The Experts below are selected from a list of 219 Experts worldwide ranked by ideXlab platform
Xiu-qun Yang - One of the best experts on this subject based on the ideXlab platform.
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What Kinds of Atmospheric Anomalies Drive Wintertime North Pacific Basin-Scale Subtropical Oceanic Front Intensity Variation?
Journal of Climate, 2020Co-Authors: Ran Zhang, Jiabei Fang, Xiu-qun YangAbstract:AbstractBasin-scale subtropical Oceanic Front zone (STFZ) is a key region for midlatitude air-sea interaction in the North Pacific. However, previous studies considered midlatitude sea surface temp...
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Two typical modes in the variabilities of wintertime North Pacific basin‐scale Oceanic Fronts and associated atmospheric eddy‐driven jet
Atmospheric Science Letters, 2017Co-Authors: Liying Wang, Xiu-qun Yang, Dejian Yang, Jiabei FangAbstract:The role of Oceanic Fronts in the midlatitude air–sea interaction remains unclear. This study defines new indexes to quantify the intensity and location of two basin-scale Oceanic Frontal zones in the wintertime North Pacific, i.e. the subtropical and subarctic Frontal zones (STFZ, SAFZ). With these indexes, two typical modes, which are closely related to two large-scale sea surface temperature (SST) anomaly patterns resembling Pacific Decadal Oscillation (PDO) and North Pacific Gyre Oscillation (NPGO), respectively, are found in the Oceanic Front variabilities as well as in their associations with the midlatitude atmospheric eddy-driven jet. Corresponding to an PDO-like SST anomaly pattern, an enhanced STFZ occurs with a southward shifted SAFZ, which is associated with enhanced overlying atmospheric Front, baroclinicity and transient eddy vorticity forcing, thus with an intensification of the westerly jet; and vice versa. On the other hand, corresponding to an NPGO-like SST pattern, an enhanced SAFZ occurs with a northward shifted STFZ, which is associated with a northward shift of the atmospheric Front, baroclinicity, transient eddy vorticity forcing, and westerly jet; and vice versa. These results suggest that the basin-scale Oceanic Frontal zone is a key region for the midlatitude air–sea interaction in which the atmospheric transient eddy's dynamical forcing is a key player in such an interaction.
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an observational study of the north pacific storm track impact on the midlatitude Oceanic Front
Journal of Geophysical Research, 2017Co-Authors: Yao Yao, Zhong Zhong, Xiu-qun YangAbstract:A lagged Maximum Covariance Analysis is used to examine the impact of North Pacific storm-track activity on midlatitude Oceanic Frontal intensity in this study. It is found that an enhanced storm track tends to intensify the Oceanic Frontal intensity with a lag of 1–2 months. The forcing effect of storm-track anomalies on Oceanic Frontal intensity is strongest in autumn, followed by that in summer and winter, and it is weakest in spring. Moreover, the mixed layer heat budget analysis suggests that sea surface temperature anomalies (SSTAs) related to Oceanic Fronts are primarily attributed to the storm-track-induced net surface heat flux and Ekman advection anomalies, while contributions of geostrophic advection and entrainment are relatively small. In summer and autumn, the impact of net surface heat flux anomalies on SSTAs plays a more important role than that of Ekman heat transport anomalies. Whereas in winter, Ekman heat transport anomaly forcing is comparable to the net surface heat flux forcing. Anomalous turbulent heat fluxes contribute to generating net surface heat flux anomalies in those three seasons, while the shortwave radiative fluxes make a strong contribution in summer but have little impact in winter. The anomalies of both net surface heat flux and Ekman heat transport are presumed to be associated with storm-track-induced surface wind anomalies. Results of the present study provide observational evidences for the positive feedback between the North Pacific storm-track activity and midlatitude Oceanic Frontal intensity.
Serge Planton - One of the best experts on this subject based on the ideXlab platform.
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modeling and analysis of ageostrophic circulation over the azores Oceanic Front during the semaphore experiment
Monthly Weather Review, 2000Co-Authors: Herve Giordani, Serge PlantonAbstract:Abstract In the conventional quasigeostrophic (QG) form of the ω equation developed by Hoskins et al., the unique forcing of vertical velocity is the geostrophic deformation. As the QG or even the semigeostrophic (SG) hypotheses are not adapted to study the Frontal dynamics in the atmospheric boundary layer, this paper proposes a generalized expression of the Hoskins et al. form of the vertical velocity. Two thermal and three dynamical sources of the vertical velocity are identified. These forcings allow for identification of each of the physical processes acting simultaneously on the ageostrophic circulation in the boundary layer. This new form of the ω equation is used to explain wind increase in the atmospheric boundary layer over the warm waters of the sea surface temperature (SST) Front observed during a fair anticyclonic day of the SEMAPHORE experiment (1993) and simulated with a nonhydrostatic mesoscale atmospheric model. Since the SST gradients are weak (of the order of 1.5°C 100 km−1), the surfac...
