scholarly journals Ambient conditions prevailing during hail events in central Europe

2020 ◽  
Author(s):  
Michael Kunz ◽  
Jan Wandel ◽  
Elody Fluck ◽  
Sven Baumstark ◽  
Susanna Mohr ◽  
...  
Keyword(s):  
Wind Shear ◽  
Deep Layer ◽  
Lapse Rate ◽  
Synoptic Scale ◽  
Ambient Conditions ◽  
Convective Storm ◽  
Convective Storms ◽  
Investigation Area ◽  
Severe Thunderstorms ◽  
Eyewitness Reports

Abstract. Around 26 000 severe convective storm tracks between 2005 and 2014 have been estimated from 2D radar reflectivity for parts of Europe, including Germany, France, Belgium, and Luxembourg. This event-set was further combined with eyewitness reports, convection-related parameters from ERA-Interim reanalysis and synoptic-scale fronts based on the same reanalysis. Our analyses reveal that about a quarter of all severe thunderstorms in the investigation area were associated with a front. Over complex terrains, such as in southern Germany, the proportion of frontal convective storms is around 10–15 %, while over flat terrain half of the events require a front to trigger convection. Frontal hailstorms on average produce larger hailstones and have a longer track. These events usually develop in a high-shear environment. Using composites of environmental conditions centered around the hailstorm tracks, we found that dynamical proxies such as deep-layer shear or storm-relative helicity become important when separating hail diameters and, in particular, their lengths; 0–3 km helicity as a dynamical proxy performs better compared to wind shear for the separation. In contrast, thermodynamical proxies such as Lifted Index or lapse rate show only small differences between the different intensity classes.

scholarly journals Ambient conditions prevailing during hail events in central Europe

2020 ◽  
Vol 20 (6) ◽  
pp. 1867-1887 ◽  
Author(s):  
Michael Kunz ◽  
Jan Wandel ◽  
Elody Fluck ◽  
Sven Baumstark ◽  
Susanna Mohr ◽  
...  
Keyword(s):  
Environmental Conditions ◽  
Lapse Rate ◽  
Storm Tracks ◽  
Synoptic Scale ◽  
Ambient Conditions ◽  
Convective Storm ◽  
Convective Storms ◽  
Investigation Area ◽  
Severe Thunderstorms ◽  
Eyewitness Reports

Abstract. Around 26 000 severe convective storm tracks between 2005 and 2014 have been estimated from 2D radar reflectivity for parts of Europe, including Germany, France, Belgium, and Luxembourg. This event set was further combined with eyewitness reports, environmental conditions, and synoptic-scale fronts based on the ERA-Interim (ECMWF Reanalysis) reanalysis. Our analyses reveal that on average about a quarter of all severe thunderstorms in the investigation area were associated with a front. Over complex terrains, such as in southern Germany, the proportion of frontal convective storms is around 10 %–15 %, while over flat terrain half of the events require a front to trigger convection. Frontal storm tracks associated with hail on average produce larger hailstones and have a longer track. These events usually develop in a high-shear environment. Using composites of environmental conditions centered around the hailstorm tracks, we found that dynamical proxies such as deep-layer shear or storm-relative helicity become important when separating hail diameters and, in particular, their lengths; 0–3 km helicity as a dynamical proxy performs better compared to wind shear for the separation. In contrast, thermodynamical proxies such as the lifted index or lapse rate show only small differences between the different intensity classes.

An Observational Examination of Long-Lived Supercells. Part II: Environmental Conditions and Forecasting

2006 ◽  
Vol 21 (5) ◽  
pp. 689-714 ◽  
Author(s):  
Matthew J. Bunkers ◽  
Jeffrey S. Johnson ◽  
Lee J. Czepyha ◽  
Jason M. Grzywacz ◽  
Brian A. Klimowski ◽  
...  
Keyword(s):  
Wind Shear ◽  
Richardson Number ◽  
Narrow Range ◽  
Deep Layer ◽  
Local Environment ◽  
Bulk Richardson Number ◽  
Synoptic Scale ◽  
Close Proximity ◽  
Strong Shear ◽  
Outflow Boundary

