Evolving outer heliosphere: Large-scale stability and time variations observed by the Interstellar Boundary Explorer

The first all-sky maps of Energetic Neutral Atoms (ENAs) from the Interstellar Boundary Explorer (IBEX) exhibited smoothly varying, globally distributed flux and a narrow ribbon of enhanced ENA emissions. In this study we compare the second set of sky maps to the first in order to assess the possibility of temporal changes over the 6 months between views of each portion of the sky. While the large-scale structure is generally stable between the two sets of maps, there are some remarkable changes that show that the heliosphere is also evolving over this short timescale. In particular, we find that (1) the overall ENA emissions coming from the outer heliosphere appear to be slightly lower in the second set of maps compared to the first, (2) both the north and south poles have significantly lower (similar to 10-15%) ENA emissions in the second set of maps compared to the first across the energy range from 0.5 to 6 keV, and (3) the knot in the northern portion of the ribbon in the first maps is less bright and appears to have spread and/or dissipated by the time the second set was acquired. Finally, the spatial distribution of fluxes in the southernmost portion of the ribbon has evolved slightly, perhaps moving as much as 6 degrees (one map pixel) equatorward on average. The observed large-scale stability and these systematic changes at smaller spatial scales provide important new information about the outer heliosphere and its global interaction with the galaxy and help inform possible mechanisms for producing the IBEX ribbon

Spectral Evolution of Energetic Neutral Atom Emissions at the Heliospheric Poles as Measured by \u3ci\u3eIBEX\u3c/i\u3e during its First Three Yeras

The Interstellar Boundary Explorer (IBEX) mission continues to measure energetic neutral atom (ENA) emissions produced by charge exchange between solar wind (SW) protons and interstellar neutrals at the edge of our heliosphere. Using the first 3 yr of IBEX-Hi ENA measurements (2009-2011), we examined the spectral evolution of ~0.5-6 keV ENAs at the polar regions (above 60°). We found the following: (1) pixels with a characteristic ankle spectra (lower spectral index at higher energies) increase by ~5% in 2010 and ~10% in 2011 compared to 2009. (2) The averaged spectral index in 2011 is smaller than that of 2009. (3) The slope of the ENA spectrum above ~1.7 keV is more variable than the slope below ~1.7 keV. The lower spectral index at higher energies of the spectrum does not appear to be caused by an increase of the ENA production at these energies, but rather from a consistent decrease at lower energies. (4) The decrease in polar ENA fluxes does not correlate significantly with the averaged SW dynamic pressure, back-traced in time to 1 AU along the flow streamlines (originating between 10° and 30° for slow SW, and 60° and 80°for fast SW), assuming these are the respective conditions of ENA progenitors back in time. These results provide insights into the complexity of relating the slow and fast SW contributions to polar ENAs and shed light on how the solar output and the resulting change in the global heliospheric structure possibly affect the heliohealth (HS) populations

CAN IBEX IDENTIFY VARIATIONS IN THE GALACTIC ENVIRONMENT OF THE SUN USING ENERGETIC NEUTRAL ATOMS?

The Interstellar Boundary Explorer (IBEX) spacecraft is providing the first all-sky maps of the energetic neutral atoms (ENAs) produced by charge exchange between interstellar neutral Ho atoms and heliospheric solar wind and pickup ions in the heliosphere boundary regions. The "edge" of the interstellar cloud presently surrounding the heliosphere extends less than 0.1 pc in the upwind direction, terminating at an unknown distance, indicating that the outer boundary conditions of the heliosphere could change during the lifetime of the IBEX satellite. Using reasonable values for future outer heliosphere boundary conditions, ENA fluxes are predicted for one possible source of ENAs coming from outside of the heliopause. The ENA-production simulations use three-dimensional MHD plasma models of the heliosphere that include a kinetic description of neutrals and a Lorentzian distribution for ions. Based on this ENA-production model, it is then shown that the sensitivities of the IBEX 1.1 keV skymaps are sufficient to detect the variations in ENA fluxes that are expected to accompany the solar transition into the next upwind cloud. Approximately 20% of the IBEX 1.1 keV pixels appear capable of detecting the predicted model differences at the 3σ level, with these pixels concentrated in the Ribbon region. Regardless of the detailed ENA production model, the success of the modeled B centerdot R ~ 0 directions in reproducing the Ribbon locus, together with our results, indicates that the Ribbon phenomenon traces the variations in the heliosphere distortion caused by the relative pressures of the interstellar magnetic and gaseous components.United States. National Aeronautics and Space Administration (NASA IBEX mission, Explorer Program, grant NNX09AG63G

IBEX: The First Five Years (2009-2013)

