Journal of the Atmospheric Sciences最新文献

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Prediction skill and practical predictability depending on the initial atmospheric states in S2S forecasts S2S预报中基于初始大气状态的预报技巧和实际可预测性
IF 3.1 3区 地球科学
Journal of the Atmospheric Sciences Pub Date : 2023-04-20 DOI: 10.1175/jas-d-22-0262.1
M. Inatsu, M. Matsueda, Naoto Nakano, S. Kawazoe
{"title":"Prediction skill and practical predictability depending on the initial atmospheric states in S2S forecasts","authors":"M. Inatsu, M. Matsueda, Naoto Nakano, S. Kawazoe","doi":"10.1175/jas-d-22-0262.1","DOIUrl":"https://doi.org/10.1175/jas-d-22-0262.1","url":null,"abstract":"\u0000The hypothesis that predictability depends on the atmospheric state in the planetary-scale low-frequency variability in boreal winter was examined. We first computed six typical weather patterns from 500-hPa geopotential height anomalies in the Northern Hemisphere using self-organising map (SOM) and k-clustering analysis. Next, using 11 models from the subseasonal-to-seasonal (S2S) operational and reforecast archive, we computed each model’s climatology as a function of lead time to evaluate model bias. Although the forecast bias depends on the model, it is consistently the largest when the forecast begins from the atmospheric state with a blocking-like pattern in the eastern North Pacific. Moreover, the ensemble-forecast spread based on S2S multi-model forecast data was compared with empirically estimated Fokker-Planck equation (FPE) parameters based on reanalysis data. The multi-model mean ensemble-forecast spread was correlated with the diffusion tensor norm; they are large for the cases when the atmospheric state started from a cluster with a blocking-like pattern. As the multi-model mean is expected to substantially reduce model biases and may approximate the predictability inherent in nature, we can summarise that the atmospheric state corresponding to the cluster was less predictable than others.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2023-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47833972","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
What are the Balanced and Unbalanced Dynamics of Tropical Cyclone? 热带气旋的平衡和不平衡动力是什么?
IF 3.1 3区 地球科学
Journal of the Atmospheric Sciences Pub Date : 2023-04-17 DOI: 10.1175/jas-d-22-0165.1
D. Ji, F. Qiao
{"title":"What are the Balanced and Unbalanced Dynamics of Tropical Cyclone?","authors":"D. Ji, F. Qiao","doi":"10.1175/jas-d-22-0165.1","DOIUrl":"https://doi.org/10.1175/jas-d-22-0165.1","url":null,"abstract":"\u0000Recently, Ji and Qiao took into account the unbalanced components and derived an extended Sawyer–Eliassen (SE) equation. This study developed a new derivation of this extended SE equation from the perspective of restoring forces, and gives a physical interpretation for the coefficients that appear in the SE equation. For an unbalanced vortex, we demonstrated that the thermodynamic fields are only determined by the distribution of gradient wind, and thus the gradient wind and thermodynamic fields always remain in balance as the unbalanced vortex evolves. Consequently, we attributed the gradient wind imbalance to the agradient wind rather than to the thermodynamic fields. Subsequently, we explored the effect of the agradient wind on the secondary circulation, and showed that the agradient wind strengthens the secondary circulation in its vicinity, which can be explained as a consequence of the restoring forces and mass continuity. Furthermore, we speculated that the SE equation, together with the radial velocity equation could reproduce the primary characteristic of the axisymmetric boundary layer dynamics by prescribing the parameterization of subgrid–scale turbulent mixing. Specifically, the noU BL and noVa BL experiments conducted by Fei et al. in an article published in 2021 were reinterpreted, and the oscillation wavelength of the agradient wind in the eyewall was approximated based on this framework. Additionally, a new numerical solution algorithm to overcome the hyperbolicity near the boundary layer was proposed. This study attempts to develop a complete dynamic theory for TC in both qualitative and quantitative perspectives.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2023-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41966892","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 1
