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Mesoscale Structure (mesoscale + structure)

Distribution by Scientific Domains

Earth and Environmental Science	75%

Selected Abstracts

Multi-sensor synthesis of the mesoscale structure of a cold-air comma cloud system

METEOROLOGICAL APPLICATIONS, Issue 2 2002
K A Browning
A multiscale study of a cold-air comma cloud that produced an area of heavy rain and locally severe weather has been undertaken by synthesising data from a research microwave Doppler radar and VHF and UHF Doppler wind profilers, along with routinely available radar-network, satellite, in situ and mesoscale-model data. The rain area was generated in the exit region of an upper-level jet characterised by laminated velocity perturbations. Some of the perturbations were attributable to inertia-gravity wave activity. The rain area itself is shown to have been composed of a well-organised set of mesoscale rainbands each being due to a mixture of upright and slantwise convection. The existence of the multiple rainbands may have been related to the multi-layered atmospheric structure upwind. Each of the rainbands had cold-frontal and warm-frontal portions, so as to form a series of mini warm sectors stacked along the axis of the comma cloud at roughly 70 km intervals. The multiple rainbands were accompanied by multiple fingers of overrunning low-,w air from part of a dry intrusion originating from just below a major tropopause fold. The fold contained an intense potential-vorticity maximum which appeared to be the focus of the overall system. The operational mesoscale version of the Met. Office's Unified Model, with its 12 km grid, is shown to have resolved many but not all of the key features of the rainbands. It is suggested that further improvements in very-short-range forecasting of important local detail could be achieved by further increasing its resolution and assimilating more mesoscale observational data. Copyright © 2002 Royal Meteorological Society [source]

Tropical-cyclone intensification and predictability in three dimensions

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 632 2008
Nguyen Van Sang
Abstract We present numerical-model experiments to investigate the dynamics of tropical-cyclone amplification and its predictability in three dimensions. For the prototype amplification problem beginning with a weak-tropical-storm-strength vortex, the emergent flow becomes highly asymmetric and dominated by deep convective vortex structures, even though the problem as posed is essentially axisymmetric. The asymmetries that develop are highly sensitive to the boundary-layer moisture distribution. When a small random moisture perturbation is added in the boundary layer at the initial time, the pattern of evolution of the flow asymmetries is changed dramatically, and a non-negligible spread in the local and azimuthally-averaged intensity results. We conclude, first, that the flow on the convective scales exhibits a degree of randomness, and only those asymmetric features that survive in an ensemble average of many realizations can be regarded as robust; and secondly, that there is an intrinsic uncertainty in the prediction of maximum intensity using either maximum-wind or minimum-surface-pressure metrics. There are clear implications for the possibility of deterministic forecasts of the mesoscale structure of tropical cyclones, which may have a major impact on the intensity and on rapid intensity changes. Some other aspects of vortex structure are addressed also, including vortex-size parameters, and sensitivity to the inclusion of different physical processes or higher spatial resolution. We investigate also the analogous problem on a ,-plane, a prototype problem for tropical-cyclone motion. A new perspective on the putative role of the wind--evaporation feedback process for tropical-cyclone intensification is offered also. The results provide new insight into the fluid dynamics of the intensification process in three dimensions, and at the same time suggest limitations of deterministic prediction for the mesoscale structure. Larger-scale characteristics, such as the radius of gale-force winds and ,-gyres, are found to be less variable than their mesoscale counterparts. Copyright © 2008 Royal Meteorological Society [source]

Polar low le Cygne: Satellite observations and numerical simulations

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 598 2004
Chantal Claud
Abstract A polar low (PL) which occurred in October 1993 over the Norwegian Sea is investigated from an observational and a numerical point of view. This PL has several unique features: it developed early in the season, it lasted for about 3 days, and its trajectory was such that it passed over weather stations so that ,conventional' observations of the low are available. The conditions of the formation, development and decay of the PL are investigated using a double approach: satellite data from several instruments are used together to document the mesoscale structure of the low, and two versions of a limited-area model are run to investigate the dynamics of the low. Numerical model fields are compared to quantities derived from TIROS-N Operational Vertical Sounder, the Special Sensor Microwave/Imager, and satellite radar altimeter data. In spite of a better spatial resolution of the models, humidity and surface wind speeds are less organized in the simulations than in satellite retrievals. The number of vertical levels, especially for the lowest layers of the atmosphere, appears to be an essential component for a good simulation of the trajectory of the low. There is, however, good overall agreement between modelled and satellite-derived fields, and the good quality of the simulations allows inferences to be made regarding the essential physical and dynamical processes taking place during the formation and development of the PL. We find that the PL was the result of favourable flow conditions at the surface in the form of a shallow arctic front established south of the ice edge, together with an upper-level potential-vorticity anomaly setting the stage for a positive interaction. Later on, the strong surface sensible- and latent-heat fluxes contributed to the extensive vertical development. This study demonstrates the usefulness of the approach adopted here, which relies not only on simulations but also on observations to get a very complete description of such disturbances. Copyright © 2004 Royal Meteorological Society. [source]

Templated and Hierarchical Assembly of CdSe/ZnS Quantum Dots,

ADVANCED MATERIALS, Issue 15 2004
Y. Babayan
CdSe/ZnS nanocrystals have been assembled into mesoscale structures (see Figure). Templates with dimensions down to 100,nm are generated via phase-shifting photolithography using composite poly(dimethylsiloxane) masks. Upon removal of the template, the CdSe/ZnS structures are found to exhibit hierarchical order over square nanometers (self-assembly of nanocrystals), square micrometers (template shape), and square centimeters (arrays of template pattern). [source]