Engineering topics

Loewenstein, M.

Publications and source records attributed to Loewenstein, M..

At least 73 records · Page 4

NASA NTRS1992

Comparison of 2-D model simulations of ozone and nitrous oxide at high latitudes with stratospheric measurements

A linear reference relationship between O3 and N2O has been used to estimate polar winter O3 loss from aircraft data taken in the lower stratosphere. Here, this relationship is evaluated at high latitudes by comparing it with a 2D model simulation and with NIMBUS 7 satellite measurements. Although comparisons with satellite measurements are limited to January through May, the model simulations are compared during other seasons. The model simulations and the satellite data are found to be consistent with the winter O3 loss analysis. It is shown that such analyses are likely to be inappropriate during other seasons.

Proffitt, M. H.↗

NASA NTRS1991

Nitrous Oxide In The Antarctic Stratosphere

Paper reports on measurements of nitrous oxide (N2O) in upper atmosphere of Southern Hemisphere, made by tunable-laser absorption spectrometer on airplane. Measurements fill gap in information about distribution of N2O over Antarctic while ozone hole forming.

Podolske, J. R.↗

NASA NTRS1990

Ozone loss in the Arctic polar vortex inferred from high-altitude aircraft measurements

The Arctic polar vortex in winter is known to be chemically primed for ozone depletion, yet it does not exhibit the large seasonal ozone decrease that characterizes its southern counterpart. This difference may be due in part to a net flux of ozone-rich air through the Arctic vortex, which can mask ozone loss. But by using a chemically conserved tracer as a reference, significant ozone loss can be identified. This loss is found to be correlated with high levels of chlorine monoxide, suggesting that much of the decrease in ozone is caused by anthropogenic emissions of chlorofluorocarbons.

Proffitt, M. H.↗

NASA NTRS1990

A diagnostic for denitrification in the winter polar stratospheres

The pairwise correlation of NO(y) and N2O data from the Southern and Northern Hemispheres is presented. Both data sets show a linear correlation region, defined as a reference state, and regions of denitrification where the correlation breaks down. Using two-dimensional photochemical model simulations of the atmosphere, a similar linear correlation is found between NO(y) and N2O, thereby establishing a theoretical framework for the reference state. This general approach, which can be extended to other pairs of molecules, should prove to be powerful in further comparisons of aircraft data with numerical models.

Fahey, D. W.↗

NASA NTRS1990

Observations of denitrification and dehydration in the winter polar stratospheres

It is argued that denitrification of the Arctic stratosphere can be explained by the selective growth and sedimentation of aerosol particles rich in nitric acid. Because reactive nitrogen species moderate the destruction of ozone by chlorine-catalyzed reactions by sequestering chlorine in reservoir species such as ClONO2, the possibility of the removal of reactive nitrogen without dehydration should be allowed for in attempts to model ozone depletion in the Arctic. Indeed, denitrification along with elevated concentrations of reactive chlorine observed in 1989 indicate that the Arctic was chemically primed for ozone destruction without an extended period of temperatures below the frost point, as is characteristic of the Antarctic.

Fahey, D. W.↗

NASA NTRS1990

Airborne lidar observations in the wintertime Arctic stratosphere - Ozone

Large-scale distributions of ozone (O3) were measured with an airborne lidar system as part of the 1989 Airborne Arctic Stratospheric Expedition. Measurements of O3 distributions were obtained between January 6 and February 15, 1989, on 15 long-range flights into the polar vortex from the Solar Air Station, Norway. The observed O3 distribution was found to clearly indicate the edge of the polar vortex and to be an effective tracer of dynamical processes in the lower stratosphere. On the last two flights of the expedition, large regions with reduced O3 levels were observed by the lidar inside the polar vortex. Ozone had decreased by as much as 17 percent in the center of these areas, and using the in situ measurements made on the ER-2 aircraft, it was concluded that this decline was due to chemical O3 destruction.

Browell, E. V.↗

NASA NTRS1990

Measurements of condensation nuclei in the Airborne Arctic Stratospheric Expedition - Observations of particle production in the polar vortex

The ER-2 Condensation Nucleus Counter (ER-2 CNC) was operated in the Airborne Arctic Stratospheric Expedition (AASE) in January and February 1989. The ER-2 CNC measures the mixing ratio of particles, CN, with diameters from approximately 0.02 to approximately 1 micron. The spatial distribution of CN in the Arctic polar vortex was found to resemble that measured in the Antarctic in the Spring of 1987. The vertical profile of CN in the vortex was lowered by subsidence. At altitudes above the minimum in the CN mixing ratio profile, CN mixing ratios correlated negatively with that of N2O, demonstrating new particle production. CN serve as nuclei in the formation of Polar Stratospheric Clouds (PSCs) and the concentration of CN can affect PSC properties.

