Particle Signatures Research Articles

Far‐Field Optical Microscopy of Single Metal Nanoparticles

AbstractFor Abstract see ChemInform Abstract in Full Text.

Tracing water and suspended matter in Raritan and Lower New York Bays using dissolved and particulate elemental concentrations

Geochemical tracers were used to examine the mixing of water and particles in Lower New York and Raritan Bays in August 1999 during low-flow conditions. Four brackish water masses (20 ≤ S ≤ 28) originating in the Raritan and Shrewsbury Rivers, Arthur Kill, and Upper New York Bay were characterized by their dissolved metals concentrations. The mixing lines of dissolved Cu, Ni, and Pb in Lower New York Bay were similar to those in Upper New York Bay, the source of most of the freshwater to the system. Dissolved Cd and Mn seemed to have been removed by particles in several regions of the study. Dissolved Cu, Ni and Pb in the Raritan River fell below the mixing lines of the Lower New York Bay. In contrast, the concentrations of dissolved Co and Mn in the Raritan River were distinctly higher than those in the Lower New York Bay, while dissolved Cu and Ni were elevated in the Arthur Kill. A plot of dissolved Co versus dissolved Ni clearly differentiated among three water masses: (1) Upper and Lower New York Bays and Sandy Hood Bay, (2) the Raritan River, and (3) Arthur Kill–Raritan Bay–Shrewsbury River. The concentrations of 22 elements also were measured in the suspended matter of Raritan and Lower New York Bays and brackish water sources. The elemental composition of the suspended matter in surface and bottom waters was correlated with Fe concentrations, which ranged between 50 and 900 μmol g − 1 . Statistical differences among the geographical regions were detected in the relationships of Ti, Ni, Co, As, and U with Fe, with particulate As being an especially strong geochemical indicator of Raritan River particles. The geochemical signatures of Lower New York Bay particles were similar to those of Upper New York Bay. The geochemical signatures of Raritan River particles were distinctly different than those of the Upper New York Bay, but the influence of Raritan River particles appeared to be limited to only inner Raritan Bay. This study illustrates the utility of trace elements for characterization of physical processes in complex estuaries.

October/November 2003 interplanetary coronal mass ejections: ACE/EPAM solar energetic particle observations

In late October and early November 2003 the ACE spacecraft at 1 AU detected two shock‐associated interplanetary coronal mass ejections (ICMEs). In the sheath region formed in front of both ICMEs, some of the highest speeds ever directly measured in the solar wind were observed. We analyze in detail the energetic particle signatures measured at 1 AU by the EPAM experiment on board ACE during the passage and in the vicinity of these ICMEs. Solar energetic particles (SEPs) are utilized as diagnostic tracers of the large‐scale structure and topology of the interplanetary magnetic field (IMF) embedded within both ICME events. In order to explain the bidirectional particle flows observed within both ICMEs, we have examined two candidate scenarios for these ICMEs in terms of open and closed magnetic field configurations. In the context of an open field configuration, the enhanced magnetic field regions associated with the CME‐driven shocks mirror the energetic particles and hence the observed bidirectional flows. In the context of a closed field configuration, bidirectional flows result from particle circulation and reflection in a looped field configuration. Furthermore, we use the ACE/EPAM observations to reassess the leading and trailing boundaries of the ICMEs with respect to those previously proposed based upon ACE/SWEPAM solar wind plasma, suprathermal electron measurements, and ACE/MAG magnetic field data.

Application of a thin double-sided microstrip detector for the registration of [formula omitted]-delayed charge particles: The 6He [formula omitted] decay into the two-body continuum of 6Li

We present a method for the detection of charged particles, emitted following β decay, that allows to reduce the background due to β radiation and thus to facilitate separation of the delayed-particle events. The isotopes of interest are implanted into a highly segmented double-sided silicon strip detector, resulting in excellent precision on the overall normalisation. The characteristics of the detector and the particle signatures are discussed. This method can be applied to a variety of systems close to the proton and neutron driplines; a region which the recent availability of post-accelerated radioactive beams has opened up for study. To demonstrate this, we measured the branching ratio of 6He β decay into the α + d two-body continuum of 6Li. We obtained a value of ( 1.7 ± 0.4 ) × 10 - 6 for energies α + d above 525 keV.

