a region of enhanced convection resulting from flow over the coastal ranges.
Three different types of east-coast cyclone have been identified. Types 1 and 3 are very small systems which can have lifetimes as short as 16 hours, during which hurricane force winds have been observed to develop. The other, type 2, system is a meso/synoptic-scale cyclone that can bring sustained strong winds and flood rainfall over several days. Because of their intensity, rapid development, and occasional tiny size, these systems are a major forecast problem.
Abstract
The meteorological conditions for the development of Australian east-coast cyclones are described. The main synoptic precursor is a trough (or “dip”) in the easterly wind regime over eastern Australia. The cyclones are a mesoscale development which occurs on the coast in this synoptic environment. They form preferentially at night, in the vicinity of a marked low-level baroclinic zone, and just equatorward of a region of enhanced convection resulting from flow over the coastal ranges.
Three different types of east-coast cyclone have been identified. Types 1 and 3 are very small systems which can have lifetimes as short as 16 hours, during which hurricane force winds have been observed to develop. The other, type 2, system is a meso/synoptic-scale cyclone that can bring sustained strong winds and flood rainfall over several days. Because of their intensity, rapid development, and occasional tiny size, these systems are a major forecast problem.
Abstract
A series of numerical modeling simulations are made of the type 2 east-coast cyclone described in Holland et al. The aims are (i) to show that this mesoscale development can be successfully forecast from initial synoptic scale data and (ii) to diagnose the relative roles of large-scale processes, convection, topography, and surface fluxes in producing this development. We show that the development can be forecast successfully with the current Australian limited-area prediction model, but that high resolution is needed to capture fully the intensity, structure and track of the system.
We show also that both large- and small-scale processes contribute to the development of the east-coast cyclone. Large-scale moist baroclinic processes provide the favorable environment and initial development of a weak, synoptic-scale cyclone. Subsequent development of the intense, mesoscale system requires convective release of latent heat, local orographic forcing, and high resolution surface energy fluxes.
Abstract
A series of numerical modeling simulations are made of the type 2 east-coast cyclone described in Holland et al. The aims are (i) to show that this mesoscale development can be successfully forecast from initial synoptic scale data and (ii) to diagnose the relative roles of large-scale processes, convection, topography, and surface fluxes in producing this development. We show that the development can be forecast successfully with the current Australian limited-area prediction model, but that high resolution is needed to capture fully the intensity, structure and track of the system.
We show also that both large- and small-scale processes contribute to the development of the east-coast cyclone. Large-scale moist baroclinic processes provide the favorable environment and initial development of a weak, synoptic-scale cyclone. Subsequent development of the intense, mesoscale system requires convective release of latent heat, local orographic forcing, and high resolution surface energy fluxes.
Abstract
Observations are presented of a phenomenal upper tropospheric mesoscale temperature perturbation arising from the interaction between dissipating Tropical Cyclone Kerry (1979) and a midlatitude trough in the westerlies, which we describe as a black hole from its appearance on satellite imagery. We propose that this perturbation arose from dynamically forced subsidence along a confluence between the environments flow and outflow from a major convective complex. The frequency of occurrence and subsequent adjustment of the atmosphere is described and discussed.
Abstract
Observations are presented of a phenomenal upper tropospheric mesoscale temperature perturbation arising from the interaction between dissipating Tropical Cyclone Kerry (1979) and a midlatitude trough in the westerlies, which we describe as a black hole from its appearance on satellite imagery. We propose that this perturbation arose from dynamically forced subsidence along a confluence between the environments flow and outflow from a major convective complex. The frequency of occurrence and subsequent adjustment of the atmosphere is described and discussed.
Abstract
No abstract available.
Abstract
No abstract available.
Abstract
A revision to the Holland parametric approach to modeling the radial profile of winds in hurricanes is presented. The approach adopted uses information readily available from hurricane archives or in hurricane warning information and the profile can be readily incorporated into existing parametric models of the hurricane surface wind field. The original model utilized central and environmental surface pressures, maximum winds, and radius of maximum winds. In the revision a capacity to incorporate additional wind observations at some radius within the hurricane circulation was included. If surface observations are used, then a surface wind profile will result, obviating the need for deriving a boundary layer reduction from the gradient wind level. The model has considerably less sensitivity to data errors compared to the original and is shown to reproduce hurricane reconnaissance and surface wind profiles with high accuracy.
Abstract
A revision to the Holland parametric approach to modeling the radial profile of winds in hurricanes is presented. The approach adopted uses information readily available from hurricane archives or in hurricane warning information and the profile can be readily incorporated into existing parametric models of the hurricane surface wind field. The original model utilized central and environmental surface pressures, maximum winds, and radius of maximum winds. In the revision a capacity to incorporate additional wind observations at some radius within the hurricane circulation was included. If surface observations are used, then a surface wind profile will result, obviating the need for deriving a boundary layer reduction from the gradient wind level. The model has considerably less sensitivity to data errors compared to the original and is shown to reproduce hurricane reconnaissance and surface wind profiles with high accuracy.
Abstract
This paper investigates the performance of two recently developed thermodynamic models of maximum tropical cyclone intensity (K. A. Emanuel’s referred to here as E1 and G. J. Holland’s referred to here as H1), which are designed to estimate the most intense storm possible given the ambient environmental conditions. The study involves estimating the maximum potential tropical cyclone intensity (MPI) from climatological information in three ocean regions, where relatively reliable atmospheric soundings and tropical cyclone intensity data exist. The monthly MPI was estimated for 28 locations across the northwest Pacific, southwest Pacific, and North Atlantic Ocean regions. Empirically derived relationships between observed maximum storm intensity and sea surface temperature were also utilized in the examination of regional MPI model performance.
