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NASA NTRS1995

The heliospheric sector boundary as a distented magnetic cloud

A magnetic cloud was detected both near Earth and by Pioneer 11 located 43 deg east of Earth at 4.8 AU. The magnetic field within the cloud rotated smoothly from toward to away polarity, marking sector boundary passage. Interpreted as a flux rope, the cloud had a vertical axis, implying that its cylindrical cross-section in the ecliptic plane was distended along the sector boundary by at least 43, forming an extensive occlusion in the heliospheric current sheet. At 1 AU the cloud had plasma signatures typical of a fast coronal mass ejection with low temperature and a leading shock. In contrast, at 4.8 AU, only the cloud signature remained. Its radial dimension was the same at both locations, consistent with little expansion beyond 1 AU. Energetic particle data at 4.8 AU show high fluxes preceding the cloud but not extending forward to the corotating shock that marked entry into the interaction region containing the cloud. The streaming direction was antisunward, consistent with possible acceleration in a low-beta region of field line draping around the cloud's western (upstream) end. The fluxes dropped upon entry into the cloud and became essentially isotropic one third of the way through it. On the basis of sector boundary characteristics published in the past, we suggest that distended clouds may be common heliospheric current sheet occlusions.

Crooker, N. U.↗
NASA NTRS1995

Observations of the solar wind speed near the sun

Two-antenna scintillation (IPS) observations can provide accurate measurements of the velocity with which electron density fluctuations drift past the line of sight. We will present recent IPS measurements made with the EISCAT and VLBA arrays. It is common, particularly during declining activity. for the line of sight to pass through plasma with a wide range of speed. Therefore it is important to account for the line of sight integration. It is clear from ULYSSES measurements that the speed is bimodal in nature, i.e., either 'fast' or 'slow.' Thus it is not necessary to model a continuous velocity distribution - one need only locate the 'fast-slow' interface. In addition one must consider the possibility that the density fluctuations are moving with respect to the flow of particles. Alfven waves propagating through field-aligned density fluctuations can mimic a sound wave in this respect, so the apparent IPS velocity can be the flow speed plus the Alfven speed. In modeling the IPS it is important that the scattering be 'weak,' because the weak scattering model requires only 1 spatial parameter instead of 3. Furthermore the effect of multiple velocities in much more distinct in weak scattering. EISCAT can only operate near 933 MHz, which limits the observations to outside of 17R(solar mass). The VLBA is the only facility with the combination of high frequency operation and long baselines required to observe inside of 15R(solar mass). A simple bimodal model has been successfully used to interpret our IPS observations near the sun. Farther out interaction regions have built up significantly and a two speed model is no longer valid. An apparent deceleration in the fast polar wind is sometimes evident when compared to the ULYSSES observation. The density variance delta N(exp 2)e in the fast wind appears to decrease from equator to pole.

Grall, R. R.↗
NASA NTRS1995

A conjecture on global flow dynamics

Recent observations by the Yohkoh and Ulysses spacecraft have instilled a new appreciation for the role of the ever-evolving geometry and topology of the coronal magnetic structure in shaping and influencing the global solar wind outflow. While many issues concerning the global evolution of large-scale interplanetary flow structures await resolution, we focus here on one specific problem. Namely, we argue that when considering the impact of solar activity on heliosphere scales, rather more attention should be directed toward ascertaining the nature and implications of long-term. Large-scale changes in the corona than toward the more dramatic and highly visible manifestations of solar activity, such as flares and coronal mass ejections (CMEs). That is, while energetic CMEs unquestionably disrupt the interplanetary medium locally and for a time by the broader measure they prompt lasting, wide-spread heliospheric response only when they occur as the agent of substantial, long-term change in the global configuration of the corona. In support, we point to various evidences of coronal change associated with major episodes of heliospheric disruption, and we discuss the limitations imposed by current observation techniques. In addition, we offer dynamical arguments (illustrated by a simple dynamical simulation) that when the coronal configuration changes quickly enough over sufficient spatial scale, a re-adjustment wave linking the initial and final quasi-steady flow states must propagate out from the Sun. This wave is transitory and global, and its amplitude can grow to substantial proportions with heliocentric distance. Moreover, the readjustment wave occurs whether or not the corona needs to expel CMEs to reconfigure itself. We suggest that it is this wave (and not so much the remnants of the initiating CMEs) that constitutes global merged interaction regions in the outer heliosphere.

