Satellite measurements of upper tropospheric water

Water vapour and clouds in the upper troposphere have strong influence on the Earth\u27s climate system. The present uncertainties regarding the distribution and feedback mechanisms of water to a changing climate are today among the greatest limitations for accurate climate predictions.The poor knowledge of upper tropospheric water results from the inability of earlier measurement systems to give a complete view of the upper troposphere.In-situ instruments are restricted in spatial coverage and satellite observations are needed to provide global coverage. Traditional infrared and optical satellite observations are mainly sensitive to the middle troposphere and applicable only in relatively cloud-free conditions.In this thesis satellite microwave limb-sounding is shown to be an advantageous technique to observe the upper troposphere with high vertical resolution and capability to penetrate thin cirrus clouds. Present measurement systems have the potential to give accurate measurements of both upper tropospheric humidity and ice water content.Retrieval methods have been developed for the sub-millimeter limb-sounding observations of Odin-SMR. The retrieved quantities are the all-weather upper tropospheric humidity at 12 and 15 km in altitude and a partial ice water path above 12 km.The humidity results agree within 10% with data from other microwave limb-sounders and high quality in-situ measurements. A comparison with infrared measurements emphasizes the necessity of microwave observations to measure in presence of clouds. The cloud ice retrieval shows a general agreement with other microwave data sets. The comparison highlights the difficulty of cloud ice retrieval since important assumptions on cloud microphysics and 3D inhomogeneities are presently unavoidable.Microwave measurements from Aura-MLS and CloudSat are used to investigate the relative amounts of water vapour and ice in the upper troposphere. Ice is found to dominate the total water budget at 14 km over regions of deep convection, but appears to give a small contribution to the moistening of the upper troposphere

Sub-Millimetre Measurements of Upper Tropospheric Humidity

Humidity and clouds in the upper troposphere are important factors for the Earth\u27s radiative balance.Consequently a weakness in global climate models is that very little is known about the concentration of water vapour or the distribution and properties of clouds in this altitude region.The balloon sondes that are regularly launched around the globe show very poor agreement in the upper troposphere and available satellite data have problems connected to spatial resolution and the occurrence of clouds.The frequent cloud cover restricts satellite applications of visible and infrared to down-looking geometries, resulting in low vertical resolution and measurements most sensitive to the middle troposphere.Observations in the microwave region are less sensitive to cloud scattering and therefore limb sounding can be performed to give improved vertical resolution in the upper troposphere.The sub-millimetre radiometer onboard the Odin satellite, Odin-SMR, performs limb sounding at frequencies around 500 GHz since its launch in 2001. The observations have sensitivity down to 10 km, but tangent altitudes inside the troposphere have up to now been ignored due to cloud scattering. This effect can now be simulated by a new radiative transfer software and first retrievals of tropospheric quantities are possible.The thesis presents the steps taken towards a first retrieval of upper tropospheric humidity and ice cloud properties.A thorough investigation of the Odin-SMR calibration at high brightness temperature has been performed. The results show that the systematic calibration error is low, and that a retrieval of humidity from the tropospheric spectra is achievable.A method to retrieve upper tropospheric humidity from the lowest tangent altitudes has been realised, including a cloud correction scheme, used for spectra with apparent cloud signature. The products of the retrieval are the all-weather humidity field and ice cloud signal. Together with an accompanying method to derive ice cloud properties, the retrieved ice cloud signal can be translated into ice water content with additional altitude information

Sub-Millimetre Measurements of Upper Tropospheric Humidity

Humidity and clouds in the upper troposphere are important factors for the Earth\u27s radiative balance.Consequently a weakness in global climate models is that very little is known about the concentration of water vapour or the distribution and properties of clouds in this altitude region.The balloon sondes that are regularly launched around the globe show very poor agreement in the upper troposphere and available satellite data have problems connected to spatial resolution and the occurrence of clouds.The frequent cloud cover restricts satellite applications of visible and infrared to down-looking geometries, resulting in low vertical resolution and measurements most sensitive to the middle troposphere.Observations in the microwave region are less sensitive to cloud scattering and therefore limb sounding can be performed to give improved vertical resolution in the upper troposphere.The sub-millimetre radiometer onboard the Odin satellite, Odin-SMR, performs limb sounding at frequencies around 500 GHz since its launch in 2001. The observations have sensitivity down to 10 km, but tangent altitudes inside the troposphere have up to now been ignored due to cloud scattering. This effect can now be simulated by a new radiative transfer software and first retrievals of tropospheric quantities are possible.The thesis presents the steps taken towards a first retrieval of upper tropospheric humidity and ice cloud properties.A thorough investigation of the Odin-SMR calibration at high brightness temperature has been performed. The results show that the systematic calibration error is low, and that a retrieval of humidity from the tropospheric spectra is achievable.A method to retrieve upper tropospheric humidity from the lowest tangent altitudes has been realised, including a cloud correction scheme, used for spectra with apparent cloud signature. The products of the retrieval are the all-weather humidity field and ice cloud signal. Together with an accompanying method to derive ice cloud properties, the retrieved ice cloud signal can be translated into ice water content with additional altitude information

