Peter Brechner, G. McFarquhar, A. Schwarzenboeck, A. Korolev
Total ice water content (IWC) derived from an isokinetic evaporator probe and ice crystal particle size distributions (PSDs) measured by a two-dimensional stereo probe and precipitation imaging probe installed on an aircraft during the 2014 European High Altitude Ice Crystals – North American High IWC field campaign (HAIC/HIWC) were used to characterize regions of high IWC consisting mainly of small ice crystals (HIWC_S) with IWC ≥ 1.0 g m−3 and median mass diameter (MMD) < 0.5 mm. A novel fitting routine developed to automatically determine whether a unimodal, bimodal, or trimodal gamma distribution best fits a PSD was used to compare characteristics of HIWC_S and other PSDs (e.g., multimodality, gamma fit parameters, etc.) for HIWC_S simulations. The variation of these characteristics and bulk properties (MMD, IWC) was regressed with temperature, IWC, and vertical velocity. HIWC_S regions were most pronounced in updraft cores. The three modes of the PSD reveal different dominant processes contributing to ice growth: nucleation for maximum dimension D < 0.15 mm, diffusion for 0.15 mm < D < 1.0 mm, and aggregation for D > 1.0 mm. The frequency of trimodal distributions increased with temperature. The volumes of equally plausible parameters derived in the phase space of gamma fit parameters increased with temperature for unimodal distributions and, for temperatures less than −27°C, for multimodal distributions. Bimodal distributions with 0.4 mm in the larger mode were most common in updraft cores and HIWC_S regions; bimodal distributions with 0.4 mm in the smaller mode were least common in convective cores.
在2014年欧洲高海拔冰晶-北美高IWC野外活动(HAIC/HIWC)期间，采用等温蒸发器探头测量的总冰水含量(IWC)和安装在飞机上的二维立体探头和降水成像探头测量的冰晶粒度分布(PSDs)来表征高IWC主要由小冰晶(HIWC_S)组成的区域，其中IWC≥1.0 g m−3，中位质量直径(MMD) < 0.5 mm。开发了一种新的拟合程序，用于自动确定单峰、双峰或三峰伽马分布是否最适合PSD，以比较HIWC_S和其他PSD的特征(例如，HIWC_S模拟的多峰、伽马拟合参数等)。这些特征和体积性质(MMD, IWC)随温度、IWC和垂直速度的变化进行了回归。HIWC_S区域在上升气流核中最为明显。PSD的三种模式揭示了促进冰生长的不同主导过程:最大尺寸D < 0.15 mm时成核，0.15 mm < D < 1.0 mm时扩散，D > 1.0 mm时聚集。三峰分布的频率随温度升高而增加。对于单峰分布，在伽马拟合参数的相空间中导出的同样似是而非的参数体积随着温度的升高而增加，对于温度低于- 27°C的多峰分布，同样似是而非的参数体积随着温度的升高而增加。0.4 mm的大模态双峰分布在上升岩心和HIWC_S区域最为常见;较小模态0.4 mm的双峰分布在对流核中最不常见。
{"title":"Ice Crystal Size Distributions in Tropical Mesoscale Convective Systems in the Vicinity of Darwin, Australia: Results from the HAIC/HIWC Campaign","authors":"Peter Brechner, G. McFarquhar, A. Schwarzenboeck, A. Korolev","doi":"10.1175/jas-d-22-0209.1","DOIUrl":"https://doi.org/10.1175/jas-d-22-0209.1","url":null,"abstract":"Total ice water content (IWC) derived from an isokinetic evaporator probe and ice crystal particle size distributions (PSDs) measured by a two-dimensional stereo probe and precipitation imaging probe installed on an aircraft during the 2014 European High Altitude Ice Crystals – North American High IWC field campaign (HAIC/HIWC) were used to characterize regions of high IWC consisting mainly of small ice crystals (HIWC_S) with IWC ≥ 1.0 g m−3 and median mass diameter (MMD) < 0.5 mm. A novel fitting routine developed to automatically determine whether a unimodal, bimodal, or trimodal gamma distribution best fits a PSD was used to compare characteristics of HIWC_S and other PSDs (e.g., multimodality, gamma fit parameters, etc.) for HIWC_S simulations. The variation of these characteristics and bulk properties (MMD, IWC) was regressed with temperature, IWC, and vertical velocity. HIWC_S regions were most pronounced in updraft cores. The three modes of the PSD reveal different dominant processes contributing to ice growth: nucleation for maximum dimension D < 0.15 mm, diffusion for 0.15 mm < D < 1.0 mm, and aggregation for D > 1.0 mm. The frequency of trimodal distributions increased with temperature. The volumes of equally plausible parameters derived in the phase space of gamma fit parameters increased with temperature for unimodal distributions and, for temperatures less than −27°C, for multimodal distributions. Bimodal distributions with 0.4 mm in the larger mode were most common in updraft cores and HIWC_S regions; bimodal distributions with 0.4 mm in the smaller mode were least common in convective cores.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2023-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42456687","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 slope of the quasi-linear relation between planetary outgoing longwave radiation (OLR) and surface temperature (TS) is an important parameter measuring the sensitivity of the Earth’s climate system. The primary objective of this study is to seek a general explanation for the quasi-linear OLR-TS relation that remains valid regardless of the strength of the atmospheric window’s narrowing effect on planetary thermal emission at higher temperatures. The physical understanding of the quasi-linear OLR-TS relation and its slope is gained from observation analysis, climate simulations with