The Experts below are selected from a list of 315 Experts worldwide ranked by ideXlab platform
Lars Hoffmann - One of the best experts on this subject based on the ideXlab platform.
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MJO‐Related Intraseasonal Variation in the Stratosphere: Gravity Waves and Zonal Winds
Journal of Geophysical Research: Atmospheres, 2018Co-Authors: M. J. Alexander, Alison W. Grimsdell, Claudia Christine Stephan, Lars HoffmannAbstract:Previous work has shown eastward migrating regions of enhanced temperature variance due to long-vertical wavelength stratospheric gravity waves that are in sync with Intraseasonal precipitation and tropopause wind anomalies associated with the Madden-Julian Oscillation (MJO). Here the origin of these Intraseasonal gravity wave Variations is investigated with a set of idealized gravity wave-resolving model experiments. The experiments specifically test whether tropopause winds act to control gravity wave propagation into the stratosphere by a critical level filtering mechanism or play a role in gravity wave generation through an obstacle source effect. All experiments use identical convective latent heating variability but the large-scale horizontal wind profile is varied to investigate relationships between stratospheric gravity waves and zonal winds at different levels. Results show that the observed long vertical wavelength gravity waves are primarily sensitive to stratospheric zonal wind Variations, while tropopause wind Variations have only a very small effect. Thus neither the critical level filter mechanism nor the obstacle source play much of a role in the observed Intraseasonal gravity wave Variations. Instead the results suggest that the stratospheric waves follow the MJO precipitation sources, and tropopause wind anomalies follow the same sources. We further find evidence of Intraseasonal wave drag effects on the stratospheric circulation in reanalyzed winds. The results suggest that waves drive Intraseasonal stratospheric zonal wind anomalies that descend in altitude with increasing MJO phases 3 through 7. Eastward anomalies descend further than westward, suggesting that MJO-related stratospheric waves cause larger eastward drag forces
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mjo related Intraseasonal Variation in the stratosphere gravity waves and zonal winds
Journal of Geophysical Research, 2017Co-Authors: M. J. Alexander, Alison W. Grimsdell, Claudia Christine Stephan, Lars HoffmannAbstract:Previous work has shown eastward migrating regions of enhanced temperature variance due to long-vertical wavelength stratospheric gravity waves that are in sync with Intraseasonal precipitation and tropopause wind anomalies associated with the Madden-Julian Oscillation (MJO). Here the origin of these Intraseasonal gravity wave Variations is investigated with a set of idealized gravity wave-resolving model experiments. The experiments specifically test whether tropopause winds act to control gravity wave propagation into the stratosphere by a critical level filtering mechanism or play a role in gravity wave generation through an obstacle source effect. All experiments use identical convective latent heating variability but the large-scale horizontal wind profile is varied to investigate relationships between stratospheric gravity waves and zonal winds at different levels. Results show that the observed long vertical wavelength gravity waves are primarily sensitive to stratospheric zonal wind Variations, while tropopause wind Variations have only a very small effect. Thus neither the critical level filter mechanism nor the obstacle source play much of a role in the observed Intraseasonal gravity wave Variations. Instead the results suggest that the stratospheric waves follow the MJO precipitation sources, and tropopause wind anomalies follow the same sources. We further find evidence of Intraseasonal wave drag effects on the stratospheric circulation in reanalyzed winds. The results suggest that waves drive Intraseasonal stratospheric zonal wind anomalies that descend in altitude with increasing MJO phases 3 through 7. Eastward anomalies descend further than westward, suggesting that MJO-related stratospheric waves cause larger eastward drag forces.
