Differential Reflectivity Research Articles

In Situ Differential Reflectance Spectroscopy Monitoring the Asynchronous Transient Response at the Edge and Center of the Disk Electrode

The resistance for the current flow to a disk electrode in an electrochemical cell is a function of radius according to the pioneer work by Newman,(1) which results in the varying RC constant along the electrode surface. Theoretical calculations by Oldhan showed a spatial dispersion of the RC constant from zero at the edge to 2 RC at the center for the disk electrode.(2) In this work, the asynchronous transient responses at the edge and center of a gold disk electrode are monitored by in situ differential reflectance spectroscopy (DRS). The DRS spectrum collected in 10mM perchloric acid shows that the edge of the electrode achieves the equilibrium sooner than the center does in chronoamperometry.The cyclic voltammetry of the gold electrode sweeping at 1V/s in 0.1M HClO4 electrolyte and the corresponding reflectance spectrum are shown in panels A and B, Figure 1. The DRS intensity is defined asΔR/R=|Rs-Rref|/Rref whereis Rs the intensity of reflectance at any potential and Rref is the intensity of reflectance at the reference potential (0.4V). Overall, ΔR/R varies in the range of 2.5% while scanning the potential of the electrode. In the forward scan, ΔR/R decreases linearly with potential from 0.4 to 1.3V. A sharper decrease starts at 1.3V, i.e., the onset of gold oxidation, until the end of gold oxidation reaction at 1.5V in the backward scan. ΔR/R resumes back to 0 at 0.4V after the reduction of gold oxide, indicating the surface is recovered back to the initial state. ΔR/R at 1 V and 0.4V are chosen as Rs and Rref in the chronoamperometry since only the double layer charging/discharging occurs, i.e., no redox reactions, resembling a circuit of capacitor and resistor.Shown in Figure 2 is the chronoamperometry and in situ DRS of the gold electrode collected in a more resistive electrolyte, 10 mM HClO4. The RC constant of the electrode is determined to be 68 ms by fitting the i-t curve (Panel A) with the exponential function. The reflectance spectrum without any smoothing is shown in Panel B, Figure 2. The RC constant at the center (red curve) is 142 ms, which is comparable to 2RC. The RC constant at the edge (black curve) is 51 ms, much smaller than that at the center. RC constants at the edge in both 0.1M and 10mM HClO4 electrolytes are not zero because the laser covers a large area of the electrode. J. Newman, J Electrochem Soc, 113, 501 (1966).K. B. Oldham, Electrochem Commun, 6, 210 (2004). Figure 1

Enhanced photocatalytic degradation of rhodamine B over Ag3PO4/Polyaniline/NiFe2O4 nanocomposite under solar light irradiation

In this study, a nanocomposite of Ag3PO4/Polyaniline(PANI)/NiFe2O4 was synthesized and studied on degradation of rhodamine B (RhB) in water under solar light irradiation. The nanocomposite was characterized using powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and Ultraviolet–visible (UV–vis) differential reflectance spectroscopy (DRS). The best photocatalytic nanocomposite (Ag3PO4/3%PANI/10%NiFe2O4) showed six-fold higher degradation rate constant than of pristine Ag3PO4. Moreover, introduction of PANI/NiFe2O4 into Ag3PO4 significantly enhance the recyclability of the nanocomposite (stable after 3 cycles) whereas pristine Ag3PO4 degraded even after first cycle. Radical scavenger studies with t-butyl alcohol, disodium ethylenediaminetetraacetic acid, and ascorbic acid indicated that both holes and electron participate in the degradation of RhB. We hypothesized that the presence of PANI and NiFe2O4 in the nanocomposite enhanced its hole and electron transport, respectively, facilitating efficient electron–hole separation. Therefore, large number of holes accumulates in valance band of Ag3PO4 that enhanced the degradation of RhB dye in water under solar light irradiation.

Wafer-Scale Uniform Growth of an Atomically Thin MoS2 Film with Controlled Layer Numbers by Metal-Organic Chemical Vapor Deposition.

