Home About us Contact
|
Home About us Contact | ||
|
|
||
Regional Circulation (regional + circulation)
Selected AbstractsLarval transport and retention of the spiny lobster, Panulirus argus, in the coastal zone of the Florida Keys, USAFISHERIES OCEANOGRAPHY, Issue 5 2002Cynthia Yeung Abstract The spiny lobster Panulirus argus is of ecological and commercial importance in the South Florida coast of the continental USA and throughout the Intra-Americas Sea. Essential spiny lobster habitat in South Florida is primarily located in the Florida Keys coastal zone (including the Dry Tortugas), where the dynamic regional circulation coupled with the long planktonic larval duration (6,12 months) of P. argus raises questions of larval retention and recruitment. Locally spawned phyllosomata entrained in the Florida Current are likely to be expatriated out of the Straits of Florida, which implies that the local spiny lobster population is sustained by the transport of larval recruits from upstream locations. We examined the physical processes that may influence recruitment. Transport processes in the Keys coastal zone are spatially variable. Observed and modelled data suggest that the upper Keys is a point of onshore larval transport via the inshore meandering of the Florida Current, and the lower Keys to Dry Tortugas region apoint of retention through wind-driven onshore/countercurrents and eddy recirculation. Eddies that propagate between the Dry Tortugas and the lower Keys facilitate the exchange of larvae between the Florida Current and the coastal zone. Northerly wind events associated with cold fronts can enhance recirculation of larvae in the upper Keys. The association of older larvae with the Florida Current front supports the hypothesis that spiny lobster larval recruits come from upstream sources in the Caribbean. [source] Interannual variability in rainy season characteristics over the Limpopo region of southern AfricaINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 14 2005C. J. C. Reason Abstract This study focuses on the interannual variability of dry spell frequencies, dry and wet spell characteristics and onset dates of the austral summer rainy season over the Limpopo region (22,25 °S, 27,32 °E) of northern South Africa. These characteristics of the rainy season are of considerable interest to farmers, water resource managers and other user groups. The Limpopo region supports a large rural population dependent on rain-fed agriculture as well as significant biodiversity, particularly in the Kruger National/Limpopo Transfrontier Park. It is also a region prone to devastating floods and droughts. Evidence is presented that summer dry spell frequency and onset date are related to ENSO via changes in regional circulation. Niño 3.4 sea surface temperature (SST) anomalies appear to show a robust relationship with dry spell frequency during the 1979,2002 period analysed. Anomalies in onset date of the rainy season during 1979,2002 appear to be inversely related to Niño 3.4 SST, with the relationship strengthening after 1986. These results suggest that there may be some predictability in these parameters, particularly in dry spell frequency during austral summer, based on existing skill in predicting tropical Pacific SST. Copyright © 2005 Royal Meteorological Society. [source] January northern hemisphere circumpolar vortex variability and its relationship with hemispheric temperature and regional teleconnectionsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 11 2005Robert V. Rohli Abstract Variability in the hemispheric-scale atmospheric circulation can be directly linked to variations in surface environmental features, such as temperature, precipitation, salinity of water bodies, and pollutant transport. One indicator of the behavior of the hemispheric-scale circulation is the circumpolar vortex (CPV). This research utilizes a geographic information system approach to characterize variability in the Northern Hemispheric (NH) CPV. Specifically, the area, shape, and centroid of the January NHCPV are analyzed for 1959,2001 because it may provide insight about relationships between hemispheric-scale circulation and global temperature change. We also use a new means of characterizing the hemispheric-scale circulation using a ,circularity ratio' (Rc). Results suggest that the January NHCPV has exhibited no long-term trends in area or shape, and that the mean centroid is positioned at approximately 85.3°N, 178.0°W. Regional patterns emerge, which suggest that the area and circularity are associated with variability in surface temperature and moist static energy. Furthermore, the area of the January NHCPV is associated with variability in the Arctic Oscillation, while the shape is tied to variability in the Pacific-North American teleconnection pattern. These results will facilitate understanding of the relationship between hemispheric-scale circulation, regional circulation, and local temperatures. Copyright © 2005 Royal Meteorological Society. [source] Sensitivity of an Arctic regional climate model to the horizontal resolution during winter: implications for aerosol simulationINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 11 2005Eric Girard Abstract Our ability to properly simulate current climate and its future change depends upon the exactitude of the physical processes that are parameterized on the one hand, and on model configuration on the other hand. In this paper, we focus on the latter and investigate the effect of the horizontal grid resolution on the simulation of a month of January over the Arctic. A limited-area numerical climate model is used to simulate the month of January 1990 over a grid that includes the Arctic and sub-Arctic regions. Two grid resolutions are used: 50 km and 100 km. Results show that finer