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structure of the marine atmospheric boundary layer over an Oceanic thermal Front semaphore experiment
Journal of Geophysical Research, 1998Co-Authors: B H Kwon, Herve Giordani, B Benech, D Lambert, P Durand, A Druilhet, Serge PlantonAbstract:The Structure des Echanges Mer-Atmosphere, Proprietes des Heterogeneites Oceaniques: Recherche Experimentale (SEMAPHORE) experiment, the third phase of which took place between October 4 and November 17, 1993, was conducted over the Oceanic Azores Current located in the Azores basin and mainly marked at the surface by a thermal Front due to the gradient of the sea surface temperature (SST) of about 1° to 2°C per 100 km. The evolution of the marine atmospheric boundary layer (MABL) over the SST Front was studied with two aircraft and a ship in different meteorological conditions. For each case, the influence of the incoming air direction with respect to the orientation of the Oceanic Front was taken into account. During the campaign, advanced very high resolution radiometer pictures did not show any relation between the SST field and the cloud cover. The MABL was systematically thicker on the warm side than on the cold side. The mean MABL structure described from aircraft data collected in a vertical plane crossing the Oceanic Front was characterized by (1) an atmospheric horizontal gradient of 1° to 2°C per 100 km in the whole depth of the mixed layer and (2) an increase of the wind intensity from the cold to the warm side when the synoptic wind blew from the cold side. The surface sensible heat (latent heat) flux always increased from the cold to the warm sector owing to the increase of the wind and of the temperature (specific humidity) difference between the surface and the air. Turbulence increased from the cold to the warm side in conjunction with the MABL thickening, but the normalized profiles presented the same structure, regardless of the position over the SST Front. In agreement with the Action de Recherche Programme te Petite Echelle and Grande Echelle model, the mean temperature and momentum budgets were highly influenced by the horizontal temperature gradient. In particular, the strong ageostrophic influence in the MABL above the SST Front seems linked with the secondary circulation due to the SST Front.
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structure of the marine atmospheric boundary layer over an Oceanic thermal Front semaphore experiment
Journal of Geophysical Research, 1998Co-Authors: B H Kwon, Herve Giordani, B Benech, D Lambert, P Durand, A Druilhet, Serge PlantonAbstract:The Structure des Echanges Mer-Atmosphere, Proprietes des Heterogeneites Oceaniques: Recherche Experimentale (SEMAPHORE) experiment, the third phase of which took place between October 4 and November 17, 1993, was conducted over the Oceanic Azores Current located in the Azores basin and mainly marked at the surface by a thermal Front due to the gradient of the sea surface temperature (SST) of about 1° to 2°C per 100 km. The evolution of the marine atmospheric boundary layer (MABL) over the SST Front was studied with two aircraft and a ship in different meteorological conditions. For each case, the influence of the incoming air direction with respect to the orientation of the Oceanic Front was taken into account. During the campaign, advanced very high resolution radiometer pictures did not show any relation between the SST field and the cloud cover. The MABL was systematically thicker on the warm side than on the cold side. The mean MABL structure described from aircraft data collected in a vertical plane crossing the Oceanic Front was characterized by (1) an atmospheric horizontal gradient of 1° to 2°C per 100 km in the whole depth of the mixed layer and (2) an increase of the wind intensity from the cold to the warm side when the synoptic wind blew from the cold side. The surface sensible heat (latent heat) flux always increased from the cold to the warm sector owing to the increase of the wind and of the temperature (specific humidity) difference between the surface and the air. Turbulence increased from the cold to the warm side in conjunction with the MABL thickening, but the normalized profiles presented the same structure, regardless of the position over the SST Front. In agreement with the Action de Recherche Programme te Petite Echelle and Grande Echelle model, the mean temperature and momentum budgets were highly influenced by the horizontal temperature gradient. In particular, the strong ageostrophic influence in the MABL above the SST Front seems linked with the secondary circulation due to the SST Front.
Hisashi Nakamura - One of the best experts on this subject based on the ideXlab platform.