In situ observations of small scale neutral and plasma dynamics in the mesosphere/lower thermosphere at 79°N

From June 29 to July 6 2003, the German-Norwegian ROMA-SvalRak campaign (ROMA = Rocket borne Observations in the Middle Atmosphere) took place at the SvalRak rocket range, Ny-Ålesund (78.9°N, 11.9°E; Spitzbergen). The main scientific aim of this campaign was to study polar mesosphere summer echoes (PMSE) and mesospheric turbulence. During this campaign a total of three instrumented sounding rockets was launched. In addition, ground based observations with a VHF radar and a potassium lidar at Longyearbyen complemented the in situ measurements. All three sounding rockets were equipped with the CONE (COmbined sensor for Neutrals and Electrons) instrument to measure small scale structure of neutral air and electron density, and neutral temperature. The PIP (positive ion probe) instrument was used to measure small scale structure of the positive ion density. Furthermore, two cold plasma probes were flown to measure electron temperature, and a particle detector was employed to detect signatures of charged aerosols. During the first launch, an electric field experiment was also incorporated, while during the other two launches, Faraday rotation experiments yielded absolute electron number densities. During all three rocket flights a PMSE was observed by the VHF radar, whereas the potassium lidar detected a noctilucent cloud (NLC) only during the second launch. Signatures of charged particles forming the PMSE and NLC layers were recorded by the onboard particle detectors.

Far-Field Optical Microscopy of Single Metal Nanoparticles

Individual noble-metal particles, with sizes ranging from a few tenths to some hundreds of nanometers, can now be detected by far-field optics. Single-particle microscopy gives access to inhomogeneity, distributions, and fluctuations, which were previously hidden in ensemble experiments. Scattering methods rely on dark-field illumination, spectral signatures of the metal particles, or both. More advanced techniques provide high sensitivity and improved selectivity with respect to other scatterers by isolating metal-specific signals, for example the refractive index change due to heating of the environment by a pump beam or the time-resolved optical response of the particle to a short pump pulse. We review and compare linear and nonlinear methods in far-field optical microscopy that have reached the single-particle regime by means of scattered light, thermal effects, photoluminescence, or nonlinear frequency generation.

Energetic particle signatures of geoeffective coronal mass ejections

We have studied statistically associations of moderate and intense geomagnetic storms with coronal mass ejections (CMEs) and energetic particle events. The goal was to identify specific energetic particle signatures, which could be used to improve the predictions of the geoeffectiveness of full and partial halo CMEs. Protons in the range 1–110 MeV from the ERNE experiment onboard SOHO are used in the analysis. The study covers the time period from August 1996 to July 2000. We demonstrate the feasibility of energetic particle observations as an additional source of information in evaluating the geoeffectiveness of full and partial halo CMEs. Based on the observed onset times of solar energetic particle (SEP) events and energetic storm particle (ESP) events, we derive a proxy for the transit times of shocks driven by the interplanetary counterparts of coronal mass ejections from the Sun to the Earth. For a limited number of geomagnetic storms which can be associated to both SEP and ESP signatures, we found that this transit time correlates with the strength of geomagnetic storms.

