Earth's Troposphere Research Articles

Isomerization of Simple Alkoxyl Radicals: New Temperature-Dependent Rate Data and Structure Activity Relationship

Relative-rate experiments have been carried out, at several different temperatures between 240 and 340 K, to determine the Arrhenius rate parameters for the isomerization of the 1-pentoxyl, 2-pentoxyl, and 5-methyl-2-hexoxyl radicals. Isomerization rates were measured relative to the bimolecular reaction of each alkoxyl radical (RO•) with O2. The order of reactivity, in terms of the rate of reaction for isomerization, was 5-methyl-2-hexoxyl > 1-pentoxyl > 2-pentoxyl, reflecting the relative-strengths of tertiary, secondary, and primary C−H bonds, i.e., the nature of the bond cleaved in the isomerization process. In addition to this, the measured Arrhenius activation barriers, and reported barriers for bimolecular reactions of the methoxyl radical with several simple hydrocarbons, are shown to correlate linearly with the bond strength of the cleaving C−H bond. The A-factors obtained for the three isomerization processes also scale linearly with the number of available abstractable H atoms, with a value of 3.0 × 1010 s-1 per H atom. This value combined with the activation barrier correlation constitutes a structure activity relationship for the estimation of the kinetics of the isomerization of simple alkoxyl radicals, at temperatures pertaining to the Earth's troposphere.

Development of Satellite Methods for Radio Holographic Surveys of the Earth's Surface and Atmosphere

The methods of studying the Earth's surface and troposphere with the help of coherent radio waves radiated by satellites are considered. Some examples of measurements of the local relief of the Earth's surface by the method of radar interferometer are presented, as well as refraction profiles of the troposphere obtained by the radio holographic method. The described methods are promising for investigations of the local relief of the Earth's surface and its changes, for studying the characteristics of sea heaving, and for monitoring atmospheric processes.

Comparative range delay and variability of the earth's troposphere and the ionosphere

The relative magnitudes of the range delays encountered by signals from GPS satellites due to the earth’s ionosphere and the troposphere can be comparable at times. Of course, there are major differences in the variability of these two components of range delay, as well as different methods of correcting for them. In this short paper, the differences between ionospheric and tropospheric range delay are briefly described, and suggestions are made on how best to correct for each of these components of delay for an individual user station. The range delay of the troposphere and the ionosphere differs in several important aspects. The range delay of the earth’s troposphere is not dispersive; that is, it is not a function of frequency, at least not over the normal radio frequency range used for ranging to artificial earth satellites. The range delay of the ionosphere, on the other hand, is dispersive; that is, it varies inversely with frequency in the following manner:

Use of Radar Inferometry for Study of Dynamics of the Earth's Surface and Troposphere

The results of interferometric processing of survey data for the northern shores of the Caspian Sea by synthetic aperture radar (SAR) are presented. The survey was made in May 1996 from near-earth orbits of the ERS-1 and ERS-2 satellites, respectively, on successive days in the C range with vertical polarization. A map of the coherence of the radar images was compiled and an interferogram was obtained. The types of surface cover classified and the changes occurring during the time between the surveys are described, including shifts of the scattering surface and changes in phase path length of radio waves attributable to fluctuations of the tropospheric refraction coefficient.

Variations of solar spectral irradiance from near UV to the infrared—measurements and results

Solar spectral irradiance variations are known to exhibit a strong wavelength dependence with the amount of variability increasing towards shorter wavelengths. The bulk of solar radiation is emitted at visible and infrared wavelengths. Thus, the spectral radiation length of 300 nm accounts for 99% of the total solar radiative output. Deposited in the Earth's troposphere and biosphere, this part of the solar irradiance spectrum determines direct solar radiative forcing and is therefore of particular interest for climate studies. First, measurements of solar irradiance and irradiance variability from near UV to the IR are reviewed with particular emphasis on the results obtained from the Variability of Irradiance and Gravity Oscillations (VIRGO) on SOHO and Solar Spectrum Measurement (SOLSPEC) instruments. In the second part a model is presented which describes solar spectral irradiance variations in terms of the changing distribution of solar surface magnetic features.

