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Investigations of boundary layer structure, cloud characteristics and vertical mixing of aerosols at Barbados with large eddy simulations
Large eddy simulations (LESs) are performed for the area of the Caribbean island Barbados to investigate island effects on boundary layer modification, cloud generation and vertical mixing of aerosols. Due to the presence of a topographically structured island surface in the domain center, the model setup has to be designed with open lateral boundaries. In order to generate inflow turbulence consistent with the upstream marine boundary layer forcing, we use the cell perturbation method based on finite amplitude potential temperature perturbations. In this work, this method is for the first time tested and validated for moist boundary layer simulations with open lateral boundary conditions. Observational data obtained from the SALTRACE field campaign is used for both model initialization and a comparison with Doppler wind and Raman lidar data. Several numerical sensitivity tests are carried out to demonstrate the problems related to “gray zone modeling” when using coarser spatial grid spacings beyond the inertial subrange of three-dimensional turbulence or when the turbulent marine boundary layer flow is replaced by laminar winds. Especially cloud properties in the downwind area west of Barbados are markedly affected in these kinds of simulations. Results of an additional simulation with a strong trade-wind inversion reveal its effect on cloud layer depth and location. Saharan dust layers that reach Barbados via long-range transport over the North Atlantic are included as passive tracers in the model. Effects of layer thinning, subsidence and turbulent downward transport near the layer bottom at z ≈ 1800 m become apparent. The exact position of these layers and strength of downward mixing is found to be mainly controlled atmospheric stability (especially inversion strength) and wind shear. Comparisons of LES model output with wind lidar data show similarities in the downwind vertical wind structure. Additionally, the model results accurately reproduce the development of the daytime convective boundary layer measured by the Raman lidar
A new roughness length parameterization accounting for wind–wave (mis)alignment
Two-way feedback occurs between offshore wind and waves.
However, the influence of the waves on the wind profile remains understudied,
in particular the momentum transfer between the sea surface and the
atmosphere. Previous studies showed that for swell waves it is possible to
have increasing wind speeds in case of aligned wind–wave directions. However,
the opposite is valid for opposed wind–wave directions, where a decrease in
wind velocity is observed. Up to now, this behavior has not been included in
most numerical models due to the lack of an appropriate parameterization of
the resulting effective roughness length. Using an extensive data set of
offshore measurements in the North Sea and the Atlantic Ocean, we show that
the wave roughness length affecting the wind is indeed dependent on the
alignment between the wind and wave directions. Moreover, we propose a new
roughness length parameterization, taking into account the dependence on
alignment, consisting of an enhanced roughness length for increasing
misalignment. Using this new roughness length parameterization in numerical
models might facilitate a better representation of offshore wind, which is
relevant to many applications including offshore wind energy and climate
modeling.</p
Large-eddy simulation sensitivities to variations of configuration and forcing parameters in canonical boundary-layer flows for wind energy applications
The sensitivities of idealized large-eddy simulations (LESs) to variations of
model configuration and forcing parameters on quantities of interest to wind
power applications are examined. Simulated wind speed, turbulent fluxes,
spectra and cospectra are assessed in relation to variations in two physical
factors, geostrophic wind speed and surface roughness length, and several
model configuration choices, including mesh size and grid aspect ratio,
turbulence model, and numerical discretization schemes, in three different
code bases. Two case studies representing nearly steady neutral and
convective atmospheric boundary layer (ABL) flow conditions over nearly flat
and homogeneous terrain were used to force and assess idealized LESs, using
periodic lateral boundary conditions. Comparison with fast-response velocity
measurements at 10 heights within the lowest 100 m indicates that most model
configurations performed similarly overall, with differences between observed
and predicted wind speed generally smaller than measurement variability.