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mjo related Intraseasonal Variation of gravity waves in the southern hemisphere tropical stratosphere revealed by high resolution airs observations
Journal of Geophysical Research, 2016Co-Authors: Chikara Tsuchiya, Kaoru Sato, Joan M Alexander, Lars HoffmannAbstract:The Intraseasonal variability of gravity waves (GWs) in the austral summer middle stratosphere was examined using dedicated high-resolution temperature retrieval from the Atmospheric Infrared Sounder data. Composite maps were made of stratospheric GW temperature variances, large-scale zonal winds around the tropopause, and precipitation based on the real-time multivariate Madden-Julian Oscillation (MJO) index. Regional distributions of these quantities are synchronized with the MJO: The GW variances are larger for stronger precipitation and for more strongly westward wind around the tropopause at a given precipitation. These results suggest that the GWs observed by Atmospheric Infrared Sounder (AIRS) in the stratosphere originate from convection. Moreover, it is shown that the zonal wind around the tropopause likely controls the GW propagation into the stratosphere by a critical level filtering mechanism and/or the GW generation by an obstacle source effect. This means that the MJO can modulate the middle atmospheric circulation by regulating the GWs in two ways, namely, generation and propagation.
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resolution AIRS
2016Co-Authors: Chikara Tsuchiya, Kaoru Sato, Joan M. Alex, Lars HoffmannAbstract:MJO-related Intraseasonal Variation of gravity waves in the southern hemisphere subtropical stratosphere revealed by high
Song Yang - One of the best experts on this subject based on the ideXlab platform.
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Correction to: Intraseasonal Variation of the summer rainfall over the Southeastern United States
Climate Dynamics, 2018Co-Authors: Wei Wei, Yi Deng, Song YangAbstract:The HTML version of this article was published with incorrect copyright line. The correct copyright line is “The Author(s) 2018”. This error has been corrected.
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Intraseasonal Variation of the summer rainfall over the Southeastern United States.
Climate dynamics, 2018Co-Authors: Wei Wei, Yi Deng, Song YangAbstract:This study characterizes the Intraseasonal variability (ISV) in the Southeastern United States (SE US) rainfall in boreal summer and delineates the associated dynamical processes featuring three-way interactions among the SE US rainfall, the central US low-level jet (LLJ), and the North Atlantic subtropical high (NASH). The analysis reveals that the ISV of the SE summer rainfall peaks at the 10‒20-day timescales. The physical mechanisms for the three-way interactions on the 10‒20-day timescales are proposed. When the NASH attains a minimum strength, the reduced size of the NASH is accompanied with an eastward retreat of the western ridge of the NASH, leading to a decrease in the zonal pressure gradient and consequently a weakening of the LLJ 1 day after. The weakened LLJ and the eastward-shifted NASH western ridge induces anomalous cyclonic circulation over the SE US, moves preferred regions of moisture convergence from central US to the SE US, and 3 days later the SE US rainfall attains its maximum strength. The excessive latent heating associated with the enhanced SE US rainfall excites an anomalous anticyclone northeast of the rainfall region, resulting in an increase in the NASH intensity that peaks 2 days after the maximum SE US rainfall. The NASH subsequently expands with its western ridge moving westward, zonal pressure gradient restored, and LLJ strength recovered. An anomalous anticyclone then emerges over the SE US and suppresses rainfall, marking the shift from an Intraseasonal wet phase to dry phase in this region. A more rigorous proof of these causalities demand carefully designed numerical experiments and further statistical analysis in future. Our results suggest that improved prediction of SE US summer rainfall across Intraseasonal scales depends critically on the model representation of the three-way coupling among the NASH, the central US LLJ, and the SE US rainfall.
Yangxing Zheng - One of the best experts on this subject based on the ideXlab platform.