radiative-convective equilibrium and general circulation models, and a series of online feedback suppression experiments. The observed quasi-linear OLR-TS relation manifests a climate footprint of radiative (such as the greenhouse effect) and non-radiative processes (poleward energy transport). The former acts to increase the meridional gradient of surface temperature and the latter decreases the meridional gradient of atmospheric temperatures, causing the flattening of the meridional profile of the OLR. Radiative processes alone can lead to a quasi-linear OLR-TS relation that is more steeply sloped. The atmospheric poleward energy transport alone can also lead to a quasi-linear OLR-TS relation by rerouting part of the OLR to be emitted from a warmer place to a colder place. The combined effects of radiative and non-radiative processes make the quasi-linear OLR-TS relation less sloped with a higher degree of linearity. In response to anthropogenic radiative forcing, the slope of the quasi-linear OLR-TS relation is further reduced via stronger water vapor feedback and enhanced poleward energy transport.
{"title":"The quasi-linear relation between planetary outgoing longwave radiation and surface temperature: a climate footprint of radiative and non-radiative processes","authors":"M. Cai, Jie Sun, F. Ding, W. Kang, Xiaoming Hu","doi":"10.1175/jas-d-22-0261.1","DOIUrl":"https://doi.org/10.1175/jas-d-22-0261.1","url":null,"abstract":"\u0000The slope of the quasi-linear relation between planetary outgoing longwave radiation (OLR) and surface temperature (TS) is an important parameter measuring the sensitivity of the Earth’s climate system. The primary objective of this study is to seek a general explanation for the quasi-linear OLR-TS relation that remains valid regardless of the strength of the atmospheric window’s narrowing effect on planetary thermal emission at higher temperatures. The physical understanding of the quasi-linear OLR-TS relation and its slope is gained from observation analysis, climate simulations with radiative-convective equilibrium and general circulation models, and a series of online feedback suppression experiments.\u0000The observed quasi-linear OLR-TS relation manifests a climate footprint of radiative (such as the greenhouse effect) and non-radiative processes (poleward energy transport). The former acts to increase the meridional gradient of surface temperature and the latter decreases the meridional gradient of atmospheric temperatures, causing the flattening of the meridional profile of the OLR. Radiative processes alone can lead to a quasi-linear OLR-TS relation that is more steeply sloped. The atmospheric poleward energy transport alone can also lead to a quasi-linear OLR-TS relation by rerouting part of the OLR to be emitted from a warmer place to a colder place. The combined effects of radiative and non-radiative processes make the quasi-linear OLR-TS relation less sloped with a higher degree of linearity. In response to anthropogenic radiative forcing, the slope of the quasi-linear OLR-TS relation is further reduced via stronger water vapor feedback and enhanced poleward energy transport.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2023-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42830994","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}
This study aimed to reveal the seasonal climatic variations in the microphysical properties of precipitation over the Asian monsoon region. We used the Dual-frequency Precipitation Radar satellite product aboard the Global Precipitation Measurement Mission Core Observatory for eight years from 2014 to 2021 to statistically analyze the mass-weighted mean diameter (Dm) and frequency of heavy ice precipitation (graupel and hail). The results showed statistically significant seasonal changes. The microphysical characteristics of large Dm and frequent heavy ice precipitation were observed over the Indian subcontinent and Indochina Peninsula in the pre-monsoon season and over the western Himalayan region in the mature-monsoon season, which can be related to the intense and deeply developed precipitation systems. The relationship between precipitation rate and Dm was also examined. The results indicated that changes in Dm were not caused only by changes in precipitation rate but were probably induced by changes in precipitation characteristics. In terms of the relationship between the microphysical properties, heavy ice precipitation particles in the upper atmosphere above the melting layer were observed more frequently as Dm near the surface increased. We also studied lower atmospheric instability by investigating the vertical gradients of the dry and moist static energies. The results indicated that instability properties were different; dry and wet instabilities were dominant in the pre-monsoon and monsoon seasons, respectively, consistent with the results of the precipitation characteristics.
