118 research outputs found
A Radar-Based Hail Climatology of Australia
In Australia, hailstorms present considerable public safety and economic
risks, where they are considered the most damaging natural hazard in terms of
annual insured losses. Despite these impacts, the current climatological
distribution of hailfall across the continent is still comparatively poorly
understood. This study aims to supplement previous national hail climatologies,
such as those based on environmental proxies or satellite radiometer data, with
more direct radar-based hail observations. The heterogeneous and incomplete
nature of the Australian radar network complicates this task and prompts the
introduction of some novel methodological elements. We introduce an empirical
correction technique to account for hail reflectivity biases at C-band, derived
by comparing overlapping C- and S-band observations. Furthermore, we
demonstrate how object-based hail swath analysis may be used to produce
resolution-invariant hail frequencies, and describe an interpolation method
used to create a spatially continuous hail climatology. The Maximum Estimated
Size of Hail (MESH) parameter is then applied to a mixture of over fifty
operational radars in the Australian radar archive, resulting in the first
nationwide, radar-based hail climatology. The spatiotemporal distribution of
hailstorms is examined, including their physical characteristics, seasonal and
diurnal frequency, and regional variations of such properties across the
continent.Comment: Revision 1 of manuscript submitted to Monthly Weather Revie
The Effects of Spatial Interpolation on a Novel, Dual-Doppler 3D Wind Retrieval Technique
Three-dimensional wind retrievals from ground-based Doppler radars have
played an important role in meteorological research and nowcasting over the
past four decades. However, in recent years, the proliferation of open-source
software and increased demands from applications such as convective
parameterizations in numerical weather prediction models has led to a renewed
interest in these analyses. In this study, we analyze how a major, yet
often-overlooked, error source effects the quality of retrieved 3D wind fields.
Namely, we investigate the effects of spatial interpolation, and show how the
common practice of pre-gridding radial velocity data can degrade the accuracy
of the results. Alternatively, we show that assimilating radar data directly at
their observation locations improves the retrieval of important dynamic
features such as the rear flank downdraft and mesocyclone within a simulated
supercell, while also reducing errors in vertical vorticity, horizontal
divergence, and all three velocity components.Comment: Revised version submitted to JTECH. Includes new section with a real
data cas
The development of rainfall retrievals from radar at Darwin
17 USC 105 interim-entered record; under review.The article of record as published may be found at https://doi.org/10.5194/amt-14-53-2021The U.S. Department of Energy Atmospheric Radiation Measurement program Tropical Western Pacific site hosted a C-band polarization (CPOL) radar in Darwin, Australia. It provides 2 decades of tropical rainfall characteristics useful for validating global circulation models. Rainfall retrievals from radar assume characteristics about the droplet size distribution (DSD) that vary significantly. To minimize the uncertainty associated with DSD variability, new radar rainfall techniques use dual polarization and specific attenuation estimates. This study challenges the applicability of several specific attenuation and dual-polarization-based rainfall estimators in tropical settings using a 4-year archive of Darwin disdrometer datasets in conjunction with CPOL observations. This assessment is based on three metrics: statistical uncertainty estimates, principal component analysis (PCA), and comparisons of various retrievals from CPOL data. The PCA shows that the variability in R can be consistently attributed to reflectivity, but dependence on dualpolarization quantities was wavelength dependent for 1 10 mm hâ1 . Rainfall estimates during these conditions primarily originate from deep convective clouds with median drop diameters greater than 1.5 mm. An uncertainty analysis and intercomparison with CPOL show that a Colorado State University blended technique for tropical oceans, with modified estimators developed from video disdrometer observations, is most appropriate for use in all cases, such as when 1 10 mm hâ1 (deeper convective rain).Argonne National Laboratoryâs work was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, under contract DE-AC02-06CH11357. This work has been supported by the Office of Biological and Environmental Research (OBER) of the U.S. Department of Energy (DOE) as part of the Climate Model Development and Validation activity. NOAA PSL contributes effort with funding from the Weather Program Officeâs Precipitation Prediction Grand Challenge. The development of the Python ARM radar toolkit was funded by the ARM program part of the Office of Biological and Environmental Research (OBER) of the U.S. Department of Energy (DOE). The work from Monash University and the Bureau of Meteorology was partly supported by the U.S. Department of Energy Atmospheric Systems Research Program through the grant DE-SC0014063. BD contributions are supported by the U.S. Department of Energy Atmospheric Systems Research Program through the grant DE-SC0017977
Analysis of Blue Corona Discharges at the Top of Tropical Thunderstorm Clouds in Different Phases of Convection
