Vertical Scale Height Research Articles

Evaluating the IRI topside model for the South African region: An overview of the modelling techniques

The representation of the topside ionosphere (the region above the F2 peak) is critical because of the limited experimental data available. Over the years, a wide range of models have been developed in an effort to represent the behaviour and the shape of the electron density ( Ne) profile of the topside ionosphere. Various studies have been centred around calculating the vertical scale height (VSH) and have included (a) obtaining VSH from Global Positioning System (GPS) derived total electron content (TEC), (b) calculating the VSH from ground-based ionosonde measurements, (c) using topside sounder vertical Ne profiles to obtain the VSH. One or a combination of the topside profilers (Chapman function, exponential function, sech-squared (Epstein) function, and/or parabolic function) is then used to reconstruct the topside Ne profile. The different approaches and the modelling techniques are discussed with a view to identifying the most adequate approach to apply to the South African region’s topside modelling efforts. The IRI-2001 topside model is evaluated based on how well it reproduces measured topside profiles over the South African region. This study is a first step in the process of developing a South African topside ionosphere model.

AnHST/ACS investigation of the spatial and chemical structure and sub-structure of NGC 891, a Milky Way analogue

We present a structural analysis of NGC891, an edge-on galaxy that has long been considered to be an analogue of the Milky Way. Using starcounts derived from deep HST/ACS images, we detect the presence of a thick disk component in this galaxy with vertical scale height 1.44+/-0.03 kpc and radial scale length 4.8+/-0.1 kpc, only slightly longer than that of the thin disk. A stellar spheroid with a de Vaucouleurs-like profile is detected from a radial distance of 0.5 kpc to the edge of the survey at 25 kpc; the structure appears to become more flattened with distance, reaching q = 0.50 in the outermost halo region probed. The halo inside of 15 kpc is moderately metal-rich (median [Fe/H] ~ -1.1) and approximately uniform in median metallicity. Beyond that distance a modest chemical gradient is detected, with the median reaching [Fe/H] ~ -1.3 at 20 kpc. We find evidence for subtle, but very significant, small-scale variations in the median colour and density over the halo survey area. We argue that the colour variations are unlikely to be due to internal extinction or foreground extinction, and reflect instead variations in the stellar metallicity. Their presence suggests a startling conclusion: that the halo of this galaxy is composed of a large number of incompletely-mixed sub-populations, testifying to its origin in a deluge of small accretions.

HiClouds in the Lower Halo. I. The Galactic All‐Sky Survey Pilot Region

We have detected over 400 H I clouds in the lower halo of the Galaxy within the pilot region of the Galactic All-Sky Survey (GASS), a region of the fourth quadrant that spans -->18° in longitude, -->40° in latitude, and is centered on the Galactic equator. These clouds have a median peak brightness temperature of 0.6 K, a median velocity width of 12.8 km s−1, and angular sizes 1°. The motion of these clouds is dominated by Galactic rotation with a random cloud-to-cloud velocity dispersion of 18 km s−1. A sample of clouds likely to be near tangent points was analyzed in detail. These clouds have radii on the order of 30 pc and a median H I mass of 630 -->M☉. The population has a vertical scale height of 400 pc and is concentrated in Galactocentric radius, peaking at -->R = 3.8 kpc. This confined structure suggests that the clouds are linked to spiral features, while morphological evidence that many clouds are aligned with loops and filaments is suggestive of a relationship with star formation. The clouds might result from supernovae and stellar winds in the form of fragmenting shells and gas that has been pushed into the halo rather than from a galactic fountain.

Topside ionospheric scale heights retrieved from Constellation Observing System for Meteorology, Ionosphere, and Climate radio occultation measurements

