			Home About us Contact

Frontal Systems (frontal + system)

Distribution by Scientific Domains

Earth and Environmental Science	77%

Selected Abstracts

Spatial correspondence between areas of concentration of Patagonian scallop (Zygochlamys patagonica) and frontal systems in the southwestern Atlantic

FISHERIES OCEANOGRAPHY, Issue 5 2005
EUGENIA BOGAZZI
Abstract It has been hypothesized that the geographical location of scallop beds in extensive shelf regions mirrors hydrographic structures (e.g. frontal systems) that favor the retention/concentration of pelagic larvae. Large, discontinuous concentrations of the Patagonian scallop (Zygochlamys patagonica) are known to have occurred recurrently (for more than 30 yr) at certain geographical locations over the extensive Patagonian shelf. These stocks, exploited since 1996, currently support one of the most important scallop fisheries in the world. Here, we investigate whether those aggregations are spatially coincidental with major frontal systems. Several pieces of information were used: historical survey data documenting the geographic distribution of the Patagonian scallop beds, catch and effort data from the commercial fleet, oceanographic data on frontal systems, and remote sensing imagery. We found that large-scale aggregations do match the location of three major and very different frontal systems in the southwestern Atlantic: the Shelf-Break Frontal System, the Northern Patagonia Frontal System, and the Southern Patagonia Frontal System. We describe the three frontal systems and their associated scallops fishing grounds and discuss which processes can contribute to sustaining the productivity of the scallop grounds in each case. [source]

A study of twentieth-century extreme rainfall events in the United Kingdom with implications for forecasting

METEOROLOGICAL APPLICATIONS, Issue 1 2004
William H. Hand
Rainfall events in the United Kingdom during the twentieth century have been surveyed and those identified as extreme by the Flood Studies Report (1975) standards have been examined for common features. Events of duration up to 60 hours were considered in order to investigate those that could cause flash floods. More than half of the 50 events identified were short-period convective storms. The rainfall events were classified by meteorological situation, location and season, allowing the identification of conditions under which extreme rainfall occurred. Suitable conditions for extreme rainfall were split into three categories: orographic, frontal and convective. The frontal and convective classes were then divided into two sub-classes according to whether significant embedded instability was present in the frontal cases and the nature of the convection in the convective cases. The study revealed a lot of commonality between the cases. For example, all of the orographic events occurred in winter in moist west to southwest airflows, and 80% of the frontal cases involved a slow-moving depression to the south or east and also a slow moving frontal system. A conceptual airflow diagram has been developed for some of the frontal cases. The key result, however, was the discovery that each category of meteorological situation occupied a unique space in a rainfall amount versus duration diagram for each extreme event. This offers exciting opportunities for applying the results of this study and a framework for studying future events. Copyright © 2004 Royal Meteorological Society. [source]

The Pelagos Sanctuary for Mediterranean marine mammals

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 4 2008
Giuseppe Notarbartolo-di-Sciara
Abstract 1.In February 2002, France, Italy and Monaco agreed to establish an international sanctuary for Mediterranean marine mammals. The resulting Pelagos Sanctuary encompasses over 87500 km2 of the north-western Mediterranean Sea, extending between south-eastern France, Monaco, north-western Italy and northern Sardinia, and surrounding Corsica and the Tuscan Archipelago. 2.The Pelagos Sanctuary illustrates how the tenets of Marine Protected Area (MPA) design can be reconciled with the dynamic nature of oceanic systems, because its spatial scale was defined by oceanographic and ecological considerations, specifically the location of the Ligurian permanent frontal system. 3.By expanding protective measures beyond national waters, the Pelagos Sanctuary also sets a precedent for the implementation of pelagic protected areas in the high seas. The Pelagos Sanctuary will contribute to the conservation of the Mediterranean Sea at two scales: (i) locally, by protecting important cetacean foraging and breeding grounds in the Ligurian Sea, and by providing ,umbrella' protection to other marine predators in this area; and (ii) regionally, by empowering other conservation measures, such as the Specially Protected Areas Protocol of the Barcelona Convention and the wider goals of the Agreement on the Conservation of Cetaceans of the Black and Mediterranean Seas (ACCOBAMS). 4.However, because few cetacean species are resident within the Sanctuary, their effective long-term conservation will require large-scale management and coordinated monitoring throughout the Mediterranean basin. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Spatial correspondence between areas of concentration of Patagonian scallop (Zygochlamys patagonica) and frontal systems in the southwestern Atlantic

Downscaling of global climate models for flood frequency analysis: where are we now?

