Doppler Radar Observations on the Structure and Characteristics of Tropical Clouds during the TOGA-COARE IOP in Manus, Papua New Guinea
Hiroshi UyedaYoshio AsumaNobuhiro TakahashiShuji ShimizuOsamu KikuchiAtsushi KinoshitaSeiki MatsuokaMasaki KatsumataKensuke TakeuchiTatsuo EndohMasayuki OhiShinsuke SatohYoshihiro TachibanaTomoki UshiyamaYasushi FujiyoshiRyuichi ShirookaNoriyuki NishiTomohiko TomitaHiroaki UedaTatsuo SuedaAkimasa Sumi
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Observations of tropical convection and cloud clusters with two X-band Doppler radars were carried out on Manus Island, Papua New Guinea for two and a half months from 12 November 1992 during the Intensive Observation Period (IOP) of the TOGA-COARE. Several different types of clouds were observed by Doppler radars during the period, such as squall lines, convective clouds and stratiform clouds associated with cloud clusters, isolated convective clouds over the island in the day time, etc. Outlines of the observations on Manus Island and brief reviews of the results of these observations are described. Preliminary summaries of the analyses on the observations are: 1) A warm rain process dominates at the beginning stage of radar echo development and the maximum radar reflectivity is recognized at this stage, 2) The maximum echo top height is observed within 3 hours from the first echo, 3) The maximum echo area within the radar range was analyzed a few to several hours later than the time of maximum echo top height corresponding to the size of cloud cluster, 4) In the long-lasting stratiform echo, updrafts independent from those below the melting layer were identified above the melting layer. It is concluded that further studies utilizing these observational data may reveal the structure and the evolution mechanism of tropical cloud clusters.Keywords:
Squall line
Manus
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New guinea
Based on GMS satellite data,the formations of the six severe dust-devil events over the North-west of China are analysed The results indicate that the genesis of dust-devil is caused by mesoscale systems,which include the mesoscale-α squall line system,the mesoscale- β paēě severe convective system and the mesoscale convective complex The characteristics,development process and large scale environment of these mesoscale systems are also analysed in the work
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A numerical model designed for the simulations of mesoscale flows perturbed by deep convective clouds is discussed. It is based on the time dependent coupling between a three-dimensional nonhydrostatic mesoscale model and a quasi-one-dimensional cloud model. The evolution and motion of individual convective cells are simulated by the cloud model since they cannot be explicitly resolved by the mesoscale model. This implies that in cloudy areas each model simulates the time evolution of the same variable at the same location and at the same time, under the influence of different processes (large-scale processes for the mesoscale model and microphysical processes for the cloud model). The comparison between the cloud and mesoscale rates of change leads to an evaluation of the coupling terms which transmit the cloud influences into the mesoscale model so that mesoscale fields are perturbed accordingly. For example, the nonhydrostatic pressure field reacts to the cloud development by building up an overpressure dome above the cloud top. On the other hand, the environmental conditions of each cell, including the vertical gradient of the nonhydrostatic pressure, represent the mesoscale influence on the cloud model. These conditions are deduced from the local values of the perturbed mesoscale fields at each cloud position. A particular simulation is analyzed. Analysis reveals that the main characteristics of the flow perturbed by the convective cells are similar to those of a squall line deduced from ground station measurement. The typical signatures of the gust front are simulated, even though the magnitude of the perturbations are not all well simulated. The convective transport of horizontal momentum appears to be of fundamental importance to the organization process.