Photocatalysis and Photosorption in the Earth's Atmosphere

The troposphere of Earth is abundant in particles of solid and liquid aerosols which have a large specific surface area and can be activated by visible light and mild ultraviolet (UV) solar radiation with wavelengths λ > 300 nm for promoting different photocatalytic and photoadsorption processes. This paper discusses possible heterogeneous photocatalytic and photosorption phenomena on the surface of solid tropospheric aerosols. These phenomena can proceed in nature at ambient conditions and can make an important contribution to the global chemistry of the Earth's atmosphere. For example, the particles of semiconductor metal oxides like TiO2, ZnO, and Fe2O3 are able to photocatalyze oxidation of organic compounds from the atmosphere by air oxygen and even mineralize them. For insulator metal oxides like SiO2, Al2O3, MgO, and CaO, which are the main components of tropospheric solid aerosols, a substantial depletion of many halogen-containing organic compounds (freons) is possible via their destructive photoadsorption. All mentioned processes appear to be driven by mild solar UV radiation and can proceed in the troposphere, in contrast to direct photochemistry which can take place only in the upper layers of the atmosphere.

Dynamical climatology of the NASA Langley Research Center Interactive Modeling Project for Atmospheric Chemistry and Transport (IMPACT) model

A comparison of the NASA Langley Research Center (LaRC) Interactive Modeling Project for Atmospheric Chemistry and Transport (IMPACT) model's dynamical characteristics with assimilated data sets and observations is presented to demonstrate the ability of the model to represent the dynamical characteristics of Earth's troposphere and stratosphere. The LaRC IMPACT model is a coupled chemical/dynamical general circulation model (GCM) of the Earth's atmosphere extending from the surface to the lower mesosphere. It has been developed as a tool for assessing the effects of chemical, dynamical, and radiative coupling in the stratosphere on the Earth's climate. The LaRC IMPACT model winds and temperatures are found to be in fairly good agreement with Upper Atmospheric Research Satellite (UARS) United Kingdom Meteorological Office (UKMO) assimilated winds and temperatures in the lower stratosphere. The model upper stratospheric zonal mean temperatures are also in good agreement with the UARS‐UKMO climatology except for a cold winter pole which results from the upward extension of the cold vortex temperatures and an elevated winter stratopause in the model. The cold pole bias is consistent with the overprediction of the winter stratospheric jet strength, and is characteristic of stratospheric GCMs in general. The model northern and southern hemisphere stratospheric eddy heat and momentum fluxes are within the expected interannual variability of the UARS‐UKMO climatology. The combined effects of water vapor transport, radiative, convective, and planetary boundary layer parameterizations are shown to produce tropospheric winds and circulation statistics that are in good agreement with the UARS‐UKMO climatology, although the model tropopause and upper tropospheric temperatures are generally cold relative to the UARS‐UKMO temperatures. Comparisons between the model and UARS‐UKMO climatology indicate that the model does a reasonable job in reproducing the frequency of observed synoptic‐scale storms during the northern and southern hemisphere winters. Generally good agreement is found between the model and observations in the distribution of outgoing longwave radiation and precipitable water. However, the model precipitation and cloud distributions are influenced by spectral truncation errors which indicate that the T32 spectral resolution of the model is probably not adequate to accurately represent coupling between localized convection and large‐scale water vapor transport. The agreement between the observed and model stratospheric circulation and temperatures, reasonableness of the model stratospheric wave driving, and stability of the model climatology provides confidence that the LaRC IMPACT model is appropriate for multiyear coupled radiation/chemistry/dynamics studies of the stratosphere.

Cloud photochemistry and its effect on the composition of the upper atmosphere of Venus

Laboratory studies of the 248 nm photooxidation of Fe(II) to Fe(III) in concentrated sulfuric acid solutions indicate that photochemical reactions in the sulfuric acid clouds of Venus are capable of affecting the composition of the atmosphere at high altitudes, by removing O2 and CO and regenerating CO2. Major primary processes are the production of SO3− radical ions by photolysis of solvated SO2, and of SO4− radical ions by photolysis of complex ions containing Fe(III), if traces of iron salts are present. Secondary processes are similar to those which result in the formation of acid rain in Earth's troposphere.

