UMBC Physics Department

Permanent URI for this collection

http://hdl.handle.net/11603/57

The mission of the Department of Physics at UMBC is based on three pillars: education, research and service to society. We strive to provide outstanding educational opportunities, through instruction and research, for undergraduate physics majors seeking preparation for graduate school or entry into the workforce. We also aim to train graduate students to be leaders in their field of research. Our research goal is to grow and sustain internationally recognized research groups in atmospheric physics, astrophysics, condensed matter physics and quantum optics and information science. Through our teaching of physics to non-science and non-physics majors and through our Physics for Secondary Education Teachers program, we provide professional service to the university community and the State.

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Now showing 1 - 20 of 2054

Linear Computing and Thermodynamics
(2024/01/01) Aifer, Maxwell; Deffner, Sebastian; Physics; Physics
A large part of computing deals with the doing, undoing, and reinterpretation of linear transformations on vector spaces. These operations are essential to the description of most physical phenomena, are a core part of machine learning, and also form the basic building blocks of quantum algorithms. The tendency of all things to evolve towards thermal equilibrium poses challenges for efficient and accurate computation, which often appear in the form of energy dissipation and errors caused by thermal noise. While thermal physics has provided some insights about physical limitations on computing, less is known about the particular considerations that apply to linear algebraic computations. Here, I study the application of thermodynamics to such problems, in both classical and quantum systems. Several new algorithms are given for linear algebra problems using specialized hardware, which have theoretical advantages over previously existing algorithms. Additionally, new bounds are proven for the energy cost of unitary transformations of quantum states, as well as for the efficiency of communication between quantum systems.
Characterization of the role of oxide spacers in multilayer-enhanced SERS probes
(SPIE, 2015-05-13) Strobbia, Pietro; Henegar, Alex; Gougousi, Theodosia; Cullum, Brian
Surface enhanced Raman spectroscopy (SERS) has several advantages as a transduction method for many types of optical sensors, due to its sensitivity and potential for multiplexed detection. Over the years, SERS probes have been developed to be capable of extreme sensitivities, with single molecule SERS having been achieved in randomly located hot-spots of colloidal aggregates. However, these structures suffer from significant irreproducibility, due to the randomness of the aggregation. Alternatively, strategies such as ordered 2D arrays or enhancement based on single probes (e.g. immunno-nanosensors, nanostars) have high reproducibilities but limited enhancement factors. In our laboratory a widely applicable enhancing geometry based on metal thin films interleaved with dielectric spacers that takes advantage of interaction into the volume of the probe (perpendicularly to the surface) to enhance the signal independently from the underlying structure has been developed. Preliminary evidence into the mechanism of this enhancement suggests that the dielectric spacer material and thickness play a key role in the magnitude of the resulting enhancement. In this paper we investigate the thickness dependence of the multilayer enhancement using substrates fabricated using ultrathin oxide deposited by atomic layer deposition as spacers. The SERS enhancement measured for substrates based on semiconductor and dielectric materials have been characterized in order to understand the origin of this dependence. In addition a model to describe the mechanism by which the spacer properties influence the multilayer enhancement will also be discussed.