{"title":"Seasonal differences of precipitation and microphysical characteristics over the Asian monsoon region using spaceborne dual-frequency precipitation radar","authors":"Moeka Yamaji, H. Takahashi","doi":"10.1175/jas-d-22-0198.1","DOIUrl":"https://doi.org/10.1175/jas-d-22-0198.1","url":null,"abstract":"\u0000This study aimed to reveal the seasonal climatic variations in the microphysical properties of precipitation over the Asian monsoon region. We used the Dual-frequency Precipitation Radar satellite product aboard the Global Precipitation Measurement Mission Core Observatory for eight years from 2014 to 2021 to statistically analyze the mass-weighted mean diameter (Dm) and frequency of heavy ice precipitation (graupel and hail). The results showed statistically significant seasonal changes. The microphysical characteristics of large Dm and frequent heavy ice precipitation were observed over the Indian subcontinent and Indochina Peninsula in the pre-monsoon season and over the western Himalayan region in the mature-monsoon season, which can be related to the intense and deeply developed precipitation systems. The relationship between precipitation rate and Dm was also examined. The results indicated that changes in Dm were not caused only by changes in precipitation rate but were probably induced by changes in precipitation characteristics. In terms of the relationship between the microphysical properties, heavy ice precipitation particles in the upper atmosphere above the melting layer were observed more frequently as Dm near the surface increased. We also studied lower atmospheric instability by investigating the vertical gradients of the dry and moist static energies. The results indicated that instability properties were different; dry and wet instabilities were dominant in the pre-monsoon and monsoon seasons, respectively, consistent with the results of the precipitation characteristics.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2023-06-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43195952","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}
A companion paper by Fritts et al. (2023a) reviews evidence for Kelvin-Helmholtz instability (KHI) “tube” and “knot” (T&K) dynamics that appear to be widespread throughout the atmosphere. Here we describe the results of an idealized direct numerical simulation of multi-scale gravity wave dynamics that reveals multiple larger- and smaller-scale KHI T&K events. The results enable assessments of the environments in which these dynamics arise and their competition with concurrent gravity wave breaking in driving turbulence and energy dissipation. A larger-scale event is diagnosed in detail and reveals diverse and intense T&K dynamics driving more intense turbulence than occurs due to gravity wave breaking in the same environment. Smaller-scale events reveal that KHI T&K dynamics readily extend to weaker, smaller-scale, and increasingly viscous shear flows. Our results suggest that KHI T&K dynamics should be widespread, perhaps ubiquitous, wherever superposed gravity waves induce intensifying shear layers, because such layers are virtually always present. A second companion paper (Fritts et al. 2023b) demonstrates that KHI T&K dynamics exhibit elevated turbulence generation and energy dissipation rates extending to smaller Reynolds numbers for relevant KHI scales wherever they arise. These dynamics are suggested to be significant sources of turbulence and mixing throughout the atmosphere that are currently ignored or under-represented in turbulence parameterizations in regional and global models.
