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Browell, Edward V.

Publications and source records attributed to Browell, Edward V..

At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Airborne lidar measurements of ozone and aerosols in the summertime Arctic troposphere

Ozone (O3) and aerosol distributions were remotely measured from an aircraft using a differential absorption lidar (DIAL) system as part of the 1988 NASA Global Tropospheric Experiment - Arctic Boundary Layer Experiment (ABLE-3A). The airborne DIAL system made simultaneous measurements of O3 and aerosols from the surface to above the tropopause. These measurements were made in a broad range of atmospheric conditions over the tundra, ice, and ocean regions near Barrow and Bethel, Alaska, during July and August 1988. The tropospheric composition over the Arctic was found to be strongly influenced by stratospheric intrusions. Regions of low aerosol scattering and enhanced O3 mixing ratios were usually correlated with descending air from the upper troposphere or lower stratosphere. Several cases of enhanced O3 were observed during ABLE-3A in conjunction with enhanced aerosol layers in the free troposphere resulting from biomass burning. As was found in the Amazon, the products of biomass burning can significantly alter O3 concentrations in the troposphere. This paper describes the NASA airborne DIAL system and discusses the large-scale variations of O3 and aerosols observed with the airborne DIAL system during ABLE-3A.

Browell, Edward V.↗
NASA NTRS1991

Airborne lidar observations of ozone and aerosols in the wintertime Arctic stratosphere

The procedures used in making the lidar measurements of O3 and aerosols are discussed, and selected data samples of O3 and aerosol distributions observed during flights between Stavanger (59 deg N, 3 deg E) and the North Pole between about 40 deg W and 20 deg E meridians are presented. The 'on' and 'off'; laser wavelengths used for the DIAL measurements during the Airborne Arctic Stratospheric Expedition (AASE) were 301.5 and 311 nm, respectively. An intercomparison between airborne DIAL and ozonesonde measurements of O3 in the vicinity of Bear Island is shown. The DIAL profiles were obtained by averaging the lidar returns over a 5-min period and then calculating the DIAL O3 profile. Lidar measurements at 603 and 1064 nm are used to infer physical characteristics of the different types of aerosols observed during the AASE.

Browell, Edward V.↗
NASA NTRS1990

Ozone and aerosol distributions over the Amazon Basin during the wet season

Results are presented of O3 and aerosol measurements made in the lower troposphere from April 13 through May 10, 1987, as part of the wet season field experiment. Aircraft flights on the NASA Electra were conducted in the vicinity of Manaus, Brazil and between Manaus and the mouth of the Amazon River. Airborne O3 measurements were made in situ and with a lidar system pointed below the aircraft in nadir mode of operation. Data collection and results concerning the distributions of O3 and aerosols observed during the wet season from within the mixed layer to the middle troposphere over the central Amazon basin and between Manaus and Belem are discussed, and these observations are compared to the measurements obtained in the 1985 dry season. Ozone mixing ratio values are found to be lower than those of the 1985 dry season by 6-8 ppbv, indicating a strong removal process near the surface during wet season. It is also found that within the mixed layer O3 levels appeared to be lower over the forest compared to over the ocean.

Browell, Edward V.↗
NASA NTRS1990

Amazon Basin ozone and aerosol - Wet season observations

The ozone and aerosol number density data obtained from aircraft flights over the Amazon Basin (AB) during April and May of 1987 are summarized with particular attention given to the general characteristics of ozone and aerosol for wet season (WS), compared to dry season (DS), meteorology. It is concluded that the AB provides favorable conditions for the production of hydroxyl radical and subsequent chemical and photochemical reactions which generate or consume key atmospheric trace species. It is determined that a negative ozone gradient exists within the mixed layer (ML). WSML ozone is about 7 ppbv lower than that of DS. The net sink characteristics of the WSML are seen throughout the troposphere of the AB in that the ozone at 3-4 km altitude is typically 15-25 ppbv as compared to DS values of 30-35 ppbv. In terms of aerosol source characteristics of the AB, ML aerosols are 5-10 times higher than observed in the troposphere with ML values of 100-200 aerosols/cu cm. An analysis of aerosol size distribution data is presented.

Gregory, Gerald L.↗
NASA NTRS1990

Ozone measurements in Amazonia - Dry season versus wet season

Recent ozone measurements taken in the Amazonian rain forest environment during the wet season (April-May 1987) are described, revealling new aspects of the regional atmospheric chemistry. The measurements were part of the Amazon Boundary Layer Experiment (ABLE 2B) mission and utilized UV absorption as a measurement technique to obtain surface ozone data; 20 ozonesondes were launched in order to obtain vertical ozone profiles used to describe the upper troposphere and stratosphere. The major differences in comparison to a previous dry season experiment, which found ozone concentrations to be lower in the whole troposphere by nearly a factor of 2, are stressed.

