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Loewenstein, M.

Publications and source records attributed to Loewenstein, M..

At least 37 records · Page 2
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NASA NTRS1998

Troposphere-to-Stratosphere Transport in the Lowermost Stratosphere from Measurements of H2O, CO2, N2O, and O3

The origin of air in the lowermost stratosphere is investigated with measurements from the NASA ER-2 aircraft. Air with high water vapor mixing ratios was observed in the stratosphere at theta approximately 330-380 K near 40 N in May 1995, indicating the influence of intrusions of tropospheric air. Assuming that observed tracer-tracer relationships reflect mixing lines between tropospheric and stratospheric air masses, we calculate mixing ratios of H2O (12-24 ppmv) and CO2 for the admixed tropospheric air at theta = 352-364 K. Temperatures on the 355 K surface 20-40 N were low enough to dehydrate air to these values. While most ER-2 CO2 data in both hemispheres are consistent with tropical or subtropical air entering the lowermost stratosphere, measurements from May 1995 for theta < 362 K suggest that entry of air from the midlatitude upper troposphere can occur in conjunction with mixing processes near the tropopause.

Hintsa, E. J.↗
NASA NTRS1998

Troposphere-to-Stratosphere Transport in the Lowermost Stratosphere from Measurements of H2O, CO2, N2O and O3

The origin of air in the lowermost stratosphere is investigated with measurements from the NASA ER-2 aircraft. Air with high water vapor mixing ratios was observed in the stratosphere at theta = 330-380 K near 40 N in May 1995, indicating the influence of intrusions of tropospheric air. Assuming that observed tracer-tracer relationships reflect mixing lines between tropospheric and stratospheric air masses, we calculate mixing ratios of H2O (12-24 ppmv) and CO2 for the admixed tropospheric air at theta = 352-364 K. Temperatures on the 355 K surface at 20-40 N were low enough to dehydrate air to these values. While most ER-2 CO2 data in both hemispheres are consistent with tropical or subtropical air entering the lowermost stratosphere, measurements from May 1995 for theta < 362 K suggest that entry of air from the midlatitude upper troposphere can occur in conjunction with mixing processes near the tropopause.

Hintsa, E. J.↗
NASA NTRS1996

A Comparison of Measurements from ATMOS and Instruments Aboard the ER-2 Aircraft: Tracers of Atmospheric Transport and Halogenated Gases

We compare volume mixing ratio profiles of N2O, O3, NO(y), H2O, CH4, and CO in the mid-latitude lower stratosphere measured by the ATMOS Fourier transform spectrometer on the ATLAS-3 Space Shuttle Mission with in situ measurements acquired from the NASA ER-2 aircraft during Nov 1994. ATMOS and ER-2 observations of (N2O) show good agreement, as do measured correlations of (O3), (NO(y)), (H2O), and (CH4) with (N2O). Thus a consistent measure of the hydrogen (H2O, CH4) content of the lower stratosphere is provided by the two platforms. The similarity of (NO(y)) determined by detection of individual species by ATMOS and the total (NOy) measurement on the ER-2 provides strong corroboration for the accuracy of both techniques. A 25% discrepancy in lower stratospheric (CO) observed by ATMOS and the ER-2 remains unexplained. Otherwise, the agreement for measurements of long-lived tracers demonstrates the ability to combine ATMOS data with in situ observations for quantifying atmospheric transport.

Chang, A. Y.↗
NASA NTRS1996

A Comparison of Measurements from ATMOS and Instruments Aboard the ER-2 Aircraft: Halogenated Gases

We compare volume mixing ratio profiles of N2O, CFC-11, CFC-12, CCl4, SF6, and HCl in the mid-latitude lower stratosphere measured by the ATMOS Fourier transform spectrometer on the ATLAS-3 Space Shuttle Mission with in situ measurements acquired from the NASA ER-2 aircraft during Nov. 1994. Good agreement is found between ATMOS and in situ correlations of [CFC-11], [CFC-12], and [SF6] with [N2O]. ATMOS measurements of [CCl4] are 15% high compared to ER-2 data, but agree within the systematic uncertainties. ATMOS observations of [HCl] vs [N2O] are within approximately 10% of ER-2 data for [HCl] > 1 ppbv, but exceed in situ measurements by larger fractional amounts for smaller [HCl]. ATMOS measurements of [ClONO2] agree well with values inferred from in situ observations of [ClO], [NO], and [O3]. The sum of [HCl] and [ClONO2] observed by ATMOS, supplemented by a minor contribution from [ClO] estimated with a photochemical model, is consistent with the levels of inorganic chlorine inferred from in situ measurements of chlorine source gases.