Fritts等人(2023a)的一篇同伴论文回顾了开尔文-亥姆霍兹不稳定性(KHI)“管”和“结”(T&K)动力学在整个大气中普遍存在的证据。在这里，我们描述了多尺度重力波动力学的理想直接数值模拟结果，揭示了多个较大和较小尺度的KHI T&K事件。这些结果能够评估这些动力学产生的环境，以及它们与同步重力波破裂在驱动湍流和能量耗散方面的竞争。详细诊断了一个更大规模的事件，并揭示了在相同环境下由于重力波破裂而产生的更强烈的湍流的多样化和强烈的T&K动力学。较小尺度的事件表明，KHI T&K动力学很容易扩展到更弱、更小尺度和越来越粘滞的剪切流动。我们的研究结果表明，KHI - T&K动力学应该是广泛的，也许是无处不在的，只要叠加的重力波引起增强的剪切层，因为这样的层实际上总是存在的。第二篇论文(Fritts et al. 2023b)表明，KHI T&K动力学表现出更高的湍流产生和能量耗散率，在相关KHI尺度上，无论它们出现在哪里，都可以扩展到更小的雷诺数。这些动力被认为是整个大气湍流和混合的重要来源，目前在区域和全球模式的湍流参数化中被忽略或代表性不足。
{"title":"Kelvin Helmholtz Instability “Tube” and “Knot” Dynamics, Part II: KHI T&K Dynamics in a Multi-Scale Gravity Wave Direct Numerical Simulation","authors":"D. Fritts, Ling Wang","doi":"10.1175/jas-d-22-0193.1","DOIUrl":"https://doi.org/10.1175/jas-d-22-0193.1","url":null,"abstract":"\u0000A companion paper by Fritts et al. (2023a) reviews evidence for Kelvin-Helmholtz instability (KHI) “tube” and “knot” (T&K) dynamics that appear to be widespread throughout the atmosphere. Here we describe the results of an idealized direct numerical simulation of multi-scale gravity wave dynamics that reveals multiple larger- and smaller-scale KHI T&K events. The results enable assessments of the environments in which these dynamics arise and their competition with concurrent gravity wave breaking in driving turbulence and energy dissipation. A larger-scale event is diagnosed in detail and reveals diverse and intense T&K dynamics driving more intense turbulence than occurs due to gravity wave breaking in the same environment. Smaller-scale events reveal that KHI T&K dynamics readily extend to weaker, smaller-scale, and increasingly viscous shear flows. Our results suggest that KHI T&K dynamics should be widespread, perhaps ubiquitous, wherever superposed gravity waves induce intensifying shear layers, because such layers are virtually always present. A second companion paper (Fritts et al. 2023b) demonstrates that KHI T&K dynamics exhibit elevated turbulence generation and energy dissipation rates extending to smaller Reynolds numbers for relevant KHI scales wherever they arise. These dynamics are suggested to be significant sources of turbulence and mixing throughout the atmosphere that are currently ignored or under-represented in turbulence parameterizations in regional and global models.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2023-06-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48676524","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 transition layer in the trades has long been observed and simulated, but the physical processes producing its structure remain little investigated. Using extensive observations from the Elucidating the Role of Clouds–Circulation Coupling in Climate (EUREC4A) field campaign, we propose a new conceptual picture of the trade wind transition layer, occurring between the mixed-layer top (around 550 m) and subcloud-layer top (around 700 m). The theory of cloud-free convective boundary layers suggests a transition-layer structure with strong jumps at the mixed-layer top, yet such strong jumps are only observed rarely. Despite cloud-base cloud fraction measured as only 5.3% ± 3.2%, the canonical cloud-free convective boundary layer structure is infrequent and confined to large [O(200) km] cloud-free areas. We show that the majority of cloud bases form within the transition layer, instead of above it, and that the cloud-top height distribution is bimodal, with a first population of very shallow clouds (tops below 1.3 km) and a second population of deeper clouds (extending to 2–3 km depth). We then show that the life cycle of this first cloud population maintains the transition-layer structure. That is, very shallow clouds smooth vertical thermodynamic gradients in the transition layer by a condensation–evaporation mechanism, which is fully coupled to the mixed layer. Inferences from mixed-layer theory and mixing diagrams, moreover, suggest that the observed transition-layer structure does not affect the rate of entrainment mixing, but rather the properties of the air incorporated into the mixed layer, primarily to enhance its rate of moistening. The physical processes producing the structure of the trade wind transition layer, a thin atmospheric layer thought to be important for regulating convection, are not yet well understood. Using extensive observations from a recent field campaign, we find that the cloud-free convective boundary layer structure, with an abrupt discontinuity in thermodynamic variables, is infrequent, despite cloud-base cloud fraction being small. We show that very shallow clouds both forming and dissipating within the transition layer smooth vertical gradients compared to a jump, except in large [O(200) km] cloud-free areas. This condensation–evaporation mechanism, which is fully coupled to the mixed layer, does not appear to affect the rate of entrainment mixing, but rather the properties of air incorporated into the mixed layer.
