David H. Marsico, Joseph A. Biello, Matthew R. Igel
Abstract The so-called traditional approximation, wherein the component of the Coriolis force proportional to the cosine of latitude is ignored, is frequently made in order to simplify the equations of atmospheric circulation. For velocity fields whose vertical component is comparable to their horizontal component (such as convective circulations), and in the tropics where the sine of latitude vanishes, the traditional approximation is not justified. We introduce a framework for studying the effect of diabatic heating on circulations in the presence of both traditional and non-traditional terms in the Coriolis force. The framework is intended to describe steady convective circulations on an f-plane in the presence of radiation and momentum damping. We derive a single elliptic equation for the horizontal velocity potential, which is a generalization of the weak temperature Gradient (WTG) approximation. The elliptic operator depends on latitude, radiative damping, and momentum damping coefficients. We show how all other dynamical fields can be diagnosed from this velocity potential; the horizontal velocity induced by the Coriolis force has a particularly simple expression in terms of the velocity potential. Limiting examples occur at the equator, where only the non-traditional terms are present, at the poles, where only the traditional terms appear, and in the absence of radiative damping where the WTG approximation is recovered. We discuss how the framework will be used to construct dynamical, nonlinear convective models, in order to diagnose their consequent upscale momentum and temperature fluxes.
{"title":"Balanced Convective Circulations in a Stratified Atmosphere. Part I: A Framework for Assessing Radiation, the Coriolis Force, and Drag","authors":"David H. Marsico, Joseph A. Biello, Matthew R. Igel","doi":"10.1175/jas-d-22-0254.1","DOIUrl":"https://doi.org/10.1175/jas-d-22-0254.1","url":null,"abstract":"Abstract The so-called traditional approximation, wherein the component of the Coriolis force proportional to the cosine of latitude is ignored, is frequently made in order to simplify the equations of atmospheric circulation. For velocity fields whose vertical component is comparable to their horizontal component (such as convective circulations), and in the tropics where the sine of latitude vanishes, the traditional approximation is not justified. We introduce a framework for studying the effect of diabatic heating on circulations in the presence of both traditional and non-traditional terms in the Coriolis force. The framework is intended to describe steady convective circulations on an f-plane in the presence of radiation and momentum damping. We derive a single elliptic equation for the horizontal velocity potential, which is a generalization of the weak temperature Gradient (WTG) approximation. The elliptic operator depends on latitude, radiative damping, and momentum damping coefficients. We show how all other dynamical fields can be diagnosed from this velocity potential; the horizontal velocity induced by the Coriolis force has a particularly simple expression in terms of the velocity potential. Limiting examples occur at the equator, where only the non-traditional terms are present, at the poles, where only the traditional terms appear, and in the absence of radiative damping where the WTG approximation is recovered. We discuss how the framework will be used to construct dynamical, nonlinear convective models, in order to diagnose their consequent upscale momentum and temperature fluxes.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":"106 2","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135341958","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}
Brandon Wolding, Adam Rydbeck, Juliana Dias, Fiaz Ahmed, Maria Gehne, George Kiladis, Emily M. Riley Dellaripa, Xingchao Chen, Isabel L. McCoy
Abstract An energy budget combining atmospheric moist static energy (MSE) and upper ocean heat content (OHC) is used to examine the processes impacting day-to-day convective variability in the tropical Indian and western Pacific oceans. Feedbacks arising from atmospheric and oceanic transport processes, surface fluxes, and radiation drive the cyclical amplification and decay of convection around suppressed and enhanced convective equilibrium states, referred to as shallow and deep convective discharge-recharge (D-R) cycles respectively. The shallow convective D-R cycle is characterized by alternating enhancements of shallow cumulus and stratocumulus, often in the presence of extensive cirrus clouds. The deep convective D-R cycle is characterized by sequential increases in shallow cumulus, congestus, narrow deep precipitation, wide deep precipitation, a mix of detached anvil and alto-stratus and alto-cumulus, and once again shallow cumulus cloud types. Transitions from the shallow to deep D-R cycle are favored by a positive “column process” feedback, while discharge of convective instability and OHC by mesoscale convective systems (MCSs) contributes to transitions from the deep to shallow D-R cycle. Variability in the processes impacting MSE is comparable in magnitude to, but considerably more balanced than, variability in the processes impacting OHC. Variations in the quantity of atmosphere-ocean coupled static energy (MSE+OHC) result primarily from atmospheric and oceanic transport processes, but are mainly realized as changes in OHC. MCSs are unique in their ability to rapidly discharge both lower tropospheric convective instability and OHC.