The vertical scale height (VSH) in the topside ionosphere can be derived from electron density profiles. In this study, the electron density profiles retrieved from the COSMIC/FORMOSAT‐3 (a Constellation Observing System for Meteorology, Ionosphere, and Climate mission; C/F3 for short) ionospheric radio occultation (IRO) observations have been collected to investigate the local time, seasonal, latitudinal, and longitudinal variations of the VSH. With the postprocessed C/F3 IRO electron density profiles during the interval from day of year (DOY) 194 in 2006 to DOY 60 in 2008, we conduct an analysis on the behaviors of VSH at an altitude of 400 km. There are appreciable latitudinal variations in VSH. A new finding is a significant peak around dip equator during daytime in four seasons. Away from the equatorial peak, it is obvious that the VSH generally increases at higher latitudes. The equatorial VSH undergoes a significant diurnal variation with a local noon maximum. The peak shifts to sunrise time with increasing dip latitude, and the values of daytime VSH become comparable with those at nighttime at low latitude in both hemispheres, which is somewhat different from the feature revealed from Arecibo incoherent scatter radar observations. One of the crucial findings in our results is the most outstanding feature of VSH, that is, the presence of a substantial longitudinal structure in equatorial regions. A wave‐like longitudinal feature is found in equatorial VSH during the daytime in four seasons, while it becomes weaker or absent at other local time intervals and at higher latitudes. This investigation also confirms that the behaviors of VSH are not strongly consistent with those of the neutral or plasma‐scale heights.

First Three‐Dimensional Reconstructions of Coronal Loops with theSTEREO AandBSpacecraft. I. Geometry

We present one of the first triangulations and 3D reconstructions of coronal loops, using the EUVI telescopes of the two STEREO A and B spacecraft. The first triangulation of coronal loops was performed in an active region, observed with STEREO A and B on 2007 May 9 with a spacecraft separation angle of αsep = 7.3°, at a wavelength of 171 Å. We identify 30 loop structures (7 complete loops and 23 partial segments) and compute their 3D coordinates (x,y,z) (the full 3D coordinates are available as an electronic file). We quantify the height range, the stereoscopic height measurement errors, the loop plane inclination angles, and the coplanarity and circularity of the analyzed loops. The knowledge of the exact 3D geometry of a loop with respect to the observer's line of sight has important consequences for determining the correct vertical density scale height (used in hydrostatic models), the aspect angle of loop cross sections (used in inferring electron densities from optically thin emission measures), the absolute flow speeds (used in siphon flow models), the correct loop length (used in loop scaling laws), and the 3D vectors of the coronal magnetic field (used in testing theoretical magnetic field extrapolation models). The hydrodynamic and magnetic modeling of the analyzed loops will be described in subsequent papers.

Resolving distance ambiguities towards 6.7 GHz methanol masers

Context. Distances to most star forming regions are determined using kinematics, through the assumption that the observed radial velocity arises from the motion of the source with respect to the Sun resulting from the differential rotation of Galaxy. The primary challenge associated with the application of this technique in the inner Galaxy is the kinematic distance ambiguity. Aims. In this work, we aim to resolve the kinematic distance ambiguity towards a sample of 6.7 GHz methanol masers, which are signposts of the early stages of massive star formation. Methods. We measured 21 cm H I absorption spectra using the Very Large Array in C and CnB configurations. A comparison of the maximum velocity of H I absorption with the source velocity and tangent point velocity was used to resolve the kinematic distance ambiguity. Results. We resolved the distance ambiguity towards 41 sources. Distance determinations that are in conflict with previous measurements are discussed. The NE2001 spiral arm model is broadly consistent with the locations of the star forming complexes. We find that the use of vertical scale height arguments to resolve the distance ambiguity can lead to erroneous classifications for a significant fraction of sources.

Effects of solar activity variations on the low latitude topside nighttime ionosphere

We have studied the topside nighttime ionosphere of the low latitude region using data obtained from DMSP F15, ROCSAT-1, KOMPSAT-1, and GUVI on the TIMED satellite for the period of 2000–2004, during which solar activity decreased from its maximum. As these satellites operated at different altitudes, we were able to discriminate altitude dependence of several key ionospheric parameters on the level of solar activity. For example, with intensifying solar activity, electron density was seen to increase more rapidly at higher altitudes than at lower altitudes, implying that the corresponding scale height also increased. The density increased without saturation at all observed altitudes when plotted against solar EUV flux instead of F10.7. The results of the present study, as compared with those of previous studies for lower altitudes, indicate that topside vertical scale height increases with altitude and that, when solar activity increases, topside vertical scale height increases more rapidly at higher altitudes than at lower altitudes. Temperature also increased more rapidly at higher altitudes than at lower altitudes as solar activity increased. In addition, the height of the F2 peak was seen to increase with increasing solar activity, along with the oxygen ion fraction measured above the F2 peak. These results confirm that the topside ionosphere rises and expands with increasing solar activity.

