The Mechanisms Responsible for Large Near-Surface Vertical Vorticity within Simulated Supercells and Quasi-Linear Storms

2020 ◽  
Vol 148 (10) ◽  
pp. 4281-4297 ◽  
Author(s):  
Christian H. Boyer ◽  
Johannes M. L. Dahl
Keyword(s):  
Severe Weather ◽  
Common Mechanism ◽  
Near Surface ◽  
Vertical Vorticity ◽  
Convective Systems ◽  
Structural Differences ◽  
History Of ◽  
Low Levels

AbstractDespite their structural differences, supercells and quasi-linear convective systems (QLCS) are both capable of producing severe weather, including tornadoes. Previous research has highlighted multiple potential mechanisms by which horizontal vorticity may be reoriented into the vertical at low levels, but it is not clear in which situation what mechanism dominates. In this study, we use the CM1 model to simulate three different storm modes, each of which developed relatively large near-surface vertical vorticity. Using forward-integrated parcel trajectories, we analyze vorticity budgets and demonstrate that there seems to be a common mechanism for maintaining the near-surface vortices across storm structures. The parcels do not acquire vertical vorticity until they reach the base of the vortices. The vertical vorticity results from vigorous upward tilting of horizontal vorticity and simultaneous vertical stretching. While the parcels analyzed in our simulations do have a history of descent, they do not acquire appreciable vertical vorticity during their descent. Rather, during the analysis period relatively large horizontal vorticity develops as a result of horizontal stretching, and therefore this vorticity can be effectively tilted into the vertical.

scholarly journals “Near Ground” Vertical Vorticity in Supercell Thunderstorm Models

2017 ◽  
Vol 74 (6) ◽  
pp. 1757-1766 ◽  
Author(s):  
Richard Rotunno ◽  
Paul M. Markowski ◽  
George H. Bryan
Keyword(s):  
Numerical Models ◽  
Vertical Axis ◽  
Lower Surface ◽  
Lagrangian Analysis ◽  
Near Surface ◽  
Vertical Vorticity ◽  
Final Approach ◽  
History Of ◽  
Vorticity Dynamics ◽  
Supercell Thunderstorm

Abstract Numerical models of supercell thunderstorms produce near-ground rotation about a vertical axis (i.e., vertical vorticity) after the development of rain-cooled outflows and downdrafts. The physical processes involved in the production of near-ground vertical vorticity in simulated supercells have been a subject of discussion in the literature for over 30 years. One cause for this lengthy discussion is the difficulty in applying the principles of inviscid vorticity dynamics in a continuous fluid to the viscous evolution of discrete Eulerian simulations. The present paper reports on a Lagrangian analysis of near-ground vorticity from an idealized-supercell simulation with enhanced vertical resolution near the lower surface. The parcel that enters the low-level maximum of vertical vorticity has a history of descent during which its horizontal vorticity is considerably enhanced. In its final approach to this region, the parcel’s enhanced horizontal vorticity is tilted to produce vertical vorticity, which is then amplified through vertical stretching as the parcel rises. A simplified theoretical model is developed that exhibits these same features. The principal conclusion is that vertical vorticity at the parcel’s nadir (its lowest point), although helpful, does not need to be positive for rapid near-surface amplification of vertical vorticity.

scholarly journals Large Sensitivity of Near-Surface Vertical Vorticity Development to Heat Sink Location in Idealized Simulations of Supercell-Like Storms

2017 ◽  
Vol 74 (4) ◽  
pp. 1095-1104 ◽  
Author(s):  
Paul M. Markowski ◽  
Yvette P. Richardson
Keyword(s):  
Heat Sink ◽  
Vertical Axis ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Near Surface ◽  
Vertical Vorticity ◽  
Supercell Storm ◽  
History Of ◽  
Perturbation Pressure ◽  
Negative Buoyancy

Abstract In idealized numerical simulations of supercell-like “pseudostorms” generated by a heat source and sink in a vertically sheared environment, a tornado-like vortex develops if air possessing large circulation about a vertical axis at the lowest model levels can be converged. This is most likely to happen if the circulation-rich air possesses only weak negative buoyancy (the circulation-rich air has a history of descent, so typically possesses at least some negative buoyancy) and is subjected to an upward-directed vertical perturbation pressure gradient force. This paper further explores the sensitivity of the development of near-surface vertical vorticity to the horizontal position of the heat sink. Shifting the position of the heat sink by only 2–3 km can significantly influence vortex intensity by altering both the baroclinic generation of circulation and the buoyancy of circulation-rich air. Many of the changes in the pseudostorms that arise from shifting the position of the heat sink would be difficult to anticipate. The sensitivity of the pseudostorms to heat sink position probably at least partly explains the well-known sensitivity of near-surface vertical vorticity development to the microphysics parameterizations in more realistic supercell storm simulations, as well as some of the failures of actual supercells to produce tornadoes in seemingly favorable environments.

