The atmospheric kinetic energy spectrum and energy cascade are investigated in idealised simulations of radiative-convective equilibrium (RCE). WRF is employed to perform cloud-resolving simulation of an idealized radiative-convective equilibrium with and without aggregation with Δx = 4 km. The horizontal kinetic energy (HKE) spectrum for the aggregated simulation in the upper troposphere is steeper than the non-aggregated case and closer to -5/3. The HKE spectra for the non-aggregated simulation in the upper troposphere and the lower stratosphere are much shallower than the -5/3 spectrum. In the upper troposphere, the divergent kinetic energy has a similar magnitude to the rotational kinetic energy in both the non-aggregated simulation and aggregated simulation. Energy is mainly gained from the buoyancy flux and mainly lost from the vertical energy flux for scales larger than 20 km. Downscale energy transfer is found in the upper troposphere. Numerical dissipation is the main source of energy loss at small scales. In the lower stratosphere, the divergent kinetic energy dominates the kinetic energy spectrum in both simulations. Energy is mainly gained from the vertical energy flux and is balanced by the loss from the buoyancy flux term, transfer term and dissipation. An Eliassen-Palm flux analysis suggests that wave-mean-flow interaction may be responsible for the upscale energy transfer found in the lower stratosphere. The magnitudes of our kinetic energy spectra are similar to spectra calculated from aircraft data. Rotation is found to promote aggregation and steepen the energy spectrum.
{"title":"Kinetic Energy Spectra and Spectral Budget of Radiative-Convective Equilibrium","authors":"KwanTo Lai, Michael L. Waite","doi":"10.1175/jas-d-22-0173.1","DOIUrl":"https://doi.org/10.1175/jas-d-22-0173.1","url":null,"abstract":"\u0000The atmospheric kinetic energy spectrum and energy cascade are investigated in idealised simulations of radiative-convective equilibrium (RCE). WRF is employed to perform cloud-resolving simulation of an idealized radiative-convective equilibrium with and without aggregation with Δx = 4 km. The horizontal kinetic energy (HKE) spectrum for the aggregated simulation in the upper troposphere is steeper than the non-aggregated case and closer to -5/3. The HKE spectra for the non-aggregated simulation in the upper troposphere and the lower stratosphere are much shallower than the -5/3 spectrum. In the upper troposphere, the divergent kinetic energy has a similar magnitude to the rotational kinetic energy in both the non-aggregated simulation and aggregated simulation. Energy is mainly gained from the buoyancy flux and mainly lost from the vertical energy flux for scales larger than 20 km. Downscale energy transfer is found in the upper troposphere. Numerical dissipation is the main source of energy loss at small scales. In the lower stratosphere, the divergent kinetic energy dominates the kinetic energy spectrum in both simulations. Energy is mainly gained from the vertical energy flux and is balanced by the loss from the buoyancy flux term, transfer term and dissipation. An Eliassen-Palm flux analysis suggests that wave-mean-flow interaction may be responsible for the upscale energy transfer found in the lower stratosphere. The magnitudes of our kinetic energy spectra are similar to spectra calculated from aircraft data. Rotation is found to promote aggregation and steepen the energy spectrum.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2023-05-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43890184","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}
Pub Date : 2023-05-17eCollection Date: 2023-01-01DOI: 10.1080/01658107.2023.2212756
Jonathan A Alexis, Jane Lock, Lay Kho, Andrew L Thompson, David A Prentice
An Asian man in his 20s developed asymptomatic ipsilateral moyamoya-like vascular changes following orbital and head trauma. An ipsilateral traumatic optic neuropathy with extensive optic cupping ensued. The complex embryology of the ocular vascular development is reviewed as having a potential causative role in the intracranial carotid vasculopathy.