Phase matrix characterization of long-range transported Saharan dust using multiwavelength polarized polar imaging nephelometry
(EGU, 2024-08-14) Bazo, Elena; Perez-Ramirez, Daniel; Valenzuela, Antonio; Martins, J. Vanderlei; Titos, Gloria; Cazorla, Alberto; Rejano, Fernando; Patrón, Diego; Diaz-Zurita, Arlett; Garcia-Izquierdo, Francisco Jose; Fuertes, David; Alados-Arboledas, Lucas; Olmo, Francisco Jose
This work investigates the scattering matrix elements during different Saharan dust outbreaks over Granada (South-East Spain) in 2022 using the Polarized Imaging Nephelometer (PI-Neph PIN100, GRASP-Earth). The PI-Neph is a unique instrument capable of measuring continuously the phase function and polarized phase function (F₁₁ and -F₁₂/F₁₁) at three different wavelengths (405, 515 and 660 nm) with 1° resolution. Extreme dust events (PM₁₀ concentration above 1000 µgm⁻³) occurring in March 2022 are compared with more frequent and moderate events registered in summer 2022 (PM₁₀ concentration between 50 and 100 µgm⁻³). For F₁₁ there are no remarkable differences between extreme and moderate events. However, results of -F₁₂/F₁₁ show large differences between extreme and moderate events, especially for the 405 nm wavelength. These differences are also observed when studying the temporal evolutions during the extreme events and reveal that -F₁₂/F₁₁ patterns similar to laboratory measurements occurred during the more intense periods of dust influence. Other aerosol optical properties were derived from the PI-Neph, such as the asymmetry parameter (g), the fraction of backscattered light (Bs) and the lidar ratio (LR). In general, g and Bs show typical values (g > 0.65 and Bs ~ 0.1) for both extreme and moderate Saharan dust events. However, the LR shows more variable values for the different dust events, ranging from 20 to 60 sr⁻¹. The combination with additional in-situ instrumentation allowed to obtain scattering (SAE) and absorption (AAE) Ångström exponents and to conduct a typing classification that revealed extreme dust events as pure dust while moderate dust events were classified as a mixture of dust with urban background pollution. In addition, model simulations with the Generalized Retrieval of Atmosphere and Surface Properties (GRASP) code reproduce well the PI-Neph measurements. Therefore, our results confirm that differences in the phase matrix elements of Saharan dust outbreaks of varying intensity can be explained by the mixing conditions of dust with the background particles, which varies from almost pure dust particles during extreme events, to a mixture of dust with local pollution during moderate events.
Disciplinary Differences in STEM Faculty and Student Use of Learning Objectives: Implications for Teaching and Learning
(Taylor & Francis, 2024-07-22) Leupen, Sarah; Williams, Tory; Hodges, Linda C.; Ott, Laura E.; Anderson, Eric C.; Cui, Lili; Nanes, Kalman M.; Perks, H. Mark; Wagner, Cynthia R.
Using learning objectives to guide course design is often considered an educational best practice, but little research exists that explores how students use them over time and across courses. We surveyed students on their use and perceived value of learning objectives as the semester progressed across four science, technology, engineering, and mathematics (STEM) disciplines, examined students’ ability to match exam questions with learning objectives, and analyzed how their course performance related to these qualities. We also gathered instructors’ information on their implementation of learning objectives in these courses. We identified distinct disciplinary differences both in students’ use and perceived benefit of learning objectives and in instructors’ implementation of them. Students in less quantitatively focused courses, i.e., biology and organic chemistry, reported valuing and using learning objectives more than students in more quantitatively focused math and physics courses. Students’ ability to match learning objectives with exam questions, however, positively correlated with exam score and final course grade in all our study courses. Our results have implications for considering disciplinary practices for use of learning objectives as instructors design and implement courses, educational researchers plan studies, and assessment specialists formulate institutional assessment plans.
Multiwavelength Investigation of γ-ray Source MGRO J1908+06 Emission Using Fermi--LAT, VERITAS, and HAWC
(2024-08-02) Shang, Ruo-Yu; Eagle, Jordan; Kumar, Sajan; De León, S. Coutiño; Valverde, J
This paper investigates the origin of the γ-ray emission from MGRO J1908+06 in the GeV-TeV energy band. By analyzing the data collected by Fermi--LAT, VERITAS, and HAWC, with the addition of spectral data previously reported by LHAASO, a multiwavelength (MW) study of the morphological and spectral features of MGRO J1908+06 provides insight into the origin of the γ-ray emission. The mechanism behind the bright TeV emission is studied by constraining the magnetic field strength, the source age, and the distance through detailed broadband modeling. Both spectral shape and energy-dependent morphology support the scenario that inverse-Compton (IC) emission of an evolved pulsar wind nebula (PWN) associated with PSR J1907+0602 is responsible for the MGRO J1908+06 γ-ray emission with a best-fit true age of T=22±9 kyr and a magnetic field of B=5.4±0.8 µG, assuming the distance to the pulsar dₚₛᵣ=3.2 kpc.
