The Experts below are selected from a list of 246 Experts worldwide ranked by ideXlab platform

Richard Kleeman - One of the best experts on this subject based on the ideXlab platform.

  • The singular vectors of a coupled ocean‐atmosphere model of Enso. I: Thermodynamics, energetics and error growth
    Quarterly Journal of the Royal Meteorological Society, 1997
    Co-Authors: Andrew M. Moore, Richard Kleeman
    Abstract:

    The singular vectors of a dynamical system are the most rapidly growing perturbations that can exist in the system before nonlinearity becomes important. We have studied the singular vectors of an intermediate coupled ocean-atmosphere model of El Nino/Southern Oscillation (ENSO) in an effort to understand the dynamics responsible for the growth of small perturbations in the tropics. In particular, we have examined how the singular vectors of the observed seasonal cycle are influenced by various thermodynamic processes which operate in the upper-ocean mixed-layer, and which affect sea-surface temperature (SST). These processes include vertical movements of the main thermocline, zonal advection and vertical upwelling. the main findings are: the singular vector spectrum is dominated by the fastest growing member, regardless of which thermodynamic processes are active; the growth factors of the singular vectors exhibit a strong seasonal dependence; the western and central parts of the Pacific Ocean are the areas most often favoured for growth by the singular vectors, and the general criteria that must be met for singular-vector growth have been determined; at a given time of year, the growth factors of the singular vectors are sensitive to different combinations of thermodynamic processes, although the configuration of the dominant singular-vector wind field after optimal growth has been achieved is very similar in all cases. This suggests that in the tropics, the coupled system has a Preferred Response that the ocean thermodynamics controlling SST conspire to produce, regardless of which processes are operating in the mixed layer; the observed ENSO cycle is likely to influence singular-vector growth significantly. These results and ideas have important ramifications for the growth of errors and uncertainties in models during ENSO forecasts, and for the way this influences the predictability of ENSO. They also have important ramifications for the way perturbations grow in the real coupled ocean-atmosphere system.

  • The singular vectors of a coupled ocean-atmosphere model of ENSO. II: Sensitivity studies and dynamical interpretation
    Quarterly Journal of the Royal Meteorological Society, 1997
    Co-Authors: Andrew M. Moore, Richard Kleeman
    Abstract:

    We have studied the singular vectors of an intermediate coupled ocean-atmosphere model of El Nino Southern Oscillation in an attempt to understand the factors which influence the growth of perturbations in the coupled system in the tropics. the singular vectors are important because they are the fastest growing perturbations that can exist in the system before nonlinearity becomes important. In this study, we have examined how the model singular-vectors are affected by variations in certain model parameters, some of which mathematically define the singular vectors. the important findings of this study can be summarized as follows: the behaviour of the model singular-vectors can be understood in terms of a superposition of the linear modes of the coupled system which are non-orthogonal. In some cases, the gravest modes are oscillatory in time and this leads to resonances in the singular-vector growth-factors. the singular-vector spectrum is generally dominated by its fastest-growing member whose wind structure is relatively insensitive to the parameters that define the singular vectors mathematically. This result is in accord with the findings of Part I, and suggests that, in the tropics, the coupled system has a Preferred Response to perturbations, and that this Response will readily manifest itself if conditions are favourable. Favourably configured perturbations can undergo rapid transient growth over the entire regime in which the coupled model is asymptotically stable (i.e. when there are no unstable modes in the system). In this regime, rapid transient growth can occur over a wide range of timescales from 1 week to 24 months. The results and ideas presented here have important ramifications for the way in which the real coupled oceanatmosphere system will respond in the tropics to perturbations arising from stochastic forcing inherent in the system. the dynamical operators that govern the early stages of linear perturbation-development are non-normal which means that the ubiquitous stochastic noise present in the tropics can be amplified. the dynamical mechanisms by which this can occur are the same as those responsible for the growth of the system singular-vectors. the dominant singular-vectors of the coupled model bear a remarkable resemblance to the tropical-cyclone pairs that are often observed spanning the equator in the western Pacific Ocean accompanied by strong westerly wind bursts, and thought to be precursors of El Nino events. We propose that both westerly and easterly wind bursts occuring in nature are a Preferred Response of the coupled system in the tropics to its inherent stochastic noise component.

