| 1. |
- Achtert, Peggy, 1982-
(author)
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Lidar Measurements of Polar Stratospheric Clouds in the Arctic
- 2013
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Doctoral thesis (other academic/artistic)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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| 2. |
- Achtert, Peggy, 1982-, et al.
(author)
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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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In: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 12:8, s. 3791-3798
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Journal article (peer-reviewed)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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| 3. |
- Achtert, Peggy, 1982-, et al.
(author)
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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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In: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 6:1, s. 91-98
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Journal article (peer-reviewed)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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| 4. |
- Amyx, K., et al.
(author)
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In-situ measurement of smoke particles in the wintertime polar mesosphere between 80 and 85 km altitude
- 2008
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In: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826. ; 70, s. 61-70
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Journal article (peer-reviewed)abstract
- The MAGIC sounding rocket, launched in January 2005 into the polar mesosphere, carried two detectors for charged aerosol particles. The detectors are graphite patch collectors mounted flush with the skin of the payload and are connected to sensitive electrometers. The measured signal is the net current deposited on the detectors by heavy aerosol particles. The collection of electrons and ions is prevented by magnetic shielding and a small positive bias, respectively. Both instruments detected a layer of heavy aerosol particles between 80 and 85 km with a number density approximately 103 cm−3. Aerodynamic flow simulations imply that the collected particles are larger than 1 nm in radius. The particles are detected as a net positive charge deposited on the graphite collectors. It is suggested that the measured positive polarity is due to the electrification of the smoke particles upon impact on the graphite collectors.
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| 5. |
- Belova, E., et al.
(author)
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Multi-radar observations of polar mesosphere summer echoes during the PHOCUS campaign on 20-22 July 2011
- 2014
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In: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 118, s. 199-205
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Journal article (peer-reviewed)abstract
- During the PHOCUS rocket campaign, on 20-22 July 2011, the observations of polar mesosphere summer echoes (PMSE) were made by three mesosphere-stratosphere-troposphere radars, operating at about 50 MHz. One radar, ESRAD is located at Esrange in Sweden, where the rocket was launched, two other radars, MAARSY and MORRO, are located 250 km north-west and 200 km north of the ESRAD, respectively, on the other side of the Scandinavian mountain ridge. We compared PMSE as measured by these three radars in terms of their strength, spectral width and wave modulation. Time-altitude maps of PMSE strength look very similar for all three radars. Cross-correlations with maximum values 0.5-0.6 were found between the signal powers over the three days of observations for each pair of radars. By using cross-spectrum analysis of PMSE signals, we show that some waves with periods of a few hours were observed by all three radars. Unlike the strengths, simultaneous values of PMSE spectral width, which is related to turbulence, sometimes differ significantly between the radars. For interpretation of the results we suggested that large-scale fields of neutral temperature, ice particles and electron density, which are more or less uniform over 150-250 km horizontal extent were 'modulated' by waves and smaller patches of turbulence.
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| 6. |
- Benze, Susanne, et al.
(author)
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Making limb and nadir measurements comparable : A common volume study of PMC brightness observed by Odin OSIRIS and AIM CIPS
- 2018
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In: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 167, s. 66-73
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Journal article (peer-reviewed)abstract
- Combining limb and nadir satellite observations of Polar Mesospheric Clouds (PMCs) has long been recognized as problematic due to differences in observation geometry, scattering conditions, and retrieval approaches. This study offers a method of comparing PMC brightness observations from the nadir-viewing Aeronomy of Ice in the Mesosphere (AIM) Cloud Imaging and Particle Size (CIPS) instrument and the limb-viewing Odin Optical Spectrograph and InfraRed Imaging System (OSIRIS). OSIRIS and CIPS measurements are made comparable by defining a common volume for overlapping OSIRIS and CIPS observations for two northern hemisphere (NH) PMC seasons: NH08 and NH09. We define a scattering intensity quantity that is suitable for either nadir or limb observations and for different scattering conditions. A known CIPS bias is applied, differences in instrument sensitivity are analyzed and taken into account, and effects of cloud inhomogeneity and common volume definition on the comparison are discussed. Not accounting for instrument sensitivity differences or inhomogeneities in the PMC field, the mean relative difference in cloud brightness (CIPS - OSIRIS) is -102 +/- 55%. The differences are largest for coincidences with very inhomogeneous clouds that are dominated by pixels that CIPS reports as non-cloud points. Removing these coincidences, the mean relative difference in cloud brightness reduces to -6 +/- 14%. The correlation coefficient between the CIPS and OSIRIS measurements of PMC brightness variations in space and time is remarkably high, at 0.94. Overall, the comparison shows excellent agreement despite different retrieval approaches and observation geometries.
