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Cloud System (cloud + system)
Selected AbstractsCloud systems leading to flood events in Europe: an overview and classificationMETEOROLOGICAL APPLICATIONS, Issue 3 2003Federico Porcú Over recent years most European countries have experienced destructive precipitation events, many of which have generated floods resulting in the loss of lives and economic damage. Rather surprisingly, Europe has no common database for flood events, which continue to be monitored by different national and/or local authorities, with different criteria. In the light of this situation, the main aim of the present work is to propose a classification scheme for a European-level flood database, in which severe flood episodes are related to meteorological conditions and mesoscale settings. The meteorological systems relating to the most severe events (22 events) over a five-year period (1992,1996) were analysed using Meteosat imagery and conventional meteorological data. Most of the observed events were related to extra tropical cyclone development. The results are discussed in terms of conceptual models currently used for extra tropical cyclones: the structure and dynamics of Atlantic cyclones can very often be interpreted in terms of well- known conceptual models, while characteristics of Mediterranean systems are not fully rendered by current descriptions. Our study underpins the need to improve the knowledge of Mediterranean systems, possibly introducing new conceptual models and/or refining the current ones. Copyright © 2003 Royal Meteorological Society [source] Multi-sensor synthesis of the mesoscale structure of a cold-air comma cloud systemMETEOROLOGICAL APPLICATIONS, Issue 2 2002K 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] Intercomparison of model simulations of mixed-phase clouds observed during the ARM Mixed-Phase Arctic Cloud Experiment.THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 641 2009II: Multilayer cloud Abstract Results are presented from an intercomparison of single-column and cloud-resolving model simulations of a deep, multilayered, mixed-phase cloud system observed during the Atmospheric Radiation Measurement (ARM) Mixed-Phase Arctic Cloud Experiment. This cloud system was associated with strong surface turbulent sensible and latent heat fluxes as cold air flowed over the open Arctic Ocean, combined with a low pressure system that supplied moisture at mid-levels. The simulations, performed by 13 single-column and 4 cloud-resolving models, generally overestimate liquid water path and strongly underestimate ice water path, although there is a large spread among models. This finding is in contrast with results for the single-layer, low-level mixed-phase stratocumulus case in Part I, as well as previous studies of shallow mixed-phase Arctic clouds, that showed an underprediction of liquid water path. These results suggest important differences in the ability of models to simulate deeper Arctic mixed-phase clouds versus the shallow, single-layered mixed-phase clouds in Part I. The observed liquid-ice mass ratios were much smaller than in Part I, despite the similarity of cloud temperatures. Thus, models employing microphysics schemes with temperature-based partitioning of cloud liquid and ice masses are not able to produce results consistent with observations for both cases. Models with more sophisticated, two-moment treatment of cloud microphysics produce a somewhat smaller liquid water path closer to observations. Cloud-resolving models tend to produce a larger cloud fraction than single-column models. The liquid water path and cloud fraction have a large impact on the cloud radiative forcing at the surface, which is dominated by long-wave flux. Copyright © 2009 Royal Meteorological Society [source] A modelling study of aerosol impacts on cloud microphysics and radiative propertiesTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 623 2007Chao-Tzuen Cheng Abstract A warm cloud microphysical parameterization was incorporated into a regional model to study the sensitivity to aerosols of cloud-radiative properties and precipitation. Assuming a trimodal lognormal aerosol size distribution, the aerosol numbers were explicitly calculated from prognostic aerosol masses, considering advection, diffusion, and cloud and raindrop activation/deactivation processes. Clean continental, average continental and urban aerosols, each with different modal parameters, were used to serve as condensation nuclei (CCN) of cloud- and raindrops, whose activations depended on supersaturation and aerosol composition. Consistent with other studies, simulations conducted for a warm cloud system indicate that more aerosols result in more cloud water and more, but smaller, cloud drops, yielding increases in cloud albedo and decreases in surface precipitation. For example, the cloud drop effective radius decreased from ,9 µm for clean continental aerosols to ,5 and ,2 µm, respectively, for average continental and urban aerosols, resulting in an increase in the respective cloud water path by ,10% and ,35% and cloud albedo by ,6% and ,12%. On the other hand, the accumulated precipitation decreased from 2.2 mm for clean continental aerosols to 1.9 and 1.2 mm, respectively, for average continental and urban aerosols. The presence of giant nuclei increased both the cloud drop effective radius and the precipitation, while the use of volumetric cloud drop radius tended to result in larger estimated cloud solar radiative forcing than the use of effective cloud drop radius. Copyright © 2007 Royal Meteorological Society [source] A new IR technique for monitoring low cloud properties using geostationary satellite dataATMOSPHERIC SCIENCE LETTERS, Issue 2 2009Qingyuan Han Abstract A new technique of using satellite infrared radiance data for retrieving cloud properties is developed and applied to SEVIRI data, which is based on direct radiative transfer calculations, not on the emissivity approximation as used by other satellite IR only techniques. Instantaneous atmospheric profiles are used in the new technique for improving the accuracy of retrievals. Comparison of the retrieved results with coincident observations of