Kirchhoff, V. W. J. H.↗
NASA NTRS1990

Cloud draft structure and trace gas transport

During the second Amazon Boundary Layer Experiment (ABLE 2B), meteorological observations, chemical measurements, and model simulations are utilized in order to interpret convective cloud draft structure and to analyze its role in transport and vertical distribution of trace gases. One-dimensional photochemical model results suggest that the observed poststorm changes in ozone concentration can be attributed to convective transports rather than photochemical production and the results of a two-dimensional time-dependent cloud model simulation are presented for the May 6, 1987 squall system. The mesoscale convective system exhibited evidence of significant midlevel detrainment in addition to transports to anvil heights. Chemical measurements of O3 and CO obtained in the convective environment are used to predict photochemical production within the troposphere and to corroborate the cloud model results.

Scala, John R.↗
NASA NTRS1990

Lidar instruments proposed for Eos

Lidar, an acronym for light detection and ranging, represents a class of instruments that utilize lasers to send probe beams into the atmosphere or onto the surface of the Earth and detect the backscattered return in order to measure properties of the atmosphere or surface. The associated technology has matured to the point where two lidar facilities, Geodynamics Laser Ranging System (GLRS), and Laser Atmospheric Wind Sensor (LAWS) were accepted for Phase 2 studies for Eos. A third lidar facility Laser Atmospheric Sounder and Altimeter (LASA), with the lidar experiment EAGLE (Eos Atmospheric Global Lidar Experiment) was proposed for Eos. The generic lidar system has a number of components. They include controlling electronics, laser transmitters, collimating optics, a receiving telescope, spectral filters, detectors, signal chain electronics, and a data system. Lidar systems that measure atmospheric constituents or meteorological parameters record the signal versus time as the beam propagates through the atmosphere. The backscatter arises from molecular (Rayleigh) and aerosol (Mie) scattering, while attenuation arises from molecular and aerosol scattering and absorption. Lidar systems that measure distance to the Earth's surface or retroreflectors in a ranging mode record signals with high temporal resolution over a short time period. The overall characteristics and measurements objectives of the three lidar systems proposed for Eos are given.

Grant, William B.↗
NASA NTRS1990

Optimization of the alexandrite laser tuning elements for a water vapor lidar

An overview of some of the developments completed on an alexandrite laser for making water vapor DIAL measurements is presented in this paper. A computer control for active stabilization of the two intracavity etalons has been implemented and recently tested in an aircraft environment. Long-term frequency drift (i.e., 2 hours) of less than 0.7 pm has been observed in the laboratory. An alignment technique to get the optimum free spectral range ratio for the two etalons is also developed.

Ponsardin, Patrick↗
NASA NTRS1990

Airborne water vapor DIAL system development

A differential absorption lidar (DIAL) system developed at NASA Langley Research Center for the remote measurement of atmospheric H2O and aerosols from an aircraft is briefly discussed. This DIAL system utilizes a Nd:YAG laser-pumped dye laser as the off-line transmitter and a narrowband, tunable Alexandrite laser as the on-line transmitter. A 1-m monochromator and a multipass absorption cell are used to position the on-line laser to the center of the H2O line. The receiver system has a 14-in. diameter, f/7 Celestron telescope to collect the backscattered laser light and focus in into the detector optics. Return signals are converted to electrical signals by the optical detector and are digitalized and stored on magnetic tape. The results of fligh tests of the system are shown.

Higdon, Noah S.↗
NASA NTRS1990

Airborne lidar stratospheric ozone and aerosol investigations

The objectives are to study the distribution of ozone (O3) and aerosols across the polar regions during the winter and spring periods and to relate these observations to chemical and dynamical processes that can contribute to the chemical perturbation of the polar stratosphere and the possible destruction of O3. The distribution and characteristics of stratospheric aerosols and polar stratospheric clouds (PSCs) are required to understand heterogeneous chemical processes that can lead to O3 depletion, and observation of O3 variations are important in the direct detection of O3 depletion and in tracing atmospheric dynamics. An airborne Differential Absorption Lidar (DIAL) system is operated in a zenith mode from the NASA DC-8 aircraft to obtain data on the large scale spatial variability of O3, and aerosol/PSC's in the lower stratosphere from about 11 to 23 km for O3, and 11 to 28 km for aerosols. The variability of O3 and aerosols/PSCs is studied in relation to chemical processes that can produce O3 depletion and to dynamics in the lower stratosphere that transport gases and aerosols inside the vortex and in some cases, across the edge of the vortex.