Pizzo, V. J.↗
NASA NTRS1995

Stream interfaces and energetic ions 2: Ulysses test of Pioneer results

Ulysses measurements of energetic and solar wind particles taken near 5 AU between 20 and 30 degrees south latitude during a well-developed recurring corotating interaction region (CIR) show that the CIR's corotating energetic ion population (CEIP) associated with the trailing reverse shock starts within the CIR at the stream interface. This is consistent with an earlier result obtained by Pioneers 10 and 11 in the ecliptic plane between 4 and 6 AU. The Ulysses/Pioneer finding noteworthy since the stream interface is not magnetically connected to the reverse shock but lies 12-17 corotation hours from it. Thus, the finding to be inconsistent with the basic model that generates CEIP particles at the reverse shock and propagates them along field lines Eliminating the inconsistency probably entails an extension of the standard model. We consider two possible extensions cross-field diffusion and energetic particles generation closer to the sun in the gap between the stream interface and the reverse shock.

Intriligator, Devrie S.↗
NASA NTRS1995

Density fluctuations in solar wind flow types at 1 AU: Comparison to Doppler scintillation measurements

Density fluctuations with periods 10 minutes to 1 hour have been investigated in ISEE 3 plasma measurements of solar wind flows at l AU. Coronal hole, interstream, plasma sheet, coronal mass ejection, and interaction region flow types are considered. The ISEE 3 results support the interpretation of the large-scale variations in density fluctuations observed by Doppler scintillation measurement techniques inside 0.2 AU. The highest absolute and relative density fluctuations occur ahead of and within the plasma from coronal mass ejections, with the maximum values occurring between the associated interplanetary shocks and the driver gas. For the quasi-stationary solar wind, density and relative density fluctuations are highest around the heliospheric current sheet and lowest in the high-speed coronal flow. Superposed epoch analysis shows that the region of enhanced density fluctuations and its abrupt boundaries observed in the vicinity of the heliospheric current sheet near the Sun persists to l AU, providing further support for the filamentary nature of the extensions of coronal streamers. The results of this study confirm the advantages of using density fluctuations rather than density as a tracer of solar wind flows with differing origins at the Sun and as a detector of propagating interplanetary disturbances.

Huddleston, D. E.↗
NASA NTRS1995

Multi-dimensional modelling of the solar wind-LISM interaction including neutrals: A Boltzmann equation approach

The importance of interstellar neutrals in understanding and modelling the global interaction of the solar wind with the local interstellar medium is becoming increasingly apparent. Unfortunately the self-consistent inclusion of a neutral interstellar component into time-dependent, dynamical models is formidably difficult due to the extremely large mean free paths associated with the neutrals and the creation of essentially different neutral distributions from different interaction regions of the solar wind and LISM. In full generality, one has to address the problem by treating the neutrals kinetically with the appropriate extinction and creation source terms. In this paper, a limited set of simulations will be presented in which the solar wind and interstellar plasma is described as a 2D fully compressible time-dependent fluid while the interstellar neutral distribution is derived by solving the appropriate Boltzmann equation directly.

Zank, G. P.↗
NASA NTRS1996

Mission Operations and Data Analysis Phase of the SupraThermal through Energetic Particle detector (STEP) of the EPACT experiment on the Wind Spacecraft

Scientific studies of energetic particle populations observed by STEP are summarized. Science highlights cover: upstream He-3 events general upstream events, energy spectra of ions accelerated in impulsive and gradual solar events, impulsive solar particle events, and corotating interaction regions. Bibliographies of journal publications and papers presented at conferences are also provided.

Mason, G. M.↗
NASA NTRS1996

Radio Emissions from the Outer Heliosphere

For nearly fifteen years the Voyager 1 and 2 spacecraft have been detecting an unusual radio emission in the outer heliosphere in the frequency range from about 2 to 3 kHz. Two major events have been observed, the first in 1983-84 and the second in 1992-93. In both cases the onset of the radio emission occurred about 400 days after a period of intense solar activity, the first in mid-July 1982, and the second in May-June 1991. These two periods of solar activity produced the two deepest cosmic ray Forbush decreases ever observed. Forbush decreases are indicative of a system of strong shocks and associated disturbances propagating outward through the heliosphere. The radio emission is believed to have been produced when this system of shocks and disturbances interacted with one of the outer boundaries of the heliosphere, most likely in the vicinity of the the heliopause. The emission is believed to be generated by the shock-driven Langmuir-wave mode conversion mechanism, which produces radiation at the plasma frequency (f(sub p)) and at twice the plasma frequency (2f(sub p)). From the 400-day travel time and the known speed of the shocks, the distance to the interaction region can be computed, and is estimated to be in the range from about 110 to 160 AU.

