| 1. |
- Achtert, Peggy, 1982-, et al.
(författare)
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Investigation of polar stratospheric clouds in January 2008 by means of ground-based and spaceborne lidar measurements and microphysical box model simulations
- 2011
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 116, s. D07201-
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Tidskriftsartikel (refereegranskat)abstract
- Polar stratospheric clouds (PSCs) play a key role in heterogeneous chemistry and ozone depletion in the lower stratosphere. The type of PSC as well as their temporal and spatial extent are important for the occurrence of heterogeneous reactions and, thus, ozone depletion. In this study a combination of ground-based and spaceborne lidar measurements were used together with microphysical box model simulations along back trajectories to investigate the formation and alteration of Arctic PSCs. The measurements were made by the Rayleigh/Mie/Raman lidar system at Esrange and by the Cloud-Aerosol Lidar with Orthogonal Polarization aboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite. Between 20 and 23 January 2008 PSCs composed of liquid particles were observed by CALIPSO between Greenland and the western side of the Scandinavian Mountains. Between 21 and 23 January 2008 the Esrange lidar observed a PSC composed of distinct layers of liquid and solid particles on the eastern side of the mountain range. Microphysical box model simulations along air parcel back trajectories indicate that liquid particles had formed at least 40 h before the observation at Esrange. Furthermore, the model indicates a high HNO(3) uptake into the liquid layer between 10 and 20 h before the observation. The PSC was formed when the air mass was over Greenland. On two occasions during these 20 h, CALIPSO observed PSCs when its measurement tracks crossed the air parcel back trajectory ending at the location of the Esrange lidar. Backscatter ratios calculated from the output of the box model simulation indicate good agreement with the values observed with the Esrange lidar and by CALIPSO. The box model simulations along the back trajectories from Esrange to the CALIPSO ground track and beyond provide us with the unique opportunity to relate ground-based and spaceborne lidar measurements that were not performed at the same spatial location and time. Furthermore, possible differences in the observations from ground and space can be traced to temporal and/or geographically induced changes in particle microphysics within the measured PSCs.
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| 2. |
- Achtert, Peggy, 1982-
(författare)
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Lidar Measurements of Polar Stratospheric Clouds in the Arctic
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Polar Stratospheric Clouds (PSCs) play a key role for ozone depletion in the polar stratosphere. Its magnitude depends on the type of PSC and its lifetime and extent. This thesis presents PSC observations conducted with the Esrange lidar and the space-borne CALIPSO lidar.PSCs are separated into three types according to their optical properties. The occurrence rate of the different types which are often observed simultaneously as well as their interaction and connection is not well understood. To better understand the processes that govern PSC formation, observations need to be combined with a detailed view of the atmospheric background in which PSCs develop, exist, and are transformed from one type to another.This thesis introduces a new channel of the Esrange lidar for temperature profiling at heights below 35 km. The design of this channel and first temperature measurements within PSCs and cirrus clouds are presented. This is an important step since the majority of PSC-related literature extracts temperatures within PSCs from reanalysis data.In contrast to ground–based measurements space–borne lidar does not rely on cloud–free conditions. Hence, it provides an unprecedented opportunity for studying the connection between PSCs and the underlying synoptic–scale conditions which manifest as tropospheric clouds. This thesis shows that most of the PSCs observed in the Arctic during winter 2007/08 occurred in connection with tropospheric clouds.A combined analysis of ground-based and space-borne lidar observation of PSCs in combination with microphysical modeling can improve our understanding of PSC formation. A first case study of this approach shows how a PSC that was formed by synoptic-scale processes is transformed into another type while passing the Scandinavian mountains.Today a variety of classification schemes provides inconsistent information on PSC properties and types. This thesis suggests a unified classification scheme for lidar measurements of PSCs.
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| 3. |
- Achtert, Peggy, 1982-, et al.
(författare)
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On the linkage between tropospheric and Polar Stratospheric clouds in the Arctic as observed by space-borne lidar
- 2012
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 12:8, s. 3791-3798
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Tidskriftsartikel (refereegranskat)abstract
- The type of Polar stratospheric clouds (PSCs) as well as their temporal and spatial extent are important for the occurrence of heterogeneous reactions in the polar stratosphere. The formation of PSCs depends strongly on temperature. However, the mechanisms of the formation of solid PSCs are still poorly understood. Recent satellite studies of Antarctic PSCs have shown that their formation can be associated with deep-tropospheric clouds which have the ability to cool the lower stratosphere radiatively and/or adiabatically. In the present study, lidar measurements aboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite were used to investigate whether the formation of Arctic PSCs can be associated with deep-tropospheric clouds as well. Deep-tropospheric cloud systems have a vertical extent of more than 6.5 km with a cloud top height above 7 km altitude. PSCs observed by CALIPSO during the Arctic winter 2007/2008 were classified according to their type (STS, NAT, or ice) and to the kind of underlying tropospheric clouds. Our analysis reveals that 172 out of 211 observed PSCs occurred in connection with tropospheric clouds. 72% of these 172 observed PSCs occurred above deep-tropospheric clouds. We also find that the type of PSC seems to be connected to the characteristics of the underlying tropospheric cloud system. During the Arctic winter 2007/2008 PSCs consisting of ice were mainly observed in connection with deep-tropospheric cloud systems while no ice PSC was detected above cirrus. Furthermore, we find no correlation between the occurrence of PSCs and the top temperature of tropospheric clouds. Thus, our findings suggest that Arctic PSC formation is connected to adiabatice cooling, i.e. dynamic effects rather than radiative cooling.
