S. Freeman, D. Posselt, Jeffrey S. Reid, S. C. van den Heever
We have quantified the impacts of varying thermodynamic environments on tropical congestus and cumulonimbus clouds (CCCs) within maritime tropical regions. To elucidate this relationship, we employed the Regional Atmospheric Modeling System (RAMS) to conduct high-resolution (1km) simulations of convection over the Philippine Archipelago for a month-long period in 2019. We subsequently performed a cloud-object-based analysis, identifying and tracking hundreds of thousands of individual CCCs using the Tracking and Object-Based Analysis of Clouds (tobac) tracking library. Using this object-oriented dataset of tracked cells, we examined differences in individual storm strength, organization, and morphology due to the storm’s initial environment. We found that storm strength, defined here as maximum midlevel updraft velocity, was controlled primarily by Convective Available Potential Energy (CAPE) and Precipitable Water (PW); high CAPE (>2500 J kg−1) and high (approximately 63 mm) PW were both required for midlevel CCC updraft velocities to reach at least 10 m s−1. Of the CCCs with the most vigorous updrafts, 80.9% were also in the upper tercile of precipitation rates, with the strongest precipitation rates requiring even higher PW. Further, we found that vertical wind shear was the primary differentiator between organized and isolated convective storms. Within the set of organized storms, linearly-oriented CCC systems have significantly weaker vertical wind shear than nonlinear CCCs in low- (0–1 km, 0–3 km) and mid-levels (0–5 km, 2–7 km). Overall, these results provide new insights into the environmental conditions determining the CCC properties in maritime tropical regions.
{"title":"Dynamic and Thermodynamic Environmental Modulation of Tropical Congestus and Cumulonimbus in Maritime Tropical Regions","authors":"S. Freeman, D. Posselt, Jeffrey S. Reid, S. C. van den Heever","doi":"10.1175/jas-d-24-0055.1","DOIUrl":"https://doi.org/10.1175/jas-d-24-0055.1","url":null,"abstract":"\u0000We have quantified the impacts of varying thermodynamic environments on tropical congestus and cumulonimbus clouds (CCCs) within maritime tropical regions. To elucidate this relationship, we employed the Regional Atmospheric Modeling System (RAMS) to conduct high-resolution (1km) simulations of convection over the Philippine Archipelago for a month-long period in 2019. We subsequently performed a cloud-object-based analysis, identifying and tracking hundreds of thousands of individual CCCs using the Tracking and Object-Based Analysis of Clouds (tobac) tracking library. Using this object-oriented dataset of tracked cells, we examined differences in individual storm strength, organization, and morphology due to the storm’s initial environment. We found that storm strength, defined here as maximum midlevel updraft velocity, was controlled primarily by Convective Available Potential Energy (CAPE) and Precipitable Water (PW); high CAPE (>2500 J kg−1) and high (approximately 63 mm) PW were both required for midlevel CCC updraft velocities to reach at least 10 m s−1. Of the CCCs with the most vigorous updrafts, 80.9% were also in the upper tercile of precipitation rates, with the strongest precipitation rates requiring even higher PW. Further, we found that vertical wind shear was the primary differentiator between organized and isolated convective storms. Within the set of organized storms, linearly-oriented CCC systems have significantly weaker vertical wind shear than nonlinear CCCs in low- (0–1 km, 0–3 km) and mid-levels (0–5 km, 2–7 km). Overall, these results provide new insights into the environmental conditions determining the CCC properties in maritime tropical regions.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":null,"pages":null},"PeriodicalIF":3.0,"publicationDate":"2024-07-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141800711","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}
Aggregation efficiency in the upper troposphere is highly uncertain because of the lack of laboratory experiments and aircraft measurements, especially at atmospheric temperatures below −30°C. Aggregation is physically broken down into collision and sticking. In this study, theory-based parameterizations for the collision efficiency and sticking efficiency are newly implemented into a double moment bulk cloud microphysics scheme. Satellite observations of the global ice cloud distribution are used to evaluate the aggregation efficiency modeling. Sensitivity experiments of 9-day global simulations using a high-resolution climate model show that the use of collision efficiency parameterization causes a slight increase in the cloud ice amount above the freezing level over the tropics to midlatitudes and that the use of our new sticking efficiency parameterization causes a significant increase in the cloud ice amount and a slight decrease in the snow amount particularly in the upper troposphere over the tropics. The increase/decrease in the cloud ice/snow amount in the upper troposphere over the tropics is consistent with the vertical profile of radar echoes. Moreover, the ice fraction of the cloud optical thickness is still underestimated worldwide. Finally, the cloud radiative forcing increases over the tropics to reduce the bias in the radiation budget. These results indicate that our new aggregation efficiency modeling reasonably functions even at atmospheric temperatures below −30°C; however, further improvements of the ice cloud modeling are needed.