Comparison of bar strengths in optical and near-infrared for the OSUBSGS sample

Abstract We use a gravitational bar torque method to compare bar strengths (the maximum tangential force normalized by radial force) in B and H-band images of 152 galaxies from the Ohio State University Bright Spiral Galaxy Survey. Our main motivation is to check how much the difference in the rest-frame wavelength could affect the comparisons of bar strengths in low- and high-redshift observations. Between these two bands, we find an average bar strength ratio QB/H= 1.25 which factor is nearly independent of the morphological type. We show that QB/H > 1 is mostly due to reduced bulge dilution of radial forces in the B band. The bar torque method needs an estimate for the vertical scaleheight of the galaxy, based on the radial scalelength of the disc and the galaxy's morphological type. Since these two might not always be possible to determine at high redshifts in a reliable manner, we also checked that similar results are obtained with vertical scaleheights estimated from the radii corresponding to the K-band surface brightness of 20 mag arcsec−2. Also, we made a simple test of the usability of the bar torque method at high redshifts by checking the effects of image degradation (nearest neighbour sampling without any adjustment of noise levels): we found that the estimated bar strengths varied by ±10 per cent at most as long as the total extent of the bar was at least 10 pixels. Overall, we show that the gravitational bar torque method should provide a proficient tool for quantifying bar strengths also at high redshifts.

Variations of topside ionospheric scale heights over Millstone Hill during the 30-day incoherent scatter radar experiment

Abstract. A 30-day incoherent scatter radar (ISR) experiment was conducted at Millstone Hill (288.5° E, 42.6° N) from 4 October to 4 November 2002. The altitude profiles of electron density Ne, ion and electron temperature (Ti and Te), and line-of-sight velocity during this experiment were processed to deduce the topside plasma scale height Hp, vertical scale height VSH, Chapman scale height Hm, ion velocity, and the relative altitude gradient of plasma temperature (dTp/dh)/Tp, as well as the F2 layer electron density (NmF2) and height (hmF2). These data are analyzed to explore the variations of the ionosphere over Millstone Hill under geomagnetically quiet and disturbed conditions. Results show that ionospheric parameters generally follow their median behavior under geomagnetically quiet conditions, while the main feature of the scale heights, as well as other parameters, deviated significantly from their median behaviors under disturbed conditions. The enhanced variability of ionospheric scale heights during the storm-times suggests that the geomagnetic activity has a major impact on the behavior of ionospheric scale heights, as well as the shape of the topside electron density profiles. Over Millstone Hill, the diurnal behaviors of the median VSH and Hm are very similar to each other and are not so tightly correlated with that of the plasma scale height Hp or the plasma temperature. The present study confirms the sensitivity of the ionospheric scale heights over Millstone Hill to thermal structure and dynamics. The values of VSH/Hp tend to decrease as (dTp/dh)/Tp becomes larger or the dynamic processes become enhanced.

Particle stirring in turbulent gas disks: Including orbital oscillations

We describe the diffusion and random velocities of solid particles due to stochastic forcing by turbulent gas. We include the orbital dynamics of Keplerian disks, both in-plane epicycles and vertical oscillations. We obtain a new result for the diffusion of solids. The Schmidt number (ratio of gas to particle diffusivity) is Sc ≈ 1 + ( Ω t stop ) 2 , in terms of the particle stopping time t stop and the orbital frequency Ω. The standard result, Sc = 1 + t stop / t eddy , in terms of the eddy turnover time, t eddy , is shown to be incorrect. The main difference is that Sc rises quadratically, not linearly, with stopping time. Consequently, particles larger than ∼10 cm in protoplanetary disks will suffer less radial diffusion and will settle closer to the midplane. Such a layer of boulders would be more prone to gravitational collapse. Our predictions of RMS speeds, vertical scale height and diffusion coefficients will help interpret numerical simulations. We confirm previous results for the vertical stirring of particles (scale heights and random velocities), and add a correction for arbitrary ratios of eddy to orbital times. The particle layer becomes thinner for t eddy > 1 / Ω with the strength of turbulent diffusion held fixed. We use two analytic techniques—the Hinze–Tchen formalism and the Fokker–Planck equation with velocity diffusion—with identical results when the regimes of validity overlap. We include simple physical arguments for the scaling of our results.