Laura Wilcox - One of the best experts on this subject based on the ideXlab platform.

  • Preferred Response of the east asian summer monsoon to local and non local anthropogenic sulphur dioxide emissions
    Climate Dynamics, 2016
    Co-Authors: Buwen Dong, Rowan Sutton, E J Highwood, Laura Wilcox
    Abstract:

    In this study, the atmospheric component of a state-of-the-art climate model (HadGEM2-ES) that includes earth system components such as interactive chemistry and eight species of tropospheric aerosols considering aerosol direct, indirect, and semi-direct effects, has been used to investigate the impacts of local and non-local emissions of anthropogenic sulphur dioxide on the East Asian summer monsoon (EASM). The study focuses on the fast Responses (including land surface feedbacks, but without sea surface temperature feedbacks) to sudden changes in emissions from Asia and Europe. The initial Responses, over days 1–40, to Asian and European emissions show large differences. The Response to Asian emissions involves a direct impact on the sulphate burden over Asia, with immediate consequences for the shortwave energy budget through aerosol–radiation and aerosol–cloud interactions. These changes lead to cooling of East Asia and a weakening of the EASM. In contrast, European emissions have no significant impact on the sulphate burden over Asia, but they induce mid-tropospheric cooling and drying over the European sector. Subsequently, however, this cold and dry anomaly is advected into Asia, where it induces atmospheric and surface feedbacks over Asia and the Western North Pacific (WNP), which also weaken the EASM. In spite of very different perturbations to the local aerosol burden in Response to Asian and European sulphur dioxide emissions, the large scale pattern of changes in land–sea thermal contrast, atmospheric circulation and local precipitation over East Asia from days 40 onward exhibits similar structures, indicating a Preferred Response, and suggesting that emissions from both regions likely contributed to the observed weakening of the EASM. Cooling and drying of the troposphere over Asia, together with warming and moistening over the WNP, reduces the land–sea thermal contrast between the Asian continent and surrounding oceans. This leads to high sea level pressure (SLP) anomalies over Asia and low SLP anomalies over the WNP, associated with a weakened EASM. In Response to emissions from both regions warming and moistening over the WNP plays an important role and determines the time scale of the Response.

  • Preferred Response of the East Asian summer monsoon to local and non‑local anthropogenic sulphur dioxide emissions
    Climate Dynamics, 2015
    Co-Authors: Buwen Dong, Rowan Sutton, E J Highwood, Laura Wilcox
    Abstract:

    In this study, the atmospheric component of a state-of-the-art climate model (HadGEM2-ES) that includes earth system components such as interactive chemistry and eight species of tropospheric aerosols considering aerosol direct, indirect, and semi-direct effects, has been used to investigate the impacts of local and non-local emissions of anthropogenic sulphur dioxide on the East Asian summer monsoon (EASM). The study focuses on the fast Responses (including land surface feedbacks, but without sea surface temperature feedbacks) to sudden changes in emissions from Asia and Europe. The initial Responses, over days 1–40, to Asian and European emissions show large differences. The Response to Asian emissions involves a direct impact on the sulphate burden over Asia, with immediate consequences for the shortwave energy budget through aerosol–radiation and aerosol–cloud interactions. These changes lead to cooling of East Asia and a weakening of the EASM. In contrast, European emissions have no significant impact on the sulphate burden over Asia, but they induce mid-tropospheric cooling and drying over the European sector. Subsequently, however, this cold and dry anomaly is advected into Asia, where it induces atmospheric and surface feedbacks over Asia and the Western North Pacific (WNP), which also weaken the EASM. In spite of very different perturbations to the local aerosol burden in Response to Asian and European sulphur dioxide emissions, the large scale pattern of changes in land–sea thermal contrast, atmospheric circulation and local precipitation over East Asia from days 40 onward exhibits similar structures, indicating a Preferred Response, and suggesting that emissions from both regions likely contributed to the observed weakening of the EASM. Cooling and drying of the troposphere over Asia, together with warming and moistening over the WNP, reduces the land–sea thermal contrast between the Asian continent and surrounding oceans. This leads to high sea level pressure (SLP) anomalies over Asia and low SLP anomalies over the WNP, associated with a weakened EASM. In Response to emissions from both regions warming and moistening over the WNP plays an important role and determines the time scale of the Response.