{"title":"Moyamoya-Like Vasculopathy and Orbital Trauma: An Association.","authors":"Jonathan A Alexis, Jane Lock, Lay Kho, Andrew L Thompson, David A Prentice","doi":"10.1080/01658107.2023.2212756","DOIUrl":"10.1080/01658107.2023.2212756","url":null,"abstract":"<p><p>An Asian man in his 20s developed asymptomatic ipsilateral moyamoya-like vascular changes following orbital and head trauma. An ipsilateral traumatic optic neuropathy with extensive optic cupping ensued. The complex embryology of the ocular vascular development is reviewed as having a potential causative role in the intracranial carotid vasculopathy.</p>","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":"54 1","pages":"262-268"},"PeriodicalIF":0.8,"publicationDate":"2023-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10732633/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86796829","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D. Fritts, G. Baumgarten, P. Pautet, J. Hecht, B. Williams, N. Kaifler, B. Kaifler, C. Kjellstrand, Ling Wang, M. Taylor, A. Miller
Multiple recent observations in the mesosphere have revealed large-scale Kelvin-Helmholtz instabilities (KHI) exhibiting diverse spatial features and temporal evolutions. The first event reported by Hecht et al. (2021) exhibited multiple features resembling those seen to arise in early laboratory shear-flow studies described as “Tube” and “Knot” (T&K) dynamics by Thorpe (1985, 1987). The potential importance of T&K dynamics in the atmosphere, and in the oceans and other stratified and sheared fluids, is due to their accelerated turbulence transitions and elevated energy dissipation rates relative to KHI turbulence transitions occurring in their absence. Motivated by these studies, we survey recent observational evidence of multi-scale Kelvin-Helmholtz instabilities throughout the atmosphere, many features of which closely resemble T&K dynamics observed in the laboratory and idealized initial modeling. These efforts will guide further modeling assessing the potential importance of these T&K dynamics in turbulence generation, energy dissipation, and mixing throughout the atmosphere and other fluids. We expect these dynamics to have implications for parameterizing mixing and transport in stratified shear flows in the atmosphere and oceans that have not been considered to date. Companion papers describe results of a multi-scale gravity wave direct numerical simulation (DNS) that serendipitously exhibits a number of KHI T&K events and an idealized multi-scale DNS of KHI T&K dynamics without gravity wave influences.
{"title":"Kelvin Helmholtz Instability “Tube” & “Knot” Dynamics, Part I: Expanding Observational Evidence of Occurrence and Environmental Influences","authors":"D. Fritts, G. Baumgarten, P. Pautet, J. Hecht, B. Williams, N. Kaifler, B. Kaifler, C. Kjellstrand, Ling Wang, M. Taylor, A. Miller","doi":"10.1175/jas-d-22-0189.1","DOIUrl":"https://doi.org/10.1175/jas-d-22-0189.1","url":null,"abstract":"\u0000Multiple recent observations in the mesosphere have revealed large-scale Kelvin-Helmholtz instabilities (KHI) exhibiting diverse spatial features and temporal evolutions. The first event reported by Hecht et al. (2021) exhibited multiple features resembling those seen to arise in early laboratory shear-flow studies described as “Tube” and “Knot” (T&K) dynamics by Thorpe (1985, 1987). The potential importance of T&K dynamics in the atmosphere, and in the oceans and other stratified and sheared fluids, is due to their accelerated turbulence transitions and elevated energy dissipation rates relative to KHI turbulence transitions occurring in their absence. Motivated by these studies, we survey recent observational evidence of multi-scale Kelvin-Helmholtz instabilities throughout the atmosphere, many features of which closely resemble T&K dynamics observed in the laboratory and idealized initial modeling. These efforts will guide further modeling assessing the potential importance of these T&K dynamics in turbulence generation, energy dissipation, and mixing throughout the atmosphere and other fluids. We expect these dynamics to have implications for parameterizing mixing and transport in stratified shear flows in the atmosphere and oceans that have not been considered to date. Companion papers describe results of a multi-scale gravity wave direct numerical simulation (DNS) that serendipitously exhibits a number of KHI T&K events and an idealized multi-scale DNS of KHI T&K dynamics without gravity wave influences.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2023-05-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42847349","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}