{"title":"Atmosphere-Ocean Coupled Energy Budgets of Tropical Convective Discharge-Recharge Cycles","authors":"Brandon Wolding, Adam Rydbeck, Juliana Dias, Fiaz Ahmed, Maria Gehne, George Kiladis, Emily M. Riley Dellaripa, Xingchao Chen, Isabel L. McCoy","doi":"10.1175/jas-d-23-0061.1","DOIUrl":"https://doi.org/10.1175/jas-d-23-0061.1","url":null,"abstract":"Abstract An energy budget combining atmospheric moist static energy (MSE) and upper ocean heat content (OHC) is used to examine the processes impacting day-to-day convective variability in the tropical Indian and western Pacific oceans. Feedbacks arising from atmospheric and oceanic transport processes, surface fluxes, and radiation drive the cyclical amplification and decay of convection around suppressed and enhanced convective equilibrium states, referred to as shallow and deep convective discharge-recharge (D-R) cycles respectively. The shallow convective D-R cycle is characterized by alternating enhancements of shallow cumulus and stratocumulus, often in the presence of extensive cirrus clouds. The deep convective D-R cycle is characterized by sequential increases in shallow cumulus, congestus, narrow deep precipitation, wide deep precipitation, a mix of detached anvil and alto-stratus and alto-cumulus, and once again shallow cumulus cloud types. Transitions from the shallow to deep D-R cycle are favored by a positive “column process” feedback, while discharge of convective instability and OHC by mesoscale convective systems (MCSs) contributes to transitions from the deep to shallow D-R cycle. Variability in the processes impacting MSE is comparable in magnitude to, but considerably more balanced than, variability in the processes impacting OHC. Variations in the quantity of atmosphere-ocean coupled static energy (MSE+OHC) result primarily from atmospheric and oceanic transport processes, but are mainly realized as changes in OHC. MCSs are unique in their ability to rapidly discharge both lower tropospheric convective instability and OHC.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":"8 3","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135973250","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}
Abstract Three-level and thee-layer models of tropical cyclones (TCs) have provided a more conceptual view of TC dynamics than conventional numerical models. They have been purpose-built, with special treatments of boundary layers and/or convection. We show that a further simplification with minimal parameterization and a seamless connection to higher resolution captures TCs about as well. The framework of radiative–convective equilibrium avoids ambiguities from temporal and spatial boundaries. For the TCs, the minimal grid provides one level for outflow and one level for most of the inflow. A version with 10 levels is used for comparison. For the same average pressure intensity, the wind field is slightly broader around the three-level vortices, with stronger subsidence in the core and 25% more mass and moisture flux. However, thermodynamic efficiency, mechanical efficiency, and TC counts are about the same. Across runs with different surface temperatures and cooling rates, global energy scaling makes reasonable predictions of the maximum velocity allowing for variations in the effective forcing/dissipation area and surface humidity. TC count is inconsistent with theories for size as a function of Coriolis parameter. An overturning circuit is isolated within a composite vortex and analyzed using energy and entropy budgets to mirror analytical models. Effective radiation and dissipation temperatures are less extreme than often assumed in such models, yielding a smaller thermodynamic efficiency near the global value of ∼0.1. The pressure deficit arises mostly from inflow enthalpy increase, as expected, but dissipation reduces the contribution from an outflow pressure increase. The influence of ambient CAPE makes up most of the difference.
