Two-dimensional simulations of katabatic layers observed during the GIMEX experiment

Abstract. The hydrostatic model SALSA is used to simulate a particular event observed during the Greenland Ice Margin EXperiment "GIMEX" (on July 12th, 1991). The time evolution of the large-scale flow was incorporated in the model through time dependent boundary conditions which were updated using the closest upwind sounding. A turbulent scheme for the stable boundary layer and an appropriate parametrization of the surface fluxes implemented in the same model, are used for this study. The simulation results are discussed and compared to the available observations. The computed turbulent fluxes are correctly estimated. The model predicts a mixing zone of about 1500 m high which is in good agreement with tundra site observations. Over the ice cap, the katabatic layer is correctly simulated by the model. Its height of 80-300 m is well estimated. The comparison between the simulation and observations taken at ice cap sites is reasonably valid. The ablation computed along the ice cap corresponds well to the values reconstructed of observations at sites 4 and 9. Finally, a sensibility study to a specified westward geostrophic wind (2 ms-1) shows that the consideration of this latter improves the simulated tundra wind evolution.Key words. Meteorology and atmospheric dynamics (mesoscale meteorology; polar meteorology; turbulance)

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Development of Two-Dimensional Non-Hydrostatic Wave Model Based on Central-Upwind Scheme

Journal of Marine Science and Engineering ◽

10.3390/jmse8070505 ◽

2020 ◽

Vol 8 (7) ◽

pp. 505

Author(s):

Gangfeng Wu ◽

Ying-Tien Lin ◽

Ping Dong ◽

Kefeng Zhang

Keyword(s):

Hydrostatic Pressure ◽

Large Scale ◽

Wave Model ◽

Water Model ◽

Two Dimensional ◽

Shallow Water Model ◽

Practical Engineering ◽

Hydrostatic Model ◽

Good Agreement ◽

Biconjugate Gradient

In this study, a two-dimensional depth-integrated non-hydrostatic wave model is developed. The model solves the governing equations with hydrostatic and non-hydrostatic pressure separately. The velocities under hydrostatic pressure conditions are firstly obtained and then modified using the biconjugate gradient stabilized method. The hydrostatic front approximation (HFA) method is used to deal with the wave breaking issue, and after the wave breaks, the non-hydrostatic model is transformed into the hydrostatic shallow water model, where the non-hydrostatic pressure and vertical velocity are set to zero. Several analytical solutions and laboratory experiments are used to verify the accuracy and robustness of the developed model. In general, the numerical simulations are in good agreement with the theoretical or experimental results, which indicates that the model is able to simulate large-scale wave motions in practical engineering applications.

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Numerical Simulation of Natural Convection in Stationary and Rotating Cavities

Volume 4: Turbo Expo 2004 ◽

10.1115/gt2004-53528 ◽

2004 ◽

Cited By ~ 18

Author(s):

Zixiang Sun ◽

Alistair Kifoil ◽

John W. Chew ◽

Nicholas J. Hills

Keyword(s):

Heat Transfer ◽

Centrifugal Force ◽

Large Scale ◽

Transfer Rates ◽

Buoyancy Driven Flows ◽

Gravity Driven ◽

Gravity Driven Flow ◽

Large Scale Flow ◽

Rayleigh Numbers ◽

Good Agreement

In compressor inter-disc cavities with a central axial throughflow it is known that the flow and heat transfer is strongly affected by buoyancy in the centrifugal force field. As a step towards developing CFD methods for such flows, buoyancy-driven flows under gravity in a closed cube and under centrifugal force in a sealed rotating annulus have been studied. Numerical simulations are compared with the experimental results of Kirkpatrick and Bohn (1986) and Bohn et al (1993). Two different CFD codes have been used and are shown to agree for the stationary cube problem. Unsteady simulations for the stationary cube show good agreement with measurements of heat transfer, temperature fluctuations, and velocity fluctuations for Rayleigh numbers up to 2 × 1010. Similar simulations for the rotating annulus also show good agreement with measured heat transfer rates. The CFD results confirm Bohn et al’s results, showing reduced heat transfer and a different Rayleigh number dependency compared to gravity-driven flow. Large scale flow structures are found to occur, at all Rayleigh numbers considered.

