Aircraft measurements of photolysis rate coefficients for ozone and nitrogen dioxide under cloudy conditions

Pfister, Gabriele; Baumgartner, D.; Maderbacher, R.; Putz, E.

doi:10.1016/s1352-2310(00)00149-7

Cited by 24 publications

(22 citation statements)

References 24 publications

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“…Vertical (and horizontal) distributions of photolysis frequencies are much more complex in the presence of clouds (Junkermann, 1994;Pfister et al, 2000;Früh et al, 2000;Lefer et al, 2003;Kylling et al, 2005). The possible cloud impact can be seen for example in Figure 9.42.…”

Section: Temporal and Spatial Distributionsmentioning

confidence: 99%

Measurement of Photolysis Frequencies in the Atmosphere

Hofzumahaus¹

2006

Analytical Techniques for Atmospheric Measurement

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Section: Temporal and Spatial Distributionsmentioning

confidence: 99%

Measurement of Photolysis Frequencies in the Atmosphere

Hofzumahaus¹

2006

Analytical Techniques for Atmospheric Measurement

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“…assuming homogeneous cloudiness horizontally (reducing the problem from three dimensions to one), vertical discretization into uniform layers, and analytic approximations of the scattering phase functions. Actinic flux measurements confirm the high variability in the presence of clouds (Junkermann, 1994;Pfister et al, 2000;Lefer et al, 2003;Shetter et al, 2003;Thiel et al, 2008) but in most cases the detailed information needed as input to radiative transfer models is not available.…”

Section: Introductionmentioning

confidence: 99%

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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“…13b) is required to explain the observed slopes for the cloud at 1.5-2.5 km. High reflectivity marine stratocumulus clouds increase the actinic flux and therefore increase the photolysis rates to produce ozone above lowaltitude clouds (Madronich, 1987;Pfister et al, 2000). Pfister et al (2000) show that the j O 3 above clouds is about 50% higher than the corresponding clear-sky values.…”

Section: Marine Stratocumulus Clouds and Enhanced Tropospheric Ozonementioning

confidence: 99%

“…High reflectivity marine stratocumulus clouds increase the actinic flux and therefore increase the photolysis rates to produce ozone above lowaltitude clouds (Madronich, 1987;Pfister et al, 2000). Pfister et al (2000) show that the j O 3 above clouds is about 50% higher than the corresponding clear-sky values. Because there is a high frequency of stratocumulus clouds (Thompson et al, 1993;Stowe et al, 1989) and rich ozone precursors during the biomass season at WCSAF (Lee et al, 1998), it is possible to photochemically produce 3-6 DU more ozone relative to clear-sky conditions.…”

Section: Marine Stratocumulus Clouds and Enhanced Tropospheric Ozonementioning

confidence: 99%

Occurrence of ozone anomalies over cloudy areas in TOMS version-7 level-2 data

2003

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Abstract. This study investigates anomalous ozone distributions over cloudy areas in Nimbus-7 (N7) and Earth-Probe (EP) TOMS version-7 data and analyzes the causes for ozone anomaly formation. A 5 • -longitude by 5 • -latitude region is defined to contain a Positive Ozone Anomaly (POA) or Negative Ozone Anomaly (NOA) if the correlation coefficient between total ozone and reflectivity is ≥ 0.5 or ≤ −0.5. The average fractions of ozone anomalies among all cloud fields are 31.8 ± 7.7% and 35.8 ± 7.7% in the N7 and EP TOMS data, respectively. Some ozone anomalies are caused by ozone retrieval errors, and others are caused by actual geophysical phenomena. Large cloud-height errors are found in the TOMS version-7 algorithm in comparison to the Temperature Humidity Infrared Radiometer (THIR) cloud data. On average, cloud-top pressures are overestimated by ∼200 hPa (THIR cloud-top pressure ≤ 200 hPa) for high-altitude clouds and underestimated by ∼150 hPa for low-altitude clouds (THIR cloud-top pressure ≥ 750 hPa). Most tropical NOAs result from negative errors induced by large cloud-height errors, and most tropical POAs are caused by positive errors due to intra-cloud ozone absorption enhancement. However, positive and negative errors offset each other, reducing the ozone anomaly occurrence in TOMS data. Large ozone/reflectivity slopes for mid-latitude POAs show seasonal variation consistent with total ozone fluctuation, indicating that they result mainly from synoptic and planetary wave disturbances. POAs with an occurrence fraction of 30-60% occur in regions of marine stratocumulus off the west coast of South Africa and off the west coast of South America. Both fractions and ozone/reflectivity slopes of these POAs show seasonal variations consistent with that in the tropospheric ozone. About half the ozone/reflectivity slope can be explained by ozone retrieval errors over clear and cloudy areas. The remaining slope may result from there being more ozone production because of rich ozone precurCorrespondence to: X. Liu (xliu@cfa.harvard.edu) sors and higher photolysis rates over high-frequency, lowaltitude clouds than in clear areas. Ozone anomalies due to ozone retrieval errors have important implications in TOMS applications such as tropospheric ozone derivation and analysis of ozone seasonal variation.

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Aircraft measurements of photolysis rate coefficients for ozone and nitrogen dioxide under cloudy conditions

Cited by 24 publications

References 24 publications

Measurement of Photolysis Frequencies in the Atmosphere

Measurement of Photolysis Frequencies in the Atmosphere

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

Occurrence of ozone anomalies over cloudy areas in TOMS version-7 level-2 data

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