{"title":"TC Worlds in a Three-Level Model","authors":"Stephen T. Garner","doi":"10.1175/jas-d-22-0089.1","DOIUrl":"https://doi.org/10.1175/jas-d-22-0089.1","url":null,"abstract":"Abstract Three-level and thee-layer models of tropical cyclones (TCs) have provided a more conceptual view of TC dynamics than conventional numerical models. They have been purpose-built, with special treatments of boundary layers and/or convection. We show that a further simplification with minimal parameterization and a seamless connection to higher resolution captures TCs about as well. The framework of radiative–convective equilibrium avoids ambiguities from temporal and spatial boundaries. For the TCs, the minimal grid provides one level for outflow and one level for most of the inflow. A version with 10 levels is used for comparison. For the same average pressure intensity, the wind field is slightly broader around the three-level vortices, with stronger subsidence in the core and 25% more mass and moisture flux. However, thermodynamic efficiency, mechanical efficiency, and TC counts are about the same. Across runs with different surface temperatures and cooling rates, global energy scaling makes reasonable predictions of the maximum velocity allowing for variations in the effective forcing/dissipation area and surface humidity. TC count is inconsistent with theories for size as a function of Coriolis parameter. An overturning circuit is isolated within a composite vortex and analyzed using energy and entropy budgets to mirror analytical models. Effective radiation and dissipation temperatures are less extreme than often assumed in such models, yielding a smaller thermodynamic efficiency near the global value of ∼0.1. The pressure deficit arises mostly from inflow enthalpy increase, as expected, but dissipation reduces the contribution from an outflow pressure increase. The influence of ambient CAPE makes up most of the difference.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":"140 4","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135161004","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}
Abstract Banner clouds are clouds in the lee of steep mountains or sharp ridges on otherwise cloud-free days. Previous studies investigated various aspects of banner cloud formation in numerical simulations, most of which were based on idealized orography and a neutrally stratified ambient atmosphere. The present study extends these simulations in two important directions by 1) examining the impact of various types of orography ranging from an idealized pyramid to the realistic orography of Mount Matterhorn and 2) accounting for an ambient atmosphere that turns from neutral to stably stratified below the mountain summit. Not surprisingly, realistic orography introduces asymmetries in the spanwise direction. At the same time, banner cloud occurrence remains associated with a coherent area of strong uplift, although this region does not have to be located exclusively in the lee of the mountain any longer. In the case of Mount Matterhorn with a westerly ambient flow, a large fraction of air parcels rises along the southern face of the mountain, before they reach the lee and are lifted into the banner cloud. The presence of a shallow boundary layer with its top below the mountain summit introduces more complex behavior compared to a neutrally stratified boundary layer; in particular, it introduces a dependence on wind speed, because strong wind is associated with strong turbulence that is able to raise the boundary layer height and, thus, facilitates the formation of a banner cloud.