{"title":"Evaluation of the aggregation efficiency modeling at colder atmospheric temperatures in comparison to satellite observations","authors":"Tatsuya Seiki, Takashi M. Nagao","doi":"10.1175/jas-d-23-0208.1","DOIUrl":"https://doi.org/10.1175/jas-d-23-0208.1","url":null,"abstract":"\u0000Aggregation efficiency in the upper troposphere is highly uncertain because of the lack of laboratory experiments and aircraft measurements, especially at atmospheric temperatures below −30°C. Aggregation is physically broken down into collision and sticking. In this study, theory-based parameterizations for the collision efficiency and sticking efficiency are newly implemented into a double moment bulk cloud microphysics scheme. Satellite observations of the global ice cloud distribution are used to evaluate the aggregation efficiency modeling.\u0000Sensitivity experiments of 9-day global simulations using a high-resolution climate model show that the use of collision efficiency parameterization causes a slight increase in the cloud ice amount above the freezing level over the tropics to midlatitudes and that the use of our new sticking efficiency parameterization causes a significant increase in the cloud ice amount and a slight decrease in the snow amount particularly in the upper troposphere over the tropics. The increase/decrease in the cloud ice/snow amount in the upper troposphere over the tropics is consistent with the vertical profile of radar echoes. Moreover, the ice fraction of the cloud optical thickness is still underestimated worldwide. Finally, the cloud radiative forcing increases over the tropics to reduce the bias in the radiation budget. These results indicate that our new aggregation efficiency modeling reasonably functions even at atmospheric temperatures below −30°C; however, further improvements of the ice cloud modeling are needed.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":null,"pages":null},"PeriodicalIF":3.0,"publicationDate":"2024-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141822501","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}
Previous observational studies have indicated that mesoscale convective systems (MCSs) contribute the majority of precipitation over the Bay of Bengal (BoB) during the summer monsoon season, yet their initiation and propagation remain incompletely understood. To fill this knowledge gap, we conducted a comprehensive study using a combination of 20-year satellite observations, MCS tracking, reanalysis data, and a theoretical linear model. Satellite observations reveal clear diurnal propagation signals of MCS initiation frequency and rainfall from the west coast of the BoB toward the central BoB, with the MCS rainfall propagating slightly slower than the MCS initiation frequency. Global reanalysis data indicates a strong association between the offshore-propagating MCS initiation frequency/rainfall and diurnal low-level wind perturbations, implying the potential role of gravity waves. To verify the hypothesis, we developed a 2-D linear model that can be driven by realistic meteorological fields from reanalysis. The linear model realistically reproduces the characteristics of offshore-propagating diurnal wind perturbations. The wind perturbations, as well as the offshore propagation signals of MCS initiation frequency and rainfall, are associated with diurnal gravity waves emitted from the coastal regions, which in turn are caused by the diurnal land-sea thermal contrast. The ambient wind speed and vertical wind shear play crucial roles in modulating the timing, propagation, and amplitude of diurnal gravity waves. Using the linear model and satellite observations, we further show that the stronger monsoonal flows lead to faster offshore propagation of diurnal gravity waves, which subsequently control the offshore propagation signals of MCS initiation and rainfall.