Wilson, J. C.↗

NASA NTRS1990

Observed particle evolution in the polar stratospheric cloud of January 24, 1989

Particle-size distributions measured from the NASA ER-2 with the new Forward Scattering Spectrometer Probe 300 in a type I polar stratospheric cloud (PSC) on January 24, 1989 show a volume mode near 0.8 micron in diameter. The large increase in particle concentration and volume after cloud entry did not occur until the apparent saturation ratio of nitric acid with respect to nitric acid trihydrate reached 10, but at ratios near 1 subtle changes in the size distribution suggest some type I particles were present. Particle concentrations in cloud of 15-17/cu cm were greater than the CN concentrations of 5-7/cu cm just outside of cloud, suggesting nucleation on more than just sulfate particles. Some particles greater than 4 microns in diameter were observed in a region which was saturated with respect to ice.

Dye, J. E.↗

NASA NTRS1990

The January 30, 1989 Arctic polar stratospheric clouds (PSC) event - Evidence for a mechanism of dehydration

In-situ particle measurements made aboard the NASA ER-2 in the Arctic on 890130 (YYMMDD) show Type 1 PSC particles over much of the flight, with instances of embedded Type 2 PSCs. The Type 2 particles were observed at temperatures warmer than the local frost-point temperature of water; extended up to the upper size cutoff of the instrument (about 24-micron diameter); and are shown to contain too large a volume to be primarily NAT. Based on measured vertical temperature profiles, it is concluded that the Type 2 particles observed on this day were formed above the aircraft in a region where saturation with respect to ice was achieved and were sufficiently large to have fallen into the path of the ER-2. Although the amount of material in the particles, expressed as water, is small by comparison to the total (vapor + aerosol) water concentration, the flux of water from the falling particles is of sufficient magnitude, if sustained, to lead to dehydration of the source region. These observations verify the mechanism for dehydration of polar vortex air masses by precipitation of ice particles.

Gandrud, B. W.↗

NASA NTRS1990

A comparison of ER-2 measurements of stratospheric water vapor between the 1987 Antarctic and 1989 Arctic Airborne missions

Vertical profiles of water vapor inside the Antarctic vortex have been compared with those taken outside it over Punta Arenas (53 deg S, 71 deg W). A similar exercise was performed with Arctic vortex profiles and those taken over Stavanger (59 deg N, 6 deg E). Residual water, defined as the stratospheric water vapor mixing ratio with the contribution from methane oxidation subtracted, is also shown as profiles inside and outside the vortex for both missions. The Arctic and Antarctic profiles of water vapor and residual water are compared. Locally dehydrated air was evident both inside and outside the Antarctic vortex, but such dehydration was not evident in and around the Arctic vortex. Arctic profiles of residual water are consistent with nontropical entry for some air.

Kelly, K. K.↗

NASA NTRS1990

N2O as a dynamical tracer in the Arctic vortex

This paper reports N2O measurements obtained by the Airborne Tunable Laser Absorption Spectrometer from 14 flights of the NASA ER-2 aircraft during the 1989 Airborne Arctic Stratospheric Expedition field campaign. In the altitude range expected for ozone loss, N2O has a long photochemical lifetime, making it an excellent tracer of lower stratospheric air motions. As in the southern hemisphere, the zonal wind speed maximum and large gradients of potential vorticity and N2O identify the vortex edge. The N2O profiles inside the vortex indicate net descent relative to outside the vortex and to the summer polar lower stratosphere. The descent of the N2O profile during the Arctic night relative to the summer profile is comparable to the downward shift in the vertical profile observed in the 1987 Antarctic winter vortex. Winter profiles at the poles are very similar above the 435 K potential temperature surface, but divergent below.

Loewenstein, M.↗

NASA NTRS1990

ATLAS instrument characterization - Accuracy of the AASE and AAOE nitrous oxide data sets

The Airborne Tunabel Laser Absorption Spectrometer ATLAS was used to measure nitrous oxide in the 1987 Airborne Antarctic Ozone Experiment (AAOE) and in the 1989 Airborne Arctic Stratospheric Expedition (AASE). After the AASE, a detailed study of the ATLAS characteristics was undertaken to quantify the error inherent in the in situ measurement of atmospheric N2O. Using the latest calibration of the ATLAS (June 1989) and incorporating the recognized errors arising in the flight environment of ATLAS, it was established that, for both the AASE and the AAOE, most of the acquired N2O data sets are accurate to + or - 10 percent (2 sigma).

Loewenstein, M.↗

NASA NTRS1990

Measurements of total reactive nitrogen during the Airborne Arctic Stratospheric Expedition

Composite distributions of measured total reactive nitrogen NO(y), from the NASA ER-2 during the Airborne Arctic Stratospheric Expedition are presented. The observed features of these distributions are discussed in terms of the controlling dynamical, chemical and microphysical processes. In the latitudinal profile from 58 deg N to within about 4 deg poleward of the polar vortex boundary, NO(y) conforms closely to predictions of NO(y) based on N2O measurements. Poleward of 5 deg of latitude within the boundary, the average NO(y) decreases sharply and is significantly lower than that predicted from N2O. This feature is consistent with loss of NO(y) through sedimentation of particles containing NO(y) in polar stratospheric clouds.

