Isabelle Bunge, Adam Sobel, Michela Biasutti, Shuguang Wang
Abstract Surface winds and precipitation over the tropical oceans are related to sea surface temperature (SST) through multiple mechanisms. Greater SST is associated with greater conditional instability, which in turn is more conducive to deep convection. The associated mass and flow responses can extend to the surface, via associated pressure gradients imprinted on the top of the planetary boundary layer (PBL). SST also influences surface pressure and wind directly through its control over PBL temperature, as explained by Lindzen and Nigam (1987). The authors examine the relative magnitudes of these two influences over the eastern tropical Pacific on subseasonal precipitation variability during northern summer, when and where SST gradients are largest and the direct influence via PBL temperature is expected to be strongest. Geopotential at 1000 hPa is partitioned into two components: the geopotential at PBL top (PBL top is chosen to be 850 hPa, supported by an analysis of the vertical structure of geopotential and temperature), and the PBL thickness. These fields are composited on quintiles of daily ITCZ precipitation both with and without a high-pass filter that isolates subseasonal timescales. The PBL thickness varies little between the highest and lowest precipitation quintiles, while the PBL top geopotential varies much more. This supports a view in which the direct contribution of SST to the surface pressure and flow fields, including the associated PBL convergence over sharp SST maxima, can be viewed as a steady forcing on the rest of the column, while free-tropospheric transients contribute most of the variability associated with precipitation on subseasonal timescales.
{"title":"Variable Rainfall over Steady SST: The Effect of the Free Troposphere on Surface Pressure in the East Pacific","authors":"Isabelle Bunge, Adam Sobel, Michela Biasutti, Shuguang Wang","doi":"10.1175/jas-d-23-0101.1","DOIUrl":"https://doi.org/10.1175/jas-d-23-0101.1","url":null,"abstract":"Abstract Surface winds and precipitation over the tropical oceans are related to sea surface temperature (SST) through multiple mechanisms. Greater SST is associated with greater conditional instability, which in turn is more conducive to deep convection. The associated mass and flow responses can extend to the surface, via associated pressure gradients imprinted on the top of the planetary boundary layer (PBL). SST also influences surface pressure and wind directly through its control over PBL temperature, as explained by Lindzen and Nigam (1987). The authors examine the relative magnitudes of these two influences over the eastern tropical Pacific on subseasonal precipitation variability during northern summer, when and where SST gradients are largest and the direct influence via PBL temperature is expected to be strongest. Geopotential at 1000 hPa is partitioned into two components: the geopotential at PBL top (PBL top is chosen to be 850 hPa, supported by an analysis of the vertical structure of geopotential and temperature), and the PBL thickness. These fields are composited on quintiles of daily ITCZ precipitation both with and without a high-pass filter that isolates subseasonal timescales. The PBL thickness varies little between the highest and lowest precipitation quintiles, while the PBL top geopotential varies much more. This supports a view in which the direct contribution of SST to the surface pressure and flow fields, including the associated PBL convergence over sharp SST maxima, can be viewed as a steady forcing on the rest of the column, while free-tropospheric transients contribute most of the variability associated with precipitation on subseasonal timescales.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135366464","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}
Stamen I. Dolaptchiev, Peter Spichtinger, Manuel Baumgartner, Ulrich Achatz
Abstract We present an asymptotic approach for the systematic investigation of the effect of gravity waves (GW) on ice clouds formed through homogeneous nucleation. In particular, we consider high- and mid-frequency GW in the tropopause region driving the formation of ice clouds, modeled with a double-moment bulk ice microphysics scheme. The asymptotic approach allows for identifying reduced equations for self-consistent description of the ice dynamics forced by GW including the effects of diffusional growth and nucleation of ice crystals. Further, corresponding analytical solutions for a monochromatic GW are derived under a single-parcel approximation. The results provide a simple expression for the nucleated number of ice crystals in a nucleation event. It is demonstrated that the asymptotic solutions capture the dynamics of the full ice model and accurately predict the nucleated ice crystal number. The present approach is extended to allow for superposition of GW, as well as, for variable ice crystal mean mass in the deposition. Implications of the results for an improved representation of GW variability in cirrus parameterizations are discussed.
