We are very much looking forward to attend the first virtual AMS annual meeting on 10-15 January 2021 where we have the opportunity to present work from the INTEXseas project. The presentation by Heini Wernli on “Characteristics and dynamics of extreme seasons – a research topic at the interface of weather and climate” provides an overview of the project activities and achievements in the first two years. Mauro Hermann presents recent results from Matthias Röthlisberger et al. about “A new framework for identifying and investigating seasonal climate extremes” in data from ERA-Interim and the CESM large ensemble. And Luise Fischer uses data from the same large ensemble to investigate “How do North Atlantic – European weather regimes change with climate change?”. We are curious to receive feedback about our work from the AMS community!
Philipp joins us from Karlsruhe Institute of Technology (KIT), where he recently obtained his PhD. Philipp is an expert on heat wave dynamics and intensively studied heat waves across Europe from a Lagrangian point of view.
Philipp now joins the INTEXseas project as a PostDoc. In INTEXseas, Philipp will investigate, among other things, under which temperature regimes large amounts of precipitation occur and he will study the meteorological reasons for that. Moreover, Philipp plans to identify extreme summer objects in numerous large ensemble simulations from various modelling centers using an identifiaction scheme that has previousely been developped in INTEXseas.
In a study led by Emmanouil Flaounas we identified and studied the occurrence and synoptic dynamics of extreme wet seasons unsing ERA-Interim and an extensive collection of weather feature identification climatologies. In this study we employed a temporally flexible definition of “wet seasons” and their extremes by identifying at each grid point the 90-day periods with the most accumulated precipitation. Connecting these extreme wet seasons to spatial objects (see figure below) then allows to study the dynamical drivers of these individual events. These analyses reveal a wide palette of synoptic storylines for extreme wet seasons that strongly vary in space. For example, an extreme wet season over the tropical Atlantic resulted from a single particularly strong tropical cyclone, while over Iberia and the US West Coast extreme wet seasons occurred due to anomalousely frequent tropical moisture exports and extratropical cyclones and an extreme wet season over Northern Australia resulted form a complex interplay between extratropical Rossby wave breaking, a landfalling tropical cyclone and anomalousely frequent surface cyclones. This paper is the first to comprehensively chracterize extreme wet seasons around to globe with regard to their weather feature characteirstics and is now in the discussion phase in Weather and Climate Dynamics.
The Figure above shows the 100 largest extreme wet season objects in the ERA-Interim period 1979-2018.
Together with colleagues from Karlsruhe Institute of Technology (Germany) and University of Bergen (Norway) we have analyzed the dynamical mechanisms that lead to concurrent and sequential heat waves in Scandinavia and Central Europe. Such events are socio-economically relevant, because the affected area of concurrent and sequential heat waves can far exceed the area affected by individual heat waves. The study led by Clemens Spensberger (University of Bergen) has now been accepted in the Quarterly Journal of the Royal Meteorological Society (QJRMS). Several INTEXseas members (Maxi Böttcher, Lukas Papritz, Michael Sprenger and Matthias Röthlisberger) contributed to this study which highlights the relevance of weak pressure gradient situations over Central Europe for co-occurring Central European and Scandianvian heat waves. Such weak pressure gradient situations are conducive to heat waves over central Europe and typically form at the southern fringe of the a blocking anticyclone, which fosters heat over Scandinavia. Moreover, concurrent heat waves are observed more frequently than one would expect under the assumption that Scandinavian heat waves are statistically independend from Central European heat waves. Overall, the study thus highlights several key dynamical aspects of heat waves affecting unusually large areas.
Mauro Hermann and his former MSc thesis supervisors (Lukas Papritz, Heini Wernli) recently submitted a study on Greenland melt events in Weather and Climate Dynamics. The use of Lagrangian backward trajectories – calculated with the powerful LAGRANTO tool also used in the INTEXseas project – gave them insight into the dynamical and thermodynamic processes acting on air masses, which end up just above the surface of the Greenland Ice Sheet during extensive melt periods.
The authors found that an upper-tropospheric ridge southeast of Greenland is mostly present during the 77 identified melt events in 1979-2017. Surprisingly, their intuitive idea that subsidence-induced adiabatic warming is an important contribution to the observed warm anomaly, as for air masses associated with near-surface heatwaves in the midlatitudes or the Central Arctic, was not confirmed. Instead, strong poleward transport from a climatologically warmer region (at lower levels and/or at lower latitudes) causes the air mass warmth. Latent heat release occurring as the air masses are forced to ascend orographically or dynamically is of secondary importance. The dynamical perspective helped the INTEXseas team members to systematically identify synoptic patterns and thermodynamic mechanisms, which are associated with air masses causing melt of the Greenland Ice Sheet.
The figure shows 10-day trajectories arriving over melting ice during the most extensive melt event in July 2012, colored according to their pressure, show illustratively the low-level and low-latitude origin of these air masses. Five representative example trajectories represent characteristic airstreams (S, C, E, N1, N2), shown in thicker lines with one circle per day colored from white (t = -240 h) to black (t = 0 h).
Find the discussion paper here.