Chang, A. Y.↗
NASA NTRS1996

A Comparison of Measurements from ATMOS and Instruments Aboard the ER-2 Aircraft: Tracers of Atmospheric Transport

We compare volume mixing ratio profiles of N2O, O3, NO(y) H2O, CH4, and CO in the mid-latitude lower stratosphere measured by the ATMOS Fourier transform spectrometer on the ATLAS-3 Space Shuttle Mission with in situ measurements acquired from the NASA ER-2 aircraft during Nov 1994. ATMOS and ER-2 observations of [N2O] show good agreement, as do measured correlations of [O3], [NO(y)], [H2O], and [CH4] with [N2O]. Thus a consistent measure of the hydrogen (H2O, CH4) content of the lower stratosphere is provided by the two platforms. The similarity of [NO(y)] determined by detection of individual species by ATMOS and the total [NO(y)] measurement on the ER-2 provides strong corroboration for the accuracy of both techniques. A 25% discrepancy in lower stratospheric [CO] observed by ATMOS and the ER-2 remains unexplained. Otherwise, the agreement for measurements of long-lived tracers demonstrates the ability to combine ATMOS data with in situ observations for quantifying atmospheric transport.

Chang, A. Y.↗
NASA NTRS1996

Bulk Properties of Isentropic Mixing into the Tropics in the Lower Stratosphere

Timescales for mixing of midlatitude air into the tropical lower stratosphere are deduced from observations of long-lived tracers N2O and CCl3F. Bulk mixing between tropical and midlatitude regions is assumed to be isentropic and relatively slow compared with local mixing within each region. The mean value of the mixing timescale ranges from 12 to 18 months near 20 km. There is a tendency for shorter mixing times at higher and lower altitudes, although vertical profiles of mixing cannot be definitively established by the data. A more robust quantity is given by the fraction of midlatitude air entrained into the tropical upwelling region. Implied mixing fractions exceed 50% above 22 km.

Minschwaner, K.↗
NASA NTRS1996

Quantifying Transport Between the Tropical and Mid-Latitude Lower Stratosphere

Because exchange with the tropics is slower than multi-dimensional models generally assume, ozone at mid-latitudes apears to be more sensitive to elevated levels of industrial chlorine than currently predicted. Nevertheless, approximately 45% of air in the tropical ascent region at 21 km has been entrained from mid-latitudes, implying that emissions from supersonic aircraft could deplete ozone in the middle stratosphere.

stratosphere↗
NASA NTRS1994

Detections of hard X-ray emissions from bright early-type galaxies with ASCA

Five bright elliptical galaxies in the Virgo Cluster, NGC 4365, NGC 4374 (M84), NGC 4406 (M86), NGC 4472 (M49), and NGC 4636, were observed with ASCA. In addition to the extended thermal X-ray emission of temperature kT approximately 1 keV, harder X-rays with color temperature kT greater than or equal to 2 keV were detected from all of them. The 2-10 keV luminosities of this hard component for the five galaxies, integrated within 5 min, are distributed within a relatively narrow range of (1-4) x 10(exp 40) ergs/s. The hard X-ray component is primarily attributed to the integrated emission from discrete X-ray sources. In NGC 4406 and NGC 4374 the data indicate that the hard component is contributed additionally by foreground/background emission from the hot intracluster medium (ICM) of the Virgo Cluster. The hard component of NGC 4472 seems also contributed by the Virgo ICM emission, but in this case there is evidence that the ICM brightness is locally enhanced within approximately 10 min of NGC 4472.

Matsushita, K.↗
NASA NTRS1994

Discovery and implications of very low metal abundances in NGC 1404 and NGC 4374

We present our analysis of ASCA PV phase observations of the elliptical galaxies NGC 1404 and NGC 4374 (M84). The average metallicities in the hot gas derived from the SIS spectra are exceptionally low, Z approximately 0.15 solar, while the temperatures are 'typical,' kT approximately 0.75 keV. We also place upper limits on intrinsic column densities. The low abundances lend support to the theory of Fe enrichment of intracluster media by protogalactic Type II supernova-driven winds and raise the possibility of a fundamental connection between baryon fraction, dissipation, and abundances in elliptical galaxies.

