180 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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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
Surface Energy Budgets of Arctic Tundra During Growing Season
This study analyzed summer observations of diurnal and seasonal surface energy budgets across several monitoring sites within the Arctic tundra underlain by permafrost. In these areas, latent and sensible heat fluxes have comparable magnitudes, and ground heat flux enters the subsurface during short summer intervals of the growing period, leading to seasonal thaw. The maximum entropy production (MEP) model was tested as an input and parameter parsimonious model of surface heat fluxes for the simulation of energy budgets of these permafrostâunderlain environments. Using net radiation, surface temperature, and a single parameter characterizing the thermal inertia of the heat exchanging surface, the MEP model estimates latent, sensible, and ground heat fluxes that agree closely with observations at five sites for which detailed flux data are available. The MEP potential evapotranspiration model reproduces estimates of the PenmanâMonteith potential evapotranspiration model that requires at least five input meteorological variables (net radiation, ground heat flux, air temperature, air humidity, and wind speed) and empirical parameters of surface resistance. The potential and challenges of MEP model application in sparsely monitored areas of the Arctic are discussed, highlighting the need for accurate measurements and constraints of ground heat flux.Plain Language SummaryGrowing season latent and sensible heat fluxes are nearly equal over the Arctic permafrost tundra regions. Persistent ground heat flux into the subsurface layer leads to seasonal thaw of the top permafrost layer. The maximum energy production model accurately estimates the latent, sensible, and ground heat flux of the surface energy budget of the Arctic permafrost regions.Key PointThe MEP model is parsimonious and well suited to modeling surface energy budget in dataâsparse permafrost environmentsPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/150560/1/jgrd55584.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150560/2/jgrd55584_am.pd
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
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