In two earlier articles (Tappin, Eyles and Davies in Solar Phys.
290
, 2143,
2015
, and Solar Phys.
292
, 28,
2017
), we used the stellar photometry to determine the calibration parameters and ...long-term trends of the Heliospheric Imagers (HI) on board the Solar Terrestrial Relations Observatory (STEREO). In this article we provide an update on these determinations for the ahead spacecraft (STEREO-A) to incorporate the interval after solar superior conjunction (when STEREO-B was non-operational). We describe the modifications needed to our photometry procedures to accommodate the reduced pointing stability following the switch-off of the spacecraft gyros shortly prior to conjunction. We find a small revision to the absolute levels is required. We also show that the very low rates of degradation (less than 0.2% per year) found in the earlier determinations have continued beyond solar conjunction.
Inelastic scattering is a fundamental collisional process that plays an important role in many areas of chemistry, and its detailed study can provide valuable insight into more complex chemical ...systems. Here, we report the measurement of differential cross-sections for the rotationally inelastic scattering of NO(X2Π1/2, v=0, j=0.5, f) by Ar at a collision energy of 530 cm(-1) in unprecedented detail, with full Λ-doublet (hence total NO parity) resolution in both the initial and final rotational quantum states. The observed differential cross-sections depend sensitively on the change in total NO parity on collision. Differential cross-sections for total parity-conserving and changing collisions have distinct, novel quantum-mechanical interference structures, reflecting different sensitivities to specific homonuclear and heteronuclear terms in the interaction potential. The experimental data agree remarkably well with rigorous quantum-mechanical scattering calculations, and reveal the role played by total parity in acting as a potential energy landscape filter.
Magnetars are strongly magnetized, isolated neutron stars
with magnetic fields up to around 10
gauss, luminosities of approximately 10
-10
ergs per second and rotation periods of about 0.3-12.0 s. ...Very energetic giant flares from galactic magnetars (peak luminosities of 10
-10
ergs per second, lasting approximately 0.1 s) have been detected in hard X-rays and soft γ-rays
, and only one has been detected from outside our galaxy
. During such giant flares, quasi-periodic oscillations (QPOs) with low (less than 150 hertz) and high (greater than 500 hertz) frequencies have been observed
, but their statistical significance has been questioned
. High-frequency QPOs have been seen only during the tail phase of the flare
. Here we report the observation of two broad QPOs at approximately 2,132 hertz and 4,250 hertz in the main peak of a giant γ-ray flare
in the direction of the NGC 253 galaxy
, disappearing after 3.5 milliseconds. The flare was detected on 15 April 2020 by the Atmosphere-Space Interactions Monitor instrument
aboard the International Space Station, which was the only instrument that recorded the main burst phase (0.8-3.2 milliseconds) in the full energy range (50 × 10
to 40 × 10
electronvolts) without suffering from saturation effects such as deadtime and pile-up. Along with sudden spectral variations, these extremely high-frequency oscillations in the burst peak are a crucial component that will aid our understanding of magnetar giant flares.
The Heliospheric Imager (HI) instruments on board the STEREO spacecraft are used to analyze the solar wind during August and September 2007. We show how HI can be used to image the streamer belt and, ...in particular, the variability of the slow solar wind which originates inside and in the vicinity of the streamer belt. Intermittent mass flows are observed in HI difference images, streaming out along the extension of helmet streamers. These flows can appear very differently in images: plasma distributed on twisted flux ropes, V‐shaped structures, or “blobs.” The variety of these transient features may highlight the richness of phenomena that could occur near helmet streamers: emergence of flux ropes, reconnection of magnetic field lines at the tip of helmet streamers, or disconnection of open magnetic field lines. The plasma released with these transient events forms part of the solar wind in the higher corona; HI observations show that these transients are frequently entrained by corotating interaction regions (CIRs), leading to the formation of larger, brighter plasma structures in HI images. This entrainment is used to estimate the trajectory of these plasma ejecta. In doing so, we demonstrate that successive transients can be entrained by the same CIR in the high corona if they emanate from the same corotating source. Some parts of the streamers are more effective sources of transients than others. Surprisingly, evidence is given for the outflow of a recurring twisted magnetic structure, suggesting that the emergence of flux ropes can be recurrent.
Heliospheric Images of the Solar Wind at Earth Sheeley, Jr., N. R; Herbst, A. D; Palatchi, C. A ...
The Astrophysical journal,
03/2008, Letnik:
675, Številka:
1
Journal Article, Web Resource
Recenzirano
Odprti dostop
During relatively quiet solar conditions throughout the spring and summer of 2007, the SECCHI HI2 white-light telescope on the STEREO B solar- orbiting spacecraft observed a succession of wave fronts ...sweeping past Earth. We have compared these heliospheric images with in situ plasma and magnetic field measurements obtained by near-Earth spacecraft, and we have found a near perfect association between the occurrence of these waves and the arrival of density enhancements at the leading edges of high-speed solar wind streams. Virtually all of the strong corotating interaction regions are accompanied by large-scale waves, and the low-density regions between them lack such waves. Because the Sun was dominated by long-lived coronal holes and recurrent solar wind streams during this interval, there is little doubt that we have been observing the compression regions that are formed at low latitude as solar rotation causes the high-speed wind from coronal holes to run into lower speed wind ahead of it.