The growth control of a molybdenum disulfide (MoS2) thin film, including the number of layers, growth rate, and electrical property modulation, remains a challenge. In this study, we synthesized MoS2 thin films using the metal-organic chemical vapor deposition (MOCVD) method with a 2 inch wafer scale and achieved high thickness uniformity according to the positions on the substrate. In addition, we successfully controlled the number of MoS2 layers to range from one to five, with a growth rate of 10 min per layer. The layer-dependent optical and electrical properties were characterized by photoluminescence, Raman spectroscopy, differential reflectance spectroscopy, and field effect transistors. To guide the growth of MoS2, we summarized the relation between the growth aspects and the precursor control in the form of a growth map. Reference to this growth map enabled control of the growth rate, domain density, and domain size according to the application purposes. Finally, we confirmed the electrical performance of MOCVD-grown MoS2 with five layers under a high-κ dielectric environment, which exhibited an on/off current ratio of 10∼6 and a maximum field effect mobility of 8.6 cm2 V-1 s-1.

Study of ultrafast Rabi flopping in colloidal quantum dots at room temperature

The interaction between high-intensity ultrashort optical pulses and materials has led to a number of fascinating optical phenomena, including Rabi flopping and self-induced transparency. Until now, there have been few reports on ultrashort coherent pulse propagation and reshaping in semiconductor materials. Here we investigate Rabi flopping and Rabi splitting in colloidal quantum dots with Fabry-Perot cavity of SU8/Si. The Rabi flopping phenomenon is monitored via the pump-probe differential reflection spectroscopy. A high excitation power reshapes the temporal oscillations so that the fast Fourier transform spectra display several peaks. The photoluminescence spectrum by continuous-wave excitation splits under a proper incident angle, and the splitted photoluminescence spectrum is generally consistent with the amplitude of differential reflectivity as function of wavelength. These results demonstrate that both of the temporal oscillations and the splitting of the continuous-wave excited photoluminescence spectra are due to strong coupling between colloidal quantum dots and the Fabry-Perot cavity.

Precipitation Properties of Supercell Hook Echoes

Recent studies have suggested that thermodynamic properties of supercell rear-flank downdrafts (RFDs) can affect whether or not tornadogenesis occurs. The thermodynamic characteristics of RFDs are determined in part by microphysical processes such as evaporation of raindrops and melting of hailstones. Whereas in situ measurements of hook-echo particle size distributions (PSDs) are exceedingly rare, polarimetric radars can be used to determine the bulk characteristics of these PSDs remotely. A preliminary analysis of polarimetric radar data from a small sample of supercell hook echoes reveals unusual drop size distributions compared to typical rainfall in Oklahoma, as well as spatially inhomogeneous structures. The inner edge of the hook echo is often characterized by low or moderate reflectivity factor at horizontal polarization (ZH), with very high differential reflectivity factor (ZDR), indicating a sparse population of very large drops. The southern and/or western (back) portion of the hook is characterized by moderate to high ZH and rather low ZDR, indicating a surplus of small drops and/or a lack of larger drops. Hypotheses explaining the unusual drop size distributions are presented. Additionally, the time evolution of these characteristics is explored using data collected with a special rapid scanning strategy.

Silver-Doped BaSrTiO₃ Nanocomposite: Synthesis, Characterization, Antibacterial and Photocatalytic Activities.

In this research, strontium titanate (SrTiO₃), barium titanate (BaTiO₃), barium strontium titanate (BaSrTiO₃), and Ag-doped BaSrTiO₃ nanocomposites with different Ag contents were fabricated using the sol-gel chemical route. The prepared samples were characterized by several techniques including scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), differential reflectance spectroscopy (DRS), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), inductively coupled plasma spectroscopy (ICP), and Brunauer-Emmett-Teller (BET) measurement. The EDS results indicated that the synthesized nanoparticles had a cube perovskite-like structure. The EDS and ICP results revealed that Ag was doped into the Ba0.5Sr0.5TiO₃ structure. The SEM and TEM images demonstrated that the particle size of 15 mol% Ag-doped Ba0.5Sr0.5TiO₃ was smaller than that of pure Ba0.5Sr0.5TiO₃ as confirmed by surface area results. The photocatalytic properties of undoped titanate samples and Ag-doped Ba0.5Sr0.5TiO₃ were studied by the photodecomposition of Eosin yellowish (EY) and methylene blue (MB) dyes. The results illustrated that the photodegradation efficiency of the Ag-doped Ba0.5Sr0.5TiO₃ was far higher than the undoped titanate sample, and the optimum Ag doping was 15 mol%. The antibacterial activities of pure Ba0.5Sr0.5TiO₃ and Ag-doped Ba0.5Sr0.5Ti0₃ were studied against Staphylococcus aureus as Gram-positive (+) and Pseudomonas aeruginosa and Escherichia coli as Gram-negative (-) bacteria. In comparison with the bare Ba0.5Sr0.5TiO₃ nanoparticles, the Ag-doped sample showed a significant enhancement in antibacterial activities against both Gram-negative and Gram-positive bacterial strains.