Recently we presented a classification of ‘primitive’ relative humidity (RH) profiles into 8 distinct clusters over Earth’s oceans, based on about 18 years (2003-2020) of observations from the AIRS on NASA’s Aqua satellite. Here we investigate the seasonal variability and decadal trends, both in the vertical structure of these profiles, and in their associated area of occurrence. Since vertical structures (except in the marine boundary layer) of each RH-class are generally robust across all seasons and change only weakly in a warming climate, seasonal or decadal changes to their occurrence areas shift patterns of global moisture distribution. Globally, the marine boundary layer exhibits non-linear moistening effects after about 2010, the end of thewarming hiatus. Annual timeseries of ocean areas dominated by RH-classes have linear trends, which are positive only for the most moist and driest RH-classes (in terms of the free troposphere) associated with deep convection and large-scale subsidence favouring conditions for low-level stratocumulus clouds, respectively. Based on estimated linear trends of RH-class occurrences and sea-surface temperatures, we infer projected linear responses of RH in a warming climate. Ocean areas dominated by most moist and driest RH-classes (in terms of the free atmosphere) are estimated to increase by about 1 and 2 %, respectively (corresponding to about 2.5%K−1 and 4.5%K−1, respectively). The averaged global and tropical RH-structure remain almost constant in a warming climate. While this is consistent with other studies, our results show how increases in most moist and dry areas compensate each other, indicating possible increases in the frequency or persistence of future extreme events.
{"title":"Changes in relative humidity profiles over Earth’s oceans in a warming climate: a satellite data based inference","authors":"Carsten Abraham, C. Goldblatt","doi":"10.1175/jas-d-22-0119.1","DOIUrl":"https://doi.org/10.1175/jas-d-22-0119.1","url":null,"abstract":"\u0000Recently we presented a classification of ‘primitive’ relative humidity (RH) profiles into 8 distinct clusters over Earth’s oceans, based on about 18 years (2003-2020) of observations from the AIRS on NASA’s Aqua satellite. Here we investigate the seasonal variability and decadal trends, both in the vertical structure of these profiles, and in their associated area of occurrence. Since vertical structures (except in the marine boundary layer) of each RH-class are generally robust across all seasons and change only weakly in a warming climate, seasonal or decadal changes to their occurrence areas shift patterns of global moisture distribution. Globally, the marine boundary layer exhibits non-linear moistening effects after about 2010, the end of thewarming hiatus. Annual timeseries of ocean areas dominated by RH-classes have linear trends, which are positive only for the most moist and driest RH-classes (in terms of the free troposphere) associated with deep convection and large-scale subsidence favouring conditions for low-level stratocumulus clouds, respectively. Based on estimated linear trends of RH-class occurrences and sea-surface temperatures, we infer projected linear responses of RH in a warming climate. Ocean areas dominated by most moist and driest RH-classes (in terms of the free atmosphere) are estimated to increase by about 1 and 2 %, respectively (corresponding to about 2.5%K−1 and 4.5%K−1, respectively). The averaged global and tropical RH-structure remain almost constant in a warming climate. While this is consistent with other studies, our results show how increases in most moist and dry areas compensate each other, indicating possible increases in the frequency or persistence of future extreme events.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2023-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43917553","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}
The semiannual oscillation (SAO) in zonally averaged zonal winds develops just above the quasi-biennial oscillation (QBO) and dominates the seasonal variability in the tropical upper stratosphere and lower mesosphere. The magnitude, seasonality, and latitudinal structure of the SAO vary with the phase of the QBO. There is also an annual oscillation (AO) whose magnitude at the equator is smaller than those of the SAO and QBO but not negligible. This work presents the relation between the SAO, QBO, AO, and time-mean wind in the tropical upper stratosphere and lower mesosphere using winds derived from satellite geopotential height observations. The winds are generally more westerly during the easterly phase of the QBO. The SAO extends to lower altitudes during periods where the QBO is characterized by deep easterly winds. The differences in the SAO associated with the QBO are roughly confined to the latitudes where the QBO has appreciable amplitude, suggesting that the mechanism is controlled by vertical coupling. The westerly phases of the SAO and AO show downward propagation with time. This analysis suggests that forcing by dissipation of waves with westerly momentum is responsible for the westerly acceleration of both the SAO and AO. The timing and structure of the easterly phases of the SAO and AO near the stratopause are consistent with the response to meridional advection of momentum across the equator during solstices; it is not apparent that local wave processes play important roles in the easterly phases in the region of the stratopause.