{"title":"Sensitivity of Banner Cloud Formation to Orography and the Ambient Atmosphere: Transition From Idealized to More Realistic Scenarios","authors":"Marius Levin Thomas, Volkmar Wirth","doi":"10.1175/jas-d-23-0106.1","DOIUrl":"https://doi.org/10.1175/jas-d-23-0106.1","url":null,"abstract":"Abstract Banner clouds are clouds in the lee of steep mountains or sharp ridges on otherwise cloud-free days. Previous studies investigated various aspects of banner cloud formation in numerical simulations, most of which were based on idealized orography and a neutrally stratified ambient atmosphere. The present study extends these simulations in two important directions by 1) examining the impact of various types of orography ranging from an idealized pyramid to the realistic orography of Mount Matterhorn and 2) accounting for an ambient atmosphere that turns from neutral to stably stratified below the mountain summit. Not surprisingly, realistic orography introduces asymmetries in the spanwise direction. At the same time, banner cloud occurrence remains associated with a coherent area of strong uplift, although this region does not have to be located exclusively in the lee of the mountain any longer. In the case of Mount Matterhorn with a westerly ambient flow, a large fraction of air parcels rises along the southern face of the mountain, before they reach the lee and are lifted into the banner cloud. The presence of a shallow boundary layer with its top below the mountain summit introduces more complex behavior compared to a neutrally stratified boundary layer; in particular, it introduces a dependence on wind speed, because strong wind is associated with strong turbulence that is able to raise the boundary layer height and, thus, facilitates the formation of a banner cloud.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":"6 3","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134995898","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}
Abstract Boundary-layer convergence lines (CLs) are highly effective at deep-convection initiation (DCI), suggesting that their associated updraft properties differ from those of more widespread turbulent updrafts in the planetary boundary layer (PBL). This study exploits observations at the Atmospheric Radiation Measurement Southern Great Plains (ARM-SGP) observatory in Oklahoma from 2011-2016 to quantify CL properties and their relation to turbulent PBL eddies preceding CL arrival. Two independent methods for estimating CL properties are developed at two locations in the SGP region, both relying on the assumption of a 2D circulation in the CL-normal plane but using different combinations of instruments. The first (the radar method) relies mainly on scanning radar data and is applied to 61 CLs passing near a high-resolution scanning radar based in Nardin, OK, while the second (the surface method) relies mainly on surface wind data and is applied to 68 CLs crossing the SGP facility in nearby Lamont, OK. Mean daytime (10:00-19:00 LST) CL width (∼2 km) and convergence magnitude (∼0.003 s−1) are similar for both methods, and mean daytime CL depth is ∼ 0.75 km. The two methods disagree at night (00:00-10:00 LST and 19:00-24:00 LST), where the surface method estimates wider and weaker CLs than the radar method. This difference may stem from the radar beam overshooting the shallow, highly stable nocturnal PBL. The largest CL updrafts are slightly wider (∼ 20%) and stronger (∼ 40%) than the largest PBL updrafts in the pre-CL period, generating 50-100% larger updraft mass fluxes over most of the PBL depth.
{"title":"Observations of boundary-layer convergence lines and associated updrafts in the US Southern Great Plains","authors":"Shanhe Liu, Kapil D. Sindhu, Daniel J. Kirshbaum","doi":"10.1175/jas-d-23-0089.1","DOIUrl":"https://doi.org/10.1175/jas-d-23-0089.1","url":null,"abstract":"Abstract Boundary-layer convergence lines (CLs) are highly effective at deep-convection initiation (DCI), suggesting that their associated updraft properties differ from those of more widespread turbulent updrafts in the planetary boundary layer (PBL). This study exploits observations at the Atmospheric Radiation Measurement Southern Great Plains (ARM-SGP) observatory in Oklahoma from 2011-2016 to quantify CL properties and their relation to turbulent PBL eddies preceding CL arrival. Two independent methods for estimating CL properties are developed at two locations in the SGP region, both relying on the assumption of a 2D circulation in the CL-normal plane but using different combinations of instruments. The first (the radar method) relies mainly on scanning radar data and is applied to 61 CLs passing near a high-resolution scanning radar based in Nardin, OK, while the second (the surface method) relies mainly on surface wind data and is applied to 68 CLs crossing the SGP facility in nearby Lamont, OK. Mean daytime (10:00-19:00 LST) CL width (∼2 km) and convergence magnitude (∼0.003 s−1) are similar for both methods, and mean daytime CL depth is ∼ 0.75 km. The two methods disagree at night (00:00-10:00 LST and 19:00-24:00 LST), where the surface method estimates wider and weaker CLs than the radar method. This difference may stem from the radar beam overshooting the shallow, highly stable nocturnal PBL. The largest CL updrafts are slightly wider (∼ 20%) and stronger (∼ 40%) than the largest PBL updrafts in the pre-CL period, generating 50-100% larger updraft mass fluxes over most of the PBL depth.