The Experts below are selected from a list of 213 Experts worldwide ranked by ideXlab platform

Toshio Yamagata - One of the best experts on this subject based on the ideXlab platform.

  • Subtropical Dipole Modes Simulated in a Coupled General Circulation Model
    Journal of Climate, 2012
    Co-Authors: Yushi Morioka, Tomoki Tozuka, Sébastien Masson, Pascal Terray, Jing-jia Luo, Toshio Yamagata
    Abstract:

    The growth and decay mechanisms of subtropical dipole modes in the southern Indian and South Atlantic Oceans and their impacts on southern African rainfall are investigated using results from a coupled general circulation model originally developed for predicting tropical climate variations. The second (most) dominant mode of interannual sea surface temperature (SST) variations in the southern Indian (South Atlantic) Ocean represents a northeast–southwest oriented dipole, now called subtropical dipole mode. The positive (negative) SST interannual anomaly pole starts to grow in austral spring and reaches its peak in February. In austral late spring, the suppressed (enhanced) latent heat flux loss associated with the variations in the subtropical high causes a thinner (thicker) than normal mixed layer thickness that, in turn, enhances (reduces) the warming of the mixed layer by the climatological shortwave radiation. The positive (negative) pole gradually decays in austral fall because the mixed layer cooling by the entrainment is enhanced (reduced), mostly owing to the larger (smaller) temperature difference between the mixed layer and the Entrained Water. The increased (decreased) latent heat loss due to the warmer (colder) SST also contributes to the decay of the positive (negative) pole. Although further verification using longer observational data is required, the present coupled model suggests that the South Atlantic subtropical dipole may play a more important role in rainfall variations over the southern African region than the Indian Ocean subtropical dipole.

  • On the Growth and Decay of the Subtropical Dipole Mode in the South Atlantic
    Journal of Climate, 2011
    Co-Authors: Yushi Morioka, Tomoki Tozuka, Toshio Yamagata
    Abstract:

    AbstractUsing observational data and outputs from an ocean general circulation model, the growth and decay of the South Atlantic subtropical dipole (SASD) are studied. The SASD is the most dominant mode of interannual variability in the South Atlantic Ocean, and its sea surface temperature (SST) anomaly shows a dipole pattern that is oriented in the northeast–southwest direction. The positive (negative) pole develops because the warming of the mixed layer by the contribution from the climatological shortwave radiation is enhanced (suppressed) when the mixed layer is thinner (thicker) than normal. The mixed layer depth anomaly over the positive (negative) pole is due to the suppressed (enhanced) latent heat flux loss associated with the southward migration and strengthening of the subtropical high. During the decay phase, since the temperature difference between the mixed layer and the Entrained Water becomes anomalously large (small) as a result of the positive (negative) mixed layer temperature anomaly, ...

Yushi Morioka - One of the best experts on this subject based on the ideXlab platform.

  • Subtropical Dipole Modes Simulated in a Coupled General Circulation Model
    Journal of Climate, 2012
    Co-Authors: Yushi Morioka, Tomoki Tozuka, Sébastien Masson, Pascal Terray, Jing-jia Luo, Toshio Yamagata
    Abstract:

    The growth and decay mechanisms of subtropical dipole modes in the southern Indian and South Atlantic Oceans and their impacts on southern African rainfall are investigated using results from a coupled general circulation model originally developed for predicting tropical climate variations. The second (most) dominant mode of interannual sea surface temperature (SST) variations in the southern Indian (South Atlantic) Ocean represents a northeast–southwest oriented dipole, now called subtropical dipole mode. The positive (negative) SST interannual anomaly pole starts to grow in austral spring and reaches its peak in February. In austral late spring, the suppressed (enhanced) latent heat flux loss associated with the variations in the subtropical high causes a thinner (thicker) than normal mixed layer thickness that, in turn, enhances (reduces) the warming of the mixed layer by the climatological shortwave radiation. The positive (negative) pole gradually decays in austral fall because the mixed layer cooling by the entrainment is enhanced (reduced), mostly owing to the larger (smaller) temperature difference between the mixed layer and the Entrained Water. The increased (decreased) latent heat loss due to the warmer (colder) SST also contributes to the decay of the positive (negative) pole. Although further verification using longer observational data is required, the present coupled model suggests that the South Atlantic subtropical dipole may play a more important role in rainfall variations over the southern African region than the Indian Ocean subtropical dipole.