details appear for regional circulation, temperature, and humidity when increasing horizontal resolution. This is particularly true for continental and sea ice boundaries, which are much better resolved by high-resolution model simulations. The Canadian Archipelago and rivers in northern Russia appear to benefit the most from higher horizontal resolution. High-resolution simulations capture some frozen rivers and narrow straits between islands. Therefore, much colder surface air temperature is simulated over these areas. Precipitation is generally increased in those areas and over topography due to a better representation of surface heterogeneities when increasing resolution. Large-scale atmospheric circulation is substantially changed when horizontal resolution is increased. Feedback processes occur between surface air temperature change over heterogeneous surfaces and atmospheric circulation. High-resolution simulations develop a stronger polar vortex. The mean sea-level pressure increases over the western Arctic and Iceland and decreases over the eastern Arctic. This circulation leads to a substantial cooling of the eastern Arctic and enhanced synoptic activity over the Arctic associated with an intensification of the baroclinic zone. Aerosol mass loading, which is simulated explicitly in this model, is significantly altered by the grid resolution change with the largest differences in aerosol concentration over areas where precipitation and atmospheric circulation are the most affected. The implications of this sensitivity study to the evaluation of indirect radiative effects of anthropogenic aerosols are discussed. Copyright © 2005 Royal Meteorological Society. [source] Sensitivity of the southern African circulation to dipole sea-surface temperature patterns in the south Indian OceanINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 4 2002C. J. C. Reason Abstract Previous observational work suggests that when sea-surface temperature (SST) is warm (cool) in the southwest Indian Ocean and cool (warm) in the southeast Indian Ocean, increased (decreased) summer rains may occur over large areas of southeastern Africa. In this study, an atmospheric general circulation model is used to investigate the sensitivity of the regional circulation and rainfall over southern Africa to these dipole SST anomalies in the subtropical south Indian Ocean. When the model is forced with positive SST anomalies in the west and negative SST anomalies in the east, increased rainfall occurs over southeastern Africa as a result of the enhanced convergence of moister than average air over the region. Enhanced evaporation occurs over the warm pole in the southwest Indian Ocean and this moist air is advected towards southeastern Africa as a result of the low-pressure anomaly generated over this pole, which strengthens the onshore flow. Increased and more intense extra-tropical cyclones occur to the southeast of South Africa, favourable for tropical,temperate trough formation. When the SST poles are reversed in sign, decreased precipitation occurs over southeastern Africa as a result of increased low-level divergence of low-level flow and this flow being drier than average. Weaker and fewer extra-tropical cyclones occur southeast of South Africa in this case. The model results are sensitive to the proximity of the southwest Indian Ocean pole to southeastern Africa. There is also sensitivity in the model low-level wind changes and precipitation anomaly over low-latitude southern Africa (but not over South Africa to any significant extent) to the presence or absence of the SST pole over the southeast Indian Ocean. Although the model resolution does not capture the details of the local SST and topographic gradients as well as one would like, the changes in model circulation and precipitation in the experiments with different SST anomalies are consistent with previous observational and theoretical work, hence increasing confidence in the robustness of the results. Copyright © 2002 Royal Meteorological Society [source] Regulation of Endothelial Cell Adhesion Molecule Expression in an Experimental Model of Cerebral MalariaMICROCIRCULATION, Issue 6 2002PHILLIPE R. BAUER ABSTRACT Objective: Plasmodium falciparum malaria in humans and animal models of this disease have revealed changes in the infected host that are consistent with a systemic inflammatory response. Although it has been proposed that endothelial cell adhesion molecules (CAM) contribute to the adhesive interactions of Plasmodium -infected erythrocytes and immune cells with vascular endothelial cells, ECAM expression has not been systematically studied in Plasmodium -infected animals. Methods: In this study, the dual radiolabeled monoclonal antibody method was used to quantify the expression of different ECAMs (ICAM-1, VCAM-1, P-selectin, E-selectin) in different regional vascular beds of Plasmodium berghei ANKA-inffected mice (PbA), a well-recognized model of human cerebral malaria. The roles of T lymphocytes and certain cytokines (TNF-,, IL-12, IFN-,) in mediating the infection-induced expression of ICAM-1 and P-selectin were assessed by using relevant mutant mice. Results: Wild-type (WT) mice exhibited highly significant increases in the expression of ICAM-1, VCAM-1, and P-selectin (but not E-selectin) in all vascular beds on the 6th day of PbA infection. The PbA -induced upregulation of ICAM-1 was significantly blunted in mice that were either deficient in IFN-,, IL-12 (but not TNF1b) or T lymphocytes (Rag-1 deficiency); however, these responses were tissue specific. Conclusions: These findings indicate that vascular endothelial cells in most regional circulations assume an inflammatory phenotype and that cytokines and immune cells mediate this response in a tissue-specific manner. [source] | ||||||||||