scholarly journals Near-Surface Characteristics of the Turbulence Structure during a Mountain-Wave Event

2011 ◽  
Vol 50 (5) ◽  
pp. 1088-1106 ◽  
Author(s):  
Željko Večenaj ◽  
Stephan F. J. De Wekker ◽  
Vanda Grubišić
Keyword(s):  
Wave Activity ◽  
Western Slope ◽  
Spatial And Temporal Variability ◽  
Turbulence Structure ◽  
Mountain Wave ◽  
Owens Valley ◽  
Turbulent Length Scale ◽  
Near Surface ◽  
Aerosol Backscatter

AbstractA case study of mountain-wave-induced turbulence observed during the Terrain-Induced Rotor Experiment (T-REX) in Owens Valley, California, is presented. During this case study, large spatial and temporal variability in aerosol backscatter associated with mountain-wave activity was observed in the valley atmosphere by an aerosol lidar. The corresponding along- and cross-valley turbulence structure was investigated using data collected by three 30-m flux towers equipped with six levels of ultrasonic anemometers. Time series of turbulent kinetic energy (TKE) show higher levels of TKE on the sloping western part of the valley when compared with the valley center. The magnitude of the TKE is highly dependent on the averaging time on the western slope, however, indicating that mesoscale transport associated with mountain-wave activity is important here. Analysis of the TKE budget shows that in the central parts of the valley mechanical production of turbulence dominates and is balanced by turbulent dissipation, whereas advective effects appear to play a dominant role over the western slope. In agreement with the aerosol backscatter observations, spatial variability of a turbulent-length-scale parameter suggests the presence of larger turbulent eddies over the western slope than along the valley center. The data and findings from this case study can be used to evaluate the performance of turbulence parameterization schemes in mountainous terrain.

scholarly journals The Near-Surface Small-Scale Spatial and Temporal Variability of Sensible and Latent Heat Exchange in the Svalbard Region: A Case Study

2012 ◽  
Vol 2012 ◽  
pp. 1-14 ◽  
Author(s):  
Georg Jocher ◽  
Florian Karner ◽  
Christoph Ritter ◽  
Roland Neuber ◽  
Klaus Dethloff ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
Latent Heat ◽  
Small Scale ◽  
Katabatic Wind ◽  
Spatial And Temporal Variability ◽  
Eddy Covariance Method ◽  
Near Surface ◽  
Short Period ◽  
The Village

We present data from two eddy covariance systems for determining the sensible and latent heat flux and the shear stress near the earth's surface. One measures continuously since September 2010 close to the village Ny-Ålesund, Svalbard, the other one was located on Kongsvegen glacier for a short period in April 2011. Two examples for small-scale variability are discussed: near surface external gravity waves associated with katabatic wind from the Broggerbreen glacier located a few kilometres southwestern of Ny-Ålesund, and an episode when the two eddy systems at the different measurement sites captured very different conditions at the same time. In case of gravity wave motion the eddy covariance method results in fictitious positive fluxes due to the strong correlation between temperature and vertical wind, which has to be considered carefully. The comparison between the two sites showed that generally the dynamical processes near the Earth’s surface for Ny-Ålesund and the Kongsvegen glacier are different and local. But there are also cases of synchronization due to synoptic influences, and then the same processes are visible at the two measurement sites. Both examples show that the boundary layer in Ny-Ålesund is not only affected by the main glaciers in the east of the village, but also by other orographical characteristics and synoptic issues. Therefore, the only meaningful way to deal with point measurements is to consider them in context with the surrounding orography and the general meteorological conditions.

