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  • 1
    In: Reviews of Geophysics, American Geophysical Union (AGU), Vol. 56, No. 2 ( 2018-06), p. 409-453
    Abstract: Satellite cloud droplet concentration uncertainties of 78% for pixel‐level retrievals and 54% for 1 by 1 degree retrievals are estimated The effective radius retrieval is the most important aspect for improvement, and more in situ evaluation is needed Potential improvements using passive and active satellite, and ground‐based instruments are discussed
    Type of Medium: Online Resource
    ISSN: 8755-1209 , 1944-9208
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2018
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    detail.hit.zdb_id: 209852-0
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    SSG: 16,13
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  • 2
    In: Bulletin of the American Meteorological Society, American Meteorological Society, ( 2023-09-06)
    Abstract: Numerical weather prediction models operate on grid spacings of a few kilometers, where deep convection begins to become resolvable. Around this scale, the emergence of coherent structures in the planetary boundary layer, often hypothesized to be caused by cold pools, forces the transition from shallow to deep convection. Yet, the kilometer-scale range is typically not resolved by standard surface operational measurement networks. The measurement campaign FESSTVaL aimed at addressing this gap by observing atmospheric variability at the hectometer to kilometer scale, with a particular emphasis on cold pools, wind gusts and coherent patterns in the planetary boundary layer during summer. A unique feature was the distribution of 150 self-developed and low-cost instruments. More specifically, FESSTVaL included dense networks of 80 autonomous cold pool loggers, 19 weather stations and 83 soil sensor systems, all installed in a rural region of 15-km radius in eastern Germany, as well as self-developed weather stations handed out to citizens. Boundary layer and upper air observations were provided by 8 Doppler lidars and 4 microwave radiometers distributed at 3 supersites; water vapor and temperature were also measured by advanced lidar systems and an infrared spectrometer; and rain was observed by a X-band radar. An uncrewed aircraft, multicopters and a small radiometer network carried out additional measurements during a four-week period. In this paper, we present FESSTVaL’s measurement strategy and show first observational results including unprecedented highly-resolved spatio-temporal cold-pool structures, both in the horizontal as well as in the vertical dimension, associated with overpassing convective systems.
    Type of Medium: Online Resource
    ISSN: 0003-0007 , 1520-0477
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2023
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  • 3
    In: Quarterly Journal of the Royal Meteorological Society, Wiley
    Abstract: In a joint effort, MeteoSwiss and Deutscher Wetterdienst (DWD) address the need for improving the initial state of the atmospheric boundary layer (ABL) by exploiting ground‐based profiling observations that aim to fill the existing observational gap in the ABL. We implemented brightness‐temperature observations from ground‐based microwave radiometers (MWRs) in our data assimilation systems using a local ensemble transform Kalman filter (LETKF) with Radiative Transfer for TIROS Operational Vertical Sounder, ground‐based (RTTOV‐gb) as a forward operator. We were able to obtain a positive impact on the brightness temperature first guess and analysis, as well as a slight impact on the ABL humidity, using two MWRs at MeteoSwiss. These results led to a subsequent operational implementation of the observing system at MeteoSwiss. Furthermore, we performed an extensive set of assimilation experiments at DWD to investigate further various aspects such as the vertical localisation of selected single channels. We obtained a positive impact on the 6‐hr forecast of ABL temperature and humidity by assimilating two channels employing a dynamical localisation based on the sensitivity functions of RTTOV‐gb but also with a static localisation in a single‐channel setup. Our experiments indicate the importance of vertical localisation when using more than one channel, although reliable improvements are challenging to obtain without a larger number of observations for both assimilation and verification.
    Type of Medium: Online Resource
    ISSN: 0035-9009 , 1477-870X
    RVK:
    RVK:
    Language: English
    Publisher: Wiley
    Publication Date: 2024
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  • 4
    Online Resource
    Online Resource
    American Meteorological Society ; 2022
    In:  Journal of Atmospheric and Oceanic Technology Vol. 39, No. 2 ( 2022-02), p. 163-180
    In: Journal of Atmospheric and Oceanic Technology, American Meteorological Society, Vol. 39, No. 2 ( 2022-02), p. 163-180
    Abstract: A detailed description is given of how the liquid water content (LWC) and the ice water content (IWC) can be determined accurately and absolutely from the measured water Raman spectra of clouds. All instrumental and spectroscopic parameters that affect the accuracy of the water-content measurement are discussed and quantified; specifically, these are the effective absolute differential Raman backscattering cross section of water vapor , and the molecular Raman backscattering efficiencies η liq and η ice of liquid and frozen microparticles, respectively. The latter two are determined following rigorous theoretical approaches combined with Raman Lidar for Atmospheric Moisture Sensing (RAMSES) measurements. For η ice , this includes a new experimental method that assumes continuity of the number of water molecules across the vertical extent of the melting layer. Examples of water-content measurements are presented, including supercooled liquid-water clouds and melting layers. Error sources are discussed; one effect that stands out is interfering fluorescence by aerosols. Aerosol effects and calibration issues are the main reasons why spectral Raman measurements are required for quantitative measurements of LWC and IWC. The presented study lays the foundation for cloud microphysical investigations and for the evaluation of cloud models or the cloud data products of other instruments. As a first application, IWC retrieval methods are evaluated that are based on either lidar extinction or radar reflectivity measurements. While the lidar-based retrievals show unsatisfactory agreement with the RAMSES IWC measurements, the radar-based IWC retrieval which is used in the Cloudnet project performs reasonably well. On average, retrieved IWC agrees within 20% to 30% (dry bias) with measured IWC.
    Type of Medium: Online Resource
    ISSN: 0739-0572 , 1520-0426
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2022
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