VALIDATING VERTICAL VELOCITY GRADIENTS IN NEAR-SURFACE REFRACTION SEISMOLOGY

2013 ◽  
Author(s):  
Derecke Palmer
Keyword(s):  
Vertical Velocity ◽  
Near Surface ◽  
Refraction Seismology ◽  
Velocity Gradients

scholarly journals Joint Modeling of Severe Dust Storm Events in Arid and Hyper Arid Regions Based on Copula Theory: A Case Study in the Yazd Province, Iran

Climate ◽  
2020 ◽  
Vol 8 (5) ◽  
pp. 64 ◽  
Author(s):  
Tayyebeh Mesbahzadeh ◽  
Maryam Mirakbari ◽  
Mohsen Mohseni Saravi ◽  
Farshad Soleimani Sardoo ◽  
Nir Y. Krakauer
Keyword(s):  
Wind Speed ◽  
Natural Disasters ◽  
Return Period ◽  
Vertical Velocity ◽  
Geopotential Height ◽  
Dust Storms ◽  
Maximum Wind Speed ◽  
Near Surface ◽  
Copula Theory ◽  
Maximum Wind

Natural disasters such as dust storms are random phenomena created by complicated mechanisms involving many parameters. In this study, we used copula theory for bivariate modeling of dust storms. Copula theory is a suitable method for multivariate modeling of natural disasters. We identified 40 severe dust storms, as defined by the World Meteorological Organization, during 1982–2017 in Yazd province, central Iran. We used parameters at two spatial vertical levels (near-surface and upper atmosphere) that included surface maximum wind speed, and geopotential height and vertical velocity at 500, 850, and 1000 hPa. We compared two bivariate models based on the pairs of maximum wind speed–geopotential height and maximum wind speed–vertical velocity. We determined the bivariate return period using Student t and Gaussian copulas, which were considered as the most suitable functions for these variables. The results obtained for maximum wind speed–geopotential height indicated that the maximum return period was consistent with the observed frequency of severe dust storms. The bivariate modeling of dust storms based on maximum wind speed and geopotential height better described the conditions of severe dust storms than modeling based on maximum wind speed and vertical velocity. The finding of this study can be useful to improve risk management and mitigate the impacts of severe dust storms.

scholarly journals High-Resolution, Rapid-Scan Dual-Doppler Retrievals of Vertical Velocity in a Simulated Supercell

2019 ◽  
Vol 36 (8) ◽  
pp. 1477-1500 ◽  
Author(s):  
Nathan A. Dahl ◽  
Alan Shapiro ◽  
Corey K. Potvin ◽  
Adam Theisen ◽  
Joshua G. Gebauer ◽  
...  
Keyword(s):  
Variational Method ◽  
Vertical Velocity ◽  
Traditional Method ◽  
Mass Conservation ◽  
Conservation Equation ◽  
Observation System ◽  
Near Surface ◽  
Rapid Scan ◽  
Close Range ◽  
The Impact

AbstractObservation system simulation experiments are used to evaluate different dual-Doppler analysis (DDA) methods for retrieving vertical velocity w at grid spacings on the order of 100 m within a simulated tornadic supercell. Variational approaches with and without a vertical vorticity equation constraint are tested, along with a typical (traditional) method involving vertical integration of the mass conservation equation. The analyses employ emulated radar data from dual-Doppler placements 15, 30, and 45 km east of the mesocyclone, with volume scan intervals ranging from 10 to 150 s. The effect of near-surface data loss is examined by denying observations below 1 km in some of the analyses. At the longer radar ranges and when no data denial is imposed, the “traditional” method produces results similar to those of the variational method and is much less expensive to implement. However, at close range and/or with data denial, the variational method is much more accurate, confirming results from previous studies. The vorticity constraint shows the potential to improve the variational analysis substantially, reducing errors in the w retrieval by up to 30% for rapid-scan observations (≤30 s) at close range when the local vorticity tendency is estimated using spatially variable advection correction. However, the vorticity constraint also degrades the analysis for longer scan intervals, and the impact diminishes with increased range. Furthermore, analyses using 30-s data also frequently outperform analyses using 10-s data, suggesting a limit to the benefit of increasing the radar scan rate for variational DDA employing the vorticity constraint.

Mechanisms behind the precipitation increase in Norway

2021 ◽  
Author(s):  
Kjersti Konstali ◽  
Asgeir Sorteberg
Keyword(s):  
Relative Humidity ◽  
Interannual Variability ◽  
Vertical Velocity ◽  
Absolute Magnitude ◽  
Diagnostic Model ◽  
Positive Trend ◽  
Water Vapour Content ◽  
Near Surface ◽  
Precipitation Increase

