For the determination of photolysis rates at large zenith angles it has been demonstrated that refraction by the earth's atmosphere must be taken into account. In fact, due to the modified optical ...path the optical transmittance is thereby increased in most instances. Here we show that in addition the divergence of sun-rays, which is also caused by refraction but which reduces the direct solar irradiance, should not be neglected. Our calculations are based on a spherically symmetric atmosphere and include extinction by Rayleigh scattering, ozone, and background aerosol. For rays with 10 km tangent altitude the divergence yields a reduction of about 10% to 40% at solar zenith angles of 91° to 96°. Moreover, we find that the divergence effect can completely cancel the relative enhancement caused by the increase of transmittance.
Multiannual integrations with the Karlsruhe Simulation Model of the Middle Atmosphere (KASIMA) have been performed using meteorological analyses of vorticity and divergence up to 10 hPa to analyze ...the influence of a simplified SF sub(6) mesospheric chemistry on estimation of mean age of air and to compare profiles of SF sub(6) mixing ratios observed in the stratosphere with model simulations. The chemical degradation scheme includes electron attachment of SF sub(6) and subsequent reactions of SF super(-) sub(6), such as photodetachment and charge transfer with ozone. Several combinations of reaction rate constants and electron profiles have been tested. Good agreement with observations is found for inert SF sub(6) transport. However, when mesospheric loss is included in the model, significant deviations are found for polar winter observations above 25 km. Chemical loss by electron attachment without reactions yielding SF sub(6) again is not compatible with observations. The atmospheric lifetime of SF sub(6) spans 400 to 10,000 years, depending on the assumed loss mechanism and the value for the electron density in the stratosphere.
Vertical profiles of stratospheric ozone and ozone‐related trace gases were measured in winter 1999/2000 using the ground‐based millimeter‐wave radiometer MIRA 2 and a Fourier‐transform infrared ...spectrometer (FTIR) located at the Swedish Institute of Space Physics at Kiruna. The MIRA 2 measurements covered all three SOLVE/THESEO 2000 flight phases. An almost complete time series of O3 profiles and complementary profiles of ClO, HNO3, and N2O were achieved. Profiles of O3, HCl, HNO3, and N2O, as well as stratospheric column amounts of NO2, ClONO2, and ClO, were obtained from the continuous ground‐based FTIR measurements between January and March 2000. From the measurements of N2O and HF, a diabatic subsidence inside the polar vortex of about 1.2 km between January and March for altitudes of about 20 km was deduced. On 26 and 28 January, an uptake of about 25% of stratospheric HNO3 by polar stratospheric clouds (PSCs) could be measured and between January and March, an significant denitrification of the lower stratosphere was derived from the measurements. Strong chlorine activation was detected by both instruments in January and March, resulting in an ozone loss of more than 1 ppmv in a layer below 23 km. In comparison to recent cold winters, this layer was found to be quite thin. Therefore the total loss measured in column amount of (1.2–1.4) × 1022 molec/m2 was smaller than the losses in previous cold winters.
Global distributions of profiles of sulphur hexafluoride (SF sub(6)) have been retrieved from limb emission spectra recorded by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) ...on Envisat covering the period September 2002 to March 2004. Individual SF sub(6) profiles have a precision of 0.5 pptv below 25 km altitude and a vertical resolution of 4-6 km up to 35 km altitude. These data have been validated versus in situ observations obtained during balloon flights of a cryogenic whole-air sampler. For the tropical troposphere a trend of 0.230+/-0.008 pptv/yr has been derived from the MIPAS data, which is in excellent agreement with the trend from ground-based flask and in situ measurements from the National Oceanic and Atmospheric Administration Earth System Research Laboratory, Global Monitoring Division. For the data set currently available, based on at least three days of data per month, monthly 5 degree latitude mean values have a 1Ie standard error of 1%. From the global SF sub(6) distributions, global daily and monthly distributions of the apparent mean age of air are inferred by application of the tropical tropospheric trend derived from MIPAS data. The inferred mean ages are provided for the full globe up to 90 degree N/S, and have a 1Ie standard error of 0.25 yr. They range between 0 (near the tropical tropopause) and 7 years (except for situations of mesospheric intrusions) and agree well with earlier observations. The seasonal variation of the mean age of stratospheric air indicates episodes of severe intrusion of mesospheric air during each Northern and Southern polar winter observed, long-lasting remnants of old, subsided polar winter air over the spring and summer poles, and a rather short period of mixing with midlatitude air and/or upward transport during fall in October/November (NH) and April/May (SH), respectively, with small latitudinal gradients, immediately before the new polar vortex starts to form. The mean age distributions further confirm that SF sub(6) is destroyed in the mesosphere to a considerable degree. Model calculations with the Karlsruhe simulation model of the middle atmosphere (KASIMA) chemical transport model agree well with observed global distributions of the mean age only if the SF sub(6) sink reactions in the mesosphere are included in the model.
