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At least 703 records · Page 39
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NASA NTRS1988

Extinction and backscatter measurements of Antarctic PSC's, 1987: Implications for particle and vapor removal

The temperature dependence is examined of optical properties measured in the Antarctic during 1987 at the 70 mb level (near 18 km), a level chosen to correlate the results with in situ measurements made from the NASA-Ames ER-2 aircraft during the 1987 Airborne Antarctic Ozone Experiment (AAOE). The data set consists of extinction measurements by Sam 2 inside the Antarctic polar vortex from May to October 1987; and backscatter measurements by the UV-DIAL (Ultraviolet Differential Absorption Lidar) system aboard the Ames DC-8 aircraft during selected AAOE flights. Observed trends are compared with results from a revised version of Pole and McCormick's model to classify the PSC observations by Type (1 or 2) and infer the temporal behavior of the ambient aerosol and ambient vapor mixing ratios. The sample figures show monthly ensembles of the 70-mb Sam 2 extinction ratio (the ratio of aerosol or PSC extinction to molecule extinction) as a function of NMC temperature at the beginning (June) and (October) of the 1987 Antarctic winter. Both ensembles show two rather distinct clusters of points: one oriented in the near vertical direction which depicts the change with temperature of the ambient aerosol extinction ratio; and a second cluster oriented in the near horizontal direction whose position on the vertical scale marks a change in particle phase (i.e., PSC formation) and whose length (the extinction enhancement related to that of the ambient aerosol) is an indicator of PSC type.

Poole, L. R.↗
NASA NTRS1988

Temporal and spatial distribution of stratospheric trace gases over Antarctica in August and September, 1987

There have been a large number of suggestions made concerning the origin of the Antarctic 'ozone hole' since its discovery; these changes include stratospheric chemistry, or changes in the solar input, or combinations of these effects. Supporting or refuting these theories requires a wide variety of data for comparison with the predictions. In Aug. and Sept., 1987, a field observation expedition was made over Antarctica from a base in Punta Arenas, Chile. Two aircraft, an ER-2 with in-situ instruments flew at altitudes up to 18 km measuring ozone, water, ClO, BrO, NO sub x, particles, and meteorological parameters in the ozone layer. A DC-8 flew at altitudes of 10 to 12 km, below the ozone layer, using remote sensing instruments for measuring composition and aerosol content of the ozone layer, as well as in-situ instruments for measuring composition at aircraft altitudes. The obsevation of a number of chemical species and their correlation with each other and with meteorological parameters gives a useful set of data for comparison with various theories.

Coffey, M. T.↗
NASA NTRS1988

Measurements of ozone in the Antarctic region during August and September of 1987

Mixing ratios are presented for ozone in the austral polar atmosphere during Aug. and Sept. of 1987. Since the mid-1970's, there has been a continuing decrease in the total column abundance of ozone over Antarctica during the late winter and early spring. This reduction now amounts to about one-half of the historical October mean. The results presented are derived from an ultraviolet ozone photometer. The ER-2 aircraft carrying 14 instruments participated in a major effort to penetrate the region of depletion. Data were gathered between altitudes of 53 deg and 72 deg S at pressure altitudes up to 21 km in a series of 12 flights. Additional data were obtained between latitudes of 37 deg N and 53 deg S on the 3 flight legs required to reach Punta Arenas from Moffett Field, CA, and on the same return legs to Moffett Field. The observed ozone mixing ratios indicate the effects of chemistry as well as the effects of the stratospheric polar vortex. Examples of the distributions of ozone mixing ratios as a function of altitude, latitude, or a time and the relationships to temperature and other trace gases are presented.