Browell, Edward V.↗
NASA NTRS1989

Water-vapor line broadening and shifting by air, nitrogen, oxygen, and argon in the 720-nm wavelength region

High-resolution spectroscopic measurements of H2O vapor in the 720-nm wavelength region were conducted to investigate the broadening and shifting of H2O lines by air, nitrogen, oxygen, and argon over a wide range of pressures and temperatures. For each of the buffer gases under study, a linear relationship was found between the widths and the shifts, with the broader lines having the smaller pressure shifts. The pressure shifts measured compared favorably with theoretical values reported by Bykov et al. (1988). The temperature-dependence exponents for air-broadening were found to be J-dependent, with the lower-J lines having the higher exponents.

Grossmann, Benoist E.↗
NASA NTRS1989

Airborne and spaceborne lidar measurements of water vapor profiles - A sensitivity analysis

This paper presents an evaluation of the random and systematic error sources associated with differential absorption lidar (DIAL) measurements of tropospheric water vapor profiles from airborne and spaceborne platforms. The results of this analysis are used in the development and performance evaluation of the Lidar Atmospheric Sensing Experiment (LASE) H2O DIAL system presently under development at the NASA Langley Research Center for operation on a high altitude ER-2 aircraft. The analysis shows that a less than 10-percent H2O profile measurement accuracy is possible for the LASE system with a vertical and horizontal resolution of 200 m and 10 km, respectively, at night and 300 m and 20 km during the day. Global measurements of H2O profiles from spaceborne DIAL systems can be made to a similar accuracy with a vertical resolution of 500 m and a horizontal resolution of 100 km.

Ismail, Syed↗
NASA NTRS1989

Light scattering characteristics of various aerosol types derived from multiple wavelength lidar observations

The present study demonstrates the potential of a multiple-wavelength lidar for discriminating between several aerosol types on the basis of the wavelength dependence of the aerosol backscatter coefficient. The two-component lidar equation was solved under the assumption of similarity in the derived profiles of backscatter coefficients for each wavelength. It is shown that a three-wavelength lidar system operating at 300, 600, and 1064nm can provide unique information for discriminating between various aerosol types (continental, maritime, Saharan-dust, stratospheric aerosols in a tropopause fold event, and tropical forest aerosols). Mie calculations were made using in situ aerosol data and aerosol models to compare with the lidar results. The disagreement between the theoretical and empirical results in some cases was substantial. These differences may be partly due to uncertainties in the lidar data analysis and aerosol characteristics and also due to the conventional assumption of aerosol sphericity for the aerosol Mie calculations.

Sasano, Yasuhiro↗
NASA NTRS1989

Differential absorption lidar sensing of ozone

The differential absorption lidar (DIAL) technique for deriving O3 profiles from lidar measurements is discussed. The NASA airborne DIAL system is described, and examples of a broad range of O3 and aerosol measurements are presented from a number of field experiments. These airborne and ground-based DIAL measurements demonstrate the outstanding capability of lidar for conducting O3 investigations throughout the troposphere and lower stratosphere under widely different atmospheric conditions.

Browell, Edward V.↗
NASA NTRS1988

Large-scale variations in ozone and polar stratospheric clouds measured with airborne lidar during formation of the 1987 ozone hole over Antarctica

A joint field experiment between NASA and NOAA was conducted during August to September 1987 to obtain in situ and remote measurements of key gases and aerosols from aircraft platforms during the formation of the ozone (O3) hole over Antarctica. The ER-2 (advanced U-2) and DC-8 aircraft from the NASA Ames Research Center were used in this field experiment. The NASA Langley Research Center's airborne differential absorption lidar (DIAL) system was operated from the DC-8 to obtain profiles of O3 and polar stratospheric clouds in the lower stratosphere during long-range flights over Antarctica from August 28 to September 29, 1987. The airborne DIAL system was configured to transmit simultaneously four laser wavelengths (301, 311, 622, and 1064 nm) above the DC-8 for DIAL measurements of O3 profiles between 11 to 20 km ASL (geometric altitude above sea level) and multiple wavelength aerosol backscatter measurements between 11 to 24 km ASL. A total of 13 DC-8 flights were made over Antarctica with 2 flights reaching the South Pole. Polar stratospheric clouds (PSC's) were detected in multiple thin layers in the 11 to 21 km ASL altitude range with each layer having a typical thickness of less than 1 km. Two types of PSC's were found based on aerosol backscattering ratios: predominantly water ice clouds (type 2) and clouds with scattering characteristics consistent with binary solid nitric acid/water clouds (type 1). Large-scale cross sections of O3 distributions were obtained. The data provides additional information about a potentially important transport mechanism that may influence the O3 budget inside the vortex. There is also some evidence that strong low pressure systems in the troposphere are associated with regions of lower stratospheric O3. This paper discusses the spatial and temporal variations of O3 inside and outside the polar vortex region during the development of the O3 hole and relates these data to other measurements obtained during this field experiment.

Browell, Edward V.↗