Observed Turbulent Dissipation Rate in a Landfalling Tropical Cyclone Boundary Layer 登陆热带气旋边界层湍流耗散率观测
IF 3.1 3区 地球科学
Journal of the Atmospheric Sciences Pub Date : 2023-04-14 DOI: 10.1175/jas-d-22-0265.1
Qingguo Fang, Kekuan Chu, Bowen Zhou, Xunlai Chen, Zhen Peng, Chunsheng Zhang, M. Luo, Chunyang Zhao
{"title":"Observed Turbulent Dissipation Rate in a Landfalling Tropical Cyclone Boundary Layer","authors":"Qingguo Fang, Kekuan Chu, Bowen Zhou, Xunlai Chen, Zhen Peng, Chunsheng Zhang, M. Luo, Chunyang Zhao","doi":"10.1175/jas-d-22-0265.1","DOIUrl":"https://doi.org/10.1175/jas-d-22-0265.1","url":null,"abstract":"\u0000Based on turbulence measurements from sonic anemometers instrumented at multiple levels on a 356 m-tall meteorological tower located on the south coast of China, an observation study of the turbulent dissipation rate (ε) in a landfalling tropical cyclone boundary layer (TCBL) is conducted. Three indirect methods (i.e., the power spectra, the 2nd- and the 3rd-order structure functions) are compared for the calculation of ε. The 3rd-order structure function computes the smallest ε among the 3 methods, but shows the largest uncertainty. The 2nd-order structure function gives similar ε estimates as the power spectra, and is adopted for its reduced uncertainty. The measured ε in the landfalling TCBL is of O(10−1) m2 s−3, much greater than typical atmospheric boundary layer values as well as oceanic TCBL values. ε is found to scale with the local friction velocity rather than the surface friction velocity, implying a highly localized nature of turbulence. Conventional parameterizations of ε are evaluated against observations. Process-based ε models assuming a local balance between shear production and dissipation prove inadequate, as shear production merely accounts for half of the dissipation away from the surface. In comparison, scaling-based ε models used by planetary boundary layer (PBL) schemes are more advantageous. With both tuning of the model coefficients and adjustment of the dissipation length scale, the performance of an ε model in a widely used PBL scheme is shown to produce similar values to the observations.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":"1 1","pages":""},"PeriodicalIF":3.1,"publicationDate":"2023-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"64553025","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 1
No warm-phase invigoration of convection detected during GoAmazon GoAmazon期间未检测到热相对流增强
IF 3.1 3区 地球科学
Journal of the Atmospheric Sciences Pub Date : 2023-04-13 DOI: 10.1175/jas-d-22-0241.1
R. Öktem, D. Romps, A. Varble
{"title":"No warm-phase invigoration of convection detected during GoAmazon","authors":"R. Öktem, D. Romps, A. Varble","doi":"10.1175/jas-d-22-0241.1","DOIUrl":"https://doi.org/10.1175/jas-d-22-0241.1","url":null,"abstract":"\u0000It has been proposed that air pollution increases the updraft speeds of warm-phase convective clouds by reducing their supersaturation and, thereby, enhancing their buoyancy. Observations from the GoAmazon field campaign, sampled using subjective criteria, have been offered as evidence for this warm-phase invigoration. Here, we reexamine those GoAmazon observations using objective criteria and find no indication that air pollution increases warm-phase updraft speeds. In addition, the observations yield no statistically significant relationship between aerosol concentrations and either moist-convective vertical velocity or reflectivity in either the lower or upper troposphere.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2023-04-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41755747","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 1
The role of North Atlantic blocking high during large-scale heavy rainfall events over central India 北大西洋阻塞高压在印度中部大范围强降雨事件中的作用
IF 3.1 3区 地球科学
Journal of the Atmospheric Sciences Pub Date : 2023-04-07 DOI: 10.1175/jas-d-22-0185.1
Akshaya C. Nikumbh, A. Thakur, A. Chakraborty, G. S. Bhat, J. Sukhatme