Starr, Walter L.↗
NASA NTRS1988

In situ observations of ClO in the Antarctic: Evidence for chlorine catalyzed destruction of ozone

Results from a series of 12 ER-2 aircraft flights into the Antarctic polar vortex are summarized. These in situ data define the spatial and temporal distribution of ClO as the aircraft flew at an altitude of approx. 18 km from Punta Arenas (54 deg S latitude) to the base of the Palmer Peninsula (72 deg S latitude), executed a rapid descent to approx. 13 km, turned north and climbed bach to approximately 18 km, returning to Punta Arenas. A general pattern in the ClO distribution is reported: mixing ratios of approximately 10 ppt are found at altitude in the vicinity of 55 deg S increasing to 50 ppt at 60 degrees S. In the vicinity of 65 deg S latitude a steep gradient in the ClO mixing ratio is observed. At a fixed potential temperature, the ClO mixing ratio through this sharp transition increases by an order of magnitude within a very few degrees of latitude, thus defining the edge of the chemical containment vessel. From the edge of that containment vessel to the southern extension of the flights, 72 deg S, a dome of slowly increasing ClO best describes the distribution. Conclusion are drawn from the data.

Anderson, J. G.↗
NASA NTRS1988

Southern Hemispheric nitrous oxide measurements obtained during 1987 airborne Antarctic ozone experiment

The chemical lifetime of N2O is about 150 years, which makes it an excellent dynamical tracer of air motion on the time scale of the ozone depletion event. For these reasons it was chosen to help test whether dynamical theories of ozone loss over Antarctica were plausible, particularly the theory that upwelling ozone-poor air from the troposphere was replacing ozone-rich stratospheric air. The N2O measurements were made with the Airborne Tunable Laser Absorption Spectrometer (ATLAS) aboard the NASA ER-2 aircraft. The detection technique involves measuring the diffential absorption of the IR laser radiation as it is rapidly scanned over an N2O absorption feature. For the AAOE mission, the instrument was capable of making measurements with a 1 ppb sensitivity, 1 second response time, over an altitude range of 10 to 20 kilometers. The AAOE mission consisted of a series of 12 flights from Punta Arenas (53S) into the polar vortex (approximately 72S) at which time a vertical profile from 65 to 45 km and back was performed. Comparison of the observed profiles inside the vortex with N2O profiles obtained by balloon flights during the austral summer showed that an overall subsidence had occurred during the winter of about 5 to 6 km. Also, over the course of the mission (mid-August to late September), no trend in the N2O vertical profile, either upward or downward, was discernible, eliminating the possibility that upwelling was the cause of the observed ozone decrease.

Podolske, J. R.↗
NASA NTRS1988

Observational results of microwave temperature profile measurements from the airborne Antarctic ozone experiment

The Microwave Temperature Profiler, MTP, is installed on NASA's ER-2 aircraft. MTP measures profiles of air temperature versus altitude. Temperatures are obtained every 13.7 seconds for 15 altitudes in an altitude region that is approximately 5 km thick (at high flight levels). MTP is a passive microwave radiometer, operating at the frequencies 57.3 and 58.8 GHz. Thermal emission from oxygen molecules provides the signal that is converted to air temperature. MTP is unique in that it is the only airborne instrument of its kind. The MTP instrument was used during the Airborne Antarctic Ozone Experiment, AAOE, to enable potential vorticity to be measured along the flight track. Other uses for the MTP data have become apparent. The most intriguing unexpected use is the detection and characterization of mountain waves that were encountered during flights over the Palmer Peninsula. Mountain waves that propagate into the polar vortex may have implications for the formation of the ozone hole. Upward excursions of air parcels lead to a brief cooling. This can begin the process of cloud formation. It is important to determine how much additional formation of polar stratospheric cloud (PSC) material is possible by the passage of air parcels through a mountain wave pattern that endures for long periods. Other mountain wave effects have been suggested, such as a speeding up of the vortex, and a consequent cooling of large air volumes (which in turn might add to PSC production).

