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Quasi‐biennial oscillations (QBOs) in thirteen atmospheric general circulation models forced with both observed and annually repeating sea surface temperatures (SSTs) are evaluated. In most models the QBO period is close to, but shorter than, the observed period of 28 months. Amplitudes are within ±20% of the observed QBO amplitude at 10 hPa, but typically about half of that observed at lower altitudes (50 and 70 hPa). For almost all models, the oscillation's amplitude profile shows an overall upward shift compared to reanalysis and its meridional extent is too narrow. Asymmetry in the duration of eastward and westward phases is reasonably well captured, though not all models replicate the observed slowing of the descending westward shear. Westward phases are generally too weak, and most models have an eastward time mean wind bias throughout the depth of the QBO. The intercycle period variability is realistic and in some models is enhanced in the experiment with observed SSTs compared to the experiment with repeated annual cycle SSTs. Mean periods are also sensitive to this difference between SSTs, but only when parametrized non‐orographic gravity wave (NOGW) sources are coupled to tropospheric parameters and not prescribed with a fixed value. Overall, however, modelled QBOs are very similar whether or not the prescribed SSTs vary interannually. A portrait of the overall ensemble performance is provided by a normalized grading of QBO metrics. To simulate a QBO, all but one model used parametrized NOGWs, which provided the majority of the total wave forcing at altitudes above 70 hPa in most models. Hence the representation of NOGWs either explicitly or through parametrization is still a major uncertainty underlying QBO simulation in these present‐day experiments. [ABSTRACT FROM AUTHOR]

The Quasi‐Biennial Oscillation initiative (QBOi) is a model intercomparison programme that specifically targets simulation of the QBO in current global climate models. Eleven of the models or model versions that participated in a QBOi intercomparison study have upper boundaries in or above the mesosphere and therefore simulate the region where the stratopause semiannual oscillation (SAO) is the dominant mode of variability of zonal winds in the tropical upper stratosphere. Comparisons of the SAO simulations in these models are presented here. These show that the model simulations of the amplitudes and phases of the SAO in zonal‐mean zonal wind near the stratopause agree well with the information derived from available observations. However, most of the models simulate time‐average zonal winds that are more westward than determined from observations, in some cases by several tens of m·s–1. Validation of wave activity in the models is hampered by the limited observations of tropical waves in the upper stratosphere but suggests a deficit of eastward forcing either by large‐scale waves, such as Kelvin waves, or by gravity waves. [ABSTRACT FROM AUTHOR]

The article discusses the study that evaluates the IASI carbon monoxide (CO) total column product for 2008. It indicates that the IASI total columns generally show an equal distribution of under- and overestimation. It suggests the need for further work to identify the source of discrepancies observed on individual measurements, such as the specific contaminations due to fire pollution plumes.

Vertical profiles of NO2 and NO have been obtained from solar occultation measurements by the Atmospheric Chemistry Experiment (ACE), using an infrared Fourier Transform Spectrometer (ACE-FTS) and (for NO2) an ultraviolet-visible-near-infrared spectrometer, MAESTRO (Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation). In this paper, the quality of the ACE-FTS version 2.2 NO2 and NO and the MAESTRO version 1.2 NO2 data are assessed using other solar occultation measurements (HALOE, SAGE II, SAGEIII, POAMIII, SCIAMACHY), stellar occultation measurements (GOMOS), limb measurements (MIPAS, OSIRIS), nadir measurements (SCIAMACHY), balloon-borne measurements (SPIRALE, SAOZ) and ground-based measurements (UV-VIS, FTIR). Time differences between the comparison measurements were reduced using either a tight coincidence criterion, or where possible, chemical box models. ACE-FTS NO2 and NO and the MAESTRO NO2 are generally consistent with the correlative data. The ACE-FTS and MAESTRO NO2 volume mixing ratio (VMR) profiles agree with the profiles from other satellite data sets to within about 20% between 25 and 40 km, with the exception of MIPAS ESA (for ACE-FTS) and SAGEII (for ACE-FTS (sunrise) and MAESTRO) and suggest a negative bias between 23 and 40 km of about 10%. MAESTRO reports larger VMR values than the ACE-FTS. In comparisons with HALOE, ACE-FTS NO VMRs typically (on average) agree to ±8% from 22 to 64 km and to +10% from 93 to 105 km, with maxima of 21% and 36%, respectively. Partial column comparisons for NO2 show that there is quite good agreement between the ACE instruments and the FTIRs, with a mean difference of +7.3% for ACEFTS and +12.8% for MAESTRO. [ABSTRACT FROM AUTHOR]

