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- ItemDetection of convective initiation using Meteosat SEVIRI: Implementation in and verification with the tracking and nowcasting algorithm Cb-TRAM(München : European Geopyhsical Union, 2013) Merk, D.; Zinner, T.In this paper a new detection scheme for convective initiation (CI) under day and night conditions is presented. The new algorithm combines the strengths of two existing methods for detecting CI with geostationary satellite data. It uses the channels of the Spinning Enhanced Visible and Infrared Imager (SEVIRI) onboard Meteosat Second Generation (MSG). For the new algorithm five infrared (IR) criteria from the Satellite Convection Analysis and Tracking algorithm (SATCAST) and one high-resolution visible channel (HRV) criteria from Cb-TRAM were adapted. This set of criteria aims to identify the typical development of quickly developing convective cells in an early stage. The different criteria include time trends of the 10.8 IR channel, and IR channel differences, as well as their time trends. To provide the trend fields an optical-flow-based method is used: the pyramidal matching algorithm, which is part of Cb-TRAM. The new detection scheme is implemented in Cb-TRAM, and is verified for seven days which comprise different weather situations in central Europe. Contrasted with the original early-stage detection scheme of Cb-TRAM, skill scores are provided. From the comparison against detections of later thunderstorm stages, which are also provided by Cb-TRAM, a decrease in false prior warnings (false alarm ratio) from 91 to 81% is presented, an increase of the critical success index from 7.4 to 12.7%, and a decrease of the BIAS from 320 to 146% for normal scan mode. Similar trends are found for rapid scan mode. Most obvious is the decline of false alarms found for the synoptic class "cold air" masses.
- ItemSimultaneous and co-located wind measurements in the middle atmosphere by lidar and rocket-borne techniques(München : European Geopyhsical Union, 2016) Lübken, Franz-Josef; Baumgarten, Gerd; Hildebrand, Jens; Schmidlin, Francis J.We present the first comparison of a new lidar technique to measure winds in the middle atmosphere, called DoRIS (Doppler Rayleigh Iodine Spectrometer), with a rocket-borne in situ method, which relies on measuring the horizontal drift of a target (“starute”) by a tracking radar. The launches took place from the Andøya Space Center (ASC), very close to the ALOMAR observatory (Arctic Lidar Observatory for Middle Atmosphere Research) at 69° N. DoRIS is part of a steerable twin lidar system installed at ALOMAR. The observations were made simultaneously and with a horizontal distance between the two lidar beams and the starute trajectories of typically 0–40 km only. DoRIS measured winds from 14 March 2015, 17:00 UTC, to 15 March 2015, 11:30 UTC. A total of eight starute flights were launched successfully from 14 March, 19:00 UTC, to 15 March, 00:19 UTC. In general there is excellent agreement between DoRIS and the in situ measurements, considering the combined range of uncertainties. This concerns not only the general height structures of zonal and meridional winds and their temporal developments, but also some wavy structures. Considering the comparison between all starute flights and all DoRIS observations in a time period of ±20 min around each individual starute flight, we arrive at mean differences of typically ±5–10 m s−1 for both wind components. Part of the remaining differences are most likely due to the detection of different wave fronts of gravity waves. There is no systematic difference between DoRIS and the in situ observations above 30 km. Below ∼ 30 km, winds from DoRIS are systematically too large by up to 10–20 m s−1, which can be explained by the presence of aerosols. This is proven by deriving the backscatter ratios at two different wavelengths. These ratios are larger than unity, which is an indication of the presence of aerosols.