Spatial distribution and galactic model parameters of cataclysmic variables

The spatial distribution, galactic model parameters and luminosity function of cataclysmic variables (CVs) in the solar neighbourhood have been determined from a carefully established sample of 459 CVs. The sample contains all of the CVs with distances computed from the period-luminosity-colours (PLCs) relation of CVs which has been recently derived and calibrated with 2MASS photometric data. It has been found that an exponential function fits best to the observational z-distributions of all of the CVs in the sample, non-magnetic CVs and dwarf novae, while the sech 2 function is more appropriate for nova-like stars and polars. The vertical scaleheight of CVs is 158 ± 14 pc for the 2MASS J-band limiting apparent magnitude of 15.8. On the other hand, the vertical scaleheights are 128 ± 20 and 160 ± 5 pc for dwarf novae and nova-like stars, respectively. The local space density of CVs is found to be ∼3 × 10 −5 pc −3 which is in agreement with the lower limit of the theoretical predictions. The luminosity function of CVs shows an increasing trend toward higher space densities at low luminosities, implying that the number of short-period systems should be high. The discrepancies between the theoretical and observational population studies of CVs will almost disappear if for the z-dependence of the space density the sech 2 density function is used.

An analysis of the scale heights in the lower topside ionosphere based on the Arecibo incoherent scatter radar measurements

We statistically analyze the ionospheric scale heights in the lower topside ionosphere based on the electron density (Ne) and temperature profiles observed from the incoherent scatter radar (ISR) at Arecibo (293.2°E, 18.3°N), Puerto Rico. In this study, a database containing the Arecibo ISR observations from 1966 to 2002 has been used in order to investigate the diurnal and seasonal variations and solar activity dependences of the vertical scale height (VSH), which is deduced from the electron concentration profiles defined as the value of −dh/d(ln(Ne)), and the effective scale height (Hm), which is defined as the scale height in the Chapman‐α function to approximate the Ne profiles. As a measure of the slope of the height profiles of the topside electron density, the derived VSH and Hm show marked diurnal and seasonal variations and solar activity dependences. Their features are discussed in terms of thermal structures in the lower topside ionosphere. We also investigate the quantitative relationships between Hm, VSH, and plasma scale height (Hp) over Arecibo. The similarities and differences in these scale heights are discussed. Results suggest that both the contributions from topside temperature structure and diffusion processes can also greatly control VSH and Hm through changing the profile shape.

The Stellar Populations in the Outer Regions of M33. II. Deep ACS Imaging

Studying the stellar populations in the outskirts of spiral galaxies can provide important constraints on their structure, formation, and evolution. To that end, we present VI photometry obtained with the Advanced Camera for Surveys for three fields located ~20'-30' in projected distance southeast of M33's nucleus (corresponding to approximately four to six visual scale lengths or ~9-13 kpc in deprojected radius). The color-magnitude diagrams reveal a mixed stellar population whose youngest constituents have ages no greater than ~100 Myr and whose oldest members have ages of at least several gigayears. The presence of stars as massive as 3-5 M⊙ is consistent with global star formation thresholds in disk galaxies but could argue for a threshold in M33 that is on the low end of observational and theoretical expectations. The metallicity gradient as inferred by comparing the observed red giant branch (RGB) to the Galactic globular clusters is consistent with M33's inner disk gradient traced by several other studies. The surface density of the RGB stars drops off exponentially with a radial scale length of 4.7' ± 0.1'. The scale length increases with age in a manner similar to the vertical scale height of several nearby late-type spirals. Based on the metallicity gradient, density gradient, and mixed nature of the stellar populations, we conclude that these fields are dominated by a disk population, although we cannot rule out the presence of a small halo component.

Mid-plane sedimentation of large solid bodies in turbulent protoplanetary discs

We study the vertical settling of solid bodies in a turbulent protoplanetary disc. We consider the situation when the coupling to the gas is weak or equivalently when the particle stopping time τ st due to friction with the gas is long compared to the orbital time-scale Ω -1 . An analytical model, which takes into account the stochastic nature of the sedimentation process using a Fokker-Planck equation for the particle distribution function in phase space, is used to obtain the vertical scaleheight of the solid layer as a function of the vertical component of the turbulent gas velocity correlation function and the particle stopping time. This is found to be of the same form as the relation obtained for strongly coupled particles in previous work. We compare the predictions of this model with results obtained from local shearing box magnetohydrodynamic simulations of solid particles embedded in a vertically stratified disc in which there is turbulence driven by the magnetorotational instability. We find that the ratio of the dust disc thickness to the gas disc thickness satisfies H d /H = 0.08 (Ωτ st ) -1/2 , which is in very good agreement with the analytical model. By discussing the conditions for gravitational instability in the outer regions of protoplanetary discs in which there is a similar level of turbulence, we find that bodies in the size range 50-600 m can aggregate to form Kuiper belt-like objects with characteristic radii ranging from tens to hundreds of kilometres.

