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Abstract
This paper describes a 30-yr spinup experiment of the North Atlantic Ocean with the Miami isopycnic-coordinate ocean model, which, when compared with previous experiments, possesses improved horizontal resolution, surface forcing functions, and bathymetry, and is extended to higher latitudes. Overall, there is a conversion of lighter to heavier water masses, and waters of densities 1027.95 and 1028.05 kg m−3 are produced in the Greenland-lceland Norwegian basin, and of density 1027.75 kg m−3 in the Labrador and Irminger basins. These water masses flow primarily southward. The main purpose of this present study, however, is to investigate the ventilation of the subtropical gyre. The role of Ekman pumping and lateral induction in driving the subduction process is examined and the relative importance of the latter is confirmed. The paper also illustrates how the mixed layer waters are drawn southward and westward into the ocean interior in a continuous spectrum of mode waters with densities ranging between 1026.40 and 1027.30 kg m−3. These are organized into a regular fashion by the model from a relatively disorganized initial state. The evolution of the model gyre during spinup is governed by mixed layer cooling in the central North Atlantic, which causes the ventilation patterns to move southwestward, the layers to rise, and surprisingly, to become warmer. This warming is explained by thermodynamic considerations. Finally, it is shown that the rate of change of potential vorticity following a fluid pathway in the subtropical gyre is governed by the diffusion of layer thickness, which represents subgrid-scale mixing processes in the model. This leads to increasing potential vorticity along pathways that ventilate from the thickest outcrop regions as fluid is diffused laterally and to decreasing potential vorticity along neighboring trajectories.
Abstract
This paper describes a 30-yr spinup experiment of the North Atlantic Ocean with the Miami isopycnic-coordinate ocean model, which, when compared with previous experiments, possesses improved horizontal resolution, surface forcing functions, and bathymetry, and is extended to higher latitudes. Overall, there is a conversion of lighter to heavier water masses, and waters of densities 1027.95 and 1028.05 kg m−3 are produced in the Greenland-lceland Norwegian basin, and of density 1027.75 kg m−3 in the Labrador and Irminger basins. These water masses flow primarily southward. The main purpose of this present study, however, is to investigate the ventilation of the subtropical gyre. The role of Ekman pumping and lateral induction in driving the subduction process is examined and the relative importance of the latter is confirmed. The paper also illustrates how the mixed layer waters are drawn southward and westward into the ocean interior in a continuous spectrum of mode waters with densities ranging between 1026.40 and 1027.30 kg m−3. These are organized into a regular fashion by the model from a relatively disorganized initial state. The evolution of the model gyre during spinup is governed by mixed layer cooling in the central North Atlantic, which causes the ventilation patterns to move southwestward, the layers to rise, and surprisingly, to become warmer. This warming is explained by thermodynamic considerations. Finally, it is shown that the rate of change of potential vorticity following a fluid pathway in the subtropical gyre is governed by the diffusion of layer thickness, which represents subgrid-scale mixing processes in the model. This leads to increasing potential vorticity along pathways that ventilate from the thickest outcrop regions as fluid is diffused laterally and to decreasing potential vorticity along neighboring trajectories.
Abstract
Scatterometer ocean surface winds have been providing very valuable information to researchers and operational weather forecasters for over 10 years. However, the scatterometer wind retrievals are compromised when rain is present. Merely flagging all rain-affected areas removes the most dynamic and interesting areas from the wind analysis. Fortunately, the Advanced Earth Observing Satellite II (ADEOS-II) mission carried a radiometer [the Advanced Microwave Scanning Radiometer (AMSR)] and a scatterometer, allowing for independent, collocated retrievals of rain. The authors developed an algorithm that uses AMSR observations to estimate the rain inside the scatterometer beam. This is the first in a series of papers that describe their approach to providing rain estimation and correction to scatterometer observations. This paper describes the retrieval algorithm and evaluates it using simulated data. Part II will present its validation when applied to AMSR observations. This passive microwave rain retrieval algorithm addresses the issues of nonuniform beam filling and hydrometeor uncertainty in a novel way by 1) using a large number of soundings to develop the retrieval database, thus accounting for the geographically varying atmospheric parameters; 2) addressing the spatial inhomogeneity of rain by developing multiple retrieval databases with different built-in inhomogeneity and rain intensity, along with a “rain indicator” to select the most appropriate database for each observed scene; 3) developing a new cloud-versus-rain partitioning that allows the use of a variety of drop size distribution assumptions to account for some of the natural variability diagnosed from the soundings; and 4) retrieving atmospheric and surface parameters just outside the rainy areas, thus providing information about the environment to help decrease the uncertainty of the rain estimates.
Abstract
Scatterometer ocean surface winds have been providing very valuable information to researchers and operational weather forecasters for over 10 years. However, the scatterometer wind retrievals are compromised when rain is present. Merely flagging all rain-affected areas removes the most dynamic and interesting areas from the wind analysis. Fortunately, the Advanced Earth Observing Satellite II (ADEOS-II) mission carried a radiometer [the Advanced Microwave Scanning Radiometer (AMSR)] and a scatterometer, allowing for independent, collocated retrievals of rain. The authors developed an algorithm that uses AMSR observations to estimate the rain inside the scatterometer beam. This is the first in a series of papers that describe their approach to providing rain estimation and correction to scatterometer observations. This paper describes the retrieval algorithm and evaluates it using simulated data. Part II will present its validation when applied to AMSR observations. This passive microwave rain retrieval algorithm addresses the issues of nonuniform beam filling and hydrometeor uncertainty in a novel way by 1) using a large number of soundings to develop the retrieval database, thus accounting for the geographically varying atmospheric parameters; 2) addressing the spatial inhomogeneity of rain by developing multiple retrieval databases with different built-in inhomogeneity and rain intensity, along with a “rain indicator” to select the most appropriate database for each observed scene; 3) developing a new cloud-versus-rain partitioning that allows the use of a variety of drop size distribution assumptions to account for some of the natural variability diagnosed from the soundings; and 4) retrieving atmospheric and surface parameters just outside the rainy areas, thus providing information about the environment to help decrease the uncertainty of the rain estimates.
