Abstract Current bulk microphysical parameterization schemes underpredict precipitation intensities and drop size distributions (DSDs) during warm rain periods, particularly upwind of coastal terrain. To help address this deficiency, this study introduces a set of modifications, called RCON, to the liquid-phase (warm rain) parameterization currently used in the Thompson-Eidhammer microphysical parameterization scheme. RCON introduces several model modifications, motivated by evaluating simulations from a bin scheme, which together result in more accurate precipitation simulations during periods of warm rain. Among the most significant changes are (1) the use of a wider cloud water DSD of lognormal shape instead of the gamma DSD used by the Thompson-Eidhammer parameterization, and (2) enhancement of the cloud-to-rain autoconversion parameterization. Evaluation of RCON is performed for two warm rain events and an extended period during the Olympic Mountains Experiment (OLYMPEX) field campaign of winter 2015-16. We show that RCON modifications produce more realistic precipitation distributions and rain DSDs than the default Thompson-Eidhammer configuration. For the multi-month OLYMPEX period, we show that rain rates, rain water mixing ratios, and rain drop number concentrations were increased relative to the Thompson-Eidhammer microphysical parameterization, while concurrently decreasing rain drop diameters in liquid-phase clouds. These changes are consistent with an increase in simulated warm rain. Finally, real-time evaluation of the scheme from August 2021 to August 2022 demonstrated improved precipitation prediction over coastal areas of the Pacific Northwest.
{"title":"Improving simulations of warm rain in a bulk microphysics scheme","authors":"Robert Conrick, Clifford F. Mass, Lynn McMurdie","doi":"10.1175/mwr-d-23-0035.1","DOIUrl":"https://doi.org/10.1175/mwr-d-23-0035.1","url":null,"abstract":"Abstract Current bulk microphysical parameterization schemes underpredict precipitation intensities and drop size distributions (DSDs) during warm rain periods, particularly upwind of coastal terrain. To help address this deficiency, this study introduces a set of modifications, called RCON, to the liquid-phase (warm rain) parameterization currently used in the Thompson-Eidhammer microphysical parameterization scheme. RCON introduces several model modifications, motivated by evaluating simulations from a bin scheme, which together result in more accurate precipitation simulations during periods of warm rain. Among the most significant changes are (1) the use of a wider cloud water DSD of lognormal shape instead of the gamma DSD used by the Thompson-Eidhammer parameterization, and (2) enhancement of the cloud-to-rain autoconversion parameterization. Evaluation of RCON is performed for two warm rain events and an extended period during the Olympic Mountains Experiment (OLYMPEX) field campaign of winter 2015-16. We show that RCON modifications produce more realistic precipitation distributions and rain DSDs than the default Thompson-Eidhammer configuration. For the multi-month OLYMPEX period, we show that rain rates, rain water mixing ratios, and rain drop number concentrations were increased relative to the Thompson-Eidhammer microphysical parameterization, while concurrently decreasing rain drop diameters in liquid-phase clouds. These changes are consistent with an increase in simulated warm rain. Finally, real-time evaluation of the scheme from August 2021 to August 2022 demonstrated improved precipitation prediction over coastal areas of the Pacific Northwest.","PeriodicalId":18824,"journal":{"name":"Monthly Weather Review","volume":"73 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135934045","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}
Han Li, Ziyu Yan, Melinda Peng, Xuyang Ge, Zhuo Wang
Abstract Tropical cyclones (TCs) accompanied by an upper tropospheric cold low (CL) can experience unusual tracks. Idealized simulations resembling observed scenarios are designed in this study to investigate the impacts of a CL on TC tracks. The sensitivity of the TC motion to its location relative to the CL is examined. The results show that a TC follows a counterclockwise semicircle track if initially located east of a CL while a TC experiences a small southward looping track, followed by a sudden northward turn if initially located west of a CL. A TC on the west side experiences opposing CL and β steering, while they act in the same direction when a TC is on the east side of CL. The steering flow analyses show that the steering vector is dominated by upper-level flow induced by the CL at early stage. The influence of CL extends downward and contributes to the lower-tropospheric asymmetric flow pattern of TC. As these two systems approach, the TC divergent outflow erodes the CL. The CL circulation is deformed and eventually merged with the TC when they are close. Since the erosion of CL, the TC motion is primarily related to β gyres at later stage. The sensitivity of TC motion to the CL depth is also examined. TCs located west of a CL experience a westward track if the CL is shallow. In contrast, TCs initially located east of a CL all take a smooth track irrespective of the CL depth, and the CL depth mainly influences the track curvature and the TC translation speed.