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Numerical Simulations of Fog Events in Southern Portugal

Advances in Meteorology ◽

10.1155/2017/1276784 ◽

2017 ◽

Vol 2017 ◽

pp. 1-16 ◽

Cited By ~ 7

Author(s):

Carlos Policarpo ◽

Rui Salgado ◽

Maria João Costa

Keyword(s):

Large Scale ◽

Surface Fluxes ◽

Large Reservoir ◽

Spatial Coverage ◽

Southern Portugal ◽

Alqueva Reservoir ◽

Temporal Persistence ◽

Formation And Evolution ◽

Forcing Mechanisms ◽

Good Agreement

This work aims at improving the knowledge on fog formation and its evolution in the Alentejo region (Portugal). For this purpose, brief regional fog climatology, essentially based on information from the Beja Air Base meteorological station, was produced and several numerical high resolution simulations were performed using the Meso-NH. The ECOCLIMAP database used to generate the model physiography was improved to include the Alqueva reservoir (~250 km2), filled in 2003. The model results were compared with surface and satellite observations, showing good agreement in terms of fog occurrence and persistence. Various forcing mechanisms for formation, development, and dissipation of fog were identified, confirming the influence of two small mountains that block the moist air from the Atlantic Ocean, preventing the fog from reaching innermost regions. The introduction of the Alqueva large reservoir induces changes in the landscape and environment. The effects of the water vapour addition and of the changes in mass and energy surface fluxes on fog formation and evolution were studied. It was found that the reservoir may have a direct impact on fog formation over the lake and its vicinity. Depending on the large scale meteorological conditions, their influence can be both positive and negative, in terms of spatial coverage and temporal persistence.

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Composite Vertical-Motion Patterns near North American Polar–Subtropical Jet Superposition Events

Monthly Weather Review ◽

10.1175/mwr-d-20-0140.1 ◽

2020 ◽

Vol 148 (11) ◽

pp. 4565-4585

Author(s):

Andrew C. Winters ◽

Daniel Keyser ◽

Lance F. Bosart

Keyword(s):

Large Scale ◽

Vertical Motion ◽

Geostrophic Wind ◽

Single Step ◽

Subsequent Formation ◽

Motion Patterns ◽

Wind Speeds ◽

Middle Latitudes ◽

Subtropical Jet ◽

Large Scale Flow

AbstractA polar–subtropical jet superposition is preceded by the development of a polar cyclonic potential vorticity (PV) anomaly at high latitudes and a tropical anticyclonic PV anomaly at subtropical latitudes. A confluent large-scale flow pattern can lead to the juxtaposition of these respective PV anomalies at middle latitudes, resulting in the addition of the nondivergent circulations induced by each PV anomaly and an increase in upper-tropospheric wind speeds at the location of jet superposition. Once these PV anomalies become juxtaposed, vertical motion within the near-jet environment facilitates the advection and diabatic redistribution of tropopause-level PV, and the subsequent formation of the steep, single-step tropopause structure that characterizes a jet superposition. Given the importance of vertical motion during the formation of jet superpositions, this study adopts a quasigeostrophic (QG) diagnostic approach to quantify the production of vertical motion during three types of jet superposition events: polar dominant, eastern subtropical dominant, and western subtropical dominant. The diagnosis reveals that the geostrophic wind induced by polar cyclonic QGPV anomalies is predominantly responsible for QG vertical motion in the vicinity of jet superpositions. The QG vertical motion diagnosed from the along-isotherm component of the Q vector, which represents the vertical motion associated with synoptic-scale waves, is dominant within the near-jet environment. The QG vertical motion diagnosed from the across-isotherm component of the Q vector, which represents the vertical motion associated with frontal circulations in the vicinity of the jet, is subordinate within the near-jet environment, but is relatively more important during eastern subtropical dominant events compared to polar dominant and western subtropical dominant events.

