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  • 1
    Online Resource
    Online Resource
    The Mississippi Valley Convection Minimum on Summer Afternoons: Observations and Numerical Simulations
    American Meteorological Society ; 2016
    In:  Monthly Weather Review Vol. 144, No. 1 ( 2016-01-01), p. 263-272
    Details
    In: Monthly Weather Review, American Meteorological Society, Vol. 144, No. 1 ( 2016-01-01), p. 263-272
    Abstract: Analysis of 15 years of composite radar images over the continental United States reveals a distinct minimum of deep-convection occurrence over the interior lower Mississippi Valley on summer afternoons, relative to surrounding areas. To understand the mechanisms behind this convection signature, quasi-idealized numerical simulations with the Weather Research and Forecasting (WRF) Model are performed. The simulations, which broadly reproduce the valley convection minimum, suggest that convective inhibition is maximized, and low-level ascent minimized, over the flat valley terrain. By contrast, weaker inhibition and stronger mechanically forced ascent over the hills flanking the valley combine to initiate convection more readily. Although the orography of the region is unremarkable, it has a stronger influence on the regional convection pattern than do variations in land use.
    Type of Medium: Online Resource
    ISSN: 0027-0644 , 1520-0493
    URL: Article
    DOI: 10.1175/MWR-D-15-0238.1
    RVK:
    RA 1000
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2016
    detail.hit.zdb_id: 2033056-X
    detail.hit.zdb_id: 202616-8
    SSG: 14
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  • 2
    Online Resource
    Online Resource
    Diabatic processes modulating the vertical structure of the jet stream above the cold front of an extratropical cyclone: sensitivity to deep convection schemes
    Copernicus GmbH ; 2022
    In:  Weather and Climate Dynamics Vol. 3, No. 3 ( 2022-08-04), p. 863-882
    Details
    In: Weather and Climate Dynamics, Copernicus GmbH, Vol. 3, No. 3 ( 2022-08-04), p. 863-882
    Abstract: Abstract. The effect of deep convection parameterisation on the jet stream above the cold front of an explosive extratropical cyclone is investigated in the global numerical weather prediction model ARPEGE, operational at Météo-France. Two hindcast simulations differing only in the deep convection scheme used are systematically compared with each other, with (re)analysis datasets and with NAWDEX airborne observations. The deep convection representation has an important effect on the vertical structure of the jet stream above the cold front at 1-d lead time. The simulation with the less active scheme shows a deeper jet stream, associated with a stronger potential vorticity (PV) gradient in the middle troposphere. This is due to a larger deepening of the dynamical tropopause on the cold air side of the jet and a higher PV destruction on the warm air side, near 600 hPa. To better understand the origin of this stronger PV gradient, Lagrangian backward trajectories are computed. On the cold air side of the jet, numerous trajectories undergo a rapid ascent from the boundary layer to the mid-levels in the simulation with the less active deep convection scheme, whereas they stay at mid-levels in the other simulation. This ascent explains the higher PV noted on that side of the jet in the simulation with the less active deep convection scheme. These ascending air masses form mid-level ice clouds that are not observed in the microphysical retrievals from airborne radar-lidar measurements. On the warm air side of the jet, in the warm conveyor belt ascending region, the Lagrangian trajectories with the less active deep convection scheme undergo a higher PV destruction due to a stronger heating occurring in the lower and middle troposphere. In contrast, in the simulation with the most active deep convection scheme, both the heating and PV destruction extend further up into the upper troposphere.
    Type of Medium: Online Resource
    ISSN: 2698-4016
    URL: Article
    URL: Article
    DOI: 10.5194/wcd-3-863-2022
    DOI: 10.5194/wcd-3-863-2022-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2022
    detail.hit.zdb_id: 2982467-9
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  • 3
    Online Resource
    Online Resource
    The North Atlantic Waveguide and Downstream Impact Experiment
    American Meteorological Society ; 2018
    In:  Bulletin of the American Meteorological Society Vol. 99, No. 8 ( 2018-08), p. 1607-1637
    Details
    In: Bulletin of the American Meteorological Society, American Meteorological Society, Vol. 99, No. 8 ( 2018-08), p. 1607-1637
    Abstract: The North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX) explored the impact of diabatic processes on disturbances of the jet stream and their influence on downstream high-impact weather through the deployment of four research aircraft, each with a sophisticated set of remote sensing and in situ instruments, and coordinated with a suite of ground-based measurements. A total of 49 research flights were performed, including, for the first time, coordinated flights of the four aircraft: the German High Altitude and Long Range Research Aircraft (HALO), the Deutsches Zentrum für Luft- und Raumfahrt (DLR) Dassault Falcon 20, the French Service des Avions Français Instrumentés pour la Recherche en Environnement (SAFIRE) Falcon 20, and the British Facility for Airborne Atmospheric Measurements (FAAM) BAe 146. The observation period from 17 September to 22 October 2016 with frequently occurring extratropical and tropical cyclones was ideal for investigating midlatitude weather over the North Atlantic. NAWDEX featured three sequences of upstream triggers of waveguide disturbances, as well as their dynamic interaction with the jet stream, subsequent development, and eventual downstream weather impact on Europe. Examples are presented to highlight the wealth of phenomena that were sampled, the comprehensive coverage, and the multifaceted nature of the measurements. This unique dataset forms the basis for future case studies and detailed evaluations of weather and climate predictions to improve our understanding of diabatic influences on Rossby waves and the downstream impacts of weather systems affecting Europe.
