Laboratory Study of Topographic Effects on the Near-surface Tornado Flow Field

Although draped magnetic surveys contain more information about the magnetization of the rocks near the surface of the earth than surveys at constant elevation, allowance for the effects of the terrain is critical for their correct interpretation. A new method for calculating the magnetic effect of the topography from a digital terrain model by integrating analytically in the vertical direction and then numerically in the horizontal plane is presented. This method lends itself to the calculation of anomalies when the magnetization of the rocks varies with position and thus is well suited to the inversion of draped aeromagnetic surveys to obtain the apparent magnetization of the surficial rocks. This inversion is achieved by repeated use of an approximate inverse function in the form of a two‐dimensional (2-D) filter that is applied to gridded data. An example, using draped magnetic data collected over White Island, an active volcanic island of high relief, shows that although the anomaly pattern is dominated by topographic effects, the distribution of near‐surface magnetic bodies can be determined by a joint inversion of the data and the topography. One of the highly magnetized areas of White Island is interestingly in the vicinity of the active crater, with another near the inner wall of the caldera where there are numerous fumaroles. It may be expected that the higher temperatures in these areas would reduce the magnetization. However, it appears that an explanation for the higher magnetization can be found in the stability field of the mineral magnetite.

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Effects of the flow field on small scale phytoplankton patchiness

Hydrology Research ◽

10.2166/nh.2005.0007 ◽

2005 ◽

Vol 36 (1) ◽

pp. 85-98 ◽

Cited By ~ 9

Author(s):

Gerald Schernewski ◽

Victor Podsetchine ◽

Timo Huttula

Keyword(s):

Flow Field ◽

Water Surface ◽

Large Degree ◽

Low Flow ◽

Small Scale ◽

Central Basin ◽

The South ◽

Near Surface ◽

Light Gradient ◽

Wind Sheltering

We present an example of small scale (10–100 m) horizontal, subsurface patchiness of phytoplankton (Ceratium) during an intensive bloom in August 1993 and link it to the flow field. In the small Lake Belau (1.1 km2) in northern Germany large areas of the water surface are sheltered from wind, due to vegetation. Wind sheltering effects decrease with wind speed and below 2 m/s a spatially homogeneous wind field is observed. Under weak wind conditions near-surface Ceratium patches with local chlorophyll-concentrations up to 200 mg/m3 were observed in the south bay (0.3 m depth) as well as in parts of the central basin (1 m depth). Detailed flow simulations show very good agreement between location and size of current gyres and phytoplankton patches. Inside the gyres we find low flow velocities with low vertical turbulence. This allows Ceratium to form distinct vertical layers with high densities close to the water surface, according to the light gradient. Especially in the south bay flow eddies are determined by the course of the coastline and their location and intensity is, to a large degree, independent of prevailing wind directions.

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Precipitation simulation for Dronning Maud Land using the COSMO Model

Antarctic Science ◽

10.1017/s0954102009990149 ◽

2009 ◽

Vol 21 (6) ◽

pp. 643-662 ◽

Cited By ~ 7

Author(s):

Ulrike Wacker ◽

Hinnerk Ries ◽

Ulrich Schättler

Keyword(s):

High Resolution ◽

Extreme Event ◽

Temporal Distribution ◽

Mesh Size ◽

Weather Forecast ◽

Horizontal Distribution ◽

Topographic Effects ◽

Near Surface ◽

Cosmo Model ◽

Dronning Maud Land

AbstractA weather episode, characterized by the passage of synoptic disturbances, is investigated for Dronning Maud Land, Antarctica. Due to the sparsity of observations, information about the spatial and temporal distribution of precipitation at high resolution can be gained only by modelling. The simulations presented here are performed with the high-resolution, non-hydrostatic weather forecast COSMO Model with a horizontal mesh size of 7 km. The comparison with observations at four stations shows that the simulation captures the general meteorological conditions well, while a warm bias and a weak daily cycle are found in near-surface temperatures. With regard to precipitation, the timing relates well to the observations; the amount of precipitation, however, is that of an extreme event and possibly overestimated in some regions. The horizontal distribution of precipitation is dominated by topographic effects. The simulations show the general decrease of precipitation toward the interior, as seen in the accumulation climatology, however, the decrease is not monotonous. For example, in the simulations horizontal structures such as precipitation bands of some 100 km width appear on the plateau, which can only be resolved by models with mesh sizes of 10 km or less.