Population Genetics ofCaenorhabditis elegans: The Paradox of Low Polymorphism in a Widespread Species

Genetics ◽  
2003 ◽  
Vol 163 (1) ◽  
pp. 147-157 ◽  
Author(s):  
Arjun Sivasundar ◽  
Jody Hey
Keyword(s):  
Genetic Variation ◽  
Microsatellite Loci ◽  
Population Expansion ◽  
Widespread Species ◽  
C Elegans ◽  
Model Research ◽  
The World ◽  
Natural Isolates ◽  
History Of ◽  
Low Levels

AbstractCaenorhabditis elegans has become one of the most widely used model research organisms, yet we have little information on evolutionary processes and recent evolutionary history of this widespread species. We examined patterns of variation at 20 microsatellite loci in a sample of 23 natural isolates of C. elegans from various parts of the world. One-half of the loci were monomorphic among all strains, and overall genetic variation at microsatellite loci was low, relative to most other species. Some population structure was detected, but there was no association between the genetic and geographic distances among different natural isolates. Thus, despite the nearly worldwide occurrence of C. elegans, little evidence was found for local adaptation in strains derived from different parts of the world. The low levels of genetic variation within and among populations suggest that recent colonization and population expansion might have occurred. However, the patterns of variation are not consistent with population expansion. A possible explanation for the observed patterns is the action of background selection to reduce polymorphism, coupled with ongoing gene flow among populations worldwide.

scholarly journals North polar trough formation due to in-situ erosion as a source of young ice in mid-latitudinal mantles on Mars

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
J. Alexis P. Rodriguez ◽  
Kenneth L. Tanaka ◽  
Ali M. Bramson ◽  
Gregory J. Leonard ◽  
Victor R. Baker ◽  
...  
Keyword(s):  
Katabatic Wind ◽  
Spiral Pattern ◽  
Near Surface ◽  
Valuable Source ◽  
History Of ◽  
North Polar ◽  
Human Exploration ◽  
Erosional Event

AbstractThe clockwise spiral of troughs marking the Martian north polar plateau forms one of the planet’s youngest megastructures. One popular hypothesis posits that the spiral pattern resulted as troughs underwent poleward migration. Here, we show that the troughs are extensively segmented into enclosed depressions (or cells). Many cell interiors display concentric layers that connect pole- and equator-facing slopes, demonstrating in-situ trough erosion. The segmentation patterns indicate a history of gradual trough growth transversely to katabatic wind directions, whereby increases in trough intersections generated their spiral arrangement. The erosional event recorded in the truncated strata and trough segmentation may have supplied up to ~25% of the volume of the mid-latitude icy mantles. Topographically subtle undulations transition into troughs and have distributions that mimic and extend the troughs’ spiraling pattern, indicating that they probably represent buried trough sections. The retention of the spiral pattern in surface and subsurface troughs is consistent with the megastructure’s stabilization before its partial burial. A previously suggested warm paleoclimatic spike indicates that the erosion could have occurred as recently as ~50 Ka. Hence, if the removed ice was redeposited to form the mid-latitude mantles, they could provide a valuable source of near-surface, clean ice for future human exploration.

scholarly journals Between communism and capitalism: long-term inequality in Poland, 1892–2015

2021 ◽  
Author(s):  
Paweł Bukowski ◽  
Filip Novokmet
Keyword(s):  
Household Survey ◽  
National Accounts ◽  
Capital Income ◽  
Sharp Rise ◽  
Long Run ◽  
History Of ◽  
Low Levels ◽  
Distribution Of Income

AbstractWe construct the first consistent series on the long-term distribution of income in Poland by combining tax, household survey and national accounts data. We document a U-shaped evolution of inequalities from the end of the nineteenth century until today: (1) inequality was high before WWII; (2) abruptly fell after the introduction of communism in 1947 and stagnated at low levels during the whole communist period; (3) experienced a sharp rise with the return to capitalism in 1989. We find that official survey-based measures strongly under-estimate the rise in inequality since 1989. Our results highlight the prominent role of capital income in driving the U-shaped evolution of top income shares. The unique inequality history of Poland speaks to the central role of institutions and policies in shaping inequality in the long run.