Derived MPIs generally agreed well with observed maximum intensities during the tropical cyclone season. The H1 model tended to underestimate the maximum intensity of storms early and late in the tropical cyclone season and at stations between 10° and 20°N in the northwest Pacific, where the effect of continental air led to weak model estimates for the given surface energy conditions. Additionally, extremely intense H1 estimates were predicted at some stations in the Australian/southwest Pacific region where particularly unstable atmospheric conditions and low ambient surface pressure values are observed. These features of model performance are largely due to the sensitivity of H1 to warm environmental upper-level temperatures. The E1 model displayed a poor seasonality, frequently predicting the occurrence of storms during winter months. Emanuel MPI estimates were at times underestimated for stations in the North Atlantic and northwest Pacific. The E1 model estimates in the northwest Pacific were affected by particularly warm upper-level conditions, while relatively high ambient surface pressures in the North Atlantic at 25°N lead to MPI estimates, which are weaker than observed in this region.
Abstract
This paper investigates the performance of two recently developed thermodynamic models of maximum tropical cyclone intensity (K. A. Emanuel’s referred to here as E1 and G. J. Holland’s referred to here as H1), which are designed to estimate the most intense storm possible given the ambient environmental conditions. The study involves estimating the maximum potential tropical cyclone intensity (MPI) from climatological information in three ocean regions, where relatively reliable atmospheric soundings and tropical cyclone intensity data exist. The monthly MPI was estimated for 28 locations across the northwest Pacific, southwest Pacific, and North Atlantic Ocean regions. Empirically derived relationships between observed maximum storm intensity and sea surface temperature were also utilized in the examination of regional MPI model performance.
Derived MPIs generally agreed well with observed maximum intensities during the tropical cyclone season. The H1 model tended to underestimate the maximum intensity of storms early and late in the tropical cyclone season and at stations between 10° and 20°N in the northwest Pacific, where the effect of continental air led to weak model estimates for the given surface energy conditions. Additionally, extremely intense H1 estimates were predicted at some stations in the Australian/southwest Pacific region where particularly unstable atmospheric conditions and low ambient surface pressure values are observed. These features of model performance are largely due to the sensitivity of H1 to warm environmental upper-level temperatures. The E1 model displayed a poor seasonality, frequently predicting the occurrence of storms during winter months. Emanuel MPI estimates were at times underestimated for stations in the North Atlantic and northwest Pacific. The E1 model estimates in the northwest Pacific were affected by particularly warm upper-level conditions, while relatively high ambient surface pressures in the North Atlantic at 25°N lead to MPI estimates, which are weaker than observed in this region.
Abstract
This paper presents a preliminary evaluation of meteorological measurements made by the Aerosonde (using Vaisala, Inc., RS90 sensors) by comparing them with closely correlated measurements made using traditional balloonborne sondes (Vaisala RS80-A/-H). Eighteen comparisons were completed in temperatures ranging from −20° to 10°C. Although the Aerosonde generally performed well in comparison with the radiosonde, calibration errors and time-lag errors similar to those observed between radiosonde and dropsonde observations were evident in some of the temperature and relative humidity profiles. The average temperature differences between the Aerosonde and radiosonde profiles varied between 0.01° and 1.2°C, with the Aerosonde observations being consistently warmer than the radiosonde measurements. A dry bias was also generally present in the radiosonde relative humidity observations relative to the Aerosonde observations. Wind observations were comparable. Mean wind magnitude differences ranged from 0.02 to 1.7 m s−1, with the mean wind direction differences between 0.1° and 19.1°. After application of ground-check corrections, the most prominent causes of disparity between the Aerosonde and radiosonde profiles are the inevitable temporal and spatial dislocation between the Aerosonde and radiosonde soundings and aerodynamic factors that influence the Aerosonde sensor measurements. These differences are inherent in this very different observing platform. Kinetic heating, the different sensor types, chemical contamination, storage and handling inconsistencies, and sensor age are likely to play a lesser role.
Abstract
This paper presents a preliminary evaluation of meteorological measurements made by the Aerosonde (using Vaisala, Inc., RS90 sensors) by comparing them with closely correlated measurements made using traditional balloonborne sondes (Vaisala RS80-A/-H). Eighteen comparisons were completed in temperatures ranging from −20° to 10°C. Although the Aerosonde generally performed well in comparison with the radiosonde, calibration errors and time-lag errors similar to those observed between radiosonde and dropsonde observations were evident in some of the temperature and relative humidity profiles. The average temperature differences between the Aerosonde and radiosonde profiles varied between 0.01° and 1.2°C, with the Aerosonde observations being consistently warmer than the radiosonde measurements. A dry bias was also generally present in the radiosonde relative humidity observations relative to the Aerosonde observations. Wind observations were comparable. Mean wind magnitude differences ranged from 0.02 to 1.7 m s−1, with the mean wind direction differences between 0.1° and 19.1°. After application of ground-check corrections, the most prominent causes of disparity between the Aerosonde and radiosonde profiles are the inevitable temporal and spatial dislocation between the Aerosonde and radiosonde soundings and aerodynamic factors that influence the Aerosonde sensor measurements. These differences are inherent in this very different observing platform. Kinetic heating, the different sensor types, chemical contamination, storage and handling inconsistencies, and sensor age are likely to play a lesser role.