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| 4. |
- Achtert, Peggy, 1982-, et al.
(författare)
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Pure rotational-Raman channels of the Esrange lidar for temperature and particle extinction measurements in the troposphere and lower stratosphere
- 2013
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Ingår i: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 6:1, s. 91-98
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Tidskriftsartikel (refereegranskat)abstract
- The Department of Meteorology at Stockholm University operates the Esrange Rayleigh/Raman lidar at Esrange(68° N, 21° E) near the Swedish city of Kiruna. This paper describes the design and first measurements of the newpure rotational-Raman channel of the Esrange lidar. The Esrange lidar uses a pulsed Nd:YAG solid-state laser operating at 532 nm as light source with a repetition rate of 20 Hz and a pulse energy of 350 mJ. The minimum vertical resolution is 150m and the integration time for one profile is 5000 shots. The newly implemented channel allows for measurements of atmospheric temperature at altitudes below 35 km and is currently optimized for temperature measurements between 180 and 200 K. This corresponds to conditions in the lower Arctic stratosphere during winter. In addition to the temperature measurements, the aerosol extinction coefficientand the aerosol backscatter coefficient at 532 nm can be measured in dependently. Our filter-based design minimizes the systematic error in the obtained temperature profile to less than 0.51 K. By combining rotational-Raman measurements (5–35 km height) and the integration technique (30–80 kmheight), the Esrange lidar is now capable of measuring atmospheric temperature profiles from the upper troposphere up to the mesosphere. With the improved setup, the system can be used to validate current lidar-based polar stratospheric cloud classification schemes. The new capability of the instrument measuring temperature and aerosol extinction furthermore enables studies of the thermal structure and variability of the upper troposphere/lower stratosphere. Although several lidars are operated at polar latitudes, there are few instruments that are capable of measuring temperature profiles in the troposphere, stratosphere, and mesosphere, as well as aerosols extinction in the troposphere and lower stratospherewith daylight capability.
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| 5. |
- Baron, Phillippe, et al.
(författare)
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Observation of horizontal winds in the middle-atmosphere between 30° S and 55° N during the northern winter 2009–2010
- 2012
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 13, s. 6049-6064
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Tidskriftsartikel (refereegranskat)abstract
- Although the links between stratospheric dynamics, climate and weather have been demonstrated, direct observations of stratospheric winds are lacking. We report observations of winds between 8 and 0.01 hPa (~35–80 km) from October 2009 to April 2010 by the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) on the International Space Station. The altitude range covers the region between 35–60 km where previous space-borne wind instruments show a lack of sensitivity. Both zonal and meridional wind components were obtained, though not simultaneously, in the latitude range from 30° S to 55° N and with a single profile precision of 7–9 m s−1 between 8 and 0.6 hPa and better than 20 m s−1 at altitudes above. The vertical resolution is 5–7 km except in the upper part of the retrieval range (10 km at 0.01 hPa). In the region between 1–0.05 hPa, a mean difference <2 m s−1 is found between SMILES profiles retrieved from different spectroscopic lines and instrumental settings. Good agreement (mean difference of ~2 m s−1) is also found with the European Centre for Medium-Range Weather Forecasts (ECMWF) analysis in most of the stratosphere except for the zonal winds over the equator (mean difference of 5–10 m s−1). In the mesosphere, SMILES and ECMWF zonal winds exhibit large differences (> 20 m s−1), especially in the tropics. We illustrate our results by showing daily and monthly zonal wind variations, namely the semi-annual oscillation in the tropics and reversals of the flow direction between 50° N–55° N during sudden stratospheric warmings in the stratosphere. The daily comparison with ECMWF winds reveals that in the beginning of February, a significantly stronger zonal westward flow is measured in the tropics at 2 hPa compared to the flow computed in the analysis (difference of ~20 m s−1). The results show that the comparison between SMILES and ECMWF winds is not only relevant for the quality assessment of the new SMILES winds but it also provides insights on the quality of the ECMWF winds themselves. Although the instrument was not specifically designed for measuring winds, the results demonstrate that space-borne sub-mm wave radiometers have the potential to provide good quality data for improving the stratospheric winds in atmospheric models.
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| 6. |
- Blum, Ulrich, et al.
