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At least 1,297 records · Page 72
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

The role of isoprene oxidation in the tropospheric ozone budget in the tropics

A comprehensive chemical mechanism for the oxidation of isoprene (a hydrocarbon, C5H8 emitted primarily by vegetation) by OH and O3 in the troposphere was developed and incorporated into a one-dimensional steady-state photochemical model of the troposphere. Flux boundary conditions for NOx (NO + NO2), HNO3, O3, and CO were used to investigate the changes produced in the tropospheric concentrations and integrated column of ozone from including isoprene chemistry in the model. Two calculations were performed at 15 deg N latitude for annual conditions using identical flux boundary conditions for NOx, HNO3, O3, and CO; in one calculation, the chemistry describing isoprene oxidation was included while in the other it was not. Both sets of calculations included reactions describing the chemistry of anthropogenic nonmethane hydrocarbons. The calculations showed decreases in concentrations of ozone throughout the troposphere when isoprene chemistry was included. Concentrations of NOx and HNO3 increased in the lower troposphere and decreased in the upper troposphere while concentrations of CO and PAN increased throughout the troposphere when isoprene chemistry was included. Implications of this study to the budgets of these species in the tropics is discussed.

Brewer, D. A.↗
NASA NTRS1986

Continuous wind measurement in the tropical Pacific using VHF radars

Very High Frequency (VHF) Radar Wind Profilers are being installed on Ponape, East Caroline Islands and Christmas Island, Republic of Kiribati to continuously monitor winds aloft. The purpose of this experiment is to study wind fluctuations on time scales between minutes and days, to determine the longitudinal character of these fluctuations, and to examine their relationship to climate variability. Six-hourly wind profiles will be provided via satellite to the scientific community for Project TOGA (Tropical Ocean Global Atmosphere).

Balsley, B. B.↗
NASA NTRS1986

Canopy reflectance modeling in a tropical wooded grassland

Geometric/optical canopy reflectance modeling and spatial/spectral pattern recognition are used to study the form and structure of savanna in West Africa. An invertible plant canopy reflectance model is tested for its ability to estimate the amount of woody vegetation cover in areas of sparsely wooded grassland from remotely sensed data. Dry woodlands and wooded grasslands, commonly referred to as savannas, are important ecologically and economically in Africa, and cover approximately forty percent of the continent by some estimates. The Sahelian and Sudanian savanna make up the important and sensitive transition zone between the tropical forests and the arid Saharan region. The depletion of woody cover, used for fodder and fuel in these regions, has become a very severe problem for the people living there. LANDSAT Thematic Mapper (TM) data is used to stratify woodland and wooded grassland into areas of relatively homogeneous canopy cover, and then by applying an invertible forest canopy reflectance model to estimate directly the height and spacing of the trees in the stands. Since height and spacing are proportional to biomass in some cases, a successful application of the segmentation/modeling techniques will allow direct estimation of woody biomass, as well as cover density, over significant areas of these valuable and sensitive ecosystems. Sahelian savanna sites in the Gourma area of Mali being used by the NASA/GIMMS project (Global Inventory Modeling and Monitoring System, at Goddard Space Flight Center), in conjunction with CIPEA/Mali (Centre International pour l'Elevage en Afrique) will be used for testing the canopy model. The model will also be tested in a Sudanian zone crop/woodland area in the Region of Segou, Mali.