{"title":"Monsoonal MCS Initiation, Rainfall, and Diurnal Gravity Waves over the Bay of Bengal: Observation and a Linear Model","authors":"Chin‐Hsuan Peng, Xingchao Chen","doi":"10.1175/jas-d-23-0230.1","DOIUrl":"https://doi.org/10.1175/jas-d-23-0230.1","url":null,"abstract":"\u0000Previous observational studies have indicated that mesoscale convective systems (MCSs) contribute the majority of precipitation over the Bay of Bengal (BoB) during the summer monsoon season, yet their initiation and propagation remain incompletely understood. To fill this knowledge gap, we conducted a comprehensive study using a combination of 20-year satellite observations, MCS tracking, reanalysis data, and a theoretical linear model. Satellite observations reveal clear diurnal propagation signals of MCS initiation frequency and rainfall from the west coast of the BoB toward the central BoB, with the MCS rainfall propagating slightly slower than the MCS initiation frequency. Global reanalysis data indicates a strong association between the offshore-propagating MCS initiation frequency/rainfall and diurnal low-level wind perturbations, implying the potential role of gravity waves. To verify the hypothesis, we developed a 2-D linear model that can be driven by realistic meteorological fields from reanalysis. The linear model realistically reproduces the characteristics of offshore-propagating diurnal wind perturbations. The wind perturbations, as well as the offshore propagation signals of MCS initiation frequency and rainfall, are associated with diurnal gravity waves emitted from the coastal regions, which in turn are caused by the diurnal land-sea thermal contrast. The ambient wind speed and vertical wind shear play crucial roles in modulating the timing, propagation, and amplitude of diurnal gravity waves. Using the linear model and satellite observations, we further show that the stronger monsoonal flows lead to faster offshore propagation of diurnal gravity waves, which subsequently control the offshore propagation signals of MCS initiation and rainfall.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":null,"pages":null},"PeriodicalIF":3.1,"publicationDate":"2024-06-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141351862","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}
We investigate the mechanism for eye formation in hurricane-like vortices, using a formulation adapted from Oruba et al. (2017). Numerical simulations are performed using an axisymmetric model of dry rotating Rayleigh-Bénard convection under the Boussinesq approximation. The fluxes of heat and momentum at the sea surface are described using the bulk aerodynamic formula. A simplified model for radiative cooling is also implemented. We find that the mechanism for eye formation introduced in Oruba et al. (2017), relying on vorticity stripping from the boundary layer, is robust in dry hurricane-like vortices. Furthermore, with these boundary conditions the structure of the flow is closer to the flow of actual tropical cyclones. The applicability of this mechanism to the moist case however remains uncertain and deserves further study. Finally, energy budgets, obtained either by a heat engine approach, or by a direct estimation of the work of buoyancy forces, are investigated. They provide estimations of the surface wind speed as a function of the controlling parameters.
{"title":"Eye Formation and energetics in a dry model of hurricane-like vortices","authors":"Emmanuel Dormy, L. Oruba, Kerry Emanuel","doi":"10.1175/jas-d-23-0191.1","DOIUrl":"https://doi.org/10.1175/jas-d-23-0191.1","url":null,"abstract":"\u0000We investigate the mechanism for eye formation in hurricane-like vortices, using a formulation adapted from Oruba et al. (2017). Numerical simulations are performed using an axisymmetric model of dry rotating Rayleigh-Bénard convection under the Boussinesq approximation. The fluxes of heat and momentum at the sea surface are described using the bulk aerodynamic formula. A simplified model for radiative cooling is also implemented. We find that the mechanism for eye formation introduced in Oruba et al. (2017), relying on vorticity stripping from the boundary layer, is robust in dry hurricane-like vortices. Furthermore, with these boundary conditions the structure of the flow is closer to the flow of actual tropical cyclones. The applicability of this mechanism to the moist case however remains uncertain and deserves further study. Finally, energy budgets, obtained either by a heat engine approach, or by a direct estimation of the work of buoyancy forces, are investigated. They provide estimations of the surface wind speed as a function of the controlling parameters.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":null,"pages":null},"PeriodicalIF":3.1,"publicationDate":"2024-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141372960","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, George H. Bryan, R. Rotunno, Peter P. Sullivan, David H. Richter
Improved representation of turbulent processes in numerical models of tropical cyclones (TCs) is expected to improve intensity forecasts. To this end, the authors use a large-eddy simulation (with 31-m horizontal grid spacing) of an idealized Category 5 TC to understand the role of turbulent processes in the inner core of TCs and their role on the mean intensity. Azimuthally and temporally averaged budgets of the momentum fields show that TC turbulence acts to weaken the maximum tangential velocity, diminish the strength of radial inflow into the eye, and suppress the magnitude of the mean eyewall updraft. Turbulent flux divergences in both the vertical and radial directions are shown to influence the TC mean wind field, with the vertical being dominant in most of the inflowing boundary layer and the eyewall (analogous to traditional atmospheric boundary layer flows), while the radial becomes important only in the eyewall. The validity of the down-gradient eddy viscosity hypothesis is largely confirmed for mean velocity fields, except in narrow regions which generally correspond to weak gradients of the mean fields, as well as a narrow region in the eye. This study also provides guidance for values of effective eddy viscosities and vertical mixing length in the most turbulent regions of intense TCs, which have rarely been measured observationally. A generalized formulation of effective eddy viscosity (including the Reynolds normal stresses) is presented.
