234 research outputs found
The METCRAX II Field Experiment: A Study of Downslope Windstorm-Type Flows in Arizona\u2019s Meteor Crater
The second Meteor Crater Experiment (METCRAX II) was conducted in October 2013 at Arizona\u2019s Meteor Crater. The experiment was designed to investigate nighttime downslope windstorm 12type flows that form regularly above the inner southwest sidewall of the 1.2-km diameter crater as a southwesterly mesoscale katabatic flow cascades over the crater rim. The objective of METCRAX II is to determine the causes of these strong, intermittent, and turbulent inflows that bring warm-air intrusions into the southwest part of the crater. This article provides an overview of the scientific goals of the experiment; summarizes the measurements, the crater topography, and the synoptic meteorology of the study period; and presents initial analysis results
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An overview of ISCAT 2000
The Investigation of Sulfur Chemistry in the Antarctic Troposphere (ISCAT) took place over the timer period of 15 November to 31 December in the year 2000. The study location was the Amundsen Scott Station in Antarctica. ISCAT 2000 defines the second phase of a program designed to explore tropospheric chemistry in Antarctica. As in 1998, the 2000 ISCAT study revealed a strong oxidizing environment at South Pole (SP). During the 2000 investigation, however, the suite of measurements was greatly expanded. These new measurements established the recycling of reactive nitrogen as a critical component of this unique environment. This paper first presents the historical background leading up to the ISCAT 2000 observations; then it focuses on providing a summary of the year 2000 results and contrasts these with those recorded during 1998. Important developments made during the 2000 study included the recording of SP data for several species being emitted from the snowpack. These included NO, H 2O2 and CH2O. In this context, eddy-diffusion flux measurements provided the first quantitative estimates of the SP NO and NOx snow-to-atmosphere fluxes. This study also revealed that HNO 3 and HO2NO2 were major sink species for HOx and NOx radicals. And, it identified the critical factors responsible for SP NO levels exceeding those at other polar sites by nearly an order of magnitude. Finally, it reports on the levels of gas phase sulfur species and provides evidence indicating that the absence of DMS at SP is most likely due to its greatly shorten chemical lifetime in the near vicinity of the plateau. It is proposed that this is due to the influence of NO on the distribution of OH in the lower free troposphere over a region that extends well beyond the plateau itself. Details related to each of the above findings plus others can be found in the 11 accompanying Special Issue papers. © 2004 Elsevier Ltd. All rights reserved
Observational and Modeling Analysis of LandâAtmopshere Coupling over Adjacent Irrigated and Rainfed Cropland during the GRAINEX Field Campaign
The Great Plains Irrigation Experiment (GRAINEX) was conducted in the spring and summer of 2018 to investigate Land-Atmosphere (L-A) coupling just prior to and through the growing season across adjacent, but distinctly unique, soil moisture regimes (contrasting irrigated and rainfed fields). GRAINEX was uniquely designed for the development and analysis of an extensive observational dataset for comprehensive process studies of L-A coupling, by focusing on irrigated and rainfed croplands in a ~100 x 100 km domain in southeastern Nebraska. Observation platforms included multiple NCAR EOL Integrated Surface Flux Systems and Integrated Sounding Systems, NCAR CSWR Doppler Radar on Wheels, 1200 radiosonde balloon launches from 5 sites, the NASA GREX airborne L-Band radiometer, and 75 University of Alabama-Huntsville Environmental Monitoring Economic Monitoring Sensor Hubs (EMESH mesonet stations). An integrated observational and modeling approach to advance knowledge of L-A coupling processes and precipitation impacts in regions of heterogeneous soil moisture will be presented. Specifically, through observation of land surface states, surface fluxes, near surface meteorology, and properties of the atmospheric column, an examination of the diurnal planetary boundary layer evolving characteristics will be presented. Results from a hierarchy of modeling platforms (e.g. single column, large-eddy, and mesoscale simulations) will also be presented to complement the observational findings. The modeling effort will generate high spatiotemporal resolution datasets to: 1) generate a multi-physics ensemble to test the robustness and potentially advance physical parameterizations in high resolution weather and climate models, 2) comparison of prescribed forcing from observations and those from offline land surface model simulations and high resolution operational analyses, 3) determine the ability of model simulations to reproduce observed boundary layer evolution, with particular attention to the processes that compose the L-A coupling chain and metrics (e.g. mixing ratio diagrams), and 4) in combination with observations, isolate the impacts of soil moisture heterogeneity on planetary boundary layer characteristics, cloud development, precipitation, mesoscale circulation patters and boundary layer development. Initial results from the observational and modeling analysis will be presented
Solar Site Survey for the Advanced Technology Solar Telecope. I. Analysis of the Seeing Data
The site survey for the Advanced Technology Solar Telescope concluded
recently after more than two years of data gathering and analysis. Six
locations, including lake, island and continental sites, were thoroughly probed
for image quality and sky brightness. The present paper describes the analysis
methodology employed to determine the height stratification of the atmospheric
turbulence. This information is crucial because day-time seeing is often very
different between the actual telescope aperture (~30 m) and the ground. Two
independent inversion codes have been developed to analyze simultaneously data
from a scintillometer array and a solar differential image monitor. We show
here the results of applying them to a sample subset of data from May 2003,
which was used for testing. Both codes retrieve a similar seeing stratification
through the height range of interest. A quantitative comparison between our
analysis procedure and actual in situ measurements confirms the validity of the
inversions. The sample data presented in this paper reveal a qualitatively
different behavior for the lake sites (dominated by high-altitude seeing) and
the rest (dominated by near-ground turbulence).Comment: To appear in the Publications of the Astronomical Society of the
Pacific (PASP). Note: Figures are low resolution versions due to file size
limitation
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Assessing the accuracy of microwave radiometers and radio acoustic sounding systems for wind energy applications
To assess current remote-sensing capabilities for wind energy
applications, a remote-sensing system evaluation study, called XPIA
(eXperimental Planetary boundary layer Instrument Assessment), was held in
the spring of 2015 at NOAA's Boulder Atmospheric Observatory (BAO) facility.