Loewenstein, M.↗
NASA NTRS1994

ASCA observation of NGC 4636: Dark matter and metallicity gradient

We present our analysis of ASCA PV phase observation of the elliptical galaxy NGC 4636. Solid state imaging spectrometer (SIS) spectra in six concentric annuli centered on NGC 4636 are used to derive temperature, metallicity, and column density profiles for the hot interstellar medium. Outside of the central 3 min the temperature is roughly constant at approximately 0.85 keV, while the metallicity decreases from greater than 0.36 solar at the center to less than 0.12 solar at R approximately 9 min. The implications of this gradient for elliptical galaxy formation and the enrichment of intracluster gas are discussed. We derive a detailed mass profile consistent with the stellar velocity dispersion and with ROSAT position sensitive proportional counter (PSPC) and ASCA SIS X-ray temperature profiles. We find that NGC 4636 becomes dark matter dominated at roughly the de Vaucouleurs radius, and, at r approximately 100 kpc, the ratio of dark to luminous matter density is approximately 80 and solar mass/solar luminosity approximately equal to 150. Evidence for the presence of a cooling flow is also discussed.

Mushotzky, R. F.↗
NASA NTRS1994

Fine-scale, poleward transport of tropical air during AASE 2

The poleward transport of tropical air in the lower stratosphere during the winter period of the second Airborne Arctic Stratospheric Expedition (AASE 2) (December 1991-March 1992) is examined using contour advection calcutions. These calculations show that filaments of tropical air extend into mid-latitudes, and are wrapped around the equatorward edge of the polar jet. Simultaneously filaments are drawn from the polar vortex and are intermingled with the filaments of tropical air. The tropical filaments are consistent with measurements of chemical tracers taken aboard the ER-2 and DC-8 aircraft which show localized regions, in mid-latitudes, of air with the characteristics of tropical air.

Waugh, D. W.↗
NASA NTRS1994

Spread of denitrification from 1987 Antarctic and 1988-1989 Arctic stratospheric vortices

Vertical profiles of N2O and NO(y) taken by the ER-2 outside the vortex are used to construct average vertical profiles of F(NO(y)) = NO(y)/(A-N2O), where A is the tropospheric content of N2O three years prior to the measurements. The southern hemisphere had less nitrous oxide in the range 400 less than Theta less than 470 K, by up to 25% relative to the northern hemisphere. F(NO(y)) is the ratio of NOy produced to N2O lost in a stratospheric air mass since entry from the troposphere. The profiles of F(NO(y)) have the following characteristics: (1) Relative to 1991-1992, a year without denitrification inside or outside the vortex, the northern hemisphere in 1988-1989 showed denitrification outside the vortex ranging up to 25% and averaging 17% above Theta = 425 K. (2) Relative to the northern hemisphere in 1991-1992, the southern hemisphere in 1987 showed denitrification outside the vortex ranging up to 32% and averaging 20% above Theta = 400 K. (3) Below Theta = 400 K the southern hemisphere showed enhancements of F(NO(y)) relative to the northern hemisphere in 1991-1992 ranging up to 200% at Theta = 375 K, outside the vortex. Corresponding profiles of residual water, R(H2O) = H2O - 2(1.6 - CH4), are considered and shown to be consistent with those of F(NO(y)) in the sense that they show deficits outside the Antarctic vortex, which was both dehydrated and denitrified, but not outside the 1988-1989 Arctic vortex, which was denitrified but not dehydrated. R(H2O) is the water content of stratospheric air with the contribution from methane oxidation subtracted. Comparison of F(NO(y)) and R(H2O) below 400 K outside the Antarctic vortex leads to the suggetion that dehydration in the Antarctic vortex occurs by the sedimentation of ice crystals large enough to fall out of the stratosphere, whereas denitrification occurs mainly on mixed nitric acid-water crystals which evaporate below the base of the vortex at Theta = 400 K but above the tropopause.