(författare)
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Simultaneous lidar observations of a polar stratospheric cloud on the east and west side of the Scandinavian mountains and microphysical box model simulations
- 2006
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Ingår i: Annales Geophysicae. ; 24, s. 3267-3277
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Tidskriftsartikel (refereegranskat)abstract
- The importance of polar stratospheric clouds (PSC) for polar ozone depletion is well established. Lidar experiments are well suited to observe and classify polar stratospheric clouds. On 5 January 2005 a PSC was observed simultaneously on the east and west sides of the Scandinavian mountains by ground-based lidars. This cloud was composed of liquid particles with a mixture of solid particles in the upper part of the cloud. Multi-colour measurements revealed that the liquid particles had a mode radius of r~300 nm, a distribution width of ~1.04 and an altitude dependent number density of N~2–20 cm−3. Simulations with a microphysical box model show that the cloud had formed about 20 h before observation. High HNO3 concentrations in the PSC of 40–50 weight percent were simulated in the altitude regions where the liquid particles were observed, while this concentration was reduced to about 10 weight percent in that part of the cloud where a mixture between solid and liquid particles was observed by the lidar. The model simulations also revealed a very narrow particle size distribution with values similar to the lidar observations. Below and above the cloud almost no HNO3 uptake was simulated. Although the PSC shows distinct wave signatures, no gravity wave activity was observed in the temperature profiles measured by the lidars and meteorological analyses support this observation. The observed cloud must have formed in a wave field above Iceland about 20 h prior to the measurements and the cloud wave pattern was advected by the background wind to Scandinavia. In this wave field above Iceland temperatures potentially dropped below the ice formation temperature, so that ice clouds may have formed which can act as condensation nuclei for the nitric acid trihydrate (NAT) particles observed at the cloud top above Esrange.
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| 7. |
- Khosrawi, Farahnaz, et al.
(författare)
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Assessment of the interannual variability and influence of the QBO and upwelling on tracer-tracer distributions of N2O and O3 in the tropical lower stratosphere
- 2013
-
Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 13:7, s. 3619-3641
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Tidskriftsartikel (refereegranskat)abstract
- A modified form of tracer-tracer correlations of N2O and O3 has been used as a tool for the evaluation of atmospheric photochemical models. Applying this method monthly averages of N2O and O3 are derived for both hemispheres by partitioning the data into altitude (or potential temperature) bins and then averaging over a fixed interval of N2O. In a previous study, the method has been successfully applied to the validation of two Chemical Transport Models (CTMs) and one Chemistry-Climate Model (CCM) using 1-year climatology derived from the Odin Sub Millimetre Radiometer (Odin/SMR). However, the applicability of a 1-year climatology of monthly averages of N2O and O3 has been questioned due to the inability of some CCMs to simulate a specific year for the evaluation of CCMs. In this study, satellite measurements from Odin/SMR, the Aura Microwave Limb Sounder (Aura/MLS), the Michelson Interferometer for Passive Atmospheric Sounding on ENVISAT (ENVISAT/MIPAS), and the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA-1 and CRISTA-2) as well as model simulations from the Whole Atmosphere Community Climate Model (WACCM) are considered. By using seven to eight years of satellite measurements derived between 2003 and 2010 from Odin/SMR, Aura/MLS, ENVISAT/MIPAS and six years of model simulations from WACCM the interannual variability of lower stratospheric monthly averages of N2O and O3 is assessed. It is shown that the interannual variability of the monthly averages of N2O and O3 is low and thus can be easily distinguished from model deficiencies. Further, it is investigated why large differences between Odin/SMR observations and model simulations from the Karlsruhe Simulation Model of the Middle Atmosphere (KASIMA) and the atmospheric general circulation model ECHAM5/Messy1 are found for the Northern and Southern Hemisphere tropics (0° to 30° N and 0° to −30° S, respectively). The differences between model simulations and observations are most likely caused by an underestimation of the quasi-biennial oscillation and tropical upwelling by the models as well as due to biases and/or instrument noise from the satellite instruments. Finally, an inter-comparison between Odin/SMR, Aura/MLS, ENVISAT/MIPAS and WACCM was performed. The comparison shows that these data sets are generally in good agreement but that also some known biases of the data sets are clearly visible in the monthly averages, thus showing that this method is not only a valuable tool for model evaluation but also for satellite inter-comparisons.
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| 8. |
- Khosrawi, Farahnaz, et al.
(författare)
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Dehydration in the Northern Hemisphere midlatitude tropopause region observed during STREAM 1998
- 2006
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Ingår i: Tellus. ; 58B, s. 206-217
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Tidskriftsartikel (refereegranskat)abstract
- Measurements in the vicinity of the polar jet stream during the STREAM 1998 campaign in Timmins, Canada, show that during the flight on 15 July, a deep intrusion of stratospheric air into the troposphere occurred. At the edge of the deep intrusion dehydration was observed. The dehydration can be identified in tracer–tracer correlations of H2O and O3 and by the comparison of these correlations with correlations of H2O and O3 derived from two other flights of the STREAM 1998 campaign. Trajectories, calculated backwards for 10 days starting at each point of the measurement for the flight on 15 July, show that the saturation ratios required for homogeneous freezing are reached. However, boxmodel simulations along the trajectories indicate no substantial growth of H2SO4/H2O particles due to H2O uptake. Since ice nuclei were not measured during the campaign, it cannot be precisely determined which freezing process, heterogeneous or homogeneous, is responsible for the formation of the ice particles. Most likely, both processes were involved in the formation of ice particles that led to the observed dehydration on 15 July 1998.
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| 9. |
- Khosrawi, Farahnaz, et al.