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Topographic Effects on Titan’s Dune-forming Winds

Atmosphere ◽

10.3390/atmos10100600 ◽

2019 ◽

Vol 10 (10) ◽

pp. 600

Author(s):

Larson

Keyword(s):

Surface Wind ◽

Topographic Effects ◽

Wind Regime ◽

Near Surface ◽

Global Circulation ◽

Global Circulation Models ◽

Community Atmosphere Model ◽

Active Debate ◽

The Tropics ◽

The Impact

The Cassini mission made an unexpected discovery when it found evidence of linear dune fields on Titan’s surface. The orientation of the dunes and their interaction with topography allow scientists to estimate the dominant wind direction on the surface of Titan. There is some consensus in the community that the dune-forming winds must be net westerly, however, there is an active debate about the dune-forming wind regime. This debate has been guided by several studies of Earth dune fields considered analogous to the Titan dunes including those in Namibia, the Sahara, the Serengeti, and China. Complicating this active debate about the surface wind regime is the fact that global circulation models (GCMs) have historically not been able to reproduce westerly surface winds in the tropics. Here we use the Titan Community Atmosphere Model (CAM) to quantify the impact of topography and an added torque on Titan’s dune-forming winds. Dunes tend to form at higher elevations on Titan, and adding topography to the model alters the near-surface wind directions, making them more westerly and consistent with the dune orientations. The addition of topography and added torque create a wind regime that is consistent with linear dunes in areas of stabilized sediment.

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Study of turbulent mixing processes at a mesoscale confluence through aerial drone imagery and eddy-resolved modelling

10.5194/egusphere-egu21-9676 ◽

2021 ◽

Author(s):

Jason Duguay ◽

Pascale Biron ◽

Thomas Buffin-Bélanger

Keyword(s):

Flow Field ◽

Suspended Sediment ◽

Large Scale ◽

Surface Flow ◽

Mean Flow ◽

Turbulent Structures ◽

Mixing Processes ◽

Near Surface ◽

Vortical Structures ◽

Instantaneous Flow Field

<p>The large-scale turbulent structures that develop at confluences fall into three main categories: vertically orientated (Kelvin-Helmholtz) vortices, large-scale secondary flow helical cells and smaller strongly coherent streamwise orientated vortices. The causal mechanisms of each class, how they interact with one another and their respective contributions to mixing is still unclear. Our investigation emphasises the role played by the instantaneous flow field in mixing at a mesoscale confluence (Mitis-Neigette, Quebec, Canada) by complementing aerial drone observations of turbulent suspended sediment mixing processes with results from a high-resolution eddy-resolved numerical simulation. The high velocity near-surface flow of the main channel (Mitis) separates at the crest of the scour hole before downwelling upon collision with the slower tributary (Neigette). Fed by incursions of lateral momentum of the Mitis, shear generated Kelvin-Helmholtz instabilities expand as they advect along the mixing-interface. As the instabilities shed, water from the deeper Neigette passes underneath the fast, over-topping Mitis, causing a large portion of the Neigette&#8217;s discharge to cross under the mixing-interface in a short distance. The remaining flow of the tributary crosses over inside large-scale lateral incursions farther downstream. The downwelling Mitis, upwelling Neigette and recirculatory cell interact to generate coherent streamwise vortical structures which assist in rapidly mixing the waters of the two rivers in the vicinity of the mixing-interface. Evidence of large-scale helical cells were not observed in the flow field. Results suggest that flow interaction with bathymetry, and both vertical and streamwise orientated coherent turbulent structures play important roles in mixing at confluences. Our findings strongly suggest that investigating mixing at confluences cannot be based solely on mean flow field variables as this approach can be misleading. Visualization of a confluence&#8217;s mixing processes as revealed by suspended sediment gradients captured in aerial drone imagery complemented with eddy-resolved numerical modelling of the underlying flow is a promising means to gain insights on the role of large-scale turbulent structures on mixing at confluences.</p>