{"title":"A New Conceptual Picture of the Trade Wind Transition Layer","authors":"Anna Lea Albright, B. Stevens, S. Bony, R. Vogel","doi":"10.1175/jas-d-22-0184.1","DOIUrl":"https://doi.org/10.1175/jas-d-22-0184.1","url":null,"abstract":"\u0000The transition layer in the trades has long been observed and simulated, but the physical processes producing its structure remain little investigated. Using extensive observations from the Elucidating the Role of Clouds–Circulation Coupling in Climate (EUREC4A) field campaign, we propose a new conceptual picture of the trade wind transition layer, occurring between the mixed-layer top (around 550 m) and subcloud-layer top (around 700 m). The theory of cloud-free convective boundary layers suggests a transition-layer structure with strong jumps at the mixed-layer top, yet such strong jumps are only observed rarely. Despite cloud-base cloud fraction measured as only 5.3% ± 3.2%, the canonical cloud-free convective boundary layer structure is infrequent and confined to large [O(200) km] cloud-free areas. We show that the majority of cloud bases form within the transition layer, instead of above it, and that the cloud-top height distribution is bimodal, with a first population of very shallow clouds (tops below 1.3 km) and a second population of deeper clouds (extending to 2–3 km depth). We then show that the life cycle of this first cloud population maintains the transition-layer structure. That is, very shallow clouds smooth vertical thermodynamic gradients in the transition layer by a condensation–evaporation mechanism, which is fully coupled to the mixed layer. Inferences from mixed-layer theory and mixing diagrams, moreover, suggest that the observed transition-layer structure does not affect the rate of entrainment mixing, but rather the properties of the air incorporated into the mixed layer, primarily to enhance its rate of moistening.\u0000\u0000\u0000The physical processes producing the structure of the trade wind transition layer, a thin atmospheric layer thought to be important for regulating convection, are not yet well understood. Using extensive observations from a recent field campaign, we find that the cloud-free convective boundary layer structure, with an abrupt discontinuity in thermodynamic variables, is infrequent, despite cloud-base cloud fraction being small. We show that very shallow clouds both forming and dissipating within the transition layer smooth vertical gradients compared to a jump, except in large [O(200) km] cloud-free areas. This condensation–evaporation mechanism, which is fully coupled to the mixed layer, does not appear to affect the rate of entrainment mixing, but rather the properties of air incorporated into the mixed layer.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2023-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42022230","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}
Jin-De Huang, Ching-Shu Hung, Chien‐Ming Wu, H. Miura
Convective variability is used to diagnose different pathways towards convective self-aggregation (CSA) in radiative-convective equilibrium simulations with two cloud-resolving models, SCALE and VVM. The results show that convection undergoes gradual growth in SCALE and fast transition in VVM, which is associated with different mechanisms between the two models. In SCALE, strong radiative cooling associated with a dry environment drives the circulation from the dry region, and the dry environment results from strong subsidence and insufficient surface flux supply. The circulation driven by the radiative cooling then pushes convection aggregating, which is the dry-radiation pathway. In VVM, CSA develops due to the rapid strengthening of circulation driven by convective systems in the moist region, which is the convection-upscaling pathway. The different pathways of CSA development can be attributed to the upscale process of convective structures identified by the cloud size spectrum. The upscaling of large-size convective systems can enhance circulation from the moist region in VVM. In SCALE, the infrequent appearance of large convective systems is insufficient to generate circulation, as compensating subsidence can occur within the moist region even in the absence of convective systems. This study shows that the convective variabilities between models can lead to different pathways of CSA, and mechanism-denial experiments also support our analyses.