{"title":"Interactions between gravity waves and cirrus clouds: asymptotic modeling of wave induced ice nucleation","authors":"Stamen I. Dolaptchiev, Peter Spichtinger, Manuel Baumgartner, Ulrich Achatz","doi":"10.1175/jas-d-22-0234.1","DOIUrl":"https://doi.org/10.1175/jas-d-22-0234.1","url":null,"abstract":"Abstract We present an asymptotic approach for the systematic investigation of the effect of gravity waves (GW) on ice clouds formed through homogeneous nucleation. In particular, we consider high- and mid-frequency GW in the tropopause region driving the formation of ice clouds, modeled with a double-moment bulk ice microphysics scheme. The asymptotic approach allows for identifying reduced equations for self-consistent description of the ice dynamics forced by GW including the effects of diffusional growth and nucleation of ice crystals. Further, corresponding analytical solutions for a monochromatic GW are derived under a single-parcel approximation. The results provide a simple expression for the nucleated number of ice crystals in a nucleation event. It is demonstrated that the asymptotic solutions capture the dynamics of the full ice model and accurately predict the nucleated ice crystal number. The present approach is extended to allow for superposition of GW, as well as, for variable ice crystal mean mass in the deposition. Implications of the results for an improved representation of GW variability in cirrus parameterizations are discussed.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":"38 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135730186","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 An idealized case of gradual oceanic transition from shallow to deep convection based on Kuang and Bretherton (2006) is simulated at three different horizontal resolutions: one that resolves most of the turbulent eddies, one typical of cloud-resolving models and one typical of general circulation models. The former serves as a reference, and allows the identification of clouds as individual objects, distinguishing shallow cumulus, congestus and cumulonimbus. At coarser resolutions, parameterizations of convection are included and assessed, with a particular focus on congestus clouds and precipitation associated with shallow convective clouds. Congestus clouds are found to contribute the most to turbulent transport during the transition, while occupying a volume comparable to shallow cumulus and cumulonimbus. Kilometer-scale horizontal resolutions prove to be insufficient to resolve congestus, and parameterization schemes of shallow and deep convection are not necessarily appropriate to represent those intermediate clouds. The representation of rainfall in the shallow convection scheme plays a key role in the transition. Sensitivity experiments show that enhanced rainfall inhibits convection in single-column simulations, while it favors resolved convection and spatial heterogeneities in three-dimensional simulations with kilometer-scale resolution. Results highlight the need for an appropriate parameterization of congestus in both kilometer-scale and large-scale models. The case study and the methods presented here are proposed as a useful framework to evaluate models and their parameterizations in a shallow-to-deep convection transition context.
{"title":"Simulating the transition from shallow to deep convection across scales: the role of congestus clouds","authors":"Aude Champouillon, Catherine Rio, Fleur Couvreux","doi":"10.1175/jas-d-23-0027.1","DOIUrl":"https://doi.org/10.1175/jas-d-23-0027.1","url":null,"abstract":"Abstract An idealized case of gradual oceanic transition from shallow to deep convection based on Kuang and Bretherton (2006) is simulated at three different horizontal resolutions: one that resolves most of the turbulent eddies, one typical of cloud-resolving models and one typical of general circulation models. The former serves as a reference, and allows the identification of clouds as individual objects, distinguishing shallow cumulus, congestus and cumulonimbus. At coarser resolutions, parameterizations of convection are included and assessed, with a particular focus on congestus clouds and precipitation associated with shallow convective clouds. Congestus clouds are found to contribute the most to turbulent transport during the transition, while occupying a volume comparable to shallow cumulus and cumulonimbus. Kilometer-scale horizontal resolutions prove to be insufficient to resolve congestus, and parameterization schemes of shallow and deep convection are not necessarily appropriate to represent those intermediate clouds. The representation of rainfall in the shallow convection scheme plays a key role in the transition. Sensitivity experiments show that enhanced rainfall inhibits convection in single-column simulations, while it favors resolved convection and spatial heterogeneities in three-dimensional simulations with kilometer-scale resolution. Results highlight the need for an appropriate parameterization of congestus in both kilometer-scale and large-scale models. The case study and the methods presented here are proposed as a useful framework to evaluate models and their parameterizations in a shallow-to-deep convection transition context.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":"33 5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135888186","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}
