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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Flight tests of a range-resolved airborne dial with two min-tea CO2 lasers

It is important to measure regional distributions of ozone concentrations in a short time for understanding a mechanism of photo-chemical smog development. An airborne Differential Absorption Lidar (DIAL) system with two low-power mini-TEA CO2 lasers was developed for measuring three-dimensional distributions of ozone in the lower troposphere. The CO2 DIAL is a nadir-looking system and is designed to measure ozone profiles between ground and airplane by using atmospheric aerosols as a distributed radar target. First flight test with a single laser were conducted in February 1985 over the Tokyo area. The system was operated at an altitude of 5000 ft. Results of the first flight tests show that the height profiles of the received power in the boundary layer were different between over land and ocean. The received power has to be inverted to an expression of a single optical parameter to see real aerosol distributions. Inversion of the lidar signal to the aerosol extinction was performed by using Klett's solution.

Itabe, T.↗
NASA NTRS1986

Aerosol sampling for the August 7th, and 9th, 1985 SAGE II validation experiment

Comparisons are made between aerosol size distributions measured by instrumented aircraft and the SAGE II sensor on the ERB satellite performing limb scans of the same atmospheric region. Particle radii ranging from 0.0001-200 microns were detected, with good agreement being obtained between the size distributions detected by impactors and probes at radii over 0.15 micron. The distributions were used to calculate aerosol extinction values which were compared with values from SAGE II scans.

Oberbeck, V. R.↗
NASA NTRS1988

SAM 2 data user's guide

This document is intended to serve as a guide to the use of the data products from the Stratospheric Aerosol Measurement (SAM) 2 experiment for scientific investigations of polar stratospheric aerosols. Included is a detailed description of the Beta and Aerosol Number Density Archive Tape (BANAT), which is the SAM 2 data product containing the aerosol extinction data available for these investigations. Also included are brief descriptions of the instrument operation, data collection, processing and validation, and some of the scientific analyses conducted to date.

Chu, W. P.↗
NASA NTRS1987

Background stratospheric aerosol reference model

Nearly global SAGE I satellite observations in the nonvolcanic period from March 1979 to February 1980 are used to produce a reference background stratospheric aerosol optical model. Zonally average profiles of the 1.0-micron aerosol extinction for the tropics, midlatitudes, and high latitudes for both hemispheres are given in graphical and tabulated form for the different seasons. A third order polynomial fit to the vertical profile data set is used to derive analytic expressions for the seasonal global means and the yearly global mean. The results have application to the simulation of atmospheric radiative transfer and radiance calculations in atmospheric remote sensing.

Mccormick, M. P.↗
NASA NTRS1988

Comparison of in situ aerosol measurements with SAGE 2 and SAM 2 aerosol measurements during the airborne Antarctic ozone experiment

Models indicate that stratospheric aerosols play a major role in the destruction of ozone during the Austral winter. Although many in situ measurements of stratospheric aerosols were made during the Airborne Antarctic Ozone Experiment, changes of aerosol concentration and size distributions across the polar vortex are important to understanding changes of chemical species taking place during this time. Therefore comparing the in situ measurements with measurements made by satellites scanning wider areas will give a clearer picture of the possible role played by aerosols during this period. The wire impactor size distributions are compared to those from the aerosol spectrometers and a best fit size distribution determined. Aerosol extinctions are calculated from the in situ measurements and compared to the extinctions measured by the satellites. Five comparisons are made with SAGE 2 and four with SAM 2. Extinctions agree as close as a factor of two.

Ferry, G. V.↗
NASA NTRS1989

Aerosol backscatter profile derived from SAGE II and lidar observations

This paper examines the stratospheric aerosol measurements made on September 16, 1986 by the SAGE II satellite instrument and the 48-inch lidar system of the NASA/Langley Research Center at Hampton, Virginia. The results of the analysis show an excellent agreement between the aerosol backscatter profile calculated from the SAGE II multiwavelength aerosol extinctions and the 48-inch lidar observations in the lower stratosphere between altitudes 17 km - 29 km.

Wang, Pi-Huan↗
NASA NTRS1989

SAGE II aerosol data validation - Comparative studies of SAGE II and SAM II data sets

Data from the Stratospheric Aerosol and Gas Experiment (SAGE II) satellite are compared with data from the Stratospheric Aerosol Measurement (SAM II) satellite. Both experiments produce aerosol extinction profiles by measuring the attenuation of solar radiation during each sunrise and sunset observed by the satelltie. The SAGE II obtains profiles at 1.02 microns and three smaller wavelengths, whereas the SAM II measures at only one radiometric channel at 1.0 microns. It is found that the differences between the two sets of data are generally within the error bars associated with each measurement. In addition, the sunrise and sunset data from SAGE II are analyzed.

