| 1. |
- Benze, Susanne, et al.
(författare)
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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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Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 167, s. 66-73
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Tidskriftsartikel (refereegranskat)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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| 2. |
- Broman, Lina, et al.
(författare)
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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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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 19:19, s. 12455-12475
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Tidskriftsartikel (refereegranskat)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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| 3. |
- Christensen, Ole Martin, 1984, et al.
(författare)
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The relationship between polar mesospheric clouds and their background atmosphere as observed by Odin-SMR and Odin-OSIRIS
- 2016
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 16:19, s. 12587-12600
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Tidskriftsartikel (refereegranskat)abstract
- In this study the properties of polar mesospheric clouds (PMCs) and the background atmosphere in which they exist are studied using measurements from two instruments, OSIRIS and SMR, on board the Odin satellite. The data comes from a set of tomographic measurements conducted by the satellite during 2010 and 2011. The expected ice mass density and cloud frequency for conditions of thermodynamic equilibrium, calculated using the temperature and water vapour as measured by SMR, are compared to the ice mass density and cloud frequency as measured by OSIRIS. We find that assuming thermodynamic equilibrium reproduces the seasonal, latitudinal and vertical variations in ice mass density and cloud frequency, but with a high bias of a factor of 2 in ice mass density. To investigate this bias, we use a simple ice particle growth model to estimate the time it would take for the observed clouds to sublimate completely and the time it takes for these clouds to reform. We find a difference in the median sublimation time (1.8 h) and the reformation time (3.2 h) at peak cloud altitudes (82-84 km). This difference implies that temperature variations on these timescales have a tendency to reduce the ice content of the clouds, possibly explaining the high bias of the equilibrium model. Finally, we detect and are, for the first time, able to positively identify cloud features with horizontal scales of 100 to 300 km extending far below the region of supersaturation (>2 km). Using the growth model, we conclude these features cannot be explained by sedimentation alone and suggest that these events may be an indication of strong vertical transport.
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| 4. |
- Christensen, Ole Martin, 1984, et al.
(författare)
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Tomographic retrieval of water vapour and temperature around polar mesospheric clouds using Odin-SMR
- 2015
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Ingår i: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 8:5, s. 1981-1999
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Tidskriftsartikel (refereegranskat)abstract
- A special observation mode of the Odin satellite provides the first simultaneous measurements of water vapour, temperature and polar mesospheric cloud (PMC) brightness over a large geographical area while still resolving both horizontal and vertical structures in the clouds and background atmosphere. The observation mode was activated during June, July and August of 2010 and 2011, and for latitudes between 50 and 82 degrees N. This paper focuses on the water vapour and temperature measurements carried out with Odin's sub-millimetre radiometer (SMR). The tomographic retrieval approach used provides water vapour and temperature between 75 and 90 km with a vertical resolution of about 2.5 km and a horizontal resolution of about 200 km. The precision of the measurements is estimated to 0.2 ppmv for water vapour and 2K for temperature. Due to limited information about the pressure at the measured altitudes, the results have large uncertainties (> 3 ppmv) in the retrieved water vapour. These errors, however, influence mainly the mean atmosphere retrieved for each orbit, and variations around this mean are still reliably captured by the measurements. SMR measurements are performed using two different mixer chains, denoted as frequency mode 19 and 13. Systematic differences between the two frontends have been noted. A first comparison with the Solar Occultation For Ice Experiment instrument (SOFIE) on-board the Aeronomy of Ice in the Mesosphere (AIM) satellite and the Fourier Transform Spectrometer of the Atmospheric Chemistry Experiment (ACE-FTS) on-board SCISAT indicates that the measurements using the frequency mode 19 have a significant low bias in both temperature (> 15 K) and water vapour (> 0.5 ppmv), while the measurements using frequency mode 13 agree with the other instruments considering estimated errors. PMC brightness data is provided by OSIRIS, Odin's other sensor. Combined SMR and OSIRIS data for some example orbits is considered. For these orbits, effects of PMCs on the water vapour distribution are clearly seen. Areas depleted of water vapour are found above layers with PMC, while regions of enhanced water vapour due to ice particle sedimentation are primarily placed between and under the clouds.
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| 5. |
- Eberhart, Martin, et al.