(författare)
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Denitrification and polar stratospheric cloud formation during the Arctic winter 2009/2010
- 2011
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 11:16, s. 8471-8487
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Tidskriftsartikel (refereegranskat)abstract
- The sedimentation of HNO3 containing PolarStratospheric Cloud (PSC) particles leads to a permanent re-moval of HNO3 and thus to a denitrification of the strato-sphere, an effect which plays an important role in strato-spheric ozone depletion. The polar vortex in the Arctic win-ter 2009/2010 was very cold and stable between end of De-cember and end of January. Strong denitrification between 475 to 525 K was observed in the Arctic in mid of Januaryby the Odin Sub Millimetre Radiometer (Odin/SMR). Thiswas the strongest denitrification that had been observed inthe entire Odin/SMR measuring period (2001–2010). Lidarmeasurements of PSCs were performed in the area of Kiruna,Northern Sweden with the IRF (Institutet för Rymdfysik) li-odar and with the Esrange lidar in January 2010. The measurements show that PSCs were present over the area of Kirunaduring the entire period of observations. The formation ofPSCs during the Arctic winter 2009/2010 is investigated using a microphysical box model. Box model simulationsare performed along air parcel trajectories calculated sixdays backward according to the PSC measurements with the ground-based lidar in the Kiruna area. From the temperaturehistory of the backward trajectories and the box model simulations we find two PSC regions, one over Kiruna accordingto the measurements made in Kiruna and one north of Scandinavia which is much colder, reaching also temperatures below Tice. Using the box model trajectories together with the observations of Odin/SMR,Aura/MLS (Microwave Limb Sounder), CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations)and the ground-based lidar we investigate how and by whichtype of PSC particles the denitrification that was observedduring the Arctic winter 2009/2010 was caused. From ouranalysis we find that due to an unusually strong synopticcooling event in mid January, ice particle formation on NATmay be a possible formation mechanism during that particu-lar winter that may have caused the denitrification observed in mid January. In contrast, the denitrification that was observed in the beginning of January could have been caused by the sedimentation of NAT particles that formed on moun-tain wave ice clouds.
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| 10. |
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| 11. |
- Khosrawi, Farahnaz, et al.
(författare)
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Enhanced particle formation and growth due to mixing processes in the tropopause region
- 2003
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Ingår i: Atmospheric Environment. ; 37:7, s. 703-710
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Tidskriftsartikel (refereegranskat)abstract
- Enhancement of the binary homogeneous nucleation rate of H2SO4 and H2O and condensation of H2O and HNO3 on liquid sulphate aerosol particles due to mixing processes in the tropopause region were investigated by conducting theoretical studies and by using a sectional aerosol box model. If two air parcels with a large initial temperature and humidity difference are mixed with each other the nucleation rate within the resulting air parcel will be enhanced. This is due to the curvature of the saturation vapour pressure curve. The theoretical studies show that in the tropopause region enhancements of the nucleation rate of up to five orders of magnitude can occur. Since the mixing causes strong supersaturations also the condensation rate will be enhanced, especially for HNO3. The simulation with the sectional aerosol box model shows that after the mixing of two air parcels up to 40wt\% of HNO3 is taken up by the smallest aerosol particles. Since the initial air parcels are initialized with 0 wt% HNO3 this corresponds to a very strong enhancement. Measurements during the STREAM 1998 campaign show an entrainment of stratospheric air into the troposphere during the flight on 15 July leading to a production of new particles. Box model studies reproduce fairly well the measured number of newly formed particles.
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| 12. |
- Khosrawi, Farahnaz, 1971-, et al.
(författare)
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Evaluation of CLaMS, KASIMA and ECHAM5/MESSy1 simulations in the lower stratosphere using observations of Odin/SMR and ILAS/ILAS-II
- 2009
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 9:15, s. 5759-5783
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Tidskriftsartikel (refereegranskat)abstract
- 1-year data sets of monthly averaged nitrous oxide (N2O) and ozone (O3) derived from satellite measurements were used as a tool for the evaluation of atmospheric photochemical models. Two 1-year data sets, one solar occultation data set derived from the Improved Limb Atmospheric Spectrometer (ILAS and ILAS-II) and one limb sounding data set derived from the Odin Sub-Millimetre Radiometer (Odin/SMR) were employed. Here, these data sets are used for the evaluation of two Chemical Transport Models (CTMs), the Karlsruhe Simulation Model of the Middle Atmosphere (KASIMA) and the Chemical Lagrangian Model of the Stratosphere (CLaMS) as well as for one Chemistry-Climate Model (CCM), the atmospheric chemistry general circulation model ECHAM5/MESSy1 (E5M1) in the lower stratosphere with focus on the Northern Hemisphere. Since the Odin/SMR measurements cover the entire hemisphere, the evaluation is performed for the entire hemisphere as well as for the low latitudes, midlatitudes and high latitudes using the Odin/SMR 1-year data set as reference. To assess the impact of using different data sets for such an evaluation study we repeat the evaluation for the polar lower stratosphere using the ILAS/ILAS-II data set. Only small differences were found using ILAS/ILAS-II instead of Odin/SMR as a reference, thus, showing that the results are not influenced by the particular satellite data set used for the evaluation. The evaluation of CLaMS, KASIMA and E5M1 shows that all models are in agreement with Odin/SMR and ILAS/ILAS-II. Differences are generally in the range of ±20%. Larger differences (up to −40%) are found in all models at 500±25 K for N2O mixing ratios greater than 200 ppbv, thus in air masses of tropical character. Generally, the largest differences were found for the tropics and the lowest for the polar regions. However, an underestimation of polar winter ozone loss was found both in KASIMA and E5M1 both in the Northern and Southern Hemisphere.