Pulsed flows at the high-altitude cusp poleward boundary, and associated ionospheric convection and particle signatures, during a Cluster - FAST - SuperDARN- Søndrestrøm conjunction under a southwest IMF

Abstract. Particle and magnetic field observations during a magnetic conjunction Cluster 1-FAST-Søndrestrøm within the field of view of SuperDARN radars on 21 January 2001 allow us to draw a detailed, comprehensive and self-consistent picture at three heights of signatures associated with transient reconnection under a steady south-westerly IMF (clock angle ≈130°). Cluster 1 was outbound through the high altitude (~12RE) exterior northern cusp tailward of the bifurcation line (geomagnetic Bx>0) when a solar wind dynamic pressure release shifted the spacecraft into a boundary layer downstream of the cusp. The centerpiece of the investigation is a series of flow bursts observed there by the spacecraft, which were accompanied by strong field perturbations and tailward flow deflections. Analysis shows these to be Alfvén waves. We interpret these flow events as being due to a sequence of reconnected flux tubes, with field-aligned currents in the associated Alfvén waves carrying stresses to the underlying ionosphere, a view strengthened by the other observations. At the magnetic footprint of the region of Cluster flow bursts, FAST observed an ion energy-latitude disperison of the stepped cusp type, with individual cusp ion steps corresponding to individual flow bursts. Simultaneously, the SuperDARN Stokkseyri radar observed very strong poleward-moving radar auroral forms (PMRAFs) which were conjugate to the flow bursts at Cluster. FAST was traversing these PMRAFs when it observed the cusp ion steps. The Søndrestrøm radar observed pulsed ionospheric flows (PIFs) just poleward of the convection reversal boundary. As at Cluster, the flow was eastward (tailward), implying a coherent eastward (tailward) motion of the hypothesized open flux tubes. The joint Søndrestrøm and FAST observations indicate that the open/closed field line boundary was equatorward of the convection reversal boundary by ~2°. The unprecedented accuracy of the conjunction argues strongly for the validity of the interpretation of the various signatures as resulting from transient reconnection. In particular, the cusp ion steps arise on this pass from this origin, in consonance with the original pulsating cusp model. The observations point to the need of extending current ideas on the response of the ionosphere to transient reconnection. Specifically, it argues in favor of re-establishing the high-latitude boundary layer downstream of the cusp as an active site of momentum transfer.

Dust size evidence for opposite regional atmospheric circulation changes over east Antarctica during the last climatic transition

Three east Antarctic ice cores (Dome B, EPICA-Dome C and Komsomolskaia) give evidence for a uniform dust input to the polar plateau during the last glacial maximum (LGM)/Holocene transition (20 to 10 kyr BP) and the 87Sr/86Sr versus 143Nd/144Nd isotopic signature of the mineral particles highlights a common provenance from southern South America at that time. However, the size distribution of dust from the three ice cores highlights important differences within the east Antarctic during the LGM and shows clearly opposite regional trends during the climatic transition. Between Dome B and Dome C the timing of these changes is also different. A geographical diversity also arises from the different phasing of the short-term (multi-secular scale) dust size oscillations that are superposed at all sites on the main trends of glacial to interglacial changes. We hypothesize the dust grading is controlled by size fractionation inresponse to its atmospheric pathway, either in terms of horizontal trajectory or in altitude of transport. Such mechanism is supported also by the dust size changes observed during a volcanic event recorded in Vostok ice. Ice core dust size data suggest preferential upper air subsidence over the EDC-KMS region and easier penetration of relatively lower air masses to the DB area during the LGM. At the end of the last glacial period and during the climatic transition the region of relatively higher subsidence progressively moved southward. The scenario proposed, supported also by the LGM/Holocene regional changes of snow accumulation, likely operates even at sub-millennial time scale.

Synthesis and Characterization of High-Energy Nanoparticles

Atomic force microscopy (AFM), scanning electron microscopy (SEM), white light imaging measurements, and Raman microscopy were employed for the characterization of hexahydro-1,3,5-trinitro-1,3,5-s-triazine (RDX) nanoparticles deposited on glass substrate surfaces. The RDX nanoparticles were prepared by exposure of glass substrate surfaces to an aerosol jet containing RDX. The spectroscopic signature of RDX particles and the two known forms of the material, β and a RDX, are compared. Raman measurements reveal that RDX nanoparticles and β deposits have similar spectroscopic signatures between 750 and 1000 cm - 1 .