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An Analysis of the Secondary Flow Around a Tandem Blade Under the Presence of a Tip Gap in a High-Speed Linear Compressor Cascade

Journal of Turbomachinery ◽

10.1115/1.4051558 ◽

2021 ◽

pp. 1-20

Author(s):

Liesbeth Konrath ◽

Dieter Peitsch ◽

Alexander Heinrich

Keyword(s):

Flow Field ◽

High Speed ◽

Tip Clearance ◽

Compressor Cascade ◽

Complex Flow ◽

Flow Topology ◽

Linear Compressor ◽

Near Surface ◽

Oil Flow ◽

Linear Compressor Cascade

Abstract Tandem blades have often been under investigation, experimentally as well as numerically, but most studies have been about tandem blade stators without tip gap. This work analyzes the influence of a tip gap on the flow field of a tandem blade for engine core compressors. Experiments have been conducted in a high-speed linear compressor cascade on a tandem and a reference geometry. The flow is analyzed using five-hole probe measurements in the wake of the blades and oil flow visualization to show the near surface stream lines. First, the results for design conditions (tandem and conventional blade) are compared to measurements on corresponding blades without tip gap. Similarities and differences in the flow topology due to the tip clearance are analyzed, showing that the introduction of the tip clearance has a similar influence on the loss and turning development for the tandem and the conventional blade. The tandem blade features two tip clearance vortices with a complex flow interaction and the possible formation of a third counter-rotating vortex between them. An incidence variation from 0deg to 5deg for both blades indicates at first a similar behavior. After a separation of the flow field into gap and non-gap half it becomes apparent that the tandem blade shows higher losses on the gap side, while featuring a close-to-constant behavior on the non-gap side. Further investigation of the flow on the gap side shows indicators of the front blade exhibiting tip clearance vortex break down.

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A Laboratory Study on the Ion-Flow Field Model of the DC Wires in Stable Wind

IEEE Transactions on Power Delivery ◽

10.1109/tpwrd.2015.2444372 ◽

2015 ◽

Vol 30 (5) ◽

pp. 2346-2352 ◽

Cited By ~ 8

Author(s):

Yongzan Zhen ◽

Xiang Cui ◽

Tiebing Lu ◽

Xiaobo Wang ◽

Donglai Wang ◽

...

Keyword(s):

Flow Field ◽

Laboratory Study ◽

Field Model ◽

Ion Flow

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Formation of RADARSAT backscatter feature and undulating firn stratigraphy at an ice-stream margin

Annals of Glaciology ◽

10.3189/2013aog64a202 ◽

2013 ◽

Vol 54 (64) ◽

pp. 90-96 ◽

Cited By ~ 3

Author(s):

Felix Ng ◽

Edward C. King

Keyword(s):

Flow Field ◽

Steady Flow ◽

Kinematic Model ◽

Ice Sheets ◽

Surface Flow ◽

Three Dimensions ◽

West Antarctica ◽

Near Surface ◽

Backscatter Intensity ◽

Ice Stream

AbstractOn RADARSAT imagery, the southern margin of the onset zone of Bindschadler Ice Stream, West Antarctica, manifests a multi-banded feature, with brightness varying across the bands and oscillating along each band. Ground-based radar profiles across the margin reveal folds in the firn stratigraphy associated with this pattern and provide evidence for correlation between the depth of shallow isochrones and the RADARSAT backscatter intensity on each profile, allowing us to interpret the banded feature for firn-layer geometry in three dimensions. We use a kinematic model of isochrone depth evolution to show how layer folding and the band expression may result from deformation and advection in the near-surface flow field at ice-stream margins, even with steady flow. The model predicts the formation of longitudinally patterned bands when the ice-stream acceleration fluctuates along flow. Concerted study of the planform and stratigraphy of other RADARSAT-detected features on the ice sheets may help us understand their origin.

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