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At least 631 records · Page 35

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NASA NTRS1989

Comparison of parameterized nitric acid rainout rates using a coupled stochastic-photochemical tropospheric model

A major tropospheric loss of soluble species such as nitric acid results from scavenging by water droplets. Several theoretical formulations have been advanced which relate an effective time-independent loss rate for soluble species to statistical properties of precipitation such as the wet fraction and length of a precipitation cycle. In this paper, various 'effective' loss rates that have been proposed are compared with the results of detailed time-dependent model calculations carried out over a seasonal time scale. The model is a stochastic precipitation model coupled to a tropospheric photochemical model. The results of numerous time-dependent seasonal model runs are used to derive numerical values for the nitric acid residence time for several assumed sets of preciptation statistics. These values are then compared with the results obtained by utilizing theoretical 'effective' loss rates in time-independent models.

Stewart, Richard W.↗

NASA NTRS1989

Ground-based infrared measurements of tropospheric source gases over Antarctica during the 1986 austral spring

Simultaneous measurements of the atmospheric burdens of CH4, N2O, CO2, CF2Cl2, and CO above McMurdo Station, Antarctica, have been derived from solar absorption spectra obtained by the Jet Propulsion Laboratory high-resolution Fourier transform spectrometer. In all cases the burdens are smaller than midlatitude values. Furthermore, retrievals of N2O and CH4 indicate that the tropospheric mixing ratios were normal and that the depletion of the burdens can best be accounted for by a downward shift of the volume mixing ratio profiles by some 6-8 km. This rules out the possibility of large-scale upwelling of ozone-poor tropospheric air into the stratosphere being the cause of the Antarctic springtime ozone depletion.

Toon, G. C.↗

NASA NTRS1989

Tropospheric monitoring technology for gravity wave experiments

Tropospheric refractivity fluctuations are an important error source for gravity wave detection by Doppler tracking in that they alter the phase and phase rate of electromagnetic signals. Estimates are presented of the effect of tropospheric fluctuations on the Doppler signal and some examples are suggested of methods which minimize the effect. A model of the fluctuations is utilized to achieve those goals. Four possible methods for reducing the fluctuation effect are suggested: (1) observation and analysis strategies, which separate the atmospheric and gravity wave signatures; (2) water vapor radiometry for the wet component; (3) calibration using Global Positioning System (GPS) satellites; and (4) Doppler observations from multiple antennas to average fluctuation effects. The last two techniques could be used to calibrate both wet and dry fluctuations, or could be used in conjunction with water vapor radiometry to calibrate only the dry component.

Treuhaft, R. N.↗

NASA NTRS1989

The global consequences of increasing tropospheric ozone concentrations

Recent analyses of long term records of tropospheric ozone measurements in the Northern Hemisphere suggest that it is increasing at a rate of 1 to 2 percent per year. Because of this, it is argued that the amount of atmospheric warming due to increasing tropospheric ozone is comparable to, or possibly even greater than, the amount of warming due to the increase of carbon dioxide. Unlike all other climatically important trace gases, ozone is toxic, and increases in its concentration will result in serious environmental damage, as well as impairment of human health.

Fishman, Jack↗

NASA NTRS1989

Solar activity, the QBO, and tropospheric responses

The suggestion that galactic cosmic rays (GCR) as modulated by the solar wind are the carriers of the component of solar variability that affects weather and climate has been discussed in the literature for 30 years, and there is now a considerable body of evidence that supports it. Variations of GCR occur with the 11 year solar cycle, matching the time scale of recent results for atmospheric variations, as modulated by the quasibiennial oscillation of equatorial stratospheric winds (the QBO). Variations in GCR occur on the time scale of centuries with a well defined peak in the coldest decade of the little ice age. New evidence is presented on the meteorological responses to GCR variations on the time scale of a few days. These responses include changes in the vertical temperature profile in the troposphere and lower stratosphere in the two days following solar flare related high speed plasma streams and associated GCR decreases, and in decreases in Vorticity Area Index (VAI) following Forbush decreases of GCR. The occurrence of correlations of GCR and meteorological responses on all three time scales strengthens the hypothesis of GCR as carriers of solar variability to the lower atmosphere. Both short and long term tropospheric responses are understandable as changes in the intensity of cyclonic storms initiated by mechanisms involving cloud microphysical and cloud electrification processes, due to changes in local ion production from changes in GCR fluxes and other high energy particles in the MeV to low GeV range. The nature of these mechanisms remains undetermined. Possible stratospheric wind (particularly QBO) effects on the transport of HNO3 and other constituents incorporated in cluster ions and possible condensation and freezing nuclei are considered as relevant to the long term variations.

Tinsley, Brian A.↗

NASA NTRS1989

The distribution of middle tropospheric carbon monoxide during early October 1984

The distribution of middle tropospheric carbon monoxide measure by the Measurement of Air Pollution from Satellites (MAPS) instrument carried aboard the space shuttle is reported. The data represent average mixing ratios in the middle troposphere and are presented in the form of maps that show the carbon monoxide mixing ratios averaged for 6 days of the mission. Comparisons with concurrent, direct measurements taken aboard aircraft show that the inferred concentrations are systematically low by from 20 to 40 percent depending upon which direct measurement calibration standard is used. The data show that there are very large CO sources resulting from biomass burning over South America and southern Africa. Measured mixing ratios were high over northeast Asia and were highly variable over Europe.