The Atmospheric Chemistry Experiment (ACE), also known as SCISAT, was launched on 12 August 2003, carrying two instruments that measure vertical profiles of atmospheric constituents using the solar occultation technique. One of these instruments, the ACE Fourier Transform Spectrometer (ACE-FTS), is measuring volume mixing ratio (VMR) profiles of nitrous oxide (N2O) from the upper troposphere to the lower mesosphere at a vertical resolution of about 3-4 km. In this study, the quality of the ACE-FTS version 2.2 N2O data is assessed through comparisons with coincident measurements made by other satellite, balloonborne, aircraft, and ground-based instruments. These consist of vertical profile comparisons with the SMR, MLS, and MIPAS satellite instruments, multiple aircraft flights of ASUR, and single balloon flights of SPIRALE and FIRS-2, and partial column comparisons with a network of groundbased Fourier Transform InfraRed spectrometers (FTIRs). Between 6 and 30 km, the mean absolute differences for the satellite comparisons lie between -42 ppbv and +17 ppbv, with most within ±20 ppbv. This corresponds to relative deviations from the mean that are within ±15%, except for comparisons with MIPAS near 30 km, for which they are as large as 22.5%. Between 18 and 30 km, the mean absolute differences for the satellite comparisons are generally within ±10 ppbv. From 30 to 60 km, the mean absolute differences are within ±4 ppbv, and are mostly between -2 and +1 ppbv. Given the small N2O VMR in this region, the relative deviations from the mean are therefore large at these altitudes, with most suggesting a negative bias in the ACE-FTS data between 30 and 50 km. In the comparisons with the FTIRs, the mean relative differences between the ACE-FTS and FTIR partial columns (which cover a mean altitude range of 14 to 27 km) are within ±5.6% for eleven of the twelve contributing stations. This mean relative difference is negative at ten stations, suggesting a small negative bias in the ACE-FTS partial columns over the altitude regions compared. Excellent correlation (R=0.964) is observed between the ACE-FTS and FTIR partial columns, with a slope of 1.01 and an intercept of -0.20 on the line fitted to the data. [ABSTRACT FROM AUTHOR]

The Atmospheric Chemistry Experiment (ACE) satellite was launched on 12 August 2003. Its two instruments measure vertical profiles of over 30 atmospheric trace gases by analyzing solar occultation spectra in the ultraviolet/visible and infrared wavelength regions. The reservoir gases HNO3, ClONO2, and N2O5 are three of the key species provided by the primary instrument, the ACE Fourier Transform Spectrometer (ACE-FTS). This paper describes the ACE-FTS version 2.2 data products, including the N2O5 update, for the three species and presents validation comparisons with available observations. We have compared volume mixing ratio (VMR) profiles of HNO3, ClONO2, and N2O5 with measurements by other satellite instruments (SMR, MLS, MIPAS), aircraft measurements (ASUR), and single balloon-flights (SPIRALE, FIRS-2). Partial columns of HNO3 and ClONO2 were also compared with measurements by ground-based Fourier Transform Infrared (FTIR) spectrometers. Overall the quality of the ACE-FTS v2.2 HNO3 VMR profiles is good from 18 to 35 km. For the statistical satellite comparisons, the mean absolute differences are generally within ±1 ppbv (±20%) from 18 to 35 km. For MIPAS and MLS comparisons only, mean relative differences lie within ±10% between 10 and 36 km. ACE-FTS HNO3 partial columns (∼15-30 km) show a slight negative bias of -1.3% relative to the ground-based FTIRs at latitudes ranging from 77.8° S-76.5° N. Good agreement between ACEFTS ClONO2 and MIPAS, using the Institut für Meteorologie und Klimaforschung and Instituto de Astrofísica de Andalucía (IMK-IAA) data processor is seen. Mean absolute differences are typically within ±0.01 ppbv between 16 and 27 km and less than +0.09 ppbv between 27 and 34 km. The ClONO2 partial column comparisons show varying degrees of agreement, depending on the location and the quality of the FTIR measurements. Good agreement was found for the comparisons with the midlatitude Jungfraujoch partial columns for which the mean relative difference is 4.7%. ACE-FTS N2O5 has a low bias relative to MIPAS IMK-IAA, reaching -0.25 ppbv at the altitude of the N2O5 maximum (around 30 km). Mean absolute differences at lower altitudes (16-27 km) are typically -0.05 ppbv for MIPAS nighttime and ±0.02 ppbv for MIPAS daytime measurements. [ABSTRACT FROM AUTHOR]