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ozone induced climate change propped up by the southern hemisphere Oceanic Front
Geophysical Research Letters, 2015Co-Authors: Fumiaki Ogawa, Nour-eddine Omrani, Kazuaki Nishii, Hisashi Nakamura, Noel KeenlysideAbstract:The late twentieth century was marked by a significant summertime trend in the Southern Annular Mode (SAM), the dominant mode of tropospheric variability in the extratropical Southern Hemisphere (SH). This trend with poleward shifting tropospheric westerlies was attributed to downward propagation of stratospheric changes induced by ozone depletion. However, the role of the ocean in setting the SAM response to ozone depletion and its dynamical forcing remains unclear. Here we show, using idealized experiments with a state-of-the-art atmospheric model and analysis of Intergovernmental Panel on Climate Change climate simulations, that Frontal sea surface temperature gradients in the midlatitude SH are critical for translating the ozone-induced stratospheric changes down to the surface. This happens through excitation of wave forcing, which controls the vertical connection of the tropospheric SAM with the stratosphere and shows the importance of internal tropospheric dynamics for stratosphere/troposphere coupling. Thus, improved simulation of Oceanic Fronts may reduce uncertainties in simulating SH ozone-induced climate changes.
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Ozone‐induced climate change propped up by the Southern Hemisphere Oceanic Front
Geophysical Research Letters, 2015Co-Authors: Fumiaki Ogawa, Nour-eddine Omrani, Kazuaki Nishii, Hisashi Nakamura, Noel KeenlysideAbstract:The late twentieth century was marked by a significant summertime trend in the Southern Annular Mode (SAM), the dominant mode of tropospheric variability in the extratropical Southern Hemisphere (SH). This trend with poleward shifting tropospheric westerlies was attributed to downward propagation of stratospheric changes induced by ozone depletion. However, the role of the ocean in setting the SAM response to ozone depletion and its dynamical forcing remains unclear. Here we show, using idealized experiments with a state-of-the-art atmospheric model and analysis of Intergovernmental Panel on Climate Change climate simulations, that Frontal sea surface temperature gradients in the midlatitude SH are critical for translating the ozone-induced stratospheric changes down to the surface. This happens through excitation of wave forcing, which controls the vertical connection of the tropospheric SAM with the stratosphere and shows the importance of internal tropospheric dynamics for stratosphere/troposphere coupling. Thus, improved simulation of Oceanic Fronts may reduce uncertainties in simulating SH ozone-induced climate changes.
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Earth's Climate - Observed Associations Among Storm Tracks, Jet Streams and Midlatitude Oceanic Fronts
Geophysical monograph, 2013Co-Authors: Hisashi Nakamura, Takeaki Sampe, Youichi Tanimoto, Akihiko ShimpoAbstract:An association is discussed among a midlatitude storm track, a westerly polar-Front jet stream and an underlying Oceanic Frontal zone. Their close association is observed when a subtropical jet stream is weak, as in the Southern Hemisphere summer or in the North Atlantic. Along a near-surface baroclinic zone that tends to be anchored around a Frontal zone, storm track activity is enhanced within a well-defined polar-Front jet with modest core velocity. This eddy-driven jet exhibits a deep structure with the strong surface westerlies maintained mainly through a poleward eddy heat flux. The westerly wind stress exerted along the Frontal zone acts to maintain it by driving the Oceanic current system, suggestive of a feedback loop via midlatitude atmosphere-ocean interaction. It is argued that the context of this feedback must be included in interpreting the tropospheric general circulation and its variability. In fact, decadal-scale sea-surface temperature anomalies observed in the North Pacific subarctic Frontal zone controlled the anomalous heat release to the atmosphere. Seemingly, the local storm track responded consistently to the decadal-scale shift of the Frontal axis, acting to reinforce basin-scale flow anomalies. Over the North and South Pacific, the association is disturbed in winter by an intensified subtropical jet that traps eddy activity into its sharp core. The trapping impairs baroclinic interaction of upper-level eddies with the surface baroclinicity along a midlatitude Oceanic Front, leading to the suppression of eddy activity as observed in midwinter over the North Pacific.