Reichle, Henry G., Jr.↗

NASA NTRS1989

Linear properties of eddies in a Jovian troposphere forced by deep jets

A linear quasi-geostrophic beta-plane model is used to study large-scale instabilities of the Jovian upper troposphere forced from below by zonal jets. The jets are presumed to be barotropically stable in the isentropic deep interior, but barotropically unstable in the statically stable upper troposphere. The effect on this barotropic instability of weak vertical shear causing the jets to decay with height is examined. It is found that eastward jets are stabilized by weaker shear than westward jets, the most unstable eddies are strongly confined by the shear, and eddy fluxes contribute to vertical decay of the jets. The lower residual mean meridional circulation cells exhibit rising motion in regions of anticyclonic shear, but these are overlain by reverse cells.

Orsolini, Y.↗

NASA NTRS1990

Some tests of wet tropospheric calibration for the CASA Uno Global Positioning System experiment

Wet tropospheric path delay can be a major error source for Global Positioning System (GPS) geodetic experiments. Strategies for minimizing this error are investigted using data from CASA Uno, the first major GPS experiment in Central and South America, where wet path delays may be both high and variable. Wet path delay calibration using water vapor radiometers (WVRs) and residual delay estimation is compared with strategies where the entire wet path delay is estimated stochastically without prior calibration, using data from a 270-km test baseline in Costa Rica. Both approaches yield centimeter-level baseline repeatability and similar tropospheric estimates, suggesting that WVR calibration is not critical for obtaining high precision results with GPS in the CASA region.

Dixon, T. H.↗

NASA NTRS1990

Coherent wave-zonal mean flow interactions in the troposphere

A comprehensive analysis of wave-zonal mean flow variations in the troposphere is carried out using results of observations on the spatial structure and temporal evolution of synoptic time scale variations of the tropospheric zonal mean flow. Seven years of daily operational analysis are examined along with data from the NCAR GCM. Coherent wave-zonal mean flow interactions were revealed via cross-correlation analyses, including fluctuations in zonal mean temperature, three-dimensional winds, and quadratic wave quantities. It was found that tropical zonal wind tendency fluctuations are coherent with those anticipated from quasi-geostrophic wave driving, while tropical temperature tendencies are incoherent with analyzed zonal mean vertical velocities.

Randel, William J.↗

NASA NTRS1989

Upper-tropospheric influences on Western Pacific tropical cyclone intensity change as inferred from satellite ozone observations

The use of Nimbus-7 TOMS data to diagnose changes in tropical cyclone intensity is demonstrated. The relationship between upper-tropospheric environmental total ozone distribution and intensity for a tropical cyclone case study is examined. The climatological total ozone patterns are used to identify the upper-tropospheric features to differentiate between intensifying and nonintensifying Western Pacific tropical cyclones.

Rodgers, Edward B.↗

NASA NTRS1989

Remote sensing of the troposphere by infrared emission spectroscopy

This paper describes the concept of a cryogenic IR imaging Fourier transform spectrometer, called the Tropospheric Emission Spectrometer (TES), designed for observations of the troposphere and lower stratosphere from a near-earth orbit, using natural thermal emission and reflected sunlight. The principal molecular species to be measured by TES are O3, CO, CO2, N2O, H2O, H2O2, NO, NO2, HNO3, NH3, CH4, C2H6, C2H2, SO2, COS, CFCl3, and CF2Cl2. The TES is scheduled for a launch on the second polar platform of the Earth Observing System in 1998.

Beer, Reinhard↗

NASA NTRS1990

Measurements of tropospheric nitric acid over the western United States and northeastern Pacific Ocean

HNO3 measurements obtained in the free troposphere (FT) and boundary layer (BL) over the western U.S. and the NE Pacific during the NASA Global Tropospheric Experiment Chemical Instrumentation Test and Evaluation 2 (CITE 2) program in summer 1986 are reported. The CITE 2 HNO3 instruments and flight protocols are described, and the results are presented in tables and graphs. Over the ocean, the average HNO3 mixing ratios were found to be 108 parts per trillion by volume (pptv) in the FT and 62 pptv in the BL, suggesting removal of HNO3 from the BL by dry deposition. The corresponding values over land were 61 pptv for the FT and 767 pptv for the BL, and the horizontal distribution of BL HNO3 indicated an anthropogenic origin.