  • On the Growth and Decay of the Subtropical Dipole Mode in the South Atlantic
    Journal of Climate, 2011
    Co-Authors: Yushi Morioka, Tomoki Tozuka, Toshio Yamagata
    Abstract:

    AbstractUsing observational data and outputs from an ocean general circulation model, the growth and decay of the South Atlantic subtropical dipole (SASD) are studied. The SASD is the most dominant mode of interannual variability in the South Atlantic Ocean, and its sea surface temperature (SST) anomaly shows a dipole pattern that is oriented in the northeast–southwest direction. The positive (negative) pole develops because the warming of the mixed layer by the contribution from the climatological shortwave radiation is enhanced (suppressed) when the mixed layer is thinner (thicker) than normal. The mixed layer depth anomaly over the positive (negative) pole is due to the suppressed (enhanced) latent heat flux loss associated with the southward migration and strengthening of the subtropical high. During the decay phase, since the temperature difference between the mixed layer and the Entrained Water becomes anomalously large (small) as a result of the positive (negative) mixed layer temperature anomaly, ...

Tomoki Tozuka - One of the best experts on this subject based on the ideXlab platform.

  • Subtropical Dipole Modes Simulated in a Coupled General Circulation Model
    Journal of Climate, 2012
    Co-Authors: Yushi Morioka, Tomoki Tozuka, Sébastien Masson, Pascal Terray, Jing-jia Luo, Toshio Yamagata
    Abstract:

    The growth and decay mechanisms of subtropical dipole modes in the southern Indian and South Atlantic Oceans and their impacts on southern African rainfall are investigated using results from a coupled general circulation model originally developed for predicting tropical climate variations. The second (most) dominant mode of interannual sea surface temperature (SST) variations in the southern Indian (South Atlantic) Ocean represents a northeast–southwest oriented dipole, now called subtropical dipole mode. The positive (negative) SST interannual anomaly pole starts to grow in austral spring and reaches its peak in February. In austral late spring, the suppressed (enhanced) latent heat flux loss associated with the variations in the subtropical high causes a thinner (thicker) than normal mixed layer thickness that, in turn, enhances (reduces) the warming of the mixed layer by the climatological shortwave radiation. The positive (negative) pole gradually decays in austral fall because the mixed layer cooling by the entrainment is enhanced (reduced), mostly owing to the larger (smaller) temperature difference between the mixed layer and the Entrained Water. The increased (decreased) latent heat loss due to the warmer (colder) SST also contributes to the decay of the positive (negative) pole. Although further verification using longer observational data is required, the present coupled model suggests that the South Atlantic subtropical dipole may play a more important role in rainfall variations over the southern African region than the Indian Ocean subtropical dipole.

  • On the Growth and Decay of the Subtropical Dipole Mode in the South Atlantic
    Journal of Climate, 2011
    Co-Authors: Yushi Morioka, Tomoki Tozuka, Toshio Yamagata
    Abstract:

    AbstractUsing observational data and outputs from an ocean general circulation model, the growth and decay of the South Atlantic subtropical dipole (SASD) are studied. The SASD is the most dominant mode of interannual variability in the South Atlantic Ocean, and its sea surface temperature (SST) anomaly shows a dipole pattern that is oriented in the northeast–southwest direction. The positive (negative) pole develops because the warming of the mixed layer by the contribution from the climatological shortwave radiation is enhanced (suppressed) when the mixed layer is thinner (thicker) than normal. The mixed layer depth anomaly over the positive (negative) pole is due to the suppressed (enhanced) latent heat flux loss associated with the southward migration and strengthening of the subtropical high. During the decay phase, since the temperature difference between the mixed layer and the Entrained Water becomes anomalously large (small) as a result of the positive (negative) mixed layer temperature anomaly, ...

Merv Fingas - One of the best experts on this subject based on the ideXlab platform.