Abstract The local and larger-scale environments of 184 long-lived supercell events (containing one or more supercells with lifetimes ≥4 h; see Part I of this paper) are investigated and subsequently compared with those from 137 moderate-lived events (average supercell lifetime 2–4 h) and 119 short-lived events (average supercell lifetime ≤2 h) to better anticipate supercell longevity in the operational setting. Consistent with many previous studies, long-lived supercells occur in environments with much stronger 0–8-km bulk wind shear than what is observed for short-lived supercells; this strong shear leads to significant storm-relative winds in the mid- to upper levels for the longest-lived supercells. Additionally, the bulk Richardson number falls into a relatively narrow range for the longest-lived supercells—ranging mostly from 5 to 45. The mesoscale to synoptic-scale environment can also predispose a supercell to be long or short lived, somewhat independent of the local environment. For example, long-lived supercells may occur when supercells travel within a broad warm sector or else in close proximity to mesoscale or larger-scale boundaries (e.g., along or near a warm front, an old outflow boundary, or a moisture/buoyancy axis), even if the deep-layer shear is suboptimal. By way of contrast, strong atmospheric forcing can result in linear convection (and thus shorter-lived supercells) in a strongly sheared environment that would otherwise favor discrete, long-lived supercells.

scholarly journals Forecasting Tornadic Thunderstorm Potential in Alberta Using Environmental Sounding Data. Part I: Wind Shear and Buoyancy

2006 ◽  
Vol 21 (3) ◽  
pp. 325-335 ◽  
Author(s):  
Max L. Dupilka ◽  
Gerhard W. Reuter
Keyword(s):  
Potential Energy ◽  
Wind Shear ◽  
Convective Available Potential Energy ◽  
Severe Storms ◽  
Convective Storms ◽  
Available Potential Energy ◽  
Observational Dataset ◽  
Severe Thunderstorms ◽  
Tornadic Storms

Abstract This study investigates, for Alberta, Canada, whether observed sounding parameters such as wind shear and buoyant energy can be used to help distinguish between thunderstorms with significant (F2–F5) tornadoes, thunderstorms with weak (F0–F1) tornadoes, and nontornadic severe thunderstorms. The observational dataset contains 87 severe convective storms, all of which occurred within 200 km of the upper-air site at Stony Plain, Alberta, Canada. Of these storms, 13 spawned significant (F2–F5) tornadoes, 61 spawned weak (F0–F1) tornadoes, and 13 had no reported tornadoes yet produced 3 cm or larger hailstones. The observations suggest that bulk shear contained information about the probability of tornado formation and the intensity of the tornado. Significant tornadic storms tended to have stronger shear values than weak tornadic or nontornadic severe storms. All significant tornado cases had a wind shear magnitude in the 900–500-mb layer exceeding 3 m s−1 km−1. Combining the 900–500-mb shear with the 900–800-mb shear increased the probabilistic guidance for the likelihood of significant tornado occurrence. The data suggest that buoyant energy alone (quantified by the most unstable convective available potential energy) provided no skill in discriminating between tornadic and nontornadic severe storms, or between significant and weak tornadoes.

Variability of Updraft and Downdraft Characteristics in a Large Parameter Space Study of Convective Storms

2009 ◽  
Vol 137 (5) ◽  
pp. 1550-1561 ◽  
Author(s):  
Cody Kirkpatrick ◽  
Eugene W. McCaul ◽  
Charles Cohen
Keyword(s):  
Vertical Distribution ◽  
Wind Shear ◽  
Convective Available Potential Energy ◽  
Environmental Parameters ◽  
Cloud Base ◽  
Convective Storm ◽  
Convective Storms ◽  
Regression Methods ◽  
The Vertical Distribution ◽  
Large Parameter Space

Abstract Over 200 convective storm simulations are analyzed to examine the variability in storm vertical velocity and updraft area characteristics as a function of basic environmental parameters. While it is known that bulk properties of the troposphere such as convective available potential energy (CAPE) and deep-layer wind shear exert significant influence over updraft intensity and area, additional parameters such as the temperature at the cloud base, the height of the level of free convection (LFC), and the vertical distribution of buoyancy also have an effect. For example, at low CAPE, updraft strength is strongly related to the vertical distribution of buoyancy, and also to the bulk environmental wind shear. More generally, updraft area and its temporal variability both tend to increase in environments where the LFC is raised. Additionally, in environments with persistent storms, downdraft strength is sensitive to the bulk shear, environmental temperature, and LFC height. Using multiple linear regression methods, the best combinations of environmental parameters explain up to 81% of the interexperiment variance in second-hour mean peak updraft velocity, 74% for midlevel updraft area, and 64% for downdraft velocity. Downdraft variability is explained even less well (49%) when only persistent storms are considered. These idealized simulation results show that it is easier to predict storm updraft characteristics than those of the downdraft.