Biomass‐burning particle measurements: Characteristic composition and chemical processing

The NOAA Lockheed Orion WP‐3D aircraft intercepted a forest fire plume over Utah on 19 May 2002 during the Intercontinental Transport and Chemical Transformation (ITCT) mission. Large enhancements in acetonitrile (CH3CN), carbon monoxide (CO) and particle number were measured during the fire plume interception. In the 100 s plume crossing, the Particle Analysis by Laser Mass Spectrometry (PALMS) instrument acquired 202 positive mass spectra from ionizing single particles in the 0.2–5 μm size range. These particles contained carbon, potassium, organics, and ammonium ions. No pure soot particles were sampled directly from the plume. By characterizing these particle mass spectra, a qualitative biomass‐burning particle signature was developed that was then used to identify biomass‐burning particles throughout ITCT. The analysis was extended to identify biomass‐burning particles in four other missions, without the benefit of gas‐phase biomass‐burning tracers. During ITCT, approximately 33% of the particles sampled in the North American troposphere and 37% of the particles transported from Asia, not influenced by North American sources, were identified as biomass‐burning particles. During the WB‐57 Aerosol Mission (WAM), Atmospheric Chemistry of Combustion Emissions near the Tropopause (ACCENT) and ACCENT 2000 missions, 7% of stratospheric particles were identified as biomass‐burning particles. During the Cirrus Regional Study of Tropical Anvils and Cirrus Layers – Florida Area Cirrus Experiment (CRYSTAL‐FACE) this percentage increased to 52% because the regional stratosphere was strongly affected by an active fire season.

Net effect of rainfall activity on salt-marsh sediment distribution

It has been established that increased suspended sediment concentrations in tidal waters adjacent to salt-marshes occur during periods following heavy rainfall events. In this work, we present experimental data for concentration and sediment flux measurements during periods of natural moderate rainfall events from a microtidal, alochthonous salt-marsh system (North Inlet, South Carolina, USA). The results indicate that rainfall events, although responsible for increasing sediment concentration levels, do not alter the sediment flux of the system. In our results, the sediment mobilized by the rain was re-introduced to the system. Further, using the geochemical signatures of suspended particles from the same location, we found that the sediment mobilized by rainfall events is the same as the sediment present in the tidal creeks, suggesting that rainfall mobilizes only recently deposited, non-consolidated sediment and does not erode the substrate of the marsh surface.

Solar wind modulation of cusp particle signatures and their associated ionospheric flows

This paper presents a multi‐instrument case study of the northern polar cusp at a variety of altitudes in conjunction with solar wind measurements. In the midaltitude cusp the Polar spacecraft observed pulsed particle and magnetic field signatures with periodicities ranging from ∼5 to 40 min for over 3 hours. Simultaneously, the CUTLASS HF radars measured poleward moving radar auroral forms (PMRAFs) with inter‐PMRAF periods similar to the Polar periodicities but several degrees of magnetic latitude poleward of the ionospheric footprint of the spacecraft. Such PMRAFs have previously been identified as ionospheric signatures of transient reconnection and flux transfer events. During this event, both the ACE and Wind spacecraft were making measurements in the solar wind. Oscillations in the time‐shifted solar wind magnetic fields and flows and calculated reconnection electric fields were observed with the same periodicities as those seen by Polar and CUTLASS. We conclude that the solar wind Alfvén waves modulate the dayside interaction, producing periodic flux transfer events resulting in the pulsed cusp particle signatures and PMRAFs. This study is the first observation of solar wind driven pulsed cusp particle signatures and associated PMRAFs, i.e., at both magnetospheric and ionospheric altitudes, at multiple simultaneous discrete periodicities.

Gamma ray bursts and gravitational waves: triggered search strategy in the LIGO science runs

We describe a complete analysis pipeline for detecting and estimating gravitational wave signals in conjunction with observations of astrophysical phenomena with an electromagnetic or particle signature, examples of such phenomena being gamma ray bursts (GRB) and supernovae neutrino bursts. Our data analysis methods explicitly account for non-Gaussian and non-stationary features in real interferometric data. This pipeline is meant for signal searches in conjunction with individual GRB triggers and is being used for the analysis of data from the LIGO science runs (S1 and S2). However, many aspects of the pipeline are quite general and can also be used for other broadband interferometric detectors.