Gurnett, D. A.↗
NASA NTRS1997

Issues concerning the Orion gamma ray line observations: Line splitting and LiBeB origin

The phenomenon of broad gamma ray line splitting is discussed, together with a scenario for the suppression of the blue wings of these broad lines due to the geometry of the accelerated particle interaction region. The broad and narrow gamma ray line emissions are compared taking into account the line splitting effect. It is concluded that the observed gamma ray lines from Orion are most likely broad, implying that the low energy cosmic rays which produce this line emission consist mostly of C and heavier ions. The suppression of the proton and alpha particle abundances requires acceleration conditions such as the acceleration of the ejecta of the supernovae before mixing with the interstellar medium. Similar conditions are implied by observations of the B and Be in low metallicity stars formed during the first Gyr of galactic evolution.

Ramaty, R.↗
NASA NTRS1996

Sudden Radiative Braking in Colliding Hot-Star Winds

When two hot-star winds collide, their interaction centers at the point where the momentum fluxes balance. However, in WR+O systems, the imbalance in the corporeal momentum fluxes may be extreme enough to preclude a standard head-on wind/wind collision. On the other hand, an important component of the total momentum flux in radiatively driven winds is carried by photons. Thus, if the wind interaction region has sufficient scattering opacity, it can reflect stellar photons and cause important radiative terms to enter the momentum balance. This radiative input would result in additional braking of the wind. We use a radiative-hydrodynamics calculation to show that such radiative braking can be an important effect in many types of colliding hot-star winds. Characterized by sudden deceleration of the stronger wind in the vicinity of the weak-wind star, it can allow a wind ram balance that would otherwise be impossible in many WR+O systems with separations less than a few hundred solar radii. It also greatly weakens the shock strength and the encumbent X ray production. We demonstrate the significant features of this effect using V444 Cygni as a characteristic example. We also derive a general analytic theory that applies to a wide class of binaries, yielding simple predictions for when radiative braking should play an important role.

Gayley, K. G.↗
NASA NTRS1997

The Ambient and Perturbed Solar Wind: From the Sun to 1 AU

The overall objective of the proposed research was to use numerical solutions of the magnetohydrodynamic (MHD) equations along with comparisons of the computed results with observations to study the following topics: (1) ambient solar wind solutions that extend from the solar surface to 1 astronomical unit (AU), contain closed magnetic structures near the Sun, and are consistent with observed values; (2) magnetic and plasma structures in coronal mass ejections (CMES) as they propagate to the interplanetary medium; (3) relation of MHD shocks to CMEs in the interplanetary medium; (4) interaction of MHD shocks with structures (such as other shocks, corotating interaction regions, current sheets) in the interplanetary plasma; and (5) simulations of observed interplanetary structures. A planned close collaboration with data analysts served to make the model more relevant to the data. The outcome of this research program is an improved understanding of the physical processes occurring in solar-generated disturbances in the interplanetary medium between the Sun and 1 AU.

Steinolfson, R. S.↗
NASA NTRS1996

Grant Proposal for the Continuation of the Voyager Interstellar Mission: LECP Investigation