Assessing the influence of complex terrain on severe convective environments in northeastern Alabama

2021 ◽  
Author(s):  
Branden Katona ◽  
Paul Markowski
Keyword(s):  
Boundary Layer ◽  
Complex Terrain ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Spatial Distributions ◽  
Convective Storm ◽  
Self Organizing Maps ◽  
Low Level ◽  
Wind Regimes

AbstractStorms crossing complex terrain can potentially encounter rapidly changing convective environments. However, our understanding of terrain-induced variability in convective stormenvironments remains limited. HRRR data are used to create climatologies of popular convective storm forecasting parameters for different wind regimes. Self-organizing maps (SOMs) are used to generate six different low-level wind regimes, characterized by different wind directions, for which popular instability and vertical wind shear parameters are averaged. The climatologies show that both instability and vertical wind shear are highly variable in regions of complex terrain, and that the spatial distributions of perturbations relative to the terrain are dependent on the low-level wind direction. Idealized simulations are used to investigate the origins of some of the perturbations seen in the SOM climatologies. The idealized simulations replicate many of the features in the SOM climatologies, which facilitates analysis of their dynamical origins. Terrain influences are greatest when winds are approximately perpendicular to the terrain. In such cases, a standing wave can develop in the lee, leading to an increase in low-level wind speed and a reduction in vertical wind shear with the valley lee of the plateau. Additionally, CAPE tends to be decreased and LCL heights are increased in the lee of the terrain where relative humidity within the boundary layer is locally decreased.

scholarly journals Future Australian Severe Thunderstorm Environments. Part I: A Novel Evaluation and Climatology of Convective Parameters from Two Climate Models for the Late Twentieth Century

2014 ◽  
Vol 27 (10) ◽  
pp. 3827-3847 ◽  
Author(s):  
John T. Allen ◽  
David J. Karoly ◽  
Kevin J. Walsh
Keyword(s):  
Twentieth Century ◽  
Wind Shear ◽  
Climate Models ◽  
Convective Available Potential Energy ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Severe Thunderstorm ◽  
Severe Thunderstorms ◽  
Late Twentieth ◽  
Late Twentieth Century

Abstract The influence of a warming climate on the occurrence of severe thunderstorms over Australia is, as yet, poorly understood. Based on methods used in the development of a climatology of observed severe thunderstorm environments over the continent, two climate models [Commonwealth Scientific and Industrial Research Organisation Mark, version 3.6 (CSIRO Mk3.6) and the Cubic-Conformal Atmospheric Model (CCAM)] have been used to produce simulated climatologies of ingredients and environments favorable to severe thunderstorms for the late twentieth century (1980–2000). A novel evaluation of these model climatologies against data from both the ECMWF Interim Re-Analysis (ERA-Interim) and reports of severe thunderstorms from observers is used to analyze the capability of the models to represent convective environments in the current climate. This evaluation examines the representation of thunderstorm-favorable environments in terms of their frequency, seasonal cycle, and spatial distribution, while presenting a framework for future evaluations of climate model convective parameters. Both models showed the capability to explain at least 75% of the spatial variance in both vertical wind shear and convective available potential energy (CAPE). CSIRO Mk3.6 struggled to either represent the diurnal cycle over a large portion of the continent or resolve the annual cycle, while in contrast CCAM showed a tendency to underestimate CAPE and 0–6-km bulk magnitude vertical wind shear (S06). While spatial resolution likely contributes to rendering of features such as coastal moisture and significant topography, the distribution of severe thunderstorm environments is found to have greater sensitivity to model biases. This highlights the need for a consistent approach to evaluating convective parameters and severe thunderstorm environments in present-day climate: an example of which is presented here.

scholarly journals Trends in United States large hail environments and observations

2019 ◽  
Vol 2 (1) ◽  
Author(s):  
Brian H. Tang ◽  
Vittorio A. Gensini ◽  
Cameron R. Homeyer
Keyword(s):  
United States ◽  
Rocky Mountains ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Environmental Parameters ◽  
Vertical Wind ◽  
Severe Thunderstorms ◽  
Lapse Rates ◽  
The U.S

AbstractUnderstanding trends in large hail-producing environments is an important component of estimating hail risk. Here, we use two environmental parameters, the Large Hail Parameter and the Significant Hail Parameter, to assess trends in days with environments conducive for hail ≥5 cm. From 1979 to 2017, there has been an increase in days with favorable large hail environments in central and eastern portions of the U.S. This increase has been driven primarily by an increasing frequency of days with steep mid-tropospheric lapse rates and necessary combinations of instability and vertical wind shear for severe thunderstorms. Annual large hail environment area is significantly, positively correlated with (1) large hail report area east of the Rocky Mountains, and (2) large hail radar-derived area in the Midwest and Northeast. This evidence suggests that there may be an environmental fingerprint on increasing large hail risk and expanding this risk eastward.