    Type of Medium: Online Resource
    ISSN: 0003-0007 , 1520-0477
    URL: Article
    DOI: 10.1175/BAMS-D-17-0003.1
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2018
    detail.hit.zdb_id: 2029396-3
    detail.hit.zdb_id: 419957-1
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  • 4
    Online Resource
    Online Resource
    The impact of deep convection representation in a global atmospheric model on the warm conveyor belt and jet stream during NAWDEX IOP6
    Copernicus GmbH ; 2021
    In:  Weather and Climate Dynamics Vol. 2, No. 4 ( 2021-10-29), p. 1011-1031
    Details
    In: Weather and Climate Dynamics, Copernicus GmbH, Vol. 2, No. 4 ( 2021-10-29), p. 1011-1031
    Abstract: Abstract. The effect of parameterized deep convection on warm conveyor belt (WCB) activity and the jet stream is investigated by performing simulations of an explosively developing large-scale cyclone that occurred during the North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX) field campaign using the Météo-France global atmospheric model ARPEGE. Three simulations differing only from their deep convection representation are analysed. The first one was performed with the Bougeault (1985) scheme (B85), the second one with the Prognostic Condensates Microphysics and Transport (PCMT) scheme of Piriou et al. (2007), and the third one without any parameterized deep convection. In the latter simulation, the release of convective instability at the resolved scales of the model generates localized cells marked by strong heating with few degrees extent in longitude and latitude along the fronts. In runs with active parameterized deep convection (B85, PCMT), the heating rate is more homogeneously distributed along fronts as the instability release happens at subgrid scales. This difference leads to more rapid and abrupt ascents in the WCB without parameterized deep convection and more moderate but more sustained ascents with parameterized deep convection. While the number of WCB trajectories does not differ much between the three simulations, the averaged heating rates over the WCB trajectories exhibits distinct behaviour. After 1 d of simulations, the upper-level heating rate is on average larger, with the B85 scheme leading to stronger potential vorticity (PV) destruction. The difference comes from the resolved sensible and latent heating and not the parameterized one. A comparison with (re)analyses and a large variety of airborne observations from the NAWDEX field campaign (Doppler radar, Doppler lidar, dropsondes) made during the coordinated flights of two aircraft in the WCB outflow region shows that B85 performs better in the representation of the double jet structure at 1 d lead time than the other two simulations. That can be attributed to the more active WCB at upper levels. However, this effect is too strong and that simulation becomes less realistic than the other ones at forecast ranges beyond 1.5 d. The simulation with the PCMT scheme has an intermediate behaviour between the one with the B85 scheme and without parameterized deep convection, but its impact on the jet stream is closer to the latter one. Finally, additional numerical experiments show that main differences in the impact on the jet between PCMT and B85 largely come from the chosen closure, with the former being based on CAPE and the latter on moisture convergence.
    Type of Medium: Online Resource
    ISSN: 2698-4016
    URL: Article
    URL: Article
    DOI: 10.5194/wcd-2-1011-2021
    DOI: 10.5194/wcd-2-1011-2021-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2021
    detail.hit.zdb_id: 2982467-9
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  • 5
    Online Resource
    Online Resource
    Aerosol - Cloud Target Classification in HALO Lidar/Radar Collocated Measurements
    EDP Sciences ; 2020
    In:  EPJ Web of Conferences Vol. 237 ( 2020), p. 08002-
    Details
    In: EPJ Web of Conferences, EDP Sciences, Vol. 237 ( 2020), p. 08002-
    Abstract: Particle attenuated backscatter and depolarization ratio at 532 nm from the WALES (Water Vapor Lidar Experiment in Space) instrument are used in combination with the radar reflectivity from the 35 GHz MIRA35 cloud radar in order to perform an aerosol-cloud target classification on the lidar/radar collocated observations carried out with the High Altitude and LOng-range research aircraft (HALO), in high temporal and spatial resolution. The methodology is applied to the measurements conducted during the North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX) in fall 2016. Here, we present one case study to show the feasibility and information context of the aerosol-cloud discrimination, which can serve as a good complement to the Cloud target categorization applied already in the measurements. Our results demonstrate that the developed mask is capable to identify complex stratifications with different aerosol and cloud types and even aerosol layers of low signal.
