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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Radiative effects of polar stratospheric clouds during the Airborne Antarctic Ozone Experiment and the Airborne Arctic Stratospheric Expedition

Results are presented of a study of the radiative effects of polar stratospheric clouds during the Airborne Antarctic Ozone Experiment (AAOE) and the Airborne Arctic Stratospheric Expedition (AASE) in which daily 3D Type I nitric acid trihydrate (NAT) and Type II water ice polar stratospheric clouds (PSCs) were generated in the polar regions during AAOE and the AASE aircraft missions. Mission data on particular composition and size, together with NMC-analyzed temperatures, are used. For AAOE, both Type I and Type II clouds were formed for the time period August 23 to September 17, after which only Type I clouds formed. During AASE, while Type I clouds were formed for each day between January 3 and February 10, Type II clouds formed on only two days, January 24 and 31. Mie theory and a radiative transfer model are used to compute the radiative heating rates during the mission periods, for clear and cloudy lower sky cases. Only the Type II water ice clouds have a significant radiative effect, with the Type I NATO PSCs generating a net heating or cooling of 0.1 K/d or less.

Rosenfield, Joan E.↗
NASA NTRS1993

Annual variations of water vapor in the stratosphere and upper troposphere observed by the Stratospheric Aerosol and Gas Experiment II

Data collected by the Stratospheric Aerosol and Gas Experiment II are presented, showing annual variations of water vapor in the stratosphere and the upper troposphere. The altitude-time cross sections of water vapor were found to exhibit annually repeatable patterns in both hemispheres, with a yearly minimum in water vapor appearing in both hemispheres at about the same time, supporting the concept of a common source for stratospheric dry air. A linear regression analysis was applied to the three-year data set to elucidate global values and variations of water vapor ratio.

Mccormick, M. P.↗
NASA NTRS1993

Mesoscale disturbances in the tropical stratosphere excited by convection - Observations and effects on the stratospheric momentum budget

Aircraft temperature and pressure measurements as well as satellite imagery are used to establish the amplitudes and the space and time scale of potential temperature disturbances over convective systems. A conceptual model is proposed for the generation of mesoscale gravity waves by convection. The momentum forcing that a reasonable distribution of convection might exert on the tropical stratosphere through convectively excited mesoscale gravity waves of the observed amplitudes is estimated. Aircraft measurements show that presence of mesoscale disturbances in the lower stratospheric temperature, disturbances that appear to be associated with underlying convection. If the disturbances are convectively excited mesoscale gravity waves, their amplitude is sufficient that their breakdown in the upper stratosphere will exert a zonal force comparable to but probably smaller than the planetary-scale Kelvin waves.

Pfister, Leonhard↗
NASA NTRS1994

Evidence of Seasonally Dependent Stratosphere-Troposphere Exchange and Purging of Lower Stratospheric Aeroso from a Multi-Year Lidar Dataset

Tropospheric and lower stratospheric aerosol backscatter data obtained from a calibrated backscatter lidar at Pasadena, California (34 deg N latitude)over the 1984-1993 period clearly indicate tightly coupled aerosol optical properties in the upper troposphere and lower stratosphere in the winter and early spring, due to the active mid-latitude stratospheric-tropospheric (ST) exchange processes occurring at this time of year.

upper tropospheric aerosols↗
NASA NTRS1981

Stratospheric water vapor results from the limb infrared monitor of the stratosphere /LIMS/ experiment on Nimbus 7

Stratospheric water vapor results taken from the limb infrared monitor of the stratosphere experiment on Nimbus 7 are presented with emphasis on validation studies. Basic radiance data, the indicated orbital precision of the experiment and comparisons made with data collected in simultaneous balloon underflights are described. A plot of pressure versus H2O channel radiance shows the radiance variability as a function of pressure and latitude. Measured precision is in good agreement with calculated values using simulations.

Russell, J. M., III↗
NASA NTRS1984

Analysis of upper stratospheric Umkehr ozone profile data for trends and the effects of stratospheric aerosols

The effect of stratospheric aerosols on Umkehr estimates of long-term ozone depletion associated with chlorofluoromethanes (CFMs) is considered in a statistical time series trend analysis. Time series models are estimated using monthly averages of Umkehr measurements made over the last 15 to 20 years. The time series regression models incorporate seasonal, trend and noise factors and an additional factor to account for the effects of atmospheric aerosols on the Umkehr measurements. The analysis indicates a statistically significant relation with atmospheric aerosol transmission in the Umkehr layers and implies that the relation is an important factor in any time series trend analysis of Umkehr data. Taking this relation into account, statistically significant negative trends were found in the Upper Umkehr layers. It is pointed out that upper stratospheric ozone could be sensitive to long-term solar variability as well as other possible influences in addition to CFM-induced effects, and therefore the cause or causes of the estimated trend cannot be unambiguously estimated using current Umkehr data.