{"title":"The Role of Turbulence in an Intense Tropical Cyclone: Momentum Diffusion, Eddy Viscosities, and Mixing Lengths","authors":"Chibueze N. Oguejiofor, George H. Bryan, R. Rotunno, Peter P. Sullivan, David H. Richter","doi":"10.1175/jas-d-23-0209.1","DOIUrl":"https://doi.org/10.1175/jas-d-23-0209.1","url":null,"abstract":"\u0000Improved representation of turbulent processes in numerical models of tropical cyclones (TCs) is expected to improve intensity forecasts. To this end, the authors use a large-eddy simulation (with 31-m horizontal grid spacing) of an idealized Category 5 TC to understand the role of turbulent processes in the inner core of TCs and their role on the mean intensity. Azimuthally and temporally averaged budgets of the momentum fields show that TC turbulence acts to weaken the maximum tangential velocity, diminish the strength of radial inflow into the eye, and suppress the magnitude of the mean eyewall updraft. Turbulent flux divergences in both the vertical and radial directions are shown to influence the TC mean wind field, with the vertical being dominant in most of the inflowing boundary layer and the eyewall (analogous to traditional atmospheric boundary layer flows), while the radial becomes important only in the eyewall. The validity of the down-gradient eddy viscosity hypothesis is largely confirmed for mean velocity fields, except in narrow regions which generally correspond to weak gradients of the mean fields, as well as a narrow region in the eye. This study also provides guidance for values of effective eddy viscosities and vertical mixing length in the most turbulent regions of intense TCs, which have rarely been measured observationally. A generalized formulation of effective eddy viscosity (including the Reynolds normal stresses) is presented.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":null,"pages":null},"PeriodicalIF":3.1,"publicationDate":"2024-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141377205","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}
Warm-sector orographic precipitation in a mid-latitude cyclone encountering a ridge is simulated in a “Cyc+Mtn” experiment. A second “Shear” simulation is conducted with horizontally uniform unidirectional flow over the same mountain having thermodynamic and cross-mountain wind profiles identical to those on the centerline in the “Cyc+Mtn” simulation. The relationship between integrated vapor transport (IVT) and orographic precipitation in the Mtn+Cyc case is consistent with observations, yet the same IVT in the Shear simulation produces far less precipitation. The difference between the precipitation rates in the Cyc+Mtn and Shear cases is traced to differences in the cross-mountain moisture-flux convergence and is further isolated to differences is the cross-mountain-velocity convergence over the windward slope. The winds at the ridge crest are stronger in the Shear case, leading to more velocity divergence and decreased moisture-flux convergence. The stronger ridge-crest winds in the Shear case are produced by a stronger mountain wave, which persists after being generated during the artificial startup of the Shear simulation. Initializing with a gradually ramped up unidirectional flow and integrating to a quasi-steady state fails to adequately capture the processes regulating the lee-side circulations. Even worse results are obtained if the shear flow is instantaneously accelerated from rest. An alternative microphysical explanation for the precipitation difference between the Cyc+Mtn and Shear simulations is examined using additional numerical experiments that enhance the seeder-feeder process. Although such enhancements increase precipitation, the increase is too small to account for the differences between the Cyc+Mtn and Shear simulations.