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Intraseasonal Variation of winter precipitation over the western united states simulated by 14 ipcc ar4 coupled gcms
Journal of Climate, 2010Co-Authors: Jialin Lin, Toshiaki Shinoda, Taotao Qian, Weiqing Han, Paul E Roundy, Yangxing ZhengAbstract:Abstract This study evaluates the Intraseasonal Variation of winter precipitation over the western United States in 14 coupled general circulation models (GCMs) participating in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). Eight years of each model’s twentieth-century climate simulation are analyzed. The focus is on the two dominant Intraseasonal modes for the western U.S. precipitation: the 40-day mode and the 22-day mode. The results show that the models tend to overestimate the northern winter (November–April) seasonal mean precipitation over the western United States and Canada. The models also tend to produce overly strong Intraseasonal variability in western U.S. wintertime precipitation, in spite of the overly weak tropical Intraseasonal variability in most of the models. All models capture both the 40-day mode and the 22-day mode, usually with overly large variances. For the 40-day mode, models tend to reproduce its deep barotropic vertical structure and thr...
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Intraseasonal Variation of Winter Precipitation over the Western United States Simulated by 14 IPCC AR4 Coupled GCMs
Journal of Climate, 2010Co-Authors: Jialin Lin, Toshiaki Shinoda, Taotao Qian, Weiqing Han, Paul E Roundy, Yangxing ZhengAbstract:Abstract This study evaluates the Intraseasonal Variation of winter precipitation over the western United States in 14 coupled general circulation models (GCMs) participating in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). Eight years of each model’s twentieth-century climate simulation are analyzed. The focus is on the two dominant Intraseasonal modes for the western U.S. precipitation: the 40-day mode and the 22-day mode. The results show that the models tend to overestimate the northern winter (November–April) seasonal mean precipitation over the western United States and Canada. The models also tend to produce overly strong Intraseasonal variability in western U.S. wintertime precipitation, in spite of the overly weak tropical Intraseasonal variability in most of the models. All models capture both the 40-day mode and the 22-day mode, usually with overly large variances. For the 40-day mode, models tend to reproduce its deep barotropic vertical structure and three-cell horizontal structure, but only 5 of the 14 models capture its northward propagation, and only 2 models simulate its teleconnection with the Madden–Julian oscillation in the tropical Pacific. For the 22-day mode, 8 of the 14 models reproduce its coherent northward propagation, and 9 models capture its teleconnection with precipitation in the tropical Pacific.
M. J. Alexander - One of the best experts on this subject based on the ideXlab platform.
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MJO‐Related Intraseasonal Variation in the Stratosphere: Gravity Waves and Zonal Winds
Journal of Geophysical Research: Atmospheres, 2018Co-Authors: M. J. Alexander, Alison W. Grimsdell, Claudia Christine Stephan, Lars HoffmannAbstract:Previous work has shown eastward migrating regions of enhanced temperature variance due to long-vertical wavelength stratospheric gravity waves that are in sync with Intraseasonal precipitation and tropopause wind anomalies associated with the Madden-Julian Oscillation (MJO). Here the origin of these Intraseasonal gravity wave Variations is investigated with a set of idealized gravity wave-resolving model experiments. The experiments specifically test whether tropopause winds act to control gravity wave propagation into the stratosphere by a critical level filtering mechanism or play a role in gravity wave generation through an obstacle source effect. All experiments use identical convective latent heating variability but the large-scale horizontal wind profile is varied to investigate relationships between stratospheric gravity waves and zonal winds at different levels. Results show that the observed long vertical wavelength gravity waves are primarily sensitive to stratospheric zonal wind Variations, while tropopause wind Variations have only a very small effect. Thus neither the critical level filter mechanism nor the obstacle source play much of a role in the observed Intraseasonal gravity wave Variations. Instead the results suggest that the stratospheric waves follow the MJO precipitation sources, and tropopause wind anomalies follow the same sources. We further find evidence of Intraseasonal wave drag effects on the stratospheric circulation in reanalyzed winds. The results suggest that waves drive Intraseasonal stratospheric zonal wind anomalies that descend in altitude with increasing MJO phases 3 through 7. Eastward anomalies descend further than westward, suggesting that MJO-related stratospheric waves cause larger eastward drag forces