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":"76 11-12","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135272612","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}
Abstract Accurate prediction of tropical cyclone (TC) intensity is quite challenging due to multiple competing processes among the TC internal dynamics and the environment. Most previous studies have evaluated the environmental effects on TC intensity change from both internal dynamics and external influence. This study quantifies the environmental effects on TC intensity change using a simple dynamically based dynamical system (DBDS) model recently developed. In this simple model, the environmental effects are uniquely represented by a ventilation parameter B , which can be expressed as multiplicative of individual ventilation parameters of the corresponding environmental effects. Their individual ventilation parameters imply their relative importance to the bulk environmental ventilation effect and thus to the TC intensity change. Six environmental factors known to affect TC intensity change are evaluated in the DBDS model using machine learning approaches with the best-track data for TCs over the North Atlantic, central, eastern and western North Pacific and the statistical hurricane intensity prediction scheme (SHIPS) dataset during 1982–2021. Results show that the deep-layer vertical wind shear (VWS) is the dominant ventilation factor to reduce the intrinsic TC intensification rate or to drive the TC weakening, with its ventilation parameter ranging between 0.5–0.8 when environmental VWS between 200 and 850 hPa is larger than 8 m s −1 . Other environmental factors are generally secondary, with their respective ventilation parameters over 0.8. An interesting result is the strong dependence of the environmental effects on the stage of TC development.
摘要由于热带气旋内部动力学和环境的多重竞争过程，对热带气旋强度的准确预报具有很大的挑战性。以往的研究大多从内部动态和外部影响两方面来评价环境对TC强度变化的影响。本研究采用一种简单的基于动态的动态系统(DBDS)模型量化了环境对TC强度变化的影响。在这个简单的模型中，环境效应由一个通风参数B唯一地表示，它可以表示为对应环境效应的各个通风参数的乘积。它们各自的通风参数表明它们对整体环境通风效果的相对重要性，从而对TC强度变化的相对重要性。在DBDS模型中，利用1982-2021年期间北大西洋、北太平洋中部、东部和西部的TC最佳轨迹数据和统计飓风强度预测方案(SHIPS)数据集，利用机器学习方法评估了已知影响TC强度变化的六个环境因素。结果表明:当200 ~ 850 hPa环境风切变大于8 m s−1时，深层垂直风切变(VWS)是降低TC固有增强率或驱动TC减弱的主导通气因子，其通气参数在0.5 ~ 0.8之间;其他环境因素一般是次要的，它们各自的通风参数都在0.8以上。一个有趣的结果是环境影响对TC发展阶段的强烈依赖。
{"title":"Quantifying the environmental effects on tropical cyclone intensity change using a simple dynamically based dynamical system model","authors":"Jing Xu, Yuqing Wang, Chi Yang","doi":"10.1175/jas-d-23-0058.1","DOIUrl":"https://doi.org/10.1175/jas-d-23-0058.1","url":null,"abstract":"Abstract Accurate prediction of tropical cyclone (TC) intensity is quite challenging due to multiple competing processes among the TC internal dynamics and the environment. Most previous studies have evaluated the environmental effects on TC intensity change from both internal dynamics and external influence. This study quantifies the environmental effects on TC intensity change using a simple dynamically based dynamical system (DBDS) model recently developed. In this simple model, the environmental effects are uniquely represented by a ventilation parameter B , which can be expressed as multiplicative of individual ventilation parameters of the corresponding environmental effects. Their individual ventilation parameters imply their relative importance to the bulk environmental ventilation effect and thus to the TC intensity change. Six environmental factors known to affect TC intensity change are evaluated in the DBDS model using machine learning approaches with the best-track data for TCs over the North Atlantic, central, eastern and western North Pacific and the statistical hurricane intensity prediction scheme (SHIPS) dataset during 1982–2021. Results show that the deep-layer vertical wind shear (VWS) is the dominant ventilation factor to reduce the intrinsic TC intensification rate or to drive the TC weakening, with its ventilation parameter ranging between 0.5–0.8 when environmental VWS between 200 and 850 hPa is larger than 8 m s −1 . Other environmental factors are generally secondary, with their respective ventilation parameters over 0.8. An interesting result is the strong dependence of the environmental effects on the stage of TC development.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":"123 20","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135813243","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}