Tuck, A. F.↗
NASA NTRS1994

Evolution of the 1991-1992 Arctic vortex and comparison with the Geophysical Fluid Dynamics Laboratory SKYHI general circulation model

Nitrous oxide (N2O) measured on board the ER-2 aircraft during the Airborne Arctic Stratospheric Expedition 2 (AASE 2) has been used to monitor descent of air inside the Arctic vortex between October 1991 and March 1992. Monthly mean N2O fields are calculated from the flight data and then compared with mean fields calculated from the high-resolution Geophysical Fluid Dynamics Laboratory general circulation model SKYHI in order to evaluate the model's simulation of the polar vortex. From late fall through winter the model vortex evolves in much the same way as the 1991-1992 vortex, with N2O gradients at the edge becoming progressively steeper. The October to March trends in N2O profiles inside the vortex are used to verify daily net heating rates in the vortex that were computed from clear sky radiative heating rates and National Meteorological Center temperature observations. The computed heating rates successfully estimate the descent of vortex air from December through February but suggest that before December, air at high latitudes may not be isolated from the midlatitudes. SKYHI heating rates are in good agreement with the computed rates but tend to be slightly higher (i.e., less cooling) due to meteorological differences between SKYHI and the 1991-1992 winter. Three ER-2 flights measured N2O just north of the subtropical jet. These low-midlatitude profiles show only slight differences from the high-midlatitude profiles (45 deg - 60 deg N), indicating strong meridional mixing in the midlatitude 'surf zone.' Mean midwinter N2O profiles inside and outside the vortex calculated from AASE 2 data are shown to be nearly identical to 1989 AASE profiles, pointing to the N2O/potential temperature relationship as an excellent marker for vortex air.

Strahan, S. E.↗
NASA NTRS1994

Implications for gravitational lensing and the dark matter content in clusters of galaxies from spatially resolved x-ray spectra

A simple method for deriving well-behaved temperature solutions to the equation of hydrostatic equilibrium for intracluster media with X-ray imaging observations is presented and applied to a series of generalized models as well as to observations of the Perseus cluster and Abell 2256. In these applications the allowed range in the ratio of nonbaryons to baryons as a function of radius is derived, taking into account the uncertainties and crude spatial resolution of the X-ray spectra and considering a range of physically reasonable mass models with various scale heights. Particular attention is paid to the central regions of the cluster, and it is found that the dark matter can be sufficiently concentrated to be consistent with the high central mass surface densities for moderate-redshift clusters from their gravitational lensing properties.

Loewenstein, M.↗
NASA NTRS1994

Application of Tunable Diode Laser Spectrometry for Isotopic Analysis

Lead-salt tunable diode lasers are now commercially available with operating temperatures above 77 K and excellent single-mode characteristics which make them very useful for spectroscopy in the mid-IR spectral range. Using these lasers for absorption measurements in the 4.3 micrometer spectral region we have made accurate measurements of isotopic abundances in CO2. The method involves assembly language controlled data acquisition of spectra of selected adjacent isotopic rotational lines, an etalon spectral frequency calibration technique, the fitting of multiple Voigt profiles to the data, and the ratioing of absorbances from simultaneously acquired sample and reference data scans. The accuracy achieved is better than 0.4% for the C-13/C-12 ratio and 1% for the O-18/O-16 ratio. Higher accuracy is expected from improvements now being implemented.

Sauke, T. B.↗
NASA NTRS1994

Transport out of the lower stratospheric Arctic vortex by Rossby wave breaking

The fine-scale structure in lower stratospheric tracer transport during the period of the two Arctic Airborne Stratospheric Expeditions (January and February 1989; December 1991 to March 1992) is investigated using contour advection with surgery calculations. These calculations show that Rossby wave breaking is an ongoing occurrence during these periods and that air is ejected from the polar vortex in the form of long filamentary structures. There is good qualitative agreement between these filaments and measurements of chemical tracers taken aboard the NASA ER-2 aircraft. The ejected air generally remains filamentary and is stretched and mixed with midlatitude air as it is wrapped around the vortex. This process transfers vortex air into midlatitudes and also produces a narrow region of fine-scale filaments surrounding the polar vortex. Among other things, this makes it difficult to define a vortex edge. The calculations also show that strong stirring can occur inside as well as outside the vortex.

Waugh, D. W.↗