  • Handbook of Oil Spill Science and Technology - Introduction to Spill Modeling
    Handbook of Oil Spill Science and Technology, 2015
    Co-Authors: Merv Fingas
    Abstract:

    This chapter is an introduction to oil spill modeling. Summaries and well-known predictions are given of the important processes such as evaporation, Water-in-oil emulsification, natural dispersion, and dissolution. Other processes such as photooxidation, sedimentation, and oil-fines interaction are introduced. An important behavior process is that of evaporation. Evaporation for light oils could involve a loss of 30–60% of the oil's mass over a 2-day period. Algorithms for calculating evaporation are summarized. Another important behavior is that of Water uptake. Oil may uptake Water by one of the five ways: as soluble Water; no significant uptake or unstable; Entrained Water; as meso-stable or stable emulsions. The latter three mechanisms are important as they have a large influence on the further behavior of the oil and on impact countermeasures significantly.

  • studies on crude oil and petroleum product emulsions Water resolution and rheology
    Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2009
    Co-Authors: Merv Fingas, Ben Fieldhouse
    Abstract:

    Abstract Water-in-oil mixtures from more than 300 crude oils and petroleum products were made in the laboratory and studied over time. More than 140 of these yielded products resembling emulsion. Water-in-oil types were characterized by resolution of Water at 1 and 7 days, and some after 1 year. Rheology measurements were carried out at the same intervals. The objective of the study was to characterize the Water-in-oil types and relate these to starting oil properties. It was found that Water-in-oil types can be grouped into four categories: stable, unstable, meso-stable and Entrained. Each of these has distinct physical properties. A stable emulsion remains so for at least 30 days and takes up typically 80% Water. The viscosity of a stable emulsion is at least two orders-of-magnitude greater than that of the starting oil. An unstable emulsion does not retain Water volume greater than 10%. For an unstable emulsion, the viscosity is typically less than two times greater than the viscosity of the starting oil. A meso-stable emulsion has properties between unstable and stable emulsions and typically takes up 60% Water, breaking down within 7 days, losing most of this Water. A meso-stable emulsion usually has a viscosity no more than one order-of-magnitude greater than that of the starting oil. Another retention mechanism for Water in oil is that of viscous entrainment of Water droplets. This type of Water uptake, not a true emulsion, has been called Entrained. Entrained Water to the extent of typically 45% is taken up initially and this Water content declines slowly over a period of days. A stability index was developed to characterize these Water-in-oil types. This consists of the product of the ratio of viscosity increase and a ratio of the elasticity increase. This index was used to describe the Water-in-oil types and to correlate stability with starting oil composition and properties. A comparison of the properties of the starting oils before mixing with Water shows that the most important factors for Water uptake and emulsion formation are asphaltene and resin content, starting oil viscosity and density. Other factors that are shown to be important are the saturate content and asphaltene-to-resin ratio. The relationship between these factors and stability gives insights into the nature of Water-in-oil types and emulsions.

  • HOW TO MODEL Water-IN-OIL EMULSION FORMATION
    International Oil Spill Conference Proceedings, 2005
    Co-Authors: Merv Fingas, Ben Fieldhouse
    Abstract:

    ABSTRACT Water-in-oil mixtures were grouped into four states or classes: stable, mesostable, unstable, and Entrained Water. Only stable and mesostable states can be characterized as emulsions. These states were established according to lifetime, visual appearance, complex modulus, and differences in viscosity. Water-in-oil emulsions made from crude oils have different classes of stability as a result of the asp haltene and resin contents, as well as differences in the viscosity of the starting oil. In this paper a new numerical modelling scheme is proposed and is based on empirical data and the corresponding physical knowledge of emulsion formation. The density, viscosity, saturate, asphaltene and resin contents are used to compute a class index which yields either an unstable or Entrained Water-in-oil state or a meso-stable or stable emulsion. A prediction scheme is given to estimate the Water content and viscosity of the resulting Water-in-oil state and the time to formation with input of wave-height.