Synthesis, Characterization, and Photocatalytic, Bactericidal, and Molecular Docking Analysis of Cu-Fe/TiO2 Photocatalysts: Influence of Metallic Impurities and Calcination Temperature on Charge Recombination.

This research evaluated the potential photocatalytic efficiency of synthesized Cu–Fe/TiO2 photocatalysts against organic contaminants and biocontaminants through various synthesis methods (Cu-to-Fe ratio, metal loading, and calcination temperature) and reaction parameters (photocatalyst dose, irradiation time, and different initial methyl orange (MO) concentrations). In addition, the best photocatalysts were characterized through Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), differential reflectance spectroscopy (DRS), and X-ray photoelectron spectroscopy (XPS) analysis techniques. The best metal loading was 1 wt % with 5:5 Cu/Fe ratio and 300 °C calcination temperature (5Cu–5Fe/TiO2-300) having 97% MO decolorization. Further analysis indicates that the metal presence does not generate new channels for de-excitation but clearly affects the intensity and decreases charge recombination. The behavior of the photoluminescence intensity is (inversely) proportional to the activity behavior through the series, indicating that the main catalytic effect of Fe and Cu relates to charge recombination and that the Cu–Fe bimetallic catalyst optimizes such function. Moreover, the best-engineered photocatalysts asserted impactful bacteriostatic efficacy toward the tested Escherichia coli strain (in 30 min), and therefore, molecular docking studies were used to predict the inhibition pathway against E. coli β-lactamase enzyme. The photocatalyst had a high negative docking score (−5.9 kcal mol–1) due to intense interactions within the active site of the enzyme. The molecular docking study revealed that the ligand could inhibit β-lactamase from producing its bactericidal activity.

Spectroscopic Ellipsometry Investigation of Au‐Assisted Exfoliated Large‐Area Single‐Crystalline Monolayer MoS2

The recent Au‐assisted mechanical exfoliation technique has enabled scalable fabrication of millimeter‐sized, high‐quality monolayer 2D crystals. Herein, spectroscopic ellipsometry characterization of as‐exfoliated single‐crystalline monolayer MoS2 is reported. By developing layer‐by‐layer ellipsometry measurements and analysis, the complex dielectric function of monolayer MoS2 is extracted. Compared with bulk MoS2, the A and B exciton peaks in the dielectric function spectrum nearly disappear in the 1L MoS2–Au hybrid system. The charge transfer at the 1L MoS2–Au interface is responsible for this observation and the conclusion is also supported by Raman, photoluminescence, and differential reflectance measurements. These results reveal the impact of the Au substrate on the dielectric response of 2D monolayers with strong excitonic effect and will deepen our understanding of the 1L MoS2–Au interaction.

Zeolite 4A supported CdS/g-C3N4 type-II heterojunction: A novel visible-light-active ternary nanocomposite for potential photocatalytic degradation of cefoperazone