{"title":"Unusual Tropical cyclone Tracks under the Influence of Upper Tropospheric Cold Low","authors":"Han Li, Ziyu Yan, Melinda Peng, Xuyang Ge, Zhuo Wang","doi":"10.1175/mwr-d-23-0074.1","DOIUrl":"https://doi.org/10.1175/mwr-d-23-0074.1","url":null,"abstract":"Abstract Tropical cyclones (TCs) accompanied by an upper tropospheric cold low (CL) can experience unusual tracks. Idealized simulations resembling observed scenarios are designed in this study to investigate the impacts of a CL on TC tracks. The sensitivity of the TC motion to its location relative to the CL is examined. The results show that a TC follows a counterclockwise semicircle track if initially located east of a CL while a TC experiences a small southward looping track, followed by a sudden northward turn if initially located west of a CL. A TC on the west side experiences opposing CL and β steering, while they act in the same direction when a TC is on the east side of CL. The steering flow analyses show that the steering vector is dominated by upper-level flow induced by the CL at early stage. The influence of CL extends downward and contributes to the lower-tropospheric asymmetric flow pattern of TC. As these two systems approach, the TC divergent outflow erodes the CL. The CL circulation is deformed and eventually merged with the TC when they are close. Since the erosion of CL, the TC motion is primarily related to β gyres at later stage. The sensitivity of TC motion to the CL depth is also examined. TCs located west of a CL experience a westward track if the CL is shallow. In contrast, TCs initially located east of a CL all take a smooth track irrespective of the CL depth, and the CL depth mainly influences the track curvature and the TC translation speed.","PeriodicalId":18824,"journal":{"name":"Monthly Weather Review","volume":"77 3-4","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135272605","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}
Large-scale meteorological pattern (LSMP)–based analysis is used in a novel way to understand meteorological conditions before and during short-duration dry spells over the northeastern United States. These LSMPs are useful to assess models and select better-performing models for future projections. Dry-spell events are identified from histograms of consecutive dry days below a daily precipitation threshold. Events lasting 12 days or longer, which correspond to ∼10% of dry-spell events, are examined. The 500-hPa streamfunction anomaly fields for the first 12 days of each event are time averaged, and k-means clustering is applied to isolate the dry-spell-related LSMPs. The first cluster has a strong low pressure anomaly over the Atlantic Ocean, southeast of the region, and is more common in winter and spring. The second cluster has strong high pressure over east-central North America and is most common during autumn. Over the region, both clusters have negative specific humidity anomalies, negative integrated vapor transport from the north, and subsidence associated with a midlatitude jet stream dipole structure that reinforces upper-level convergence. Subsidence is supported by cold-air advection in the first cluster and the location on the east side of the lower-level high pressure in the second cluster. Extratropical cyclone storm tracks are generally shifted southward of the region during the dry spells. Individual events lie on a continuum between two distinct clusters. These clusters have similar local, but different remote, properties. Although dry spells occur with greater frequency during drought months, most dry spells occur during nondrought months. This study examines the large-scale weather patterns and meteorological conditions associated with dry-spell events lasting at least 2 weeks while affecting the northeastern United States. A statistical approach groups events together on the basis of similar atmospheric features. We find two distinct sets of patterns that we call large-scale meteorological patterns. These patterns reduce moisture, foster localized sinking, and shift the storm track southward along the Atlantic seaboard, all of which reduce precipitation. Besides greater understanding, knowing the meteorological patterns during short-term dryness in the region provides an important tool to assess how well atmospheric models reproduce these specific patterns. More dry spells occur in nondrought months than in drought months, which means that dry spells can occur without preexisting drought conditions.