Simonett, D.↗
NASA NTRS1986

Canopy reflectance modeling in a tropical wooded grassland

Geometric/optical canopy reflectance modeling and spatial/spectral pattern recognition is used to study the form and structure of savanna in West Africa. An invertible plant canopy reflectance model is tested for its ability to estimate the amount of woody vegetation from remotely sensed data in areas of sparsely wooded grassland. Dry woodlands and wooded grasslands, commonly referred to as savannas, are important ecologically and economically in Africa, and cover approximately forty percent of the continent by some estimates. The Sahel and Sudan savannas make up the important and sensitive transition zone between the tropical forests and the arid Sahara region. The depletion of woody cover, used for fodder and fuel in these regions, has become a very severe problem for the people living there. LANDSAT Thematic Mapper (TM) data is used to stratify woodland and wooded grassland into areas of relatively homogeneous canopy cover, and then an invertible forest canopy reflectance model is applied to estimate directly the height and spacing of the trees in the stands. Because height and spacing are proportional to biomass in some cases, a successful application of the segmentation/modeling techniques will allow direct estimation of tree biomass, as well as cover density, over significant areas of these valuable and sensitive ecosystems. The model being tested in sites in two different bioclimatic zones in Mali, West Africa, will be used for testing the canopy model. Sudanian zone crop/woodland test sites were located in the Region of Segou, Mali.

Simonett, David↗
NASA NTRS1986

The vertical structure of Jupiter's equatorial and tropical regions

The equatorial and tropical regions of Jupiter are presently treated in light of an inhomogeneous atmospheric model that encompasses both polarizing aerosols and methane gas, in keeping with Pioneer polarimetry and photometry data as well as the methane band data obtained by West (1979). The relative strengths of weak and strong methane bands are addressed by a two-cloud model with overlying stratospheric haze. For all the regions considered, the best fit for polarization measurements is a negatively polarizing ammonia cloud beneath a positively polarizing haze. Unlike the nearby features, the equatorial region and the Great Red Spot have a negative polarization at 80-deg phase angle, implying less gas above the clouds in these regions.

Smith, P. H.↗
NASA NTRS1986

Study of the ammonia ice cloud layer in the north tropical zone of Jupiter from the infrared interferometric experiment on Voyager

An average of 51 Voyager 1 IRIS spectra of Jupiter's North Tropical Zone was analyzed to infer the abundance, vertical extent, and size distribution of the particles making up the ammonia cloud in this region. It is assumed that the cloud base coincides with the level at which 100% saturation of ammonia vapor occurs. The vertical distribution of particulates above this level is determined by assuming a constant total ammonia mixing ratio and adjusting the two phases so that the vapor is saturated throughout the cloud. A constant scaling factor then adjusts the base number density. A radiative transfer program is used that includes the effects of absorption and emission of all relevant gases as well as anisotropic scattering by cloud particles. Mie scattering from a gaussian particle size distribution is assumed. The vertical thermal structure is inferred from a temperature retrieval program that utilizes the collision induced S(0) and S(1) molecular hydrogen lines between 300 and 700.cm, and the 1304.cm methane band.

Shaffer, William A.↗
NASA NTRS1986

Monitoring and predicting tropical cyclone movement using geosynchronous satellite remote sensing techniques

Data collected on special hurricane days by the VISSR Atmospheric Sounder (VAS) instrument flown on a satellite in 1981 and 1982 were studied for their usefulness in forecasting motion of hurricanes. The retrieved constant pressure heights for the 500-mb surface provided the basis for reasonable forecasts of 24 hour hurricane motion. The conclusions are illustrated with examples from Hurricane Harvey (1981) and Hurricane Irene (1981). Recommendations are made for future use of the VAS type instruments for tropical cyclone forecasting.

Dubach, L.↗
NASA NTRS1986

Air chemistry over the tropical forest of Guyana

A comparison is made of the atmospheric chemistry within and above the atmospheric boundary layer over the tropical forest of Guyana. The data were gathered by NASA during the Global Tropospheric Experiment program in 1984, with an instrumented aircraft being used to collect data at altitudes of 3.5 km and between 150-450 m. The synoptic data covered concentrations of O3, CO, dimethylsulfide (DMS), halocarbons and isoprene and three different aerosol particulate measurements (DIAL system). The forest boundary layer proved to be a significant sink for O3, and a source for substantial emissions of DMS. Isoprene emitted by the forest was photochemically oxidized and became a source of CO.