Abstract Tropical cyclone (TC) genesis is initiated by convective precursors or “seeds” and influenced by environmental conditions along the seed-to-TC trajectories. Genesis Potential Indices (GPIs) provide a simple way to evaluate TC genesis likelihood from environmental conditions, but have two limitations that may introduce bias. First, the globally fixed GPIs fail to represent inter-basin differences in the relationship between environments and genesis. Second, existing GPIs are only functions of local environmental conditions, whereas non-local factors may have a significant impact. We address the first limitation by constructing basin- and timescale-specific GPIs ( local-GPI s) over the Eastern North Pacific (ENP) and North Atlantic (NA) using Poisson regression. A sequential feature selection algorithm (SFS) identifies vertical wind shear and a heating condition as leading factors controlling TC genesis in the ENP and the NA, respectively. However, only a slight improvement in performance is achieved, motivating us to tackle the second limitation with a novel trajectory-based GPI ( traj-GPI ). We merge adjacent non-local environments into each grid point based on observed seed trajectory densities. The seed activity, driven mainly by upward motion, and the transition to TCs, controlled primarily by vertical wind shear or heating conditions, are captured simultaneously in the traj-GPI , yielding a better performance than the original GPIs. This study illustrates the importance of seed activity in modeling TC genesis and identifies key environmental factors that influence the process of TC genesis at different stages.
{"title":"Non-local Controls on Tropical Cyclogenesis: A Trajectory-based Genesis Potential Index","authors":"Lingwei Meng, Stephen T. Garner","doi":"10.1175/jas-d-23-0025.1","DOIUrl":"https://doi.org/10.1175/jas-d-23-0025.1","url":null,"abstract":"Abstract Tropical cyclone (TC) genesis is initiated by convective precursors or “seeds” and influenced by environmental conditions along the seed-to-TC trajectories. Genesis Potential Indices (GPIs) provide a simple way to evaluate TC genesis likelihood from environmental conditions, but have two limitations that may introduce bias. First, the globally fixed GPIs fail to represent inter-basin differences in the relationship between environments and genesis. Second, existing GPIs are only functions of local environmental conditions, whereas non-local factors may have a significant impact. We address the first limitation by constructing basin- and timescale-specific GPIs ( local-GPI s) over the Eastern North Pacific (ENP) and North Atlantic (NA) using Poisson regression. A sequential feature selection algorithm (SFS) identifies vertical wind shear and a heating condition as leading factors controlling TC genesis in the ENP and the NA, respectively. However, only a slight improvement in performance is achieved, motivating us to tackle the second limitation with a novel trajectory-based GPI ( traj-GPI ). We merge adjacent non-local environments into each grid point based on observed seed trajectory densities. The seed activity, driven mainly by upward motion, and the transition to TCs, controlled primarily by vertical wind shear or heating conditions, are captured simultaneously in the traj-GPI , yielding a better performance than the original GPIs. This study illustrates the importance of seed activity in modeling TC genesis and identifies key environmental factors that influence the process of TC genesis at different stages.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":"14 10","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135863781","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}
Florian Tornow, Andrew S. Ackerman, Ann M. Fridlind, George Tselioudis, Brian Cairns, David Painemal, Gregory Elsaesser
Abstract Marine cold-air outbreaks (CAOs) occur in the post-frontal sector of midlatitude storms, usually accompanied by dry intrusions (DIs) shaping the free-tropospheric (FT) air aloft. Substantial rain initiates overcast-to-broken regime transitions in marine boundary layer (MBL) cloud decks that form where cold air first meets relatively high sea-surface temperatures. An exemplary CAO in the northwest Atlantic shows earlier transitions (corresponding to reduced extents of overcast clouds) closer to the low-pressure center. We hypothesize that gradients in the meteorological pattern imposed by the prevailing DI induced a variability in substantial rain onset and thereby transition. We compile satellite observations, reanalysis fields, and Lagrangian large-eddy simulations (LES) translating along MBL trajectories to show that postfrontal