{"title":"Underestimates of orographic precipitation in idealized simulations. Part II: Underlying causes","authors":"Lydia Tierney, D. Durran","doi":"10.1175/jas-d-23-0176.1","DOIUrl":"https://doi.org/10.1175/jas-d-23-0176.1","url":null,"abstract":"\u0000Warm-sector orographic precipitation in a mid-latitude cyclone encountering a ridge is simulated in a “Cyc+Mtn” experiment. A second “Shear” simulation is conducted with horizontally uniform unidirectional flow over the same mountain having thermodynamic and cross-mountain wind profiles identical to those on the centerline in the “Cyc+Mtn” simulation. The relationship between integrated vapor transport (IVT) and orographic precipitation in the Mtn+Cyc case is consistent with observations, yet the same IVT in the Shear simulation produces far less precipitation. The difference between the precipitation rates in the Cyc+Mtn and Shear cases is traced to differences in the cross-mountain moisture-flux convergence and is further isolated to differences is the cross-mountain-velocity convergence over the windward slope. The winds at the ridge crest are stronger in the Shear case, leading to more velocity divergence and decreased moisture-flux convergence. The stronger ridge-crest winds in the Shear case are produced by a stronger mountain wave, which persists after being generated during the artificial startup of the Shear simulation. Initializing with a gradually ramped up unidirectional flow and integrating to a quasi-steady state fails to adequately capture the processes regulating the lee-side circulations. Even worse results are obtained if the shear flow is instantaneously accelerated from rest. An alternative microphysical explanation for the precipitation difference between the Cyc+Mtn and Shear simulations is examined using additional numerical experiments that enhance the seeder-feeder process. Although such enhancements increase precipitation, the increase is too small to account for the differences between the Cyc+Mtn and Shear simulations.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":null,"pages":null},"PeriodicalIF":3.1,"publicationDate":"2024-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141380426","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}
Heavy precipitation in midlatitude mountain ranges is largely driven by the episodic passage of weather systems. Previous studies have shown a high correlation between the integrated vapor transport (IVT) in the airstream striking a mountain and the precipitation rate. Using data collected during the OLYMPEX project from a pair of sounding stations and a dense precipitation network, we further document the tight relation between IVT and precipitation rate, and obtain results consistent with earlier work. We also survey previous studies that simulated orographic precipitation forced by unidirectional shear flows. Some of these simulations were performed using models that produce reasonably accurate rainfall totals in nested simulations of actual events driven by large-scale flows. Nevertheless, the increase in precipitation with IVT in all the simulations with unidirectional upstream flows is far lower than what would be expected based on the observationally derived correlation between IVT and precipitation rate. As a first step toward explaining this discrepancy, we conduct idealized simulations of a mid-latitude cyclone striking a north-south ridge. The relationship between IVT and rainfall rate in this “Cyc+Mtn” simulation matches that which would be expected from observations. In contrast, when the conditions upstream of the ridge in the Cyc+Mtn case were used as upstream forcing in a horizontally uniform unidirectional flow with the same IVT over the same mountain ridge, far less precipitation was produced. These idealized simulations will, therefore, be used to study the discrepancy in rainfall between simulations driven by unidirectional shear flows and observations in a companion paper.
{"title":"Underestimates of orographic precipitation in idealized simulations. Part I: Evidence from unidirectional warm-sector environments","authors":"Lydia Tierney, D. Durran","doi":"10.1175/jas-d-23-0177.1","DOIUrl":"https://doi.org/10.1175/jas-d-23-0177.1","url":null,"abstract":"\u0000Heavy precipitation in midlatitude mountain ranges is largely driven by the episodic passage of weather systems. Previous studies have shown a high correlation between the integrated vapor transport (IVT) in the airstream striking a mountain and the precipitation rate. Using data collected during the OLYMPEX project from a pair of sounding stations and a dense precipitation network, we further document the tight relation between IVT and precipitation rate, and obtain results consistent with earlier work. We also survey previous studies that simulated orographic precipitation forced by unidirectional shear flows. Some of these simulations were performed using models that produce reasonably accurate rainfall totals in nested simulations of actual events driven by large-scale flows. Nevertheless, the increase in precipitation with IVT in all the simulations with unidirectional upstream flows is far lower than what would be expected based on the observationally derived correlation between IVT and precipitation rate. As a first step toward explaining this discrepancy, we conduct idealized simulations of a mid-latitude cyclone striking a north-south ridge. The relationship between IVT and rainfall rate in this “Cyc+Mtn” simulation matches that which would be expected from observations. In contrast, when the conditions upstream of the ridge in the Cyc+Mtn case were used as upstream forcing in a horizontally uniform unidirectional flow with the same IVT over the same mountain ridge, far less precipitation was produced. These idealized simulations will, therefore, be used to study the discrepancy in rainfall between simulations driven by unidirectional shear flows and observations in a companion paper.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":null,"pages":null},"PeriodicalIF":3.1,"publicationDate":"2024-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141379097","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}
Solutions of tropical convection (vertical motion), including both the first (deep) and the second baroclinic (shallow) modes, subject to convective quasi-equilibrium (CQE) constraints are formulated. Under CQE assumption, tropical convection, ω(p, x, y), can be decomposed into a product of height-dependent variable, Ωi(p), and space-dependent variable, ∇ ⋅ vi(x, y), with the former constrained by conservation of moist static energy (MSE) or dry static energy (DSE) perturbations, depending on whether the atmospheric column is dominated by ascending or descending motions. We then evaluate the roles of deep and shallow modes of convection in transporting moisture and static energy against observations using the European Centre for Medium-Range Weather Forecasts reanalysis data. The moisture transport by deep mode produces a spatial pattern similar to observations, except for an obvious underestimate of the magnitude over the eastern Pacific convergence zone (EPCZ) and cold tongue areas, where the contribution of shallow mode may account for up to 25% of the total moisture transport. In contrast, the MSE transport by deep mode exhibits a very poor performance, especially over the EPCZ where the observational MSE transport is negative but a positive value is predicted by deep mode. Including the contribution of shallow mode immediately remedies this deficiency, due to a better representation of the bottom-heavy structure of ascending motions over the EPCZ. These improvements apply to almost the entire tropics, although the correlation tends to decrease away from the convergence zones. Since simple atmospheric models often assume a single heating (forcing) profile to represent the effect of cumulus convection, the present study highlights the importance and feasibility of including both deep and shallow modes in a simple atmospheric model, while at the same time maintaining the simple model framework, to more accurately represent the moisture and MSE transports by convection in the tropics.