Gregory, G. L.↗
NASA NTRS1986

The relationship between satellite measured convective bursts and tropical cyclone intensification

High temporal resolution satellite IR measurements are used to analyze the relationship between the mean temperature of cloud canopy tops and the future maximum winds of Atlantic Ocean tropical cyclones. The measurements showed that prolonged surges of intense convection developed in the rear region surrounding cyclone depression centers before the maximum winds initially increased. When surges lasted for 9 hr or more, and the cloud-top temperature within 222 km of the cyclone centers was 238 K or less, then 71 percent of the time the maximum winds increased by 5 m/s or more within 24 hr. When intense convection was not present, similar maximum wind increases occurred only 37 percent of the time.

Steranka, J.↗
NASA NTRS1986

Tropical climatic phase lags and earth's precession cycle

Atmospheric GCMs have shown that thermally forced monsoon circulations are enhanced by the strengthened seasonal cycle of solar heating that results when summer solstice occurs near perihelion. However, observations indicate that the tropical climatic response reaches a maximum thousands of years after solstice-perihelion alignment. The reasons for this lag are addressed by examining the response to the precession cycle. The model utilized suggests that some features of the monsoon circulation may reach maximum intensity about 3000 yr after solstice-perihelion alignment as the result of a direct thermal response to the astronomical forcing.

Short, D. A.↗
NASA NTRS1986

Pattern recognition analysis of satellite data for tropical cyclone motion and intensity forecasts

An objective empirical analysis technique is employed to investigate the extent to which satellite-obtained measurements (GOES IR and TOVS data) of a tropical cyclone and its environment can be used to predict cyclone motion. The paper describes the procedure used to process the satellite derived data in order to optimize their possible predictive value, the technique used in developing the regression algorithms, and the results of testing these algorithms using the Lachenbrach and Mickey (1968) procedure. The data were examined alone and in conjunction with available nonsatellite climatological and persistence variables for each storm. These predictors are similar to those used in the National Hurricane Center (NHC) CLIPPER model. The performances obtained using the Nichols Research Corporation CLIPPER model and the NHC CLIPPER model are compared, using homogeneous data sets for the comparisons. Major differences in results were found to be related to differences in the models.

Hunter, Herbert↗
NASA NTRS1986

Tropical storm Flossie and the Ark Royal storm

The development of the tropical storm Flossie north of Scotland on September 16-17, 1978 from the Ark Royal storm is described. Land, marine, upper air data, satellite imagery, Seasat scatterometer (SASS) wind data, and SMMR moisture data were utilized to analyze the storms' development. The factors which contributed to the formation of the Ark Royal storm are discussed. Isobaric surface charts, isotachs and streamlines of the SASS winds, and SMMR water vapor contours are provided.

Peteherych, S.↗
NASA NTRS1986

Use of satellite data to study tropospheric ozone in the tropics

Three independent examples are discussed which suggest that photochemical ozone production in the troposphere can be observed in the tropics from an analysis of total ozone data. The first finding shows that the seasonal cycle of total columnar ozone is dominated by the seasonal cycle of tropospheric ozone, even though tropospheric ozone accounts for only 5-15 percent of the total ozone. Second, a case study is presented which shows that enhanced total ozone observed over the Amazon Basin can be associated with the presence of biomass burning. In situ measurements have confirmed that biomass burning does result in the production of photochemically generated ozone, analogous to the formation of 'smog' near industrialized areas. Third, an analysis of the distribution of carbon monoxide obtained from a Space Shuttle platform is strongly correlated with the concurrent distribution of total ozone between 5 deg S and 10 deg N. Because all of the sources of carbon monoxide are located in the troposphere, this finding likewise suggests that the gradients of total ozone at low latitudes must also reflect processes occurring in the troposphere.

Fishman, Jack↗
NASA NTRS1986

A study of the response of deep tropical clouds to mesoscale processes - Three-dimensional numerical experiments

A three-dimensional numerical cloud model is utilized to study the collective feedback effects of cloud systems on the large-scale environment. The characteristic features of the cloud ensemble model are described. The model is applied to a case of a well-defined ITCZ rainband over the eastern tropical Atlantic ocean. The location, number, and configuration of the clouds that formed in the model during the simulations are examined. The cloud heating and moistening, environmental wind shear, and vertical transports of momentum are analyzed. The collective feedbacks of cloud systems on the large-scale temperature, moisture, and horizontal momentum fields are computed after each simulation. The effect of the pressure gradient force on the v-momentum flux is investigated. It is observed that there is good correlation between the model simulations and the observed data.