Andrew M. Moore - One of the best experts on this subject based on the ideXlab platform.

  • The singular vectors of a coupled ocean‐atmosphere model of Enso. I: Thermodynamics, energetics and error growth
    Quarterly Journal of the Royal Meteorological Society, 1997
    Co-Authors: Andrew M. Moore, Richard Kleeman
    Abstract:

    The singular vectors of a dynamical system are the most rapidly growing perturbations that can exist in the system before nonlinearity becomes important. We have studied the singular vectors of an intermediate coupled ocean-atmosphere model of El Nino/Southern Oscillation (ENSO) in an effort to understand the dynamics responsible for the growth of small perturbations in the tropics. In particular, we have examined how the singular vectors of the observed seasonal cycle are influenced by various thermodynamic processes which operate in the upper-ocean mixed-layer, and which affect sea-surface temperature (SST). These processes include vertical movements of the main thermocline, zonal advection and vertical upwelling. the main findings are: the singular vector spectrum is dominated by the fastest growing member, regardless of which thermodynamic processes are active; the growth factors of the singular vectors exhibit a strong seasonal dependence; the western and central parts of the Pacific Ocean are the areas most often favoured for growth by the singular vectors, and the general criteria that must be met for singular-vector growth have been determined; at a given time of year, the growth factors of the singular vectors are sensitive to different combinations of thermodynamic processes, although the configuration of the dominant singular-vector wind field after optimal growth has been achieved is very similar in all cases. This suggests that in the tropics, the coupled system has a Preferred Response that the ocean thermodynamics controlling SST conspire to produce, regardless of which processes are operating in the mixed layer; the observed ENSO cycle is likely to influence singular-vector growth significantly. These results and ideas have important ramifications for the growth of errors and uncertainties in models during ENSO forecasts, and for the way this influences the predictability of ENSO. They also have important ramifications for the way perturbations grow in the real coupled ocean-atmosphere system.

  • The singular vectors of a coupled ocean-atmosphere model of ENSO. II: Sensitivity studies and dynamical interpretation
    Quarterly Journal of the Royal Meteorological Society, 1997
    Co-Authors: Andrew M. Moore, Richard Kleeman
    Abstract:

    We have studied the singular vectors of an intermediate coupled ocean-atmosphere model of El Nino Southern Oscillation in an attempt to understand the factors which influence the growth of perturbations in the coupled system in the tropics. the singular vectors are important because they are the fastest growing perturbations that can exist in the system before nonlinearity becomes important. In this study, we have examined how the model singular-vectors are affected by variations in certain model parameters, some of which mathematically define the singular vectors. the important findings of this study can be summarized as follows: the behaviour of the model singular-vectors can be understood in terms of a superposition of the linear modes of the coupled system which are non-orthogonal. In some cases, the gravest modes are oscillatory in time and this leads to resonances in the singular-vector growth-factors. the singular-vector spectrum is generally dominated by its fastest-growing member whose wind structure is relatively insensitive to the parameters that define the singular vectors mathematically. This result is in accord with the findings of Part I, and suggests that, in the tropics, the coupled system has a Preferred Response to perturbations, and that this Response will readily manifest itself if conditions are favourable. Favourably configured perturbations can undergo rapid transient growth over the entire regime in which the coupled model is asymptotically stable (i.e. when there are no unstable modes in the system). In this regime, rapid transient growth can occur over a wide range of timescales from 1 week to 24 months. The results and ideas presented here have important ramifications for the way in which the real coupled oceanatmosphere system will respond in the tropics to perturbations arising from stochastic forcing inherent in the system. the dynamical operators that govern the early stages of linear perturbation-development are non-normal which means that the ubiquitous stochastic noise present in the tropics can be amplified. the dynamical mechanisms by which this can occur are the same as those responsible for the growth of the system singular-vectors. the dominant singular-vectors of the coupled model bear a remarkable resemblance to the tropical-cyclone pairs that are often observed spanning the equator in the western Pacific Ocean accompanied by strong westerly wind bursts, and thought to be precursors of El Nino events. We propose that both westerly and easterly wind bursts occuring in nature are a Preferred Response of the coupled system in the tropics to its inherent stochastic noise component.

Buwen Dong - One of the best experts on this subject based on the ideXlab platform.

