Heliophysics Community Research Articles

A database of interplanetary and interstellar dust detected by the Wind spacecraft

AbstractIt was recently discovered that the WAVES instrument on the Wind spacecraft has been detecting, in situ, interplanetary and interstellar dust of approximately 1 μm radius for the past 22 years. These data have the potential to enable advances in the study of cosmic dust and dust‐plasma coupling within the heliosphere due to several unique properties: the Wind dust database spans two full solar cycles; it contains over 107,000 dust detections; it contains information about dust grain direction of motion; it contains data exclusively from the space environment within 350 Earth radii of Earth; and it overlaps by 12 years with the Ulysses dust database. Further, changes to the WAVES antenna response and the plasma environment traversed by Wind over the lifetime of the Wind mission create an opportunity for these data to inform investigations of the physics governing the coupling of dust impacts on spacecraft surfaces to electric field antennas. A Wind dust database has been created to make the Wind dust data easily accessible to the heliophysics community and other researchers. This work describes the motivation, methodology, contents, and accessibility of the Wind dust database.

Where is the cosmic-ray modulation boundary of the heliosphere?

The intensity of Galactic cosmic rays in the heliosphere is modulated by solar activities. The outer boundary where the solar modulation begins has always been a subject matter of debate in the cosmic-ray and heliophysics community. Various experimental methods and theoretical model calculations have been used to determine the boundary. Although the heliopause was always suspected to be the boundary, it is only until very recently after Voyager 1 had crossed the heliopause did we confirm that the boundary is indeed the heliopause. In this paper, we use a model simulation and detailed Voyager observation of cosmic rays at the heliopause crossing to show that the modulation boundary, in fact, is a fraction of an AU beyond the heliopause. Such a conclusion requires a very low turbulence level of the interstellar magnetic field in the outer heliosheath. According to the quasi-linear theory, a low level of turbulence should result in a very large diffusion coefficient parallel to the magnetic field and a very small perpendicular diffusion coefficient. For the first time, we are confident that Voyager 1 has obtained the truly pristine local interstellar cosmic-ray spectra down to the energies below 1 MeV. The cosmic-ray intensity is rapidly filtered by a thin layer of the interstellar magnetic field immediately outside of the heliopause. Its filtration amount depends on the conditions of magnetic field turbulence on the both sides of the heliopause, thus making it solar-cycle dependent as well.

SEPARATION OF THE RIBBON FROM GLOBALLY DISTRIBUTED ENERGETIC NEUTRAL ATOM FLUX USING THE FIRST FIVE YEARS OF IBEX OBSERVATIONS

The Interstellar Boundary Explorer (IBEX) observes the IBEX ribbon, which stretches across much of the sky observed in energetic neutral atoms (ENAs). The ribbon covers a narrow (~20°-50°) region that is believed to be roughly perpendicular to the interstellar magnetic field. Superimposed on the IBEX ribbon is the globally distributed flux that is controlled by the processes and properties of the heliosheath. This is a second study that utilizes a previously developed technique to separate ENA emissions in the ribbon from the globally distributed flux. A transparency mask is applied over the ribbon and regions of high emissions. We then solve for the globally distributed flux using an interpolation scheme. Previously, ribbon separation techniques were applied to the first year of IBEX-Hi data at and above 0.71 keV. Here we extend the separation analysis down to 0.2 keV and to five years of IBEX data enabling first maps of the ribbon and the globally distributed flux across the full sky of ENA emissions. Our analysis shows the broadening of the ribbon peak at energies below 0.71 keV and demonstrates the apparent deformation of the ribbon in the nose and heliotail. We show global asymmetries of the heliosheath, including both deflection of the heliotail and differing widths of the lobes, in context of the direction, draping, and compression of the heliospheric magnetic field. We discuss implications of the ribbon maps for the wide array of concepts that attempt to explain the ribbon's origin. Thus, we present the five-year separation of the IBEX ribbon from the globally distributed flux in preparation for a formal IBEX data release of ribbon and globally distributed flux maps to the heliophysics community.