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dependence of the climatological axial latitudes of the tropospheric westerlies and storm tracks on the latitude of an extratropical Oceanic Front
Geophysical Research Letters, 2012Co-Authors: Fumiaki Ogawa, Kazuaki Nishii, Hisashi Nakamura, Takafumi Miyasaka, Akira KuwanoyoshidaAbstract:[1] Major “storm tracks”, where migratory cyclones and anticyclones recurrently develop, are observed around midlatitude Oceanic Frontal zones with strong meridional gradient of sea-surface temperature (SST). A set of atmospheric general circulation model experiments is performed with zonally uniform SST prescribed at the model lower boundary. The latitudinal SST profile for each hemisphere is characterized by a single Front. The Frontal latitude is varied systematically from one experiment to another, while the intensity of the Frontal gradient is kept unchanged. Though idealized, the experiments reveal a climatological tendency for a low-level storm track to be organized along or slightly poleward of the SST Front if located in the subtropics or midlatitudes. As a surface manifestation of an eddy-driven polar-Front jet (PFJ), surface westerly axis tends to form on the poleward flank of the Front. This anchoring effect of the SST Front is also hinted at upper levels, but the climatological positions of the storm track and PFJ are less sensitive to the Frontal latitude. For the SST Front at subpolar latitude, the joint primary axes of the upper-level storm track and PFJ form in midlatitudes away from the SST Front. Their positions correspond to their counterpart simulated with a particular SST profile from which Frontal gradient has been removed, suggesting that the anchoring effect of a subpolar SST Front on the storm track and PFJ is overshadowed by atmospheric internal dynamics, namely, the self-maintenance mechanism of a midlatitude storm track and PFJ through their interactions.
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air sea heat exchanges characteristic of a prominent midlatitude Oceanic Front in the south indian ocean as simulated in a high resolution coupled gcm
Journal of Climate, 2009Co-Authors: Masami Nonaka, Hisashi Nakamura, Akira Kuwanoyoshida, Bunmei Taguchi, Nobumasa Komori, Koutarou TakayaAbstract:Abstract An integration of a high-resolution coupled general circulation model whose ocean component is eddy permitting and thus able to reproduce a sharp gradient in sea surface temperature (SST) is analyzed to investigate air–sea heat exchanges characteristic of the midlatitude Oceanic Frontal zone. The focus of this paper is placed on a prominent SST Front in the south Indian Ocean, which is collocated with the core of the Southern Hemisphere storm track. Time-mean distribution of sensible heat flux is characterized by a distinct cross-Frontal contrast. It is upward and downward on the warmer and cooler flanks, respectively, of the SST Front, acting to maintain the sharp gradient of surface air temperature (SAT) that is important for preconditioning the environment for the recurrent development of storms and thereby anchoring the storm track. Induced by cross-Frontal advection of cold (warm) air associated with migratory atmospheric disturbances, the surface flux is highly variable with intermittent en...
Noel Keenlyside - One of the best experts on this subject based on the ideXlab platform.
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ozone induced climate change propped up by the southern hemisphere Oceanic Front
Geophysical Research Letters, 2015Co-Authors: Fumiaki Ogawa, Nour-eddine Omrani, Kazuaki Nishii, Hisashi Nakamura, Noel KeenlysideAbstract:The late twentieth century was marked by a significant summertime trend in the Southern Annular Mode (SAM), the dominant mode of tropospheric variability in the extratropical Southern Hemisphere (SH). This trend with poleward shifting tropospheric westerlies was attributed to downward propagation of stratospheric changes induced by ozone depletion. However, the role of the ocean in setting the SAM response to ozone depletion and its dynamical forcing remains unclear. Here we show, using idealized experiments with a state-of-the-art atmospheric model and analysis of Intergovernmental Panel on Climate Change climate simulations, that Frontal sea surface temperature gradients in the midlatitude SH are critical for translating the ozone-induced stratospheric changes down to the surface. This happens through excitation of wave forcing, which controls the vertical connection of the tropospheric SAM with the stratosphere and shows the importance of internal tropospheric dynamics for stratosphere/troposphere coupling. Thus, improved simulation of Oceanic Fronts may reduce uncertainties in simulating SH ozone-induced climate changes.
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Ozone‐induced climate change propped up by the Southern Hemisphere Oceanic Front
Geophysical Research Letters, 2015Co-Authors: Fumiaki Ogawa, Nour-eddine Omrani, Kazuaki Nishii, Hisashi Nakamura, Noel KeenlysideAbstract:The late twentieth century was marked by a significant summertime trend in the Southern Annular Mode (SAM), the dominant mode of tropospheric variability in the extratropical Southern Hemisphere (SH). This trend with poleward shifting tropospheric westerlies was attributed to downward propagation of stratospheric changes induced by ozone depletion. However, the role of the ocean in setting the SAM response to ozone depletion and its dynamical forcing remains unclear. Here we show, using idealized experiments with a state-of-the-art atmospheric model and analysis of Intergovernmental Panel on Climate Change climate simulations, that Frontal sea surface temperature gradients in the midlatitude SH are critical for translating the ozone-induced stratospheric changes down to the surface. This happens through excitation of wave forcing, which controls the vertical connection of the tropospheric SAM with the stratosphere and shows the importance of internal tropospheric dynamics for stratosphere/troposphere coupling. Thus, improved simulation of Oceanic Fronts may reduce uncertainties in simulating SH ozone-induced climate changes.