Haochang Luo, Ángel F. Adames Corraliza, Richard B. Rood
Abstract As one of the most prominent weather systems over the Indian subcontinent, the Indian summer monsoon low pressure systems (MLPSs) have been studied extensively over the past decades. However, the processes that govern the growth of the MLPSs are not well understood. To better understand these processes, we created an MLPS index using bandpass-filtered precipitation data. Lag regression maps and vertical cross-sections are used to document the distribution of moisture, moist static energy (MSE), geopotential, horizontal and vertical motions in these systems. It is shown that moisture governs the distribution of MSE and is in phase with precipitation, vertical motion, and geopotential during the MLPS cycle. Examination of the MSE budget reveals that longwave radiative heating maintains the MSE anomalies against dissipation from vertical MSE advection. These processes nearly cancel one another, and it is variations in horizontal MSE advection that are found to explain the growth and decay of the MSE anomalies. Horizontal MSE advection contributes to the growth of the MSE anomalies in MLPSs prior to the system attaining a maximum amplitude and contributes to decay thereafter. The horizontal MSE advection is largely due to meridional advection of mean state MSE by the anomalous winds, suggesting that the MSE anomalies undergo a moisture-vortex instability (MVI)-like growth. In contrast, perturbation kinetic energy (PKE) is generated through barotropic conversion. The structure, propagation, and energetics of the regressed MLPSs are consistent with both barotropic and moisture-vortex growth.
{"title":"Barotropic and Moisture-vortex growth of Monsoon Low Pressure Systems","authors":"Haochang Luo, Ángel F. Adames Corraliza, Richard B. Rood","doi":"10.1175/jas-d-22-0252.1","DOIUrl":"https://doi.org/10.1175/jas-d-22-0252.1","url":null,"abstract":"Abstract As one of the most prominent weather systems over the Indian subcontinent, the Indian summer monsoon low pressure systems (MLPSs) have been studied extensively over the past decades. However, the processes that govern the growth of the MLPSs are not well understood. To better understand these processes, we created an MLPS index using bandpass-filtered precipitation data. Lag regression maps and vertical cross-sections are used to document the distribution of moisture, moist static energy (MSE), geopotential, horizontal and vertical motions in these systems. It is shown that moisture governs the distribution of MSE and is in phase with precipitation, vertical motion, and geopotential during the MLPS cycle. Examination of the MSE budget reveals that longwave radiative heating maintains the MSE anomalies against dissipation from vertical MSE advection. These processes nearly cancel one another, and it is variations in horizontal MSE advection that are found to explain the growth and decay of the MSE anomalies. Horizontal MSE advection contributes to the growth of the MSE anomalies in MLPSs prior to the system attaining a maximum amplitude and contributes to decay thereafter. The horizontal MSE advection is largely due to meridional advection of mean state MSE by the anomalous winds, suggesting that the MSE anomalies undergo a moisture-vortex instability (MVI)-like growth. In contrast, perturbation kinetic energy (PKE) is generated through barotropic conversion. The structure, propagation, and energetics of the regressed MLPSs are consistent with both barotropic and moisture-vortex growth.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136112891","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}
Xuanyu Chen, Juliana Dias, Brandon Wolding, Robert Pincus, Charlotte DeMott, Gary Wick, Elizabeth J. Thompson, Chris W. Fairall
Abstract The impact of weak submeso- to meso-scale SST anomalies on daily averaged trade cumulus cloudiness is investigated using satellite observations that have been validated against ship-board measurements from the Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC). Daily spatial SST anomalies are identified from GOES-POES blended SST analysis within a 10° by 10° region during January and February 2020. Daily-averaged cloud fraction and 10-m neutral wind from satellite observations and reanalysis are composited over the identified SST features, using a common coordinate system based on the near surface background wind directions. Composites of satellite cloud fraction show a statistically significant increase of cloudiness over the SST warm core with a reduction of cloudiness away from it. These responses are largely the same but with opposite signs over SST cold anomalies, suggesting that spatial heterogeneity in SST can locally imprint on daily cloud fraction. Composites of daily 10-m wind speed and wind convergence anomalies from both satellite and reanalysis show that surface wind speed is increased over SST warm anomalies, implying enhanced turbulence over warmer SSTs. Correspondingly, the surface convergence anomalies in these composites are located around the maximum downwind SST gradient, offset downwind from the cloudiness anomalies. These results indicate that the response of daily cloudiness to these SST anomalies is more likely generated by spatial variability of surface-driven turbulence and surface fluxes rather than that of surface or boundary layer convergence.
