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Abstract
Three subjective and two objective analysis techniques were employed to prepare height data for a synoptic case over North America. These heights were used as input to a ten-level quasi-geostrophic model for computation of omegas (vertical velocities in pressure coordinate system) over a grid 2° latitude square. Using a subjective analysis prepared by F. Sanders as a standard, all the techniques gave synoptically acceptable patterns locating the 500-mb low center within one grid square with the intensity within ±20 m. The average height differences at each level for each technique never exceeded 11 m. One subjective and one objective technique did slightly better than the others for the height field.
Comparison of the quasi-geostrophic omegas with the Sanders' values shows good agreement for all analysis techniques for the broad scale rising and sinking centers and zero lines. The 500-mb centers are located within one grid interval with the main central values generally within 10–20% of the Sanders' value. Areas enclosed by a given omega isopleth show even better agreement. Overall the subjective analysis prepared by the team of Johnson, Golden, Hudson and Cotter (JGHC) agrees best with the Sanders' results, but the results via Inman's Objective Height Analysis (HOBAN) were quite close.
Abstract
Three subjective and two objective analysis techniques were employed to prepare height data for a synoptic case over North America. These heights were used as input to a ten-level quasi-geostrophic model for computation of omegas (vertical velocities in pressure coordinate system) over a grid 2° latitude square. Using a subjective analysis prepared by F. Sanders as a standard, all the techniques gave synoptically acceptable patterns locating the 500-mb low center within one grid square with the intensity within ±20 m. The average height differences at each level for each technique never exceeded 11 m. One subjective and one objective technique did slightly better than the others for the height field.
Comparison of the quasi-geostrophic omegas with the Sanders' values shows good agreement for all analysis techniques for the broad scale rising and sinking centers and zero lines. The 500-mb centers are located within one grid interval with the main central values generally within 10–20% of the Sanders' value. Areas enclosed by a given omega isopleth show even better agreement. Overall the subjective analysis prepared by the team of Johnson, Golden, Hudson and Cotter (JGHC) agrees best with the Sanders' results, but the results via Inman's Objective Height Analysis (HOBAN) were quite close.
Abstract
The quasi-geostrophic omega equation is employed to perform a diagnostic case study of the baroclinic structure of a developing system. The model employs height data at ten pressure levels to obtain the vertical motion along with the divergence and twisting terms at four pressure levels all evaluated in a fairly objective manner. Results are presented for one synoptic time prior to the development of a cut-off low of the Nevada type. These clearly show the scale and magnitude of the baroclinic features and the relative importance of the twisting and divergence terms for producing vorticity changes on a moving parcel. These results suggest a possible sequence of events leading to the cut-off low and the type of detail that filtered prediction models should employ to allow us to evaluate completely the ability of filtered models to handle mid-tropospheric development.
Abstract
The quasi-geostrophic omega equation is employed to perform a diagnostic case study of the baroclinic structure of a developing system. The model employs height data at ten pressure levels to obtain the vertical motion along with the divergence and twisting terms at four pressure levels all evaluated in a fairly objective manner. Results are presented for one synoptic time prior to the development of a cut-off low of the Nevada type. These clearly show the scale and magnitude of the baroclinic features and the relative importance of the twisting and divergence terms for producing vorticity changes on a moving parcel. These results suggest a possible sequence of events leading to the cut-off low and the type of detail that filtered prediction models should employ to allow us to evaluate completely the ability of filtered models to handle mid-tropospheric development.
Abstract
Temporal and spatial variations in the structure of the lower atmosphere off Oregon's central coast are studied. The response of the wind and thermal fields to a synoptic-scale realignment aloft that causes a rapid shift from surface southerly to northerly winds is detailed. The effects and importance of the infrequent southerlies on the marine inversion, sea breezes and upwelling is also investigated.
A vast array of meteorological and oceanographic observations were measured by aircraft, land stations, buoys and ships during the first Coastal Upwelling Experiment I (CUE-I). The winds, air and water temperature, and currents from the surface ocean layer to 1.5 km are compared during 16–29 August 1972. The period of southerly surface winds created a warm moist lower atmosphere, weak sea breezes, and brought about a cessation to previous upwelling. In contrast, northerlies and ridging aloft produced a distinct marine inversion, strong sea breezes, and an upwelling event. The marked changes reveal the potential effect summer southerlies have on coastal Oregon's air-sea environment.
Abstract
Temporal and spatial variations in the structure of the lower atmosphere off Oregon's central coast are studied. The response of the wind and thermal fields to a synoptic-scale realignment aloft that causes a rapid shift from surface southerly to northerly winds is detailed. The effects and importance of the infrequent southerlies on the marine inversion, sea breezes and upwelling is also investigated.