HYDROLOGICAL PROCESSES, Issue 6 2002
Christel Prudhomme
Abstract The issues of downscaling the results from global climate models (GCMs) to a scale relevant for hydrological impact studies are examined. GCM outputs, typically at a spatial resolution of around 3° latitude and 4° longitude, are currently not considered reliable at time scales shorter than 1 month. Continuous rainfall-runoff modelling for flood regime assessment requires input at the daily or even hourly time-step. A review of the different methodologies suggested in the literature to downscale GCM results at smaller spatial and temporal resolutions is presented. The methods, from simple interpolation to more sophisticated dynamical modelling, through multiple regression and weather generators, are, however, mostly based directly on GCM outputs, sometimes at daily time-step. The approach adopted is a simple, empirical methodology based on modelled monthly changes from the HadCM2 greenhouse gases experiment for the time horizon 2050s. Three daily rainfall scenarios are derived from the same set of monthly changes, representing different possible changes in the rainfall regime. The first scenario represents an increase of the occurrence of frontal systems, corresponding to a decrease in the rainfall intensity; the second corresponds to an increase in convective storm-type rainfall, characterized by extreme events with higher intensity; the third one assumes an increase in the monthly rainfall without any change in rainfall variability. A continuous daily rainfall-runoff model, calibrated for the Severn catchment, was used to generate daily flow series for the 1961,90 baseline period and the 2050s, and a peaks-over-threshold analysis was undertaken to produce flood frequency distributions for the two time horizons. Though the three scenarios lead to an increase in the magnitude and the frequency of the extreme flood events, the impact is strongly influenced by the type of daily rainfall scenario applied. We conclude that if the next generation of GCMs produce more reliable rainfall variance estimates, then more appropriate ways of deriving rainfall scenarios could be developed using weather generators rather than empirical methods. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Discriminating raining from non-raining cloud areas at mid-latitudes using meteosat second generation SEVIRI night-time data

METEOROLOGICAL APPLICATIONS, Issue 2 2008
B. Thies
Abstract A new method for the delineation of precipitation during night-time using multispectral satellite data is proposed. The approach is not only applicable to the detection of mainly convective precipitation by means of the commonly used relation between infrared cloud-top temperature and rainfall probability but enables also the detection of stratiform precipitation (e.g. in connection with mid-latitude frontal systems). The presented scheme is based on the conceptual model that precipitating clouds are characterized by a combination of particles large enough to fall, an adequate vertical extension [both represented by the cloud water path (CWP)], and the existence of ice particles in the upper part of the cloud. As no operational retrieval exists for Meteosat Second Generation (MSG) to compute the CWP during night-time, suitable combinations of brightness temperature differences (,T) between the thermal bands of Meteosat Second Generation-Spinning Enhanced Visible and InfraRed Imager (MSG SEVIRI, ,T3.9,10.8, ,T3.9,7.3, ,T8.7,10.8, ,T10.8,12.1) are used to infer implicit information about the CWP and to compute a rainfall confidence level. ,T8.7,10.8 and ,T10.8,12.1 are particularly considered to supply information about the cloud phase. Rain area delineation is realized by using a minimum threshold of the rainfall confidence. To obtain a statistical transfer function between the rainfall confidence and the channel differences, the value combination of the channel differences is compared with ground-based radar data. The retrieval is validated against independent radar data not used for deriving the transfer function and shows an encouraging performance as well as clear improvements compared to existing optical retrieval techniques using only IR thresholds for cloud-top temperature. Copyright © 2008 Royal Meteorological Society [source]

Spatial interpolation of GPS integrated water vapour measurements made in the Swiss Alps

METEOROLOGICAL APPLICATIONS, Issue 1 2007
June Morland
Abstract The 31 stations in the Swiss GPS network are located at altitudes between 330 and 3584 m and have provided hourly Integrated Water Vapour (IWV) measurements since November 2000. A correction based on an exponential relationship is proposed for the decrease in IWV with altitude. The scale height depends on the ratio of IWV measured at Jungfraujoch (3584 m) to that measured at Payerne (498 m). An additional coefficient, dependent on the east-west and north-south spatial differences in the IWV, improves the fit to the data. The IWV at heights between 750 and 3500 m was estimated from GPS measurements at Payerne and compared with the Payerne radiosounding. The altitude correction introduced an additional bias of 0.2 to 0.4 mm between GPS and radiosonde. The IWV was normalized to 500 m and the increases and decreases due to the passage of a series of frontal systems between 11 and 14 January 2004 were mapped. A four-year climatology of IWV normalized to 500 m showed that the Alpine stations are more moist in spring, summer and autumn than the stations in the Swiss plains to the north of the Alps. This was attributed to more moist Mediterranean air being blocked by the Alps. Copyright © 2007 Royal Meteorological Society [source]