The CdS/g-C3N4 heterojunction photocatalyst supported on 4A zeolite was successfully synthesized using a simple chemical precipitation method. The physicochemical characteristics of the as-prepared ternary composite were assessed using X-Ray diffraction (XRD), field emission- scanning electron microscopy (FE-SEM), energy dispersive X-Ray (EDX), transmission electron microscopy (TEM), N2 adsorption–desorption, differential reflectance spectroscopy (UV–Vis-DRS), and photoluminescence (PL) techniques. The results confirmed the successful synthesis of the CdS/g-C3N4/4AZ nanocomposite and introduction of the CdS and g-C3N4 on the substrate of 4A zeolite. Cefoperazone (CFP) antibiotic was tested as the model pollutant to assess the photocatalytic performance of the synthesized nanocomposite under visible light irradiation. The response surface methodology (RSM) and artificial neural network (ANN) showed desirable reasonability for the prediction of the CFP degradation efficiency. More than 93% of CFP with a concentration of 17 mg L-1 degraded in the presence of the 0.4 g L-1 of the catalyst at pH of 9 after 80 min treatment time (RSM-based optimization results). The pH of the solution, irradiation time, catalyst dosage, and the initial concentration of the CFP affected degradation efficiency with a percentage impact of 37, 29, 19, and 15 %, respectively (ANN-based modeling results). The addition of 1 mM of isopropanol, benzoquinone, and sodium oxalate reduced the CFP degradation efficiency from 93.23% to 85.18, 41.16, and 32.47%, respectively, proving the decisive role of the °O2– and h+ in the photodegradation process. The kinetic studies indicated the following of the process from the Langmuir-Hinshelwood’s pseudo-first-order model (kapp = 3.71 × 10-2 min−1). The structure of the identified by-products using GC-MS analysis confirmed that CFP mainly decomposed through the cleavage of C-S, C-N, and N-N bonds. Moreover, the formation of the aliphatic compounds and carboxylic acids as by-products confirmed nearly complete mineralization of the CFP to non-toxic products.

The adsorption of perchlorate, sulfate, selenate and water on Au(111)-textured electrodes from aqueous solutions: Simultaneous voltammetric, optical and microgravimetric studies

The adsorption of perchlorate, ClO4−(aq), sulfate, SO42−(aq) and selenate, SeO42−(aq) on Au(111)-textured single crystals from aqueous acidic solutions was examined as a function of the applied potential, E, by simultaneous voltammetry, normal incidence differential reflectance spectroscopy, ΔR/R, and electrochemical quartz crystal microbalance, EQCM, techniques. In particular, ΔR/R vs E data collected in pure 0.1 M HClO4 or the same electrolyte containing either 1 mM Na2SO4 or 1 mM Na2SeO4 could be quantitatively accounted for by using a simple model introduced in similar studies reported earlier in this laboratory. This model regards the ΔR/R response as arising from a sum of contributions from bare and adsorbate covered areas of the surface, which are, in each case, linear functions of the applied potential. Adsorption isotherms for ClO4−(aq), and SO42−(aq) on Au(111) from the literature allowed fitting of the model to data obtained in 1 mM Na2SO4 in 0.1 M HClO4 solutions. The two oxyanions were found to co-adsorb over a wide potential range, with SO42−(aq) fully displacing ClO4−(aq) for E > 1.25 V vs RHE. Analogous ΔR/R measurements involving 1 mM Na2SeO4 in 0.1 M HClO4 solutions combined with the model allowed calculation of the coverage of the two oxyanions as a function of E. The experimental isotherms enabled calculation of the mass densities for the adsorbed oxyanions, ρth, yielding values virtually identical to those derived from EQCM experiments, ρexp, for data recorded in the range ca. E < 0.73 V vs RHE in all three solutions. At higher potentials, however, ρexp were significantly larger than those predicted by the optical measurements, a behavior consistent with water co-adsorption.

Remote Sensing of Electric Fields Observed Within Winter Precipitation During the 2020 Investigation of Microphysics and Precipitation for Atlantic Coast‐Threatening Snowstorms (IMPACTS) Field Campaign

AbstractAircraft electric fields from NASA's Lightning Instrument Package (LIP) were coupled with other airborne and ground‐based, and in situ measurements to understand electrification in winter clouds that did not produce lightning. The measurements were made during seven research flights by a NASA ER‐2 during the 2020 Investigation of Microphysics and Precipitation for Atlantic Coast‐Threatening Snowstorms (IMPACTS) campaign. Observed total electric field magnitudes were as high as 80 V m−1 and variability in the electric field was observed along the flight path of the ER‐2, indicating horizontal and/or vertical inhomogeneity in the cloud's electrical structure. X‐band airborne radar data indicated 20‐dBZ echo tops above 5 km in regions where electrification exceeded 10 V m−1. In these regions, 85‐GHz brightness temperatures (TB) from an airborne radiometer were lower than 265 K, with the lowest TB (∼210 K) associated with ice scattering collocated with the strongest electric fields. In situ microphysical measurements from the NASA P‐3 aircraft on February 7 indicated that regions near strong electric field contained supercooled water, rimed ice hydrometeors, ice water p‐ content as high as 1 g m−3, liquid water content as high as 0.15 g m−3, and supersaturation as high as 3.5%. These observations support the role of mixed phase microphysics in the generation of electric fields in clouds. In three case studies, ground based S‐band polarimetric radar observed depolarization streaks in differential reflectivity near areas where the strongest electrification was observed. This observation reinforces the utility of depolarization streaks to identify areas of electrification prior to lightning occurrence.