{"title":"Ubiquitous Sea Surface Temperature Anomalies Increase Spatial Heterogeneity of Trade-Wind Cloudiness on Daily Timescale","authors":"Xuanyu Chen, Juliana Dias, Brandon Wolding, Robert Pincus, Charlotte DeMott, Gary Wick, Elizabeth J. Thompson, Chris W. Fairall","doi":"10.1175/jas-d-23-0075.1","DOIUrl":"https://doi.org/10.1175/jas-d-23-0075.1","url":null,"abstract":"Abstract The impact of weak submeso- to meso-scale SST anomalies on daily averaged trade cumulus cloudiness is investigated using satellite observations that have been validated against ship-board measurements from the Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC). Daily spatial SST anomalies are identified from GOES-POES blended SST analysis within a 10° by 10° region during January and February 2020. Daily-averaged cloud fraction and 10-m neutral wind from satellite observations and reanalysis are composited over the identified SST features, using a common coordinate system based on the near surface background wind directions. Composites of satellite cloud fraction show a statistically significant increase of cloudiness over the SST warm core with a reduction of cloudiness away from it. These responses are largely the same but with opposite signs over SST cold anomalies, suggesting that spatial heterogeneity in SST can locally imprint on daily cloud fraction. Composites of daily 10-m wind speed and wind convergence anomalies from both satellite and reanalysis show that surface wind speed is increased over SST warm anomalies, implying enhanced turbulence over warmer SSTs. Correspondingly, the surface convergence anomalies in these composites are located around the maximum downwind SST gradient, offset downwind from the cloudiness anomalies. These results indicate that the response of daily cloudiness to these SST anomalies is more likely generated by spatial variability of surface-driven turbulence and surface fluxes rather than that of surface or boundary layer convergence.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":"28 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136114004","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}
I. Chunchuzov, O. Chkhetiani, S. Kulichkov, O. Popov, B Belan, A. Fofonov, G Ivlev, A. Kozlov
Abstract The results of airborne measurements and statistical characteristics of mesoscale fluctuations of wind velocity, temperature and concentrations of gas constituents at different heights of stably stratified troposphere are presented. The measurements were carried out in September 2022 in the Arctic region of Russia with the aircraft-laboratory Tu-134 "Optik". The obtained spectra and structure functions of the fluctuations are interpreted with the theoretical model of formation of the spectrum of mesoscale wind velocity and temperature fluctuations described in the paper. The presence at high wave numbers of a steep section in the obtained horizontal wave number spectra of the fluctuations of wind velocity and greenhouse gas concentration with a slope close to −3 is discussed. The fluctuation spectra along different slanted tracks of the aircraft crossing the tropospheric layer between altitudes of 1 and 9 km are also obtained and analyzed with the theoretical model.
