| 1. |
- Buehler, Stefan, et al.
(författare)
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A concept for a satellite mission to measure cloud ice water path, ice particle size, and cloud altitude
- 2007
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Ingår i: Quarterly Journal of the Royal Meteorological Society. - : Wiley. - 0035-9009 .- 1477-870X. ; 133:S2, s. 109-128
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Tidskriftsartikel (refereegranskat)abstract
- A passive satellite radiometer operating at submillimetre wavelengths can measure cloud ice water path (IWP), ice particle size, and cloud altitude. The paper first discusses the scientific background for such measurements. Formal scientific mission requirements are derived, based on this background and earlier assessments. The paper then presents a comprehensive prototype instrument and mission concept, and demonstrates that it meets the requirements. The instrument is a conically scanning 12-channel radiometer with channels between 183 and 664 GHz, proposed to fly in tandem with one of the Metop satellites. It can measure IWP with a relative accuracy of approximately 20% and a detection threshold of approximately 2 g m−2. The median mass equivalent sphere diameter of the ice particles can be measured with an accuracy of approximately 30 µm, and the median IWP cloud altitude can be measured with an accuracy of approximately 300 m. All the above accuracies are median absolute error values; root mean square error values are approximately twice as high, due to rare outliers.
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| 2. |
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| 3. |
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| 4. |
- Jiménez, C., et al.
(författare)
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Performance simulations for a submillimetre-wave satellite instrument to measure cloud ice
- 2007
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Ingår i: Quarterly Journal of the Royal Meteorological Society. - : Wiley. - 0035-9009 .- 1477-870X. ; 133:S2, s. 129-149
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Tidskriftsartikel (refereegranskat)abstract
- The performance of a conically scanning satellite instrument for the measurement of cloud ice was studied. The instrument measures radiances in 12 channels placed around the 183, 325 and 448 GHz water vapour lines and the 243, 664 and 874 GHz window channels, and is designed to provide estimations of ice water path (IWP), the equivalent sphere diameter (DME), and the median ice mass height (ZME). Overall median relative errors of around 20% for IWP, 33 µm for DME, and 240 m for ZME for a midlatitude winter scenario, and 17% for IWP, 30 µm for DME, and 310 m for ZME for a tropical scenario were found. Detection limits (relative retrieval error reaching 100%) of around 2 gm−2 were estimated for both scenarios. The performance of a five-receiver instrument, where either the 664 or 874 GHz channel is dropped, was close, but with increased errors for very thin and high clouds. A trade-off between having the 874 GHz receiver or two infrared channels at 10.7 and 12 µm emerged, as very similar performance was found between the six-receiver instrument and the five-receiver instrument with the infrared channels. Another trade-off between receiver selection and noise was also apparent, with some of the four-receiver selections operating at half noise levels being able to compete with the standard six-receiver instrument. Dual-polarized measurements were also tested, but they did not significantly improve the retrievals of IWP or DME.
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| 5. |
- John, Viju Oommen, et al.
(författare)
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Understanding the variability of clear-sky outgoing long-wave radiation based on ship-based temperature and water vapour measurements
- 2006
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Ingår i: Quarterly Journal of the Royal Meteorological Society. - : Wiley. - 0035-9009 .- 1477-870X. ; 132:621, s. 2675-2691
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Tidskriftsartikel (refereegranskat)abstract
- High-resolution radiative transfer model calculations with the Atmospheric Radiative Transfer Simulator (ARTS) were used to simulate the clear-sky outgoing long-wave radiative flux (OLR) at the top of the atmosphere. The unique set of radiosonde data collected by the research vessel Polarstern of the Alfred Wegener Institute for Polar and Marine Research during 27 expeditions in the years 1982 to 2003 was used to investigate the sources of clear-sky OLR variability for ocean areas in different climate zones and seasons. For this dataset, tropospheric temperature variations contribute approximately 33 W m(-2) OLR variability. tropospheric relative humidity variations 8.5 W m(-2), and vertical structure 2.3-3.4 W m(-2). Of these, 0.3-1.0 W m(-2) are due to structures on a vertical scale smaller than 4 km, which cannot be resolved by conventional remote-sensing instruments. It was also found that the poor absolute accuracy of current humidity data in the upper troposphere, approximately 40% relative error in relative humidity, leads to a significant uncertainty in OLR of about 3.8 W m(-2) (for a midlatitude summer atmosphere), which should be put in the context of the double CO2 effect of only 2.6 W m(-2) (for the same atmosphere).
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| 6. |
- Lahoz, William A., et al.