This proposal documents the plans of the Low Energy Charged Particle (LECP) investigation team for participation in NASA's Voyager Interstellar Mission (VIM) as the Voyager 1 and 2 spacecraft explore the outer reaches of the heliosphere and search for the termination shock and the heliopause. The proposal covers the four year period from 1 January 1997 to 31 December 2000. The LECP instruments on Voyager 1 and 2 measure in situ intensities of charged particles with energies from about 30 keV to 100 MeV for ions, and about 20 keV to greater than 10 MeV for electrons. The instruments provide detailed spectral, angular, and compositional information about the particles. Composition is available for greater than 200 keV/nuc using multi-parameter measurements. Angular information is obtained by a mechanically scanned platform that rotates at various commanded rates. Measurements of low energy ion and electron intensities versus time and spatial location within the heliosphere contain an abundance of information regarding various transport and acceleration processes on both local (approx. 1 hr, approx. 0.01 AU) and global (approx. 11 yrs, approx. 100 AU) scales. The LECP instruments provide unique observations of such dynamical processes, and we anticipate that it will return critical information regarding the boundaries of the heliosphere. Several recent and exciting discoveries based on LECP measurements emphasize the important role that low energy charged particle distributions play in physical processes in the interplanetary medium. Yet, at the same time, these discoveries also underscore the fact that our understanding of processes in the outer heliosphere is, in most cases, incomplete, and in others, only rudimentary at best. Among the discoveries referred to above are the following: (1) Shocks: Examination of greater than 30 keV ion intensities have revealed: (a) a total absence of acceleration beyond only -100-200 keV at a strong transient shock in May 1991 at 35 AU, despite an enhanced level of seed particles; (b) a large transient shock in September 1991 of global scale, with intensities of shock-accelerated ions greater than or equal to 30 keV to approx. 30 MeV showing complex, highly energy-dependent spatial evolution, and small-scale (approx. few gyroradii), often anisotropic, micro-structures; (c) recurrent intensity increases in greater than or equal to 30 keV to -few MeV ions, with structures that, in some cases, show no correlation with the associated corotating shock. (2) Superthermal ion pressure: A global merged interaction region with a leading shock, downstream of which the superthermal ion (greater than or equal to 30 keV to approx. 4 MeV) pressure is comparable to that of the thermal plasma, and the total particle pressure yields a plasma beta of order unity. (3) Pickup ions: Measurements of the C/O ratio within transient structures at 35-45 AU showing the first clear evidence that transient shocks can pre-accelerate interstellar pickup ions from approx. 1 keV/nuc to at least 1 MeV/nuc. (4) Seed particles: Injection of ions for acceleration to high energies at the termination shock is unlikely to be a problem, since interplanetary transient and recurrent shocks are continually accelerating ions, of solar wind or interstellar origin, to highly superthermal energies. (5) Precursor electrons: Ambient solar electrons (greater than or equal to few tens of keV) that exist in the outer heliosphere ca form a broad precursor, several days wide, that is upstream of the termination shock and potentially observable a few months prior to the shock crossing. (6) Solar wind velocity at Voyager 1: We can use LECP ion data to obtain the solar wind velocity at Voyager 1, enabling us to provide critical measurement of the plasma flow as we approach and encounter the termination shock and other regions (necessary due to the partial failure of the Voyager 1 PLS experiment). The work of the LECP investigator team during the VIM will include: (1) Continuing operations with regard to the receipt, processing, verification, cataloging, display, and distribution of the data from the LECP instruments on Voyager 1 and 2, (2) Monitoring the health and performance of the LECP instruments, and evaluating and characterizing the response of the LECP instruments to various energetic particle and plasma environments, (3) Participating in, and supporting Voyager Project planning exercises and other coordinated activities relevant to exploration of the outer heliosphere, (4) Developing analysis techniques and operational procedures suitable for searching for and characterizing the boundaries and unique regions of the outher heliosphere, (5) Continuing the preparation of data sets appropriate for submission to the National Space Sciences Data Center (NSSDC) and, where appropriate, the Planetary Data System (PDS), (6) Maintaining direct Web access to online LECP data through the JHU/APL Voyager LECP home page, (7) Performing scientific evaluations of the Voyager 1 and 2 LECP data sets in conjunction with other data sets and other investigators, with particular focus on the outer regions of the heliosphere, and (8) Publishing the results of these evaluations in the scientific literature and presenting the results in scientific conferences.

Krimigis, Stamatios M.↗
NASA NTRS1959

Experimental Investigation of the Pressure Rise Required for the Incipient Separation of Turbulent Boundary Layers in Two-Dimensional Supersonic Flow