Case studies of the vertical structure of the direct shortwave aerosol radiative forcing during TARFOX

The vertical structure of aerosol‐induced radiative flux changes in the Earth's troposphere affects local heating rates and thereby convective processes, the formation and lifetime of clouds, and hence the distribution of chemical constituents. We present observationally based estimates of the vertical structure of direct shortwave aerosol radiative forcing for two case studies from the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX) which took place on the U.S. east coast in July 1996. The aerosol radiative forcings are computed using the Fu‐Liou broadband radiative transfer model. The aerosol optical properties used in the radiative transfer simulations are calculated from independent vertically resolved estimates of the complex aerosol indices of refraction in two to three distinct vertical layers, using profiles of in situ particle size distributions measured aboard the University of Washington research aircraft. Aerosol single‐scattering albedos at 450 nm thus determined range from 0.9 to 0.985, while the asymmetry factor varies from 0.6 to 0.8. The instantaneous shortwave aerosol radiative forcings derived from the optical properties of the aerosols are of the order of −36 W m−2 at the top of the atmosphere and about −56 W m−2 at the surface for both case studies.

Velocidade de propagação da frente de distúrbios no modelo hidrostático da atmosfera politrópica

There are no acoustic waves in a hydrostatic model of the atmosphere. Among the other waves, the most fast ones are the Lamb waves that propagate horizontally. Their speed is comparable with the speed of sound. Its exact value depends on the choice of the basic state of the atmosphere which is used to linearize the hydrothermodynamic equations. It is a state with a polytropic stratification where the temperature decreases linearly with altitude at a constant lapse-rate G that corresponds to the actual conditions of the Earth's troposphere. It is assumed that all the atmosphere has a politropic stratification, i.e., it is finite with altitude because G >0. We suppose also that the stratification is statically stable or neutral . The vertical profile of the eigenmodes in the polytropic model is described with the help of the Bessel functions. Therefore, the dispersion equation that determines the eigenvalues of the problem, and consequently an oscillation spectrum, is transcendental. The highest propagation speed (the front speed) corresponds to the minimum solution of this equation, i.e., the minimum eigenvalue. When , the minimum eigenvalue can be calculated using the development of the solution into the series by powers of the small difference . It is proved that a simple analytical formula, obtained by keeping in the series only the two first terms, gives a good approximation not only of this limit but of the opposite limit when G=0 , too. A comparison of the results obtained by the analytical formula and using the complete dispersion equation shows a good precision of the formula in the whole range of .

Systematic errors in atmospheric profiles obtained from Abelian inversion of radio occultation data: Effects of large‐scale horizontal gradients

Reduction of radio occultation data to retrieve atmospheric profiles (T‐p(r)) requires knowledge or assumption of the horizontal structure of the atmosphere. In the case of terrestrial planets the atmosphere in the vicinity of ray periapsides usually is assumed to be spherically symmetric. This assumption leads to an integral transform relationship between the profiles of refractivity versus radius and the total bending angle versus the asymptotic closest approach of rays, where the latter is directly obtainable from occultation frequency data and trajectory information. Occultation studies of the giant planets have demonstrated that departures from spherical symmetry, if not accounted for, can result in serious errors in derived T‐p(r) profiles. We analyze errors in atmospheric profiles due to large‐scale departures from spherical symmetry. For analytic convenience we represent departures from spherical symmetry as locally spherical structures with center of curvature offset in three dimensions from the center of mass, from which follow analytic expressions for errors in bending angle and impact parameter as functions of the offset and trajectory parameters. Since these expressions are not restricted to any specific occultation type, it is easy to identify the geometrical configurations and the specific trajectory parameters that enhance or suppress these errors. Errors in bending angle and impact parameter carry over into the refractivity and radius profiles, while at the same time, new errors are introduced because the bending angle versus impact parameter profile is integrated along a nonvertical path in the presence of large‐scale departures from spherical symmetry, to obtain refractivity and radius profiles. Similarly, refractivity and radius errors propagate into the temperature and pressure profiles, while a nonvertical path of integration in the presence of horizontal gradients provides another opportunity for new errors to be introduced. We estimate that fractional errors in temperature profiles can be as large as a few percent for the Martian atmosphere above 20 km, decreasing in magnitude closer to the surface. For Earth, such errors are estimated to be less than 1% above 30 km. In the lower parts of Earth's atmosphere, however, and especially in the lower troposphere, these errors can be very sensitive to horizontal gradients and hence highly variable; typically, the error magnitude remains less than 2% for the dry regions of Earth's troposphere. We have not addressed the effect on errors of water vapor gradients, or of more extreme structures such as sharp weather fronts. A small variation on this approach can incorporate errors due to imprecise knowledge of the transmitter and receiver trajectories.

