| 1. |
- Aires, F., et al.
(författare)
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Microwave hyperspectral measurements for temperature and humidity atmospheric profiling from satellite: The clear-sky case
- 2015
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202 .- 2169-897X .- 2169-8996. ; 120:21, s. 11334-11351
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates the benefits of a satellite HYperspectral Microwave Sensor (HYMS) for the retrieval of atmospheric temperature and humidity profiles, in the context of numerical weather prediction (NWP). In the infrared, hyperspectral instruments have already improved the accuracy of NWP forecasts. Microwave instruments so far only provide observations for a limited number of carefully selected channels. An information content analysis is conducted here to assess the impact of hyperspectral microwave measurements on the retrieval of temperature and water vapor profiles under clear-sky conditions. It uses radiative transfer simulations over a large variety of atmospheric situations. It accounts for realistic observation (instrument and radiative transfer) noise and for a priori information assumptions compatible with NWP practices. The estimated retrieval performance of the HYMS instrument is compared to those of the microwave instruments to be deployed on board the future generation of European operational meteorological satellites (MetOp-SG). The results confirm the positive impact of a HYMS instrument on the atmospheric profiling capabilities compared to MetOp-SG. Temperature retrieval uncertainty, compared to a priori information, is reduced by 2 to 10%, depending on the atmospheric height, and improvement rates are much higher than what will be obtained with MetOp-SG. For humidity sounding these improvements can reach 30%, a significant benefit as compared to MetOp-SG results especially below 250 hPa. The results are not very sensitive to the instrument noise, under our assumptions. The main impact provided by the hyperspectral information originates from the higher resolution in the O2 band around 60 GHz. The results are presented over ocean at nadir, but similar conclusions are obtained for other incidence angles and over land. Key Points A hyperspectral MW instrument could improve temperature & humidity retrieval compared to MetOp-SG The main impact from HYMS comes from higher resolution in the O2 band around 60 GHz Hyperspectral information is not really sensitive to instrument noise.
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| 2. |
- Barret, B., et al.
(författare)
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Intercomparisons of trace gases profiles from the Odin/SMR and Aura/MLS limb sounders
- 2006
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 111:D21
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the intercomparison of O(3), HNO(3), ClO, N(2)O and CO profiles measured by the two spaceborne microwave instruments MLS ( Microwave Limb Sounder) and SMR ( Submillimetre Radiometer) on board the Aura and Odin satellites, respectively. We compared version 1.5 level 2 data from MLS with level 2 data produced by the French data processor version 222 and 225 and by the Swedish data processor version 2.0 for several days in September 2004 and in March 2005. For the five gases studied, an overall good agreement is found between both instruments. Most of the observed discrepancies between SMR and MLS are consistent with results from other intercomparison studies involving MLS or SMR. O(3) profiles retrieved from the SMR 501.8 GHz band are noisier than MLS profiles but mean biases between both instruments do not exceed 10%. SMR HNO(3) profiles are biased low relative to MLS's by similar to 30% above the profile peak. In the lower stratosphere, MLS ClO profiles are biased low by up to 0.3 ppbv relative to coincident SMR profiles, except in the Southern Hemisphere polar vortex in the presence of chlorine activation. N(2)O profiles from both instruments are in very good agreement with mean biases not exceeding 15%. Finally, the intercomparison between SMR and MLS CO profiles has shown a good agreement from the middle stratosphere to the middle mesosphere in spite of strong oscillations in the MLS profiles. In the upper mesosphere, MLS CO concentrations are biased high relative to SMR while negative values in the MLS retrievals are responsible for a negative bias in the tropics around 30 hPa.
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| 3. |
- Emde, Claudia, et al.