A Multiwavelength Portrait of the 3C 220.3 Lensed System
(2024-07-30) Hyman, Sóley Ó; Wilkes, Belinda J.; Willner, S. P.; Kuraszkiewicz, Joanna; Azadi, Mojegan; Worrall, D. M.; Foord, Adi; Vegetti, Simona; Ashby, Matthew L. N.; Birkinshaw, Mark; Fassnacht, Christopher; Haas, Martin; Stern, Daniel
The 3C 220.3 system is a rare case of a foreground narrow-line radio galaxy (“galaxy A,” zₐ = 0.6850) lensing a background submillimeter galaxy (zₛₘG₁ = 2.221). New spectra from MMT/Binospec confirm that the companion galaxy (“galaxy B”) is part of the lensing system with zB = 0.6835. New threecolor HST data reveal a full Einstein ring and allow a more precise lens model. The new HST images also reveal extended emission around galaxy A, and the spectra show extended [O II] emission with irregular morphology and complex velocity structure. All indications are that the two lensing galaxies are a gravitationally interacting pair. Strong [O II] emission from both galaxies A and B suggests current star formation, which could be a consequence of the interaction. This would indicate a younger stellar population than previously assumed and imply smaller stellar masses for the same luminosity. The improved lens model and expanded spectral energy distributions have enabled better stellar-mass estimates for the foreground galaxies. The resulting dark matter fractions are ~0.8, higher than previously calculated. Deeper Chandra imaging shows extended X-ray emission but no evidence for a point X-ray source associated with either galaxy. The detection of X-rays from the radio lobes of 3C 220.3 allows an estimate of ~3 nT for the magnetic fields in the lobes, a factor of ~3 below the equipartition fields, as typical for radio galaxies.
A NuSTAR Census of the X-Ray Binary Population of the M31 Disk
(AAS, 2024-07-29) Moon, Hannah; Wik, Daniel R.; Antoniou, V.; Eracleous, M.; Hornschemeier, Ann E.; Lazzarini, Margaret; Lehmer, Bret D.; Vulic, Neven; Williams, Benjamin F.; Maccarone, T. J.; Pottschmidt, Katja; Ptak, Andrew; Yukita, Mihoko; Zezas, Andreas
Using hard (E > 10 keV) X-ray observations with NuSTAR, we are able to differentiate between the accretion states, and thus compact object types, of neutron stars (NSs) and black holes (BHs) in X-ray binaries (XRBs) in M31, our nearest Milky Way–type neighbor. Using 10 moderate-depth (20–50 ks) observations of the disk of M31 covering a total of ~0.45 deg², we detect 20 sources at 2σ in the 4–25 keV bandpass, 14 of which we consider to be XRB candidates. This complements an existing, deeper (100–400 ks) survey covering ~0.2 deg² of the bulge and the northeastern disk. We make tentative classifications of nine of these sources with the use of diagnostic color–intensity and color–color diagrams, which separate sources into various NS and BH regimes, identifying three BHs and six NSs. In addition, we create X-ray luminosity functions (XLFs) for both the full (4–25 keV) and hard (12–25 keV) bands, as well as subpopulations of the full band based on compact object type and association with globular clusters. Our best-fit globular cluster XLF is shallower than the field XLF, and preliminary BH and NS XLFs suggest a difference in shape based on compact object type. We find that the cumulative disk XLFs in the full and hard band are best fit by power laws with indices of 1.32 and 1.28, respectively. This is consistent with models of the Milky Way XLF from Grimm et al., Voss & Ajello, and Doroshenko et al.