A characterization of the NOy partitioning in the warm Arctic winter 1998/1999 is given. Vertical profiles of nocturnal total reactive nitrogen (NOy = NO2 + HNO3 + ClONO2 + 2 N2O5 + HO2NO2) were ...retrieved from infrared limb emission spectra measured by the Michelson Interferometer for Passive Atmospheric Sounding, Balloon‐borne version (MIPAS‐B) instrument inside a distortion of the winter Arctic vortex from Kiruna (Sweden, 68°N) on 27 January 1999. To estimate the dynamic effects, the mixing ratios of the tracers N2O and CH4 were derived to construct a correlation between these two long‐lived species and to estimate the effects of mixing on the N2O‐NOy relationship. The measured data are compared to calculations performed with the three‐dimensional chemistry transport models (CTMs) SLIMCAT and KASIMA. The results show that despite the warm winter 1998/1999 without significant occurrence of polar stratospheric clouds, the agreement between both the measurement and the models and among the models themselves is not satisfactory. It appears that in such a dynamically active winter, mixing processes on different scales which are hard to reproduce with coarsely resolved CTMs should be taken into account to explain the differences. Nevertheless, the results indicate that the chemistry which controls the NOy partitioning is not yet understood well under the studied geophysical situation. Furthermore, chlorine activation appears to be too crudely modeled when winter temperatures are marginal for polar stratospheric cloud formation.
Vertical profiles of total reactive nitrogen (NOy = NO2 + HNO3 + ClONO2 + 2N2O5 + HO2NO2) along with the source gas N2O up to 38 km were retrieved from infrared limb emission spectra measured by the ...Michelson Interferometer for Passive Atmospheric Sounding, Balloonborne version (MIPAS‐B) instrument from Aire sur l'Adour (France, 42°N) on April 30, 1999. Three limb sequences of spectra were recorded 1 hour before, at and 3 hours after sunrise, respectively, allowing to investigate the NOy partitioning under night‐time and ‐ for the first time with the MIPAS‐B instrument ‐ also under day‐time conditions and to study the temporal evolution of the short‐lived species N2O5 and NO2 around sunrise. The MIPAS‐B data are compared to calculations performed with the 3‐D chemical transport model KASIMA (Karlsruhe Simulation model of the Middle Atmosphere). This comparison reveals a high degree of confidence in the model for the HNO3/NOy ratio in the whole altitude region and for the N2O5/NOy and NO2/NOy ratios above about 26 km. Below this altitude the N2O5/NOy ratio is significantly underestimated by the model. Also, the MIPAS‐B measurement suggests a night‐time built up of NO2 which is not reproduced by the model in an altitude region around 22 km.
Altitude profiles of ClONO sub(2) retrieved with the IMK (Institut fuer Meteorologie und Klimaforschung) science-oriented data processor from MIPAS/Envisat (Michelson Interferometer for Passive ...Atmospheric Sounding on Envisat) mid-infrared limb emission measurements between July 2002 and March 2004 have been validated by comparison with balloon-borne (Mark IV, FIRS2, MIPAS-B), airborne (MIPAS-STR), ground-based (Spitsbergen, Thule, Kiruna, Harestua, Jungfraujoch, Izana, Wollongong, Lauder), and spaceborne (ACE-FTS) observations. With few exceptions we found very good agreement between these instruments and MIPAS with no evidence for any bias in most cases and altitude regions. For balloon-borne measurements typical absolute mean differences are below 0.05 ppbv over the whole altitude range from 10 to 39 km. In case of ACE- FTS observations mean differences are below 0.03 ppbv for observations below 26 km. Above this altitude the comparison with ACE-FTS is affected by the photochemically induced diurnal variation of ClONO sub(2). Correction for this by use of a chemical transport model led to an overcompensation of the photochemical effect by up to 0.1 ppbv at altitudes of 30-35 km in case of MIPAS-ACE-FTS comparisons while for the balloon-borne observations no such inconsistency has been detected. The comparison of MIPAS derived total column amounts with ground-based observations revealed no significant bias in the MIPAS data. Mean differences between MIPAS and FTIR column abundances are 0.11+/- 0.12x10 super(14) cm super(-2) (1.0+/-1.1%) and -0.09+/-0.19x10 super(14) cm super(-2) (-0.8+/- 1.7%), depending on the coincidence criterion applied. chi super(2) tests have been performed to assess the combined precision estimates of MIPAS and the related instruments. When no exact coincidences were available as in case of MIPAS - FTIR or MIPAS - ACE-FTS comparisons it has been necessary to take into consideration a coincidence error term to account for chi super(2) deviations. From the resulting chi super(2) profiles there is no evidence for a systematic over/underestimation of the MIPAS random error analysis.