Lebel, P. J.↗

NASA NTRS1990

Observed and model-calculated NO2/NO ratios in tropospheric air sampled during the NASA GTE/CITE-2 field study

Airborne measurements of NO2/NO ratios in the free troposphere, obtained using two-photon LIF (TP-LIF) and chemiluminescence (CL) detectors during the NASA Global Tropospheric Experiment Chemical Instrumentation Test and Evaluation 2 (CITE 2) program in summer 1986, are analyzed and compared with the predictions of a photochemical model. The derivation of the model is outlined, with an emphasis on the role of peroxy radicals in the fast photochemical cycling of NO and NO2 and the production of O3; the CITE 2 instruments and flight protocols are described; and the results are presented in extensive tables and graphs and discussed in detail. It was found that on three CITE 2 flights the CL data were systematically greater than the TP-LIF data; when these data were removed, the averaged values of the two instruments agreed to within 1 percent. The NO2/NO ratios predicted by the model are shown to be consistent with the measurements, although usually 20-25 percent lower.

Chameides, W. L.↗

NASA NTRS1990

Stochastic estimation of tropospheric path delays in global positioning system geodetic measurements

Water vapor radiometric and surface meteorological measurements taken during three GPS geodetic experiments are used to calculate process noise levels for random walk and first-order Gauss-Markov temporal models of tropospheric path delays. Entire wet and combined wet and dry zenith delays at each network site are estimated simultaneously with the geodetic parameters without prior calibration. The path delays and corresponding baseline estimates are compared to those obtained with calibrated data and stochastic residual delays. In this manner, the marginal utility of a priori tropospheric calibration is assessed given the ability to estimate the path delays directly using only the GPS data. Estimation of total zenith path delays with appropriate random walk or Gauss-Markov models yields baseline repeatabilities of a few parts in 100 million. Results suggest that GPS data alone have sufficient strength to resolve centimeter-level zenith path delay fluctuations over periods of a few minutes.

Tralli, David M.↗

NASA NTRS1990

Seasonal dynamics in methane emissions from the Amazon River floodplain to the troposphere

Methane fluxes to the troposphere from the three principal habitats of the floodplain of the Amazon River main stem (open waters, emergent macrophyte beds, and flooded forests) were determined along a 1700-km reach of the river during the low-water period of the annual flood cycle (November-December 1988). Overall, emissions averaged 68 mg CH4/sq m per day and were significantly lower than similar emissions determined previously for the high-water period, 184 mg CH4/sq m per day (July-August 1986). This difference was due to significantly lower emissions from floating macrophyte environments. Low-water emissions from open waters and flooded forest areas were not significantly different than at high water. A monthly time series of methane emission from eight lakes located in the central Amazon basis showed similar results. The data were used to calculate a seasonally weighted annual emission to the troposphere from the Amazon River main stem floodplain of 5.1 Tg/yr, which indicates the importance of the area in global atmospheric chemistry.

Devol, Allan H.↗

NASA NTRS1990

Tropospheric OH in a three-dimensional chemical tracer model - An assessment based on observations of CH3CCl3

The paper introduces the representation of tropospheric chemistry allowing for calculation of chemical reaction rates within a chemical tracer model (CTM) simulation with the accuracy comparable to that of a detailed chemical model. The global distribution of tropospheric OH is calculated as a function of time, atmospheric composition, temperature, and solar irradiance. The globally integrated OH concentration weighted by frequency of reaction with CH3CCl3 is evaluated, along with the feasibility of using the observed latitudinal distribution of CH3CCl3 as a test for computed concentrations of OH. Seasonal variations of CH3CCl3 are also considered as a potential test for computed concentrations of OH. It is demonstrated that annual cycles of CH3CCl3 are controlled, or strongly influenced, by dynamical processes at latitudes northward of 25 deg South.

Spivakovsky, C. M.↗

NASA NTRS1990

Zonal motion and structure in Jupiter's upper troposphere from Voyager infrared and imaging observations

Global digital maps of Jupiter's upper-tropospheric temperature have been generated at the 270- and 150-mb pressure levels, together with IR cloud optical depths at 5 and 45 microns and the ammonia abundance near the 680-mb pressure level, on the basis of Voyager IRIS north-south mapping sequences. Attention is given to the 270-mb and 45 micron data; global digital maps are presented for violet and orange reflectivities. The dominant upper tropospheric thermal structures move at a rate far different from that of the cloud indicators, and are noted to remain stationary relative to the planet's bulk rotation. Strong stationary features are found at a zonal wavenumber of 9 near 15 deg N latitude and of 11 near 20 deg latitude.

Magalhaes, Julio A.↗

NASA NTRS1991

Seasonal cycle and secular trend of the total and tropospheric column abundance of ethane above the Jungfraujoch

The secular trend and the seasonal cycle of the total and the tropospheric column abundances of C2H6 over the Jungfraujoch Station (Switzerland) were deduced from infrared solar spectra recorded in 1951 and from 1984 to 1988. Results show a definite seasonal variation in the total vertical column abundance of C2H6, with a maximum of (1.43 + or - 0.03) x 10 to the 16th molecules/sq cm during March and April and a minimum in the fall; the ratio between the maximum and the minimum column abundances was found to be 1.62 + or - 0.11. The secular trend in the tropospheric burden above the Jungfraujoch was found to be (0.85 + or - 0.3) percent/yr.

Ehhalt, D. H.↗