Gary, Bruce L.↗
NASA NTRS1988

Photochemical trajectory modelling studies of the 1987 Antarctic spring vortex

Simulations of Antarctic ozone photochemistry performed using a photochemical model integrated along air parcel trajectories are described. This type of model has a major advantage at high latitudes of being able to simulate correctly the complex interaction between photolysis and temperature fields, which, because of the polar night cannot be represented accurately in a zonally averaged framework. Isentropic air parcel trajectories were computed using Meteorological Office global model analyses and forecast fields from positions along the ER-2 flight paths during the Airborne Antarctic Ozone Experiment in Austral Spring 1987. A photochemical model is integrated along these trajectories using the aircraft observations to initialize constituent concentrations. The model includes additional reactions of the ClO dimer and also bromine reactions, which are thought to play a significant role in Antarctica. The model also includes heterogeneous reactions which are invoked when the air parcel passes through a polar stratospheric cloud (PSC). The existence of a PSC is determined throughout the course of the model integration from the parcel temperature and the saturated vapour pressure of water over an assumed H2O/HNO3 mixture. The air parcel temperature is used to determine the saturated vapor pressure of HNO3 over the same mixture. Mixing ratios which exceed saturation result in condensation of the excess in the model and hence lead to a reduction of the amount of gas phase NO2 available for chemical reaction.

Austin, J.↗
NASA NTRS1988

Trace gas measurements from whole air samples collected over the Antarctic continent

Whole air samples collected aboard the NASA DC-8 and ER-2 aircraft as part of the Airborne Antarctic Ozone Experiment (AAOE) were analyzed in a field laboratory set up at Punta Arenas, Chile, in August and September, 1987. Mixing ratios obtained from gas chromatographic analyses of these samples are presented for N2O, CFCl3, CFCl2, C2F3Cl3, CH3CCl3, CH4, and CO. Variations in the mixing ratios of these gases along the individual flight paths of the aircraft are used as tracers to indicate the history of air masses over and near the Antarctic continent.

Heidt, L. E.↗
NASA NTRS1988

Dehydration in the lower Antarctic stratosphere in late winter and spring

The history of minimum temperatures at 50 and 70 mb is examined from NMC, UK Met 0 and ECMWF analyses. MSU channel 24 data are similarly inspected. South Pole sonde data are used to calculate saturation humidity mixing ratio as a function of altitude and time throughout 1987. Saturation with respect to ice could be maintained for water mixing ratios of 3.5 ppmv for a period of about 80 days from mid-June to mid-September. Dehydration to mixing ratios of 1 ppmv or less was possible sporadically. Data from the ER-2 flights between 53 S and 72 S are used in conjunction with particle size measurements and air parcel trajectories to demonstrate the dehydration occurring over Antarctica. Water mixing ratios at the latitude of Punta Arenas (53 S), in conjunction with tracer measurements and trajectory analysis, show that at potential temperatures from about 325 to 400 K, the dryness (less than 3 ppmv) had its origin over Antarctica rather than in the tropics. Water mixing ratios within the Antarctic vortex varied from 1.5 to 3.8 ppmv, with a strong isentropic gradient being evident in the region of high potential vorticity gradients.

Kelly, K. K.↗
NASA NTRS1988

Temporal trends and transport within and around the Antarctic polar vortex during the formation of the 1987 Antarctic ozone hole

During AAOE in 1987 an ER-2 high altitude aircraft made twelve flights out of Punta Arenas, Chile (53 S, 71 W) into the Antarctic polar vortex. The aircraft was fitted with fast response instruments for in situ measurements of many trace species including O3, ClO, BrO, NO sub y, NO, H2O, and N2O. Grab samples of long-lived tracers were also taken and a scanning microwave radiometer measured temperatures above and below the aircraft. Temperature, pressure, and wind measurements were also made on the flight tracks. Most of these flights were flown to 72 S, at a constant potential temperature, followed by a dip to a lower altitude and again assuming a sometimes different potential temperature for the return leg. The potential temperature chosen was 425 K (17 to 18 km) on 12 of the flight legs, and 5 of the flight legs were flown at 450 K (18 to 19 km). The remaining 7 legs of the 12 flights were not flown on constant potential temperature surfaces. Tracer data have been analyzed for temporal trends. Data from the ascents out of Punta Arenas, the constant potential temperature flight legs, and the dips within the vortex are used to compare tracer values inside and outside the vortex, both with respect to constant potential temperature and constant N2O. The time trend during the one-month period of August 23 through September 22, 1987, shows that ozone decreased by 50 percent or more at altitudes form 15 to 19 km. This trend is evident whether analyzed with respect to constant potential temperature or constant N2O. The trend analysis for ozone outside the vortex shows no downward trend during this period. The analysis for N2O at a constant potential temperature indicates no significant trend either inside or outside the vortex; however, a decrease in N2O with an increase in latitude is evident.