{"title":"Two Large-Scale Meteorological Patterns are Associated with Short-Duration Dry Spells in the Northeastern United States","authors":"Raymond Sukhdeo, R. Grotjahn, Paul A. Ullrich","doi":"10.1175/mwr-d-23-0141.1","DOIUrl":"https://doi.org/10.1175/mwr-d-23-0141.1","url":null,"abstract":"Large-scale meteorological pattern (LSMP)–based analysis is used in a novel way to understand meteorological conditions before and during short-duration dry spells over the northeastern United States. These LSMPs are useful to assess models and select better-performing models for future projections. Dry-spell events are identified from histograms of consecutive dry days below a daily precipitation threshold. Events lasting 12 days or longer, which correspond to ∼10% of dry-spell events, are examined. The 500-hPa streamfunction anomaly fields for the first 12 days of each event are time averaged, and k-means clustering is applied to isolate the dry-spell-related LSMPs. The first cluster has a strong low pressure anomaly over the Atlantic Ocean, southeast of the region, and is more common in winter and spring. The second cluster has strong high pressure over east-central North America and is most common during autumn. Over the region, both clusters have negative specific humidity anomalies, negative integrated vapor transport from the north, and subsidence associated with a midlatitude jet stream dipole structure that reinforces upper-level convergence. Subsidence is supported by cold-air advection in the first cluster and the location on the east side of the lower-level high pressure in the second cluster. Extratropical cyclone storm tracks are generally shifted southward of the region during the dry spells. Individual events lie on a continuum between two distinct clusters. These clusters have similar local, but different remote, properties. Although dry spells occur with greater frequency during drought months, most dry spells occur during nondrought months. This study examines the large-scale weather patterns and meteorological conditions associated with dry-spell events lasting at least 2 weeks while affecting the northeastern United States. A statistical approach groups events together on the basis of similar atmospheric features. We find two distinct sets of patterns that we call large-scale meteorological patterns. These patterns reduce moisture, foster localized sinking, and shift the storm track southward along the Atlantic seaboard, all of which reduce precipitation. Besides greater understanding, knowing the meteorological patterns during short-term dryness in the region provides an important tool to assess how well atmospheric models reproduce these specific patterns. More dry spells occur in nondrought months than in drought months, which means that dry spells can occur without preexisting drought conditions.","PeriodicalId":18824,"journal":{"name":"Monthly Weather Review","volume":"14 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139292979","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}
Michael S. Fischer, Robert F. Rogers, Paul D. Reasor, Jason P. Dunion
Abstract This study uses a recently-developed airborne Doppler radar database to explore how vortex misalignment is related to tropical cyclone (TC) precipitation structure and intensity change. It is found that for relatively weak TCs, defined here as storms with a peak 10-m wind of 65 kt or less, the magnitude of vortex tilt is closely linked to the rate of subsequent TC intensity change, especially over the next 12–36 h. In strong TCs, defined as storms with a peak 10-m wind greater than 65 kt, vortex tilt magnitude is only weakly correlated with TC intensity change. Based on these findings, this study focuses on how vortex tilt is related to TC precipitation structure and intensity change in weak TCs. To illustrate how the TC precipitation structure is related to the magnitude of vortex misalignment, weak TCs are divided into two groups: small-tilt and large-tilt TCs. In large-tilt TCs, storms display a relatively large radius of maximum wind, the precipitation structure is asymmetric, and convection occurs more frequently near the mid-tropospheric TC center than the lower-tropospheric TC center. Alternatively, small-tilt TCs exhibit a greater areal coverage of precipitation inward of a relatively small radius of maximum wind. Greater rates of TC intensification, including rapid intensification, are shown to occur preferentially for TCs with greater vertical alignment and storms in relatively favorable environments.