(författare)
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The COST 723 Action
- 2007
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Ingår i: Quarterly Journal of the Royal Meteorological Society. - : Wiley. - 0035-9009 .- 1477-870X. ; 133:S2, s. 99-108
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Tidskriftsartikel (refereegranskat)abstract
- An overview is provided of the COST 723 Action, Data Exploitation and Modelling of the Upper Troposphere and Lower Stratosphere. The three working groups are introduced and a summary of Action activities within them is provided. The achievements of the Action are: three international workshops; the LAUTLOS humidity measurement campaign; dedicated meetings to discuss the quality of upper troposphere/lower stratosphere ozone and humidity measurements; two journal special issues; more than 90 papers in the peer-reviewed literature; one international summer school; and a successor COST Action which builds on COST 723. The recommendations made are: for COST to continue to support the short-term scientific missions instrument, as they are perceived to be value for money; to encourage the use of COST money to increase links between COST Actions and other scientific communities; and for the COST secretariat to recommend that Actions consider a summer school instead of a final workshop or meeting.
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| 7. |
- Mauritsen, Thorsten, et al.
(författare)
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On the use of shear-dependent turbulent length-scales
- 2008
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Ingår i: Quarterly Journal of the Royal Meteorological Society. - : Wiley. - 0035-9009 .- 1477-870X. ; 134:631, s. 539-540
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the behaviour of the recently proposed shear-dependent turbulent length-scale in the neutrally stratified surface layer. It is found that close to ground, this shear-dependent length-scale is proportional to height, and thus, equivalent to the law of the wall. We speculate that the law of the wall could be just a special case of applying the shear-length to near-surface flows.
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| 8. |
- Orsolin, Yvan J., et al.
(författare)
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A low-ozone episode during the European heat wave of August 2003
- 2006
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Ingår i: Quarterly Journal of the Royal Meteorological Society. - : John Wiley & Sons. - 0035-9009 .- 1477-870X. ; 132:615, s. 667-680
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Tidskriftsartikel (refereegranskat)abstract
- An intense low-ozone episode (LOE) was observed over Scandinavia and the North Sea in the middle of August 2003. The LOE occurred under exceptional meteorological conditions, associated with a severe heatwave over Europe. The column ozone minimum for summer (June, July and August) 2003 was reached during the event. Using meteorological analyses, satellite ozone observations from the Total Ozone Mapping Spectrometer and the Michelson Interferometer for Passive Atmospheric Sounding aboard the Environment Satellite, we demonstrate that the LOE results from the conjunction of a deep tropospheric blocking over Europe, and a displaced Arctic pool of low-ozone air in the stratosphere, above the anticyclone. The anticyclonic anomaly is part of a Rossby wave train that is apparent throughout the troposphere, and whose influence is felt up to 50 hPa. In the mid-stratosphere (e.g. 30 hPa) long-period westward propagating planetary waves dominate, with a ridge extending over northern Europe in mid-August. We band-pass filtered the geopotential field to isolate sub-monthly fluctuations, and calculated three-dimensional wave activity fluxes for quasi-stationary, quasi-geostrophic disturbances embedded in a zonally asymmetric basic state. Results clearly indicate that upward wave fluxes in the lower stratosphere originate from the Atlantic sector, upstream of the maturing blocking.
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| 9. |
- Rydberg, Bengt, et al.
(författare)
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Prediction of cloud ice signatures in submillimeter emission spectra by means of ground-based radar and in-situ microphysical data
- 2007
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Ingår i: Quarterly Journal of the Royal Meteorological Society. - : Wiley. - 0035-9009 .- 1477-870X. ; 133:Suppl.2, s. 151-162
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Tidskriftsartikel (refereegranskat)abstract
- Submillimetre down-looking radiometry is a promising technique for global measurements of cloud ice properties. There exist no observation data of sufficient size that can be used for detailed pre-launch studies of such an instrument and other means must be found to obtain data to optimise the instrument design and similar tasks. Several aspects of the observations make traditional retrieval methods not suitable and nonlinear multidimensional regression techniques (e.g. Bayesian Monte Carlo integration and neural networks) must be applied. Such methods are based on a retrieval database and to be successful the database must mimic relevant real conditions closely. A method to generate such databases of high quality is described here. Correct vertical distributions of cloud ice are obtained by basic data from ground-based radars. Cloud ice particle microphysical properties are generated randomly where statistical parameters are selected to mimic in situ measurement data closely. Atmospheric background fields from ECMWF are perturbed to account for variation on sub-grid scales. All these data, together with sensor characteristics, are fed into a state-of-the-art radiative transfer simulator (ARTS). The method was validated by a successful comparison with AMSU data.
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