Scalable quantum control of solid-state qubit systems to counteract physical errors
(2024-01-01) Kanaar, David Wyman; Kestner, Jason P; Physics; Physics
Quantum computing allows for significant speed-up in solving certain practical problems as compared to classical computing. The current quantum computers are limited by high error rates and a limited number of qubits, quantum bits. Silicon spin qubits, the main focus of this dissertation, are a promising platform for quantum computing that also suffers from these issues. Current silicon spin quantum computers are limited in size and error rates by charge noise. The goal of this dissertation is to develop quantum control methods that can create high-fidelity gates, low-error rate operations, and scale these gates to larger qubit systems. To this end, in the first half of the dissertation numerical optimization methods are presented that create robust gates in 2-3 qubit systems. This is expanded in the later half where a method for creating robust gates in arrays of Ising coupled qubits is presented. Finally, a method to supplement robust gates by measuring charge noise in situ was proposed in the final work presented in this dissertation. The methods developed in this dissertation help move quantum computing toward becoming practical.
Spectroscopic Studies of Metals, Fluids, and Molecules on the Nanoscale Using Computational and Experimental Methods
(2024-01-01) Gelfand, Rachel; Pelton, Matthew; Physics; Physics
Light has the ability to relay information on the physical world to incredibly small scales. From the nanoscale to further below, many of the complex dynamics underpinning the behaviors of small particles, atoms, and molecules are not able to be ascertained using traditional measurement methods. In order to determine the physics at this scale, spectroscopic methods are used, exploiting light-matter interactions to extract information on the materials of interest. In the first section of the following dissertation, nanoscale fluid dynamics will be explored through spectroscopic measurements on vibrating metal nanoparticles. Transient absorption measurement analysis reveals information on the solid-liquid interface and nanoscale fluid-dynamics. The slip between the nanoparticle surface and fluid is shown to have a substantial dependence on the length of ligand molecules along the surface. This indicates one of the factors affecting nanoscale fluid flow, which is of vital importance to understanding the fundamental physics of this regime and to develop applications involving nanoscale objects in fluids. In the second portion, a comprehensive modeling procedure for transient absorption and Raman spectroscopy on noble metal nanoparticles is presented. Simulations of spectroscopic methods are able to aid in experimental data analysis as well as in the search for materials matching the specifications required for applications. The presented simulation method is accurate to real-world experiments as it includes realistic vibrational amplitudes and treats vibrational modes often considered to be non-contributing. Simulation outputs are shown for several geometries that have known spectra and geometries that have never-before been measured. In the final section, spectroscopic measurements on molecules are discussed. The measured samples, known as light-harvesting molecules, are synthetic versions of those vital for photosynthetic processes. The major interesting characteristic of these molecules are their ability to absorb incident sunlight and undergo an ultrafast transfer process to transmit the energy to another location. These molecules have a number of potential uses including solar energy conversion and in bio-compatible imaging. Transient absorption and time-resolved photoluminescence spectroscopy are used to characterize this energy transfer. In all measured samples, highly efficient energy transfer is observed, indicating that these molecules are good candidates for solar cell or imaging applications.