A hydrochemical and isotopic case study around a near surface radioactive waste disposal

2007 ◽  
Vol 95 (1) ◽  
Author(s):  
Zs. Szántó ◽  
É. Svingor ◽  
I. Futó ◽  
L. Palcsu ◽  
M. Molnár ◽  
...  
Keyword(s):  
Radioactive Waste ◽  
Waste Treatment ◽  
Radioactive Waste Disposal ◽  
Ion Chemistry ◽  
Continuous Transition ◽  
Near Surface ◽  
Disposal Facility ◽  
Treatment And Disposal ◽  
Site Characterisation

As part of the site characterisation program for the near surface radioactive waste treatment and disposal facility (RWTDF) at Püspökszilágy, Hungary, water quality and environmental isotope investigations have been carried out. Water samples for major ion chemistry, tritium,The chemical composition of groundwaters presented a continuous transition from waters situated on one side to waters on the top and on the other slope of the disposal suggesting the mixing of the three hydrochemical “endmembers”.Most of δ

scholarly journals Mesospheric Mountain Wave Activity in the Lee of the Southern Andes

2020 ◽  
Author(s):  
Pierre-Dominique Pautet ◽  
Michael J. Taylor ◽  
David C. Fritts ◽  
Diego Janches ◽  
Natalie Kaifler ◽  
...  
Keyword(s):  
Wave Activity ◽  
Mountain Wave ◽  
Southern Andes

Evaporite Palynology: a case study on the Permian (Lopgingian) Zechstein Sea

2021 ◽  
pp. jgs2020-174
Author(s):  
Martha E. Gibson ◽  
David J. Bodman
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Rapid Growth ◽  
Western Europe ◽  
Thermal Maturity ◽  
Near Surface ◽  
Wide Range ◽  
Terrestrial Environments ◽  
Insight Into

Evaporites characterize the Lopingian of Europe but present obstacles for biostratigraphic analysis. Here we present a case study for processing the Lopingian Zechstein Group evaporites of central-western Europe for the recovery of palynomorph assemblages. We demonstrate that full recovery is easily achieved with two main modes of palynomorph preservation observed; palynomorphs are either exceptionally well-preserved and orange-brown in colour, or poorly-preserved, brown-black, opaque and fragmented. The latter are reminiscent of palynomorphs of high thermal maturity. However, we propose that the intact nature of preservation is a result of the rapid growth of near-surface halite crystals, with their darkening a consequence of locally-enhanced heat flux due to the relatively high thermal conductivity of salt. This case study has enabled novel insight into an otherwise undescribed environment, and demonstrates the utility and possibility of extracting palynomorphs from a variety of rock salt types. This method should be applicable to a wide range of ancient evaporite and could also be applied to other Permian evaporite systems, which are used as analogues for extra-terrestrial environments.

scholarly journals Increasing the accuracy and temporal resolution of two-filter radon–222 measurements by correcting for the instrument response

2016 ◽  
Vol 9 (6) ◽  
pp. 2689-2707 ◽  
Author(s):  
Alan D. Griffiths ◽  
Scott D. Chambers ◽  
Alastair G. Williams ◽  
Sylvester Werczynski
Keyword(s):  
Temporal Resolution ◽  
Radon Concentration ◽  
Time Response ◽  
Slow Time ◽  
Flow Loop ◽  
Detector Performance ◽  
Convective Boundary ◽  
Near Surface ◽  
Instrument Response

Abstract. Dual-flow-loop two-filter radon detectors have a slow time response, which can affect the interpretation of their output when making continuous observations of near-surface atmospheric radon concentrations. While concentrations are routinely reported hourly, a calibrated model of detector performance shows that ∼ 40 % of the signal arrives more than an hour after a radon pulse is delivered. After investigating several possible ways to correct for the detector's slow time response, we show that a Bayesian approach using a Markov chain Monte Carlo sampler is an effective method. After deconvolution, the detector's output is redistributed into the appropriate counting interval and a 10 min temporal resolution can be achieved under test conditions when the radon concentration is controlled. In the case of existing archived observations, collected under less ideal conditions, the data can be retrospectively reprocessed at 30 min resolution. In one case study, we demonstrate that a deconvolved radon time series was consistent with the following: measurements from a fast-response carbon dioxide monitor; grab samples from an aircraft; and a simple mixing height model. In another case study, during a period of stable nights and days with well-developed convective boundary layers, a bias of 18 % in the mean daily minimum radon concentration was eliminated by correcting for the instrument response.