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| 7. |
- Broman, Lina, 1981-, et al.
(author)
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Case study of a large mesospheric front in polar mesospheric clouds
- 2022
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In: Tellus. Series A, Dynamic meteorology and oceanography. - : Stockholm University Press. - 0280-6495 .- 1600-0870. ; 74:1, s. 85-105
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Journal article (peer-reviewed)abstract
- A large mesospheric front structure was observed on 16 July 2010 in Polar Mesospheric Clouds using common volume observations performed by the Aeronomy of Ice in the Mesosphere (AIM) Cloud Imaging and Particle Size (CIPS) instrument and the Odin Optical Spectrograph and Infrared Imager System (OSIRIS) at ∼ 75◦ N, 144◦ E. During the 4.5 hours long observation time, the front structure manifested in the PMC layer as an ice free elongated structure with sharp edges to the surrounding cloud field. A propagation direction from Southeast to Northwest and simultaneous clockwise rotation of 12 deg/hour is observed and the horizontal extent of the structure is found to be about 1800 km long and 190 km wide. Common volume observations of the mesospheric environment in terms of temperatures and water vapor provided by the Odin Sub-Millimetre Radiometer (SMR) indicate an extensive elevated warm air mass during the occurrence of the front structure and colder temperatures at the sharp front edge. The presence of a wave structure with λz ∼ 6 km at an altitude of 70-90 km coincides with a sharpening of the front edge. We compare the general characteristics of the current mesospheric front to earlier reports on mesospheric fronts based on ground-based and space-borne airglow and PMC observations.
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| 8. |
- Broman, Lina, et al.
(author)
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Common volume satellite studies of polar mesospheric clouds with Odin/OSIRIS tomography and AIM/CIPS nadir imaging
- 2019
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In: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 19:19, s. 12455-12475
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Journal article (peer-reviewed)abstract
- Two important approaches for satellite studies of polar mesospheric clouds (PMCs) are nadir measurements adapting phase function analysis and limb measurements adapting spectroscopic analysis. Combining both approaches enables new studies of cloud structures and microphysical processes but is complicated by differences in scattering conditions, observation geometry and sensitivity. In this study, we compare common volume PMC observations from the nadir-viewing Cloud Imaging and Particle Size (CIPS) instrument on the Aeronomy of Ice in the Mesosphere (AIM) satellite and a special set of tomographic limb observations from the Optical Spectrograph and InfraRed Imager System (OSIRIS) on the Odin satellite performed over 18 d for the years 2010 and 2011 and the latitude range 78 to 80 degrees N. While CIPS provides preeminent horizontal resolution, the OSIRIS tomographic analysis provides combined horizontal and vertical PMC information. This first direct comparison is an important step towards co-analysing CIPS and OSIRIS data, aiming at unprecedented insights into horizontal and vertical cloud processes. Important scientific questions on how the PMC life cycle is affected by changes in humidity and temperature due to atmospheric gravity waves, planetary waves and tides can be addressed by combining PMC observations in multiple dimensions. Two- and three-dimensional cloud structures simultaneously observed by CIPS and tomographic OSIRIS provide a useful tool for studies of cloud growth and sublimation Moreover, the combined CIPS/tomographic OSIRIS dataset can be used for studies of even more fundamental character, such as the question of the assumption of the PMC particle size distribution. We perform the first thorough error characterization of OSIRIS tomographic cloud brightness and cloud ice water content (IWC). We establish a consistent method for comparing cloud properties from limb tomography and nadir observations, accounting for differences in scattering conditions, resolution and sensitivity. Based on an extensive common volume and a temporal coincidence criterion of only 5 min, our method enables a detailed comparison of PMC regions of varying brightness and IWC. However, since the dataset is limited to 18 d of observations this study does not include a comparison of cloud frequency. The cloud properties of the OSIRIS tomographic dataset are vertically resolved, while the cloud properties of the CIPS dataset is vertically integrated. To make these different quantities comparable, the OSIRIS tomographic cloud properties cloud scattering coefficient and ice mass density (IMD) have been integrated over the vertical extent of the cloud to form cloud albedo and IWC of the same quantity as CIPS cloud products. We find that the OSIRIS albedo (obtained from the vertical integration of the primary OSIRIS tomography product, cloud scattering coefficient) shows very good agreement with the primary CIPS product, cloud albedo, with a correlation coefficient of 0.96. However, OSIRIS systematically reports brighter clouds than CIPS and the bias between the instruments (OSIRIS -CIPS) is 3.4 x 10(-6) sr(-1) (+/- 2.9x 10(-6) sr(-1)) on average. The OSIRIS tomography IWC (obtained from the vertical integration of IMD) agrees well with the CIPS IWC, with a correlation coefficient of 0.91. However, the IWC reported by OSIRIS is lower than CIPS, and we quantify the bias to -22 g km(-2) (+/- 14 g km(-2)) on average.