{"title":"The role of North Atlantic blocking high during large-scale heavy rainfall events over central India","authors":"Akshaya C. Nikumbh, A. Thakur, A. Chakraborty, G. S. Bhat, J. Sukhatme","doi":"10.1175/jas-d-22-0185.1","DOIUrl":"https://doi.org/10.1175/jas-d-22-0185.1","url":null,"abstract":"\u0000Large-scale extreme rainfall events (LEREs) over central India are produced by monsoon low-pressure systems (LPSs) when assisted by a secondary cyclonic vortex (SCV). Both the LPS and the SCV are embedded in a monsoon trough and form mainly during the positive phase of the boreal summer intraseasonal oscillation. Here, we observe that tropical-extratropical interactions exist during LEREs. Using ray tracing, we show that extratropical Rossby waves propagate to the Indian subcontinent during the summer monsoon season. Stationary Rossby wave rays originating over the north Atlantic ocean reach India following approximately a great circle path at mid-tropospheric levels. This pathway appears to play an important role in tropical-extratropical interactions during LEREs. 77%of LEREs are preceded by a north Atlantic blocking high and 90 % by a quasi-stationary central Asian high. The Atlantic blocking high triggers a quasi-stationary Rossby wave response and strengthens the downstream central Asian high. In turn, the quasi-stationary central Asian high facilitates Rossby wave breaking, transporting high PV streamers and cut-offs equatorward. The central Asian high is in close proximity to the monsoon trough in the mid and lower troposphere. It interacts with the monsoon trough over the northwest Indian subcontinent. The equatorial monsoon trough is strengthened due to the supply of dynamic forcing and static instabilities from the extratropics. This additional forcing from the extratropics creates an environment that is conducive for LEREs.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2023-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44280942","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Stability Analysis of Ice Crystal Orientation 冰晶取向的稳定性分析
IF 3.1 3区 地球科学
Journal of the Atmospheric Sciences Pub Date : 2023-04-07 DOI: 10.1175/jas-d-22-0223.1
Xiping Zeng, Z. Ulanowski, A. Heymsfield, Yansen Wang, Xiaowen Li
{"title":"Stability Analysis of Ice Crystal Orientation","authors":"Xiping Zeng, Z. Ulanowski, A. Heymsfield, Yansen Wang, Xiaowen Li","doi":"10.1175/jas-d-22-0223.1","DOIUrl":"https://doi.org/10.1175/jas-d-22-0223.1","url":null,"abstract":"\u0000The stability of ice crystal orientation is studied by modeling the air flow around ice crystals at moderate Reynolds number, where an ice crystal is approximated by a cylinder with three parameters: diameter D, length L, and zenith angle of the axis θ. In this paper the torque acting on ice crystals is simulated at different θ first and then a special θ with zero horizontal torque, denoted as θe, is sought as an equilibrium of ice crystal orientation. The equilibrium is classified into two kinds: stable and unstable. Ice crystals rotate to θe of stable equilibriums while deviating from θe of unstable ones once they are released into quiet air.\u0000Multiple equilibriums of ice crystal orientation are found via numerical simulations. A cylinder with D/L close to one has three equilibriums, two of which are stable (i.e., θe = 0 and 90°). A cylinder with D/L away from one has only two equilibriums, one of which is stable (i.e., either θe = 0 or 90°). In addition, an asymmetric cylinder has two, three or five equilibriums, and their θ e is sensitive to the distance between its geometrical center and its center of gravity. The sensitivity of θe to crystal asymmetry suggests large symmetric ice crystals tend to become asymmetric (or irregular) and subsequently oriented randomly.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2023-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45104477","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
The Onset of a Blocking Event as a “Traffic Jam”: Characterization with Ensemble Sensitivity Analysis 阻塞事件作为“交通堵塞”的开始:用集合灵敏度分析表征
IF 3.1 3区 地球科学
Journal of the Atmospheric Sciences Pub Date : 2023-04-05 DOI: 10.1175/jas-d-21-0312.1
Christopher Polster, V. Wirth