Reinsel, G. C.↗
NASA NTRS1984

VHF Radar Observations in the Stratosphere and Mesosphere During a Stratospheric Warming

The SOUSY-VHF-radar was used to carry out measurements during minor and a major stratospheric warming in February and March 1980, respectively. Echoes have been received from the stratosphere up to an altitude of about 30 km continuously during day and night, whereas echoes from the mesosphere were restricted to the daytime and occurred sporadically at different heights within the altitude range from 60 to 90 km. The three dimensional velocity vector was derived from Doppler measurements made in three different antenna beam directions with a height resolution of 1.5 km. In particular, the results obtained during disturbed conditions show the change of the zonal winds at mesospheric heights from westerly to easterly. A spectral analysis reveals a diurnal and a weaker semidiurnal tide of the zonal wind component.

Ruster, R.↗
NASA NTRS1985

The impact of polar stratospheric clouds on the heating rates of the winter polar stratosphere

The perturbation affecting IR radiative heating rates of the lower stratosphere that are prompted by the occurrence of polar stratospheric clouds (PSCs) during the Arctic and Antarctic winter are presently calculated by means of a multispectral radiative transfer code that allows for scattering, absorption, and thermal emission by particles and gases. Attention is given to perturbations arising from both the particulate opacity of the PSCs and the decrease of H2O vapor accompanying their formation. For plausible values of model parameters, the former, direct effect is always one of increased radiative cooling, while the indirect effect is always one of decreased cooling.

Pollack, J. B.↗
NASA NTRS1988

Aerosol measurements in the winter/spring Antarctic stratosphere. I - Correlative measurements with ozone. II - Impact on polar stratospheric cloud theories

Aerosol measurements collected from August 25-November 3, 1986 at McMurdo Station using balloon-borne optical particle counters are examined in order to study the relationship between aerosol and ozone distribution and the formation of polar stratospheric clouds (PSCs). Ozone, aerosol, and condensation nuclei profiles, and pressure, temperature, and humidity measurements are analyzed. It is observed that the height of the stratospheric sulfate layer decreases over the period of measurement suggesting that upwelling in the votex is not important in the zone depletion process. Three theories on PSC formation are described, and the effects of the aerosol measurements on the theories are considered. The three theories are: (1) the original theory of water vapor pressure over a solution of H2SO4 of Steele et al. (1983) and Hamill and Mc Master (1984); (2) the nitric acid theory of PSCs of Toon et al. (1986) and Hamill et al. (1986); and (3) the quasi-cirrus cloud theory of Heymsfield (1986).

Hofmann, D. J.↗
NASA NTRS1989

Meteorological atlas of the Northern Hemisphere lower stratosphere for January and February 1989 during the Airborne Arctic Stratospheric Expedition

Northern Hemisphere meteorological data for the months of January and February 1989 in the lower stratosphere are shown. National Meteorological Center (NMC) data, and Total Ozone Mapping Spectrometer (TOMS) data are used to display polar stereographic projections of 100-mb temperatures, 50-mb temperatures, 50-mb geopotential heights, total ozone, and Ertel's potential vorticity (Epv) on both 400 K and 460 K isentropic surfaces. In addition, latitude/height cross sections at 10 E of balanced wind isotachs, wind vectors, potential temperature, and temperature are also shown. Horizontal traces of NASA ER-2 and DC-8 flight tracks are also included. Vertical profiles of NMC temperatures following flight paths of both aircraft are shown. In addition, vertical profiles of wind speed are contoured following the ER-2 for estimating the lateral penetration into the polar vortex, while vertical profiles of Ertel's potential vorticity are included for estimating the vertical penetration of the DC-8 into the stratosphere.

Newman, Paul A.↗
NASA NTRS1989

Measurements of stratospheric hydrogen cyanide at McMurdo Station, Antarctica - Further evidence of winter stratospheric subsidence?

Measurements of hydrogen cyanide in the springtime Antarctic stratosphere were made using ground-based millimeter wave spectroscopy. A steeper decrease in volume mixing ratio with altitude was found, than that found at tropical latitudes, from an assumed value of about 160 pptv in the troposphere to a value of 65 + or - 30 pptv at 40 km, which may be further evidence of substantial vertical subsidence of the Antarctic winter stratosphere.

Jaramillo, M.↗
NASA NTRS1990

Comparison of stratospheric ozone profiles and their seasonal variations as measured by lidar and Stratospheric Aerosol and Gas Experiment during 1988

A ground-based, high power, laser remote sensing system for measurements of stratospheric ozone concentration profiles has been in operation at the Jet Propulsion Laboratory Table Mountain Facility located in southern California, since January 1988. The seasonal variations observed in the ozone profiles, during 1988 and as a function of altitude, are described here. These profiles are compared with those from the Stratospheric Aerosol and Gas Experiment satellite instrument made within a radius of 1000 km from the lidar and also with the zonal mean measurements made in the band 34.4 +/- 5 deg. Comparison with the proposed new CIRA ozone reference model has also been carried out. The seasonal variations, between 25 and 50 km, observed by the two instruments and indicated by the reference model are in good agreement.