FORTE satellite constraints on ultrahigh energy cosmic particle fluxes

The FORTE (Fast On-orbit Recording of Transient Events) satellite records bursts of electromagnetic waves arising from near the Earth's surface in the radio frequency (rf) range of 30 to 300 MHz with a dual polarization antenna. We investigate the possible rf signature of ultrahigh energy cosmic-ray particles in the form of coherent Cherenkov radiation from cascades in ice. We calculate the sensitivity of the FORTE satellite to ultrahigh energy neutrino (UHE $\ensuremath{\nu})$ fluxes at different energies beyond the Greisen-Zatsepin-Kuzmin cutoff. Some constraints on supersymmetry model parameters are also estimated due to the limits that FORTE sets on the UHE neutralino flux. The FORTE database consists of over 4 million recorded events to date, including in principle some events associated with UHE $\ensuremath{\nu}.$ We search for candidate FORTE events in the period from September 1997 to December 1999. The candidate production mechanism is via coherent VHF radiation from a UHE $\ensuremath{\nu}$ shower in the Greenland ice sheet. We demonstrate a high efficiency for selection against lightning and anthropogenic backgrounds. A single candidate out of several thousand raw triggers survives all cuts, and we set limits on the corresponding particle fluxes assuming this event represents our background level.

Coordinated interhemispheric SuperDARN radar observations of the ionospheric response to flux transfer events observed by the Cluster spacecraft at the high-latitude magnetopause

Abstract. At 10:00 UT on 14 February 2001, the quartet of ESA Cluster spacecraft were approaching the Northern Hemisphere high-latitude magnetopause in the post-noon sector on an outbound trajectory. At this time, the interplanetary magnetic field incident upon the dayside magnetopause was oriented southward and duskward (BZ negative, BY positive), having turned from a northward orientation just over 1 hour earlier. As they neared the magnetopause the magnetic field, electron, and ion sensors on board the Cluster spacecraft observed characteristic field and particle signatures of magnetospheric flux transfer events (FTEs). Following the traversal of a boundary layer and the magnetopause, the spacecraft went on to observe further signatures of FTEs in the magnetosheath. During this interval of ongoing pulsed reconnection at the high-latitude post-noon magnetopause, the footprints of the Cluster spacecraft were located in the fields-of-view of the SuperDARN Finland and Syowa East radars located in the Northern and Southern Hemispheres, respectively. This study extends upon the initial survey of Wild et al. (2001) by comparing for the first time in situ magnetic field and plasma signatures of FTEs (here observed by the Cluster 1 spacecraft) with the simultaneous flow modulations in the conjugate ionospheres in the two hemispheres. During the period under scrutiny, the flow disturbances in the conjugate ionospheres are manifest as classic "pulsed ionospheric flows" (PIFs) and "poleward moving radar auroral forms" (PMRAFs). We demonstrate that the ionospheric flows excited in response to FTEs at the magnetopause are not those expected for a spatially limited reconnection region, somewhere in the vicinity of the Cluster 1 spacecraft. By examining the large- and small-scale flows in the high-latitude ionosphere, and the inter-hemispheric correspondence exhibited during this interval, we conclude that the reconnection processes that result in the generation of PIFs/PMRAFs must extend over many (at least 4) hours of magnetic local time on the pre- and post-noon magnetopause.Key words. Ionosphere (plasma convection) – Magnetospheric physics (magnetosphere-ionosphere interactions; magnetospheric configuration and dynamics)

Electron signatures and Alfvén waves

We identify two distinct electron populations associated with Alfvén waves in the Freja data set using the high time resolution state of the art electron detector. One of the populations, detected together with an Alfvén wave, is field‐aligned and can be seen as trapped within the wave. The other electron population is detected before the wave and consists of electrons which have left the wave at a point with a velocity higher than the local Alfvén speed. In the paper, the electrons leaving wave are modeled for different density profiles and are compared with the observed data. Depending on the density profile, the model can produce the same energy‐time and pitch angle‐time dispersion that is observed in the Freja data. The conclusion of the paper is that the Alfvén wave can explain the observed particle signatures. It is shown that the Alfvén wave acceleration can create electron signatures similar to inverted‐V structures. The density distribution along a flux tube has an important role in the type of particle signatures that can be detected at low altitudes.