{"title":"Solutions of Tropical Vertical Motion under Convective Quasi-Equilibrium Assumption","authors":"Dong-Pha Dang, Jia-Yuh Yu","doi":"10.1175/jas-d-23-0218.1","DOIUrl":"https://doi.org/10.1175/jas-d-23-0218.1","url":null,"abstract":"\u0000Solutions of tropical convection (vertical motion), including both the first (deep) and the second baroclinic (shallow) modes, subject to convective quasi-equilibrium (CQE) constraints are formulated. Under CQE assumption, tropical convection, ω(p, x, y), can be decomposed into a product of height-dependent variable, Ωi(p), and space-dependent variable, ∇ ⋅ vi(x, y), with the former constrained by conservation of moist static energy (MSE) or dry static energy (DSE) perturbations, depending on whether the atmospheric column is dominated by ascending or descending motions. We then evaluate the roles of deep and shallow modes of convection in transporting moisture and static energy against observations using the European Centre for Medium-Range Weather Forecasts reanalysis data. The moisture transport by deep mode produces a spatial pattern similar to observations, except for an obvious underestimate of the magnitude over the eastern Pacific convergence zone (EPCZ) and cold tongue areas, where the contribution of shallow mode may account for up to 25% of the total moisture transport. In contrast, the MSE transport by deep mode exhibits a very poor performance, especially over the EPCZ where the observational MSE transport is negative but a positive value is predicted by deep mode. Including the contribution of shallow mode immediately remedies this deficiency, due to a better representation of the bottom-heavy structure of ascending motions over the EPCZ. These improvements apply to almost the entire tropics, although the correlation tends to decrease away from the convergence zones. Since simple atmospheric models often assume a single heating (forcing) profile to represent the effect of cumulus convection, the present study highlights the importance and feasibility of including both deep and shallow modes in a simple atmospheric model, while at the same time maintaining the simple model framework, to more accurately represent the moisture and MSE transports by convection in the tropics.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":null,"pages":null},"PeriodicalIF":3.1,"publicationDate":"2024-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141383094","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}
In the present study, the tropical tropopause inversion layer (TIL) Kelvin waves are extracted from the Global Navigation Satellite System (GNSS) radio occultation (RO) temperature data of multiple missions from January 2007 to December 2020. We focus on the variations of TIL Kelvin waves in two longitude regions, the Maritime Continent (MC; 90°–150°E) and the Pacific Ocean (PO; 170°–230°E). The results show that over both regions, ENSO leads to the opposite variations of TIL Kelvin wave temperature amplitude during different ENSO phases. Specifically, during La Niña, the strong (weak) deep convection over MC (PO) leads to strengthened (weakened) static stability. With enhanced easterly (westerly) winds and strengthened (weakened) static stability, the TIL Kelvin wave temperature amplitudes are stronger (weaker) over MC (PO). The opposite phenomenon occurs during El Niño. The zonal-mean zonal winds affect TIL Kelvin wave temperature amplitudes by two mechanisms. First, the prevalence of easterlies (westerlies) in the upper troposphere affects the upward propagation of Kelvin waves, resulting in stronger (weaker) TIL Kelvin wave temperature amplitudes over MC (PO). Second, the TIL Kelvin wave temperature amplitude peaks about 2 months before the zero-wind line of the descending westerly QBO phase occurs, due to dissipation on the critical line. Additionally, the rapid increase of zonal-mean static stability significantly affects the annual variation of TIL Kelvin wave temperature amplitudes. They both reach maxima during DJF and minima during JJA, which should be related to the annual cycles of temperature and ozone mixing ratio in the TIL. Recent studies indicate that the Kelvin wave temperature amplitudes in the tropical tropopause inversion layer (TIL) exhibit distinct characteristics compared with those in other height levels, while the modulation mechanisms of the TIL Kelvin waves need further investigation. The present study aims to study the differences in the variabilities and the modulation factors of TIL Kelvin waves over two longitude regions. Our findings suggest that the different responses of background conditions during ENSO phases influence the spatiotemporal distribution of the TIL Kelvin waves. Besides, the zonal winds and the static stability significantly affect the temporal variations of TIL Kelvin waves. Our work fills the research gap of TIL Kelvin waves and contributes to understanding the dynamics of tropical tropopause variations.