{"title":"An Observational Analysis of the Relationship between Tropical Cyclone Vortex Tilt, Precipitation Structure, and Intensity Change","authors":"Michael S. Fischer, Robert F. Rogers, Paul D. Reasor, Jason P. Dunion","doi":"10.1175/mwr-d-23-0089.1","DOIUrl":"https://doi.org/10.1175/mwr-d-23-0089.1","url":null,"abstract":"Abstract This study uses a recently-developed airborne Doppler radar database to explore how vortex misalignment is related to tropical cyclone (TC) precipitation structure and intensity change. It is found that for relatively weak TCs, defined here as storms with a peak 10-m wind of 65 kt or less, the magnitude of vortex tilt is closely linked to the rate of subsequent TC intensity change, especially over the next 12–36 h. In strong TCs, defined as storms with a peak 10-m wind greater than 65 kt, vortex tilt magnitude is only weakly correlated with TC intensity change. Based on these findings, this study focuses on how vortex tilt is related to TC precipitation structure and intensity change in weak TCs. To illustrate how the TC precipitation structure is related to the magnitude of vortex misalignment, weak TCs are divided into two groups: small-tilt and large-tilt TCs. In large-tilt TCs, storms display a relatively large radius of maximum wind, the precipitation structure is asymmetric, and convection occurs more frequently near the mid-tropospheric TC center than the lower-tropospheric TC center. Alternatively, small-tilt TCs exhibit a greater areal coverage of precipitation inward of a relatively small radius of maximum wind. Greater rates of TC intensification, including rapid intensification, are shown to occur preferentially for TCs with greater vertical alignment and storms in relatively favorable environments.","PeriodicalId":18824,"journal":{"name":"Monthly Weather Review","volume":"422 ","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135813752","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 Doppler weather radars are powerful tools for investigating the inner-core structure and intensity of tropical cyclones (TCs). The Doppler velocity can provide quantitative information on the vortex structure in the TCs. The Generalized Velocity Track Display (GVTD) technique has been used to retrieve the axisymmetric circulations and asymmetric tangential flows in the TCs from ground-based single-Doppler radar observations. GVTD can have limited applicability to asymmetric vortices due to the closure assumption of no asymmetric radial flows. The present study proposes a new closure formulation that includes asymmetric radial flows, based on the Helmholtz decomposition. Here it is assumed that the horizontal flow is predominantly rotational and expressed with a streamfunction, but limited inclusion of wavenumber-1 divergence is available. Unlike the original GVTD, the decomposition introduces consistency along radius by solving all equations simultaneously. The new approach, named GVTD-X, is applied to analytical vortices and a real TC with asymmetric structures. This approach makes the retrieval of axisymmetric flow relatively insensitive to the contamination from asymmetric flows and to small errors in storm center location. For an analytical vortex with a wavenumber-2 asymmetry, the maximum relative error of the axisymmetric tangential wind retrieved by GVTD-X is less than 2% at the radius of the maximum wind speed. In practical applications, errors can be evaluated by comparing results for different maximum wavenumbers. When applied to a real TC, GVTD-X largely suppressed an artificial periodic fluctuation that occurs in GVTD from the aliasing of the neglected asymmetric radial flows.