Several remote-sensing platforms were evaluated to determine their
suitability for the verification and validation processes used to test the
accuracy of numerical weather prediction models.The evaluation of these platforms was performed with respect to well-defined
reference systems: the BAO's 300âŻm tower equipped at six levels (50, 100, 150,
200, 250, and 300âŻm) with 12 sonic anemometers and six temperature (T) and relative
humidity (RH) sensors; and approximately 60 radiosonde launches.In this study we first employ these reference measurements to validate
temperature profiles retrieved by two co-located microwave radiometers (MWRs) as
well as virtual temperature (Tv) measured by co-located wind profiling radars
equipped with radio acoustic sounding systems (RASSs). Results indicate a mean
absolute error (MAE) in the temperature retrieved by the microwave radiometers
below 1.5âŻK in the lowest 5âŻkm of the atmosphere and a mean absolute error
in the virtual temperature measured by the radio acoustic sounding systems
below 0.8âŻK in the layer of the atmosphere covered by these measurements (up
to approximately 1.6â2âŻkm). We also investigated the benefit of the
vertical velocity correction applied to the speed of sound before computing
the virtual temperature by the radio acoustic sounding systems. We find that
using this correction frequently increases the RASS error, and that it
should not be routinely applied to all data.Water vapor density (WVD) profiles measured by the MWRs were also compared with
similar measurements from the soundings, showing the capability of MWRs to
follow the vertical profile measured by the sounding and finding a mean
absolute error below 0.5âŻgâŻmâ3 in the lowest 5âŻkm of the atmosphere.
However, the relative humidity profiles measured by the microwave radiometer
lack the high-resolution details available from radiosonde profiles. An
encouraging and significant finding of this study was that the coefficient
of determination between the lapse rate measured by the microwave radiometer
and the tower measurements over the tower levels between 50 and 300âŻm ranged
from 0.76 to 0.91, proving that these remote-sensing instruments can provide
accurate information on atmospheric stability conditions in the lower
boundary layer
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Lake-induced atmospheric circulations during BOREAS
Lake-induced atmospheric circulations over three lakes ranging from 3 to 10 km width are analyzed using data from three aircraft during the 1994 Boreal Ecosystem-Atmosphere Study (BOREAS). A well-defined divergent lake breeze circulation is observed over all three lakes during the day. Under light wind conditions, the lake breeze is not very sensitive to the water temperature, and the strength of the divergence over the lake decreases with increasing lake size. The boundary-layer development over the surrounding land can be very important for generating a horizontal pressure difference which drives the lake breeze. Diurnal and seasonal variations of lake breezes are investigated on the basis of repeated passes from the different aircraft at different altitudes from late spring to early fall of 1994. The lake breeze divergence increases with time during the day and reaches a maximum around 1300 LST. The latent heat flux over 10-km-wide Candle Lake increases steadily from spring to fall as the lake temperature increases. The latent heat flux over the land reaches a maximum during the summer due to evapotranspiration. The lake effect on area-averaged fluxes sometimes leads to a negative heat transfer coefficient for an averaging scale of several times the lake width
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Evaluation of single and multiple Doppler lidar techniques to measure complex flow during the XPIA field campaign
Accurate three-dimensional information of wind flow fields can be an
important tool in not only visualizing complex flow but also understanding
the underlying physical processes and improving flow modeling. However, a
thorough analysis of the measurement uncertainties is required to properly
interpret results. The XPIA (eXperimental Planetary boundary layer
Instrumentation Assessment) field campaign conducted at the Boulder
Atmospheric Observatory (BAO) in Erie, CO, from 2 March to 31 May 2015 brought
together a large suite of in situ and remote sensing measurement platforms to
evaluate complex flow measurement strategies.