  • Preferred Response of the east asian summer monsoon to local and non local anthropogenic sulphur dioxide emissions
    Climate Dynamics, 2016
    Co-Authors: Buwen Dong, Rowan Sutton, E J Highwood, Laura Wilcox
    Abstract:

    In this study, the atmospheric component of a state-of-the-art climate model (HadGEM2-ES) that includes earth system components such as interactive chemistry and eight species of tropospheric aerosols considering aerosol direct, indirect, and semi-direct effects, has been used to investigate the impacts of local and non-local emissions of anthropogenic sulphur dioxide on the East Asian summer monsoon (EASM). The study focuses on the fast Responses (including land surface feedbacks, but without sea surface temperature feedbacks) to sudden changes in emissions from Asia and Europe. The initial Responses, over days 1–40, to Asian and European emissions show large differences. The Response to Asian emissions involves a direct impact on the sulphate burden over Asia, with immediate consequences for the shortwave energy budget through aerosol–radiation and aerosol–cloud interactions. These changes lead to cooling of East Asia and a weakening of the EASM. In contrast, European emissions have no significant impact on the sulphate burden over Asia, but they induce mid-tropospheric cooling and drying over the European sector. Subsequently, however, this cold and dry anomaly is advected into Asia, where it induces atmospheric and surface feedbacks over Asia and the Western North Pacific (WNP), which also weaken the EASM. In spite of very different perturbations to the local aerosol burden in Response to Asian and European sulphur dioxide emissions, the large scale pattern of changes in land–sea thermal contrast, atmospheric circulation and local precipitation over East Asia from days 40 onward exhibits similar structures, indicating a Preferred Response, and suggesting that emissions from both regions likely contributed to the observed weakening of the EASM. Cooling and drying of the troposphere over Asia, together with warming and moistening over the WNP, reduces the land–sea thermal contrast between the Asian continent and surrounding oceans. This leads to high sea level pressure (SLP) anomalies over Asia and low SLP anomalies over the WNP, associated with a weakened EASM. In Response to emissions from both regions warming and moistening over the WNP plays an important role and determines the time scale of the Response.

  • Preferred Response of the East Asian summer monsoon to local and non‑local anthropogenic sulphur dioxide emissions
    Climate Dynamics, 2015
    Co-Authors: Buwen Dong, Rowan Sutton, E J Highwood, Laura Wilcox
    Abstract:

    In this study, the atmospheric component of a state-of-the-art climate model (HadGEM2-ES) that includes earth system components such as interactive chemistry and eight species of tropospheric aerosols considering aerosol direct, indirect, and semi-direct effects, has been used to investigate the impacts of local and non-local emissions of anthropogenic sulphur dioxide on the East Asian summer monsoon (EASM). The study focuses on the fast Responses (including land surface feedbacks, but without sea surface temperature feedbacks) to sudden changes in emissions from Asia and Europe. The initial Responses, over days 1–40, to Asian and European emissions show large differences. The Response to Asian emissions involves a direct impact on the sulphate burden over Asia, with immediate consequences for the shortwave energy budget through aerosol–radiation and aerosol–cloud interactions. These changes lead to cooling of East Asia and a weakening of the EASM. In contrast, European emissions have no significant impact on the sulphate burden over Asia, but they induce mid-tropospheric cooling and drying over the European sector. Subsequently, however, this cold and dry anomaly is advected into Asia, where it induces atmospheric and surface feedbacks over Asia and the Western North Pacific (WNP), which also weaken the EASM. In spite of very different perturbations to the local aerosol burden in Response to Asian and European sulphur dioxide emissions, the large scale pattern of changes in land–sea thermal contrast, atmospheric circulation and local precipitation over East Asia from days 40 onward exhibits similar structures, indicating a Preferred Response, and suggesting that emissions from both regions likely contributed to the observed weakening of the EASM. Cooling and drying of the troposphere over Asia, together with warming and moistening over the WNP, reduces the land–sea thermal contrast between the Asian continent and surrounding oceans. This leads to high sea level pressure (SLP) anomalies over Asia and low SLP anomalies over the WNP, associated with a weakened EASM. In Response to emissions from both regions warming and moistening over the WNP plays an important role and determines the time scale of the Response.