{"title":"Statistical characteristics of mesoscale fluctuations of wind velocity, temperature, and gas concentrations obtained from aircraft measurements in the troposphere of the Arctic region","authors":"I. Chunchuzov, O. Chkhetiani, S. Kulichkov, O. Popov, B Belan, A. Fofonov, G Ivlev, A. Kozlov","doi":"10.1175/jas-d-23-0021.1","DOIUrl":"https://doi.org/10.1175/jas-d-23-0021.1","url":null,"abstract":"Abstract The results of airborne measurements and statistical characteristics of mesoscale fluctuations of wind velocity, temperature and concentrations of gas constituents at different heights of stably stratified troposphere are presented. The measurements were carried out in September 2022 in the Arctic region of Russia with the aircraft-laboratory Tu-134 \"Optik\". The obtained spectra and structure functions of the fluctuations are interpreted with the theoretical model of formation of the spectrum of mesoscale wind velocity and temperature fluctuations described in the paper. The presence at high wave numbers of a steep section in the obtained horizontal wave number spectra of the fluctuations of wind velocity and greenhouse gas concentration with a slope close to −3 is discussed. The fluctuation spectra along different slanted tracks of the aircraft crossing the tropospheric layer between altitudes of 1 and 9 km are also obtained and analyzed with the theoretical model.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":"4 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135918374","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}
Andrew Janiszeski, Robert M. Rauber, Brian F. Jewett, Greg M. McFarquhar, Troy J. Zaremba, John E. Yorks
Abstract This paper explores whether particles within uniformly-spaced generating cells falling at terminal velocity within observed 2-D wind fields and idealized deformation flow beneath cloud top can be reorganized consistent with the presence of single and multi-banded structures present on WSR-88D radars. In the first experiment, two-dimensional wind fields, calculated along cross-sections normal to the long-axis of snow bands observed during three Northeast U.S. winter storms, were taken from the initialization of the High Resolution Rapid Refresh model. This experiment demonstrated that the greater the residence time of the particles in each of the three storms, the greater particle reorganization occurred. For experiments with longer residence times, increases in particle concentrations were nearly or directly collocated with reflectivity bands. For experiments with shorter residence times, particle reorganization still conformed to the band features but with less concentration enhancement. This experiment demonstrates that the combination of long particle residence time and net convergent cross-sectional flow through the cloud depth is sufficient to re-organize particles into locations consistent with precipitation bands. Increased concentrations of ice particles can then contribute, along with any dynamic forcing, to the low-level reflectivity bands seen on WSR-88D radars. In a second experiment, the impact of flow deformation on the re-organization of falling ice particles was investigated using an idealized kinematic model with stretching deformation flow of different depths and magnitudes. These experiments showed that deformation flow provides for little particle reorganization given typical deformation layer depths and magnitudes within the comma head of such storms.
{"title":"A Kinematic Modeling Study of the Re-Organization of Snowfall between Cloud-top Generating Cells and low-level Snow Bands in Midlatitude Winter Storms","authors":"Andrew Janiszeski, Robert M. Rauber, Brian F. Jewett, Greg M. McFarquhar, Troy J. Zaremba, John E. Yorks","doi":"10.1175/jas-d-23-0024.1","DOIUrl":"https://doi.org/10.1175/jas-d-23-0024.1","url":null,"abstract":"Abstract This paper explores whether particles within uniformly-spaced generating cells falling at terminal velocity within observed 2-D wind fields and idealized deformation flow beneath cloud top can be reorganized consistent with the presence of single and multi-banded structures present on WSR-88D radars. In the first experiment, two-dimensional wind fields, calculated along cross-sections normal to the long-axis of snow bands observed during three Northeast U.S. winter storms, were taken from the initialization of the High Resolution Rapid Refresh model. This experiment demonstrated that the greater the residence time of the particles in each of the three storms, the greater particle reorganization occurred. For experiments with longer residence times, increases in particle concentrations were nearly or directly collocated with reflectivity bands. For experiments with shorter residence times, particle reorganization still conformed to the band features but with less concentration enhancement. This experiment demonstrates that the combination of long particle residence time and net convergent cross-sectional flow through the cloud depth is sufficient to re-organize particles into locations consistent with precipitation bands. Increased concentrations of ice particles can then contribute, along with any dynamic forcing, to the low-level reflectivity bands seen on WSR-88D radars. In a second experiment, the impact of flow deformation on the re-organization of falling ice particles was investigated using an idealized kinematic model with stretching deformation flow of different depths and magnitudes. These experiments showed that deformation flow provides for little particle reorganization given typical deformation layer depths and magnitudes within the comma head of such storms.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":"60 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135387254","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 Organized systems of deep convective clouds are often associated with high-impact weather and changes in such systems may have implications for climate sensitivity. This has motivated the derivation of many organization indices that attempt to measure the level of deep convective aggregation in models and observations. Here we conduct a comprehensive review of existing methodologies and highlight some of their relative drawbacks, such as only measuring organization in a relative sense, being biased towards particular spatial scales, or being very sensitive to the details of the calculation algorithm. One widely used metric, I org , uses statistics of nearest-neighbor distances between convective storms to address the first of these concerns, but we show here that it is insensitive to organization beyond the β -mesoscale and very contingent on the details of the implementation. We thus introduce a new and complementary metric, L org , based on all-pair convective storm distances, which is also an absolute metric that can discern regular, random and clustered cloud scenes. It is linearly sensitive to spatial scale in most applications and robust to the implementation methodology. We also derive a discrete form suited to gridded data and provide corrections to account for cyclic boundary conditions and finite, open boundary domains of non-equal aspect ratios. We demonstrate the use of the metric with idealized synthetic configurations, as well as model output and satellite rainfall retrievals in the tropics. We claim that this new metric usefully supplements the existing family of indices that can help understand convective organization across spatial scales.