Tao, Wei-Kuo↗
NASA NTRS1986

The quasi-biennial oscillation of ozone in the tropical middle stratosphere - A one-dimensional model

A one-dimensional model of the quasi-biennial oscillation (QBO) of ozone in the tropical middle stratosphere is derived based on assumed (observed) zonal wind QBO in a coupled dynamic, radiative/photochemical system. It is found that the derived vertical variation of the ozone QBO amplitude has two maxima, one at 32 km and the other at 22 km, and a minimum at 28 km. These are in qualitative agreement with observations. In the height interval 30-35 km, the ozone QBO is closely related to temperature dependent photochemistry, and the ozone and temperature variations are out of phase. Below 28 km, where vertical ozone and thermal transports are important, ozone and temperature oscillations are in phase, but both are approximately 270 deg out of phase with the vertical wind variation.

Ling, Xiu-De↗
NASA NTRS1986

Small-scale motions observed by aircraft in the tropical lower stratosphere - Evidence for mixing and its relationship to large-scale flows

Measurements of temperature and ozone from instrumented aircraft in the tropical lower stratosphere show the presence of small-scale disturbances generated by underlying cumulus convection and Kelvin-Helmholtz instability. The disturbances associated with underlying convection have peak-to-peak vertical parcel excursions of about 300 m. Flying conditions were smooth, suggesting an ensemble of gravity waves and little or no turbulent mixing. It is nevertheless possible that these waves break at other altitudes, leading to turbulent mixing and net fluxes of vertically stratified tracers. Disturbances attributed to KH instability implied vertical parcel excursions of 300-400 m. The disturbances coincided with rough flying conditions, suggesting turbulent mixing. A linear stability analysis of the atmospheric basic state defined by high-resolution radiosondes shows fastest growing waves with horizontal wavelengths of 1.4-1.8 km, consistent with the aircraft observations. The strong shears responsible for the KH instability are due to large-scale waves propagating into a region of small intrinsic frequency. Radiosonde observations show that the zonal length scale of these waves is about 1000 km.

Pfister, Leonhard↗
NASA NTRS1986

Comparisons of FGGE IIb and IIIb winds in a tropical synoptic system

The ECMWF wind analysis of a moisture burst over the NE Pacific Ocean occurring during a 9-day period in January 1979 is discussed. The availability of the data in synoptically active regions, and the horizontal, vertical, and temporal correlations of the data are considered. The accuracy of the wind data and the divergence in the tropics are examined. It is noted that it is necessary to maximize wind accuracy, and procedures for relating divergence to synoptic activity and satellite imagery to data correction are needed.

Mcguirk, J. P.↗
NASA NTRS1987

Significance of the South Pacific Convergence Zone (SPCZ) in the energy budget of the Southern Hemisphere tropics

An in-depth investigation of the energetics, including boundary transports, was conducted on four equal-area regions in the tropical Southern Hemisphere during the SOP-1 period in 1979. The regions, each approximately centered on one of the wave axes of maximum warm rising air, include the SPCZ (115 deg W - 155 deg E) and the Australian (155-65 deg E), the African (65 deg E - 25 deg W), and the South American (25-115 deg W) regions. Daily variations of the energy conversions were examined, and time-averaged result of energy contents, conversions, and boundary transports were compiled for January 10-27. Results show that the eddy kinetic energy (KE) exceeds the eddy available potential energy (AE) in all four regions, with the largest excess being in the SPCZ. Of the conversion and flux terms, only the conversion of AE to KE is significant (again, with the greatest value in the SPCZ). An evaluation of boundary fluxes of KE indicates that the only significant transport between regions is a flow of KE from the SPCZ region into the South American region.

Hurrell, James W.↗