Photodissociation rates in the atmosphere below 100km

Turco, R. P.

doi:10.1007/bf01447907

Cited by 47 publications

(24 citation statements)

References 72 publications

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“…For cloud-free conditions, the calculation of the actinic flux with radiative transfer models is relatively straightforward (e.g. Turco, 1975;Meier et al, 1997) and is generally in good agreement with observations. During the International Photolysis Measurement and Model Intercomparison spectroscopic, radiometric, and actinometric measurements were made at the surface under cloud-free skies and compared with 16 models, of which the majority (11) agreed within ±6% for solar zenith angles smaller than ∼60 • .…”

Section: Introductionmentioning

confidence: 89%

Ultraviolet actinic flux in clear and cloudy atmospheres: model calculations and aircraft-based measurements

et al. 2011

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Both cloudy and cloud-free conditions were encountered. For cloud-free conditions, the ratio of observed to clearsky-model actinic flux (integrated from 298 to 422 nm) was 1.01±0.04, i.e. in good agreement with observations. The agreement improved to 1.00±0.03 for the down-welling component under clear sky conditions. In the presence of clouds and depending on their position relative to the aircraft, the up-welling component was frequently enhanced (by as much as a factor of 8 relative to cloud-free values) while the down-welling component showed both reductions and enhancements of up to a few tens of percent. Including all conditions, the ratio of the observed actinic flux to the cloud-free model value was 1.1±0.3 for the total, or separately 1.0±0.2 for the down-welling and 1.5±0.8 for the up-welling components. The correlations between up-welling and downwelling deviations are well reproduced with sensitivity studies using the TUV model, and are understood qualitatively with a simple conceptual model. This analysis of actinic flux observations illustrates opportunities for future evaluations of photolysis rates in three-dimensional chemistry-transport models.

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Section: Introductionmentioning

confidence: 89%

Ultraviolet actinic flux in clear and cloudy atmospheres: model calculations and aircraft-based measurements

et al. 2011

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“…The chemistry model was developed over a period of years [Turco andWhitten, 1974, 1977;Turco, 1975;Elliott et al, 1993Elliott et al, , 1995Zhao, 1995]. A highly stable numerical scheme allows computational speed to be maintained at a fixed time step as large as 2 hours.…”

Section: Chemistry Componentmentioning

confidence: 99%

Aerosol‐induced chemical perturbations of stratospheric ozone: Three‐dimensional simulations and analysis of mechanisms

Zhao¹,

Turco²,

Kao³

et al. 1997

J. Geophys. Res.

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Abstract. An atmospheric general circulation model is coupled with a stratospheric photochemical model to simulate the chemical/dynamical perturbations associated with background and volcanically perturbed aerosols in the lower stratosphere. The present work focuses on short-term anomalies at middle and high latitudes in the northern hemisphere, where large ozone depletions have been observed in late winter and early spring, particularly following the eruption of Mount Pinatubo. Five fully coupled simulations are analyzed, corresponding to a control case with only gas phase chemistry, and cases including heterogeneous chemistry on background aerosols, on E1 Chich6n-type, and on Pinatubo-type aerosols. It is found that heterogeneous reactions occurring on sulfate aerosols (background or postvolcanic) can strongly perturb the chemical partitioning in the lower stratosphere, leading to significant ozone depletion through enhanced chlorine, bromine, and odd-hydrogen catalytic cycles. In the Arctic lower stratosphere, the maximum zonal and March monthly mean local ozone reductions (with respect to the control case) can exceed 15% for the background aerosol case, 40% for the E1 Chich6n case, and 50% for the Pinatubo case. The corresponding zonal mean total column ozone decreases are roughly 5% and 15% for the background and volcanic aerosol cases, respectively. In the most extreme case tested (post-Pinatubo), a large ozone depletion below 30 mbar is offset to some extent by an ozone increase above that level. The results of a sensitivity study (in which the aerosols are distributed closer to the tropics, as might occur early after an eruption at low latitude) lead to relatively small total ozone depletions at northern high latitudes, and small ozone increases in the tropical lower stratosphere. The reduced impact on total ozone at high latitudes is associated both with local ozone increases above 30 mbar and with poleward transport of enhanced ozone from the tropical lower stratosphere. The ozone increase at low latitudes is the net result of compensating changes in the catalytic destruction cycles involving odd-nitrogen and chlorine species activated by heterogeneous processes at the low temperatures and abundant sunlight found near the tropical tropopause. Our simulations indicate that ozone variations triggered by volcanic injections of aerosols depend on the global distribution as well as the abundance of the particles and their evolution over time, and on the initial dynamical-radiative-chemical state of the atmosphere, which itself exhibits large seasonal and interannual variability.

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“…However, that process is not very significant in the mesosphere, as one can see from Figure 9. For a more detailed discussion see Turco (1975).…”

Section: Interaction Of Solar Radiationmentioning

confidence: 99%

The mesosphere

Poppoff

Whitten

1976

Geophysical Surveys

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Abstract. The mesosphere, which extends from about 50 to 90 km altitude~ is an atmospheric region characterized by a negative gradient of solar energy absorption, and thus, temperature. Although the disMbution of most minor constituents is dominated by photochemistry, vertical transport does have a pronounced effect on many of them. Hence, we discuss the basic dynamic principles and their application to the important mesopheric motions: acoustic-gravity waves, tides, planetary scale waves, and eddy motions.The most important minor electrically neutral constituents are compounds of oxygen, hydrogen, and nitrogen. In fact, the allotropes of oxygen are in many ways the most significant because they screen out solar ultraviolet radiation and provide the principal source of mesospheric heating (absorption of solar UV by 02 and ozone). We also discuss oxides of nitrogen and hydrogen which strongly influence the balance of odd oxygen (O and 03). Brief discussions of the chemistry of carbon compounds and of excited species are also included.The chemistry of ionic species present in the mesosphere is very important because it strongly influences the propagation and absorption of radio waves. Because of ion clustering and negative-ion formation, such chemistry is extremely complex, and it is only very recently that we have begun to understand it. The current state of knowledge is discussed in some detail. The principles involved in constructing models for predicting the distribution of minor constituents, both neutral and ionic, are presented.

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Photodissociation rates in the atmosphere below 100km

Cited by 47 publications

References 72 publications

Ultraviolet actinic flux in clear and cloudy atmospheres: model calculations and aircraft-based measurements

Ultraviolet actinic flux in clear and cloudy atmospheres: model calculations and aircraft-based measurements

Aerosol‐induced chemical perturbations of stratospheric ozone: Three‐dimensional simulations and analysis of mechanisms

The mesosphere

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