Rowan Sutton - One of the best experts on this subject based on the ideXlab platform.

  • Preferred Response of the east asian summer monsoon to local and non local anthropogenic sulphur dioxide emissions
    Climate Dynamics, 2016
    Co-Authors: Buwen Dong, Rowan Sutton, E J Highwood, Laura Wilcox
    Abstract:

    In this study, the atmospheric component of a state-of-the-art climate model (HadGEM2-ES) that includes earth system components such as interactive chemistry and eight species of tropospheric aerosols considering aerosol direct, indirect, and semi-direct effects, has been used to investigate the impacts of local and non-local emissions of anthropogenic sulphur dioxide on the East Asian summer monsoon (EASM). The study focuses on the fast Responses (including land surface feedbacks, but without sea surface temperature feedbacks) to sudden changes in emissions from Asia and Europe. The initial Responses, over days 1–40, to Asian and European emissions show large differences. The Response to Asian emissions involves a direct impact on the sulphate burden over Asia, with immediate consequences for the shortwave energy budget through aerosol–radiation and aerosol–cloud interactions. These changes lead to cooling of East Asia and a weakening of the EASM. In contrast, European emissions have no significant impact on the sulphate burden over Asia, but they induce mid-tropospheric cooling and drying over the European sector. Subsequently, however, this cold and dry anomaly is advected into Asia, where it induces atmospheric and surface feedbacks over Asia and the Western North Pacific (WNP), which also weaken the EASM. In spite of very different perturbations to the local aerosol burden in Response to Asian and European sulphur dioxide emissions, the large scale pattern of changes in land–sea thermal contrast, atmospheric circulation and local precipitation over East Asia from days 40 onward exhibits similar structures, indicating a Preferred Response, and suggesting that emissions from both regions likely contributed to the observed weakening of the EASM. Cooling and drying of the troposphere over Asia, together with warming and moistening over the WNP, reduces the land–sea thermal contrast between the Asian continent and surrounding oceans. This leads to high sea level pressure (SLP) anomalies over Asia and low SLP anomalies over the WNP, associated with a weakened EASM. In Response to emissions from both regions warming and moistening over the WNP plays an important role and determines the time scale of the Response.

  • Preferred Response of the East Asian summer monsoon to local and non‑local anthropogenic sulphur dioxide emissions
    Climate Dynamics, 2015
    Co-Authors: Buwen Dong, Rowan Sutton, E J Highwood, Laura Wilcox
    Abstract:

    In this study, the atmospheric component of a state-of-the-art climate model (HadGEM2-ES) that includes earth system components such as interactive chemistry and eight species of tropospheric aerosols considering aerosol direct, indirect, and semi-direct effects, has been used to investigate the impacts of local and non-local emissions of anthropogenic sulphur dioxide on the East Asian summer monsoon (EASM). The study focuses on the fast Responses (including land surface feedbacks, but without sea surface temperature feedbacks) to sudden changes in emissions from Asia and Europe. The initial Responses, over days 1–40, to Asian and European emissions show large differences. The Response to Asian emissions involves a direct impact on the sulphate burden over Asia, with immediate consequences for the shortwave energy budget through aerosol–radiation and aerosol–cloud interactions. These changes lead to cooling of East Asia and a weakening of the EASM. In contrast, European emissions have no significant impact on the sulphate burden over Asia, but they induce mid-tropospheric cooling and drying over the European sector. Subsequently, however, this cold and dry anomaly is advected into Asia, where it induces atmospheric and surface feedbacks over Asia and the Western North Pacific (WNP), which also weaken the EASM. In spite of very different perturbations to the local aerosol burden in Response to Asian and European sulphur dioxide emissions, the large scale pattern of changes in land–sea thermal contrast, atmospheric circulation and local precipitation over East Asia from days 40 onward exhibits similar structures, indicating a Preferred Response, and suggesting that emissions from both regions likely contributed to the observed weakening of the EASM. Cooling and drying of the troposphere over Asia, together with warming and moistening over the WNP, reduces the land–sea thermal contrast between the Asian continent and surrounding oceans. This leads to high sea level pressure (SLP) anomalies over Asia and low SLP anomalies over the WNP, associated with a weakened EASM. In Response to emissions from both regions warming and moistening over the WNP plays an important role and determines the time scale of the Response.