Mcdermid, I. Stuart↗
NASA NTRS1992

Lidar Observations of Polar Stratospheric Clouds and Stratospheric Temperatures at the South Pole

Polar stratospheric clouds (PSC's) play a crucial role in the ozone chemistry of the polar regions. Current chemical models rely on the presence of these clouds to explain the rapid destruction of ozone observed each spring in Antarctica. We present lidar observations of PCS's and stratospheric temperatures at the South Pole throughout the Antarctic winter and spring of 1990.

Collins, Richard L.↗
NASA NTRS1992

A comparison of Nimbus 7 limb infrared monitor of the stratosphere and radiosonde temperatures in the lower stratosphere poleward of 60N

The quality of the more widely used, mapped version of the LIMS temperature data set (LAMAT) is assessed for the polar lower stratosphere by comparison with lower stratospheric radiosonde (RAOB) temperatures at a set of 22 stations. Average LIMS minus uncorrected RAOB values are within +/-0.3 K at 30, 50, and 70 hPa, and -1.2 +/-2.2 K at 100 hPa. The generally excellent LIMS/RAOB temperature comparisons at 10 to 70 hPa support the contention that there are no significant temperature bias errors in the LIMS constituent distributions for polar regions. LIMS minus RAOB differences at 100 hPa are slightly negative for the present station set, in agreement with that found by Grose et al. (1988). The month-by-month LIMS minus RAOB analysis at 100 hPa showed that LIMS is -1.9 +/-1.8 K too cold in November and December.

Remsberg, Ellis E.↗
NASA NTRS1994

Polar stratospheric cloud climatology based on Stratospheric Aerosol Measurement II observations from 1978 to 1989

The probability of polar stratospheric cloud (PSC) occurrence in the Antarctic and Arctic has been estimated using Stratospheric Aerosol Measurement (SAM) II aerosol extinction data from 1978 to 1989. Antarctic PSCs are typically observed by SAM II from mid-May to early November, with a maximum zonal average probability of about 0.6 at 18-20 km in August. The typical Arctic PSC season extends only from late November to early March, with a peak zonal average probability of about 0.1 in early February at 20-22 km. There is considerable year-to-year variability in Arctic PSC sightings because of changes in the dynamics of the northern polar vortex. Year-to-year variability in Antarctic sightings is most prominent in the number of late season clouds. Maximum PSC sighting probabilities in both polar regions occur in the region from 90 deg W through the Greenwich meridian to 90 deg E, where temperatures are coldest on average. Arctic sighting probabilities approach zero outside this region, but clouds have been sighted in the Antarctic at all longitudes during most months. Inferred PSC formation temperatures remain constant throughout the Arctic winter and are similar to those in early Antarctic winter. PSC formation temperatures in the Antarctic drop markedly in the 15 to 20-km region by September, a pattern consistent with the irreversible loss of HNO3 and H2O vapor in sedimenting PSC particles.

Poole, Lamont R.↗
NASA NTRS1977

Monte Carlo analysis of uncertainty propagation in a stratospheric model. 1: Development of a concise stratospheric model

A concise model has been developed to analyze uncertainties in stratospheric perturbations, yet uses a minimum of computer time and is complete enough to represent the results of more complex models. The steady state model applies iteration to achieve coupling between interacting species. The species are determined from diffusion equations with appropriate sources and sinks. Diurnal effects due to chlorine nitrate formation are accounted for by analytic approximation. The model has been used to evaluate steady state perturbations due to injections of chlorine and NO(X).

Rundel, R. D.↗
NASA NTRS1978

Uncertainty propagation in a stratospheric model. I - Development of a concise stratospheric model. II - Monte Carlo analysis of imprecisions due to reaction rates

The paper discusses the development of a concise stratospheric model which uses iteration to obtain coupling between interacting species. The one-dimensional, steady-state, diurnally-averaged model generates diffusion equations with appropriate sources and sinks for species odd oxygen, H2O, H2, CO, N2O, odd nitrogen, CH4, CH3Cl, CCl4, CF2Cl2, CFCl3, and odd chlorine. The model evaluates steady-state perturbations caused by injections of chlorine and NO(x) and may be used to predict ozone depletion. The model is used in a Monte Carlo study of the propagation of reaction-rate imprecisions by calculating an ozone perturbation caused by the addition of chlorine. Since the model is sensitive to only 10 of the more than 50 reaction rates considered, only about 1000 Monte Carlo cases are required to span the space of possible results.

Rundel, R. D.↗