HARP2 Pre-Launch Calibration Overview: The Effects of a Wide Field of View
(EGU, 2024-07-18) Sienkiewicz, Noah; Martins, J. Vanderlei; McBride, Brent; Xu, Xiaoguang; Puthukkudy, Anin; Smith, Rachel; Fernandez-Borda, Roberto
The HyperAngular Rainbow Polarimeter (HARP2) is a wide field-of-view (FOV) polarimeter built for the NASA Plankton Aerosol Cloud and Ocean Ecosystem mission launched in early 2024. HARP2 measures the linear Stokes parameters across a 114° × 100° (along-track by cross-track) FOV. In the Fall of 2022, HARP2 underwent calibration at NASA Goddard Space Flight Center (GSFC) Calibration Laboratory (Code 618). HARP2 was characterized for radiometric and polarimetric response across its FOV. We have used telecentric calibration methodology on prior iterations of HARP that involved the normalization of pixels across the FOV such that calibration parameters determined at the center of the charged coupled device (CCD) detector can be used across the entire scene. By using a dual-axis yaw/pitch motorized mount, we devised two scan patterns to evaluate this methodology for HARP2. The results show that pure intensity measurements do indeed vary minimally across the FOV and therefore can utilize the flat-field normalization (telecentric) technique. On the other hand, images of polarized targets change significantly across the FOV, and calibration parameters determined at the center of the detector used in the wide FOV perform significantly worse than calibration parameters determined at or near to the location of the test (up to 5 % mean absolute error in degree of linear polarization, DoLP). We evaluated the use of a paraboloid fit of the polarized calibration parameters, at discrete FOV locations, to determine those parameters at a pixel-level resolution. According to the wide FOV results, this process shows a marked improvement for fully polarized (DoLP = 1) calibration data to less than 1 % uncertainty after using the paraboloid fit. These results are important for the development of any wide FOV polarimeter, especially those like HARP2 which use a front lens which causes significant barrel distortion and a division of amplitude central optical element leveraging multiple reflections. Full characterization of the source of these optical effects remains a part of future work.
Prediction of Frequency-Dependent Optical Spectrum for Solid Materials: A Multi-Output & Multi-Fidelity Machine Learning Approach
(2024-07-10) Ibrahim, Akram; Ataca, Can
The frequency-dependent optical spectrum is pivotal for a broad range of applications, from material characterization to optoelectronics and energy harvesting. Data-driven surrogate models, trained on density functional theory (DFT) data, have effectively alleviated the scalability limitations of DFT while preserving its chemical accuracy, expediting material discovery. However, prevailing machine learning (ML) efforts often focus on scalar properties such as the band gap, overlooking the complexities of optical spectra. In this work, we employ deep graph neural networks (GNNs) to predict the frequency-dependent complex-valued dielectric function across the infrared, visible, and ultraviolet spectra directly from crystal structures. We explore multiple architectures for multi-output spectral representation of the dielectric function and utilize various multi-fidelity learning strategies, such as transfer learning and fidelity embedding, to address the challenges associated with the scarcity of high-fidelity DFT data. Additionally, we model key solar cell absorption efficiency metrics, demonstrating that learning these parameters is enhanced when integrated through a learning bias within the learning of the frequency-dependent absorption coefficient. This study demonstrates that leveraging multi-output and multi-fidelity ML techniques enables accurate predictions of optical spectra from crystal structures, providing a versatile tool for rapidly screening materials for optoelectronics, optical sensing, and solar energy applications across an extensive frequency spectrum.
INTEGRAL/IBIS polarization detection in the hard and soft intermediate states of Swift J1727.8-1613
(edp sciences, 2024-07-30) Bouchet, Tristan; Rodriguez, Jérôme; Cangemi, Floriane; Thalhammer, Philipp; Laurent, Philippe; Grinberg, Victoria; Wilms, Joern; Pottschmidt, Katja
Aims. Soft γ-ray emission (100 keV–10 MeV) has previously been detected in the hard state of several microquasars. In some sources, this emission was found to be highly polarized and was suggested to be emitted at the base of the jet. Until now, no γ-ray polarization had been found in any other state. Methods. Using INTEGRAL/IBIS, we studied the soft γ-ray spectral and polarization properties of Swift J1727.8−1613 throughout its outburst. Results. We detect a highly polarized spectral component in both the hard intermediate state and the early stages of the soft intermediate state above 210 keV. In the hard intermediate state, the polarization angle significantly deviates from the compact jet angle projected onto the sky, whereas in the soft intermediate they are closely aligned. This constitutes the first detection of jet-aligned polarization in the soft γ-ray for a microquasar. We attribute this polarized spectral component to synchrotron emission from the jet, which indicates that some of the jet might persist into the softer states.