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| 9. |
- Broman, Lina, 1981-, et al.
(author)
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Hemispheric comparison of polar mesospheric cloud structures and microphysics using the Odin satellite tomographic dataset
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Other publication (other academic/artistic)abstract
- Satellite-based tomography provides a new approach to studying Polar Mesospheric Clouds (PMCs). In this paper, we explore the tomographic dataset from the Odin satellite to study structures and microphysics of PMCs. The dataset is based on special limb scans over limited altitude ranges during 256 orbits in the years 2010-2014. The focus of the analysis is on latitudinal and hemispheric variation. The basic results are in line with earlier studies by lidars and conventional satellite limb measurements. We find a decrease with decreasing latitude of PMC occurrence frequency, brightness, ice water content and particle size. As for hemispheric differences, we find that occurrence frequency, brightness, ice water content and particle size are generally less in the Southern Hemisphere than in the Northern Hemisphere. Our limited Southern Hemisphere dataset does not show the general finding of lidar studies that PMCs in the South occur at higher altitudes than in the North. All data products show substantial diurnal variations, likely connected to tidal activity. As a basic microphysical parameter, the altitude gradient of the PMC particle size does not show any significant latitudinal or hemispheric dependence. This suggests a PMC growth/sedimentation process that is largely the same everywhere. The data presented here demonstrate the value of satellite-based tomography as a complement to lidars and conventional satellite measurements by providing global coverage in combination with both vertical and horizontal resolution.
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| 10. |
- Broman, Lina, 1981-
(author)
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Multi-satellite views on mesospheric microphysics and dynamics
- 2021
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Doctoral thesis (other academic/artistic)abstract
- Atmospheric gravity waves of different scales and origins strongly modulate the wind field and temperature structure of the higher parts of the atmosphere. Direct and continuous measurements of these processes are particularly complicated in the mesosphere at about 50 to 100 km height due to the remote location of this region. Polar mesospheric clouds (PMCs) that form in the summertime between 80 and 90 km over the polar regions are highly sensitive to changes in the background atmosphere, and in particular to waves. This makes them an ideal tracer for atmospheric conditions and wave activity. However, in order to use them as a tracer, we need to better understand the influence of waves on the clouds on a local scale.In this thesis, tomographic measurements from the limb viewing OSIRIS spectrograph on the Swedish Odin satellite are used to study 2D structures of PMCs. The aim is to improve our understanding of the clouds’ life cycle and of their interactions with waves and dynamics on different scales. First, a method is developed that combines the tomographic PMC measurements from the OSIRIS instrument with simultaneous measurements from the downward viewing CIPS instrument on NASA’s AIM satellite. The method allows studies of clouds in a common observational volume with a combined high vertical and horizontal resolution of cloud structures. Measurements of cloud brightness and ice content from the two instruments agree very well, and it is demonstrated that the combined dataset is well suited for studies of cloud structures and cloud microphysics. The combined dataset is further investigated to study assumptions on the particle size distribution of PMCs. We find that the commonly used Gaussian assumption cannot simultaneously describe the size distribution as seen by a column-integrating instrument (CIPS) and by a limb-integrating instrument (OSIRIS). Instead, we show that the particle population seen by a limb-integrating instrument is better represented by a broad lognormal distribution. In an atmospheric case study, the combined PMC dataset is used together with simultaneous temperature and water vapor measurements from the SMR instrument on Odin to study a special event of a mesospheric front structure. We characterize the temporal and structural development of the front as seen by both satellites and discuss possible generating mechanisms.Finally, we extend OSIRIS’ tomographic view to the southern hemisphere. The structure and dynamics of the atmosphere are not symmetric, but hemispheric differences in Earth’s topography cause differences in wind systems at all atmospheric altitudes. We therefore apply the tomographic approach to study differences between the northern and southern hemispheres in PMC morphology and microphysics.
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