(författare)
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A polarized discrete ordinate scattering model for simulations of limb and nadir long-wave measurements in 1-D/3-D spherical atmospheres
- 2004
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 109:24, s. 24207-
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Tidskriftsartikel (refereegranskat)abstract
- This article describes one of the scattering algorithms of the three-dimensional polarized radiative transfer model ARTS (Atmospheric Radiative Transfer Simulator) which has been implemented to study for example the influence of cirrus clouds on microwave limb sounding. The model uses the DOIT (Discrete Ordinate Iterative) method to solve the vector radiative transfer equation. The implementation of a discrete ordinate method is challenging due to the spherical geometry of the model atmosphere which is required for the simulation of limb radiances. The involved numerical issues, which are grid optimization and interpolation methods, are discussed in this paper. Scattering simulations are presented for limb- and down-looking geometries, for one-dimensional and three-dimensional spherical atmospheres. They show the impact of cloud particle size, shape, and orientation on the brightness temperatures and on the polarization of microwave radiation in the atmosphere. The cloud effect is much larger for limb radiances than for nadir radiances. Particle size is a very important parameter in all simulations. The polarization signal is negligible for simulations with completely randomly oriented particles, whereas for horizontally aligned particles with random azimuthal orientation the polarization signal is significant. Moreover, the effect of particle shape is only relevant for oriented cloud particles. The simulations show that it is essential to use a three-dimensional scattering model for inhomogeneous cloud layers.
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| 4. |
- Forkman, Peter, 1959, et al.
(författare)
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Observing the Vertical Branch of the Mesospheric Circulation at lat N 60° Using Ground Based Measurements of CO and H2O
- 2005
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 110:D5, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- In this report daily ground-based measurements of vertical profiles of CO and H2O from 2002 are used to trace the vertical movement of air caused by the seasonally varying mean meridional circulation. In the spring (days 100-130) the estimated ascending velocity is found to vary with time and altitude from about between 250 m/day at 65 km altitude on day 100 to a maximum of similar to 450 m/day at 85-90 km altitude on day 130. In the late summer and fall the descending velocity goes from 0 (when the downwelling starts) to similar to 250 m/day at 75 km day 280. The mesospheric adiabatic temperature changes caused by the vertical movement of air are compared to mesopause temperature as estimated by the radiance of the Meinel band OH airglow.
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| 5. |
- Galligani, V. S., et al.
(författare)
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The impact of the melting layer on the passive microwave cloud scattering signal observed from satellites: A study using TRMM microwave passive and active measurements
- 2013
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Ingår i: Journal of Geophysical Research. - : American Geophysical Union (AGU). - 0148-0227 .- 2156-2202 .- 2169-897X. ; 118:11, s. 5667-5678
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Tidskriftsartikel (refereegranskat)abstract
- Concurrent passive and active microwave measurements onboard the Tropical Rainfall Measurement Mission (TRMM) show that under cloudy conditions, when a melting layer is detected by the precipitation radar, a polarized scattering signal at 85GHz in passive mode is often observed. Radiative transfer simulations confirm the role of large horizontally oriented non-spherical particles on the polarized scattering signal and assess the effect of changes in particle phase, from solid ice to dry snow to melting snow, on the radiative properties. We conclude on the necessity to account for this polarization generated by the clouds in passive microwave rain retrievals and to use this specific signature to help diagnose the precipitation type and derive more accurate algorithms. In addition, analysis of the passive microwave polarized scattering is a unique way to get insight into microphysical properties of clouds at global scale, and this potential should be explored at millimeter and submillimeter frequencies that are more sensitive to the scattering generated by smaller particles.
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| 6. |
- Haefele, A., et al.