Yue, G. K.↗
NASA NTRS1989

SAGE II aerosol data validation based on retrieved aerosol model size distribution from SAGE II aerosol measurements

Consideration is given to aerosol correlative measurements experiments for the Stratospheric Aerosol and Gas Experiment (SAGE) II, conducted between November 1984 and July 1986. The correlative measurements were taken with an impactor/laser probe, a dustsonde, and an airborne 36-cm lidar system. The primary aerosol quantities measured by the ground-based instruments are compared with those calculated from the aerosol size distributions from SAGE II aerosol extinction measurements. Good agreement is found between the two sets of measurements.

Wang, Pi-Huan↗
NASA NTRS1989

Persistence of polar stratospheric clouds in the southern polar region

Observations of Antarctic polar stratospheric clouds (PSCs) were examined using the 1-micron aerosol extinction ratio data from the SAM II satellite experiment for the years 1979-1982 and 1984-1987. PSCs were sighted between 10 and 25 km and were usually first observed by mid-June. Clouds disappeared earlier at higher altitudes (late August near 24 km, in most cases) and later at lower altitudes (late September or October near 16 km). It was found that PSCs persisted longer in 1985 and 1987 at 18 km and were more frequently observed in September and October 1987 than the other years. Inference of likely PSC formation regions from National Meteorological Center temperature data indicated that clouds would begin forming in late May and usually disappear in September. This analysis confirmed the persistence of colder conditions during the spring of 1987.

Mccormick, M. P.↗
NASA NTRS1991

A determination of the infrared optical depth of the El Chichon volcanic cloud

Infrared transmission spectra of the atmosphere above 11-km altitude were obtained in December 1982 and April/May 1983 from a NASA Convair 990 aircraft. The observations on the first flight series encompassed low and middle latitudes in the Northern Hemisphere, while the observations on the second series covered a wide range of latitudes in both hemispheres. These data have been analyzed to derive the optical depth of the El Chichon volcanic cloud at a wavelength of 8.4 microns. These data imply that concentrated sulfuric acid was the dominant source of aerosol extinction in the 8- to 12-microns window region of the earth's atmosphere and that the volume modal particle radius equalled 0.6 + or - 0.1 mu at the time of the observations. At these times, the volcanic particles produced a significant warming of the lower stratosphere and had a nontrivial impact on the radiation budget of the troposphere and ground in the Northern Hemisphere.

Pollack, James B.↗
NASA NTRS1992

SAGE 1 data user's guide

A guide for using the data products from the Stratospheric Aerosol and Gas Experiment 1 (SAGE 1) for scientific investigations of stratospheric chemistry related to aerosol, ozone, nitrogen dioxide, dynamics, and climate change is presented. A detailed description of the aerosol profile tape, the ozone profile tape, and the nitrogen dioxide profile tape is included. These tapes are the SAGE 1 data products containing aerosol extinction data and ozone and nitrogen dioxide concentration data for use in the different scientific investigations. Brief descriptions of the instrument operation, data collection, processing, and validation, and some of the scientific analyses that were conducted are also included.

Mcmaster, Leonard R.↗
NASA NTRS1992

Climate forcing by stratospheric aerosols

It is illustrated how climate forcing by stratospheric aerosols depends on aerosol properties. The climate forcing is a function of aerosols size distribution, but the size dependence can be described well by a single parameter: the area-weighted mean radius, r(eff). If r(eff) is greater than about 2 microns, the global average greenhouse effect of the aerosols exceeds the albedo effect, causing a surface heating. The aerosol climate forcing is less sensitive to other characteristics of the size distribution, the aerosol composition, and the altitude of the aerosols. Thus stratospheric aerosol forcing can be defined accurately from measurements of aerosol extinction over a broad wavelength range.

Lacis, Andrew↗
NASA NTRS1993

The Halogen Occultation Experiment

The Halogen Occultation Experiment (HALOE) uses solar occultation to measure vertical profiles of O3, HCl, HF, CH4, H2O, NO, NO2, aerosol extinction, and temperature versus pressure with an instantaneous vertical field of view of 1.6 km at the earth limb. Latitudinal coverage is from 80 deg S to 80 deg N over the course of 1 year and includes extensive observations of the Antarctic region during spring. The altitude range of the measurements extends from about 15 km to about 60-130 km, depending on channel. Experiment operations have been essentially flawless, and all performance criteria either meet or exceed specifications. Internal data consistency checks, comparisons with correlative measurements, and qualitative comparisons with 1985 atmospheric trace molecule spectroscopy (ATMOS) results are in good agreement. Examples of pressure versus latitude cross sections and a global orthographic projection for the September 21 to October 15, 1992, period show the utility of CH4, HF, and H2O as tracers, the occurrence of dehydration in the Antarctic lower stratosphere, the presence of the water vapor hygropause in the tropics, evidence of Antarctic air in the tropics, the influence of Hadley tropical upwelling, and the first global distribution of HCl, HF, and NO throughout the stratosphere. Nitric oxide measurements extend through the lower thermosphere.