  • Formation of Water-in-oil emulsions and application to oil spill modelling.
    Journal of hazardous materials, 2004
    Co-Authors: Merv Fingas, Ben Fieldhouse
    Abstract:

    Water-in-oil mixtures were grouped into four states or classes: stable, mesostable, unstable, and Entrained Water. Of these, only stable and mesostable states can be characterized as emulsions. These states were established according to lifetime, visual appearance, complex modulus, and differences in viscosity. Water content at formation was not an important factor. Water-in-oil emulsions made from crude oils have different classes of stability as a result of the asphaltene and resin contents, as well as differences in the viscosity of the starting oil. The different types of Water-in-oil classes are readily distinguished simply by appearance, as well as by rheological properties. A review of past modelling efforts to predict emulsion formation showed that these older schemes were based on first-order rate equations that were developed before extensive work on emulsion physics took place. These results do not correspond to either laboratory or field results. The present authors suggest that both the formation and characteristics of emulsions could be predicted using empirical data. If the same oil type as already studied is to be modelled, the laboratory data on the state and properties can be used directly. In this paper, a new numerical modelling scheme is proposed and is based on empirical data and the corresponding physical knowledge of emulsion formation. The density, viscosity, saturate, asphaltene and resin contents are used to compute a class index which yields either an unstable or Entrained Water-in-oil state or a mesostable or stable emulsion. A prediction scheme is given to estimate the Water content and viscosity of the resulting Water-in-oil state and the time to formation with input of wave height.

  • Studies of the formation process of Water-in-oil emulsions.
    Marine pollution bulletin, 2003
    Co-Authors: Merv Fingas, Ben Fieldhouse
    Abstract:

    This paper summarizes studies to determine the formation process of Water-in-oil emulsions and the stability of such emulsions formed in the laboratory and in a large test tank. These studies have confirmed that Water-in-oil mixtures can be grouped into four states: stable emulsions, unstable Water-in-oil mixtures, mesostable emulsions, and Entrained Water. These states are differentiated by rheological properties as well as by differences in visual appearance. The viscosity of a stable emulsion at a shear rate of one reciprocal second is about three orders of magnitude greater than that of the starting oil. An unstable emulsion usually has a viscosity no more than about 20 times greater than that of the starting oil. A stable emulsion has a significant elasticity, whereas an unstable emulsion does not. A mesostable emulsion has properties between stable and unstable, but breaks down within a few days of standing. The usual situation is that emulsions are either obviously stable, mesostable, or unstable. Entrained Water, Water suspended in oil by viscous forces alone, is also evident. Very few emulsions have questionable stability. Analytical techniques were developed to test these observations. The type of emulsion produced is determined primarily by the properties of the starting oil. The most important of these properties are the asphaltene and resin content and the viscosity of the oil. The composition and property ranges of the starting oil that would be required to form each of the Water-in-oil states are discussed in this paper.

Ben Fieldhouse - One of the best experts on this subject based on the ideXlab platform.

  • studies on crude oil and petroleum product emulsions Water resolution and rheology
    Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2009
    Co-Authors: Merv Fingas, Ben Fieldhouse
    Abstract:

    Abstract Water-in-oil mixtures from more than 300 crude oils and petroleum products were made in the laboratory and studied over time. More than 140 of these yielded products resembling emulsion. Water-in-oil types were characterized by resolution of Water at 1 and 7 days, and some after 1 year. Rheology measurements were carried out at the same intervals. The objective of the study was to characterize the Water-in-oil types and relate these to starting oil properties. It was found that Water-in-oil types can be grouped into four categories: stable, unstable, meso-stable and Entrained. Each of these has distinct physical properties. A stable emulsion remains so for at least 30 days and takes up typically 80% Water. The viscosity of a stable emulsion is at least two orders-of-magnitude greater than that of the starting oil. An unstable emulsion does not retain Water volume greater than 10%. For an unstable emulsion, the viscosity is typically less than two times greater than the viscosity of the starting oil. A meso-stable emulsion has properties between unstable and stable emulsions and typically takes up 60% Water, breaking down within 7 days, losing most of this Water. A meso-stable emulsion usually has a viscosity no more than one order-of-magnitude greater than that of the starting oil. Another retention mechanism for Water in oil is that of viscous entrainment of Water droplets. This type of Water uptake, not a true emulsion, has been called Entrained. Entrained Water to the extent of typically 45% is taken up initially and this Water content declines slowly over a period of days. A stability index was developed to characterize these Water-in-oil types. This consists of the product of the ratio of viscosity increase and a ratio of the elasticity increase. This index was used to describe the Water-in-oil types and to correlate stability with starting oil composition and properties. A comparison of the properties of the starting oils before mixing with Water shows that the most important factors for Water uptake and emulsion formation are asphaltene and resin content, starting oil viscosity and density. Other factors that are shown to be important are the saturate content and asphaltene-to-resin ratio. The relationship between these factors and stability gives insights into the nature of Water-in-oil types and emulsions.