Formation of a star and planets around it through a gravitational instability in a disk of gas and dust

The position is adopted that involve a simultaneous formation of a star and planets around it through a gravitational Jeans-type instability in a protostellar disk of gas and dust. The possibility that the disk is dynamically unstable to axisymmetric (radial) and nonaxisymmetric (spiral) gravity perturbations (e.g., those produced by a spontaneous disturbance or, in rare cases, a satellite system) with characteristic scales much larger than the vertical scale height is discussed, using a local WKB approximation. It is shown analytically that the dynamically cold thin disk is likely subject to both radial and spiral Jeans instabilities of small-amplitude perturbations and might therefore be clumpy. The mass of a typical clump in actual disks is coincident in order of magnitude with the masses of giant planets in the solar system. These gravitationally bound clumps may further collapse to become planets. In unstable, inhomogeneous disks spiral perturbations can effectively transfer angular momentum outward to the outer parts of the system, as mass flows inward to the growing star through gravitational torques. It is proposed that the spontaneous generation of Jeans-unstable modes of collective oscillations is the source of self-sustained hydrodynamic turbulence in protostellar disks; in the nonlinear regime, gravitational instabilities can produce self-gravitating turbulence with outward angular momentum transport. The turbulence is related to stochastic motions of gas elements, and allows potential energy to be converted into kinetic energy which can then be dissipated. Equations are derived to describe the turbulent heating of the disk that results from the buildup of Jeans instability. The heating and the mass redistribution bring the disk toward stability—unless some cooling mechanism is available, e.g., by radiation—against all perturbations, including the most unstable nonaxisymmetric ones. As cooling process always exists in the systems, the Jeans instability can be considered to be a long-term generating mechanism for fresh, gravitationally unstable density waves, thereby leading to recurrent short-lived ∼ 10 4 yr arc-and-lump or spiral patterns in the protostellar (protoplanetary) disks. N-body experiments that simulate the nonlinear development of gravitational instabilities are also used to test the validities of the theory.

Discovery of an 86 AU Radius Debris Ring around HD 181327

HST/NICMOS PSF-subtracted coronagraphic observations of HD 181327 have revealed the presence of a ring-like disk of circumstellar debris seen in 1.1 micron light scattered by the disk grains, surrounded by a di use outer region of lower surface brightness. The annular disk appears to be inclined by 31.7 +/- 1.6 deg from face on with the disk major axis PA at 107 +/-2 deg . The total 1.1 micron flux density of the light scattered by the disk (at 1.2 < r < 5.0) of 9.6 mJy +/- 0.8 mJy is 0.17% +/- 0.015% of the starlight. Seventy percent of the light from the scattering grains appears to be confined in a 36 AU wide annulus centered on the peak of the radial surface brightness (SB) profile 86.3 +/- 3.9 AU from the star, well beyond the characteristic radius of thermal emission estimated from IRAS and Spitzer flux densities assuming blackbody grains (~ 22 AU). The light scattered by the ring appears bilaterally symmetric, exhibits directionally preferential scattering well represented by a Henyey-Greenstein scattering phase function with g = 0.30 +/- 0.03, and has an azimuthally medianed SB at the 86.3 AU radius of peak SB of 1.00 +/- 0.07 mJy arcsec^-2. No photocentric offset is seen in the ring relative to the position of the central star. A low surface brightness diffuse halo is seen in the NICMOS image to a distance of ~ Deeper 0.6 micron HST/ACS PSF-subtracted coronagraphic observations reveal a faint outer nebulosity, asymmetrically brighter to the North of the star. We discuss models of the disk and properties of its grains, from which we infer a maximum vertical scale height of 4 - 8 AU at the 87.6 AU radius of maximum surface density, and a total maximum dust mass of collisionally replenished grains with minimum grain sizes of ~ 1 micron of ~ 4 M(moon).