Global Climate Data and Models: A Reconciliation

The debate over the existence of global warming and climate change has been muddled because of satellite data showing a cooling trend in Earth's troposphere. This apparent cooling is in disagreement with measurements at surface stations and with climate models. In their Perspective, Hansen et al . discuss a correction to the satellite data published by Wentz and Schabel in Nature that may have profound implications for discussions of climate change. Wentz and Schabel discovered that the original satellite data, published in 1995, was not adjusted for the natural decay of spacecraft altitude caused by atmospheric drag. When this adjustment is made, the satellite data agree with both surface data and model calculations. The authors of the Perspective conclude that the question now is not whether global warming exists--it clearly does--but what should be done about it.

22 year solar modulation of Earth's northern hemisphere temperatures

As reported earlier, solar particle events originating from the Sun's polar regions affect the Earth's troposphere in a way that is opposite to solar particle events from the Sun's equatorial regions. When the Sun's magnetic field reverses every 11 years, the tropospheric response also reverses. These results are based on European temperature data. The present extension (712 northern stations) to a more worldwide coverage shows that this complex behavior is reversed on the western side of the Earth's northern hemisphere. The border separating the two regimes (East vs. West) lies close to the meridian crossing the magnetic pole. These results imply that the physical mechanism linking the solar and tropospheric changes may be sensitive to the specific spatial conditions and magnetic polarity distributions.

The effects of a discontinuous snow cover on lower atmospheric temperature and energy flux patterns

Snow cover and its interaction with the earth's troposphere has become a topic of increased interest over the past several decades. Studies have produced evidence of links between snow cover and precipitation patterns, temperature fields, and atmospheric circulation patterns. Few studies have investigated anomalous atmospheric temperature and circulation patterns over snow cover boundaries or patchy snow cover. This study provides analysis of model‐derived lower atmospheric temperatures and contributing energy fluxes within a cold air mass positioned over discontinuous snow cover. Results of the analysis show that simulated air mass temperatures were 1–4°C cooler over a patch of snow cover than over surrounding bare ground during a midday hour. The temperature differences were primarily the result of variations in the magnitude and direction of the surface layer sensible heat flux, as produced by differences between the solar radiation absorbed by the snow cover and the surrounding bare ground.

Investigation of the vertical profile of the aerosol scattering in the atmosphere by multichannel data from space station MIR

An approach is suggested and applied to determine the atmospheric optical depth parameters from spectral solar irradiance data provided by the multichannel trace spectrometric system “Spectrum 256”. The system “Spectrum 256” has been designed by scientists from the Solar-Terrestrial Influences Laboratory at the Bulgarian Academy of Sciences and has been operated onboard the MIR space station since 1988. By scanning the atmosphere with the spectrometer pointed directly at the Sun as the MIR station passed from the terminator zone to the sunset zone, the distribution of the atmospheric optical depth components in a vertical column of the Earth's troposphere in the layer between 2 km and 14 km was determined. The molecular (Rayleigh) scattering was modeled and the aerosol scattering model parameters were evaluated. The selective absorption due to gaseous components and water vapor in the 475–810 nm spectral range was determined, taking into account the influence of the optical transmission characteristics of the hatches of the MIR station.

Measurement of tropospheric OH by long‐path laser absorption at Fritz Peak Observatory, Colorado, during the OH Photochemistry Experiment, fall 1993