A vast array of meteorological and oceanographic observations were measured by aircraft, land stations, buoys and ships during the first Coastal Upwelling Experiment I (CUE-I). The winds, air and water temperature, and currents from the surface ocean layer to 1.5 km are compared during 16–29 August 1972. The period of southerly surface winds created a warm moist lower atmosphere, weak sea breezes, and brought about a cessation to previous upwelling. In contrast, northerlies and ridging aloft produced a distinct marine inversion, strong sea breezes, and an upwelling event. The marked changes reveal the potential effect summer southerlies have on coastal Oregon's air-sea environment.
Abstract
As a part of the Second Coastal Upwelling Experiment along the Oregon Coast in summer 1973, extensive thermodynamic data were gathered in a mesoscale area. These data were examined in relation to the marine inversion at seven stations along a line from Salem, Ore., to a point 22 n mi off the coast, or a distance of approximately 65 n mi. The structure of the inversion was examined via time sections of temperature and potential temperature at each station, and cross sections along the line for selected times during the intensive period. Limited time and cross sections of relative humidity were also examined. The inversion seemed to respond to even weak synoptic-scale changes, rising with low-level convergence and lowering with subsidence in high-pressure regions. It was also found that the marine inversion had a more complex structure than a single stable layer.
Abstract
As a part of the Second Coastal Upwelling Experiment along the Oregon Coast in summer 1973, extensive thermodynamic data were gathered in a mesoscale area. These data were examined in relation to the marine inversion at seven stations along a line from Salem, Ore., to a point 22 n mi off the coast, or a distance of approximately 65 n mi. The structure of the inversion was examined via time sections of temperature and potential temperature at each station, and cross sections along the line for selected times during the intensive period. Limited time and cross sections of relative humidity were also examined. The inversion seemed to respond to even weak synoptic-scale changes, rising with low-level convergence and lowering with subsidence in high-pressure regions. It was also found that the marine inversion had a more complex structure than a single stable layer.
Abstract
Coordinated meteorological and oceanographic (CTD) measurements were made near Point Conception, California, during March–April 1981. The goal of the observations was to study coastal upwelling and the local characteristics of the assumed wind driving. Results showed substantial topographically-induced spatial structure in the near-surface winds, with weaker winds generally occurring within the Santa Barbara Channel. The 1981 “spring transition” event was monitored by mews of hydrographic and sea level measurements. The details of the event suggest that it was not entirely driven by lead wind stress. The mean sea surface temperature pattern suggests the existence of an upwelling center between Points Arguello and Conception. The individual sea surface temperature charts are all dominated by patchiness on a scale of 5–15 km. The nature of these structures is not well understood, but on the one occasion when a patch was isolated by a CTD survey, its structure penetrated to at 1east 50 db.
Abstract
Coordinated meteorological and oceanographic (CTD) measurements were made near Point Conception, California, during March–April 1981. The goal of the observations was to study coastal upwelling and the local characteristics of the assumed wind driving. Results showed substantial topographically-induced spatial structure in the near-surface winds, with weaker winds generally occurring within the Santa Barbara Channel. The 1981 “spring transition” event was monitored by mews of hydrographic and sea level measurements. The details of the event suggest that it was not entirely driven by lead wind stress. The mean sea surface temperature pattern suggests the existence of an upwelling center between Points Arguello and Conception. The individual sea surface temperature charts are all dominated by patchiness on a scale of 5–15 km. The nature of these structures is not well understood, but on the one occasion when a patch was isolated by a CTD survey, its structure penetrated to at 1east 50 db.
Abstract
Results of tests for the optimum over-relaxation coefficients in the numerical relaxation of the omega equation are presented. One case considers a strong upper-level development for tests on a fixed grid using one-, two-, and three-dimensional forms of the omega equation. In the other case of a “classical storm” the omega equation is relaxed in its three-dimensional form using several different horizontal grids.
For the one- and two-dimensional tests, the relaxation scheme agreesv ery well with theory. In the three-dimensional tests, the observed over-relaxation coefficients are found to be less than the values given by the theory for all grid sizes considered. A sharp cut-off is found to occur shortly after the optimum over-relaxation value is reached regardless of the number of dimensions of the equation or the size of the grid.
Abstract
Results of tests for the optimum over-relaxation coefficients in the numerical relaxation of the omega equation are presented. One case considers a strong upper-level development for tests on a fixed grid using one-, two-, and three-dimensional forms of the omega equation. In the other case of a “classical storm” the omega equation is relaxed in its three-dimensional form using several different horizontal grids.
For the one- and two-dimensional tests, the relaxation scheme agreesv ery well with theory. In the three-dimensional tests, the observed over-relaxation coefficients are found to be less than the values given by the theory for all grid sizes considered. A sharp cut-off is found to occur shortly after the optimum over-relaxation value is reached regardless of the number of dimensions of the equation or the size of the grid.