A Parameter Study of the Electromagnetic Signatures of an Analytical Mini-Disk Model for Supermassive Binary Black Hole Systems
(2024-07-04) Porter, Kaitlyn; Noble, Scott C.; Gutierrez, Eduardo M.; Pelle, Joaquin; Campanelli, Manuela; Schnittman, Jeremy; Kelly, Bernard
Supermassive black holes (SMBHs) are thought to be located at the centers of most galactic nuclei. When galaxies merge they form supermassive black hole binary (SMBHB) systems and these central SMBHs will also merge at later times, producing gravitational waves (GWs). Because galaxy mergers are likely gas-rich environments, SMBHBs are also potential sources of electromagnetic (EM) radiation. The EM signatures depend on gas dynamics, orbital dynamics, and radiation processes. The gas dynamics are governed by general relativistic magnetohydrodynamics (MHD) in a time-dependent spacetime. Numerically solving the MHD equations for a time-dependent binary spacetime is computationally expensive. Therefore, it is challenging to conduct a full exploration of the parameter space of these systems and the resulting EM signatures. We have developed an analytical accretion disk model for the mini-disks of an SMBHB system and produced images and light curves using a general relativistic ray-tracing code and a superimposed harmonic binary black hole metric. This analytical model greatly reduces the time and computational resources needed to explore these systems, while incorporating some key information from simulations. We present a parameter space exploration of the SMBHB system in which we have studied the dependence of the EM signatures on the spins of the black holes (BHs), the mass ratio, the accretion rate, the viewing angle, and the initial binary separation. Additionally, we study how the commonly used fast-light approximation affects the EM signatures and evaluate its validity in GRMHD simulations.
Optimizing EPR pulses for broadband excitation and refocusing
(2024-05-31) Lowe, Eric R.; Stoll, Stefan; Kestner, J. P.
In this paper, we numerically optimize broadband pulse shapes that maximize Hahn echo amplitudes. Pulses are parameterized as neural networks (NN), nonlinear amplitude limited Fourier series (FS), and discrete time series (DT). These are compared to an optimized choice of the conventional hyperbolic secant (HS) pulse shape. A power constraint is included, as are realistic shape distortions due to power amplifier nonlinearity and the transfer function of the microwave resonator. We find that the NN, FS, and DT parameterizations perform equivalently, offer improvements over the best HS pulses, and contain a large number of equivalent optimal solutions, implying the flexibility to include further constraints or optimization goals in future designs.
Simon's algorithm in the NISQ cloud
(2024-06-17) Robertson, Reece; Doucet, Emery; Spicer, Ernest; Deffner, Sebastian
Simon’s algorithm was one of the first problems to demonstrate a genuine quantum advantage. The algorithm, however, assumes access to noise-free qubits. In our work we use Simon’s algorithm to benchmark the error rates of devices currently available in the “quantum cloud.” As a main result we obtain an objective comparison between the different physical platforms made available by IBM and IonQ. Our study highlights the importance of understanding the device architectures and chip topologies when transpiling quantum algorithms onto hardware. For instance, we demonstrate that two-qubit operations on spatially separated qubits on superconducting chips should be avoided.
The giant outburst of EXO 2030+375 I: Spectral and pulse profile evolution
(edp sciences, 2024-08-22) Thalhammer, P.; Ballhausen, R.; Sokolova-Lapa, E.; Stierhof, J.; Zainab, A.; Staubert, R.; Pottschmidt, Katja; Coley, J. B.; Rothschild, R. E.; Jaisawal, G. K.; West, B.; Becker, P. A.; Pradhan, P.; Kretschmar, P.; Wilms, J.