The first three Arctic winters of the ACE mission represented two extremes of winter variability: Stratospheric sudden warmings (SSWs) in 2004 and 2006 were among the strongest, most prolonged on record; 2005 was a record cold winter. Canadian Arctic Atmospheric Chemistry Experiment (ACE) Validation Campaigns were conducted at Eureka (80° N, 86° W) during each of these winters. New satellite measurements from ACE-Fourier Transform Spectrometer (ACE-FTS), Sounding of the Atmosphere using Broadband Emission Radiometry (SABER), and Aura Microwave Limb Sounder (MLS), along with meteorological analyses and Eureka lidar temperatures, are used to detail the meteorology in these winters, to demonstrate its influence on transport, and to provide a context for interpretation of ACE-FTS and validation campaign observations. During the 2004 and 2006 SSWs, the vortex broke down throughout the stratosphere, reformed quickly in the upper stratosphere, and remained weak in the middle and lower stratosphere. The stratopause reformed at very high altitude, near 75 km. ACE measurements covered both vortex and extra-vortex conditions in each winter, except in late-February through mid-March 2004 and 2006, when the strong, pole-centered vortex that reformed after the SSWs resulted in ACE sampling only inside the vortex in the middle through upper stratosphere. The 2004 and 2006 Eureka campaigns were during the recovery from the SSWs, with the redeveloping vortex over Eureka. 2005 was the coldest winter on record in the lower stratosphere, but with an early final warming in mid-March. The vortex was over Eureka at the start of the 2005 campaign, but moved away as it broke up. Disparate temperature profile structure and vortex evolution resulted in much lower (higher) temperatures in the upper (lower) stratosphere in 2004 and 2006 than in 2005. Satellite temperatures agree well with lidar data up to 50-60 km, and ACE-FTS, MLS and SABER show good agreement in high-latitude temperatures throughout the winters. Consistent with a strong, cold upper stratospheric vortex and enhanced radiative cooling after the SSWs, MLS and ACE-FTS trace gas measurements show strongly enhanced descent in the upper stratospheric vortex in late January through March 2006 compared to that in 2005. [ABSTRACT FROM AUTHOR]