The determination of the concentration of hydroxyl (OH) in the Earth's troposphere is of fundamental importance to an understanding of the chemistry of the lower atmosphere. This paper describes the results from the laser long‐path spectroscopic OH experiment used in the Tropospheric OH Photochemistry Experiment (TOHPE) held at Fritz Peak, Colorado, in fall 1993. A primary goal of TOHPE was to compare the OH concentrations measured using a variety of different techniques: a long‐path spectroscopic instrument [Mount, 1992], an in situ ion‐assisted chemical conversion instrument (Eisele and Tanner, 1991, 1993), a laser resonance fluorescence instrument [Stevens et al., 1994), and a liquid scrubber instrument (X. Chen and K. Mopper, unpublished data,; 1996), all with sensitivities at or below 1×106 molecules cm−3. In addition to the OH measurements, a nearly complete suite of trace gas species that affect the OH concentration were measured simultaneously, using both in situ and/or long‐path techniques, to provide the information necessary to understand the OH variation and concentration differences observed. Measurements of OH, NO2, CH2O, SO2, H2O, and O3 were made using long‐path spectroscopic absorption of white light or laser light and OH, NO, NO2, NOy, O3, CO, SO2, CH2O, j(O3), j(NO2), RO2/HO2, HO2, H2O, SO2, PAN, PPN, HNO3, and aerosols (size and composition) and ozone and nitrogen dioxide j‐values were measured using in situ instruments. Meteorological parameters at each end of the long path and at the Idaho Hill in situ site were also measured. The comparison of the long‐path and in situ species from this set of complementary measurements provides an effective way of interpreting air masses over the long path with those at the in situ site; this is a critical issue since the long‐path spectroscopic OH determinations provide a nonchemical and well‐calibrated measurement of OH which must be compared in a meaningful manner with the in situ determinations. Over the period of the TOHPE experiment, OH concentrations were typically low during periods of clean and clear airflow, averaging about 4×106 molecules cm−3 at noon. In contrast, during the well‐defined pollution episodes which occurred during the campaign, OH concentrations rose as high as 15×106 molecules cm−3.

Radiometric monitoring of atmospheric water vapor as it pertains to phase correction in millimeter interferometry

Water vapor in the Earth's troposphere produces fluctuations in the phase of millimeter-wavelength radiation from astronomical sources. Such fluctuations seriously limit the spatial resolution achievable with current millimeter interferometers. Since water vapor is also a source of atmospheric opacity at these wavelengths, radiometric measurements of sky brightness may be used to monitor the fluctuating water vapor content of the atmosphere and thereby the fluctuations in the interferometric phase. The atmospheric opacity depends on the frequency and on the physical conditions of those atmospheric regions in which the water vapor is located. Atmospheric temperature influences the strengths of the various absorption lines, and pressure influences the degree of line broadening. The magnitude of the phase fluctuations relative to the brightness fluctuations is therefore also dependent on frequency, temperature, and pressure. The frequency of a radiometric monitoring system may be chosen to minimize the dependence of this ratio on the atmospheric parameters.

Spacecraft Doppler tracking as a xylophone detector of gravitational radiation.

Spacecraft Doppler tracking is discussed for detecting gravitational waves in which Doppler data recorded on the ground are linearly combined with Doppler measurements made on board a spacecraft. A new method is derived for removing from combined data the frequency fluctuations due to the Earth troposphere, ionosphere, and mechanical vibrations of the antenna on the ground. The remaining non-zero gravitational wave signal could be used for detecting gravitational waves.

Orographic control of storm zones on Mars

Low-pressure cyclones and their accompanying frontal systems in the middle latitudes of the Earth's troposphere develop, travel eastwards and decay preferentially within latitudinally and longitudinally confined geographical regions known as storm zones1. These zones can be readily identified in the circulation statistics of terrestrial weather systems2. Mars, like the Earth, is a rapidly rotating solid planet and has a seasonally varying shallow atmosphere, large-scale orography, and (in a broadly defined context) continental structures3. Although there are also important differences between the two planets, travelling weather systems do exist on Mars3. This raises the question of whether storm zones also occur there, and if so, by what mechanisms. Here we report the results of numerical simulations of global atmospheric circulation patterns on Mars. We find that storm zones can exist during the northern winter, and that continental-scale orography (rather than surface thermal contrasts) is the main factor determining the development of these zones. Storm zones on Mars should play an important role in the martian climate cycle4,5, by influencing the transport of (for example) heat, momentum, water vapour and atmospheric dust3,6–8 towards the poles.

Using spacecraft range data and radar observations for the improvement of the orbital elements of planets and parameters of Mars rotation

The extremely precise Viking (1972–1982) and Mariner data (1971–1972) were processed simultaneously with the radar-ranging observations of Mars made in Goldstone, Haystack and Arecibo in 1971–1973 for the improvement of the orbital elements of Mars and Earth and parameters of Mars rotation. Reduction of measurements included relativistic corrections, effects of propagation of electromagnetic signals in the Earth troposphere and in the solar corona, corrections for topography of the Mars surface. The precision of the least squares estimates is rather high, for example formal standard deviations of semi-major axis of Mars and Earth and the Astronomical Unit were 1–2 m.