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| 13. |
- Khosrawi, Farahnaz, et al.
(författare)
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Intercomparison between Lagrangian and Eulerian simulations of mid-latitude streamers as observed by CRISTA
- 2005
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Ingår i: Atmospheric Chemistry and Physics. ; 5, s. 85-95
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Tidskriftsartikel (refereegranskat)abstract
- During the CRISTA-1 mission three pronounced fingerlike structures reaching from the lower latitudes to the mid-latitudes, so-called streamers, were observed in the measurements of several trace gases in early November 1994. A simulation of these streamers in previous studies employing the KASIMA (Karlsruhe Simulation Model of the Middle Atmosphere) and ROSE (Research on Ozone in the Stratosphere and its Evolution) model, both being Eulerian models, show that their formation is due to adiabatic transport processes. Here, the impact of mixing on the development of these streamers is investigated. These streamers were simulated with the CLaMS model (Chemical Lagrangian Model of the Stratosphere), a Lagrangian model, using N2O as longlived tracer. Using several different initialisations the results were compared to the KASIMA simulations and CRISTA (Cryogenic Infrared Spectrometer and Telescope for the Atmosphere) observations. Further, since the KASIMA model was employed to derive a 9-year climatology, the quality of the reproduction of streamers from such a study was tested by the comparison of the KASIMA results with CLaMS and CRISTA. The streamers are reproduced well for the Northern Hemisphere in the simulations of CLaMS and KASIMA for the 6 November 1994. However, in the CLaMS simulation a stronger filamentation is found while larger discrepancies between KASIMA and CRISTA were found especially for the Southern Hemisphere. Further, compared to the CRISTA observations the mixing ratios of N2O are in general underestimated in the KASIMA simulations. An improvement of the simulations with KASIMA was obtained for a simulation time according to the length of the CLaMS simulation. To quantify the differences between the simulations with CLaMS and KASIMA, and the CRISTA observations, the probability density function technique (PDF) is used to interpret the tracer distributions. While in the PDF of the KASIMA simulation the small scale structures observed by CRISTA are smoothed out due to the numerical diffusion in the model, the PDFs derived from CRISTA observations can be reproduced by CLaMS by optimising the mixing parameterisation. Further, this procedure gives information onsmall-scale variabilities not resolved by the CRISTA observations.
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| 14. |
- Khosrawi, Farahnaz, et al.
(författare)
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Monthly averaged ozone and nitrous oxide from the Improved Limb Atmospheric Spectrometer (ILAS) in the Northern and Southern Hemisphere polar regions
- 2004
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Ingår i: Journal of Geophysical Research. ; 109
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Tidskriftsartikel (refereegranskat)abstract
- Northern and southern hemispheric averaged ozone (O3) and nitrous oxide (N2O) measured by the Improved Limb Atmospheric Spectrometer (ILAS) were used to examine photochemical and dynamical changes in high-latitude O3 distributions. Using correlations of O3 versus N2O, the ILAS data are organized monthly in both hemispheres by partitioning these data into equal bins of altitude or potential temperature. The resulting families of curves help to differentiate O3 changes due to photochemistry from those due to transport. Our study extends the work of Proffitt et al. [2003] for the Northern Hemisphere to the Southern Hemisphere. Further, our study confirms and extends their results for the Northern Hemisphere by applying their analysis to a significantly greater altitude range. As in the Northern Hemisphere, the families of curves for the altitude, and potential temperature bins in the Southern Hemisphere are separated and generally do not cross. In both hemispheres a better separation is found for the potential temperature binning. In the Southern Hemisphere November and December data, preserved photochemical O3 loss is evident in the lower stratosphere. Further, summer ozone loss is evident in the Southern Hemisphere from January to March. In the Arctic, ongoing photochemical O3 loss is evident in the Northern Hemisphere spring data. While at higher altitudes the correlation between N2O and O3 is generally positive (increasing N2O with increasing O3), at lower levels the correlation is negative. This change of correlation from positive to negative can be interpreted in terms of photochemical and dynamical processes. Strong descent causes a steepening of the positively correlated curves, while the curves change their slope from positive to negative if photochemical destruction of O3 is present and descent is weak. The level of slope change is also photochemically influenced and therefore changes with season. Data sets such as the one derived here may be useful for testing atmospheric models and for identifying future changes in stratospheric ozone.
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| 15. |
- Khosrawi, Farahnaz, et al.