{"title":"Convective Variabilities Leading to Different Pathways of Convective Self-aggregation in Two Cloud-resolving Models","authors":"Jin-De Huang, Ching-Shu Hung, Chien‐Ming Wu, H. Miura","doi":"10.1175/jas-d-22-0250.1","DOIUrl":"https://doi.org/10.1175/jas-d-22-0250.1","url":null,"abstract":"\u0000Convective variability is used to diagnose different pathways towards convective self-aggregation (CSA) in radiative-convective equilibrium simulations with two cloud-resolving models, SCALE and VVM. The results show that convection undergoes gradual growth in SCALE and fast transition in VVM, which is associated with different mechanisms between the two models. In SCALE, strong radiative cooling associated with a dry environment drives the circulation from the dry region, and the dry environment results from strong subsidence and insufficient surface flux supply. The circulation driven by the radiative cooling then pushes convection aggregating, which is the dry-radiation pathway. In VVM, CSA develops due to the rapid strengthening of circulation driven by convective systems in the moist region, which is the convection-upscaling pathway. The different pathways of CSA development can be attributed to the upscale process of convective structures identified by the cloud size spectrum. The upscaling of large-size convective systems can enhance circulation from the moist region in VVM. In SCALE, the infrequent appearance of large convective systems is insufficient to generate circulation, as compensating subsidence can occur within the moist region even in the absence of convective systems. This study shows that the convective variabilities between models can lead to different pathways of CSA, and mechanism-denial experiments also support our analyses.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2023-05-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41958774","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}
Rosa M. Vargas Martes, Ángel F. Adames Corraliza, V. Mayta
The thermodynamic processes associated with convection in Tropical African and Northeastern Pacific Easterly Waves (AEWs and PEWs, respectively) are examined on the basis of Empirical Orthogonal Functions (EOFs) and a plume-buoyancy framework. Linear regression analysis reveals the relationship between temperature, moisture, buoyancy, and precipitation in EWs. Plume buoyancy is found to be highly correlated with rainfall in both AEWs and PEWs, and a near 1:1 relationship is found between a buoyancy-based diagnostic of rainfall and rainfall rates from ERA5. Close inspection of the contribution of moisture and temperature to plume buoyancy reveals that temperature and moisture contribute roughly equally to the buoyancy in AEWs, while moisture dominates the distribution of buoyancy in PEWs. A scale analysis is performed in order to understand the relative amplitudes of temperature and moisture in easterly waves. It is found that the smaller contribution of temperature to the thermodynamics of PEWs relative to AEWs is related to their slower propagation speed, which allows PEWs to more robustly adjust to weak temperature gradient (WTG) balance. The consistency of the buoyancy analysis and the scale analysis indicates that PEWs are moisture modes: waves in which water vapor plays a dominant role in their thermodynamics. AEWs, on the other hand, are mixed waves in which temperature and moisture play similar roles in their thermodynamics.
{"title":"The role of water vapor and temperature in the thermodynamics of Tropical Northeast Pacific and African easterly waves","authors":"Rosa M. Vargas Martes, Ángel F. Adames Corraliza, V. Mayta","doi":"10.1175/jas-d-22-0177.1","DOIUrl":"https://doi.org/10.1175/jas-d-22-0177.1","url":null,"abstract":"\u0000The thermodynamic processes associated with convection in Tropical African and Northeastern Pacific Easterly Waves (AEWs and PEWs, respectively) are examined on the basis of Empirical Orthogonal Functions (EOFs) and a plume-buoyancy framework. Linear regression analysis reveals the relationship between temperature, moisture, buoyancy, and precipitation in EWs. Plume buoyancy is found to be highly correlated with rainfall in both AEWs and PEWs, and a near 1:1 relationship is found between a buoyancy-based diagnostic of rainfall and rainfall rates from ERA5. Close inspection of the contribution of moisture and temperature to plume buoyancy reveals that temperature and moisture contribute roughly equally to the buoyancy in AEWs, while moisture dominates the distribution of buoyancy in PEWs. A scale analysis is performed in order to understand the relative amplitudes of temperature and moisture in easterly waves. It is found that the smaller contribution of temperature to the thermodynamics of PEWs relative to AEWs is related to their slower propagation speed, which allows PEWs to more robustly adjust to weak temperature gradient (WTG) balance. The consistency of the buoyancy analysis and the scale analysis indicates that PEWs are moisture modes: waves in which water vapor plays a dominant role in their thermodynamics. AEWs, on the other hand, are mixed waves in which temperature and moisture play similar roles in their thermodynamics.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2023-05-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42578184","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}
Chibueze N. Oguejiofor, C. Wainwright, Johna E. Rudzin, D. Richter
Predicting the rapid intensification (> 15.0 m s−1 increase in 10m wind speed over 24 hours or less) of tropical cyclones (TC) remains a challenge in the broader context of numerical weather prediction largely due to their multiscale dynamics. Ocean observations show that the size and magnitude of sea surface temperature (SST) anomalies associated with cold wakes and ocean eddies play important roles in TC dynamics. In this study, a combination of spectral and structure function analyses is utilized to generate realistic realizations of multiscale anomalies characteristic of the SST conditions in which Hurricane Irma (2017) underwent rapid intensification (RI). We investigate the impact of the length scale of these SST anomalies and the role of translation speed on the variance in RI onset timing. Length-scale-induced convective asymmetries, in addition to the mean magnitude of SST anomalies beneath the storm eye, are shown to modulate the variance in RI onset timing. The size of the associated SST length scales relative to the storm size is critical to the magnitude of variance in RI onset timing, as smaller length scales are shown to lack the spatial extent required to induce preferential convective asymmetries. Stormtranslation speed is also shown to influence the variance in RI onset timing for larger length scale ensembles by altering the exposure time of the eye to these SST anomalies. We find that an interplay between SST-induced convective asymmetries, the magnitude of SST anomalies underneath the eye/eye-wall, and storm translation speed play crucial roles in modulating the variance in RI onset timing.