(författare)
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Atomic oxygen number densities in the mesosphere-lower thermosphere region measured by solid electrolyte sensors on WADIS-2
- 2019
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Ingår i: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 12:4, s. 2445-2461
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Tidskriftsartikel (refereegranskat)abstract
- Absolute profiles of atomic oxygen number densities with high vertical resolution have been determined in the mesosphere-lower thermosphere (MLT) region from in situ measurements by several rocket-borne solid electrolyte sensors. The amperometric sensors were operated in both controlled and uncontrolled modes and with various orientations on the foredeck and aft deck of the payload. Calibration was based on mass spectrometry in a molecular beam containing atomic oxygen produced in a microwave discharge. The sensor signal is proportional to the number flux onto the electrodes, and the mass flow rate in the molecular beam was additionally measured to derive this quantity from the spectrometer reading. Numerical simulations provided aerodynamic correction factors to derive the atmospheric number density of atomic oxygen from the sensor data. The flight results indicate a preferable orientation of the electrode surface perpendicular to the rocket axis. While unstable during the upleg, the density profiles measured by these sensors show an excellent agreement with the atmospheric models and photometer results during the downleg of the trajectory. The high spatial resolution of the measurements allows for the identification of small-scale variations in the atomic oxygen concentration.
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| 6. |
- Ehard, Benedikt, et al.
(författare)
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Combination of Lidar and Model Data for Studying Deep Gravity Wave Propagation
- 2016
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Ingår i: Monthly Weather Review. - 0027-0644 .- 1520-0493. ; 144:1, s. 77-98
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Tidskriftsartikel (refereegranskat)abstract
- The paper presents a feasible method to complement ground-based middle atmospheric Rayleigh lidar temperature observations with numerical simulations in the lower stratosphere and troposphere to study gravity waves. Validated mesoscale numerical simulations are utilized to complement the temperature below 30-km altitude. For this purpose, high-temporal-resolution output of the numerical results was interpolated on the position of the lidar in the lee of the Scandinavian mountain range. Two wintertime cases of orographically induced gravity waves are analyzed. Wave parameters are derived using a wavelet analysis of the combined dataset throughout the entire altitude range from the troposphere to the mesosphere. Although similar in the tropospheric forcings, both cases differ in vertical propagation. The combined dataset reveals stratospheric wave breaking for one case, whereas the mountain waves in the other case could propagate up to about 40-km altitude. The lidar observations reveal an interaction of the vertically propagating gravity waves with the stratopause, leading to a stratopause descent in both cases.
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| 7. |
- Grygalashvyly, Mykhaylo, et al.
(författare)
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Atmospheric band fitting coefficients derived from a self-consistent rocket-borne experiment
- 2019
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 19:2, s. 1207-1220
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Tidskriftsartikel (refereegranskat)abstract
- Based on self-consistent rocket-borne measurements of temperature, the densities of atomic oxygen and neutral air, and the volume emission of the atmospheric band (762 nm), we examined the one-step and two-step excitation mechanism of O-2 (b(1)Sigma(+)(g)) for nighttime conditions. Following McDade et al. (1986), we derived the empirical fitting coefficients, which parameterize the atmospheric band emission O-2 (b(1)Sigma(+)(g) - X-3 Sigma(-)(g)) (0, 0). This allows us to derive the atomic oxygen concentration from nighttime observations of atmospheric band emission O-2 (b(1)Sigma(+)(g) - X-3 Sigma(-)(g)) (0, 0). The derived empirical parameters can also be utilized for atmospheric band modeling. Additionally, we derived the fit function and corresponding coefficients for the combined (one-and two-step) mechanism. The simultaneous common volume measurements of all the parameters involved in the theoretical calculation of the observed O-2 (b(1)Sigma(+)(g) - X-3 Sigma(-)(g)) (0, 0) emission, i.e., temperature and density of the background air, atomic oxygen density, and volume emission rate, is the novelty and the advantage of this work.
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| 8. |
- Hendrickx, Koen, 1990-, et al.