An experimental investigation has been made of turbulent boundary-layer separation associated with compression corners, curved surfaces of various radii, and incident shock waves. The purpose of the investigation was to provide design information, and to define significant physical trends, which would aid in the prediction of turbulent separation for various aerodynamic devices, such as compressor blades, flaps, spoilers, and diffusers. A characteristic change in the longitudinal static-pressure distribution (i.e., a change from a curve with one inflection point to a curve with three inflection points) was employed to detect the occurrence of separation. The effects of Reynolds number (10(exp 6) to 10(exp 7) per foot or l.5 x 10(exp 4) to 7.5 x 10(exp 4) based upon boundary-layer thickness) and Mach number (1.6 to 4.2) on the onset of turbulent boundary-layer separation were investigated. The pressure gradient of the boundary-layer flow ahead of the interaction region was essentially zero. The results show a considerable effect of Mach number on the pressure rise for incipient separation for all configurations. For a curved-surface model, the static pressure-rise ratio required to cause separation varied from about 2.5, at a Mach number of 2 to about 16, at a Mach number of 3.5. A substantial effect of Reynolds number on the pressure rise for incipient separation was observed in the upper Mach number range and in the lower Reynolds number range; namely, the pressure rise required for separation decreased with increasing Reynolds number. For low Mach numbers and high Reynolds numbers, there appeared to be no Reynolds number effect. The effects of Mach number and of Reynolds number were similar for all models. Model shape was also found to be an important variable affecting the onset of separation. Large gains were realized in the pressure-rise ratio with no separation when the radius of curvature of the model surface was increased. At a Mach number of 3.4, for instance, the pressure-rise ratio with no separation increased from about 5 to 15 as a result of an increase in the radius of curvature from approximately 0 to 30 boundary-layer thicknesses.

Kuehn, Donald M.↗
NASA NTRS1997

Remote radio tracking of interplanetary CMEs

Two examples of type 2 radio emissions associated with the propagation of earth-directed coronal mass ejections (CMEs) through the interplanetary medium are illustrated and compared. The two type 2 radio events were observed by WIND/WAVES in January and May of 1997 and exhibit very different radio characteristics. The analyses presented here use the novel approach of presenting the radio data as a function of the inverse of the frequency and time, which facilitates remote radio tracking of the CME through the interplanetary medium. It is demonstrated unequivocally that for the May 1997 event, the radio emissions were generated at the fundamental, and harmonic of the plasma frequency in the ambient plasma upstream of the CME-driven shock. For the January 1997 event, evidence is presented that some of the radio emissions were generated while the CME-driven shock passed through a corotating interaction region (CIR). This is the first time that type 2 radio emissions were shown to originate in a specific interplanetary structure.

Reiner, M. J.↗
NASA NTRS1997

Fluxes of MeV particles at Earth's orbit and their relationship with the global structure of the solar corona: Observations from SOHO

The SOHO satellite, launched on 2 December 1995, combines a unique set of instruments which allow comparative studies of the interior of the sun, the outer corona and solar to be carried out. In its halo orbit around the L1 Lagrangian point of the sun-earth system, SOHO's comprehensive suprathermal and energetic particle analyzer (COSTEP) measures in situ energetic particles in the energy range of 44 keV/particle to greater than 53 MeV/n. The MeV proton, electron and helium nuclei measurements from the COSTEP electron proton helium instrument (EPHIN) were used to investigate the relationships of intensity increases of these particle species with the large-scale structures of the solar corona and heliosphere, including temporal variations. Coronal observatons are provided by the large angle spectroscopic coronagraph (LASCO) and the extreme ultraviolet imaging telescope (EIT). It was found that during times of minimum solar activity, intensity increases of the particles have two well defined sources: corotating interaction regions (CIRs) in the heliosphere related to coronal holes at the sun and coronal mass ejections.

Posner, A.↗
NASA NTRS1999

Interplanetary Fast Shocks and Associated Drivers Observed through the Twenty-Third Solar Minimum by WIND Over its First 2.5 Years