{"title":"A New Closure Assumption and Formulation Based on the Helmholtz Decomposition for Improving Retrievals for Vortex Circulations from Single-Doppler Radar Observations","authors":"Satoki Tsujino, Takeshi Horinouchi, Udai Shimada","doi":"10.1175/mwr-d-23-0043.1","DOIUrl":"https://doi.org/10.1175/mwr-d-23-0043.1","url":null,"abstract":"Abstract Doppler weather radars are powerful tools for investigating the inner-core structure and intensity of tropical cyclones (TCs). The Doppler velocity can provide quantitative information on the vortex structure in the TCs. The Generalized Velocity Track Display (GVTD) technique has been used to retrieve the axisymmetric circulations and asymmetric tangential flows in the TCs from ground-based single-Doppler radar observations. GVTD can have limited applicability to asymmetric vortices due to the closure assumption of no asymmetric radial flows. The present study proposes a new closure formulation that includes asymmetric radial flows, based on the Helmholtz decomposition. Here it is assumed that the horizontal flow is predominantly rotational and expressed with a streamfunction, but limited inclusion of wavenumber-1 divergence is available. Unlike the original GVTD, the decomposition introduces consistency along radius by solving all equations simultaneously. The new approach, named GVTD-X, is applied to analytical vortices and a real TC with asymmetric structures. This approach makes the retrieval of axisymmetric flow relatively insensitive to the contamination from asymmetric flows and to small errors in storm center location. For an analytical vortex with a wavenumber-2 asymmetry, the maximum relative error of the axisymmetric tangential wind retrieved by GVTD-X is less than 2% at the radius of the maximum wind speed. In practical applications, errors can be evaluated by comparing results for different maximum wavenumbers. When applied to a real TC, GVTD-X largely suppressed an artificial periodic fluctuation that occurs in GVTD from the aliasing of the neglected asymmetric radial flows.","PeriodicalId":18824,"journal":{"name":"Monthly Weather Review","volume":"32 19","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135863272","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 This paper analyzes the relationships between the circulation regimes of the 500 hPa height (z500) and 250 hPa zonal winds (u250) in the Pacific North America region during boreal winter, and the 45-day Northern Hemisphere oscillation identified by Stan and Krishnamurthy (2019) in z500. The regimes were calculated using a k-means clustering applied to the leading 12 Principal Components of the combined z500/u250 anomaly fields. We divided the oscillation into 8 arbitrary phases. The oscillation phase z500 composite maps are spatially well correlated with regime z500 composites: phases 1–2 are best correlated with the Arctic Low, phases 3–5 with the Pacific Trough, phase 6 with the Arctic High, and phases 7–8 with the Alaskan Ridge. We found that these correlations are generally consistent with the regimes that tend to occur during the individual oscillation phases: the Arctic Low occurs above significance in phases 1–2, the Pacific Trough in phase 3, and Alaskan Ridge in phases 7–8. Therefore, the oscillation has a preferred order with respect to the regimes. The regime transitions indicate a pattern that moves through the Pacific Wavetrain, a regime that appears for k=5 as a mean state. Transitions out of this regime into different regimes are preferred in different phases of the oscillation. These results imply a possible enhancement to regime prediction using the low-frequency oscillations in combination with regimes.