We report on observations of corona discharges at the uppermost region of clouds characterized by emissions in a blue band of nitrogen molecules at 337 nm, with little activity in the red band of lightning leaders at 777.4 nm. Past work suggests that they are generated in cloud tops reaching the tropopause and above. Here we explore their occurrence in two convective environments of the same storm: one is developing with clouds reaching above the tropopause, and one is collapsing with lower cloud tops. We focus on those discharges that form a distinct category with rise times below 20 ÎŒs, implying that they are at the very top of the clouds. The discharges are observed in both environments. The observations suggest that a range of storm environments may generate corona discharges and that they may be common in convective surges.publishedVersio
BASTA : a 95GHz FM-ÂâCW Cloud radar
International audienceGround-based continuous observation of non-precipitating clouds and fo
Atmospheric convection and air-sea interactions over the tropical oceans: scientific progress, challenges, and opportunities
© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Hagos, S., Foltz, G. R., Zhang, C., Thompson, E., Seo, H., Chen, S., Capotondi, A., Reed, K. A., DeMott, C., & Protat, A. Atmospheric convection and air-sea interactions over the tropical oceans: scientific progress, challenges, and opportunities. Bulletin of the American Meteorological Society, 101(3), (2020): E253-E258, doi:10.1175/BAMS-D-19-0261.1.Over the past 30 years, the scientific community has made considerable progress in understanding and predicting tropical convection and airâsea interactions, thanks to sustained investments in extensive in situ and remote sensing observations, targeted field experiments, advances in numerical modeling, and vastly improved computational resources and observing technologies. Those investments would not have been fruitful as isolated advancements without the collaborative effort of the atmospheric convection and airâsea interaction research communities. In this spirit, a U.S.- and International CLIVARâsponsored workshop on âAtmospheric convection and airâsea interactions over the tropical oceansâ was held in the spring of 2019 in Boulder, Colorado. The 90 participants were observational and modeling experts from the atmospheric convection and airâsea interactions communities with varying degrees of experience, from early-career researchers and students to senior scientists. The presentations and discussions covered processes over the broad range of spatiotemporal scales (Fig. 1).The workshop was sponsored by the United States and International CLIVAR. Funding was provided by the U.S. Department of Energy, Office of Naval Research, NOAA, NSF, and the World Climate Research Programme. We thank Mike Patterson, Jennie Zhu, and Jeff Becker from the U.S. CLIVAR Project Office for coordinating the workshop
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A machine learning assisted development of a model for the populations of convective and stratiform clouds
Traditional parameterizations of the interaction between convection and the environment have relied on an assumption that the slowly-varying large-scale environment is in statistical equilibrium with a large number of small and short-lived convective clouds. They fail to capture non-equilibrium transitions such as the diurnal cycle and theformation of meso-scale convective systems as well asobserved precipitation statisticsand extremes. Informed by analysis of radar observations, cloud-permitting model simulation, theory and machine learning, this work presents a new stochastic cloud population dynamics model for characterizing the interactions between convective and stratiform clouds,with the ultimate goal of informing the representation ofthese interactions in global climate models. 15 wet seasons of precipitating cloud observations by a C-band radar at Darwin, Australia are fed into a machine learning algorithm to obtain transition functions that close a set of coupled equation relating large-scale forcing, mass flux, the convective cell size distribution and the stratiform area. Under realistic large-scale forcing, the derived transition functions show that, on the one hand, interactions with stratiform clouds act to dampen the variability in the size and number of convective cells and therefore in the convective mass flux. On the other hand, for a given convective area fraction, a larger number of smaller cells is more favorable for the growth of stratiform area than a smaller number of larger cells. The combination of these two factors gives rise to solutions with a number of convective cells embedded in a large stratiform area, reminiscent of mesoscale convective systems
Detecting range and coupling coefficient tradeoff with a multiple loops reader antenna for small size RFID LF tags
International audienceThis paper summarizes some tests with Low Frequency (LF, 125 kHz) RFID tags of two types: Card and Token. These tests were done in order to evaluate the feasibility of an identification/traceability of tags which size is constrained and supposed to be detected inside a delimited volume of 40Ă40Ă10 cm 3 . As the size of the antenna tag is supposed to be very small, we improve the detection range and volume of definition by designing different reader antennas. Reader antennas presented are of two types whether they are based on single (SL) or multiple loops (ML). Detection range was evaluated for planar antennas (3 SL and one ML). Volume of definition for the detection was estimated by designing two-level prototypes of ML antennas. Results are discussed about the optimization possibility of detection range and volume thanks to ML
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