{"title":"Measuring convective organization","authors":"Giovanni Biagioli, Adrian Mark Tompkins","doi":"10.1175/jas-d-23-0103.1","DOIUrl":"https://doi.org/10.1175/jas-d-23-0103.1","url":null,"abstract":"Abstract Organized systems of deep convective clouds are often associated with high-impact weather and changes in such systems may have implications for climate sensitivity. This has motivated the derivation of many organization indices that attempt to measure the level of deep convective aggregation in models and observations. Here we conduct a comprehensive review of existing methodologies and highlight some of their relative drawbacks, such as only measuring organization in a relative sense, being biased towards particular spatial scales, or being very sensitive to the details of the calculation algorithm. One widely used metric, I org , uses statistics of nearest-neighbor distances between convective storms to address the first of these concerns, but we show here that it is insensitive to organization beyond the β -mesoscale and very contingent on the details of the implementation. We thus introduce a new and complementary metric, L org , based on all-pair convective storm distances, which is also an absolute metric that can discern regular, random and clustered cloud scenes. It is linearly sensitive to spatial scale in most applications and robust to the implementation methodology. We also derive a discrete form suited to gridded data and provide corrections to account for cyclic boundary conditions and finite, open boundary domains of non-equal aspect ratios. We demonstrate the use of the metric with idealized synthetic configurations, as well as model output and satellite rainfall retrievals in the tropics. We claim that this new metric usefully supplements the existing family of indices that can help understand convective organization across spatial scales.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":"42 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134960035","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 The spectrum of kinetic energy of vertical motions (VKE) is less well understood compared to the kinetic energy spectrum of horizontal motions (HKE). One challenge that has limited progress in describing the VKE spectrum is a lack of a unified approach to the decomposition of vertical velocities associated with the Rossby motions and inertia-gravity (IG) wave flows. This paper presents such a unified approach using a linear Rossby-IG vertical velocity normal-mode decomposition appropriate for a spherical, hydrostatic atmosphere. New theoretical developments show that for every zonal wavenumber k , the limit VKE is proportional to the total mechanical energy and to the square of the frequency of the normal mode. The theory predicts a VKE ∝ k −5 and a VKE ∝ k 1/3 power law for the Rossby and IG waves, assuming a k −3 and a k −5/3 power law for the Rossby and IG HKE spectra, respectively. The Kelvin and mixed Rossby-gravity wave VKE spectra are predicted to follow k −1 and k −5 power laws, respectively. The VKE spectra for ERA5 analyses from August 2018 show that the Rossby VKE spectra approximately follow the predicted a k −5 power law. The expected k 1/3 power law for the gravity wave VKE spectrum is found only in the SH midlatitude stratosphere for k ≈ 10−60. The inertial range IG VKE spectra in the tropical and midlatitude troposphere reflect a mixture of ageostrophic and convection-coupled dynamics and have slopes between −1 and −1/3, likely associated with too steep IG HKE spectra. The forcing by quasi-geostrophic ageostrophic motions is seen as an IG VKE peak at synoptic scales in the SH upper troposphere which gradually moves to planetary scales in the stratosphere.