(författare)
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Validation of ground-based microwave radiometers at 22 GHz for stratospheric and mesospheric water vapor
- 2009
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 114:23
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Tidskriftsartikel (refereegranskat)abstract
- We present a detailed intercomparison of five ground-based 22 GHz microwave radiometers for stratospheric and mesospheric water vapor. Four of these instruments are members of the Network for the Detection of Atmospheric Composition Change (NDACC). The global measurements of middle atmospheric water vapor of the Microwave Limb Sounder (MLS) onboard the Aura satellite serve as reference and allow intercomparison of the ground-based systems that are located between 45 degrees S and 57 degrees N. The retrievals of water vapor profiles from the ground-based radiation measurements have been made consistent to a large extent: for the required temperature profiles, we used the global temperature measurements of MLS and we agreed on one common set of spectroscopic parameters. The agreement with the reference measurements is better than +/- 8% in the altitude range from 0.01 to 3 hPa. Strong correlation is found between the ground-based and the reference data in the mesosphere with respect to seasonal cycle and planetary waves. In the stratosphere the measurements are generally more noisy and become sensitive to instrumental instabilities toward lower levels (pressures greater than 3 hPa). We further present a compilation of a NDACC data set based on the retrieval parameters described herein but using a temperature climatology derived from the MLS record. This makes the ground-based measurements independent of additional information and allows extension of the data set for years in a homogeneous manner.
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| 7. |
- Haley, C. S., et al.
(författare)
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Retrievals of stratospheric O3 and NO2 profiles from Odin Optical Spectrograph and InfraRed Imager System (OSIRIS) limb-scattered sunlight measurements
- 2004
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 109:D16
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Tidskriftsartikel (refereegranskat)abstract
- Scientific studies of the major environmental questions of global warming and ozone depletion require global data sets of atmospheric constituents with relevant temporal and spatial resolution. In this paper global number density profiles of O3 and NO2 are retrieved from Odin/OSIRIS limb-scattered sunlight measurements, using the Maximum A Posteriori estimator. Differential Optical Absorption Spectroscopy is applied to OSIRIS radiances as an intermediate step, using the wavelength windows 571-617 nm for O3 and 435-451 nm for NO2. The method is computationally efficient for processing OSIRIS data on an operational basis. Results show that a 2-3 km height resolution is generally achievable between about 12 km and 45 km for O3 with an estimated accuracy of 13\% at the peak and between about 15 km and 40 km for NO2 with an estimated accuracy of 10\% at the peak. First validations of the retrieved data indicate a good agreement both with other retrieval techniques applied to OSIRIS measurements and with the results of other instruments. Once the validation has reached a confident level, the retrieved data will be used to study important stratospheric processes relevant to global environmental problems. The unique NO2 data set will be of particular interest for studies of nitrogen chemistry in the middle atmosphere.
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| 8. |
- Isoz, O., et al.
(författare)
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Intercalibration of microwave temperature sounders using radio occultation measurements
- 2015
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Ingår i: Journal of Geophysical Research. - : American Geophysical Union (AGU). - 0148-0227 .- 2156-2202 .- 2169-897X. ; 120:9, s. 3758-3773
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Tidskriftsartikel (refereegranskat)abstract
- This is a study of the usefulness of radio occultation (RO) data for intercomparing different microwave temperature (MWT) sounding instruments. The RO data used are from the Global Navigational Satellite System Receiver for Atmospheric Sounding on the Metop-A and B satellites. The MWT sounders investigated are the Advanced Microwave Sounding Unit-A instruments on the satellites NOAA 15, 16, and 18 and Metop-A. We collocate RO and MWT data and then use these collocations to study various aspects of the MWT instruments. In addition, two different versions of the MWT data are compared: standard operational data (OPR) and the NOAA Integrated Microwave Intercalibration Approach data (IMICA). The time series of monthly mean differences shows that there are robust patterns for each satellite and data version, which mostly drift only slowly over time. The intersatellite spread, measured by the standard deviation of the yearly mean values by all satellites, is between 0.1 and 0.4K, depending on channel, with no significant differences between OPR and IMICA data. The only notable exception is Channel 8 of NOAA 16, which appears to have a time-varying offset of 0.5-1K relative to the other instruments. At this point it is not clear whether this deviation is real or a sampling artifact, so further study is needed. Due to the large number of collocations used, it is possible to also investigate the scene brightness and scan angle dependence of the MWT bias (relative to RO). First results of such an analysis are presented and discussed. Particularly, the investigation of the scan angle dependence is novel, since this bias pattern is difficult to assess without RO data. Further work is needed on these angular dependences, before conclusions are robust enough to include in data recalibration efforts, but our overall conclusion is that RO collocations are a powerful tool for intercomparing MWT sounders.
