The Response of Tropical Cyclone Intensity to Temperature Profile Change (original) (raw)

Theory indicates that tropical cyclone intensity should respond to changes in the vertical temperature profile. While the sensitivity of tropical cyclone intensity to sea surface temperature is well understood, less is known about sensitivity to the temperature profile. In this paper, we combine historical data analysis and idealised modelling to explore the extent to which historical tropospheric warming and lower stratospheric cooling can explain observed trends in the tropical cyclone intensity distribution. Observations and modelling agree that historical global temperature profile changes coincide with higher lifetime maximum intensities. But observations suggest the response depends on the tropical cyclone intensity itself. Historical lower-and upper-tropospheric temperatures in hurricane environments have warmed significantly faster than the tropical mean. In addition, hurricane-strength storms have intensified at twice the rate of weaker storms per unit warming at the surface and at 300-hPa. Idealized simulations respond in the expected sense to various imposed changes in the temperature profile and agree with tropical cyclones operating as heat engines. Yet lower stratospheric temperature changes have little influence. Idealised modelling further shows an increasing altitude of the TC outflow but little change in outflow temperature. This enables increased efficiency for strong tropical cyclones despite the warming upper troposphere. Observed sensitivities are generally larger than modelled sensitivities, suggesting that observed tropical cyclone intensity change responds to a combination of the temperature profile change and other environmental factors. Non-Technical Summary. Understanding how tropical cyclones (TCs) are changing is key for the protection of lives and livelihoods in vulnerable regions. We know that warm oceans generally favour TC activity. Less is known about the role of air temperature above the oceans and extending into the lower stratosphere. Our analysis of historical records and computer simulations suggests that TCs strengthen in response to historical temperature change while also being influenced by other environmental factors. 1 Introduction Understanding how tropical cyclones (TCs) and their impacts respond to climate change is of critical scientific and societal importance (e.g., Knutson et al., 2020). However, TC response to environmental change is complex and multi-faceted. Here, we use observations and idealized models to examine the TC response to changes in the environmental temperature profile. Historical global surface temperature trend analyses show significant warming since the mid 1970s, attributed to anthropogenic forcing (Meehl et al., 2004; 2012). Yet trends in the vertical thermal structure and their attribution are less well understood (O'Gorman and Singh, 2013; Prein et al., 2017). Since the mid 1970s most datasets show that the troposphere has warmed while the lower stratosphere has cooled (e.g., Thompson et al., 2012; Philipona et al., 2018). However, analysing these trends is particularly challenging in the global tropics because of sparse long-term historical temperature profile records and the potential for artificial trends driven by observing system changes (Thorne et al., 2011).