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Large-Scale Flow Patterns in the Solar Atmosphere

Symposium - International Astronomical Union ◽

10.1017/s0074180900087817 ◽

1990 ◽

Vol 142 ◽

pp. 101-105

Author(s):

K.R. Sivaraman

Keyword(s):

Solar Cycle ◽

Magnetic Fields ◽

Time Evolution ◽

Large Scale ◽

Opposite Polarity ◽

Meridional Flow ◽

The Sun ◽

Solar Cycle Variation ◽

Large Scale Flow ◽

Good Agreement

It is now well established (McIntosh 1979; Makarov and Sivaraman 1983) that the filament and filament channels seen in the H-alpha spectroheliograms (or filtergrams) can be used as reliable tracers for studying the time evolution of large-scale magnetic fields on the Sun. These features represent the neutral lines between the unipolar regions of opposite polarity. Comparison of the synoptic charts compiled from H-alpha pictures with those from full-disc magnetograms for the same period shows very good agreement and hence the former can be used with confidence for time evolution studies of large-scale unipolar regions for those periods when the magnetographs did not even exist. In this paper we shall present one of the results of our study (Makarov and Sivaraman 1983, 1989) on the migration of H-alpha filaments, namely, the existence of the meridional flow on the Sun. We shall extend it further to show the participation of this meridional flow in the solar cycle variation.

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The Impact of Large-scale Flow Direction on the Formation of a Glacier Boundary Layer: Two LES Case Studies

10.5194/egusphere-egu21-2620 ◽

2021 ◽

Author(s):

Brigitta Goger ◽

Ivana Stiperski ◽

Keyword(s):

Boundary Layer ◽

Case Studies ◽

Flow Structure ◽

Large Scale ◽

Surface Fluxes ◽

Horizontal Wind ◽

Glacier Surface ◽

Ice Surface ◽

Large Scale Flow ◽

The Impact

The mass balance of mountain glaciers needs correct assessment for several applications, e. g. sea level rise estimates, catchment hydrology, and natural hazard warnings. It results, at any point on a glacier, from energy, mass, and momentum fluxes at the glacier-atmosphere interface. However, surface fluxes on glaciers are highly heterogeneous in space and time. To learn more about the processes leading to the spatial surface flux structure over a glacier surface, we employ large-eddy simulations with the WRF model at a horizontal grid mesh size of 48 m over the Hintereisferner, an approximately 6 km long valley glacier in the Austrian Alps. For model evaluation purposes, we use, besides our permanent measurement framework, four turbulence flux towers located on along- and across-glacier transects which were maintained in August 2018 on the glacier surface. Simulations were conducted for two case studies, namely one day with synoptic flow from the South-West (SW), and a day with synoptic flow from the North-West (NW). Comparison with the observations suggests that the model is able to reproduce the larger-scale flow structure and the local processes over the ice surface. On the SW day, thermally-induced flows dominate the near-surface wind patterns and a stable boundary layer forms above the ice surface due to the alignment of the katabatic glacier wind with the larger-scale flow. Under these conditions, the glacier surface is exposed to horizontal cold-air advection. However, on the NW day, the local terrain leads to the formation of a gravity wave with severe turbulence. The resulting cross-glacier flow erodes the glacier boundary layer, and the glacier ice experiences horizontal warm-air advection. In both cases, the model simulates the complex flow structure on different length scales that affect the vertical and horizontal exchange processes over the glacier surface and the local heat advection during the daytime. The spatial sensible heat flux pattern is strongly connected to the horizontal wind speed, wind direction, and TKE. The experiment suggests a major impact of the large-scale flow structure and the flow modification by the underlying terrain. Our model setup is able to resolve the relevant scales and is therefore a valuable tool to gain insight on the surface fluxes over truly complex, heterogeneous terrain.