Satellite measurements of upper tropospheric water

Water vapour and clouds in the upper troposphere have strong influence on the Earth\u27s climate system. The present uncertainties regarding the distribution and feedback mechanisms of water to a changing climate are today among the greatest limitations for accurate climate predictions.The poor knowledge of upper tropospheric water results from the inability of earlier measurement systems to give a complete view of the upper troposphere.In-situ instruments are restricted in spatial coverage and satellite observations are needed to provide global coverage. Traditional infrared and optical satellite observations are mainly sensitive to the middle troposphere and applicable only in relatively cloud-free conditions.In this thesis satellite microwave limb-sounding is shown to be an advantageous technique to observe the upper troposphere with high vertical resolution and capability to penetrate thin cirrus clouds. Present measurement systems have the potential to give accurate measurements of both upper tropospheric humidity and ice water content.Retrieval methods have been developed for the sub-millimeter limb-sounding observations of Odin-SMR. The retrieved quantities are the all-weather upper tropospheric humidity at 12 and 15 km in altitude and a partial ice water path above 12 km.The humidity results agree within 10% with data from other microwave limb-sounders and high quality in-situ measurements. A comparison with infrared measurements emphasizes the necessity of microwave observations to measure in presence of clouds. The cloud ice retrieval shows a general agreement with other microwave data sets. The comparison highlights the difficulty of cloud ice retrieval since important assumptions on cloud microphysics and 3D inhomogeneities are presently unavoidable.Microwave measurements from Aura-MLS and CloudSat are used to investigate the relative amounts of water vapour and ice in the upper troposphere. Ice is found to dominate the total water budget at 14 km over regions of deep convection, but appears to give a small contribution to the moistening of the upper troposphere

Altitude resolved ice-fraction in the uppermost tropical troposphere

The exact nature of the processes responsible for the moistening of the upper tropical troposphere is still uncertain. Altitude resolved measurements of water vapor from Aura/Microwave Limb Sounder (MLS) and cloud ice from CloudSat are used to investigate the ratio of ice mass to total water. Horizontal and vertical ice-fraction distributions in the pressure range 100-316 hPa over the tropical region are presented. They reveal that the ice-fraction is generally low, less than 10% around 316 hPa in general and outside regions of deep convection in the altitude levels above. On the other hand, the ice-fraction can be significant at higher altitudes in large regions above deep convection, reaching values of ∼90%. Below the tropical tropopause layer (TTL) ice and water vapor distributions have similar spatial patterns indicating that water in both phases is transported up to the upper troposphere by the same processes. Over regions of strong deep convection where ice is transported into the TTL, the dissimilar patterns of ice and water vapor could be interpreted as that the cloud ice gives a limited final moistening effect. Copyright 2008 by the American Geophysical Union

First Odin sub-mm retrievals in the tropical upper troposphere: humidity and cloud ice signals

International audienceOdin-SMR is a limb-sounder operating in the 500 region with the capability of performing measurements down to altitudes of about 10 with relatively low influence of ice clouds. Until now spectra from tropospheric tangent altitudes have been disregarded due to inadequate handling of scattering. A first method to extract upper tropospheric quantities has now been developed, yielding the humidity in two layers around 200 and 130 and information on cloud ice content above 200. The main concern for these retrievals is the calibration performance. A careful analysis indicates a systematic calibration error of about 1 K, but also a random component that differs between the two bands. The random calibration uncertainty results in retrieval errors of 10?60% depending on humidity and band. Presently this prohibits use of single retrievals, but averages can be presented with good accuracy. The fixed calibration error can largely be removed, leaving the spectroscopic uncertainties to dominate the humidity retrieval accuracy, estimated to be around 20%. First results are presented that are in agreement with seasonal structure obtained from other satellite measurements. An encouraging comparison between MOZAIC data and measurements for the 200 layer gives further confidence in the capability of Odin-SMR to measure humidity in the upper tropical troposphere

Microstructural evolution of welded stainless steels on integrated effect of thermal aging and low flux irradiation

The combined effect of thermal aging and irradiation on cast and welded stainless steel solidification structures is not sufficiently investigated. From theory and consecutive aging and irradiation experiments, the effect of simultaneous low rate irradiation and thermal aging is expected to accelerate and modify the aging processes of the ferrite phase. Here, a detailed analysis of long-term aged material at very low fast neutron flux at LWR operating temperatures using Atom Probe Tomography is presented. Samples of weld material from various positions in the core barrel of the Zorita PWR are examined. The welds have been exposed to 280–285 \ub0C for 38 years at three different neutron fluxes between 1 7 10 −5 and 7 7 10 −7 dpa/h to a total dose of 0.15–2 dpa. The aging of the ferrite phase occurs by spinodal decomposition, clustering and precipitation of e.g. G-phase. These phenomena are characterized and quantitatively analyzed in order to understand the effect of flux in combination with thermal aging