本文分析了太平洋北美地区冬季500 hPa高度(z500)和250 hPa纬向风(u250)的环流形式与Stan and Krishnamurthy(2019)在z500中确定的45 d北半球振荡的关系。对z500/u250组合异常场的前12个主成分进行k均值聚类计算。我们将振荡分为8个任意相位。振荡相位z500合成图在空间上与z500合成图有很好的相关性:相位1-2与北极低压相关，相位3-5与太平洋槽相关，相位6与北极高压相关，相位7-8与阿拉斯加脊相关。我们发现，这些相关性大体上与个别振荡阶段发生的情况一致:北极低压在第1-2阶段出现高于显著水平，太平洋槽在第3阶段出现，阿拉斯加脊在第7-8阶段出现。因此，振荡相对于状态有一个优先顺序。状态转换表明了一种通过太平洋波列移动的模式，这种状态在k=5时出现为平均状态。在振荡的不同阶段，优选从这个状态过渡到不同的状态。这些结果暗示了低频振荡与状态相结合对状态预测的可能增强。
{"title":"The Relationships between the Winter Circulation Regimes and the Northern Hemisphere 45-day Oscillation: A Combined Regime-Oscillation Framework","authors":"Mary H. Korendyke, David M. Straus","doi":"10.1175/mwr-d-23-0058.1","DOIUrl":"https://doi.org/10.1175/mwr-d-23-0058.1","url":null,"abstract":"Abstract This paper analyzes the relationships between the circulation regimes of the 500 hPa height (z500) and 250 hPa zonal winds (u250) in the Pacific North America region during boreal winter, and the 45-day Northern Hemisphere oscillation identified by Stan and Krishnamurthy (2019) in z500. The regimes were calculated using a k-means clustering applied to the leading 12 Principal Components of the combined z500/u250 anomaly fields. We divided the oscillation into 8 arbitrary phases. The oscillation phase z500 composite maps are spatially well correlated with regime z500 composites: phases 1–2 are best correlated with the Arctic Low, phases 3–5 with the Pacific Trough, phase 6 with the Arctic High, and phases 7–8 with the Alaskan Ridge. We found that these correlations are generally consistent with the regimes that tend to occur during the individual oscillation phases: the Arctic Low occurs above significance in phases 1–2, the Pacific Trough in phase 3, and Alaskan Ridge in phases 7–8. Therefore, the oscillation has a preferred order with respect to the regimes. The regime transitions indicate a pattern that moves through the Pacific Wavetrain, a regime that appears for k=5 as a mean state. Transitions out of this regime into different regimes are preferred in different phases of the oscillation. These results imply a possible enhancement to regime prediction using the low-frequency oscillations in combination with regimes.","PeriodicalId":18824,"journal":{"name":"Monthly Weather Review","volume":"100 ","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136067583","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}
Lauren E. Pounds, Conrad L. Ziegler, Rebecca D. Adams-Selin, Michael I. Biggerstaff
Abstract This study uses a new, unique dataset created by combining multi-Doppler radar wind and reflectivity analysis, diabatic Lagrangian analysis (DLA) retrievals of temperature and water substance, and a complex hail trajectory model to create millions of numerically simulated hail trajectories in the Kingfisher, OK supercell on 29 May 2012. The DLA output variables are used to obtain a realistic, 4-D depiction of the storm's thermal and hydrometeor structure as required input to the detailed hail growth trajectory model. Hail embryos are initialized in the hail growth module every three minutes of the radar analysis period (2251-0000 UTC) to produce over 2.7 million hail trajectories. A spatial integration technique considering all trajectories is used to identify locations within the supercell where melted particles, sub-severe, and severe hailstones reside in their lowest and highest concentrations. It is found that hailstones are more likely to reside for longer periods closer to the downshear updraft within the midlevel mesocyclone in a region of decelerated mid-level mesocyclonic horizontal flow, termed the downshear deceleration zone (DDZ). Additionally, clusters of trajectories are analyzed using a trajectory clustering method. Trajectory clusters show there are many trajectory pathways that result in hailstones ≥ 4.5 cm, including trajectories that begin upshear of the updraft away from ideal growth conditions and trajectories that grow within the DDZ. There are also trajectory clusters with similar shapes, yet experience widely different environmental and hailstones characteristics along the trajectory.