Abstract
The roughness of the seas is rarely mentioned as a major factor in the economic or social welfare of a region. In this study, the relationship between the ocean wave climate and the economy of the Western Isles of Scotland is examined. This sparsely populated region has a high dependency on marine activities, and ferry services provide vital links between communities. The seas in the region are among the roughest in the world during autumn and winter, however, making maintenance of a reliable ferry service both difficult and expensive. A deterioration in wave and wind climate either in response to natural variability or as a regional response to anthropogenic climate change is possible. Satellite altimetry and gale-frequency data are used to analyze the contemporary response of wave and wind climate to the North Atlantic Oscillation (NAO). The sensitivity of wave climate to the NAO extends to ferry routes that are only partially sheltered and are exposed to ocean waves; thus, the reliability of ferry services is sensitive to NAO. Any deterioration of the wave climate will result in a disproportionately large increase in ferry-service disruption. The impacts associated with an unusually large storm event that affected the region in January 2005 are briefly explored to provide an insight into vulnerability to future storm events.
Abstract
The roughness of the seas is rarely mentioned as a major factor in the economic or social welfare of a region. In this study, the relationship between the ocean wave climate and the economy of the Western Isles of Scotland is examined. This sparsely populated region has a high dependency on marine activities, and ferry services provide vital links between communities. The seas in the region are among the roughest in the world during autumn and winter, however, making maintenance of a reliable ferry service both difficult and expensive. A deterioration in wave and wind climate either in response to natural variability or as a regional response to anthropogenic climate change is possible. Satellite altimetry and gale-frequency data are used to analyze the contemporary response of wave and wind climate to the North Atlantic Oscillation (NAO). The sensitivity of wave climate to the NAO extends to ferry routes that are only partially sheltered and are exposed to ocean waves; thus, the reliability of ferry services is sensitive to NAO. Any deterioration of the wave climate will result in a disproportionately large increase in ferry-service disruption. The impacts associated with an unusually large storm event that affected the region in January 2005 are briefly explored to provide an insight into vulnerability to future storm events.
Abstract
For decades oceanographers have understood the Atlantic meridional overturning circulation (AMOC) to be primarily driven by changes in the production of deep-water formation in the subpolar and subarctic North Atlantic. Indeed, current Intergovernmental Panel on Climate Change (IPCC) projections of an AMOC slowdown in the twenty-first century based on climate models are attributed to the inhibition of deep convection in the North Atlantic. However, observational evidence for this linkage has been elusive: there has been no clear demonstration of AMOC variability in response to changes in deep-water formation. The motivation for understanding this linkage is compelling, since the overturning circulation has been shown to sequester heat and anthropogenic carbon in the deep ocean. Furthermore, AMOC variability is expected to impact this sequestration as well as have consequences for regional and global climates through its effect on the poleward transport of warm water. Motivated by the need for a mechanistic understanding of the AMOC, an international community has assembled an observing system, Overturning in the Subpolar North Atlantic Program (OSNAP), to provide a continuous record of the transbasin fluxes of heat, mass, and freshwater, and to link that record to convective activity and water mass transformation at high latitudes. OSNAP, in conjunction with the Rapid Climate Change–Meridional Overturning Circulation and Heatflux Array (RAPID–MOCHA) at 26°N and other observational elements, will provide a comprehensive measure of the three-dimensional AMOC and an understanding of what drives its variability. The OSNAP observing system was fully deployed in the summer of 2014, and the first OSNAP data products are expected in the fall of 2017.
Abstract
For decades oceanographers have understood the Atlantic meridional overturning circulation (AMOC) to be primarily driven by changes in the production of deep-water formation in the subpolar and subarctic North Atlantic. Indeed, current Intergovernmental Panel on Climate Change (IPCC) projections of an AMOC slowdown in the twenty-first century based on climate models are attributed to the inhibition of deep convection in the North Atlantic. However, observational evidence for this linkage has been elusive: there has been no clear demonstration of AMOC variability in response to changes in deep-water formation. The motivation for understanding this linkage is compelling, since the overturning circulation has been shown to sequester heat and anthropogenic carbon in the deep ocean. Furthermore, AMOC variability is expected to impact this sequestration as well as have consequences for regional and global climates through its effect on the poleward transport of warm water. Motivated by the need for a mechanistic understanding of the AMOC, an international community has assembled an observing system, Overturning in the Subpolar North Atlantic Program (OSNAP), to provide a continuous record of the transbasin fluxes of heat, mass, and freshwater, and to link that record to convective activity and water mass transformation at high latitudes. OSNAP, in conjunction with the Rapid Climate Change–Meridional Overturning Circulation and Heatflux Array (RAPID–MOCHA) at 26°N and other observational elements, will provide a comprehensive measure of the three-dimensional AMOC and an understanding of what drives its variability. The OSNAP observing system was fully deployed in the summer of 2014, and the first OSNAP data products are expected in the fall of 2017.