Proffitt, M. H.↗
NASA NTRS1988

Small scale structure and mixing at the edge of the Antarctic vortex

Small scale correlations and patterns in the chemical tracers measured from the NASA ER-2 aircraft in the 1987 AAOE campaign can be used to investigate the structure of the edge of the polar vortex and the chemically perturbed region within it. Examples of several types of transport processes can be found in the data. Since ClO and O3 have similar vertical gradients and opposite horizontal gradients near the chemically perturbed region, the correlation between ClO and O3 can be used to study the extent of horizontal transport at the edge of the chemically perturbed region. Horizontal transport dominates the correlation for a latitude band up to 4 degrees on each side of the boundary. This implies a transition zone containing a substantial fraction of the mass of the total polar vortex. Similar horizontal transport can be seen in other tracers as well. It has not been possible to distinguish reversible transport from irreversible mixing. One manifestation of the horizontal transport is that the edge of the chemically perturbed region is often layered rather than a vertical curtain. This can be seen from the frequent reversed vertical gradients of NO2, caused by air with high NO2 overlapping layers with lower mixing ratios. Water and NO2 are positively correlated within the chemically perturbed region. This is the opposite sign to the correlation in the unperturbed stratosphere. The extent of the positive correlation is too great to be attributed solely to horizontal mixing. Instead, it is hypothesized that dehydration and descent are closely connected on a small scale, possibly due to radiative cooling of the clouds that also cause ice to fall to lower altitudes.

Murphy, D. M.↗
NASA NTRS1988

Transport into the south polar vortex in early spring

Estimates of the mean circulation and diffusive transport of ozone and other species into the Antarctic polar vortex during the spring of 1987 are made using data from the Airborne Antarctic Ozone Experiment. Measurements of long-lived tracers of tropospheric origin remained relatively constant at the levels of the maximum rate of decline of ozone during September. At lower levels in the stratosphere some evidence exists to support intrusions of tropospheric or low latitude air. Given the distribution in latitude and height of these tracers measured from the ER-2 aircraft, it can be inferred that the Lagrangian or diabatic mean circulation was zero or downward over Antarctica during the period of the ozone decline. The observation of a decline in ozone therefore requires a photochemical sink for ozone. The magnitude of the required photochemical sink must be sufficient to offset the transport of ozone into the polar region and produce the observed decline. Quasi-isentropic mixing and downward motion are coupled and are difficult to estimate from a single tracer. The full suite of measured tracers and auxiliary information are brought together to provide an estimate of the rate at which air is cycled through the polar vortex during spring. Estimates of large scale transport of potential vorticity and ozone from previous years are generally consistent with the data from the airborne experiment in suggesting a relatively slow rate of mass flow through the polar vortex in the lower stratosphere during September.

Hartmann, D.↗
NASA NTRS1988

The evolution of AAOE observed constituents with the polar vortex

One of the difficulties in determining constituent trends from the ER-2 flight data is the large amount of day to day variability generated by the motion of the polar vortex. To reduce this variability, the observations have been transformed into the conservative (Lagrangian) reference frames consisting of the coordinate pairs, potential temperature (PT) and potential vorticity (PV), or PT and N2O. The requirement of only two independent coordinates rests on the assumption that constituent distributions and their chemical processes are nearly zonal in that coordinate system. Flight data is used everywhere for these transformation except for potential vorticity. Potential vorticity is determined from level flight segments, and NMC PV values during flight dives and takeoffs are combined with flight data in a smooth fashion.