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DYNAMICS OF LARGE SCALE FLOW AND ITS EFFECT ON HEAT TRANSFER IN TURBULENT CONVECTION

10.1615/ihtc16.cov.023932 ◽

2018 ◽

Author(s):

Arnab Kumar De ◽

P. K. Mishra

Keyword(s):

Heat Transfer ◽

Large Scale ◽

Turbulent Convection ◽

Large Scale Flow

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Large-scale flow field visualization for aneurysm treatment

ACM SIGAPP Applied Computing Review ◽

10.1145/570142.570145 ◽

2001 ◽

Vol 9 (1) ◽

pp. 3-7

Author(s):

Damon Liu ◽

Mark Burgin ◽

Walter Karplus ◽

Daniel Valentino

Keyword(s):

Flow Field ◽

Large Scale ◽

Aneurysm Treatment ◽

Large Scale Flow

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Reconstruction of large scale flow structures in a stirred tank from limited sensor data

AIChE Journal ◽

10.1002/aic.17348 ◽

2021 ◽

Author(s):

Kirill Mikhaylov ◽

Stelios Rigopoulos ◽

George Papadakis

Keyword(s):

Large Scale ◽

Sensor Data ◽

Stirred Tank ◽

Flow Structures ◽

Large Scale Flow

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EZ-ALBI Score for Predicting Hepatocellular Carcinoma Prognosis

Liver Cancer ◽

10.1159/000508971 ◽

2020 ◽

Vol 9 (6) ◽

pp. 734-743

Author(s):

Kazuya Kariyama ◽

Kazuhiro Nouso ◽

Atsushi Hiraoka ◽

Akiko Wakuta ◽

Ayano Oonishi ◽

...

Keyword(s):

Hepatocellular Carcinoma ◽

Liver Function ◽

Large Scale ◽

Regression Coefficient ◽

Information Criterion ◽

Proportional Hazard ◽

Cox Proportional Hazard ◽

Highly Correlated ◽

Survival Risk ◽

Good Agreement

Introduction: The ALBI score is acknowledged as the gold standard for the assessment of liver function in patients with hepatocellular carcinoma (HCC). Unlike the Child-Pugh score, the ALBI score uses only objective parameters, albumin (Alb) and total bilirubin (T.Bil), enabling a better evaluation. However, the complex calculation of the ALBI score limits its applicability. Therefore, we developed a simplified ALBI score, based on data from a large-scale HCC database.We used the data of 5,249 naïve HCC cases registered in eight collaborating hospitals. Methods: We developed a new score, the EZ (Easy)-ALBI score, based on regression coefficients of Alb and T.Bil for survival risk in a multivariate Cox proportional hazard model. We also developed the EZ-ALBI grade and EZ-ALBI-T grade as alternative options for the ALBI grade and ALBI-T grade and evaluated their stratifying ability. Results: The equation used to calculate the EZ-ALBI score was simple {[T.Bil (mg/dL)] – [9 × Alb (g/dL)]}; this value highly correlated with the ALBI score (correlation coefficient, 0.981; p < 0.0001). The correlation was preserved across different Barcelona clinic liver cancer grade scores (regression coefficient, 0.93–0.98) and across different hospitals (regression coefficient, 0.98–0.99), indicating good generalizability. Although a good agreement was observed between ALBI and EZ-ALBI, discrepancies were observed in patients with poor liver function (T.Bil, ≥3 mg/dL; regression coefficient, 0.877). The stratifying ability of EZ-ALBI grade and EZ-ALBI-T grade were good and their Akaike’s information criterion values (35,897 and 34,812, respectively) were comparable with those of ALBI grade and ALBI-T grade (35,914 and 34,816, respectively). Conclusions: The EZ-ALBI score, EZ-ALBI grade, and EZ-ALBI-T grade are useful, simple scores, which might replace the conventional ALBI score in the future.

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