Cyclone Workshop showcases 3D visualisation

Marc Rautenhaus (Universität Hamburg)
Tim Hewson (ECMWF)
Andrea Lang (University at Albany)

 

The 19th Cyclone Workshop took place at Kloster Seeon in southern Germany from 29 September to 4 October 2019. The biennial workshop included a special two‐hour session devoted to a ‘3D weather discussion’. The objective was to showcase recent advances in interactive 3D visualisation in the Met.3D package and to demonstrate how these can be used for rapid real‐time analysis of ensemble forecasts. A team of three (this article’s authors) led the proceedings and, with active participation from the audience, performed a real‐time analysis of the then‐current weather situation over the North Atlantic. We focused on the behaviour of Hurricane Lorenzo and its implications for the extratropical flow in ECMWF’s ensemble forecasts.

The Met.3D software is an open‐ source package originating from visualisation research at Universität Hamburg and at Technische Universität München. From its original purpose of aiding forecast exploration during aircraft‐based field campaigns (see ECMWF Newsletter No. 138), it has in recent years evolved into a general‐purpose meteorological visualisation tool. In particular, through collaboration between Tim Hewson and the Met.3D group integrated into the German Collaborative Research Centre ‘Waves to Weather’ (W2W), novel feature‐based displays for 3D jet‐stream core lines and 3D frontal surfaces have been developed. Also, a user‐friendly interface between ECMWF’s Metview software and Met.3D has been created.

Weather discussion with Met.3D. Andrea, Tim and Marc analysed ECMWF forecasts of Hurricane Lorenzo using interactive 3D visualisation whilst an active audience participated with ideas and suggestions for the forecast exploration.

Visualising Lorenzo

Hurricane Lorenzo made its way through the eastern Atlantic Ocean in late September and early October and became the easternmost Category 5 hurricane on record in the Atlantic. During the period of the workshop, the storm underwent extratropical transition and curved back towards Europe. About 125 scientists from all over the world had assembled for this workshop to discuss the structure, dynamics, hazards, and predictability of extratropical and tropical cyclones, so this meteorological situation provided an ideal focal point for an interactive discussion of the ensemble forecast in real‐time.

During the weather discussion, Met.3D was run remotely from the W2W visualisation server in Munich, although a standard PC equipped with a graphics card and data on disk would have worked equally well. We first introduced Met.3D’s philosophy of building a bridge from traditional 2D visualisations (e.g. horizontal maps, vertical sections and Skew‐T diagrams) that can be displayed and interactively moved in real time in a 3D context, to ‘pure’ 3D visualisations (including isosurfaces, direct volume rendering, trajectories and the novel jet‐stream core line and frontal surface displays). Then, we used some standard Met.3D forecast products to obtain ‘big picture’ information on the weather situation. Afterwards, the audience could make special requests.

Examples of Met.3D visualisations used to analyse the behaviour of Hurricane Lorenzo. The panels show member 24 of the ECMWF ensemble forecast (ENS) from 00 UTC 29 September 2019, valid at 00 UTC 03 October 2019. Top: Jet-stream core lines where wind speed exceeds 45 m/s (colour shows pressure in hPa, thickness scaled according to wind speed), with vertical sections showing wind speed (colour in m/s), potential temperature (grey contours), and the 2-PVU line (red contour line) to indicate the dynamical tropopause (and a Lorenzo-related ‘PV tower’). Black surface contours show mean sea level pressure. The three red vertical axes mark (from west to east) the centre of Lorenzo at 12 UTC 01 October 2019; the centre at 00 UTC 03 October 2019; the approximate location of maximum tropopause height as indicated by the 2-PVU isosurface. Bottom left: As top panel but with trajectories indicating warm conveyor belts (from 12 UTC 01 October 2019 until 00 UTC 03 October 2019, shown only where ascent is >500 hPa in 48 hours, colour shows pressure in hPa). Bottom right: 2-PVU isosurface representing the dynamic tropopause (colour shows pressure in hPa), with vertical axes as on the other panels.

The figures show examples of visualisations used during the session. For instance, there was particular interest in the structure of the dynamical tropopause as represented by the 2‐PVU isosurface, its relation to the jet‐stream configuration, and trajectories carefully selected to represent warm conveyor belts (thanks to Julian Quinting from the Karlsruhe Institute of Technology for the trajectory data). A memorable moment occurred whilst interactively moving a vertical cross section during a phase of explosive extratropical re‐ intensification of Lorenzo, in one ensemble member. The descent of the 2‐PVU isosurface to a level close to the surface near the cyclone led to great excitement in the audience! At the same time, the 3D jet lines were able to pick up cores at multiple levels, including the dynamical drivers at upper levels, and surface-wind‐related cores at low levels.

Outlook

We are very encouraged by the positive feedback from the audience and look forward to the recently started second phase of W2W, in which Met.3D research and development will be actively continued. Jet and front diagnostics will be further improved, and we will evaluate a possible integration of the techniques into ECMWF’s operational analysis toolchain in 2020.