Sunspot numbers, interplanetary magnetic field, and cosmic ray intensity at earth: Nexus for the twentieth century

The pivotal role played by the interplanetary magnetic field (B) in modulating galactic cosmic ray (GCR) intensity in the heliosphere is described. We show that the inverse correlation observed by Forbush (1958) between GCRs and sunspot numbers (SSNs) is reflected in high correlation between SSNs and B (cc=0.94). The SSN data are available since 1700 and the derived B data since 1835. The paleo-cosmic ray data are available for several millennia in the form of 10Be radionuclide sequestered in polar ice. The data of the ion chambers (ICs) at the Cheltenham–Fredericksburg–Yakutsk (CFY) sites are combined to create a data string for 1937–1988. In turn, these data are used to extend the measurements of the low energy GCR ions (>0.1GeV) at balloon altitudes at high latitudes in Russia to 1937. These data are then correlated to B and the fit parameters are used to extend the low energy ion data to 1900, creating the instrumental era GCR time series for the twentieth century. The derived GCR time series is compared to 10Be measured at two sites in Greenland, namely Dye 3 and NGRIP for 1900–2000 to check the internal consistency of datasets for the long-term trend. We find that the annual mean rate (%) for 1965 at NGRIP is an outlier. We replace it with the mean of 1964 and 1965 rates and construct a new re-normalized time series at NGIP, improving the agreement with the derived instrumental era GCR time series for the twentieth century as well. This should encourage its use by heliophysics community for varied applications.

Workflows for Heliophysics

In this paper we describe how we have introduced workflows into the working practices of a community for whom the concept of workflows is very new, namely the heliophysics community. Heliophysics is a branch of astrophysics which studies the Sun and the interactions between the Sun and the planets, by tracking solar events as they travel throughout the Solar system. Heliophysics produces two major challenges for workflow technology. Firstly it is a systems science where research is currently developed by many different communities who need reliable data models and metadata to be able to work together. Thus it has major challenges in the semantics of workflows. Secondly, the problem of time is critical in heliophysics; the workflows must take account of the propagation of events outwards from the sun. They have to address the four dimensional nature of space and time in terms of the indexing of data. We discuss how we have built an environment for Heliophysics workflows building on and extending the Taverna workflow system and utilising the myExperiment site for sharing workflows. We also describe how we have integrated the workflows into the existing practices of the communities involved in Heliophysics by developing a web portal which can hide the technical details from the users, who can concentrate on the data from their scientific point of view rather than on the methods used to integrate and process the data. This work has been developed in the EU Framework 7 project HELIO, and is being disseminated to the worldwide Heliophysics community, since Heliophysics requires integration of effort on a global scale.

Testing baseline stability of some neutron monitors in Europe, Africa, and Asia

For six decades, the global network of neutron monitors (NMs) has provided a continuous stream of very valuable data to the heliophysics community, leading to many insights into the myriad modes of charged particle transport in the tangled magnetic fields that permeate the 3D heliosphere. Earlier, Ahluwalia and Ygbuhay (2012) reported on the drifts in some high latitude NM counting rates in the American zone. We continue our enquiry by testing the stability of the counting rate baselines of some NMs operating in Europe, Africa, and Asia. The data from these detectors have been extremely valuable for the short-term time variation studies, but caution is advised in using the data for long-term studies from NMs with baselines that are drifting for cause(s) unknown.

Around the World

In science news around the world this week, Curiosity sent its first color, 360-degree look at Gale Crater to scientists at NASA's Jet Propulsion Laboratory; an unusual influenza virus is spreading from pigs to children in the U.S. Midwest; a pancreatic cancer therapy has failed; most people oppose using genetically engineered male mosquitoes to control wild mosquito populations; and a National Research Council report lays out a wish list from the heliophysics community.

Is there an instrumental drift in the counting rate of some high latitude neutron monitors?

For the last six decades the neutron monitors have provided a continuous string of very reliable data to the heliophysics community. Although neutron monitors are not the primary source of data for the galactic cosmic rays, these data serve as a baseline reference for the data collected by the detectors on board the satellites and deep space probes, far away from earth orbit. The pressure corrected hourly data are available from the World Data Centers. These data have been used to derive deep insights pertaining to the electromagnetic states of the heliosphere and the modes of transport of energetic charged particles in the tangled interplanetary magnetic fields. We present evidence that some of the high latitude neutron monitors are undergoing long-term drifts in their baselines. In particular, we argue that there is no physical basis to justify the observed long-term downward trend in the baseline of the South Pole neutron monitor. The real reason may have to do with its maintenance at a distant location with challenging logistics and an improper normalization of its data after the 26 months break in the 1970s.