The Be X-ray binary EXO 2030+375 went through its third recorded giant outburst from June 2021 to early 2022. We present the results of both spectral and timing analysis based on NICER monitoring, covering the 2−10 keV flux range from 20 to 310 mCrab. Dense monitoring with observations carried out about every second day and a total exposure time of ∼160 ks allowed us to closely track the source evolution over the outburst. Changes in the spectral shape and pulse profiles showed a stable luminosity dependence during the rise and decline. The same type of dependence has been seen in past outbursts. The pulse profile is characterized by several distinct peaks and dips. The profiles show a clear dependence on luminosity with a stark transition at a luminosity of ∼2 × 10³⁶ erg s−1, indicating a change in the emission pattern. Using relativistic raytracing, we demonstrate how anisotropic beaming of emission from an accretion channel with a constant geometrical configuration can give rise to the observed pulse profiles over a range of luminosities.
X-ray Redshifts for Obscured Active Galactic Nuclei with AXIS Deep and Intermediate Surveys
(MDPI, 2024-06-01) Peca, Alessandro; Cappelluti, Nico; Marchesi, Stefano; Hodges-Kluck, Edmund; Foord, Adi
This study presents the capabilities of the AXIS telescope in estimating redshifts from X-ray spectra alone (X-ray redshifts, XZs). Through extensive simulations, we establish that AXIS observations enable reliable XZ estimates for more than 5500 obscured active galactic nuclei (AGNs) up to redshift z ∼ 6 in the proposed deep (7 Ms) and intermediate (375 ks) surveys. Notably, at least 1600 of them are expected to be in the Compton-thick regime (log Nₕ/cm⁻²≥24), underscoring the pivotal role of AXIS in sampling these elusive objects that continue to be poorly understood. XZs provide an efficient alternative for optical/infrared faint sources, overcoming the need for time-consuming spectroscopy, the potential limitations of photometric redshifts, and potential issues related to multi-band counterpart association. This approach will significantly enhance the accuracy of constraints on the X-ray luminosity function and obscured AGN fractions up to high redshifts. This white paper is part of a series commissioned for the AXIS Probe Concept Mission; additional AXIS white papers can be found at the AXIS website.
Effects of surface coating on the shortwave and longwave radiative effects of dust aerosol in comparison with external mixing: A theoretical study
(ELSEVIER, 2024-06-07) Zhang, Zhibo; Song, Qianqian; Zheng, Jianyu; Yu, Hongbin
Dust particles can be coated with a surface layer of pollutants such as sulfate and nitrate after mixing with local pollution during long-range transport. Previous studies investigated the effects of surface coating on scattering properties and direct radiative effects (DRE) of dust in the solar shortwave (SW) spectral region. In this research, we carried out a theoretical study of the surface coating effects in both solar SW and the terrestrial longwave (LW) and compared the results with external mixing. Three dust coating schemes were developed to study a hypothetical sulfate-dust coating case, in which the thickness of the coating sulfate layer is proportional to the size, surface area, and mass of the dust core, respectively. We found that at the 0.55 µm the aerosol optical thickness (AOD) of the externally mixed dust-sulfate increases more efficiently with the increasing sulfate mass than the coated dust cases, whereas the opposite is true at the 10 µm. This is because at 0.55 µm the difference in the total geometrical cross section is the dominant factor for the AOD difference, while at the 10 µm the dominant factor is the difference in extinction cross section. The differences in dust DRE at the top of atmosphere and surface between the external mixing and coated dust cases can be largely explained by the differences in AOD. Dust absorption in the SW is found to be significantly enhanced by the surface coating of non-absorptive sulfate due to the so-called “lensing effect”. When SW and LW DREs are combined, the volume- and area-proportional coating schemes have a significantly weaker cooling effect than externally mixed dust-sulfate. This research provides the theoretical understanding of how surface coating affects the SW, LW and total dust DREs.