trajectories closer to the low-pressure center are more favorable to rain formation (and thereby cloud transitions) because of (1) weaker FT subsidence rates, (2) greater FT humidity, (3) stronger MBL winds, and (4) a colder MBL with reduced lower-tropospheric stability. LES confirms the observed variability in transitions, with substantial rain appearing earlier where there is swifter reduction of cloud condensation nucleus (CCN) concentration and increase of liquid water path (LWP). Prior to substantial rain, CCN budgets indicate dominant loss terms from FT entrainment and hydrometeor collisions. LWP-enhancing cloud thickness increases more rapidly for weaker large-scale subsidence that enables faster MBL deepening. Mere MBL warming and moistening cannot explain cloud thickness increases. The generality of such a DI-imposed cloud transition pattern merits further investigation with more cases that may additionally be convoluted by onshore aerosol gradients.
{"title":"On the impact of a dry intrusion driving cloud-regime transitions in a midlatitude cold-air outbreak","authors":"Florian Tornow, Andrew S. Ackerman, Ann M. Fridlind, George Tselioudis, Brian Cairns, David Painemal, Gregory Elsaesser","doi":"10.1175/jas-d-23-0040.1","DOIUrl":"https://doi.org/10.1175/jas-d-23-0040.1","url":null,"abstract":"Abstract Marine cold-air outbreaks (CAOs) occur in the post-frontal sector of midlatitude storms, usually accompanied by dry intrusions (DIs) shaping the free-tropospheric (FT) air aloft. Substantial rain initiates overcast-to-broken regime transitions in marine boundary layer (MBL) cloud decks that form where cold air first meets relatively high sea-surface temperatures. An exemplary CAO in the northwest Atlantic shows earlier transitions (corresponding to reduced extents of overcast clouds) closer to the low-pressure center. We hypothesize that gradients in the meteorological pattern imposed by the prevailing DI induced a variability in substantial rain onset and thereby transition. We compile satellite observations, reanalysis fields, and Lagrangian large-eddy simulations (LES) translating along MBL trajectories to show that postfrontal trajectories closer to the low-pressure center are more favorable to rain formation (and thereby cloud transitions) because of (1) weaker FT subsidence rates, (2) greater FT humidity, (3) stronger MBL winds, and (4) a colder MBL with reduced lower-tropospheric stability. LES confirms the observed variability in transitions, with substantial rain appearing earlier where there is swifter reduction of cloud condensation nucleus (CCN) concentration and increase of liquid water path (LWP). Prior to substantial rain, CCN budgets indicate dominant loss terms from FT entrainment and hydrometeor collisions. LWP-enhancing cloud thickness increases more rapidly for weaker large-scale subsidence that enables faster MBL deepening. Mere MBL warming and moistening cannot explain cloud thickness increases. The generality of such a DI-imposed cloud transition pattern merits further investigation with more cases that may additionally be convoluted by onshore aerosol gradients.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":"4 4","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136318288","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}
Rosimar Rios-Berrios, Peter M. Finocchio, Joshua J. Alland, Xiaomin Chen, Michael S. Fischer, Stephanie N. Stevenson, Dandan Tao
Abstract Tropical cyclone (TC) structure and intensity are strongly modulated by interactions with deep-layer vertical wind shear (VWS)—the vector difference between horizontal winds at 200 and 850 hPa. This paper presents a comprehensive review of more than a century of research on TC-VWS interactions. The literature broadly agrees that a TC vortex becomes vertically tilted, precipitation organizes into a wavenumber-one asymmetric pattern, and thermal and kinematic asymmetries emerge when a TC encounters an environmental sheared flow. However, these responses depend on other factors, including the magnitude and direction of horizontal winds at other vertical levels between 200 and 850 hPa, the amount and location of dry environmental air, and the underlying sea-surface temperature. While early studies investigated how VWS weakens TCs, an emerging line of research has focused on understanding how TCs intensify under moderate and strong VWS (i.e., shear magnitudes greater than 5 m s −1 ). Modeling and observational studies have identified four pathways to intensification: vortex tilt reduction, vortex reformation, axisymmetrization of precipitation, and outflow blocking. These pathways may not be uniquely different because convection and vortex asymmetries are strongly coupled to each other. Besides discussing these topics, this review presents open questions and recommendations for future research on TC-VWS interactions.
