Contrasting Various Metrics for Measuring Tropical Cyclone Activity

Abstract

Popular metrics used for measuring the tropical cyclone (TC) activity, including NTC (number of tropical cyclones), TCD (tropical cyclone days), ACE (accumulated cyclone energy), PDI (power dissipation index), along with two newly proposed indices: RACE (revised accumulated cyclone energy) and RPDI (revised power dissipation index), are compared using the JTWC (Joint Typhoon Warning Center) best-track data of TC over the western North Pacific basin. Our study shows that, while the above metrics have demonstrated various degrees of discrepancies, but in practical terms, they are all able to produce meaningful temporal and spatial changes in response to climate variability. Compared with the conventional ACE and PDI, RACE and RPDI seem to provide a more precise estimate of the total TC activity, especially in projecting the upswing trend of TC activity over the past few decades, simply because of a better approach in estimating TC wind energy. However, we would argue that there is still no need to find a "universal" or "best" metric for TC activity because different metrics are designed to stratify different aspects of TC activity, and whether the selected metric is appropriate or not should be determined solely by the purpose of study. Except for magnitude difference, the analysis results seem insensitive to the choice of the best-track datasets.

Impacts of Madden–Julian oscillation on tropical cyclone activity over the South China Sea: Observations versus HiRAM simulations

“…Although a number of metrics have been designed to measure seasonal TC activity, including total TC day (Chan, 2000; Wang and Chan, 2002), accumulative cyclone energy (Bell et al ., 2000; Waple et al ., 2002), power dissipation index (Emanuel, 2005), genesis potential index (Emanuel and Nolan, 2004) and many of their revised versions (Yu et al ., 2009; Emanuel, 2010; Murakami and Wang, 2010; Korty et al ., 2012; Yu and Chiu, 2012), TC genesis rate is still considered as the most popular one to measure TC activity due to its easy‐to‐interpret nature. Following previous studies (Kim et al ., 2008; Li and Zhou, 2013), the daily genesis rate (DGR) is utilized to quantify the frequency of TCs.…”

Evaluating the Emanuel-Nolan genesis potential index: Contrast between North Atlantic and western North Pacific

“…As in most previous studies, only TC systems reaching at least the tropical storm intensity (i.e., the maximum sustained wind speed v max ≥ 35 knots) during the period from 1979 -2010 are counted here. While a number of metrics have been designed to stratify various aspects of the basin-scale seasonal TC activity, including the "accumulated cyclone energy index" (Bell et al 2000;Waple et al 2002), "power dissipation index" (Emanuel 2005), and their revised versions (Yu et al 2009;Yu and Chiu 2012), we prefer to use the "number of tropical cyclones" (NTC) to characterize the magnitude of basin-scale seasonal TC activity as in most previous studies (Chan and Liu 2004;Holland and Webster 2007;Murakami and Wang 2010;Murakami et al 2012;Manganello et al 2014).…”

Investigating the abrupt change of tropical cyclone (TC) activity in the Western North Pacific by using different TC genesis indices

“…Emanuel (2006) used a similar algorithm and developed the “Power Dissipation Index” (PDI) based on the integrated third power of maximum surface wind velocity. Yu and Chiu (2012) noted that there is no need to find a universal or best metric for measuring the overall TC activity because different metrics are designed to stratify different aspects of TC activity.…”