{"title":"Analysis of Hail Production via Simulated Hailstone Trajectories in the 29 May 2012 Kingfisher, OK Supercell","authors":"Lauren E. Pounds, Conrad L. Ziegler, Rebecca D. Adams-Selin, Michael I. Biggerstaff","doi":"10.1175/mwr-d-23-0073.1","DOIUrl":"https://doi.org/10.1175/mwr-d-23-0073.1","url":null,"abstract":"Abstract This study uses a new, unique dataset created by combining multi-Doppler radar wind and reflectivity analysis, diabatic Lagrangian analysis (DLA) retrievals of temperature and water substance, and a complex hail trajectory model to create millions of numerically simulated hail trajectories in the Kingfisher, OK supercell on 29 May 2012. The DLA output variables are used to obtain a realistic, 4-D depiction of the storm's thermal and hydrometeor structure as required input to the detailed hail growth trajectory model. Hail embryos are initialized in the hail growth module every three minutes of the radar analysis period (2251-0000 UTC) to produce over 2.7 million hail trajectories. A spatial integration technique considering all trajectories is used to identify locations within the supercell where melted particles, sub-severe, and severe hailstones reside in their lowest and highest concentrations. It is found that hailstones are more likely to reside for longer periods closer to the downshear updraft within the midlevel mesocyclone in a region of decelerated mid-level mesocyclonic horizontal flow, termed the downshear deceleration zone (DDZ). Additionally, clusters of trajectories are analyzed using a trajectory clustering method. Trajectory clusters show there are many trajectory pathways that result in hailstones ≥ 4.5 cm, including trajectories that begin upshear of the updraft away from ideal growth conditions and trajectories that grow within the DDZ. There are also trajectory clusters with similar shapes, yet experience widely different environmental and hailstones characteristics along the trajectory.","PeriodicalId":18824,"journal":{"name":"Monthly Weather Review","volume":"4 3","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135168770","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}
Arthur Avenas, Alexis Mouche, Pierre Tandeo, Jean-Francois Piolle, Dan Chavas, Ronan Fablet, John Knaff, Bertrand Chapron
The radius of maximum wind (Rmax), an important parameter in tropical cyclones (TCs) ocean surface wind structure, is currently resolved by only a few sensors, so that, in most cases, it is estimated subjectively or via crude statistical models. Recently, a semi-empirical model relying on an outer wind radius, intensity and latitude was fit to best-track data. In this study we revise this semi-empirical model and discuss its physical basis. While intensity and latitude are taken from best-track data, Rmax observations from high-resolution (3 km) spaceborne synthetic aperture radar (SAR) and wind radii from an inter-calibrated dataset of medium-resolution radiometers and scatterometers are considered to revise the model coefficients. The new version of the model is then applied to the period 2010-2020 and yields Rmax reanalyses and trends more accurate than best-track data. SAR measurements corroborate that fundamental conservation principles constrain the radial wind structure on average, endorsing the physical basis of the model. Observations highlight that departures from the average conservation situation are mainly explained by wind profile shape variations, confirming the model’s physical basis, which further shows that radial inflow, boundary layer depth and drag coefficient also play roles. Physical understanding will benefit from improved observations of the near-core region from accumulated SAR observations and future missions. In the meantime, the revised model offers an efficient tool to provide guidance on Rmax when a radiometer or scatterometer observation is available, for either operations or reanalysis purposes.
{"title":"Reexamining the Estimation of Tropical Cyclones Radius of Maximum Wind from Outer Size with an Extensive Synthetic Aperture Radar Dataset","authors":"Arthur Avenas, Alexis Mouche, Pierre Tandeo, Jean-Francois Piolle, Dan Chavas, Ronan Fablet, John Knaff, Bertrand Chapron","doi":"10.1175/mwr-d-23-0119.1","DOIUrl":"https://doi.org/10.1175/mwr-d-23-0119.1","url":null,"abstract":"The radius of maximum wind (Rmax), an important parameter in tropical cyclones (TCs) ocean surface wind structure, is currently resolved by only a few sensors, so that, in most cases, it is estimated subjectively or via crude statistical models. Recently, a semi-empirical model relying on an outer wind radius, intensity and latitude was fit to best-track data. In this study we revise this semi-empirical model and discuss its physical basis. While intensity and latitude are taken from best-track data, Rmax observations from high-resolution (3 km) spaceborne synthetic aperture