(författare)
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Monthly averages of nitrous oxide and ozone for the Northern and Southern Hemisphere high latitudes: A ``one-year climatology'' derived from ILAS/ILAS-II observations
- 2006
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Ingår i: Journal of Geophysical Research. ; 111:D11S11
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Tidskriftsartikel (refereegranskat)abstract
- Correlations of ozone (O3) and nitrous oxide (N2O) have been suggested as a tool for validating photochemical models and as a reference for estimating high-latitude ozone loss. However, so far no analysis of ozone-tracer relations is available that provides agood temporal coverage during all months. Here we combine measurements from the Improved Limb Atmospheric Spectrometers (ILAS/ILAS-II) to derive an O3/N2O climatology for the high-latitude regions in the Northern and Southern Hemisphere foreach month of the year, thus providing a complete seasonal cycle. ILAS and ILAS-II operated on board the Advanced Earth Observing Satellite (ADEOS/ADEOS-II), and both instruments use the solar occultation technique. ILAS operated for 8 months in 1996/1997,and ILAS-II operated for 7 months in 2003. The ILAS-II measurements cover the months that are not available from ILAS. The ILAS/ILAS-II correlations of ozone versus nitrous oxide are organized monthly in both hemispheres by partitioning these data into equal bins of altitude or potential temperature. The resulting families of curves allow separation of ozone changes due to photochemistry from those due to transport. The combined ILAS/ILAS-II data set corroborates earlier findings that the families of O3/N2O curves are separated and generally do not cross and further that the separation is much clearer for the potential temperature binning than for the altitude binning. The much clearer separation for the potential temperature binning is due to transport being predominantly isentropic. Thus these curves are particularly suitable for the validation of photochemical models. The seasonal cycle of O3/N2O distributions in the Northern and Southern Hemisphere high latitudes is found to be rather different. In the Southern Hemisphere, O3/N2O distributions are influenced by the strong chemical ozone loss in the Antarctic vortex and by a much longer duration of the polar vortex. In the Northern Hemisphere, diabatic descent is much more pronounced. Solely during the setup phase of the polar vortex the N2O/O3 distributions in the two hemispheres are rather similar.
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| 16. |
- Khosrawi, Farahnaz, et al.
(författare)
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Particle formation in the Arctic free troposphere during the ASTAR 2004 campaign: A case study on the influence of vertical motion on the binary homogeneous nucleation of H2SO4/H2O
- 2010
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 10, s. 1105-1120
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Tidskriftsartikel (refereegranskat)abstract
- During the ASTAR (Arctic Study of Tropospheric Aerosol and Radiation) campaign nucleation mode particles (4 to 13 nm) were quite frequently observed at altitudes below 4000 m. However, in the upper free troposphere, nucleation mode particles were only observed once, namely during the flight on 24 May 2004 (7000 m). To investigate if vertical motion are the reason for this difference that on one particular day nucleation mode particles were observed but not on the other days we employ a microphysical box model. The box model simulations were performed along air parcel trajectories calculated 6-d backwards based on European Center for Medium-Range Weather Forecasts (ECMWF) meteorological analyses using state parameters such as pressure and temperature in combination with additional parameters such as vertical stability. Box model simulations were performed for the 24 May where nucleation mode particles were observed (nucleation event) as well as for the day with measurements before and after (22 and 26 May) which are representative for no nucleation (none nucleation event). A nucleation burst was simulated along all trajectories, however, in the majority of the simulations the nucleation rate was either too low or too high so that no nucleation mode particles were left at the time were the measurements were performed. Further, the simulation results could be divided into three cases. Thereby, we found that for case 1 the temperature was the only driving mechanism while for case 2 and 3 vertical motion have influenced the formation of new particles. The reason why nucleation mode particles were observed on 24 May, but not on the other day, can be explained by the conditions under which particle formation occurred. On 24 May the particle formation was caused by a slow updraft, while on the other two days the particle formation was caused by a fast updraft.
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| 17. |
- Khosrawi, Farahnaz, et al.
(författare)
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Seasonal cycle of averages of nitrous oxide and ozone in the Northern and Southern Hemisphere polar, midlatitude, and tropical regions derived from ILAS/ILAS-II and Odin/SMR observations
- 2008
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 113:D18, s. D18305-
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Tidskriftsartikel (refereegranskat)abstract
- Northern and Southern Hemispheric monthly averages of ozone (O-3) and nitrous oxide (N2O) have been suggested as a tool for evaluating atmospheric photochemical models. An adequate data set for such an evaluation can be derived from measurements made by satellites which, in general, have a high spatial and temporal coverage. Here, we use measurements made by the Improved Limb Atmospheric Spectrometers (ILAS and ILAS-II) which use the solar occultation technique and by the Odin-Sub-Millimetre Radiometer (Odin/SMR) which passively observes thermal emissions from the Earth's limb. From ILAS/ILAS-II and Odin/SMR observations, 1-year data sets of monthly averaged O-3 and N2O, covering a full seasonal cycle, were derived for the latitude range between 60 - 90 degrees N and 60 - 90 degrees S, respectively, by partitioning the data into equal bins of altitude or potential temperature. A comparison between both data sets in this latitude region shows a good agreement and verifies that limited sampling from satellite occultation experiments does not constitute a problem for deriving such a full seasonal cycle of monthly averaged N2O and O-3. Since Odin/SMR provides measurements globally, a 1-year data set of monthly averaged N2O and O-3 is reported here for both the entire Northern and Southern Hemispheres from these measurements. Further, these hemispheric data sets from Odin/SMR are separated into data sets of monthly averaged N2O and O-3 for the low latitudes, midlatitudes, and high latitudes. The resulting families of curves help to differentiate between O-3 changes due to photochemistry from those due to transport. These 1-year hemispheric data sets of monthly averaged N2O and O-3 from Odin/SMR and ILAS/ILAS-II as well as the data sets of monthly averaged N2O and O-3 for the specific latitude regions from Odin/SMR provide a potentially important tool for the evaluation of atmospheric photochemical models. An example of how such an evaluation can be performed is given using data from two chemical transport models (CTMs), the Chemical Lagrangian Model of the Stratosphere (CLaMS) and the Karlsruhe Simulation Model of the Middle Atmosphere (KASIMA). We find a good agreement between Odin/SMR and the CTMs CLaMS and KASIMA with differences generally less than +/- 20%.
