ALBERT

Description: In this work we will describe the technique of using an RF Sweeping Impedance Probe (SIP) to measure the AC impedance of an electrically short monopole immersed in a plasma. We analyze the SIP measurements which are taken from the payload of the Storms sounding rocket, launched from Wallops Island, Virginia, in 2007. The scientific objective of the Storms mission was to concentrate on whether density irregularities observed in midlatitude spread-F could arise from ionospheric coupling to terrestrial weather. As such, independent measurements of the electron density profile are crucial. Since the inherent nature of the SIP technique makes it relatively insensitive to errors introduced through spacecraft charging, probe contamination, and other DC effects, it is an ideal instrument to employ under disturbed plasma conditions. The instrument measures both the magnitude and phase of the AC impedance from 100 kHz to 20 MHz in 128 frequency steps, performing 45776 sweeps over the entire flight. From these measurements we infer both the absolute electron density n e and the electron neutral collision frequencies v en throughout the flight trajectory. The SIP data can be approximately analyzed using a fluid formulation and thin sheath approximation particularly at altitudes below 200 km, which allows us to match the measurements to quasistatic analytical formulas. At about 265 km on the upleg, the magnitude data transitioned to a highly damped response with increasing altitude. The phase data on the other hand continued to indicate increased plasma density and reduced collisionality as expected. For a large portion of the flight, the payload of the Storms mission exhibited an uncontrolled coning motion, making the local magnetic field orientation with respect to the dipole difficult to decipher. Despite these difficulties, we were able to obtain robust estimates of the electron density profile, using the phase information from each sweep. In addition, the electron neutral collision frequency obtained from matching to phase data alone was on the correct order of magnitude with respect to NRL-MSISE model values in the ionosphere between 100 km to 150 km.

Description: In this paper we carry out a comparative study of the daytime (7–18 LT) behavior of the near equatorial ionospheric F region at the end of the long deep solar minimum (2009) with respect to that of the previous normal solar minimum (1995) in the Indian longitude sector using ionosonde observations of F layer parameters, radar observations of E x B drift and the IRI-2012 (international reference ionosphere-2012) model. We investigate the F2- and F3-layer behaviors separately. The results reveal that the peak frequencies of the F layer (f peak ), F2 layer (foF2) and F3 layer (foF3) in 2009 are consistently lower than those in 1995. Maximum difference in f peak /foF2/foF3 between 2009 and 1995 observations is found in the equinoxes followed by winter and summer. The annual mean, seasonal mean, and ten-day mean peak electron density (corresponding to f peak ) in 2009 were lower than those in 1995 by as much as 34%, 46% and 65%, respectively. Solar rotation effect is less conspicuous in 2009 than in 1995, consistent with the solar rotation signature in F 10.7 . Observations also show considerable amount of equinoctial asymmetry in electron density, which is found to be closely linked with the corresponding asymmetry in the vertical E x B drift. Seasonal mean peak electron densities of the F layer (corresponding to f peak ) and the F2 layer (corresponding to foF2) observed during the deep solar minimum of 2009 were smaller than those corresponding to IRI-2012 model foF2 by as much as 45% and 50%, respectively, underlining the need to incorporate the data collected during the long deep minimum in the IRI model. The unusually weak ionosphere observed in 2009 is discussed in terms of the direct effect of the low solar EUV flux in 2009 as compared to 1995 and its indirect effects on ionospheric electric field, thermospheric composition (or O/N 2 ratio) and thermospheric neutral winds.

Description: This paper discusses different plausible mechanisms to account for the intrusion of dry ozone rich stratospheric air into the troposphere during the passage of the tropical cyclone Nilam-2012. The present study shows that the overshooting convection associated with the Nilam is found to be the prime candidate for the generation of turbulence in the vicinity of the tropopause (VOT). In adition, the presence of strong updarfts and downdrafts in the VOT weakened the stability of the tropopause which allows the dry ozone rich stratospheric air to penetrate downwards to the troposphere. Significant modulation of the tropopause structure is observed which is found to be accompanied by structures linked with shear instability. Concurrent ozone measurements also indicate the intrusion of stratospheric air mass to the upper and middle troposphere.