CloudSat and CALIPSO shows excellent agreement for low clouds. This study shows that, using only IR radiances, the single layer assumption would significantly underestimate cloud optical depth when multilayered cloud system is presented. Copyright © 2009 Royal Meteorological Society [source] Potential of combined spaceborne infrared and microwave radiometry for near real-time rainfall attenuation monitoring along earth-satellite linksINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 4 2001Frank S. Marzano Abstract The objective of this paper is to investigate how spaceborne remote sensors, and their derived products, can be exploited to optimize the performances of a satellite communication system in the presence of precipitating clouds along the path. The complementarity between sun-synchronous microwave (MW) and geo-stationary infrared (IR) radiometry for monitoring the earth's atmosphere is discussed and their potential as a rain detection system within near real-time countermeasure techniques for earth-satellite microwave links is analysed. A general approach, consisting in estimating rainfall intensity and attenuation by polar-orbiting microwave radiometers and temporally tracking the rainfall areas by geo-stationary infrared radiometers, is delineated. Multiple regression algorithms for predicting rainfall attenuation from spaceborne brightness temperatures and from surface rainrate, trained by radiative transfer and cloud models, are illustrated. A maximum likelihood technique is delineated to discriminate stratiform and convective rainfall from spaceborne brightness temperatures. The differences among attenuation estimates derived from layered raining-cloud structures with respect to those obtained from simple rain slabs, as recommended by ITU-R, are also quantified. A test of the proposed attenuation prediction methods is performed using raingage and Italsat data acquired in Spino d'Adda (Italy) during 1994. A description of the statistical method, based on the probability matching technique, adopted to combine MW and IR data for retrieving and tracking precipitating cloud systems in terms of path attenuation and accumulated rain at ground is finally provided together with its application to a case study over the Mediterranean area during October 1998. Copyright © 2001 John Wiley & Sons, Ltd. [source] Sensitivity of one-dimensional radiative biases to vertical cloud-structure assumptions: Validation with aircraft dataTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 608 2005F. Di Giuseppe Abstract Three representations of an observed stratocumulus system are generated by combining aircraft observations with a simple statistical model. The realizations differ in their representation of the vertical cloud structure while the horizontal variability is identical. In the control case (A) both the adiabatic liquid-water profile and the effect of wind-shear induced vertical decorrelation are represented. The second simulation (B) removes the wind-shear effect by assuming maximum overlap between adjacent layers. The third case (C) instead removes vertical variability by averaging the in-cloud liquid water for each column. For each of these scenes Monte Carlo simulated solar fluxes are compared against observed flux measurements. Cases A and B agree with observed (horizontal) flux variations within statistical uncertainty, while case C, which neglects vertical variability, is not able to reproduce the observed fluxes. The comparison between the radiative fields produced by these three representations of the stratocumulus system, calculated using a three-dimensional radiative-transfer solution, an independent pixel approximation (IPA) and a plane-parallel (PP) approach, shows substantial differences. Not accounting for the adiabatic liquid-water profile generates a systematic increase in the optical depth, , when the effective radius is computed from mean liquid-water content and droplet-number concentration, that can be responsible for a 5% increase in the reflection for shallow boundary-layer cloud systems (,,1). A much stronger effect in the radiative properties is produced by varying the cloud-overlap rule applied. While changing from maximum to random overlap does not introduce any variation in the optical depth of the cloud scene, it does introduce an increase in the reflection that is proportional to the relative change in total cloud fraction. The magnitude of these latter biases is comparable to that produced by unresolved horizontal variability. Moreover, it is shown that, when the vertical cloud structure is properly resolved, the effect of horizontal fluctuations is also reduced. Copyright © 2005 Royal Meteorological Society [source] Aircraft observations of cloud droplet number concentration: Implications for climate studiesTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 602 2004I. Gultepe Abstract Droplet number concentration (Nd) is a major parameter affecting cloud physical processes and cloud optical characteristics. In most climate models, Nd is usually assumed to be constant or a function of the droplet and aerosol number concentration (Na). Three types of cloud systems over Canada, namely Arctic clouds, maritime boundary-layer clouds, and winter storms, were studied to obtain values of Nd as a function of temperature (T). The probability density function of Nd was also calculated to show the variability of this parameter. The results show that Nd reaches a maximum at about 10 °C (200 cm,3) and then decreases gradually to a minimum (,1,3 cm,3) at about ,35°C. A comparison of relationships between Nd and Na indicates that estimates of Nd from Na can have an uncertainty of about 30,50 cm,3, resulting in up to a 42% uncertainty in cloud short-wave radiative forcing. This study concludes that the typical fixed values of Nd, which are ,100 cm,3 and ,200 cm,3 for maritime and continental clouds, respectively, and the present relationships of Nd to Na, could result in a large uncertainty in the heat and moisture budgets of the earth's atmosphere. It is suggested that the use of relationships between Nd and T can improve climate simulations. © Crown copyright, 2004. Royal Meteorological Society [source] | ||||||||||