radar (SAR) and wind radii from an inter-calibrated dataset of medium-resolution radiometers and scatterometers are considered to revise the model coefficients. The new version of the model is then applied to the period 2010-2020 and yields Rmax reanalyses and trends more accurate than best-track data. SAR measurements corroborate that fundamental conservation principles constrain the radial wind structure on average, endorsing the physical basis of the model. Observations highlight that departures from the average conservation situation are mainly explained by wind profile shape variations, confirming the model’s physical basis, which further shows that radial inflow, boundary layer depth and drag coefficient also play roles. Physical understanding will benefit from improved observations of the near-core region from accumulated SAR observations and future missions. In the meantime, the revised model offers an efficient tool to provide guidance on Rmax when a radiometer or scatterometer observation is available, for either operations or reanalysis purposes.","PeriodicalId":18824,"journal":{"name":"Monthly Weather Review","volume":"43 10","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135413221","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 Gridpoint Statistical Interpolation (GSI)-based four- and three-dimensional ensemble–variational (4DEnVar and 3DEnVar) methods are compared as a smoother and filter, respectively, for rapidly changing storms using the convective-scale direct radar reflectivity data assimilation (DA) framework. Two sets of experiments with varying DA window lengths (WLs; 20, 40, 100, and 160 min) and radar observation intervals (RIs; 20 and 5 min) are conducted for the 5–6 May 2019 case. The RI determines the temporal resolution of ensemble perturbations for the smoother and the DA interval for the filter spanning the WL. For experiments with a 20-min RI, evaluations suggest that filter and smoother have comparable performance with a 20-min WL; however, extending the WL results in the outperformance of filter over smoother. Diagnostics reveal that the degradation of smoother is attributed to the increased degree of nonlinearity and the issue of time-independent localization as the WL extends. Evaluations for experiments with different RIs under the same WL indicate that the outperformance of filter over smoother diminishes for most forecast hours at thresholds of 30 dBZ and above when shortening the RI. Diagnostics show that more frequent interruptions of the model introduce model imbalance for the filter, and the increased temporal resolution of ensemble perturbations enhances the degree of nonlinearity for the smoother. The impact of model imbalance on the filter overwhelms the enhanced nonlinearity on the smoother as the RI reduces.
{"title":"A Comparison of 3DEnVar and 4DEnVar for Convective-Scale Direct Radar Reflectivity Data Assimilation in the Context of Filter and Smoother","authors":"Yue Yang, Xuguang Wang","doi":"10.1175/mwr-d-23-0082.1","DOIUrl":"https://doi.org/10.1175/mwr-d-23-0082.1","url":null,"abstract":"Abstract The Gridpoint Statistical Interpolation (GSI)-based four- and three-dimensional ensemble–variational (4DEnVar and 3DEnVar) methods are compared as a smoother and filter, respectively, for rapidly changing storms using the convective-scale direct radar reflectivity data assimilation (DA) framework. Two sets of experiments with varying DA window lengths (WLs; 20, 40, 100, and 160 min) and radar observation intervals (RIs; 20 and 5 min) are conducted for the 5–6 May 2019 case. The RI determines the temporal resolution of ensemble perturbations for the smoother and the DA interval for the filter spanning the WL. For experiments with a 20-min RI, evaluations suggest that filter and smoother have comparable performance with a 20-min WL; however, extending the WL results in the outperformance of filter over smoother. Diagnostics reveal that the degradation of smoother is attributed to the increased degree of nonlinearity and the issue of time-independent localization as the WL extends. Evaluations for experiments with different RIs under the same WL indicate that the outperformance of filter over smoother diminishes for most forecast hours at thresholds of 30 dBZ and above when shortening the RI. Diagnostics show that more frequent interruptions of the model introduce model imbalance for the filter, and the increased temporal resolution of ensemble perturbations enhances the degree of nonlinearity for the smoother. The impact of model imbalance on the filter overwhelms the enhanced nonlinearity on the smoother as the RI reduces.","PeriodicalId":18824,"journal":{"name":"Monthly Weather Review","volume":"1982 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":"135366461","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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