The first three Canadian Arctic ACE validation campaigns were held during polar sunrise at Eureka, Nunavut, Canada (80° N, 86° W) from 2004 to 2006 in support of validation of the ACE (Atmospheric Chemistry Experiment) satellite mission. Three or four 5 zenith-sky viewing UV-visible spectrometers have taken part in each of the three campaigns. The differential slant column densities and vertical column densities from these instruments have been compared following the methods of the UV-visible Working Group of the NDACC (Network for Detection of Atmospheric Composition Change). The instruments are found to partially agree within the required accuracies for both species, although both the vertical and slant column densities are more scattered than required. This might be expected given the spatial and temporal variability of the Arctic stratosphere in spring. The vertical column densities are also compared to integrated total columns from ozonesondes and integrated partial columns from the ACE-FTS (ACE-Fourier Transform Spectrometer) and ACE-MAESTRO (ACE-Measurements of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) instruments on board ACE. For both species, the columns from the ground-based instruments and the ozonesondes are found to generally agree within their combined error bars. The ACE-FTS ozone partial columns and the ground-based total columns agree within 4.5%, averaged over the three campaigns. The ACE-MAESTRO ozone partial columns are generally smaller than those of the ground-based instruments, by an average of 9.9%, and are smaller than the ACE-FTS columns by an average of 14.4%. The ACE-FTS NO2 partial columns are an average of 13.4% smaller than the total columns from the ground-based instruments, as expected. The ACE-MAESTRO NO2 partial columns are larger than the total columns of the ground-based instruments by an average of 2.5% and larger than the partial columns of the ACE-FTS by an average of 15.5%. [ABSTRACT FROM AUTHOR]

The MANTRA (Middle Atmosphere Nitrogen TRend Assessment) 2004 campaign took place in Vanscoy, Saskatchewan, Canada (52° N, 107° W) from 3 August to 15 September, 2004. In support of the main balloon launch, a suite of five zenith-sky and direct-Sun-viewing UV-visible ground-based spectrometers was deployed, primarily measuring ozone and NO2 total columns. Three Fourier transform spectrometers (FTSs) that were part of the balloon payload also performed ground-based measurements of several species, including ozone. Ground-based measurements of ozone and NO2 differential slant column densities from the zenith-viewing UV-visible instruments are presented herein. They are found to partially agree within NDACC (Network for the Detection of Atmospheric Composition Change) standards for instruments certified for process studies and satellite validation. Vertical column densities of ozone from the zenith-sky UV-visible instruments, the FTSs, a Brewer spectrophotometer, and ozonesondes are compared, and found to agree within the combined error estimates of the instruments (15%). NO2 vertical column densities from two of the UVvisible instruments are compared, and are also found to agree within combined error (15%). [ABSTRACT FROM AUTHOR]

The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), on-board the European ENVIronmental SATellite (ENVISAT) launched on 1 March 2002, is a middle infrared Fourier Transform spectrometer measuring the atmospheric emission spectrum in limb sounding geometry. The instrument is capable to retrieve the vertical distribution of temperature and trace gases, aiming at the study of climate and atmospheric chemistry and dynamics, and at applications to data assimilation and weather forecasting. [ABSTRACT FROM AUTHOR]

The first three Canadian Arctic Atmospheric Chemistry Experiment (ACE) Validation Campaigns at Eureka (80° N, 86° W) were during two extremes of Arctic winter variability: Stratospheric sudden warmings (SSWs) in 2004 and 2006 were among the strongest, most prolonged on record; 2005 was a record cold winter. New satellite measurements from ACE-Fourier Transform Spectrometer (ACE-FTS), Sounding of the Atmosphere using Broadband Emission Radiometry, and Aura Microwave Limb Sounder (MLS), with meteorological analyses and Eureka lidar and radiosonde temperatures, are used to detail the meteorology in these winters, to demonstrate its influence on transport and chemistry, and to provide a context for interpretation of campaign observations. During the 2004 and 2006 SSWs, the vortex broke down throughout the stratosphere, reformed quickly in the upper stratosphere, and remained weak in the middle and lower stratosphere. The stratopause reformed at very high altitude, above where it could be accurately represented in the meteorological analyses. The 2004 and 2006 Eureka campaigns were during the recovery from the SSWs, with the redeveloping vortex over Eureka. 2005 was the coldest winter on record in the lower stratosphere, but with an early final warming in mid-March. The vortex was over Eureka at the start of the 2005 campaign, but moved away as it broke up. Disparate temperature profile structure and vortex evolution resulted in much lower (higher) temperatures in the upper (lower) stratosphere in 2004 and 2006 than in 2005. Satellite temperatures agree well with Eureka radiosondes, and with lidar data up to 50-60 km. Consistent with a strong, cold upper stratospheric vortex and enhanced radiative cooling after the SSWs, MLS and ACE-FTS trace gas measurements show strongly enhanced descent in the upper stratospheric vortex during the 2004 and 2006 Eureka campaigns compared to that in 2005. [ABSTRACT FROM AUTHOR]