Russell, James M., III↗
NASA NTRS1994

Observations of lower-stratospheric ClONO2, HNO3, and aerosol by the UARS CLAES experiment between January 1992 and April 1993

This paper discusses simultaneous measurements of stratospheric ClONO2, HNO3, temperature, and aerosol extinction coefficient by the Cryogenic Limb Array Etalon Spectrometer (CLAES) on the NASA Upper Atmosphere Research Satellite (UARS), obtained over the period 9 January 1992 through 23 April 1993. The discussion concentrates on the stratosphere region near 21 km of particular interest to heterogeneously driven ozone depletion. For periods between 12 June and 1 September 1992 at latitudes poleward of about 60 deg S, when temperatures were below type I polar stratospheric cloud (PSC) formation thresholds throughout the lower stratosphere, CLAES observed high levels of PSCs coincident with highly depleted fields of both HNO3 and ClONO2. By 17 September, the incidence of PSCs had greatly diminished in the lower stratosphere, but both CLONO2 and HNO3 remained highly depleted. These observations are consistent with the removal of gaseous HNO3 through the formation of nitric acid trihydrate (NAT) particles and the removal of ClONO2 through heterogeneous reactions on the particle surfaces. They also suggest substantial denitrification of the lower Antarctic vortex through sedimentation of PSC particles. In the Northern Hemisphere winter of 1992/93 far fewer PSCs were observed in the Arctic lower-stratosphere vortex, which had shorter periods and more localized regions of cold temperatures. Both HNO3 and ClONO2 maintained much higher levels inside the Arctic vortex than seen in the Antarctic throughout the winter/spring period. Following 28 February 1993 when Arctic vortex temperatures rose above 195 K, ClONO2 was observed in large quantities (greater than 2.1 ppbv near 21 km) inside the vortex. The persistence of relatively high levels of HNO3 inside the Arctic spring vortex compared with the low levels seen in the Antarctic spring vortex suggest a much lower level of denitrification in the Arctic.

Roche, A. E.↗
NASA NTRS1994

Incorporation of multiple cloud layers for ultraviolet radiation modeling studies

Cloud data sets compiled from surface observations were used to develop an algorithm for incorporating multiple cloud layers into a multiple-scattering radiative transfer model. Aerosol extinction and ozone data sets were also incorporated to estimate the seasonally averaged ultraviolet (UV) flux reaching the surface of the Earth in the Detroit, Michigan, region for the years 1979-1991, corresponding to Total Ozone Mapping Spectrometer (TOMS) version 6 ozone observations. The calculated UV spectrum was convolved with an erythema action spectrum to estimate the effective biological exposure for erythema. Calculations show that decreasing the total column density of ozone by 1% leads to an increase in erythemal exposure by approximately 1.1-1.3%, in good agreement with previous studies. A comparison of the UV radiation budget at the surface between a single cloud layer method and a multiple cloud layer method presented here is discussed, along with limitations of each technique. With improved parameterization of cloud properties, and as knowledge of biological effects of UV exposure increase, inclusion of multiple cloud layers may be important in accurately determining the biologically effective UV budget at the surface of the Earth.

Charache, Darryl H.↗
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 NTRS1994

Indices of refraction for the HITRAN compilation

Indices of refraction of sulfuric acid solutions, water, and ice, which will become part of the HITRAN database, are discussed. Representative calculations are presented for the sulfate aerosol, to illustrate the broadband spectral features of i.r. aerosol extinction spectra. Values of the sulfuric acid mass density are used in an application of the Lorentz-Lorenz equation, which is used to estimate the sensitivity of extinction coefficients to temperature dependent refractive indices.

Massie, S. T.↗
NASA NTRS1998

Validation of Saharan Dust Layer Characteristics with Lidar Observations

Lidar backscattering profiles available from the LITE data set have been used to estimate the optical depths of the Saharan dust layer over West Africa and E. Atlantic regions, in the context of validating the 3-D conceptual model of the Saharan dust plume proposed by Karyampudi and Carlson. The aerosol extinction profiles and optical depths were retrieved from LITE using the Fernald et al. (1972) method. An extinction-to-backscattering ratio, S(sub a), of 25 was selected for optical depth calculations. The spatial analysis of total column and Saharan dust layer optical depths show higher optical depths over W. Africa that decrease westward over E. Atlantic. The higher optical depths over W. Africa, in general, are associated with heavy dust being raised from the surface in dust source regions. Rapid depletion of these heavy dust particles, perhaps due to sedimentation, appear to decrease the dust loading within the dust layer as the plume leaves the west African continent. Higher optical depths are generally confined to the southern edge of the dust layer, where the middle level jet appears to transport the heavy dust concentrations that tend to mix downward from vertical mixing associated with the strong vertical shears underneath the middle jet. Thus, LITE measurements although, in general, validate the Saharan dust plume conceptual model, show maximum values of optical depths near the southern edge of the dust plume over the E. Atlantic region instead of near the center of the dust plume as described in the conceptual model.

Karyampudi, V. Mohan↗