A Revised Force–Restore Model for Land Surface Modeling

2004 ◽  
Vol 43 (11) ◽  
pp. 1768-1782 ◽  
Author(s):  
Diandong Ren ◽  
Ming Xue
Keyword(s):  
Soil Temperature ◽  
Skin Temperature ◽  
Land Surface ◽  
Deep Layer ◽  
Additional Term ◽  
Prediction Equation ◽  
Lapse Rate ◽  
Temperature Prediction ◽  
Land Surface Modeling ◽  
Definition Of

Abstract To clarify the definition of the equation for the temperature toward which the soil skin temperature is restored, the prediction equations in the commonly used force–restore model for soil temperature are rederived from the heat conduction equation. The derivation led to a deep-layer temperature, commonly denoted T2, that is defined as the soil temperature at depth πd plus a transient term, where d is the e-folding damping depth of soil temperature diurnal oscillations. The corresponding prediction equation for T2 has the same form as the commonly used one except for an additional term involving the lapse rate of the “seasonal mean” soil temperature and the damping depth d. A term involving the same also appears in the skin temperature prediction equation, which also includes a transient term. In the literature, T2 was initially defined as the short-term (over several days) mean of the skin temperature, but in practice it is often used as the deep-layer temperature. Such inconsistent use can lead to drift in T2 prediction over a several-day period, as is documented in this paper. When T2 is properly defined and initialized, large drift in T2 prediction is avoided and the surface temperature prediction is usually improved. This is confirmed by four sets of experiments, each for a period during each season of 2000, that are initialized using and verified against measurements of the Oklahoma Atmospheric Surface-Layer Instrumentation System (OASIS) project.

Observations of a Squall Line and Its Near Environment Using High-Frequency Rawinsonde Launches during VORTEX2

2010 ◽  
Vol 138 (11) ◽  
pp. 4076-4097 ◽  
Author(s):  
George H. Bryan ◽  
Matthew D. Parker
Keyword(s):  
Wind Shear ◽  
Deep Layer ◽  
Potential Temperature ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Squall Line ◽  
Cold Pool ◽  
Low Level ◽  
Stratiform Region ◽  
Gust Front

Abstract Rawinsonde data were collected before and during passage of a squall line in Oklahoma on 15 May 2009 during the Second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2). Nine soundings were released within 3 h, allowing for unprecedented analysis of the squall line’s internal structure and nearby environment. Four soundings were released in the prestorm environment and they document the following features: low-level cooling associated with the reduction of solar isolation by a cirrus anvil; abrupt warming (1.5 K in 30 min) above the boundary layer, which is probably attributable to a gravity wave; increases in both low-level and deep-layer vertical wind shear within 100 km of the squall line; and evidence of ascent extending at least 75 km ahead of the squall line. The next sounding was released ∼5 km ahead of the squall line’s gust front; it documented a moist absolutely unstable layer within a 2-km-deep layer of ascent, with vertical air velocity of approximately 6 m s−1. Another sounding was released after the gust front passed but before precipitation began; this sounding showed the cold pool to be ∼4 km deep, with a cold pool intensity C ≈ 35 m s−1, even though this sounding was located only 8 km behind the surface gust front. The final three soundings were released in the trailing stratiform region of the squall line, and they showed typical features such as: “onion”-shaped soundings, nearly uniform equivalent potential temperature over a deep layer, and an elevated rear inflow jet. The cold pool was 4.7 km deep in the trailing stratiform region, and extended ∼1 km above the melting level, suggesting that sublimation was a contributor to cold pool development. A mesoscale analysis of the sounding data shows an upshear tilt to the squall line, which is consistent with the cold pool intensity C being much larger than a measure of environmental vertical wind shear ΔU. This dataset should be useful for evaluating cloud-scale numerical model simulations and analytic theory, but the authors argue that additional observations of this type should be collected in future field projects.

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