Fumiaki Ogawa - One of the best experts on this subject based on the ideXlab platform.
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ozone induced climate change propped up by the southern hemisphere Oceanic Front
Geophysical Research Letters, 2015Co-Authors: Fumiaki Ogawa, Nour-eddine Omrani, Kazuaki Nishii, Hisashi Nakamura, Noel KeenlysideAbstract:The late twentieth century was marked by a significant summertime trend in the Southern Annular Mode (SAM), the dominant mode of tropospheric variability in the extratropical Southern Hemisphere (SH). This trend with poleward shifting tropospheric westerlies was attributed to downward propagation of stratospheric changes induced by ozone depletion. However, the role of the ocean in setting the SAM response to ozone depletion and its dynamical forcing remains unclear. Here we show, using idealized experiments with a state-of-the-art atmospheric model and analysis of Intergovernmental Panel on Climate Change climate simulations, that Frontal sea surface temperature gradients in the midlatitude SH are critical for translating the ozone-induced stratospheric changes down to the surface. This happens through excitation of wave forcing, which controls the vertical connection of the tropospheric SAM with the stratosphere and shows the importance of internal tropospheric dynamics for stratosphere/troposphere coupling. Thus, improved simulation of Oceanic Fronts may reduce uncertainties in simulating SH ozone-induced climate changes.
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Ozone‐induced climate change propped up by the Southern Hemisphere Oceanic Front
Geophysical Research Letters, 2015Co-Authors: Fumiaki Ogawa, Nour-eddine Omrani, Kazuaki Nishii, Hisashi Nakamura, Noel KeenlysideAbstract:The late twentieth century was marked by a significant summertime trend in the Southern Annular Mode (SAM), the dominant mode of tropospheric variability in the extratropical Southern Hemisphere (SH). This trend with poleward shifting tropospheric westerlies was attributed to downward propagation of stratospheric changes induced by ozone depletion. However, the role of the ocean in setting the SAM response to ozone depletion and its dynamical forcing remains unclear. Here we show, using idealized experiments with a state-of-the-art atmospheric model and analysis of Intergovernmental Panel on Climate Change climate simulations, that Frontal sea surface temperature gradients in the midlatitude SH are critical for translating the ozone-induced stratospheric changes down to the surface. This happens through excitation of wave forcing, which controls the vertical connection of the tropospheric SAM with the stratosphere and shows the importance of internal tropospheric dynamics for stratosphere/troposphere coupling. Thus, improved simulation of Oceanic Fronts may reduce uncertainties in simulating SH ozone-induced climate changes.
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dependence of the climatological axial latitudes of the tropospheric westerlies and storm tracks on the latitude of an extratropical Oceanic Front
Geophysical Research Letters, 2012Co-Authors: Fumiaki Ogawa, Kazuaki Nishii, Hisashi Nakamura, Takafumi Miyasaka, Akira KuwanoyoshidaAbstract:[1] Major “storm tracks”, where migratory cyclones and anticyclones recurrently develop, are observed around midlatitude Oceanic Frontal zones with strong meridional gradient of sea-surface temperature (SST). A set of atmospheric general circulation model experiments is performed with zonally uniform SST prescribed at the model lower boundary. The latitudinal SST profile for each hemisphere is characterized by a single Front. The Frontal latitude is varied systematically from one experiment to another, while the intensity of the Frontal gradient is kept unchanged. Though idealized, the experiments reveal a climatological tendency for a low-level storm track to be organized along or slightly poleward of the SST Front if located in the subtropics or midlatitudes. As a surface manifestation of an eddy-driven polar-Front jet (PFJ), surface westerly axis tends to form on the poleward flank of the Front. This anchoring effect of the SST Front is also hinted at upper levels, but the climatological positions of the storm track and PFJ are less sensitive to the Frontal latitude. For the SST Front at subpolar latitude, the joint primary axes of the upper-level storm track and PFJ form in midlatitudes away from the SST Front. Their positions correspond to their counterpart simulated with a particular SST profile from which Frontal gradient has been removed, suggesting that the anchoring effect of a subpolar SST Front on the storm track and PFJ is overshadowed by atmospheric internal dynamics, namely, the self-maintenance mechanism of a midlatitude storm track and PFJ through their interactions.