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mjo related Intraseasonal Variation in the stratosphere gravity waves and zonal winds
Journal of Geophysical Research, 2017Co-Authors: M. J. Alexander, Alison W. Grimsdell, Claudia Christine Stephan, Lars HoffmannAbstract:Previous work has shown eastward migrating regions of enhanced temperature variance due to long-vertical wavelength stratospheric gravity waves that are in sync with Intraseasonal precipitation and tropopause wind anomalies associated with the Madden-Julian Oscillation (MJO). Here the origin of these Intraseasonal gravity wave Variations is investigated with a set of idealized gravity wave-resolving model experiments. The experiments specifically test whether tropopause winds act to control gravity wave propagation into the stratosphere by a critical level filtering mechanism or play a role in gravity wave generation through an obstacle source effect. All experiments use identical convective latent heating variability but the large-scale horizontal wind profile is varied to investigate relationships between stratospheric gravity waves and zonal winds at different levels. Results show that the observed long vertical wavelength gravity waves are primarily sensitive to stratospheric zonal wind Variations, while tropopause wind Variations have only a very small effect. Thus neither the critical level filter mechanism nor the obstacle source play much of a role in the observed Intraseasonal gravity wave Variations. Instead the results suggest that the stratospheric waves follow the MJO precipitation sources, and tropopause wind anomalies follow the same sources. We further find evidence of Intraseasonal wave drag effects on the stratospheric circulation in reanalyzed winds. The results suggest that waves drive Intraseasonal stratospheric zonal wind anomalies that descend in altitude with increasing MJO phases 3 through 7. Eastward anomalies descend further than westward, suggesting that MJO-related stratospheric waves cause larger eastward drag forces.
Wei Wei - One of the best experts on this subject based on the ideXlab platform.
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Correction to: Intraseasonal Variation of the summer rainfall over the Southeastern United States
Climate Dynamics, 2018Co-Authors: Wei Wei, Yi Deng, Song YangAbstract:The HTML version of this article was published with incorrect copyright line. The correct copyright line is “The Author(s) 2018”. This error has been corrected.
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Intraseasonal Variation of the summer rainfall over the Southeastern United States.
Climate dynamics, 2018Co-Authors: Wei Wei, Yi Deng, Song YangAbstract:This study characterizes the Intraseasonal variability (ISV) in the Southeastern United States (SE US) rainfall in boreal summer and delineates the associated dynamical processes featuring three-way interactions among the SE US rainfall, the central US low-level jet (LLJ), and the North Atlantic subtropical high (NASH). The analysis reveals that the ISV of the SE summer rainfall peaks at the 10‒20-day timescales. The physical mechanisms for the three-way interactions on the 10‒20-day timescales are proposed. When the NASH attains a minimum strength, the reduced size of the NASH is accompanied with an eastward retreat of the western ridge of the NASH, leading to a decrease in the zonal pressure gradient and consequently a weakening of the LLJ 1 day after. The weakened LLJ and the eastward-shifted NASH western ridge induces anomalous cyclonic circulation over the SE US, moves preferred regions of moisture convergence from central US to the SE US, and 3 days later the SE US rainfall attains its maximum strength. The excessive latent heating associated with the enhanced SE US rainfall excites an anomalous anticyclone northeast of the rainfall region, resulting in an increase in the NASH intensity that peaks 2 days after the maximum SE US rainfall. The NASH subsequently expands with its western ridge moving westward, zonal pressure gradient restored, and LLJ strength recovered. An anomalous anticyclone then emerges over the SE US and suppresses rainfall, marking the shift from an Intraseasonal wet phase to dry phase in this region. A more rigorous proof of these causalities demand carefully designed numerical experiments and further statistical analysis in future. Our results suggest that improved prediction of SE US summer rainfall across Intraseasonal scales depends critically on the model representation of the three-way coupling among the NASH, the central US LLJ, and the SE US rainfall.