热带气旋(TC)的结构和强度受其与深层垂直风切变(VWS)的相互作用的强烈调节，即200和850 hPa水平风的矢量差。本文全面回顾了一个多世纪以来关于TC-VWS相互作用的研究。文献大致同意TC漩涡垂直倾斜，降水组织成波数为1的不对称模式，当TC遇到环境剪切流时，会出现热不对称和运动不对称。然而，这些响应取决于其他因素，包括200至850 hPa之间其他垂直高度的水平风的大小和方向，干燥环境空气的数量和位置，以及海底表面温度。虽然早期的研究调查了VWS如何削弱tc，但新兴的研究重点是了解中度和强VWS(即大于5 m s - 1的剪切震级)下tc如何增强。模拟和观测研究已经确定了四种增强途径:旋涡倾斜减少、旋涡改造、降水轴对称化和流出流阻塞。这些路径可能不是唯一不同的，因为对流和涡旋的不对称是彼此强耦合的。除了讨论这些主题外，本文还对TC-VWS相互作用的未来研究提出了开放性问题和建议。
{"title":"A Review of the Interactions between Tropical Cyclones and Environmental Vertical Wind Shear","authors":"Rosimar Rios-Berrios, Peter M. Finocchio, Joshua J. Alland, Xiaomin Chen, Michael S. Fischer, Stephanie N. Stevenson, Dandan Tao","doi":"10.1175/jas-d-23-0022.1","DOIUrl":"https://doi.org/10.1175/jas-d-23-0022.1","url":null,"abstract":"Abstract Tropical cyclone (TC) structure and intensity are strongly modulated by interactions with deep-layer vertical wind shear (VWS)—the vector difference between horizontal winds at 200 and 850 hPa. This paper presents a comprehensive review of more than a century of research on TC-VWS interactions. The literature broadly agrees that a TC vortex becomes vertically tilted, precipitation organizes into a wavenumber-one asymmetric pattern, and thermal and kinematic asymmetries emerge when a TC encounters an environmental sheared flow. However, these responses depend on other factors, including the magnitude and direction of horizontal winds at other vertical levels between 200 and 850 hPa, the amount and location of dry environmental air, and the underlying sea-surface temperature. While early studies investigated how VWS weakens TCs, an emerging line of research has focused on understanding how TCs intensify under moderate and strong VWS (i.e., shear magnitudes greater than 5 m s −1 ). Modeling and observational studies have identified four pathways to intensification: vortex tilt reduction, vortex reformation, axisymmetrization of precipitation, and outflow blocking. These pathways may not be uniquely different because convection and vortex asymmetries are strongly coupled to each other. Besides discussing these topics, this review presents open questions and recommendations for future research on TC-VWS interactions.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":"87 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136317707","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}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：