Description: Abstract The existence of an additional stratification in the daytime equatorial ionospheric F region (the F3 layer) was known since the 1940s. However, its characteristics and the underlying physical mechanism have been uncovered only recently. In this paper, we present and discuss the F3 layer characteristics observed by six ionosondes distributed over equatorial and low latitudes (−20° to +25° dip latitudes) in the Brazilian longitude sector during the strongest geomagnetic storm (DstMin = −223 nT) of solar cycle 24, the St. Patrick's Day storm of 17 March 2015. Two eastward prompt penetration electric field (PPEF) events, as seen in equatorial electrojet, occurred during the main phase of the storm on 17 March 2015, a strong one (~100 nT) at around ~1200 UT and a weak one (~50 nT) at around ~1725 UT. Local time variations in the F3 layer occurrence and ionospheric base height (h′F), peak height (hmF), and peak electron density (Nmax) are investigated. Notably, the F3 layer occurred at all six locations, more distinctly during the stronger PPEF event. The large latitudinal extend in the occurrence of the F3 layer in opposite hemispheres (−20° to +25° dip latitudes) covering the equatorial ionization anomaly crests observed for the first time is interpreted in terms of the combined effect of the super plasma fountain generated by the eastward PPEF and storm time equatorward neutral wind.

Description: Rare-earth (RE) monosilicates are promising candidates as environmental barrier coating (EBC) materials for ceramic matrix composites for aerospace applications. Five rare-earth monosilicate materials have been investigated: Y 2 SiO 5 , Gd 2 SiO 5 , Er 2 SiO 5 , Yb 2 SiO 5 , and Lu 2 SiO 5 produced from RE oxides and silica starting materials pressed and sintered at 1580°C under flowing air. Relative densities above 94% were obtained for all samples and ceramics were made containing 85–100 wt% of the RE monosilicate according to X-ray diffraction (XRD) with RE disilicates as the second phase in the Gd, Yb, and Lu silicate systems. Microstructures were characterized using scanning electron microscopy and XRD, and thermal properties measured including specific heat, thermal expansion, and thermal diffusivity. For the first time, specific heat capacity values are reported for the monosilicates [0.45–0.69 J·(g·K) −1 ]. Thermal expansion coefficients (TECs) of the dense samples ranged between 5.9 and 10.3 × 10 −6 K −1 measured for 473 to 1473 K. All EBCs have low thermal conductivities [1.8 W·(m·K) −1 or less] making them excellent EBC insulators.

Description: High-resolution in situ measurements from the three Swarm spacecraft, in a string-of-pearls configuration, provide new insights about the combined role of flow channel events and particle impact ionization in creating F-region electron density structures in the northern Scandinavian dayside cusp. We present a case of polar cap patch formation where a reconnection-driven low-density relative westward flow channel is eroding the dayside solar-ionized plasma but where particle impact ionization in the cusp dominates the initial plasma structuring. In the cusp, density features are observed which are twice as dense as the solar-ionized background. These features then follow the polar cap convection and become less structured and lower in amplitude. These are the first in situ observations tracking polar cap patch evolution from creation by plasma transport and enhancement by cusp precipitation, through entrainment in the polar cap flow and relaxation into smooth patches as they approach the nightside auroral oval.

Description: ABSTRACT With their unique structure and physicochemical properties, single\-walled carbon nanotubes (SWCNTs) have many potential new applications in medicine and industry. However, there is lack of detailed information concerning their impact on human health and the environment. The aim of this study was to assess the effects, after intraperitoneal injection of functionalized SWCNTs (f-SWCNT) on the induction of reactive oxygen species (ROS), frequency of structural chromosomal aberrations (SCA), frequency of micronuclei induction, mitotic index, and DNA damage in Swiss–Webster mice. Three doses of f-SWCNTs (0.25, 0.5, and 0.75 mg/kg) and two controls (negative and positive) were administered to mice, once a day for 5 days. Bone marrow and peripheral blood samples were collected 24 h after the last treatment following standard protocols. F - SWCNT exposure significantly enhanced ROS, increased ( p  〈 0.05) the number of SCA and the frequency of micronucleated cells, increased DNA damage, and decreased the mitotic index in exposed groups compared to negative control. The scientific findings reported here suggest that purified f-SWCNT have the potential to induce oxidative stress mediated genotoxicity in Swiss–Webster mice at higher level of exposure. Further characterization of their systemic toxicity, genotoxicity, and carcinogenicity is also essential. © 2015 Wiley Periodicals, Inc. Environ Toxicol, 2015.