scholarly journals Evaluation of Forecasts of a Convectively Generated Bore Using an Intensively Observed Case Study from PECAN

2018 ◽  
Vol 146 (9) ◽  
pp. 3097-3122 ◽  
Author(s):  
Aaron Johnson ◽  
Xuguang Wang ◽  
Kevin R. Haghi ◽  
David B. Parsons
Keyword(s):  
Cross Sections ◽  
Turbulent Mixing ◽  
Weather Research And Forecasting ◽  
Cold Pool ◽  
Model Errors ◽  
Near Surface ◽  
Cold Pools ◽  
Convection Model

Abstract This paper presents a case study from an intensive observing period (IOP) during the Plains Elevated Convection at Night (PECAN) field experiment that was focused on a bore generated by nocturnal convection. Observations from PECAN IOP 25 on 11 July 2015 are used to evaluate the performance of high-resolution Weather Research and Forecasting Model forecasts, initialized using the Gridpoint Statistical Interpolation (GSI)-based ensemble Kalman filter. The focus is on understanding model errors and sensitivities in order to guide forecast improvements for bores associated with nocturnal convection. Model simulations of the bore amplitude are compared against eight retrieved vertical cross sections through the bore during the IOP. Sensitivities of forecasts to microphysics and planetary boundary layer (PBL) parameterizations are also investigated. Forecasts initialized before the bore pulls away from the convection show a more realistic bore than forecasts initialized later from analyses of the bore itself, in part due to the smoothing of the existing bore in the ensemble mean. Experiments show that the different microphysics schemes impact the quality of the simulations with unrealistically weak cold pools and bores with the Thompson and Morrison microphysics schemes, cold pools too strong with the WDM6 and more accurate with the WSM6 schemes. Most PBL schemes produced a realistic bore response to the cold pool, with the exception of the Mellor–Yamada–Nakanishi–Niino (MYNN) scheme, which creates too much turbulent mixing atop the bore. A new method of objectively estimating the depth of the near-surface stable layer corresponding to a simple two-layer model is also introduced, and the impacts of turbulent mixing on this estimate are discussed.

scholarly journals Initiation and Maintenance Mechanisms for Heavy Precipitation System over a Mountainous Island under a Prevailing Monsoon Current

2016 ◽  
Vol 5 (2) ◽  
pp. 90
Author(s):  
Y.-L. Lin ◽  
K.-Y. Lee ◽  
C.-S. Chen ◽  
F.-Y. Cheng ◽  
P.-L. Lin ◽  
...  
Keyword(s):  
Heavy Rainfall ◽  
Mesoscale Model ◽  
Convective Available Potential Energy ◽  
Leading Edge ◽  
Western Slope ◽  
Mountain Range ◽  
Unstable Flow ◽  
Near Surface ◽  
Precipitation System ◽  
Early Afternoon

In this study, the initiation and maintenance mechanisms of two long-lived, summer heavy rainfall systems over Taiwan are investigated by performing observational data analyses and numerical simulations using a mesoscale model. For both cases of 9-10 July 2008 (Case A) and 18-19 August 2006 (Case B), the heavy rainfall system developed over the western slope of the Central Mountain Range (CMR) under low-level prevailing southwesterly and westerly flows in early afternoon, respectively. These heavy rainfall systems were moving westward toward Taiwan Strait from CMR, while the embedded individual cells were moving in the opposite direction, behaving like a multicell storm. It was also found these individual cells were initiated, enhanced, and then maintained at the leading edge of the near-surface cool outflow and merged with the heavy rainfall systems which became long-lived. These heavy rainfall systems were classified as an upstream propagating precipitation system in a low Froude-number, conditionally unstable flow with high convective available potential energy (CAPE) or Regime I as proposed in a previous study.

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