Interactive 3D Visual Analysis of Atmospheric Fronts

Abstract

Atmospheric fronts play a central role in meteorology, as the boundaries between different air masses and as fundamental features of extra-tropical cyclones. They appear in numerous conceptual model depictions of extra-tropical weather systems. Conceptually, fronts are three-dimensional surfaces in space possessing an innate structural complexity, yet in meteorology, both manual and objective identification and depiction have historically focused on the structure in two dimensions. In this work, we -a team of visualization scientists and meteorologists- propose a novel visualization approach to analyze the three-dimensional structure of atmospheric fronts and related physical and dynamical processes. We build upon existing approaches to objectively identify fronts as lines in two dimensions and extend these to obtain frontal surfaces in three dimensions, using the magnitude of temperature change along the gradient of a moist potential temperature field as the primary identifying factor. We introduce the use of normal curves in the temperature gradient field to visualize a frontal zone (i.e., the transitional zone between the air masses) and the distribution of atmospheric variables in such zones. To enable for the first time a statistical analysis of frontal zones, we present a new approach to obtain the volume enclosed by a zone, by classifying grid boxes that intersect with normal curves emanating from a selected front. We introduce our method by means of an idealized numerical simulation and demonstrate its use with two real-world cases using numerical weather prediction data.

Interactive 3-D visual analysis of ERA5 data: improving diagnostic indices for marine cold air outbreaks and polar lows

“…We apply Met.3D to investigate the 3-D structure of MCAOs and PLs in ERA5. For the initial explorative phase of the investigation, a set of MCAO and PL cases were selected based on previous studies (Kolstad, 2011;Føre et al, 2012;Bracegirdle, 2012) about strong MCAO events and symmetric PLs (e.g. the case on 18 December 2002 in Figs.…”

“…For the new PL index we compute the temporal average, M tr , by considering only the hourly index values, m tr , for hours with lower-level instability (m p > 0). The different temporal average for the PL index, compared with the MCAO indices, is chosen because a lower-level instability (as indicated by a non-zero MCAO index) is assumed to be a necessary condition for the occurrence of PLs (following Kolstad, 2011), and we wanted to test whether additional information about the upper-level anomaly in the areas of MCAOs, as captured in m tr , improves the performance of the index compared with the simpler new MCAO index.…”

“…Marine cold air outbreaks (MCAOs) are transport events of cold air from sea-ice-or snow-covered regions towards relatively warmer oceans (Rasmussen, 1983;Kolstad and Bracegirdle, 2008;Gryschka, 2018). Understanding MCAOs is relevant because they represent conditions favourable for extreme weather phenomena known as polar lows (PLs; Rasmussen, 1983;Ese et al, 1988;Kolstad, 2011;Michel et al, 2018). PLs are intense mesoscale cyclones, which have been called "Arctic hurricanes" (Nordeng, 1992;Føre et al, 2012;Bracegirdle, 2012) due to similarities with tropical hurricanes including symmetric vortex-like cloud patterns.…”

“…of diagnostic indices that abstract a complex atmospheric structure into a simple numerical value. To define such indices for MCAOs and PLs, various interdependent factors need to be considered, and understanding the link between MCAOs and PLs remains an area of active research (Claud et al, 2007;Kolstad and Bracegirdle, 2008;Kolstad, 2011;Terpstra et al, 2016;Afargan-Gerstman et al, 2020;Stoll et al, 2021). To diagnose MCAOs, most previous studies used an index that represents a simplified version of the Brunt-Väisälä frequency for quantifying static stability, by considering only the sign of the vertical temperature gradient between potential skin temperature of the ocean and potential air temperature aloft (e.g.…”

“…the frequency of occurrence of MCAOs in climatological assessments). Since MCAOs have been reported to be a necessary but not a sufficient condition for the occurrence of PLs (Kolstad, 2011), an open question is whether a diagnosed presence of MCAOs can be useful as a proxy for the occurrence of PLs. A recent climatological study finds a weak relation between MCAOs and the occurrence of polar mesoscale cyclones, including PLs (Michel et al, 2018).…”