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Collection Ocora - Papua New Guinea (Manus, Bougainville). One 12″ LP Record. OCORA OCR 86. Mono. Produced in cooperation with the Institute of Papua New Guinea Studies. Recordings, notes (10 pp.) and photographs by Charles Duvelle, assisted by Frédéric Duvelle, with the collaboration of Kaka Kaïs (Manus) and Leo Hannet (Bougainville). Paris: OCORA/Radio France, 1975. - Volume 9
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Back‐building squall‐lines (BBSs) cause local heavy rainfalls and lead to natural disasters. Therefore, better understanding BBSs would have a significant impact on disaster prevention and mitigation. Although a conceptual maintenance condition of BBSs is proposed by previous studies, the concept stands on a case study. We clarified that a mesoscale moist area in water vapor front localizes the continuous forming of new cells in the BBS and reinforced the concept with another case. A numerical simulation of the heavy rainfall during July 11–12, 2010, in western Japan was used to confirmation of the conceptual maintenance condition of the BBS. We found that the new cells of BBS are continually formed at the confluence zone of the synoptic‐scale cold front and the mesoscale area with large water vapor amount at low‐level. It supports the conceptual maintenance condition, and the mesoscale moist area in water vapor front is a distinct characteristic in this case. The position where new cells are formed has been anchored by the mesoscale moist area for 2 hr.
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Composites of radar and wind observations in a coordinate system attached to a moving tropical squall line confirm that such a squall system is composed of two separate circulation features: a convective squall-line region and a stratiform anvil region. The squall-line region is characterized by mesoscale boundary-layer convergence, which feeds deep convective updrafts, and mid-to-upper-level divergence associated with outflow from the cells. The anvil region is characterized by mid-level convergence, which feeds both a mesoscale downdraft below the anvil and a mesoscale updraft within the anvil cloud. Before this study, the mesoscale updraft in the anvil cloud of the tropical squall system had been somewhat speculative, and both the anvil updraft and downdraft had been inferred only qualitatively. The occurrence of the anvil updraft is now proven and quantitative profiles of the mesoscale anvil updraft and downdraft have been obtained.
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The results of a diagnostic study using radar and satellite imagery, together with surface reports and output from regional and mesoscale models, are presented for an occasion of a rapidly deepening cyclone that crossed the British Isles. The study shows how air descended from near-tropopause level in the form of mesoscale dry intrusions which appeared to overrun parts of the warm conveyor belt ahead of a surface cold front. One of the dry intrusions is analysed in detail, because it is thought to have led to the large changes that were observed in the character of the wide frontal rain band: in some places the precipitation was entirely suppressed, whilst in other places the precipitation became convective, with a tornadic squall line developing. Although the effect of the dry intrusion was seen most clearly in the precipitation distribution as determined by radar, the approach of the dry intrusion was also clearly detected in the satellite water-vapour imagery, and foreshadowed in the model forecasts. The mesoscale model, despite some limitations, reproduced many of the observed mesoscale features. It also provided insight into the detailed behaviour of the dry intrusion associated with the tornadic squall line. It showed that the dry intrusion was characterized by a mesoscale filament of high potential vorticity (PV) which was extruded from the lower part of a large region of high PV near a low tropopause. The extruded PV anomaly plunged to within a kilometre of the surface where it overran part of the warm conveyor belt. The dry intrusion was also characterized by relatively low wet-bulb potential temperature, θw, and it led to potential instability where it overran the warm air. The warm conveyor belt itself was characterized not only by a high θw but also by a separate strip of high PV generated locally, mainly by condensation. The quality of the mesoscale-model simulation gives grounds for optimism that such models are capable in principle of predicting severe mesoscale weather events when, as in this case, they are orchestrated by resolved larger-scale dynamics.
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Cold front
Mesoscale convective system
Anomaly (physics)
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By using synoptic charts,hourly GMS5 infrared TBB pictures and Doppler radar echo data,the rainstorm process on August 16,2003 has been analysed.The results show that there is an obvious mesoscale character of the rainstorm in spatial and temporal distribution.The macroscale synoptic situation supplies suitable circulation background,instability condition,energy condition and dynamical condition for the forming and development of the mesoscale system.The shear cloud system develops into a squall line.And the three mesoscale α cloud clusters and one mesoscale β cloud cluster aroused by the shear cloud system produce the heavy rainfall by analysing satellite cloud pictures.The mesoscale β shear line between east wind and west wind and the contrary wind are very important to the forming and development of the mesoscale α squall line by analysing the Dopplar radar echoes,arousing a supercell and a vmaxmesocyclone,and the mesoscale α squall line directly produces the rainstorm process.
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