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- Author or Editor: A. H. Gordon x
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Abstract
The mean upper wind structure over Bahrein and Aden in 1962 is studied. Patterns of the zonal and meridional wind speed components are presented. Eddy and advective fluxes of the momentum are calculated and mean annual height profiles drawn for both stations. The transport of momentum by synoptic scale eddies is more important at Bahrein than at Aden. Transport of momentum by the local mean meridional wind is larger in magnitude and fluctuates in an irregular way from month to month at both stations. The vertical integral of the momentum suggests export of relative momentum from the Bahrein-Aden sector in winter and import in summer. These conclusions are supported by 1963 data from the Ahmadabad-Madras sector. In the belt of latitude considered the winter surface winds have an easterly component and gain momentum from the earth while the summer surface winds have a westerly component and lose momentum to the earth. The results of the short period analysis for the sectors studied suggest broad agreement with the synoptic climatology of the region.
Abstract
The mean upper wind structure over Bahrein and Aden in 1962 is studied. Patterns of the zonal and meridional wind speed components are presented. Eddy and advective fluxes of the momentum are calculated and mean annual height profiles drawn for both stations. The transport of momentum by synoptic scale eddies is more important at Bahrein than at Aden. Transport of momentum by the local mean meridional wind is larger in magnitude and fluctuates in an irregular way from month to month at both stations. The vertical integral of the momentum suggests export of relative momentum from the Bahrein-Aden sector in winter and import in summer. These conclusions are supported by 1963 data from the Ahmadabad-Madras sector. In the belt of latitude considered the winter surface winds have an easterly component and gain momentum from the earth while the summer surface winds have a westerly component and lose momentum to the earth. The results of the short period analysis for the sectors studied suggest broad agreement with the synoptic climatology of the region.
Abstract
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Abstract
When quasi-triennial periodicities have been found in climatic data, their presence has often been attributed to QBO-SO interaction. Although a mixture of idealized QBO and SO signals can give rise to a quasi-triennial carrier wave modulated at the sunspot-cycle period, neither of the latter periods appears in spectral analysis of the resultant time series. It is therefore concluded that quasi-triennial spectral peaks are more likely to be of physical origin than a result of QBO-SO interaction.
Abstract
When quasi-triennial periodicities have been found in climatic data, their presence has often been attributed to QBO-SO interaction. Although a mixture of idealized QBO and SO signals can give rise to a quasi-triennial carrier wave modulated at the sunspot-cycle period, neither of the latter periods appears in spectral analysis of the resultant time series. It is therefore concluded that quasi-triennial spectral peaks are more likely to be of physical origin than a result of QBO-SO interaction.
Abstract
Mammatus clouds are an intriguing enigma of atmospheric fluid dynamics and cloud physics. Most commonly observed on the underside of cumulonimbus anvils, mammatus also occur on the underside of cirrus, cirrocumulus, altocumulus, altostratus, and stratocumulus, as well as in contrails from jet aircraft and pyrocumulus ash clouds from volcanic eruptions. Despite their aesthetic appearance, mammatus have been the subject of few quantitative research studies. Observations of mammatus have been obtained largely through serendipitous opportunities with a single observing system (e.g., aircraft penetrations, visual observations, lidar, radar) or tangential observations from field programs with other objectives. Theories describing mammatus remain untested, as adequate measurements for validation do not exist because of the small distance scales and short time scales of mammatus. Modeling studies of mammatus are virtually nonexistent. As a result, relatively little is known about the environment, formation mechanisms, properties, microphysics, and dynamics of mammatus.
This paper presents a review of mammatus clouds that addresses these mysteries. Previous observations of mammatus and proposed formation mechanisms are discussed. These hypothesized mechanisms are anvil subsidence, subcloud evaporation/sublimation, melting, hydrometeor fallout, cloud-base detrainment instability, radiative effects, gravity waves, Kelvin–Helmholtz instability, Rayleigh–Taylor instability, and Rayleigh–Bénard-like convection. Other issues addressed in this paper include whether mammatus are composed of ice or liquid water hydrometeors, why mammatus are smooth, what controls the temporal and spatial scales and organization of individual mammatus lobes, and what are the properties of volcanic ash clouds that produce mammatus? The similarities and differences between mammatus, virga, stalactites, and reticular clouds are also discussed. Finally, because much still remains to be learned, research opportunities are described for using mammatus as a window into the microphysical, turbulent, and dynamical processes occurring on the underside of clouds.
Abstract
Mammatus clouds are an intriguing enigma of atmospheric fluid dynamics and cloud physics. Most commonly observed on the underside of cumulonimbus anvils, mammatus also occur on the underside of cirrus, cirrocumulus, altocumulus, altostratus, and stratocumulus, as well as in contrails from jet aircraft and pyrocumulus ash clouds from volcanic eruptions. Despite their aesthetic appearance, mammatus have been the subject of few quantitative research studies. Observations of mammatus have been obtained largely through serendipitous opportunities with a single observing system (e.g., aircraft penetrations, visual observations, lidar, radar) or tangential observations from field programs with other objectives. Theories describing mammatus remain untested, as adequate measurements for validation do not exist because of the small distance scales and short time scales of mammatus. Modeling studies of mammatus are virtually nonexistent. As a result, relatively little is known about the environment, formation mechanisms, properties, microphysics, and dynamics of mammatus.
This paper presents a review of mammatus clouds that addresses these mysteries. Previous observations of mammatus and proposed formation mechanisms are discussed. These hypothesized mechanisms are anvil subsidence, subcloud evaporation/sublimation, melting, hydrometeor fallout, cloud-base detrainment instability, radiative effects, gravity waves, Kelvin–Helmholtz instability, Rayleigh–Taylor instability, and Rayleigh–Bénard-like convection. Other issues addressed in this paper include whether mammatus are composed of ice or liquid water hydrometeors, why mammatus are smooth, what controls the temporal and spatial scales and organization of individual mammatus lobes, and what are the properties of volcanic ash clouds that produce mammatus? The similarities and differences between mammatus, virga, stalactites, and reticular clouds are also discussed. Finally, because much still remains to be learned, research opportunities are described for using mammatus as a window into the microphysical, turbulent, and dynamical processes occurring on the underside of clouds.
