Lagrangian matches between observations from aircraft, lidar and radar in an orographic warm conveyor belt

• Main Authors: Boettcher, Maxi, Schäfler, Andreas, Sprenger, Michael, Sodemann, Harald, Kaufmann, Stefan, Voigt, Christiane, Schlager, Hans, Summa, Donato, Di Girolamo, Paolo, Nerini, Daniele, Germann, Urs, Wernli, Heini
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2020
• Subjects: Lidar; Wolkenphysik; Atmosphärische Spurenstoffe; North Atlantic
• Online Access: https://elib.dlr.de/138296/; https://doi.org/10.5194/acp-2020-1019

Warm conveyor belts (WCBs) are important airstreams in extratropical cyclones, often leading to the formation of intense precipitation and the amplification of upper-level ridges. This study presents a case study that involves aircraft, lidar and radar observations in a WCB ascending from western Europe towards the Baltic Sea during the field experiments HyMeX and T-NAWDEX-Falcon in October 2012. Trajectories were used to link different observations along the WCB, that is to establish so-called Lagrangian matches between observations. To this aim, wind fields of the ECMWF ensemble data assimilation system were used, which allowed for a probabilistic quantification of the WCB occurrence and the Lagrangian matches. Despite severe air traffic limitations for performing research flights over Europe, the DLR Falcon successfully sampled WCB air masses during different phases of the WCB ascent. The WCB trajectories revealed measurements in two distinct WCB branches: one branch ascended from the eastern North Atlantic over southwestern France, while the other had its inflow in the western Mediterranean. Both branches passed across the Alps, and for both branches, Lagrangian matches coincidentally occurred between lidar water vapour measurements in the inflow of the WCB south of the Alps, radar measurements during the ascent at the Alps, and in situ aircraft measurements by Falcon in the WCB outflow north of the Alps. An airborne release experiment with an inert tracer could confirm the long pathway of the WCB from the inflow in the Mediterranean boundary layer to the outflow in the upper troposphere near the Baltic Sea several hours later. The comparison of observations and ensemble analyses reveals a moist bias in the analyses in parts of the WCB inflow but a good agreement of cloud water species in the WCB during ascent. In between these two observations, a precipitation radar measured strongly precipitating WCB air located directly above the melting layer while ascending at the southern slopes of the Alps. The ...