{"title":"Onset of Tropical Cyclone Rapid Intensification: Evaluating the response to Length Scales of Sea Surface Temperature Anomalies.","authors":"Chibueze N. Oguejiofor, C. Wainwright, Johna E. Rudzin, D. Richter","doi":"10.1175/jas-d-22-0158.1","DOIUrl":"https://doi.org/10.1175/jas-d-22-0158.1","url":null,"abstract":"\u0000Predicting the rapid intensification (> 15.0 m s−1 increase in 10m wind speed over\u000024 hours or less) of tropical cyclones (TC) remains a challenge in the broader context of numerical\u0000weather prediction largely due to their multiscale dynamics. Ocean observations show that the size\u0000and magnitude of sea surface temperature (SST) anomalies associated with cold wakes and ocean\u0000eddies play important roles in TC dynamics.\u0000In this study, a combination of spectral and structure function analyses is utilized to generate realistic\u0000realizations of multiscale anomalies characteristic of the SST conditions in which Hurricane Irma\u0000(2017) underwent rapid intensification (RI). We investigate the impact of the length scale of these\u0000SST anomalies and the role of translation speed on the variance in RI onset timing.\u0000Length-scale-induced convective asymmetries, in addition to the mean magnitude of SST anomalies\u0000beneath the storm eye, are shown to modulate the variance in RI onset timing. The size of the\u0000associated SST length scales relative to the storm size is critical to the magnitude of variance in\u0000RI onset timing, as smaller length scales are shown to lack the spatial extent required to induce\u0000preferential convective asymmetries. Stormtranslation speed is also shown to influence the variance\u0000in RI onset timing for larger length scale ensembles by altering the exposure time of the eye to\u0000these SST anomalies. We find that an interplay between SST-induced convective asymmetries, the\u0000magnitude of SST anomalies underneath the eye/eye-wall, and storm translation speed play crucial\u0000roles in modulating the variance in RI onset timing.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2023-05-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46746990","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}
Reuben Demirdjian, J. Doyle, Peter M. Finocchio, C. Reynolds
The influence of the surface latent and surface sensible heat flux on the development and interaction of an idealized extratropical cyclone (termed “primary”) with an upstream cyclone (termed “upstream”) using the Navy’s Coupled Ocean-Atmosphere Mesoscale Prediction System (COAMPS) is analyzed. The primary cyclone develops from an initial perturbation to a baroclinically-unstable jet stream, while the upstream cyclone results from Rossby wave dispersion at the surface where a bottom-up style development occurs. The intensity of the upstream cyclone is strongly enhanced by surface latent heat fluxes and, to a lesser degree, by surface sensible heat fluxes. Forward trajectories initiated from the post-frontal sector of the primary cyclone travel south of the upstream anticyclone and feed into the atmospheric river and warm conveyor belt region of the upstream cyclone. Substantial moistening of this airstream is a result of upward surface latent heat flux present in both the primary cyclone’s post-frontal sector and along the southern flank of the anticyclone. Backward trajectories initiated from the same region show that these air parcels originate from a broad area north of both the anticyclone and the primary cyclone in the lower troposphere. The airstream identified represents a new pathway through which dry, descending air that is preconditioned through surface moistening enhances the development of an upstream cyclone through diabatically generated potential vorticity.