ELECTROLYTE AND NITROGEN BALANCE STUDIES IN INFANTS FOLLOWING CESSATION OF VOMITING

PEDIATRICS ◽  
1950 ◽  
Vol 5 (1) ◽  
pp. 57-67
Author(s):  
T. S. DANOWSKI ◽  
A. C. AUSTIN ◽  
R. C. GOW ◽  
F. M. MATEER ◽  
F. A. WEIGAND ◽  
...  
Keyword(s):  
Serum Potassium ◽  
Nitrogen Balance ◽  
Body Fluids ◽  
Therapeutic Implications ◽  
Low Potassium ◽  
Recurrent Vomiting ◽  
History Of ◽  
Low Levels

Abnormally low levels of serum potassium were observed prior to or during therapy of infants with a history of prolonged or recurrent vomiting. Balance studies indicate that either dilution of body fluids with low potassium solution, or transfers of potassium into cells, or both processes were responsible for the hypokalemia. The probable existence of deficits of body potassium incurred prior to the balance studies and their therapeutic implications have been discussed.

The Bow and Arrow Mesoscale Convective Structure

2013 ◽  
Vol 141 (5) ◽  
pp. 1648-1672 ◽  
Author(s):  
Kelly M. Keene ◽  
Russ S. Schumacher
Keyword(s):  
Heavy Rainfall ◽  
Prediction Models ◽  
Weather Prediction ◽  
Warm Season ◽  
Severe Weather ◽  
Cold Pool ◽  
Horizontal Shear ◽  
Convective Systems ◽  
Wind Speeds ◽  
Bow And Arrow

Abstract The accurate prediction of warm-season convective systems and the heavy rainfall and severe weather associated with them remains a challenge for numerical weather prediction models. This study looks at a circumstance in which quasi-stationary convection forms perpendicular to, and above the cold-pool behind strong bow echoes. The authors refer to this phenomenon as a “bow and arrow” because on radar imagery the two convective lines resemble an archer’s bow and arrow. The “arrow” can produce heavy rainfall and severe weather, extending over hundreds of kilometers. These events are challenging to forecast because they require an accurate forecast of earlier convection and the effects of that convection on the environment. In this study, basic characteristics of 14 events are documented, and observations of 4 events are presented to identify common environmental conditions prior to the development of the back-building convection. Simulations of three cases using the Weather Research and Forecasting Model (WRF) are analyzed in an attempt to understand the mechanisms responsible for initiating and maintaining the convective line. In each case, strong southwesterly flow (inducing warm air advection and gradual isentropic lifting), in addition to directional and speed convergence into the convective arrow appear to contribute to initiation of convection. The linear orientation of the arrow may be associated with a combination of increased wind speeds and horizontal shear in the arrow region. When these ingredients are combined with thermodynamic instability, there appears to be a greater possibility of formation and maintenance of a convective arrow behind a bow echo.

scholarly journals Evaluation of Distributed Collaborative Adaptive Sensing for Detection of Low-Level Circulations and Implications for Severe Weather Warning Operations

2010 ◽  
Vol 25 (1) ◽  
pp. 173-189 ◽  
Author(s):  
J. Brotzge ◽  
K. Hondl ◽  
B. Philips ◽  
L. Lemon ◽  
E. J. Bass ◽  
...  
Keyword(s):  
Severe Weather ◽  
Special Focus ◽  
Test Bed ◽  
Scanning Strategy ◽  
Engineering Research ◽  
Low Level ◽  
Adaptive Sensing ◽  
Low Levels ◽  
Casa System ◽  
Better Than

Abstract The Center for Collaborative Adaptive Sensing of the Atmosphere (CASA) is a multiyear engineering research center established by the National Science Foundation for the development of small, inexpensive, low-power radars designed to improve the scanning of the lowest levels (<3 km AGL) of the atmosphere. Instead of sensing autonomously, CASA radars are designed to operate as a network, collectively adapting to the changing needs of end users and the environment; this network approach to scanning is known as distributed collaborative adaptive sensing (DCAS). DCAS optimizes the low-level volume coverage scanning and maximizes the utility of each scanning cycle. A test bed of four prototype CASA radars was deployed in southwestern Oklahoma in 2006 and operated continuously while in DCAS mode from March through June of 2007. This paper analyzes three convective events observed during April–May 2007, during CASA’s intense operation period (IOP), with a special focus on evaluating the benefits and weaknesses of CASA radar system deployment and DCAS scanning strategy of detecting and tracking low-level circulations. Data collected from nearby Weather Surveillance Radar-1988 Doppler (WSR-88D) and CASA radars are compared for mesoscyclones, misocyclones, and low-level vortices. Initial results indicate that the dense, overlapping coverage at low levels provided by the CASA radars and the high temporal (60 s) resolution provided by DCAS give forecasters more detailed feature continuity and tracking. Moreover, the CASA system is able to resolve a whole class of circulations—misocyclones—far better than the WSR-88Ds. In fact, many of these are probably missed completely by the WSR-88D. The impacts of this increased detail on severe weather warnings are under investigation. Ongoing efforts include enhancing the DCAS data quality and scanning strategy, improving the DCAS data visualization, and developing a robust infrastructure to better support forecast and warning operations.