<p>We use a dataset with observations of daily precipitation from 55 homogeneity tested stations in Norway over the period 1900-2019 available from MET-Norway. These observations show that precipitation in Norway has increased monotonically by 19% since 1900. Notably, over half of the overall increase was recorded within the decade of 1980-1990. To examine possible mechanisms behind the precipitation increase, we use a diagnostic model to separate the effects of changes in vertical velocity, temperature and relative humidity. We use vertical velocity, near-surface temperature and relative humidity from two reanalysis products, ECMWF’s ERA-20C and NOAA’s 20th Century Reanalysis. The model-based precipitation estimates capture the interannual variability as well as the long-term trend, but the absolute magnitude of precipitation is underestimated. Within our model, we find that the variability in vertical velocity chiefly determines the interannual variability and long-term trends. In fact, the trend in vertical velocities contributes with more than 75% of the total modelled trend in precipitation between 1900-2019, and more than 60% of the anomalies between 1980-1990. However, over the last decades (1979 to 2019), changes in temperature and relative humidity are the main contributors to the trend. Thus, different physical processes shape the trend at different times. We hypothesize that the strong precipitation increase in the 1980’s is linked to an unusual high number of low pressure systems reaching Norway from the North-Atlantic. In recent decades, direct effects of global warming (rising temperatures and hence increased water vapour content) are thought to be the main cause of the positive trend in precipitation over Norway. </p>

Potential linkage between the atmospheric summer circulation over Eurasia and preceding sea ice anomalies southwest of Greenland

2020 ◽  
Author(s):  
Jerome Sauer ◽  
Johanna Baehr ◽  
Nedjeljka Žagar
Keyword(s):  
Sea Ice ◽  
Atmospheric Circulation ◽  
North Atlantic ◽  
Vertical Velocity ◽  
Wave Train ◽  
Labrador Sea ◽  
Momentum Exchange ◽  
Near Surface ◽  
June July ◽  
Sst Anomalies

<p>Sea ice alters the surface albedo and modulates the heat, moisture and momentum exchange between the ocean and the atmosphere. Various studies suggest an influence of the sea ice on the atmospheric circulation, whereby the focus is often on simultaneous connections and Arctic-wide sea ice conditions. Sea ice has a strong memory and we thus hypothesize a potential feedback on the atmosphere also at higher lags. Using ERA5 reanalysis data between 1983 and 2017, the present work investigates a potential connection of the summer atmospheric circulation over Eurasia to winter sea ice anomalies southwest of Greenland. Composites of the June-July geopotential height pattern show a wave-train structure throughout the troposphere and the resulting circulation anomalies are found to influence the two metre temperatures over northeastern Europe and northern Russia. These anomalies are significantly correlated with December-January sea ice anomalies. Persistent sea surface temperature (SST) anomalies associated with the strong ice memory indicates that the winter signal is partly stored in the Labrador Sea. The observations indicate a response in the June-July 500 hPa vertical velocity in proximity of the strongest SST anomalies that is dynamically consistent with the lower-level and upper-level divergence pattern. The result suggests that the vertical velocity potentially connects a vorticity forcing in the upper troposphere to near-surface conditions over the Labrador Sea that originate from the preceeding winter. <br>A further analysis shows a particularly pronounced wave-train signal when the December-January ice anomalies appear in phase with a strong North Atlantic Oscillation (NAO) index. Those years are characterized by extensive and persistent SST anomalies in the North Atlantic bearing similarities with the tripole pattern that is known to be associated with the NAO. The SST signal is accompanied by widespread heat flux anomalies hinting at a further influence coming from the central North Atlantic. The study provides a first analysis of two possible factors that potentially contribute to the linkage between winter sea ice and the summer atmospheric circulation.</p>

Compressional velocities from multichannel refraction arrivals on Georges Bank—northwest Atlantic Ocean

Geophysics ◽  
1979 ◽  
Vol 44 (6) ◽  
pp. 1022-1033 ◽  
Author(s):  
L. D. McGinnis ◽  
R. M. Otis
Keyword(s):  
Atlantic Ocean ◽  
Velocity Distribution ◽  
Vertical Velocity ◽  
Georges Bank ◽  
Overburden Pressure ◽  
Northwest Atlantic ◽  
The North ◽  
Continuous Coverage ◽  
Velocity Gradients ◽  
North Edge

Velocities were obtained from unreversed, refracted arrivals on analog records from a 48‐channel, 3.6-km hydrophone cable (3.89 km from the airgun array to the last hydrophone array). Approximately 200 records were analyzed along 1500 km of ship track on Georges Bank, northwest Atlantic Ocean, to obtain regional sediment velocity distribution to a depth of 1.4 km below sea level. This technique provides nearly continuous coverage of refraction velocities and vertical velocity gradients. Because of the length of the hydrophone cable and the vertical velocity gradients, the technique is applicable only to the Continental Shelf and the shallower parts of the Continental Slope in water depths less than 300 m. Sediment diagenesis, the influence of overburden pressure on compaction, lithology, density, and porosity are inferred from these data. Velocities of the sediment near the water‐sediment interface range from less than 1500 m/sec on the north edge of Georges Bank to 1830 m/sec for glacial deposits in the northcentral part of the bank. Velocity gradients in the upper 400 m range from [Formula: see text] on the south edge of the bank to [Formula: see text] on the north. Minimum gradients of [Formula: see text] were observed south of Nantucket Island. Velocities and velocity gradients are explained in relation to physical properties of the Cretaceous, Tertiary, and Pleistocene sediments. Isovelocity contours at 100-m/sec intervals are nearly horizontal in the upper 400 m. Isovelocity contours at greater depths show a greater difference from a mean depth because of the greater structural and lithological variation. Bottom densities inferred from the velocities range from 1.7 to [Formula: see text] and porosities range from 48 to 62 percent. The most significant factor controlling velocity distribution on Georges Bank is overburden pressure and resulting compaction. From the velocity data we conclude that Georges Bank has been partially overridden by a continental ice sheet.