Simulations of convective conditions produced turbulence quantities and
spectra that matched the observations well, while those of neutral
simulations produced good predictions of stress, but smaller than observed
magnitudes of turbulence kinetic energy, likely due to tower wakes
influencing the measurements. While sensitivities to model configuration
choices and variability in forcing can be considerable, idealized LESs are
shown to reliably reproduce quantities of interest to wind energy
applications within the lower ABL during quasi-ideal, nearly steady neutral
and convective conditions over nearly flat and homogeneous terrain.</p
Coupled mesoscale–microscale modeling of air quality in a polluted city using WRF-LES-Chem
To perform realistic high-resolution air quality modeling in a
polluted urban area, the Weather Research and Forecasting (WRF) model is
used with an embedded large-eddy simulation (LES) module and online
chemistry. As an illustration, a numerical experiment is conducted in the
megacity of Hong Kong, which is characterized by multi-type inhomogeneous
pollution sources and complex topography. The results from the
multi-resolution simulations at mesoscale and LES scales are evaluated by
comparing them with ozone sounding profiles and surface observations. The
comparisons show that both mesoscale and LES simulations reproduce the
mean concentrations of the chemical species and their diurnal variations at
the background stations well. However, the mesoscale simulations largely
underestimate the NOx concentrations and overestimate O3 at the
roadside stations due to the coarse representation of the traffic emissions.
The LES simulations improve the agreement with the measurements near the
road traffic, and the LES with the highest spatial resolution (33.3 m)
provides the best results. The large-eddy simulations show more detailed
structures in the spatial distributions of chemical species than the
mesoscale simulations, highlighting the capability of LES to resolve
high-resolution photochemical transformations in urban areas. Compared to
the mesoscale model results, the LES simulations show similar evolutions in
the profiles of the chemical species as a function of the boundary layer
development over a diurnal cycle.</p
Detection of Carbon Monoxide in the Atmosphere of WASP-39b Applying Standard Cross-Correlation Techniques to JWST NIRSpec G395H Data
Carbon monoxide was recently reported in the atmosphere of the hot Jupiter
WASP-39b using the NIRSpec PRISM transit observation of this planet, collected
as part of the JWST Transiting Exoplanet Community Early Release Science (JTEC
ERS) Program. This detection, however, could not be confidently confirmed in
the initial analysis of the higher resolution observations with NIRSpec G395H
disperser. Here we confirm the detection of CO in the atmosphere of WASP-39b
using the NIRSpec G395H data and cross-correlation techniques. We do this by
searching for the CO signal in the unbinned transmission spectrum of the planet
between 4.6 and 5.0 m, where the contribution of CO is expected to be
higher than that of other anticipated molecules in the planet's atmosphere. Our
search results in a detection of CO with a cross-correlation function (CCF)
significance of when using a template with only lines. The CCF significance of the CO signal increases to when including in the template lines from additional CO isotopologues,
with the largest contribution being from . Our results
highlight how cross-correlation techniques can be a powerful tool for unveiling
the chemical composition of exoplanetary atmospheres from medium-resolution
transmission spectra, including the detection of isotopologues.Comment: Accepted for publication in The Astrophysical Journal Letter
Characterization of germanium detectors for the first underground laboratory in Mexico
This article reports the characterization of two High Purity Germanium detectors performed by extracting and comparing their efficiencies using experimental data and Monte Carlo simulations. The efficiencies were calculated for pointlike γ-ray sources as well as for extended calibration sources. Characteristics of the detectors such as energy linearity, energy resolution and full energy peak efficiencies are reported from measurements performed on surface laboratories. The detectors will be deployed in a γ-ray assay facility that will be located in the first underground laboratory in Mexico, Laboratorio Subterr'aneo de Mineral del Chico (LABChico), in the Comarca Minera UNESCO Global Geopark [1]
Abstracts of presentations on plant protection issues at the fifth international Mango Symposium Abstracts of presentations on plant protection issues at the Xth international congress of Virology: September 1-6, 1996 Dan Panorama Hotel, Tel Aviv, Israel August 11-16, 1996 Binyanei haoma, Jerusalem, Israel
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