Climatological Changes in the Extratropical Transition of Tropical Cyclones in High-Resolution Global Simulations

Abstract

Tropical cyclones (TCs) undergoing extratropical transition (ET) can develop into intense cyclonic systems accompanied by high-impact weather in areas far removed from the original TC. This study presents an analysis of multiseasonal global simulations representative of present-day and projected future climates using the Model for Prediction Across Scales–Atmosphere (MPAS-A), with high resolution (15-km grid) throughout the Northern Hemisphere. TCs are tracked as minima in sea level pressure (SLP) accompanied by a warm core, and TC tracks are extended into the extratropical phase based on local minima in SLP and use of a cyclone phase space method. The present-day simulations adequately represent observed ET characteristics such as frequency, location, and seasonal cycles throughout the Northern Hemisphere. The most significant changes in future ET events occur in the North Atlantic (NATL) basin. Here, a more favorable background environment, a shift toward stronger TC warm cores in the lower troposphere, and a significant poleward shift in TC location lead to a ~40% increase in the number of NATL ET events and a ~6% increase in the fraction of TCs undergoing ET. This equates to approximately 1–2 additional ET events per year in this region. In the future simulations, ET in the NATL occurs markedly farther north by ~4°–5°N, and the resultant extratropical cyclones are stronger by ~6 hPa. These changes hold potentially important implications for areas directly affected by ET events, such as eastern North America, as well as for regions indirectly impacted by downstream effects, including western Europe.

Assessing Historical Variability of South Asian Monsoon Lows and Depressions With an Optimized Tracking Algorithm

“…An automated Lagrangian pointwise feature tracker, TempestExtremes, is used for extracting LPS track information from the reanalyses (Ullrich & Zarzycki, 2017). TempestExtremes has been used for tracking features including tropical cyclones, extratropical cyclones, and tropical easterly waves (Chavas et al., 2017; Michaelis & Lackmann, 2019; Ullrich & Zarzycki, 2017; Zarzycki, Thatcher, et al. 2017).…”

“…An automated Lagrangian pointwise feature tracker, TempestExtremes, is used for extracting LPS track information from the reanalyses . TempestExtremes has been used for tracking features including tropical cyclones, extratropical cyclones, and tropical easterly waves (Chavas et al, 2017;Michaelis & Lackmann, 2019;Zarzycki, Thatcher, et al 2017). The basic algorithm uses the MapReduce technique, which operates in two stages: first, parallel identification of sui- develop object tracks, eliminating candidates that do not exhibit behavior consistent with a transiting feature.…”

How Important Are Post‐Tropical Cyclones for European Windstorm Risk?

“…Liu et al (2018) and Semmler et al (2008a, 2008b) find that the fraction of TCs which undergo extratropical transition is likely to increase in the North Atlantic under RCP 4.5, the SRES‐A2 emission scenario, and a 1 K increase in SSTs, respectively. Michaelis and Lackmann (2019) find that the number of extratropical transition events may increase by 40% by the year 2100 under RCP 8.5. Without an understanding of the risks posed by PTCs for Europe in the current climate, it is difficult to deduce the consequence of a future change in PTC frequency or intensity.…”

TempestExtremes v2.1: A Community Framework for Feature Detection, Tracking and Analysis in Large Datasets

“…This module enabled cyclonic storms to be examined using the thermal wind and thermal asymmetry phase space of Hart (2003). ExTraTrack was later applied to a suite of high-resolution global simulations in Michaelis and Lackmann (2019). ETCs were also tracked in the Community Earth System Model Large Ensemble (CESM-LENS) in Zarzycki (2018) to understand the drivers responsible for snowstorms in the US Northeast.…”