    Type of Medium: Online Resource
    ISSN: 2100-014X
    URL: Article
    DOI: 10.1051/epjconf/202023708002
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2020
    detail.hit.zdb_id: 2595425-8
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  • 6
    Online Resource
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    Representation by two climate models of the dynamical and diabatic processes involved in the development of an explosively deepening cyclone during NAWDEX
    Copernicus GmbH ; 2021
    In:  Weather and Climate Dynamics Vol. 2, No. 1 ( 2021-03-22), p. 233-253
    Details
    In: Weather and Climate Dynamics, Copernicus GmbH, Vol. 2, No. 1 ( 2021-03-22), p. 233-253
    Abstract: Abstract. The dynamical and microphysical properties of a well-observed cyclone from the North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX), called the Stalactite cyclone and corresponding to intensive observation period 6, is examined using two atmospheric components (ARPEGE-Climat 6.3 and LMDZ6A) of the global climate models CNRM-CM6-1 and IPSL-CM6A, respectively. The hindcasts are performed in “weather forecast mode”, run at approximately 150–200 km (low resolution, LR) and approximately 50 km (high resolution, HR) grid spacings, and initialised during the initiation stage of the cyclone. Cyclogenesis results from the merging of two relative vorticity maxima at low levels: one associated with a diabatic Rossby vortex (DRV) and the other initiated by baroclinic interaction with a pre-existing upper-level potential vorticity (PV) cut-off. All hindcasts produce (to some extent) a DRV. However, the second vorticity maximum is almost absent in LR hindcasts because of an underestimated upper-level PV cut-off. The evolution of the cyclone is examined via the quasi-geostrophic ω equation which separates the diabatic heating component from the dynamical one. In contrast to some previous studies, there is no change in the relative importance of diabatic heating with increased resolution. The analysis shows that LMDZ6A produces stronger diabatic heating compared to ARPEGE-Climat 6.3. Hindcasts initialised during the mature stage of the cyclone are compared with airborne remote-sensing measurements. There is an underestimation of the ice water content in the model compared to the one retrieved from radar-lidar measurements. Consistent with the increased heating rate in LMDZ6A compared to ARPEGE-Climat 6.3, the sum of liquid and ice water contents is higher in LMDZ6A than ARPEGE-Climat 6.3 and, in that sense, LMDZ6A is closer to the observations. However, LMDZ6A strongly overestimates the fraction of super-cooled liquid compared to the observations by a factor of approximately 50.
    Type of Medium: Online Resource
    ISSN: 2698-4016
    URL: Article
    URL: Article
    DOI: 10.5194/wcd-2-233-2021
    DOI: 10.5194/wcd-2-233-2021-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2021
    detail.hit.zdb_id: 2982467-9
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  • 7
    Online Resource
    Online Resource
    Evolution of DARDAR-CLOUD ice cloud retrievals: new parameters and impacts on the retrieved microphysical properties
    Copernicus GmbH ; 2019
    In:  Atmospheric Measurement Techniques Vol. 12, No. 5 ( 2019-05-16), p. 2819-2835
    Details
    In: Atmospheric Measurement Techniques, Copernicus GmbH, Vol. 12, No. 5 ( 2019-05-16), p. 2819-2835
    Abstract: Abstract. In this paper we present the latest refinements brought to the DARDAR-CLOUD product, which contains ice cloud microphysical properties retrieved from the cloud radar and lidar measurements from the A-Train mission. Based on a large dataset of in situ ice cloud measurements, the parameterizations used in the microphysical model of the algorithm – i.e. the normalized particle size distribution, the mass–size relationship, and the parameterization of the a priori value of the normalized number concentration as a function of temperature – were assessed and refined to better fit the measurements, keeping the same formalism as proposed in DARDAR basis papers. Additionally, in regions where lidar measurements are available, the lidar ratio retrieved for ice clouds is shown to be well constrained by the lidar–radar synergy. Using this information, the parameterization of the lidar ratio was also refined, and the new retrieval equals on average 35±10 sr in the temperature range between −60 and −20 ∘C. The impact of those changes on the retrieved ice cloud properties is presented in terms of ice water content (IWC) and effective radius. Overall, IWC values from the new DARDAR-CLOUD product are on average 16 % smaller than the previous version, leading to a 24 % reduction in the ice water path. In parallel, the retrieved effective radii increase by 5 % to 40 %, depending on temperature and the availability of the instruments, with an average difference of +15 %. Modifications of the microphysical model strongly affect the ice water content retrievals with differences that were found to range from −50 % to +40 %, depending on temperature and the availability of the instruments. The largest differences are found for the warmest temperatures (between −20 and 0 ∘C) in regions where the cloud microphysical processes are more complex and where the retrieval is almost exclusively based on radar-only measurements. The new lidar ratio values lead to a reduction of IWC at cold temperatures, the difference between the two versions increasing from around 0 % at −30 ∘C to 70 % below −80 ∘C, whereas effective radii are not impacted.
    Type of Medium: Online Resource
    ISSN: 1867-8548
    URL: Article
    DOI: 10.5194/amt-12-2819-2019
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2019
    detail.hit.zdb_id: 2505596-3
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