Alaskan and Canadian forest fires exacerbate ozone pollution over Houston, Texas, on 19 and 20 July 2004
(AGU, 2006-09-26) Morris, Gary A.; Hersey, Scott; Thompson, Anne M.; Pawson, Steven; Nielsen, J. Eric; Colarco, Peter R.; McMillan, W. W.; Stohl, Andreas; Turquety, Solene; Warner, Juying; Johnson, Bryan J.; Kucsera, Tom L.; Larko, David E.; Oltmans, Samuel J.; Witte, Jacquelyn C.
On Monday, 19 July, and Tuesday, 20 July 2004, the air over Houston, Texas, appeared abnormally hazy. Transport model results and data from the Atmospheric Infrared Sounder (AIRS), the Moderate Resolution Imaging Spectrometer (MODIS), the Measurement of Ozone by Airbus In-service airCraft (MOZAIC) experiment, and the Total Ozone Mapping Spectrometer (TOMS) indicate that an air mass originating on 12 July 2004 over forest fires in eastern Alaska and western Canada arrived in Houston about 1 week later. Ozonesonde data from Houston on 19 and 20 July show elevated ozone at the surface (>125 ppbv) and even higher concentrations aloft (∼150 ppbv of ozone found 2 km above the surface) as compared to more typical profiles. Integrated ozone columns from the surface to 5 km increased from 17–22 DU (measured in the absence of the polluted air mass) to 34–36 DU on 19 and 20 July. The average on 20 July 2004 of the 8-hour maximum ozone values recorded by surface monitors across the Houston area was the highest of any July day during the 2001–2005 period. The combination of the ozone observations, satellite data, and model results implicates the biomass burning effluence originating in Alaska and Canada a week earlier in exacerbating pollution levels seen in Houston.
Intercontinental Chemical Transport Experiment Ozonesonde Network Study (IONS) 2004: 2. Tropospheric ozone budgets and variability over northeastern North America
(AGU, 2007-05-15) Thompson, Anne M.; Stone, Jesse B.; Witte, Jacquelyn C.; Miller, Sonya K.; Oltmans, Samuel J.; Kucsera, Tom L.; Ross, Kelly L.; Pickering, Kenneth E.; Merrill, John T.; Forbes, Gerry; Tarasick, David W.; Joseph, Everette; Schmidlin, F. J.; McMillan, W. W.; Warner, Juying; Hintsa, Eric J.; Johnson, James E.
Daily ozone soundings taken from the R/V Ronald H. Brown from 7 July through 11 August 2004 as part of the Intercontinental Chemical Transport Experiment (INTEX) Ozonesonde Network Study (IONS) are used to investigate the vertical structure of ozone over the Gulf of Maine and to characterize variability in sources of tropospheric ozone: stratosphere, regional convection and lightning, advection, and local boundary layer pollution. These soundings were part of a network of twelve IONS (http://croc.gsfc.nasa.gov/intex/ions.html) stations that launched ozonesonde-radiosonde packages over the United States and maritime Canada during the INTEX/International Consortium for Atmospheric Research on Transport and Transformation (ICARTT)/New England Air Quality Study (NEAQS) project from 1 July to 15 August 2004. Four of the IONS stations were in mid-Atlantic and northeast United States; four were in southeastern Canada. Although the INTEX/ICARTT goal was to examine pollution influences under stable high-pressure systems, northeastern North America (NENA) during IONS was dominated by weak frontal systems that mixed aged pollution and stratospheric ozone with ozone from more recent pollution and lightning. These sources are quantified to give tropospheric ozone budgets for individual soundings that are consistent with tracers and meteorological analyses. On average, for NENA stations in July-August 2004, tropospheric ozone was composed of the following: 10–15% each local boundary layer and regional sources (the latter including that due to lightning-derived NO) and 20–25% stratospheric ozone, with the balance (∼50%) a mixture of recently advected ozone and aged air of indeterminate origin.

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