The Interstellar Boundary Explorer (IBEX) returned its first five years of scientific observations from 2009 to 2013. In this study, we examine, validate, initially analyze, and provide to the broad scientific community this complete set of energetic neutral atom (ENA) observations for the first time. IBEX measures the fluxes of ENAs reaching 1 AU from sources in the outer heliosphere and most likely the very nearby interstellar space beyond the heliopause. The data, maps, and documentation provided in this study represent the fourth major release of the IBEX data, incorporate important improvements, and should be used for future studies and as the citable reference for the current version of the IBEX data. In this study, we also examine five years of time evolution in the outer heliosphere and the resulting ENA emissions. These observations show a complicated variation with a general decrease in the ENA fluxes from 2009 to 2012 over most regions of the sky, consistent with a 2-4 year recycle time for the previously decreasing solar wild flux. In contrast, the heliotail fluxes continue to decrease, again consistent with a significantly more distant source in the downwind direction. Finally, the Ribbon shows the most complicated time variations, with a leveling off in the southern hemisphere and continued decline in the northern one; these may be consistent with the Ribbon source being significantly farther away in the north than in the south. Together, the observations and results shown in this study expose the intricacies of our heliopshere\u27s interaction with the local interstellar medium

Partitioning of the reactive nitrogen reservoir in the lower sratosphere of the southern hemisphere: Observations and modeling

Measurements of nitric oxide (NO), nitrogen dioxide (NO2), and total reactive nitrogen (NOy = NO + NO2 + NO3 + HNO3 + ClONO2 + 2N2O5 + ...) were made during austral fall, winter, and spring 1994 as part of the NASA Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft mission. Comparisons between measured NO2 values and those calculated using a steady state (SS) approximation are presented for flights at mid and high latitudes. The SS results agree with the measurements to within 8%, suggesting that the kinetic rate coefficients and calculated NO2 photolysis rate used in the SS approximation are reasonably accurate for conditions in the lower stratosphere. However, NO2 values observed in the Concorde exhaust plume were significantly less than SS values. Calculated NO2 photolysis rates showed good agreement with values inferred from solar flux measurements, indicating a strong self-consistency in our understanding of UV radiation transmission in the lower stratosphere. Model comparisons using a full diurnal, photochemical steady state model also show good agreement with the NO and NO2 measurements, suggesting that the reactions affecting the partitioning of the NO2 reservoir are well understood in the lower stratosphere

Separation of the Ribbon From Globally Distributed Energetic Neutral Atom Flux Using the First Five Years of \u3ci\u3e IBEX \u3c/i\u3e 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

CubeSat Constellation Cloud Winds(C3Winds) A New Wind Observing System to Study Mesoscale Cloud Dynamics and Processes

The CubeSat Constellation Cloud Winds (C3Winds) is a NASA Earth Venture Instrument (EV-I) concept with the primary objective to better understand mesoscale dynamics and their structures in severe weather systems. With potential catastrophic damage and loss of life, strong extratropical and tropical cyclones (ETCs and TCs) have profound three-dimensional impacts on the atmospheric dynamic and thermodynamic structures, producing complex cloud precipitation patterns, strong low-level winds, extensive tropopause folds, and intense stratosphere-troposphere exchange. Employing a compact, stereo IR-visible imaging technique from two formation-flying CubeSats, C3Winds seeks to measure and map high-resolution (2 km) cloud motion vectors (CMVs) and cloud geometric height (CGH) accurately by tracking cloud features within 5-15 min. Complementary to lidar wind observations from space, the high-resolution wind fields from C3Winds will allow detailed investigations on strong low-level wind formation in an occluded ETC development, structural variations of TC inner-core rotation, and impacts of tropopause folding events on tropospheric ozone and air quality. Together with scatterometer ocean surface winds, C3Winds will provide a more comprehensive depiction of atmosphere-boundary-layer dynamics and interactive processes. Built upon mature imaging technologies and long history of stereoscopic remote sensing, C3Winds provides an innovative, cost-effective solution to global wind observations with potential of increased diurnal sampling via CubeSat constellation

A future interstellar probe on the dynamic heliosphere and its interaction with the very local interstellar medium: In-situ particle and fields measurements and remotely sensed ENAs

The recently published Interstellar Probe (ISP) study report describes a pragmatic mission concept with a launch window that starts in 2036 and is expected to reach several hundreds of astronomical units past the heliopause within a time frame of ≥50 years (https://interstellarprobe.jhuapl.edu/Interstellar-Probe-MCR.pdf). Following the ISP report, this paper, that will also be accessible from the Bulletin of the AAS (BAAS) in the framework of the Decadal Survey for Solar and Space Physics (Heliophysics) 2024–2033 (Dialynas et al., A future Interstellar Probe on the dynamic heliosphere and its interaction with the very local interstellar medium: In-situ particle and fields measurements and remotely sensed ENAs, 2022a), aims to highlight the importance of studying the physics of the interactions pertaining to the expanding solar wind that meets the plasma, gas and dust flows of the very local interstellar medium, forming the complex and vast region of our astrosphere. We focus on three fundamental open science questions that reveal the dynamical nature of the heliosphere A) Where are the heliosphere boundaries and how thick is the heliosheath B) Is there a “missing” pressure component towards exploring the dynamics of the global heliosheath and its interaction with the very local interstellar medium C) Why does the shape and size of the global heliosphere appear different in different Energetic Neutral Atom energies? We argue that these questions can only be addressed by exploiting a combination of in-situ charged particle, plasma waves and fields measurements with remotely sensed Energetic Neutral Atoms that can be measured simultaneously from the instruments of a future Interstellar Probe mission, along its trajectory from interplanetary space through the heliosheath and out to the very local interstellar medium