本研究从全球导航卫星系统（GNSS）2007年1月至2020年12月期间多个任务的无线电掩星（RO）温度数据中提取了热带对流层顶反转层（TIL）开尔文波。我们重点研究了两个经度区域 TIL 开尔文波的变化，即海洋大陆（MC；90°-150°E）和太平洋（PO；170°-230°E）。结果表明，在这两个区域，厄尔尼诺/南方涛动导致 TIL 开尔文波温度振幅在不同厄尔尼诺/南方涛动阶段出现相反的变化。具体来说，在拉尼娜期间，MC（PO）上空的强（弱）深对流导致静态稳定性增强（减弱）。随着东风（西风）的增强和静力稳定性的加强（减弱），MC（PO）上空的 TIL 开尔文波温度振幅增强（减弱）。厄尔尼诺现象则与此相反。平均地带风通过两种机制影响 TIL 开尔文波的温度振幅。首先，对流层上层盛行的东风（西风）会影响开尔文波的向上传播，导致 MC（PO）上空的 TIL 开尔文波温度振幅变强（变弱）。其次，由于临界线上的消散作用，TIL 开尔文波温度振幅在 QBO 西风下降阶段的零风线出现前约 2 个月达到峰值。此外，静稳区平均值的快速增加也对 TIL 开尔文波温度振幅的年变化产生了显著影响。最近的研究表明，热带对流层顶反转层的开尔文波温度振幅与其他高度层的开尔文波温度振幅相比表现出明显的特征，而热带对流层顶反转层开尔文波的调制机制还需要进一步研究。本研究旨在研究 TIL 开尔文波在两个经度区域的变率和调制因子的差异。我们的研究结果表明，厄尔尼诺/南方涛动阶段背景条件的不同反应会影响 TIL 开尔文波的时空分布。此外，带状风和静力稳定性对 TIL 开尔文波的时间变化也有显著影响。我们的研究填补了 TIL Kelvin 波的研究空白，有助于理解热带对流层顶的动态变化。
{"title":"Variations of Kelvin Waves around the Tropical Tropopause Inversion Layer from GNSS RO Measurements","authors":"Jiahua Li, Xiaohua Xu, Jia Luo","doi":"10.1175/jas-d-23-0114.1","DOIUrl":"https://doi.org/10.1175/jas-d-23-0114.1","url":null,"abstract":"\u0000In the present study, the tropical tropopause inversion layer (TIL) Kelvin waves are extracted from the Global Navigation Satellite System (GNSS) radio occultation (RO) temperature data of multiple missions from January 2007 to December 2020. We focus on the variations of TIL Kelvin waves in two longitude regions, the Maritime Continent (MC; 90°–150°E) and the Pacific Ocean (PO; 170°–230°E). The results show that over both regions, ENSO leads to the opposite variations of TIL Kelvin wave temperature amplitude during different ENSO phases. Specifically, during La Niña, the strong (weak) deep convection over MC (PO) leads to strengthened (weakened) static stability. With enhanced easterly (westerly) winds and strengthened (weakened) static stability, the TIL Kelvin wave temperature amplitudes are stronger (weaker) over MC (PO). The opposite phenomenon occurs during El Niño. The zonal-mean zonal winds affect TIL Kelvin wave temperature amplitudes by two mechanisms. First, the prevalence of easterlies (westerlies) in the upper troposphere affects the upward propagation of Kelvin waves, resulting in stronger (weaker) TIL Kelvin wave temperature amplitudes over MC (PO). Second, the TIL Kelvin wave temperature amplitude peaks about 2 months before the zero-wind line of the descending westerly QBO phase occurs, due to dissipation on the critical line. Additionally, the rapid increase of zonal-mean static stability significantly affects the annual variation of TIL Kelvin wave temperature amplitudes. They both reach maxima during DJF and minima during JJA, which should be related to the annual cycles of temperature and ozone mixing ratio in the TIL.\u0000\u0000\u0000Recent studies indicate that the Kelvin wave temperature amplitudes in the tropical tropopause inversion layer (TIL) exhibit distinct characteristics compared with those in other height levels, while the modulation mechanisms of the TIL Kelvin waves need further investigation. The present study aims to study the differences in the variabilities and the modulation factors of TIL Kelvin waves over two longitude regions. Our findings suggest that the different responses of background conditions during ENSO phases influence the spatiotemporal distribution of the TIL Kelvin waves. Besides, the zonal winds and the static stability significantly affect the temporal variations of TIL Kelvin waves. Our work fills the research gap of TIL Kelvin waves and contributes to understanding the dynamics of tropical tropopause variations.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":null,"pages":null},"PeriodicalIF":3.1,"publicationDate":"2024-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141231534","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 analyzes the variations in the thermodynamic cycle and energy of a tropical cyclone (TC) under the influence of vertical wind shear (VWS), exploring the possible thermodynamic pathways through which VWS affects TC intensity. The maximum energy harnessed by the TC diminishes alongside a decrease in storm intensity in the presence of VWS. In the sheared TC, the ascending branch of the thermodynamic cycles of TC shifts toward lower