The authors describe the optical design of a high-resolution Fourier Transform Spectrometer (FTS), which serves as the primary instrument at the University of Toronto Atmospheric Observatory (TAO). The FTS is dedicated to ground-based infrared solar absorption atmospheric measurements from Toronto, Ontario, Canada. Instrument performance is discussed in terms of instrumental line shape (ILS) and phase error and modulation efficiency as a function of optical path difference. Typical measurement parameters are presented together with retrieval parameters used to derive total and partial column concentrations of ozone. Retrievals at TAO employ the optimal estimation method (OEM), and some impacts of the necessary a priori constraints are examined. In March 2004, after participating in a retrieval algorithm user intercomparison exercise, the TAO FTS was granted the status of a Complementary Observation Station within the international community of high-resolution FTS users in the Network for the Detection of Atmospheric Composition and Change (NDACC). During this exercise, average differences between total columns retrieved from the same spectra by different users were below 2.1% for O3, HCl, and N2O in the blind phase, and below 1% in the open phase, when all retrieval constraints were identical. Finally, a 2.5-yr time series of monthly mean stratospheric ozone columns agrees within 3% with those retrieved from Optical Spectrograph and Infrared Imager System (OSIRIS) measurements on board the Odin satellite, which is within the errors of both measurement platforms. [ABSTRACT FROM AUTHOR]

Total column amounts of CO, CH4, CO2 and N2O retrieved from SCIAMACHY nadir observations in its near-infrared channels have been compared to data from a ground-based quasi-global network of Fourier-transform infrared (FTIR) spectrometers. The SCIAMACHY data considered here have been produced by three different retrieval algorithms, WFM-DOAS (version 0.5 for CO and CH4 and version 0.4 for CH2 and N2O), IMAP-DOAS (version 1.1 and 0.9 (for CO)) and IMLM (version 6.3) and cover the January to December 2003 time period. Comparisons have been made for individual data, as well as for monthly averages. To maximize the number of reliable coincidences that satisfy the temporal and spatial collocation criteria, the SCIAMACHY data have been compared with a temporal 3rd order polynomial interpolation of the ground-based data. Particular attention has been given to the question whether SCIAMACHY observes correctly the seasonal and latitudinal variability of the target species. The present results indicate that the individual SCIAMACHY data obtained with the actual versions of the algorithms have been significantly improved, but that the quality requirements, for estimating emissions on regional scales, are not yet met. Nevertheless, possible directions for further algorithm upgrades have been identified which should result in more reliable data products in a near future. [ABSTRACT FROM AUTHOR]

Total column amounts of CO, CH4, CO2 and N2O retrieved from SCIAMACHY nadir observations in its near-infrared channels have been compared to data from a groundbased quasi-global network of Fourier-transform infrared (FTIR) spectrometers. The SCIAMACHY data considered here have been produced by three different retrieval algorithms, WFM-DOAS (version 0.4, 0.41 for CH4), IMAP-DOAS (version 0.9) and IMLM (version 5.5) and cover the January to December 2003 time period. Comparisons have been made for individual data, as well as for monthly averages. To maximize the number of reliable coincidences that satisfy the temporal and spatial collocation criteria, the SCIAMACHY data have been compared with a temporal 3rd order polynomial interpolation of the ground-based data. Particular attention has been given to the question whether SCIAMACHY observes correctly the seasonal and latitudinal variability of the target species. The ensemble of comparisons, discussed in this paper, demonstrate the capability of SCIAMACHY, using any of the three algorithms, to deliver products for the target species under consideration, which are already useful for qualitative geophysical studies on a global scale. It is expected that the remaining uncertainties in the data products will decrease in future versions of the algorithm to also allow more quantitative investigations on a regional scale. [ABSTRACT FROM AUTHOR]