Schoeberl, Mark R.↗
NASA NTRS1988

Diagnostic studies of the 1987 Antarctic spring vortex

Dynamical fields form the UK Meteorological office global forecast model were used throughout the 1987 Airborne Antarctic Ozone Experiment (AAOE) for flight planning and diagnostic studies. Here, several studies based on the Meteorological Office global analysis (resolution 1.5 degrees lattitude x 1.875 degrees longitude, Lyne et al.) are described. The wind and temperature data derived from the model analysis are compared with observations made from both the DCB and ER-2, and an assessment of the model performance given. Derived quantities such as potential vorticity and model data and discrepancies due to the model data are discussed.

Austin, J.↗
NASA NTRS1988

Intercomparison of synthetic- and real-aperture radar observations of Arctic sea ice during winter MIZEX '87

Active microwave measurements were made of various sea ice forms in March and April 1987 during the Marginal Ice Zone Experiment, at 1, 5, 10, 18, and 35 GHz using a synthetic aperture radar (SAR) and helicopter and ship-based scatterometers. The X-band (9.8 GHz) SAR data were compared to the scatterometer data and it was determined that for 5 GHz and higher frequencies both the SAR and scatterometers can differentiate open water, new ice (5 to 30 cm), first-year ice with rubble (0.60 -1.5 m), and multiyear ice. The analysis further confirmed that the C-band (5 GHz) SAR's flying on ESA ERS-1 and Radarsat will differentiate the mentioned ice types.

Schuchmann, R. A.↗
NASA NTRS1988

Meteorological satellite products support for project COHMEX

The first year effort focussed on real-time support and satellite data collection during the field phase of COHMEX. Work efforts following the field phase of COHMEX concentrated on post-processing of the real-time data sets, and generation of enhanced, research-quality satellite data sets for selected COHMEX core days. These satellite-derived data sets will augment the special COHMEX conventional data base with high horizontal and temporal resolution information. The data sets will be examined for their usefulness in delineating important elements in the meteorological environment leading to convective activity. In addition, a limited research effort was conducted using the Cooperative Institute for Meteorological Satellite Studies (CIMSS) 4-d data assimilation system in conjunction with evaluating VISSR Atmospheric Sounder (VAS) and His-resolution Interferometer Sounder (HIS) data. The need to address the characteristics of the data types, and the problems they introduce into 4-d assimilation procedures is evident. The HIS instrument was flown aboard an ER-2 aircraft on several occasions during COHMEX. One of the flights was chosen for further study. Processed VAS soundings and COHMEX radiosonde data were also collected for this day. The case study included an evaluation of the HIS and VAS data and an impact study of the data on the assimilation system analysis.

Velden, Christopher S.↗
NASA NTRS1989

Design and verification of mechanisms for a large foldable antenna

The characteristics of the Synthetic Aperture Radar (SAR) antenna aboard the ESA Remote Sensing Satellite (ERS-1) are presented. The antenna is folded into a dense package for launch and is deployed in orbit. The design requirements and constraints, their impact on the design, and the resulting features of the mechanisms are discussed.

Luhmann, Hans Jurgen↗
NASA NTRS1988

A system overview of the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS)

The AVIRIS instrument has been designed to do high spectral resolution remote sensing of the earth. Utilizing both silicon and indium antimonide line array detectors, AVIRIS covers the spectral region from 0.41 to 2.45 microns in 10-nm bands. It was designed to fly aboard NASA's U-2 and ER-2 aircraft, where it will simulate the performance of future spacecraft instrumentation. Flying at an altitude of 20 km, it has an instantaneous field of view of 20 m and views a swath over 10 km wide. With an ability to record 40 minutes of data, it can, during a single flight, capture 500 km of flight line.

Porter, Wallace M.↗