Assessing the benefits of specific attenuation for quantitative precipitation estimation with a C-band radar network

AbstractRecent advances demonstrate the benefits of radar-derived specific attenuation at horizontal polarization (AH) for quantitative precipitation estimation (QPE) at S and X band. To date the methodology has, however, not been adapted for the widespread European C-band radars such as installed in the network of the German Meteorological Service (DWD, Deutscher Wetterdienst). Simulations based on a large dataset of drop size distributions (DSDs) measured over Germany are performed to investigate the DSD dependencies of the attenuation parameter αH for the AH estimates. The normalized raindrop concentration (Nw) and the change of differential reflectivity (ZDR) with reflectivity at horizontal polarization (ZH) are used to categorize radar observations into regimes for which scan-wise optimized αH values are derived. For heavier continental rain with ZH &gt; 40 dBZ, the AH-based rainfall retrieval R(AH) is combined with a rainfall estimator using a substitute of specific differential phase (). We also assess the performance of retrievals based on specific attenuation at vertical polarization (AV). Finally, the regime-adapted hybrid QPE algorithms are applied to four convective cases and one stratiform case from 2017 to 2019, and compared to DWD’s operational RAdar-OnLine-ANeichung (RADOLAN) RW rainfall product, which is based on Zh only but adjusted to rain gauge measurements. For the convective cases, our hybrid retrievals outperform the traditional R(Zh) and pure R(AH/V) retrievals with fixed αH/V values when evaluated with gauge measurements and outperform RW when evaluated by disdrometer measurements. Potential improvements using ray-wise αH/V and segment-wise applications of the ZPHI method along the radials are discussed.

Synergistic effects of nanoarchitecture and oxygen vacancy in nickel molybdate hollow sphere towards a high‐performance hybrid supercapacitor

The facile design and fabrication of nanoarchitectured binary transition metal oxide electrode materials are essentially required for the advancement of high-performance supercapacitors (SCs). Herein, we prepared an oxygen-vacant NiMoO4 (Ov-NiMoO4) hollow sphere via a simple hydrothermal approach and subsequent heat treatment under an argon atmosphere. In particular, the oxygen vacancy is confirmed by using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), Raman, and differential reflectance spectroscopy (DRS) UV-Vis spectra studies. Furthermore, the generation of the oxygen vacancy could enhance the electrical conductivity and improve Faradaic redox sites. Significantly, the Ov-NiMoO4 hollow sphere depicts a larger specific capacity (Csp) of 496 mA h g−1 at 1 A g−1 than the bare-NiMoO4 (b-NiMoO4; 279 mA h g−1) thermally treated under air. Furthermore, the hybrid SC (HSC) is fabricated based on the Ov-NiMoO4//activated carbon, revealing a high specific capacitance (Cs) of 120 F g−1 and providing a large energy density (ED) of 37.49 W h kg−1 and power density (PD) of 36.61 kW kg−1. Moreover, the HSC shows considerable cyclic stability of ~91.14% over 20 000 cycles. The results divulge that the poor crystallinity and the introduction of oxygen vacancies play a vital role in enhancing the charge-storage capability of the materials.