scholarly journals Brief Communication: On the influence of vertical velocity profiles on the combined power output of two model wind turbines in yaw

2017 ◽  
Author(s):  
Jannik Schottler ◽  
Agnieszka Hölling ◽  
Joachim Peinke ◽  
Michael Hölling
Keyword(s):  
Wind Turbines ◽  
Vertical Velocity ◽  
Velocity Gradient ◽  
Power Output ◽  
Velocity Profiles ◽  
Total Power ◽  
Misalignment Angle ◽  
Velocity Gradients ◽  
Total Power Output ◽  
Vertical Velocity Gradient

Abstract. The effect of vertical velocity gradients on the total power output of two aligned model wind turbines as a function of yaw misalignment of the upstream turbine is studied experimentally. It is shown that asymmetries of the power output of the downstream turbine and the combined power of both with respect to the upstream turbine's yaw misalignment angle can be linked to the vertical velocity gradient of the inflow.

Boundary Layer Turbulence and Orographic Precipitation Growth in Cold Clouds: Evidence from Profiling Airborne Radar Data

2011 ◽  
Vol 68 (10) ◽  
pp. 2344-2365 ◽  
Author(s):  
Bart Geerts ◽  
Qun Miao ◽  
Yang Yang
Keyword(s):  
Boundary Layer ◽  
Vertical Velocity ◽  
Radar Data ◽  
Windward Side ◽  
Inertial Subrange ◽  
Cloud Base ◽  
Orographic Precipitation ◽  
Turbulent Layer ◽  
Near Surface ◽  
Wide Range

Abstract Airborne vertically pointing Doppler radar data collected in 10 winter storms over the Medicine Bow Range in Wyoming are used to examine the importance of boundary layer (BL) turbulence for orographic precipitation growth. In all 10 cases, the cloud-base temperature was below 0°C and the bulk Froude number was more than 1.0, implying little or no blocking of the flow by the mountain barrier. Seven of the 10 storms sampled were postfrontal, with weak static stability and relatively shallow cloud tops. Doppler vertical velocity transects depict an approximately 1-km-deep turbulent layer draped over the terrain, sometimes clearly distinct from the stratified flow in the free troposphere aloft, where vertical motion is largely controlled by gravity wave dynamics. Spectral analysis of near-surface Doppler vertical velocity data in terrain-following coordinates reveals an inertial subrange with decreasing power with height toward the BL top. The composite of radar data profiles from the 10 flights is analyzed in frequency-by-altitude diagrams, with altitude expressed above ground level. These diagrams indicate a wide range of vertical velocities in the BL, and rapid snow growth within the BL as air rises through the cloud base, especially when BL turbulence is more intense. This snow growth is concentrated on the windward side of mountains, above the terrain–cloud base intersection. The dominant snow growth mechanism in the BL (i.e., by accretion or vapor deposition) cannot be established because of restrictions in aircraft flight level over complex terrain. Snow aggregation may have contributed to the observed rapid increase in reflectivity in the BL along the windward slope.

scholarly journals Evaluation of strain rates on Ice Stream B, Antarctica, obtained using GPS phase measurements

1994 ◽  
Vol 20 ◽  
pp. 254-262 ◽  
Author(s):  
Hulbe Christina L.
Keyword(s):  
Vertical Velocity ◽  
Stationary Waves ◽  
Strain Rates ◽  
Phase Measurements ◽  
Velocity Gradients ◽  
Ice Stream ◽  
Stop And Go ◽  
Global Positioning ◽  
Horizontal Strain ◽  
Ice Stream B

The “stop-and-go” kinematic Global Positioning System (GPS) technique was used to survey 270 stations twice within a 25 km by 10 km strain grid on the surface of Ice Stream B. One or two geodetic quality receivers operated as reference pivots, while two similar receivers traveled to grid stations. Each station was occupied for 25s. The method is rapid and reliable. Each survey was completed within 2 weeks. Calculated horizontal strain rates are accurate to 1%. Relative vertical velocities are accurate to 20 mm km1a-1. Maps of the four horizontal velocity gradients, relative vertical velocity and surface elevation are presented. The vertical velocity pattern is used to identify the part of the topography that forms stationary waves and that which is migrating. No strong quantitative link is found between the pattern in horizontal strain rate and surface topography. In particular, there is no evidence that the topography is relaxing toward isostasy. None of the “weir-type” sticky spots, which are commonly observed with other glaciers, is found but there could be two of the “submerged-boulder type”, which cause lateral flow diversion. Evidence for “hot stripes” and zones of preferred crystal orientation is not found.

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