1,736 research outputs found
Use of threshold parameter variation for tropical cyclone tracking
Assessing the capacity of numerical models to produce viable tropical cyclones, as well as assessing the climatological behavior of simulated tropical cyclones, requires an objective tracking method. These make use of parameter thresholds to determine whether a detected feature, such as a vorticity maximum or a warm core, is strong enough to indicate a tropical cyclone. The choice of parameter thresholds is generally subjective.
This study proposes and assesses the parallel use of many threshold parameter combinations, combining a number of weaker and stronger values. The tracking algorithm succeeds in tracking tropical cyclones within the model data, beginning at their aggregation stage or shortly thereafter and ending when they interact strongly with extratropical flow and transition into extratropical cyclones or when their warm core decays.
The sensitivity of accumulated cyclone energy to tracking errors is assessed. Tracking errors include the faulty initial detection and termination of valid tropical cyclones and systems falsely identified as tropical cyclones. They are found to not significantly impact the accumulated cyclone energy. Thus, the tracking algorithm produces an adequate estimate of the accumulated cyclone energy within the underlying data.</p
Polarization lidar: an extended three-signal calibration approach
We present a new formalism to calibrate a three-signal polarization lidar and
to measure highly accurate height profiles of the volume linear
depolarization ratios under realistic experimental conditions. The
methodology considers elliptically polarized laser light, angular
misalignment of the receiver unit with respect to the main polarization plane
of the laser pulses, and cross talk among the receiver channels. A case
study of a liquid-water cloud observation demonstrates the potential of the
new technique. Long-term observations of the calibration parameters
corroborate the robustness of the method and the long-term stability of the
three-signal polarization lidar. A comparison with a second polarization
lidar shows excellent agreement regarding the derived volume linear
polarization ratios in different scenarios: a biomass burning smoke event
throughout the troposphere and the lower stratosphere up to 16 km in height, a
dust case, and also a cirrus cloud case.</p
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Overview of mathematical approaches used to model bacterial chemotaxis I: the single cell
Mathematical modeling of bacterial chemotaxis systems has been influential and insightful in helping to understand experimental observations. We provide here a comprehensive overview of the range of mathematical approaches used for modeling, within a single bacterium, chemotactic processes caused by changes to external gradients in its environment. Specific areas of the bacterial system which have been studied and modeled are discussed in detail, including the modeling of adaptation in response to attractant gradients, the intracellular phosphorylation cascade, membrane receptor clustering, and spatial modeling of intracellular protein signal transduction. The importance of producing robust models that address adaptation, gain, and sensitivity are also discussed. This review highlights that while mathematical modeling has aided in understanding bacterial chemotaxis on the individual cell scale and guiding experimental design, no single model succeeds in robustly describing all of the basic elements of the cell. We conclude by discussing the importance of this and the future of modeling in this area
Extreme levels of Canadian wildfire smoke in the stratosphere over central Europe on 21â22 August 2017
Light extinction coefficients of 500 Mmâ1, about 20 times higher than
after the Pinatubo volcanic eruptions in 1991, were observed by European
Aerosol Research Lidar Network (EARLINET) lidars in the stratosphere over
central Europe on 21â22 August 2017. Pronounced smoke layers with a 1â2 km
vertical extent were found 2â5 km above the local tropopause. Optically
dense layers of Canadian wildfire smoke reached central Europe 10Â days after
their injection into the upper troposphere and lower stratosphere which was
caused by rather strong pyrocumulonimbus activity over western Canada. The
smoke-related aerosol optical thickness (AOT) identified by lidar was close
to 1.0 at 532 nm over Leipzig during the noon hours on 22 August 2017.
Smoke particles were found throughout the free troposphere (AOT
of 0.3) and in the pronounced 2 km thick stratospheric smoke layer at an
altitude of 14â16 km (AOT of 0.6). The lidar
observations indicated peak mass concentrations of
70â100 ”g mâ3 in the stratosphere. In addition to the lidar
profiles, we analyzed Moderate Resolution Imaging Spectroradiometer (MODIS)
fire radiative power (FRP) over Canada, and the distribution of MODIS AOT and
Ozone Monitoring Instrument (OMI) aerosol index across the North Atlantic.
These instruments showed a similar pattern and a clear link between the
western Canadian fires and the aerosol load over Europe. In this paper, we
also present Aerosol Robotic Network (AERONET) sun photometer observations,
compare photometer and lidar-derived AOT, and discuss an obvious bias (the
smoke AOT is too low) in the photometer observations. Finally, we compare the
strength of this record-breaking smoke event (in terms of the particle
extinction coefficient and AOT) with major and moderate volcanic events
observed over the northern midlatitudes.</p
Social preferences, accountability, and wage bargaining
We assess the extent of preferences for employment in a collective wage bargaining situation with heterogeneous workers. We vary the size of the union and introduce a treatment mechanism transforming the voting game into an individual allocation task. Our results show that highly productive workers do not take employment of low productive workers into account when making wage proposals, regardless of whether insiders determine the wage or all workers. The level of pro-social preferences is small in the voting game, while it increases as the game is transformed into an individual allocation task. We interpret this as an accountability effect
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