Assimilation of Polarimetric Radar Data in Simulation of a Supercell Storm with a Variational Approach and the WRF Model

Polarimetric radar data (PRD) have potential to be used in numerical weather prediction (NWP) models to improve convective-scale weather forecasts. However, thus far only a few studies have been undertaken in this research direction. To assimilate PRD in NWP models, a forward operator, also called a PRD simulator, is needed to establish the relation between model physics parameters and polarimetric radar variables. Such a forward operator needs to be accurate enough to make quantitative comparisons between radar observations and model output feasible, and to be computationally efficient so that these observations can be easily incorporated into a data assimilation (DA) scheme. To address this concern, a set of parameterized PRD simulators for the horizontal reflectivity, differential reflectivity, specific differential phase, and cross-correlation coefficient were developed. In this study, we have tested the performance of these new operators in a variational DA system. Firstly, the tangent linear and adjoint (TL/AD) models for these PRD simulators have been developed and checked for the validity. Then, both the forward operator and its adjoint model have been built into the three-dimensional variational (3DVAR) system. Finally, some preliminary DA experiments have been performed with an idealized supercell storm. It is found that the assimilation of PRD, including differential reflectivity and specific differential phase, in addition to radar radial velocity and horizontal reflectivity, can enhance the accuracy of both initial conditions for model hydrometer state variables and ensuing model forecasts. The usefulness of the cross-correlation coefficient is very limited in terms of improving convective-scale data analysis and NWP.

Light-Induced Charge Accumulation in PTCDI/Pentacene/Ag(111) Heterojunctions

The incorporation of singlet fission (SF) chromophores in solar cells is expected to bring significant increases in the power conversion efficiency thanks to multiexciton generation. However, efficient charge generation in the device is determined by the energy level alignment (ELA) between the active materials, which should favor exciton transport and separation under illumination. By combining ultraviolet photoemission spectroscopy and optical differential reflectance measurements, we determine the ELA in a prototypical SF heterojunction between pentacene (Pc) and perylene-tetracarboxylic-diimide (PTCDI) grown on Ag(111). Time-resolved X-ray photoelectron spectroscopy on such a system reveals light-induced modifications of the ELA; by measuring the transient shift of the core level photoemission lines we observe an accumulation of long-lived holes in the PTCDI within the first hundred picoseconds after the optical pump.

Analysis of the microphysical properties of snowfall using scanning polarimetric and vertically pointing multi-frequency Doppler radars

Abstract. Radar dual-wavelength ratio (DWR) measurements from the Stony Brook Radar Observatory Ka-band scanning polarimetric radar (KASPR, 35 GHz), a W-band profiling radar (94 GHz), and a next-generation K-band (24 GHz) micro rain radar (MRRPro) were exploited for ice particle identification using triple-frequency approaches. The results indicated that two of the radar frequencies (K and Ka band) are not sufficiently separated; thus, the triple-frequency radar approaches had limited success. On the other hand, a joint analysis of DWR, mean Doppler velocity (MDV), and polarimetric radar variables indicated potential in identifying ice particle types and distinguishing among different ice growth processes and even in revealing additional microphysical details. We investigated all DWR pairs in conjunction with MDV from the KASPR profiling measurements and differential reflectivity (ZDR) and specific differential phase (KDP) from the KASPR quasi-vertical profiles. The DWR-versus-MDV diagrams coupled with the polarimetric observables exhibited distinct separations of particle populations attributed to different rime degrees and particle growth processes. In fallstreaks, the 35–94 GHz DWR pair increased with the magnitude of MDV corresponding to the scattering calculations for aggregates with lower degrees of riming. The DWR values further increased at lower altitudes while ZDR slightly decreased, indicating further aggregation. Particle populations with higher rime degrees had a similar increase in DWR but a 1–1.5 m s−1 larger magnitude of MDV and rapid decreases in KDP and ZDR. The analysis also depicted the early stage of riming where ZDR increased with the MDV magnitude collocated with small increases in DWR. This approach will improve quantitative estimations of snow amount and microphysical quantities such as rime mass fraction. The study suggests that triple-frequency measurements are not always necessary for in-depth ice microphysical studies and that dual-frequency polarimetric and Doppler measurements can successfully be used to gain insights into ice hydrometeor microphysics.

Magneto-optical Kerr effect measurement in ultrafast Sagnac interferometry using the Jones matrix approach.

We report the Jones matrix formalism of the magneto-optic Kerr effect (MOKE) for ferromagnets using an ultrafast Sagnac interferometer. Compared to the time-resolved MOKE instrument, the Sagnac interferometer has the advantage of obtaining the real and imaginary parts of the differential MOKE signal as well as the differential reflectivity and the lattice displacement at the same time. In addition, a simple method to obtain the static values of Kerr rotation and ellipticity is presented.