  • HOW TO MODEL Water-IN-OIL EMULSION FORMATION
    International Oil Spill Conference Proceedings, 2005
    Co-Authors: Merv Fingas, Ben Fieldhouse
    Abstract:

    ABSTRACT Water-in-oil mixtures were grouped into four states or classes: stable, mesostable, unstable, and Entrained Water. Only stable and mesostable states can be characterized as emulsions. These states were established according to lifetime, visual appearance, complex modulus, and differences in viscosity. Water-in-oil emulsions made from crude oils have different classes of stability as a result of the asp haltene and resin contents, as well as differences in the viscosity of the starting oil. In this paper a new numerical modelling scheme is proposed and is based on empirical data and the corresponding physical knowledge of emulsion formation. The density, viscosity, saturate, asphaltene and resin contents are used to compute a class index which yields either an unstable or Entrained Water-in-oil state or a meso-stable or stable emulsion. A prediction scheme is given to estimate the Water content and viscosity of the resulting Water-in-oil state and the time to formation with input of wave-height.

  • Formation of Water-in-oil emulsions and application to oil spill modelling.
    Journal of hazardous materials, 2004
    Co-Authors: Merv Fingas, Ben Fieldhouse
    Abstract:

    Water-in-oil mixtures were grouped into four states or classes: stable, mesostable, unstable, and Entrained Water. Of these, only stable and mesostable states can be characterized as emulsions. These states were established according to lifetime, visual appearance, complex modulus, and differences in viscosity. Water content at formation was not an important factor. Water-in-oil emulsions made from crude oils have different classes of stability as a result of the asphaltene and resin contents, as well as differences in the viscosity of the starting oil. The different types of Water-in-oil classes are readily distinguished simply by appearance, as well as by rheological properties. A review of past modelling efforts to predict emulsion formation showed that these older schemes were based on first-order rate equations that were developed before extensive work on emulsion physics took place. These results do not correspond to either laboratory or field results. The present authors suggest that both the formation and characteristics of emulsions could be predicted using empirical data. If the same oil type as already studied is to be modelled, the laboratory data on the state and properties can be used directly. In this paper, a new numerical modelling scheme is proposed and is based on empirical data and the corresponding physical knowledge of emulsion formation. The density, viscosity, saturate, asphaltene and resin contents are used to compute a class index which yields either an unstable or Entrained Water-in-oil state or a mesostable or stable emulsion. A prediction scheme is given to estimate the Water content and viscosity of the resulting Water-in-oil state and the time to formation with input of wave height.

  • Studies of the formation process of Water-in-oil emulsions.
    Marine pollution bulletin, 2003
    Co-Authors: Merv Fingas, Ben Fieldhouse
    Abstract:

    This paper summarizes studies to determine the formation process of Water-in-oil emulsions and the stability of such emulsions formed in the laboratory and in a large test tank. These studies have confirmed that Water-in-oil mixtures can be grouped into four states: stable emulsions, unstable Water-in-oil mixtures, mesostable emulsions, and Entrained Water. These states are differentiated by rheological properties as well as by differences in visual appearance. The viscosity of a stable emulsion at a shear rate of one reciprocal second is about three orders of magnitude greater than that of the starting oil. An unstable emulsion usually has a viscosity no more than about 20 times greater than that of the starting oil. A stable emulsion has a significant elasticity, whereas an unstable emulsion does not. A mesostable emulsion has properties between stable and unstable, but breaks down within a few days of standing. The usual situation is that emulsions are either obviously stable, mesostable, or unstable. Entrained Water, Water suspended in oil by viscous forces alone, is also evident. Very few emulsions have questionable stability. Analytical techniques were developed to test these observations. The type of emulsion produced is determined primarily by the properties of the starting oil. The most important of these properties are the asphaltene and resin content and the viscosity of the oil. The composition and property ranges of the starting oil that would be required to form each of the Water-in-oil states are discussed in this paper.