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| 18. |
- Khosrawi, Farahnaz, et al.
(författare)
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Validation of CFC-12 measurements from the Improved Limb Atmospheric Spectrometer (ILAS)
- 2004
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Ingår i: Journal of Geophysical Research. ; 109:D06311
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of CFC-12 were made by the Improved Limb Atmospheric Spectrometer (ILAS) between 57 N and 72 N in the Northern Hemisphere and between 64 S and 89 S in the Southern Hemisphere. ILAS was launched on 17 August 1996 on board the Advanced Earth Observing Satellite (ADEOS). The ILAS validation balloon campaigns were carried out from Kiruna, Sweden (68 N, 21 E), in February and March 1997 and from Fairbanks, Alaska (65 N, 148 W), in April and May 1997. During these validation balloon campaigns, CFC-12 was measured with the in situ instruments ASTRID, BONBON, and SAKURA and the remote sensing spectrometers MIPAS-B, FIRS-2, and MkIV. ILAS version 6.0 CFC-12 profiles obtained at the nearest location to the validation balloon measurement are compared with these validation balloon measurements. The quality of ILAS CFC-12 data processed with the version 6.0 algorithm improved significantly compared to previous versions. Low relative differences between ILAS CFC-12 and the correlative measurements of about 10% were found between 13 and 20 km. The comparison of vertical profiles shows that ILAS CFC-12 data are useful below about 20–22 km inside the vortex and below about 25 km outside the vortex. However, at greater altitudes the relative percentage difference increases very strongly with increasing altitude. Further, correlations of CFC-12 with N2O show a good agreement with the correlative measurements for N2O values of N2O > 150 ppbv. In summary, ILAS CFC-12 data are now suitable for scientific studies in the lower stratosphere.
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| 19. |
- Lossow, Stefan, et al.
(författare)
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A reassessment of the discrepancies in the annual variation of delta D-H2O in the tropical lower stratosphere between the MIPAS and ACE-FTS satellite data sets
- 2020
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Ingår i: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 13:1, s. 287-308
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Tidskriftsartikel (refereegranskat)abstract
- The annual variation of delta D in the tropical lower stratosphere is a critical indicator for the relative importance of different processes contributing to the transport of water vapour through the cold tropical tropopause region into the stratosphere. Distinct observational discrepancies of the delta D annual variation were visible in the works of Steinwagner et al. (2010) and Randel et al. (2012). Steinwagner et al. (2010) analysed MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) observations retrieved with the IMK/IAA (Institut fur Meteorologie und Klimaforschung in Karlsruhe, Germany, in collaboration with the Instituto de Astrofisica de Andalucia in Granada, Spain) processor, while Randel et al. (2012) focused on ACE-FTS (Atmospheric Chemistry Experiment Fourier Transform Spectrometer) observations. Here we reassess the discrepancies based on newer MIPAS (IMK/IAA) and ACE-FTS data sets, also showing for completeness results from SMR (Sub-Millimetre Radiometer) observations and a ECHAM/MESSy (European Centre for Medium-Range Weather Forecasts Hamburg and Modular Earth Sub-model System) Atmospheric Chemistry (EMAC) simulation (Eichinger et al., 2015b). Similar to the old analyses, the MIPAS data set yields a pronounced annual variation (maximum about 75 parts per thousand), while that derived from the ACE-FTS data set is rather weak (maximum about 25 parts per thousand). While all data sets exhibit the phase progression typical for the tape recorder, the annual maximum in the ACE-FTS data set precedes that in the MIPAS data set by 2 to 3 months. We critically consider several possible reasons for the observed discrepancies, focusing primarily on the MIPAS data set. We show that the delta D annual variation in the MIPAS data up to an altitude of 40 hPa is substantially impacted by a start altitude effect, i.e. dependency between the lowermost altitude where MIPAS retrievals are possible and retrieved data at higher altitudes. In itself this effect does not explain the differences with the ACE-FTS data. In addition, there is a mismatch in the vertical resolution of the MIPAS HDO and H2O data (being consistently better for HDO), which actually results in an artificial tape-recorder-like signal in delta D. Considering these MIPAS characteristics largely removes any discrepancies between the MIPAS and ACE-FTS data sets and shows that the MIPAS data are consistent with a delta D tape recorder signal with an amplitude of about 25 parts per thousand in the lowermost stratosphere.
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| 20. |
- Read, William G., et al.