Validation of MIPAS {ClONO2} measurements M. Höpfner; T. von Clarmann; H. Fischer ...
Atmospheric chemistry and physics,
01/2007, Letnik:
7, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Altitude profiles of ClONO2 retrieved with the IMK (Institut für Meteorologie und Klimaforschung) science-oriented data processor from MIPAS/Envisat (Michelson Interferometer for Passive Atmospheric ...Sounding on Envisat) mid-infrared limb emission measurements between July 2002 and March 2004 have been validated by comparison with balloon-borne (Mark IV, FIRS2, MIPAS-B), airborne (MIPAS-STR), ground-based (Spitsbergen, Thule, Kiruna, Harestua, Jungfraujoch, Izaña, Wollongong, Lauder), and spaceborne (ACE-FTS) observations. With few exceptions we found very good agreement between these instruments and MIPAS with no evidence for any bias in most cases and altitude regions. For balloon-borne measurements typical absolute mean differences are below 0.05 ppbv over the whole altitude range from 10 to 39 km. In case of ACE-FTS observations mean differences are below 0.03 ppbv for observations below 26 km. Above this altitude the comparison with ACE-FTS is affected by the photochemically induced diurnal variation of ClONO2. Correction for this by use of a chemical transport model led to an overcompensation of the photochemical effect by up to 0.1 ppbv at altitudes of 30-35 km in case of MIPAS-ACE-FTS comparisons while for the balloon-borne observations no such inconsistency has been detected. The comparison of MIPAS derived total column amounts with ground-based observations revealed no significant bias in the MIPAS data. Mean differences between MIPAS and FTIR column abundances are 0.11±0.12×1014 cm−2 (1.0±1.1%) and −0.09±0.19×1014 cm−2 (−0.8±1.7%), depending on the coincidence criterion applied. χ2 tests have been performed to assess the combined precision estimates of MIPAS and the related instruments. When no exact coincidences were available as in case of MIPAS - FTIR or MIPAS - ACE-FTS comparisons it has been necessary to take into consideration a coincidence error term to account for χ2 deviations. From the resulting χ2 profiles there is no evidence for a systematic over/underestimation of the MIPAS random error analysis.
Vertical profiles of total reactive nitrogen (NO sub(y) = NO sub(2) + HNO sub(3) + ClONO sub(2) + 2N sub(2)O sub(5) + HO sub(2)NO sub(2)) along with the source gas N sub(2)O up to 38 km were ...retrieved from infrared limb emission spectra measured by the Michelson Interferometer for Passive Atmospheric Sounding, Balloonborne version (MIPAS-B) instrument from Aire sur l'Adour (France, 42 degree N) on April 30, 1999. Three limb sequences of spectra were recorded 1 hour before, at and 3 hours after sunrise, respectively, allowing to investigate the NO sub(y) partitioning under night-time and-for the first time with the MIPAS-B instrument-also under day-time conditions and to study the temporal evolution of the short-lived species N sub(2)O sub(5) and NO sub(2) around sunrise. The MIPAS-B data are compared to calculations performed with the 3-D chemical transport model KASIMA (Karlsruhe Simulation model of the Middle Atmosphere). This comparison reveals a high degree of confidence in the model for the HNO sub(3)/NO sub(y) ratio in the whole altitude region and for the N sub(2)O sub(5)/NO sub(y) and NO sub(2)/NO sub(y) ratios above about 26 km. Below this altitude the N sub(2)O sub(5)/NO sub(y) ratio is significantly underestimated by the model. Also, the MIPAS-B measurement suggests a night-time built up of NO sub(2) which is not reproduced by the model in an altitude region around 22 km.
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