{"title":"The Onset of a Blocking Event as a “Traffic Jam”: Characterization with Ensemble Sensitivity Analysis","authors":"Christopher Polster, V. Wirth","doi":"10.1175/jas-d-21-0312.1","DOIUrl":"https://doi.org/10.1175/jas-d-21-0312.1","url":null,"abstract":"\u0000Recently, Nakamura and Huang proposed a theory of blocking onset based on the budget of finite-amplitude local wave activity on the mid-latitude waveguide. Blocks form in their idealized model due to a mechanism that also describes the emergence of traffic jams in traffic theory. The currentwork investigates the development of a winter European block in terms of finite-amplitude local wave activity to evaluate the possible relevance of the “traffic jam” mechanism for the flowtransition. 200 members of a medium-range ensemble forecast of the blocking onset period are analyzed with correlation- and cluster-based sensitivity techniques. Diagnostic evidence points to a traffic jam onset on 17 December 2016. Block development is sensitive to upstream Rossby wave activity up to 1.5 days prior to its initiation and consistent with expectations from the idealized theory. Eastward transport of finite-amplitude local wave activity in the southern part of the block is suppressed by non-linear flux modification from the large-amplitude blocking pattern, consistent with the expected obstruction in the traffic jam model. The relationship of finite-amplitude local wave activity and its zonal flux as mapped by the ensemble exhibits established characteristics of a traffic jam. This study suggests that the traffic jam mechanism may play an important role in some cases of blocking onset and more generally that applying finite-amplitude local wave activity diagnostics to ensemble data is a promising approach for the further examination of individual onset events in light of the Nakamura and Huang theory.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2023-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43177736","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 1
Mesoscale Spectra of Vertical Vorticity and Horizontal Divergence in an Idealized Baroclinic Wave Simulation 理想斜压波模拟中垂直涡度和水平散度的中尺度谱
IF 3.1 3区 地球科学
Journal of the Atmospheric Sciences Pub Date : 2023-04-04 DOI: 10.1175/jas-d-22-0213.1
Jun Peng, Zongheng Li, Lifeng Zhang, Yuanshuen Wang, Hanyan Wu
{"title":"Mesoscale Spectra of Vertical Vorticity and Horizontal Divergence in an Idealized Baroclinic Wave Simulation","authors":"Jun Peng, Zongheng Li, Lifeng Zhang, Yuanshuen Wang, Hanyan Wu","doi":"10.1175/jas-d-22-0213.1","DOIUrl":"https://doi.org/10.1175/jas-d-22-0213.1","url":null,"abstract":"A new formulation of the spectral budget of vertical vorticity and horizontal divergence suitable for the mesoscale atmosphere on an f plane is derived. Compared to previous formulation in large-scale studies, there are three main improvements: (i) both the squared vorticity (SV; i.e., enstrophy as usual) and squared divergence (SD) spectra are taken into account, (ii) the spectral transfers of SV and SD between scales are exactly constructed under the nonlinear advection of the full horizontal velocity, and (iii) the general relationship between spectral energy and SV/SD transfers is derived. With this new formulation, the atmospheric spectra of divergent and rotational motion components are investigated through numerical simulation of idealized dry baroclinic waves. Spectral budget analysis shows that, in the present dry simulation, the upper troposphere is almost completely dominated by the downscale SV transfer at all scales, while the lower stratosphere is dominated by the downscale SV transfer at synoptic scales and by the downscale SD transfer at mesoscales. The pressure-related term is largely cancelled out by the conversion term between SV and SD at both levels, but at the small-scale end of lower-stratospheric mesoscales there exists a significant net positive forcing, accounting for the distinct spectral transition of the total spectrum there. An explicit association between spectral energy and SV/SD transfers is further made. In the upper troposphere, the downscale enegy cascade is mainly governed by the downscale SV transfer; while in the lower stratosphere, it is mainly governed by the residual term related to non-uniformly distributed vertical velocity.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2023-04-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47041259","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 1
Sensitivity of mountain wave drag estimates on separation methods and proposed improvements 山波阻力估计对分离方法的敏感性及改进建议
IF 3.1 3区 地球科学