(författare)
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The SPARC Water Vapor Assessment II: assessment of satellite measurements of upper tropospheric humidity
- 2022
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Ingår i: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 15:11, s. 3377-3400
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Tidskriftsartikel (refereegranskat)abstract
- Nineteen limb-viewing data sets (occultation, passive thermal, and UV scattering) and two nadir upper tropospheric humidity (UTH) data sets are intercompared and also compared to frost-point hygrometer balloon sondes. The upper troposphere considered here covers the pressure range from 300-100 hPa. UTH is a challenging measurement, because concentrations vary between 2-1000 ppmv (parts per million by volume), with sharp changes in vertical gradients near the tropopause. Cloudiness in this region also makes the measurement challenging. The atmospheric temperature is also highly variable ranging from 180-250 K. The assessment of satellite-measured UTH is based on coincident comparisons with balloon frost-point hygrometer sondes, multi-month mapped comparisons, zonal mean time series comparisons, and coincident satellite-to-satellite comparisons. While the satellite fields show similar features in maps and time series, quantitatively they can differ by a factor of 2 in concentration, with strong dependencies on the amount of UTH. Additionally, time-lag response-corrected Vaisala RS92 radiosondes are compared to satellites and the frost-point hygrometer measurements. In summary, most satellite data sets reviewed here show on average similar to 30 % agreement amongst themselves and frost-point data but with an additional similar to 30 % variability about the mean bias. The Vaisala RS92 sonde, even with a time-lag correction, shows poor behavior for pressures less than 200 hPa.
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| 21. |
- von Hobe, M, et al.
(författare)
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Reconciliation of essential process parameters for an enhanced predictability of Arctic stratospheric ozone loss and its climate interactions (RECONCILE): activities and results
- 2013
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 13:18, s. 9233-9268
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Tidskriftsartikel (refereegranskat)abstract
- The international research project RECONCILE has addressed central questions regarding polar ozone depletion, with the objective to quantify some of the most relevant yet still uncertain physical and chemical processes and thereby improve prognostic modelling capabilities to realistically predict the response of the ozone layer to climate change. This overview paper outlines the scope and the general approach of RECONCILE, and it provides a summary of observations and modelling in 2010 and 2011 that have generated an in many respects unprecedented dataset to study processes in the Arctic winter stratosphere. Principally, it summarises important outcomes of RECONCILE including (i) better constraints and enhanced consistency on the set of parameters governing catalytic ozone destruction cycles, (ii) a better understanding of the role of cold binary aerosols in heterogeneous chlorine activation, (iii) an improved scheme of polar stratospheric cloud (PSC) processes that includes heterogeneous nucleation of nitric acid trihydrate (NAT) and ice on non-volatile background aerosol leading to better model parameterisations with respect to denitrification, and (iv) long transient simulations with a chemistryclimate model (CCM) updated based on the results of RECONCILE that better reproduce past ozone trends in Antarctica and are deemed to produce more reliable predictions of future ozone trends. The process studies and the global simulations conducted in RECONCILE show that in the Arctic, ozone depletion uncertainties in the chemical and microphysical processes are now clearly smaller than the sensitivity to dynamic variability.
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| 22. |
- Weigel, Katja, et al.
(författare)
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A stratospheric intrusion at the subtropical jet over the Mediterranean Sea : air-borne remote sensing observations and model results
- 2012
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 12:18, s. 8423-8438
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Tidskriftsartikel (refereegranskat)abstract
- Remote sensing measurements from the Cryogenic Infrared Spectrometers and Telescope for the Atmosphere – New Frontiers (CRISTA-NF) during a flight on 29 July 2006 are presented. This flight is part of the AMMA-SCOUT-O3 measurement campaign, where CRISTA-NF was deployed on the high-flying research aircraft M55-Geophysica. The flight path was located over Italy and the Mediterranean Sea and crossed over the subtropical jet twice. Measurements of temperature, and the volume mixing ratios of water vapor (H2O), ozone (O3), nitric acid (HNO3) and peroxyacetyl nitrate (PAN) are available with a vertical resolution of up to 500 m between about 6 to 21 km altitude. CRISTA-NF observes these trace gases simultaneously and provides a quasi-2-D view of the transition region between the troposphere and the stratosphere. The observation of these different trace gases allows to determine tropospheric and stratospheric air masses. As expected, higher abundances are found where the main source of the trace gases is located: in the stratosphere for O3 and in the troposphere for H2O and PAN. Tracer-tracer correlations between O3 and PAN are used to identify the mixed tropospheric and lowermost stratospheric air at the subtropical jet and around the thermal tropopause north of the jet. An intrusion of stratospheric air into the troposphere associated with the subtropical jet is found in the CRISTA-NF observations. The observations indicate that the intrusion is connected to a tropopause fold which is not resolved in the ECMWF analysis data. The intrusion was reproduced in a simulation with the Chemical Lagrangian Model of the Stratosphere (CLaMS). The CLaMS simulation shows, that the lowermost stratospheric air masses in the intrusion where transported along the the subtropical jet. The tropospheric air masses around the intrusion originate from the vicinity of the Asian monsoon anticyclone. This work discusses the nature of the observed processes at the subtropical jet based on the CRISTA-NF observations and the CLaMS simulation.
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