{"title":"Evidence for the influence of the quasi-biennial oscillation on the semiannual oscillation in the tropical middle atmosphere","authors":"Anne K. Smith, L. Gray, R. Garcia","doi":"10.1175/jas-d-22-0255.1","DOIUrl":"https://doi.org/10.1175/jas-d-22-0255.1","url":null,"abstract":"\u0000The semiannual oscillation (SAO) in zonally averaged zonal winds develops just above the quasi-biennial oscillation (QBO) and dominates the seasonal variability in the tropical upper stratosphere and lower mesosphere. The magnitude, seasonality, and latitudinal structure of the SAO vary with the phase of the QBO. There is also an annual oscillation (AO) whose magnitude at the equator is smaller than those of the SAO and QBO but not negligible. This work presents the relation between the SAO, QBO, AO, and time-mean wind in the tropical upper stratosphere and lower mesosphere using winds derived from satellite geopotential height observations. The winds are generally more westerly during the easterly phase of the QBO. The SAO extends to lower altitudes during periods where the QBO is characterized by deep easterly winds. The differences in the SAO associated with the QBO are roughly confined to the latitudes where the QBO has appreciable amplitude, suggesting that the mechanism is controlled by vertical coupling. The westerly phases of the SAO and AO show downward propagation with time. This analysis suggests that forcing by dissipation of waves with westerly momentum is responsible for the westerly acceleration of both the SAO and AO. The timing and structure of the easterly phases of the SAO and AO near the stratopause are consistent with the response to meridional advection of momentum across the equator during solstices; it is not apparent that local wave processes play important roles in the easterly phases in the region of the stratopause.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2023-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46042182","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}
The effects of longwave radiation on tropical cyclone intensification, with an emphasis on the mature stage, are explored in an idealized modeling framework. Results show that although the cloud-radiative effect aids in early intensification of the vortex, it does not promote increase in the maximum tangential wind (Vmax) and could even reduce Vmax at the mature stage. At later stages, maximum radiative heating is located outside the eyewall and promotes convection there, and the secondary circulation encourages convergence of absolute angular momentum outside the eyewall instead of near the eyewall region, based on a budget analysis. Clear-sky radiative cooling helps invigorate domain-wide convection, also limiting the Vmax increase at later stages. The area-averaged frozen moist static energy (FMSE) variance increases even though Vmax decreases. In this sense, the FMSE variance is similar to the monotonically-growing integrated kinetic energy, and is more indicative of the system-scale strength than of Vmax. Sensitivity experiments are performed with random initial perturbations and varied initial soundings. An axisymmetric model with a 10-member ensemble not only confirms the results from three-dimensional simulations, but also demonstrates that the weak radiative heating outside the eyewall is indeed able to slow down Vmax within one day.