{"title":"Decomposition of vertical velocity and its zonal wavenumber kinetic energy spectra in the hydrostatic atmosphere","authors":"Nedjeljka Žagar, Valentino Neduhal, Sergiy Vasylkevych, Žiga Zaplotnik, Hiroshi L. Tanaka","doi":"10.1175/jas-d-23-0090.1","DOIUrl":"https://doi.org/10.1175/jas-d-23-0090.1","url":null,"abstract":"Abstract The spectrum of kinetic energy of vertical motions (VKE) is less well understood compared to the kinetic energy spectrum of horizontal motions (HKE). One challenge that has limited progress in describing the VKE spectrum is a lack of a unified approach to the decomposition of vertical velocities associated with the Rossby motions and inertia-gravity (IG) wave flows. This paper presents such a unified approach using a linear Rossby-IG vertical velocity normal-mode decomposition appropriate for a spherical, hydrostatic atmosphere. New theoretical developments show that for every zonal wavenumber k , the limit VKE is proportional to the total mechanical energy and to the square of the frequency of the normal mode. The theory predicts a VKE ∝ k −5 and a VKE ∝ k 1/3 power law for the Rossby and IG waves, assuming a k −3 and a k −5/3 power law for the Rossby and IG HKE spectra, respectively. The Kelvin and mixed Rossby-gravity wave VKE spectra are predicted to follow k −1 and k −5 power laws, respectively. The VKE spectra for ERA5 analyses from August 2018 show that the Rossby VKE spectra approximately follow the predicted a k −5 power law. The expected k 1/3 power law for the gravity wave VKE spectrum is found only in the SH midlatitude stratosphere for k ≈ 10−60. The inertial range IG VKE spectra in the tropical and midlatitude troposphere reflect a mixture of ageostrophic and convection-coupled dynamics and have slopes between −1 and −1/3, likely associated with too steep IG HKE spectra. The forcing by quasi-geostrophic ageostrophic motions is seen as an IG VKE peak at synoptic scales in the SH upper troposphere which gradually moves to planetary scales in the stratosphere.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":"9 1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135816591","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 The importance of the convective life cycle in tropical large-scale dynamics has long been emphasized, but without explicit analysis. The present work provides it by coupling the convective energy cycle under the framework of Arakawa and Schubert’s (1974) convection parameterization with a shallow-water analogue atmosphere. A careful derivation of the system is first presented, because it is rather missing in the literature. The squared frequency of linear convectively-coupled waves is given by a squared sum of the dry gravity-wave and the convective energy-cycle frequencies, shortening the period of the convective cycle through the large-scale coupling. In a weakly nonlinear regime, the system follows an equation analogous to the Kortweg-de Vries equation, which exhibits a solitary-wave solution, with behavior reminiscent of observed tropical westerly-wind bursts.
{"title":"Interaction of the Convective Energy Cycle and Large-Scale Dynamics","authors":"Jun-Ichi Yano, Robert S. Plant","doi":"10.1175/jas-d-23-0066.1","DOIUrl":"https://doi.org/10.1175/jas-d-23-0066.1","url":null,"abstract":"Abstract The importance of the convective life cycle in tropical large-scale dynamics has long been emphasized, but without explicit analysis. The present work provides it by coupling the convective energy cycle under the framework of Arakawa and Schubert’s (1974) convection parameterization with a shallow-water analogue atmosphere. A careful derivation of the system is first presented, because it is rather missing in the literature. The squared frequency of linear convectively-coupled waves is given by a squared sum of the dry gravity-wave and the convective energy-cycle frequencies, shortening the period of the convective cycle through the large-scale coupling. In a weakly nonlinear regime, the system follows an equation analogous to the Kortweg-de Vries equation, which exhibits a solitary-wave solution, with behavior reminiscent of observed tropical westerly-wind bursts.","PeriodicalId":17231,"journal":{"name":"Journal of the Atmospheric Sciences","volume":"37 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135816961","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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