Journal of the Atmospheric Sciences Pub Date : 2023-04-03 DOI: 10.1175/jas-d-22-0151.1
Z. Prochazkova, C. Kruse, M. Alexander, L. Hoffmann, J. Bacmeister, L. Holt, C. Wright, Kaoru Sato, S. Gisinger, M. Ern, M. Geldenhuys, P. Preusse, P. Šácha
{"title":"Sensitivity of mountain wave drag estimates on separation methods and proposed improvements","authors":"Z. Prochazkova, C. Kruse, M. Alexander, L. Hoffmann, J. Bacmeister, L. Holt, C. Wright, Kaoru Sato, S. Gisinger, M. Ern, M. Geldenhuys, P. Preusse, P. Šácha","doi":"10.1175/jas-d-22-0151.1","DOIUrl":"https://doi.org/10.1175/jas-d-22-0151.1","url":null,"abstract":"\u0000Internal gravity waves (GWs) are ubiquitous in the atmosphere, making significant contributions to the mesoscale motions. Since the majority of their spectrum is unresolved in global circulation models, their effects need to be parameterized. In recent decades GWs have been increasingly studied in high-resolution simulations, which, unlike direct observations, allow us to explore full spatio-temporal variations of the resolved wave field. In our study we analyze and refine a traditional method for GW analysis in a high-resolution simulation on a regional domain around the Drake Passage. We show that GW momentum drag estimates based on the Gaussian high-pass filter method applied to separate GW perturbations from the background are sensitive to the choice of a cutoff parameter. The impact of the cutoff parameter is higher for horizontal fluxes of horizontal momentum, which indicates higher sensitivity for horizontally propagating waves. Two modified methods, which choose the parameter value from spectral information, are proposed. The dynamically determined cutoff is mostly higher than the traditional cutoff values around 500 km, leading to larger GW fluxes and drag, and varies with time and altitude. The differences between the traditional and the modified methods are especially pronounced during events with significant drag contributions from horizontal momentum fluxes.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2023-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41553752","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Weak Equatorial Superrotation during the Past 250 Million Years 过去2.5亿年的弱赤道超自转
3区 地球科学
Journal of the Atmospheric Sciences Pub Date : 2023-04-01 DOI: 10.1175/jas-d-22-0072.1
Jiawenjing Lan, Jun Yang, Yongyun Hu, Xiang Li, Jiaqi Guo, Qifan Lin, Jing Han, Jian Zhang, Shuang Wang, Ji Nie
{"title":"Weak Equatorial Superrotation during the Past 250 Million Years","authors":"Jiawenjing Lan, Jun Yang, Yongyun Hu, Xiang Li, Jiaqi Guo, Qifan Lin, Jing Han, Jian Zhang, Shuang Wang, Ji Nie","doi":"10.1175/jas-d-22-0072.1","DOIUrl":"https://doi.org/10.1175/jas-d-22-0072.1","url":null,"abstract":"Abstract For modern Earth, the annual-mean equatorial winds in the upper troposphere are flowing from east to west (i.e., easterly winds). This is mainly due to the deceleration effect of the seasonal cross-equatorial Hadley cells, against the relatively weaker acceleration effect of coupled Rossby and Kelvin waves excited from tropical convection and latent heat release. In this work, we examine the evolution of equatorial winds during the past 250 million years using one global Earth system model, the Community Earth System Model version 1.2.2 (CESM1.2.2). Three climatic factors different from the modern Earth—solar constant, atmospheric CO 2 concentration, and land–sea configuration—are considered in the simulations. We find that the upper-tropospheric equatorial winds change sign to westerly flows (called equatorial superrotation) in certain eras, such as 250–230 and 150–50 Ma. The strength of the superrotation is below 4 m s −1 , comparable to the magnitude of the present-day easterly winds. In general, this phenomenon occurs in a warmer climate within which the tropical atmospheric circulation shifts upward in altitude, stationary and/or transient eddies are relatively stronger, and/or the Hadley cells are relatively weaker, which in turn are due to the changes of the three factors, especially CO 2 concentration and land–sea configuration.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":"48 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135067124","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
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