{"title":"Longwave radiative effects beyond the initial intensification phase of tropical cyclones","authors":"Yi Dai, M. Torn, I. N. Williams, W. Collins","doi":"10.1175/jas-d-22-0214.1","DOIUrl":"https://doi.org/10.1175/jas-d-22-0214.1","url":null,"abstract":"\u0000The effects of longwave radiation on tropical cyclone intensification, with an emphasis on the mature stage, are explored in an idealized modeling framework. Results show that although the cloud-radiative effect aids in early intensification of the vortex, it does not promote increase in the maximum tangential wind (Vmax) and could even reduce Vmax at the mature stage. At later stages, maximum radiative heating is located outside the eyewall and promotes convection there, and the secondary circulation encourages convergence of absolute angular momentum outside the eyewall instead of near the eyewall region, based on a budget analysis. Clear-sky radiative cooling helps invigorate domain-wide convection, also limiting the Vmax increase at later stages. The area-averaged frozen moist static energy (FMSE) variance increases even though Vmax decreases. In this sense, the FMSE variance is similar to the monotonically-growing integrated kinetic energy, and is more indicative of the system-scale strength than of Vmax. Sensitivity experiments are performed with random initial perturbations and varied initial soundings. An axisymmetric model with a 10-member ensemble not only confirms the results from three-dimensional simulations, but also demonstrates that the weak radiative heating outside the eyewall is indeed able to slow down Vmax within one day.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2023-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42181267","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}
Climate models and observations robustly agree that Earth’s clear-sky longwave feedback has a value of about -2 W m−2 K−1, suggesting that this feedback can be estimated from first principles. In this study, we derive an analytic model for Earth’s clear-sky longwave feedback. Our approach uses a novel spectral decomposition that splits the feedback into four components: a surface Planck feedback, and three atmospheric feedbacks from CO2, H2O, and the H2O continuum. We obtain analytic expressions for each of these terms, and the model can also be framed in terms of Simpson’s Law and deviations therefrom. We validate the model by comparing it against line-by-line radiative transfer calculations across a wide range of climates. Additionally, the model qualitatively matches the spatial feedback maps of a comprehensive climate model. For present-day Earth, our analysis shows that the clear-sky longwave feedback is dominated by the surface in the global mean and in the dry subtropics; meanwhile, atmospheric feedbacks from CO2 and H2O become important in the inner tropics. Together, these results show that a spectral view of Earth’s clear-sky longwave feedback elucidates not only its global-mean magnitude, but also its spatial pattern and its state-dependence across past and future climates.
气候模型和观测结果一致认为，地球晴朗的天空长波反馈值约为-2 W m−2 K−1，这表明这种反馈可以根据第一性原理进行估计。在这项研究中，我们推导了地球晴朗天空长波反馈的分析模型。我们的方法使用了一种新的光谱分解，将反馈分为四个部分：表面普朗克反馈，以及来自CO2、H2O和H2O连续体的三个大气反馈。我们得到了这些项中每一项的解析表达式，并且该模型也可以根据辛普森定律及其偏差来构建。我们通过将该模型与各种气候下的逐行辐射传输计算进行比较来验证该模型。此外，该模型在质量上与综合气候模型的空间反馈图相匹配。对于今天的地球，我们的分析表明，在全球平均值和干燥的亚热带，晴朗的天空长波反馈由地表主导；与此同时，来自CO2和H2O的大气反馈在热带内陆地区变得重要。总之，这些结果表明，地球晴朗天空长波反馈的光谱视图不仅阐明了其全球平均星等，还阐明了其空间模式及其在过去和未来气候中的状态依赖性。
{"title":"An Analytic Model for the Clear-Sky Longwave Feedback","authors":"D. Koll, N. Jeevanjee, N. Lutsko","doi":"10.1175/jas-d-22-0178.1","DOIUrl":"https://doi.org/10.1175/jas-d-22-0178.1","url":null,"abstract":"Climate models and observations robustly agree that Earth’s clear-sky longwave feedback has a value of about -2 W m−2 K−1, suggesting that this feedback can be estimated from first principles. In this study, we derive an analytic model for Earth’s clear-sky longwave feedback. Our approach uses a novel spectral decomposition that splits the feedback into four components: a surface Planck feedback, and three atmospheric feedbacks from CO2, H2O, and the H2O continuum. We obtain analytic expressions for each of these terms, and the model can also be framed in terms of Simpson’s Law and deviations therefrom. We validate the model by comparing it against line-by-line radiative transfer calculations across a wide range of climates. Additionally, the model qualitatively matches the spatial feedback maps of a comprehensive climate model. For present-day Earth, our analysis shows that the clear-sky longwave feedback is dominated by the surface in the global mean and in the dry subtropics; meanwhile, atmospheric feedbacks from CO2 and H2O become important in the inner tropics. Together, these results show that a spectral view of Earth’s clear-sky longwave feedback elucidates not only its global-mean magnitude, but also its spatial pattern and its state-dependence across past and future climates.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2023-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45920422","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}
The 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.
{"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}
Recently, 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.
{"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}
Based 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.
{"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}
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