Testing global storm‐time electric field models using particle spectra on multiple spacecraft

During a magnetic storm on 17–18 February 1998, several spacecraft sampled the inner magnetosphere over a wide range of L shells simultaneously and provided a unique opportunity to obtain particle spectra as a function of L shells, latitude, and local time. We present phase space modeling in a dipole magnetic field and with model electric fields during the recovery phase of that storm to explain the ion spectrograms obtained on three spacecraft (POLAR, EQUATOR‐S, and FAST). The particle signatures studied are from the late recovery phase of the storm, but the particles are affected by the electric fields along their trajectories also during main phase. Our goal is to test and possibly improve global electric field models, which are crucial to the evolution of the storm‐time particle distributions. We backtrace ion distributions from the satellite locations and keep track of charge exchange losses. We use the Volland‐Stern, Weimer 96, Weimer 2000, and modifications of Weimer models to best fit instantaneous potential measurements made by the electric field instrument on POLAR and the ion drift meter instrument on the Defense Meteorological Satellite Program fleet of satellites. We incorporate corotation and a simple, global axisymmetric inductive electric field due to the ring current changes. Significant differences with ion spectral observations do exist and cannot be accounted for simply by modification of existing models. Explaining those differences requires addition of local inductive electric fields or nightside injections.

Identification of substorm expansive phase onsets

Over the years, many different particle and electromagnetic signatures have been invoked to identify the onset of what is called a “substorm.” In this paper I shall first clarify what is generally meant by the term “substorm onset,” and I shall show that some disturbances identified as substorm onsets should be treated with care. I shall review the substorm in terms of its two recognized characteristic components: directly driven and storage/release. I shall then discuss the importance of pseudobreakups in deciding what constitutes a legitimate substorm onset and, in doing so, will illustrate the subjective nature of present substorm onset identification techniques. I shall stress that substorm‐like disturbances can take place both near the equatorward edge of the midnight sector oval (mapping to the near‐Earth magnetotail inside ∼−12 RE) and near the poleward edge of the evening sector oval (mapping to regions much farther downtail). I shall present case studies that illustrate that some poleward edge disturbances have magnetic and auroral signatures that may be incorrectly interpreted as legitimate expansive phase onsets. On the basis of this study, I suggest that what may appear to be a lengthy series of closely spaced expansive phases may, in fact, be a single expansive phase followed by an arbitrarily long period of poleward border activity.

Statistics of the mid‐altitude cusp observed by Polar

The Polar GGS space mission has allowed the northern hemispheric polar cusp region to be probed in a variety of ways to further our understanding and knowledge of the processes that occur within this region. The discovery of pulsed, energy‐dispersed ion injections on newly‐opened field lines (Pulsed Particle Signatures, or PPSs), the magnetospheric plasma signatures of transient reconnection, is one such advancement in our knowledge. Utilising a ∼22 months subset of Polar's mission, we perform a statistical study of the dayside traversals of the cusp region by the spacecraft to determine the extent and location of PPSs as well as the prevailing Interplanetary Magnetic Field (IMF) conditions under which they occur. In this paper we report upon the broad extent of these signatures in latitude and local time regardless of IMF orientation, and show that PPSs occur under both southward and northward IMF conditions in high percentages, although favouring southward directed IMF. These results are discussed in terms of previous statistical studies of reconnection signatures, and in terms of lobe and low latitude reconnection.