Description: ABSTRACT The average population density is significantly higher along the nearshore coastal zones compared to inland areas. Therefore, proper assessment and evaluation of the impact of climate change on coastal belts has immense societal benefits. The head Bay region located in the north Indian Ocean is a thickly populated area and highly vulnerable to threats from sea-level rise and extreme weather events. In this study, the wave climatology for the north Indian Ocean specifically covering the head Bay region was examined, utilizing the past 21 years of satellite altimeter data for the period ranging from 1992 to 2012. In addition, the study also examines the significant wave heights obtained from the WAVEWATCH-III (WW3) model to substantiate and evaluate the findings of the observed variability from altimeter records. The study used daily altimeter data from eight satellite missions to understand the annual and seasonal variability in wind speed and significant wave heights for the head Bay region. The annual distribution of these parameters follow the climatology, whereas the percentage variability in both wind speed and significant wave height show a clear contrasting trend exhibiting a zonal dipole. The study establishes the fact that the responsible mechanism for this contrasting trend is the variations in mean sea level pressure over the head Bay region. In addition, a comprehensive analysis using empirical orthogonal function (EOF) shows that the second mode that represents the inter-seasonal variations substantiates the trend observed in the percentage distribution of these parameters. Interestingly, the study clearly signifies that trends in both wind speed and significant wave height was lower for the western side, unlike that noticed over the eastern portions in the head Bay of Bengal region.

Description: Abstract The occurrence of late night spread F in the low and equatorial latitude regions during solar minimum is not properly understood. Radar observations have revealed occurrence of postmidnight echoes at low and equatorial latitudes during solar minimum periods. This work discusses the coordinated airglow, VHF radar and ionosonde observations of nighttime electrified medium scale traveling ionospheric disturbances (EMSTIDs) made from the low and equatorial latitude Indian region. Two nights of observations are discussed in detail in which EMSTIDs are seen to coexist with spread F in ionograms and VHF backscatter. These observations reveal that the EMSTIDs propagate to latitudes very close to dip equator at times and they can be responsible for a reasonable portion of the postmidnight radar echoes and spread F events observed at low and equatorial latitudes during low solar activity period.

Description: Abstract Ideally, probabilistic hazard assessments combine available knowledge about physical mechanisms of the hazard, data on past hazards, and any precursor information. Systematically assessing the probability of rare, yet catastrophic hazards adds a layer of difficulty due to limited observation data. Via computer models, one can exercise potentially dangerous scenarios that may not have happened in the past, but are probabilistically consistent with the aleatoric nature of previous volcanic behavior in the record. Traditional Monte Carlo based methods to calculate such hazard probabilities suffer from two issues: they are computationally expensive, and they are static. In light of new information newly available data, signs of unrest, new probabilistic analysis describing uncertainty about scenarios the Monte Carlo calculation would need to be redone under the same computational constraints. Here we present an alternative approach utilizing statistical emulators that provides an efficient way to overcome the computational bottleneck of typical Monte Carlo approaches. Moreover, this approach is independent of an aleatoric scenario model, yet can be applied rapidly to any scenario model making it dynamic. We present and apply this emulator‐based approach to create multiple probabilistic hazard maps for inundation of pyroclastic density currents in the Long Valley Volcanic Region. Further we illustrate how this approach enables an exploration of the impact of epistemic uncertainties on these probabilistic hazard forecasts. Particularly, we focus on the uncertainty of vent opening models and how that uncertainty both aleatoric and epistemic impacts the resulting probabilistic hazard maps of pyroclastic density current inundation.