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| 9. |
- Lossow, Stefan, 1977, et al.
(författare)
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Wintertime water vapor in the polar upper mesosphere and lower thermosphere : First satellite observations by Odin submillimeter radiometer
- 2009
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 114, s. D10304-
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we present Odin submillimeter radiometer (Odin/SMR) water vapor measurements in the upper mesosphere and lower thermosphere with focus on the polar latitudes in winter. Measurements since 2003 have been compiled to provide a first overview of the water vapor distribution in this altitude range. Our observations show a distinct seasonal increase of the water vapor concentration during winter at a given altitude above 90 km. Above 95 km the observations exhibit the annual water vapor maximum during wintertime. Model simulations from the Hamburg Model of the Neutral and Ionized Atmosphere (HAMMONIA) and the Whole Atmosphere Community Climate Model version 3 (WACCM3) show results that are very similar to the observations. We suggest that the observed increase in water vapor during winter is mainly caused by a combination of upwelling of moister air from lower altitudes and diffusion processes. Distinct interhemispheric differences in the winter water vapor distribution in the upper mesosphere and lower thermosphere can be observed, both in the observations and the model results. The seasonal water vapor increase in the polar regions is much more pronounced in the Southern Hemisphere winter where higher concentrations can be observed. This observation is most likely due to interhemispheric differences in the underlying dynamics and diffusion processes
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| 10. |
- Ricaud, P., et al.
(författare)
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Polar Vortex Evolution during the 2002 Antarctic Major Warming as Observed by the Odin Satellite
- 2005
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 110:D5, s. 1-12
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Tidskriftsartikel (refereegranskat)abstract
- In September 2002 the Antarctic polar vortex split in two under the influence of a sudden warming. During this event, the Odin satellite was able to measure both ozone (O(3)) and chlorine monoxide (ClO), a key constituent responsible for the so-called "ozone hole'', together with nitrous oxide (N(2)O), a dynamical tracer, and nitric acid (HNO(3)) and nitrogen dioxide (NO(2)), tracers of denitrification. The submillimeter radiometer (SMR) microwave instrument and the Optical Spectrograph and Infrared Imager System (OSIRIS) UV-visible light spectrometer (VIS) and IR instrument on board Odin have sounded the polar vortex during three different periods: before (19-20 September), during (24-25 September), and after (1-2 and 4-5 October) the vortex split. Odin observations coupled with the Reactive Processes Ruling the Ozone Budget in the Stratosphere (REPROBUS) chemical transport model at and above 500 K isentropic surfaces (heights above 18 km) reveal that on 19-20 September the Antarctic vortex was dynamically stable and chemically nominal: denitrified, with a nearly complete chlorine activation, and a 70% O(3) loss at 500 K. On 25-26 September the unusual morphology of the vortex is monitored by the N(2)O observations. The measured ClO decay is consistent with other observations performed in 2002 and in the past. The vortex split episode is followed by a nearly complete deactivation of the ClO radicals on 1-2 October, leading to the end of the chemical O(3) loss, while HNO(3) and NO(2) fields start increasing. This acceleration of the chlorine deactivation results from the warming of the Antarctic vortex in 2002, putting an early end to the polar stratospheric cloud season. The model simulation suggests that the vortex elongation toward regions of strong solar irradiance also favored the rapid reformation of ClONO(2). The observed dynamical and chemical evolution of the 2002 polar vortex is qualitatively well reproduced by REPROBUS. Quantitative differences are mainly attributable to the too weak amounts of HNO(3) in the model, which do not produce enough NO(2) in presence of sunlight to deactivate chlorine as fast as observed by Odin.
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