Kawa, S. R.↗

NASA NTRS1990

Calculations of ozone destruction during the 1988/89 Arctic winter

Calculations of ozone depletion during the 1988/89 Arctic winter using a Lagrangian coupled photochemical-microphysical model are presented. Abundances of ClO in excess of 1 ppbv were observed at the end of the Airborne Arctic Stratospheric Expedition on February 10, 1989. These are shown to be consistent with the removal of more than 90 percent of the reactive nitrogen and the conversion of more than 80 percent of reservoir chlorine to active forms. This chemical state implies that ozone losses of more than 20 ppbv/day can be sustained in heavily denitrified air throughout much of February according to current photochemistry. As much as 74 percent of the loss is calculated to be due to ClO dimer photolysis. Following the warming of the vortex in mid-February 1989, ozone loss through ClO dimer photolysis becomes less effective as the rate of thermal decomposition of the ClO dimer increases. Thus, model results suggest that thermal decomposition of the dimer plays an important role in limiting ozone loss in the Arctic spring.

Mckenna, D. S.↗

NASA NTRS1989

Observations of condensation nuclei in the Airborne Antarctic Ozone Experiment - Implications for new particle formation and polar stratospheric cloud formation

This paper discusses the results of the ER-2 Condensation Nucleus Counter operated in the Airborne Ozone Experiment in August, September, and October 1987, providing data on the mixing ratio of aerosol condensation nuclei (CN) with diameters between about 0.02 and 1 micron. It is shown that the vertical profile of the CN mixing ratio is closely related to that of N2O, and that, between the -71 and -53 deg latitude, the location of the minima in the CN mixing ratio profile was near the 160 ppbv N2O isopleth, indicating that the processes of mixing and subsidence, which determine the inclination of that isopleth, also strongly affect the spatial distribution of the sulfate aerosol. Evidence for new sulfate particle formation is presented and related to the amount of subsidence experienced by air parcels in the formation of the polar vortex. Concentrations of CN are compared with those of larger particles (with diameters between 0.81 micron and 9.75 microns) to study polar stratospheric cloud formation mechanisms.

Wilson, J. C.↗

NASA NTRS1989

Measurements of nitric oxide and total reactive nitrogen in the Antarctic stratosphere - Observations and chemical implications

Results are presented on measurements of NO and the sum of reactive nitrogen species, NO(y), which include NO, NO2, NO3, N2O5, HNO3, and ClONO2 (in addition to ClO, O3, H2O, and N2O measurements), obtained aboard the NASA ER-2 aircraft flying over the Antarctica between the latitudes of 53 and 72 deg S during the Airborne Antarctic Ozone Experiment. The boundary of the chemically perturbed region (CPR), as indicated by a sharp increase in the level of ClO, occurred near 66 deg S; outside or equatorward of the CPR, the NO(y) mixing ratios ranged between 6 and 12 ppbv, with values decreasing poleward and reaching total NO(y) levels of 4 ppbv or less within 5-deg poleward of the boundary. Data presented in this paper clearly associate the Antarctic ozone decrease with perturbed conditions of ClO, NO(y), and H2O, which are in turn associated with processes defined as nonstandard heterogeneous chemistry, denitrification, and dehydration, respectively.

Fahey, D. W.↗

NASA NTRS1989

Correlation of N2O and ozone in the southern polar vortex during the Airborne Antarctic Ozone Experiment

The correlation of N2O and ozone in the Antarctic stratosphere during the late austral winter was investigated using measurements of N2O mixing ratios obtained by an airborne laser spectrometer and in situ measurements of ozone for latitudes between 53 and 72 deg S. In addition, airborne N2O and O3 measurements taken between 13 and 20 km in the mid-latitudes (37 deg N and 53 deg S) were correlated. It was found that, while the mid-latitude ozone-N2O corelation was negative, poleward of 53 deg S, the N2O and O3 mixing ratios often showed a strong positive correlation, which approximately coincided with the edge of the polar vortex as defined by the wind-speed maximum. Inside the vortex, in lower wind speed regions, the N2O-O3 correlation became negative again, with the lowest ozone mixing ratios usually found near the boundary with the positively correlated region.

Strahan, S. E.↗

NASA NTRS1989

Stratospheric nitrous oxide distribution in the Southern Hemisphere

Nitrous oxide measurements were made in the Southern Hemisphere as part of the Airborne Antarctic Ozone Experiment in late winter and early spring 1987, covering the altitude range 14-21 km. This paper reports on N2O measurements made by the airborne tunable laser absorption spectrometer, which was flown onboard the NASA ER-2 aircraft. Average vertical N2O profiles at latitudes 72 deg S, 54 deg S, and 42 deg S are presented and compared, when possible, with equivalent summer profiles. Latitudinal gradients of N2O on isentropic surfaces are presented and discussed in terms of their implications about the inhibition of horizontal mixing near the polar vortex. Finally, a large-scale distribution of N2O for the region 72 deg S to 42 deg S latitude is presented.

Podolske, J. R.↗