We have launched into near-Earth orbit a solar mass-ejection imager (SMEI) that is capable of measuring sunlight Thomson-scattered from heliospheric electrons from elongations to as close as 18^sup ^ ...to greater than 90^sup ^ from the Sun. SMEI is designed to observe time-varying heliospheric brightness of objects such as coronal mass ejections, co-rotating structures and shock waves. The instrument evolved from the heliospheric imaging capability demonstrated by the zodiacal light photometers of the Helios spacecraft. A near-Earth imager can provide up to three days warning of the arrival of a mass ejection from the Sun. In combination with other imaging instruments in deep space, or alone by making some simple assumptions about the outward flow of the solar wind, SMEI can provide a three-dimensional reconstruction of the surrounding heliospheric density structures.PUBLICATION ABSTRACT
Summary
The North Wyke Farm Platform was established as a United Kingdom national capability for collaborative research, training and knowledge exchange in agro‐environmental sciences. Its remit is ...to research agricultural productivity and ecosystem responses to different management practices for beef and sheep production in lowland grasslands. A system based on permanent pasture was implemented on three 21‐ha farmlets to obtain baseline data on hydrology, nutrient cycling and productivity for 2 years. Since then two farmlets have been modified by either (i) planned reseeding with grasses that have been bred for enhanced sugar content or deep‐rooting traits or (ii) sowing grass and legume mixtures to reduce nitrogen fertilizer inputs. The quantities of nutrients that enter, cycle within and leave the farmlets were evaluated with data recorded from sensor technologies coupled with more traditional field study methods. We demonstrate the potential of the farm platform approach with a case study in which we investigate the effects of the weather, field topography and farm management activity on surface runoff and associated pollutant or nutrient loss from soil. We have the opportunity to do a full nutrient cycling analysis, taking account of nutrient transformations in soil, and flows to water and losses to air. The NWFP monitoring system is unique in both scale and scope for a managed land‐based capability that brings together several technologies that allow the effect of temperate grassland farming systems on soil moisture levels, runoff and associated water quality dynamics to be studied in detail.
Highlights
Can meat production systems be developed that are productive yet minimize losses to the environment?
The data are from an intensively instrumented capability, which is globally unique and topical.
We use sensing technologies and surveys to show the effect of pasture renewal on nutrient losses.
Platforms provide evidence of the effect of meteorology, topography and farm activity on nutrient loss.
The images taken by the Heliospheric Imagers (HIs), part of the SECCHI imaging package onboard the pair of STEREO spacecraft, provide information on the radial and latitudinal evolution of the plasma ...compressed inside corotating interaction regions (CIRs). A plasma density wave imaged by the HI instrument onboard STEREO-B was found to propagate towards STEREO-A, enabling a comparison between simultaneous remote-sensing and
in situ
observations of its structure to be performed.
In situ
measurements made by STEREO-A show that the plasma density wave is associated with the passage of a CIR. The magnetic field compressed after the CIR stream interface (SI) is found to have a planar distribution. Minimum variance analysis of the magnetic field vectors shows that the SI is inclined at 54° to the orbital plane of the STEREO-A spacecraft. This inclination of the CIR SI is comparable to the inclination of the associated plasma density wave observed by HI. A small-scale magnetic cloud with a flux rope topology and radial extent of 0.08 AU is also embedded prior to the SI. The pitch-angle distribution of suprathermal electrons measured by the STEREO-A SWEA instrument shows that an open magnetic field topology in the cloud replaced the heliospheric current sheet locally. These observations confirm that HI observes CIRs in difference images when a small-scale transient is caught up in the compression region.
We present the lessons learned about the degradation observed in several space solar missions, based on contributions at the Workshop about On-Orbit Degradation of Solar and Space Weather Instruments ...that took place at the Solar Terrestrial Centre of Excellence (Royal Observatory of Belgium) in Brussels on 3 May 2012. The aim of this workshop was to open discussions related to the degradation observed in Sun-observing instruments exposed to the effects of the space environment. This article summarizes the various lessons learned and offers recommendations to reduce or correct expected degradation with the goal of increasing the useful lifespan of future and ongoing space missions.
The metal hyperaccumulator plant Noccaea caerulescens is protected from disease by the accumulation of high concentrations of metals in its aerial tissues, which are toxic to many pathogens. As these ...metals can lead to the production of damaging reactive oxygen species (ROS), metal hyperaccumulator plants have developed highly effective ROS tolerance mechanisms, which might quench ROS-based signals. We therefore investigated whether metal accumulation alters defence signalling via ROS in this plant.
We studied the effect of zinc (Zn) accumulation by N. caerulescens on pathogen-induced ROS production, salicylic acid accumulation and downstream defence responses, such as callose deposition and pathogenesis-related (PR) gene expression, to the bacterial pathogen Pseudomonas syringae pv. maculicola.
The accumulation of Zn caused increased superoxide production in N. caerulescens, but inoculation with P. syringae did not elicit the defensive oxidative burst typical of most plants. Defences dependent on signalling through ROS (callose and PR gene expression) were also modified or absent in N. caerulescens, whereas salicylic acid production in response to infection was retained.
These observations suggest that metal hyperaccumulation is incompatible with defence signalling through ROS and that, as metal hyperaccumulation became effective as a form of elemental defence, normal defence responses became progressively uncoupled from ROS signalling in N. caerulescens.
PDF