{"title":"Preconditioning and Intensification of Upstream Extratropical Cyclones through Surface Fluxes","authors":"Reuben Demirdjian, J. Doyle, Peter M. Finocchio, C. Reynolds","doi":"10.1175/jas-d-22-0251.1","DOIUrl":"https://doi.org/10.1175/jas-d-22-0251.1","url":null,"abstract":"\u0000The influence of the surface latent and surface sensible heat flux on the development and interaction of an idealized extratropical cyclone (termed “primary”) with an upstream cyclone (termed “upstream”) using the Navy’s Coupled Ocean-Atmosphere Mesoscale Prediction System (COAMPS) is analyzed. The primary cyclone develops from an initial perturbation to a baroclinically-unstable jet stream, while the upstream cyclone results from Rossby wave dispersion at the surface where a bottom-up style development occurs. The intensity of the upstream cyclone is strongly enhanced by surface latent heat fluxes and, to a lesser degree, by surface sensible heat fluxes. Forward trajectories initiated from the post-frontal sector of the primary cyclone travel south of the upstream anticyclone and feed into the atmospheric river and warm conveyor belt region of the upstream cyclone. Substantial moistening of this airstream is a result of upward surface latent heat flux present in both the primary cyclone’s post-frontal sector and along the southern flank of the anticyclone. Backward trajectories initiated from the same region show that these air parcels originate from a broad area north of both the anticyclone and the primary cyclone in the lower troposphere. The airstream identified represents a new pathway through which dry, descending air that is preconditioned through surface moistening enhances the development of an upstream cyclone through diabatically generated potential vorticity.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":"1 1","pages":""},"PeriodicalIF":3.1,"publicationDate":"2023-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"64552979","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 typical blockings over the Pacific, Atlantic, and Ural Mountain regions are investigated for an understanding of their dynamical interactions in a unified treatment with their respective basic flows and high-frequency processes, respectively. Thanks to the localized nature of the new methodology as used in this study, for the first time we identify a dipolar structure (for each of the three regions) in the map of the interscale energy transfer from the basic flow to the composite blocking, with a positive center upstream and a negative center downstream. This indicates the crucial role of the instability of the basic flow in the maintenance of blockings, which has been overlooked due to the bulk nature of the spatially integrated energetics (by summing the transfer over the whole blocking, the two centers essentially cancel out, leaving an insignificant bulk transfer). For the interaction between the blocking and the high-frequency storms, the well-known critical role of the upscale forcing in blocking development is confirmed. But, unexpectedly, except for that over the Atlantic where the forcing exists throughout, over the other two regions the forcing is found to occur mainly in downstream. This is quite different from what the classical theory, e.g., the famous eddy strain mechanism of Shutts (1983), would predict.
{"title":"Upstream-downstream asymmetry in multiscale interaction underlying the Northern Hemisphere atmospheric blockings","authors":"Jiwang Ma, X. Liang","doi":"10.1175/jas-d-22-0220.1","DOIUrl":"https://doi.org/10.1175/jas-d-22-0220.1","url":null,"abstract":"\u0000The typical blockings over the Pacific, Atlantic, and Ural Mountain regions are investigated for an understanding of their dynamical interactions in a unified treatment with their respective basic flows and high-frequency processes, respectively. Thanks to the localized nature of the new methodology as used in this study, for the first time we identify a dipolar structure (for each of the three regions) in the map of the interscale energy transfer from the basic flow to the composite blocking, with a positive center upstream and a negative center downstream. This indicates the crucial role of the instability of the basic flow in the maintenance of blockings, which has been overlooked due to the bulk nature of the spatially integrated energetics (by summing the transfer over the whole blocking, the two centers essentially cancel out, leaving an insignificant bulk transfer). For the interaction between the blocking and the high-frequency storms, the well-known critical role of the upscale forcing in blocking development is confirmed. But, unexpectedly, except for that over the Atlantic where the forcing exists throughout, over the other two regions the forcing is found to occur mainly in downstream. This is quite different from what the classical theory, e.g., the famous eddy strain mechanism of Shutts (1983), would predict.","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":"43220647","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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