(författare)
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Observation of 27-day solar cycles in mesospheric production and descent of EPP-produced NO
- 2015
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 120:10, s. 8978-8988
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Tidskriftsartikel (refereegranskat)abstract
- Nitric oxide (NO) is produced by energetic particle precipitation (EPP) in the mesosphere-lower thermosphere (MLT) region, and during the polar winter, NO can descend to stratospheric altitudes where it destroys ozone. In this paper, we study the general scenario, as opposed to a case study, of NO production in the thermosphere due to energetic particles in the auroral region. We first investigate the relationship between NO production and two geomagnetic indices. The analysis indicates that the auroral electrojet index is a more suitable proxy for EPP-produced NO than the typically used midlatitude Ap index. In order to study the production and downward transport of NO from the lower thermosphere to the mesosphere, we perform superposed epoch analyses on NO observations made by the Solar Occultation For Ice Experiment instrument on board the Aeronomy of Ice in the Mesosphere satellite. The epoch analysis clearly shows the impact of the 27 day solar cycle on NO production. The effect is observed down to an altitude range of about 50 km to 65 km, depending on the hemisphere and the occurrence of stratospheric warmings. Initially, a rapid downward transport is noted during the first 10 days after EPP onset to an altitude of about 80–85 km, which is then followed by a slower downward transport of approximately 1–1.2 km/d to lower mesospheric altitudes in the order of 30 days.
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| 9. |
- Hendrickx, Koen, et al.
(författare)
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Relative Importance of Nitric Oxide Physical Drivers in the Lower Thermosphere
- 2017
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 44:19, s. 10081-10087
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Tidskriftsartikel (refereegranskat)abstract
- Nitric oxide (NO) observations from the Solar Occultation for Ice Experiment and Student Nitric Oxide Explorer satellite instruments are investigated to determine the relative importance of drivers of short-term NO variability. We study the variations of deseasonalized NO anomalies by removing a climatology, which explains between approximately 70% and 90% of the total NO budget, and relate them to variability in geomagnetic activity and solar radiation. Throughout the lower thermosphere geomagnetic activity is the dominant process at high latitudes, while in the equatorial region solar radiation is the primary source of short-term NO changes. Consistent results are obtained on estimated geomagnetic and radiation contributions of NO variations in the two data sets, which are nearly a decade apart in time. The analysis presented here can be applied to model simulations of NO to investigate the accuracy of the parametrized physical drivers.
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| 10. |
- Hendrickx, Koen, 1990-
(författare)
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Solar Forcing of Nitric Oxide in the Upper Atmosphere
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The forcing of the Sun on Earth's atmosphere manifests itself via solar radiation and energetic particle precipitation (EPP), which variations are most noticeable in the upper regions of the atmosphere. A key species in the lower thermosphere, which is influenced by solar forcing, is nitric oxide (NO). An NO reservoir is present in the lower thermosphere, from which NO-rich air can be transported downward into the mesosphere and stratosphere, where it takes part in catalytic ozone destruction cycles. For climate models to correctly simulate the solar forcing on our climate, the processes of NO production and destruction, as well as the descent into the lower atmosphere, must be understood and accurately represented.In this thesis, observations from the Solar Occultation For Ice Experiment (SOFIE) instrument onboard the Aeronomy of Ice in the Mesosphere (AIM) satellite are used to investigate temporal characteristics of NO in the mesosphere and lower thermosphere. We have developed a diagnostic method to determine the relative importance of the NO physical drivers throughout the lower thermosphere. The method shows that, at high latitudes, precipitating auroral electrons dominantly drive NO variations. Comparisons with NO measurements by the Student Nitric Oxide Experiment (SNOE), made almost a decade earlier, reveal that the impact of this forcing on NO appears to be invariant throughout the 11 year solar cycle.On shorter timescales, we have shown a clear signature of the reoccurring 27 day geomagnetic impact on NO concentrations during summer and winter, with subsequent descent into the lower mesosphere during winter. The occurrence of medium energy electrons, which precipitate to mesospheric altitudes, results in a further increase of the descending NO flux. This complicates the determination of the relative contribution of the EPP direct and indirect effect on NO, i.e. separating direct NO production from downwards transported NO, respectively, in NO enhancements at a certain altitude. Using a full-range energy spectrum from the Polar-orbiting Operational Environmental Satellites (POES), we have been able to disentangle the direct and indirect EPP effect on Southern hemispheric NO during a geomagnetic storm in 2010.Simulations of NO by the Whole Atmosphere Community Climate Model with Specified Dynamics (SD-WACCM) model reveal that the model predicts a too high climatological mean, while the short term variability is too low, as compared to SOFIE. However, even though the dynamical transport in both model and observations agrees very well, the descending NO fluxes are too low in the model.In conclusion, the results of this thesis provide a better understanding of NO variability from an observational standpoint and will enable better model representations in the future.
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