Rotation rate and velocity dispersion of planetary ring particles with size distribution II. Numerical simulation for gravitating particles

We examine rotation rates of gravitating particles in low optical depth rings, on the basis of the evolution equation of particle rotational energy derived by Ohtsuki [Ohtsuki, K., 2006. Rotation rate and velocity dispersion of planetary ring particles with size distribution. I. Formulation and analytic calculation. Icarus 183, 373–383]. We obtain the rates of evolution of particle rotation rate and velocity dispersion, using three-body orbital integration that takes into account distribution of random velocities and rotation rates. The obtained stirring and friction rates are used to calculate the evolution of velocity dispersion and rotation rate for particles in one- and two-size component rings as well as those with a narrow size distribution, and agreement with N-body simulation is confirmed. Then, we perform calculations to examine equilibrium rotation rates and velocity dispersion of gravitating ring particles with a broad size distribution, from 1 cm up to 10 m. We find that small particles spin rapidly with 〈 ω 2 〉 1 / 2 / Ω ≳ 10 2 – 10 3 , where ω and Ω are the particle rotation rate and its orbital angular frequency, respectively, while the largest particles spin slowly, with 〈 ω 2 〉 1 / 2 / Ω ≲ 1 . The vertical scale height of rapidly rotating small particles is much larger than that of slowly rotating large particles. Thus, rotational states of ring particles have vertical heterogeneity, which should be taken into account in modeling thermal infrared emission from Saturn's rings.

Model of topside ionosphere scale height based on topside sounder data

A new model of topside ionosphere scale height is developed, based on the vertical electron density (Ne) profiles obtained from topside ionosondes. The model provides the vertical scale height (VSH) as a function of month of the year, local time, geomagnetic latitude, solar flux F 107 and K p index. To define VSH, the O + scale height above the peak of the F2 layer is assumed to be represented by the lowest gradient in the measured profile. The model data base contains 170,033 VSH values, extracted from individual N(h) profiles gathered between 1962 and 1978 by Aluoette and ISIS satellites. The data sample sufficiently all parameter’s ranges. The model describes the vertical plasma scale height by a multivariable polynomial consisted from Tchebishev’s and trigonometric base-functions, which are fitted to the data in the 5-dimensional space. The overall model error is 34.6 km, or 23%. The model VSH variations along the different parameters are presented. The model results are compared with those extracted from IRI.

Gravitationally unstable protoplanetary discs

The possibility that protoplanetary gaseous discs are dynamically unstable to axisymmetric and non-axisymmetric gravity perturbations (e.g. those produced by spontaneous disturbances) with characteristic scales larger than the vertical scale height is discussed analytically, using a local Wentzel–Kramers–Brillouin (WKB) approach. It is shown that such discs might be clumpy, and these gravitationally bound clumps may later collapse to become giant planets (‘hot Jupiters’). The chief aim in this paper is to underscore a fact of vital importance for application in the planetary formation process: gravitationally unstable non-axisymmetric (spiral) perturbations can effectively transport both the angular momentum and the mass in a spatially inhomogeneous disc.

An Investigation of Diffuse Interstellar Gas toward a Large, Low‐Extinction Window into the Inner Galaxy

H? and H? spectroscopy with the Wisconsin H? Mapper (WHAM) reveals a strong concentration of high-velocity emission in a ?5? ? 5? area centered near (l, b) = (27?, - 3?), known as the Scutum cloud. The high velocities imply that we are detecting optical emission from near the plane of the Galaxy out to the tangent point at heliocentric distances of D? 6 kpc, assuming that the gas participates in circular Galactic rotation. The ratio of the H? to H? emission as a function of velocity suggests that dust along these lines of sight produces a total visual extinction of AV ? 3 at D? ~ 6 kpc. This makes it possible to use optical emission lines to explore the physical conditions of ionized gas in the inner Galaxy. At a Galactocentric distance RG ? 4 kpc, for example, we find that the H+ has an rms midplane density of ?1 cm-3 with a vertical scale height of ?300 pc. We also find evidence for an increase in the flux of Lyman continuum photons and an increase in the ratio of ionized to neutral hydrogen toward the inner Galaxy. We have extended the measurements of E(B - V) in this direction to distances far beyond what has been accessible through stellar photometry and find E(B - V)/NH to be near the local mean of 1.7 ? 10-22 cm2 mag, with evidence for an increase in this ratio at RG ? 4 kpc. Finally, our observations of [N II]??6583, [S II]??6716, and [O III]??5007 toward the window reveal that in the inner Galaxy the temperature of the gas and the ionization state of oxygen increase with increasing height from the midplane.