A list of the interplanetary (IP) shocks observed by WIND from its launch (in November 1994) to May 1997 is presented. Forty two shocks were identified. The magnetohydrodynamic nature of the shocks is investigated, and the associated shock parameters and their uncertainties are accurately computed using a practical scheme which combines two techniques. These techniques are a combination of the "pre-averaged" magnetic-coplanarity, velocity-coplanarity, and the Abraham-Schrauner-mixed methods, on the one hand, and the Vinas and Scudder [1986] technique for solving the non-linear least-squares Rankine-Hugoniot shock equations, on the other. Within acceptable limits these two techniques generally gave the same results, with some exceptions. The reasons for the exceptions are discussed. It is found that the mean strength and rate of occurrence of the shocks appears to correlated with the solar cycle. Both showed a decrease in 1996 coincident with the time of the lowest ultraviolet solar radiance, indicative of solar minimum and start of solar cycle 23, which began around June 1996. Eighteen shocks appeared to be associated with corotating interaction regions (CIRs). The distribution of their shock normals showed a mean direction peaking in the ecliptic plane and with a longitude (phi(sub n)) in that plane between perpendicular to the Parker spiral and radial from the Sun. When grouped according to the sense of the direction of propagation of the shocks the mean azimuthal (longitude) angle in GSE coordinates was approximately 194 deg for the fast-forward and approximately 20 deg for the fast-reverse shocks. Another 16 shocks were determined to be driven by solar transients, including magnetic clouds. These shocks had a broader distribution of normal directions than those of the CIR cases with a mean direction close to the Sun-Earth line. Eight shocks of unknown origin had normal orientation well off the ecliptic plane. No shock propagated with longitude phi(sub n) >= 220 +/- 10 deg, this would suggest strong hindrance to the propagation of shocks contra a rather tightly winding Parker spiral. Examination of the obliquity angle theta(sub Bn) (that between the shock normal and the upstream interplanetary magnetic field) for the full set of shocks revealed that about 58% was quasi-perpendicular, and some were very nearly perpendicular. About 32% of the shocks were oblique, and the rest (only 10%) were quasi-parallel, with one on Dec. 9, 1996 that showed field pulsations. Small uncertainty in the estimated angle theta(sub Bn) was obtained for about 10 shocks with magnetosonic Mach numbers between 1 and 2, hopefully significantly contributing to studies researching particle acceleration mechanisms at IP shocks, and to investigations where accurate values of theta(sub Bn) are crucial.

Mariani, F.↗
NASA NTRS2001

ROSAT HRI and ASCA Observations of the Spiral Galaxy NGC 6946 and its Northeast Complex of Luminous Supernova Remnants

Analysis of 80 ks ASCA (Advanced Satellite for Cosmology and Astrophysics) and 60 ks ROSAT HRI (High Resolution Image) observations of the face-on spiral galaxy NGC 6946 are presented. The ASCA image is the first observation of this galaxy above approximately 2 keV. Diffuse emission may be present in the inner approximately 4' extending to energies above approximately 2-3 keV. In the HRI data, 14 pointlike sources are detected, the brightest two being a source very close to the nucleus and a source to the northeast that corresponds to a luminous complex of interacting supernova remnants (SNRs). We detect a point source that lies approximately 30" west of the SNR complex but with a luminosity -1115 of the SNR complex. None of the point sources show evidence of strong variability; weak variability would escape our detection. The ASCA spectrum of the SNR complex shows evidence for an emission line at approximately 0.9 keV that could be either Ne IX at approximately 0.915 keV or a blend of ion stages of Fe L-shell emission if the continuum is fitted with a power law. However, a two-component, Raymond-Smith thermal spectrum with no lines gives an equally valid continuum fit and may be more physically plausible given the observed spectrum below 3 keV. Adopting this latter model, we derive a density for the SNR complex of 10-35 cm(exp -3), consistent with estimates inferred from optical emission-line ratios. The complex's extraordinary X-ray luminosity may be related more to the high density of the surrounding medium than to a small but intense interaction region where two of the complex's SNRs are apparently colliding.

Schlegel, E.↗
NASA NTRS2002

Aura Science and Validation

The EOS-Aura Mission is designed to answer three basic questions concerning the Earth's atmosphere: 1) Is ozone recovering as predicted, 2) is air quality getting worse, and 3) how is climate changing? Aura's four instruments work synergistically and are dedicated to answering these questions. These questions relate to NASA Earth Science Enterprise's overall strategic questions, which seek to understand the consequences of climate change for human civilization and determine if these changes can be predicted. NASA supports an ongoing research and analysis program, which is conducted independently and in support of satellite missions. The research program conducts several on-going field campaigns employing aircraft, balloons, and ground based systems. These campaigns have focused on exploring processes in the tropics, high latitudes, and continental outflow to explain the chemistry and transport in the troposphere and stratosphere and how these regions interact. NASA is now studying how the Aura mission and requirements of the research and analysis program might be merged to achieve its strategic goals related to global atmospheric chemistry changes. In addition, NASA field campaign resources will be folded into Aura's validation requirements. Aura validation requires correlative measurements throughout the troposphere and stratosphere under a range of observing and geophysical conditions. Because of the recent launches of Envisat and other smaller international chemistry satellites, the NASA program plans to collaborate with European space agencies in developing a series of campaigns that will provide continuity between those satellites missions and Aura.

Hilsenrath, E.↗