In this paper, measurement uncertainties for different single and
multi-Doppler strategies using simple scan geometries (conical, vertical
plane and staring) are investigated. The tradeoffs (such as timeâspace
resolution vs. spatial coverage) among the different measurement techniques
are evaluated using co-located measurements made near the BAO tower.
Sensitivity of the single-/multi-Doppler measurement uncertainties to
averaging period are investigated using the sonic anemometers installed on
the BAO tower as the standard reference. Finally, the radiometer measurements
are used to partition the measurement periods as a function of atmospheric
stability to determine their effect on measurement uncertainty.
It was found that with an increase in spatial coverage and measurement
complexity, the uncertainty in the wind measurement also increased. For
multi-Doppler techniques, the increase in uncertainty for temporally
uncoordinated measurements is possibly due to requiring additional
assumptions of stationarity along with horizontal homogeneity and less
representative line-of-sight velocity statistics. It was also found that wind speed
measurement uncertainty was lower during stable conditions compared to
unstable conditions
Connecting LandâAtmosphere Interactions to Surface Heterogeneity in CHEESEHEAD19
The Chequamegon Heterogeneous Ecosystem Energy-Balance Study Enabled by a High-Density Extensive Array of Detectors 2019 (CHEESEHEAD19) is an ongoing National Science Foundation project based on an intensive field campaign that occurred from June to October 2019. The purpose of the study is to examine how the atmospheric boundary layer (ABL) responds to spatial heterogeneity in surface energy fluxes. One of the main objectives is to test whether lack of energy balance closure measured by eddy covariance (EC) towers is related to mesoscale atmospheric processes. Finally, the project evaluates data-driven methods for scaling surface energy fluxes, with the aim to improve modelâdata comparison and integration. To address these questions, an extensive suite of ground, tower, profiling, and airborne instrumentation was deployed over a 10 km Ă 10 km domain of a heterogeneous forest ecosystem in the ChequamegonâNicolet National Forest in northern Wisconsin, United States, centered on an existing 447-m tower that anchors an AmeriFlux/NOAA supersite (US-PFa/WLEF). The project deployed one of the worldâs highest-density networks of above-canopy EC measurements of surface energy fluxes. This tower EC network was coupled with spatial measurements of EC fluxes from aircraft; maps of leaf and canopy properties derived from airborne spectroscopy, ground-based measurements of plant productivity, phenology, and physiology; and atmospheric profiles of wind, water vapor, and temperature using radar, sodar, lidar, microwave radiometers, infrared interferometers, and radiosondes. These observations are being used with large-eddy simulation and scaling experiments to better understand submesoscale processes and improve formulations of subgrid-scale processes in numerical weather and climate models
Hydrodynamic modelling of protein conformation in solution: ELLIPS and HYDRO
The last three decades has seen some important
advances in our ability to represent the conformation of
proteins in solution on the basis of hydrodynamic measurements.
Advances in theoretical modeling capabilities have
been matched by commensurate advances in the precision of
hydrodynamic measurements. We consider the advances in
whole-body (simple ellipsoid-based) modelingâstill useful
for providing an overall idea of molecular shape, particularly
for those systems where only a limited amount of data is
availableâand outline the ELLIPS suite of algorithms
which facilitates the use of this approach. We then focus
on bead modeling strategies, particularly the surface or
shellâbead approaches and the HYDRO suite of algorithms.
We demonstrate how these are providing great insights into
complex issues such as the conformation of immunoglobulins
and other multi-domain complexes
Broadband Dielectric Spectroscopy on Human Blood
Dielectric spectra of human blood reveal a rich variety of dynamic processes.
Achieving a better characterization and understanding of these processes not
only is of academic interest but also of high relevance for medical
applications as, e.g., the determination of absorption rates of electromagnetic
radiation by the human body. The dielectric properties of human blood are
studied using broadband dielectric spectroscopy, systematically investigating
the dependence on temperature and hematocrit value. By covering a frequency
range from 1 Hz to 40 GHz, information on all the typical dispersion regions of
biological matter is obtained. We find no evidence for a low-frequency
relaxation (alpha-relaxation) caused, e.g., by counterion diffusion effects as
reported for some types of biological matter. The analysis of a strong
Maxwell-Wagner relaxation arising from the polarization of the cell membranes
in the 1-100 MHz region (beta-relaxation) allows for the test of model
predictions and the determination of various intrinsic cell properties. In the
microwave region beyond 1 GHz, the reorientational motion of water molecules in
the blood plasma leads to another relaxation feature (gamma-relaxation).
Between beta- and gamma-relaxation, significant dispersion is observed, which,
however, can be explained by a superposition of these relaxation processes and
is not due to an additional delta-relaxation often found in biological matter.
Our measurements provide dielectric data on human blood of so far unsurpassed
precision for a broad parameter range. All data are provided in electronic form
to serve as basis for the calculation of the absorption rate of electromagnetic
radiation and other medical purposes. Moreover, by investigating an
exceptionally broad frequency range, valuable new information on the dynamic
processes in blood is obtained.Comment: 17 pages, 9 figure
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