Validation of X-band multi-parameter phased array weather radar by comparing data from Doppler weather radar with a parabolic dish antenna

AbstractThe multi-parameter phased array weather radar (MP-PAWR) was the first dual-polarized phased array weather radar to be commissioned in Japan (2017). When conducting a volume scan, the MP-PAWR respectively uses electronic and mechanical scanning in the elevation and azimuth angles to achieve rapid scanning and high-density observations. Although the effectiveness of the MP-PAWR has been demonstrated in case studies, its observation accuracy is yet to be quantitatively analyzed. Therefore, this study compared data of MP-PAWR with that of an operational dual-polarized weather radar with a parabolic-type antenna (X-MP radar) using 2,347,097 data samples obtained over 14 h. The results showed that the observation accuracy of the MP-PAWR was approximately the same as that of the X-MP radar at low elevations. The correlations of observational parameters (radar reflectivity factor, differential resistivity, specific differential phase, and Doppler velocity) between the MP-PAWR and X-MP radar ranged from 0.77–0.99 when MP-PAWR data were recorded within 15 s of the X-MP radar observations. The correlation between the observational parameters of the two radars decreased as the observation time difference between the X-MP radar and MP-PAWR increased. In particular, the correlation coefficients between the specific differential phase and the differential reflectivity were considerably lower than the single-polarization parameter at observation time difference of 240–300 s. By providing high-frequency and high-density dual-polarization observations, the MP-PAWR can contribute to rainfall prediction in Japan and reduce the damage caused by localized, rapidly developing cumulonimbus clouds.

Improving Time-Efficiency of Variational Specific Differential Phase Estimation

This study presents a variational approach for optimized estimation of specific differential phase ( K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DP</sub> ) for polarimetric radars using a linear forward operator. A cubic B-spline interpolating filter is included to mitigate the impact of measurement error in the total differential phase and ensure the spatial continuity of K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DP</sub> . For rain, non-negative constraints are introduced to ensure that the K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DP</sub> estimates are within the physical bounds. The variational approach is flexible to incorporate the background information constructed from the measurements of horizontal reflectivity factor ( Z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</sub> ) and differential reflectivity ( Z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DR</sub> ) based on the self-consistent relationship of polarimetric variables. The variational approach is evaluated using simulated experiments, as well as real observations from an S-band operational weather radar. Without including background information, the variational approach has slightly better performance compared to the approach based on linear programming (LP), and the background information helps to further improve the performance. In addition, the linear forward operator makes this variational approach computationally efficient. It needs less than 3% computational power required by the approach based on LP, making it more suitable for real-time operational applications.

Polarimetric Observations and Simulations of Sublimating Snow: Implications for Nowcasting

AbstractSnow sublimating in dry air is a forecasting challenge and can delay the onset of surface snowfall and affect storm-total accumulations. Despite this, it remains comparatively less studied than other microphysical processes. Herein, the characteristics of sublimating snow and the potential for nowcasting snowfall reaching the surface are explored through the use of dual-polarization radar. Twelve cases featuring prolific sublimation were analyzed using range-defined quasi-vertical profiles (RDQVPs) and compared with environmental model analyses. Overall, reflectivity Z significantly decreases, differential reflectivity ZDR slightly decreases, and copolar-correlation coefficient ρhv remains nearly constant through the sublimation layer. Regions of enhanced specific differential phase Kdp were frequently observed in the sublimation layer and are believed to be polarimetric evidence of secondary ice production via sublimation. A 1D bin model was initialized using particle size distributions retrieved from the RDQVPs using numerous novel polarimetric snowretrieval relations for a wide range of forecast lead times, with the model environment evolving in response to sublimation. It was found that the model was largely able to predict the snowfall start time up to six hours in advance, with a 6-h median bias of just -18.5 minutes. A more detailed case study of the 08 December 2013 snowstorm in the Philadelphia region was also performed, demonstrating good correspondence with observations and examples of model fields (e.g., cooling rate) hypothetically available from such a tool. The proof-of-concept results herein demonstrate the potential benefits of incorporating spatially averaged radar data in conjunction with simple 1D models into the nowcasting process.