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Jet streams are important sources of non‐orographic internal gravity waves and clear air turbulence (CAT). We analyze non‐orographic gravity waves and CAT during a merger of the polar front jet stream (PFJ) with the subtropical jet stream (STJ) above the southern Atlantic. Thereby, we use a novel combination of airborne observations covering the meso‐scale and turbulent scale in combination with high‐resolution deterministic short‐term forecasts. Coherent phase lines of temperature perturbations by gravity waves stretching along a highly sheared tropopause fold are simulated by the ECMWF IFS (integrated forecast system) forecasts. During the merging event, the PFJ reverses its direction from approximately antiparallel to parallel with respect to the STJ, going along with strong wind shear and horizontal deformation. Temperature perturbations in limb‐imaging and lidar observations onboard the research aircraft HALO during the SouthTRAC campaign show remarkable agreement with the IFS data. Ten hours earlier, the IFS data show an "X‐shaped" pattern in the temperature perturbations emanating from the sheared tropopause fold. Tendencies of the IFS wind components show that these gravity waves are excited by spontaneous emission adjusting the strongly divergent flow when the PFJ impinges the STJ. In situ observations of temperature and wind components at 100 Hz confirm upward propagation of the probed portion of the gravity waves. They furthermore reveal embedded episodes of light‐to‐moderate CAT, Kelvin Helmholtz waves, and indications for partial wave reflection. Patches of low Richardson numbers in the IFS data coincide with the CAT observations, suggesting that this event was accessible to turbulence forecasting. Plain Language Summary: Gravity waves play an in important role in vertical and horizontal energy transport in the atmosphere and are significant factors in wheather forecasting and climate projections. Among other processes, tropospheric jet streams are known to be sources of gravity waves. They furthermore can be accompanied by tropopause folds (i.e., local tropopause depressions, where stratospheric air can reach deeply into the troposphere) and turbulence, which is relevant for aviation safety. Using a novel combination of airborne observations and data by a state‐of‐the‐art forecasting system, we analyze gravity waves and turbulence during a merger of tropospheric jet streams above the southern Atlantic. The observations show a high degree of agreement with the forecast data from the troposphere to the stratosphere. Ten hours earlier, the forcast data show an "X‐shaped" gravity wave structure that emerges from a highly sheared tropopause fold between the merging jet streams. Fast in situ observations at the flight level provide information on the characteristics of the observed waves and show light‐to‐moderate turbulence, small‐scale waves and indications for partial wave reflection. The observed turbulence events are consistently located in regions where the forecast data suggest potential for turbulence. Key Points: Non‐orographic internal gravity waves and clear air turbulence are observed in merging jet streamsState‐of‐the art high resolution forecast agrees with novel combination of airborne sensors"X‐shaped" gravity wave feature resulting from merging jet streams at a highly sheared tropopause fold [ABSTRACT FROM AUTHOR]

Background and purpose: In contrast to anterior circulation stroke (ACS), there is no evidence from randomized trials that mechanical thrombectomy (MT) with modern stent retrievers or thromboaspiration is safe and effective in posterior circulation stroke (PCS). Methods: The present analysis was based on the prospective multicentre Registry on Revascularization in Ischemic Stroke Patients (REVASK) in Germany. Demographic data, periprocedural times and complications, recanalization rates, and functional outcome at discharge and after 3 months were compared between 139 consecutive patients with PCS (84.9% basilar artery, 16.5% vertebral artery and 4.3% posterior cerebral artery occlusion) and 961 patients with ACS treated with MT. Results: Compared to ACS, PCS patients were significantly younger (65 vs. 69 years, P = 0.021) and had a lower median National Institutes of Health Stroke Scale (NIHSS) score at baseline (12 vs. 15, P = 0.024). Patients with PCS had a significantly longer time delay between symptom onset and both start and end of the MT procedure. Successful recanalization and thrombectomy passes did not significantly differ between the two groups. No symptomatic intracranial haemorrhage occurred in PCS compared to 3% in ACS (P = 0.010). The median NIHSS score at discharge was 3 in PCS and 4 in ACS. Favourable functional outcome at 3 months (modified Rankin Scale 0–2 38.0% vs. 42.6%, P = 0.392) and mortality (33.7% vs. 30.8%, P = 0.539) did not differ significantly between PCS and ACS. Conclusions: The study suggests that MT in PCS shows a lower risk of symptomatic intracranial haemorrhage and similar effectiveness compared to ACS. PCS patients also seem to benefit from MT started beyond 6 h after symptom onset. [ABSTRACT FROM AUTHOR]

The novel airborne Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) measures infrared emission of atmospheric trace constituents. GLORIA comprises a cooled imaging Fourier transform spectrometer which is operated in unpressurized aircraft compartments at ambient temperature. The whole spectrometer is pointed by the gimbal towards the atmospheric target. In order to reach the required sensitivity for atmospheric emission measurements the spectrometer optics needs to operate at a temperature below 220 K. A lightweight and compact design is mandatory due to limited space and high agility requirements. The cooled optical system needs to withstand high pressure and temperature gradients, humidity, and vibrations. A new cooling system based on carbon dioxide and liquid nitrogen combined with highperformance insulation has been developed to meet the mechanical, thermal, and logistical demands. The challenging mechanical and spatial requirements lead to the development of a novel rigid linear slide design in order to achieve the large optical path difference for high spectral resolution. This paper describes the mechanical and thermal setup of GLORIA and presents the performance results on two different research aircrafts. [ABSTRACT FROM AUTHOR]