40 Ar— 39 Ar ages and irradiation history of Luna 24 basalts

1980 ◽  
Vol 297 (1428) ◽  
pp. 27-39 ◽  
Keyword(s):  
Solar Wind ◽  
High Temperature ◽  
Production Rate ◽  
Cosmic Ray ◽  
Spectral Information ◽  
Near Surface ◽  
Surface Sample ◽  
History Of ◽  
Impact Events ◽  
The Way

The Luna 24 mission sampled a variety of lithologies in a single core. Two of these lithologies, a metabasalt (24196) and a crushed basalt (24170) have been subjected to 40 Ar- 39 Ar dating experiments to determine if metamorphism significantly post-dated basalt extrusion. The metabasalt exhibited symptoms of both solar wind contamination and 39 Ar recoil; in view of these effects an age may only be defined by making extreme assumptions. High temperature release fractions give an age of 3.36 ± 0.11 Ga, while the cumulate 40 Ar/ 39 Ar ratio gives 3.14 ± 0.16 Ga; both are comparable with the basalt (24170) age and suggest that the metabasalts represent thermally penecontemporaneously metamorphosed flow margins, rather than the products of later impact events. The feldspar from the microgabbro yielded an age of 3.37 ± 0.20 Ga. The ratios of cosmogenic 38 Ar to Ca in pyroxene and feldspar are within error identical, indicating that 38 Ar production from Fe in the pyroxene is small. This is the first definitive use of Fe-produced 38 Ar as a spectral hardness indicator and implies that the microgabbro received much of its cosmic ray exposure at depth in the regolith. By taking account of the dependence of 38 Ar production rate with depth it is inferred that the microgabbro layer was deposited within the last 350-500 Ma. By implication, the regolith layers above the microgabbro at the Luna 24 site are younger. The metabasalt has an identical cosmogenic 38 Ar/Ca ratio; however, because of the decrease of production rate with depth it could have experienced a 20 % pre-exposure before deposition of the microgabbro. Spectral information has also been obtained from a reappraisal of published argon data and indicates a much harder spectrum for a near surface sample. The way in which the Ca- and Fe-produced 38 Ar e follow the broad trend of the instantaneous production profiles suggests that the regolith at the Luna 24 site has been relatively undisturbed for much of the last 300 Ma.

scholarly journals Long-term time-lapse microgravity and geotechnical monitoring of relict salt mines, Marston, Cheshire, U. K.

Geophysics ◽  
2012 ◽  
Vol 77 (6) ◽  
pp. B287-B294 ◽  
Author(s):  
Jamie K. Pringle ◽  
Peter Styles ◽  
Claire P. Howell ◽  
Michael W. Branston ◽  
Rebecca Furner ◽  
...  
Keyword(s):  
Time Lapse ◽  
Ground Subsidence ◽  
Near Surface ◽  
Geotechnical Monitoring ◽  
Salt Mines ◽  
History Of ◽  
Mine Workings ◽  
The Village ◽  
The Town

The area around the town of Northwich in Cheshire, U. K., has a long history of catastrophic ground subsidence caused by a combination of natural dissolution and collapsing abandoned mine workings within the underlying Triassic halite bedrock geology. In the village of Marston, the Trent and Mersey Canal crosses several abandoned salt mine workings and previously subsiding areas, the canal being breached by a catastrophic subsidence event in 1953. This canal section is the focus of a long-term monitoring study by conventional geotechnical topographic and microgravity surveys. Results of 20 years of topographic time-lapse surveys indicate specific areas of local subsidence that could not be predicted by available site and mine abandonment plan and shaft data. Subsidence has subsequently necessitated four phases of temporary canal bank remediation. Ten years of microgravity time-lapse data have recorded major deepening negative anomalies in specific sections that correlate with topographic data. Gravity 2D modeling using available site data found upwardly propagating voids, and associated collapse material produced a good match with observed microgravity data. Intrusive investigations have confirmed a void at the major anomaly. The advantages of undertaking such long-term studies for near-surface geophysicists, geotechnical engineers, and researchers working in other application areas are discussed.

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