entropy, which is related to the reduction of entropy in the eyewall and/or the increase of entropy and enhanced upward motion outside the eyewall. Moreover, the descending leg to shift toward higher entropy due to the increase in entropy and weakening of downward motion in both the ambient environment and upper troposphere. These changes in the ascending and descending branches could reduce the work done by the heat engine cycle, with the former playing a primary role in the presence of VWS. Given that the ascending branch is influenced by the eyewall and the rainbands outside the eyewall under VWS, the thermodynamic pathways could be categorized into inner ventilation and outer ventilation based on the location of their roles. The pathways associated with inner ventilation primarily reduce the entropy in the eyewall. In addition to the conventional low- and mid-level ventilation, the inner ventilation also encompasses new pathways entering the mid-level eyewall after descending from the upper level and ascending from the boundary layer. Conversely, the pathways of outer ventilation are related to the increase the entropy outside the eyewall. These include the ascent of high-entropy air to the middle and upper troposphere related to the inner and outer rainbands, the outward advection of high-entropy air from the eyewall in the mid- and upper-levels, and air warming by the descending draft from the upper to the mid-level troposphere. These insights contribute to a nuanced understanding of the sophisticated interactions within TCs and their response to VWS.
{"title":"Thermodynamic pathways of vertical wind shear impacting tropical cyclone intensity change: Energetics and Lagrangian analysis","authors":"Zi-Qi Liu, Zhe-Min Tan","doi":"10.1175/jas-d-23-0182.1","DOIUrl":"https://doi.org/10.1175/jas-d-23-0182.1","url":null,"abstract":"\u0000This study analyzes the variations in the thermodynamic cycle and energy of a tropical cyclone (TC) under the influence of vertical wind shear (VWS), exploring the possible thermodynamic pathways through which VWS affects TC intensity. The maximum energy harnessed by the TC diminishes alongside a decrease in storm intensity in the presence of VWS. In the sheared TC, the ascending branch of the thermodynamic cycles of TC shifts toward lower entropy, which is related to the reduction of entropy in the eyewall and/or the increase of entropy and enhanced upward motion outside the eyewall. Moreover, the descending leg to shift toward higher entropy due to the increase in entropy and weakening of downward motion in both the ambient environment and upper troposphere. These changes in the ascending and descending branches could reduce the work done by the heat engine cycle, with the former playing a primary role in the presence of VWS.\u0000Given that the ascending branch is influenced by the eyewall and the rainbands outside the eyewall under VWS, the thermodynamic pathways could be categorized into inner ventilation and outer ventilation based on the location of their roles. The pathways associated with inner ventilation primarily reduce the entropy in the eyewall. In addition to the conventional low- and mid-level ventilation, the inner ventilation also encompasses new pathways entering the mid-level eyewall after descending from the upper level and ascending from the boundary layer. Conversely, the pathways of outer ventilation are related to the increase the entropy outside the eyewall. These include the ascent of high-entropy air to the middle and upper troposphere related to the inner and outer rainbands, the outward advection of high-entropy air from the eyewall in the mid- and upper-levels, and air warming by the descending draft from the upper to the mid-level troposphere. These insights contribute to a nuanced understanding of the sophisticated interactions within TCs and their response to VWS.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":null,"pages":null},"PeriodicalIF":3.1,"publicationDate":"2024-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141112859","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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