Recent global decrease in the inner-core rain rate of tropical cyclones

Abstract

Heavy rainfall is one of the major aspects of tropical cyclones (TC) and can cause substantial damages. Here, we show, based on satellite observational rainfall data and numerical model results, that between 1999 and 2018, the rain rate in the outer region of TCs has been increasing, but it has decreased significantly in the inner-core. Globally, the TC rain rate has increased by 8 ± 4% during this period, which is mainly contributed by an increase in rain rate in the TC outer region due to increasing water vapor availability in the atmosphere with rising surface temperature. On the other hand, the rain rate in the inner-core of TCs has decreased by 24 ± 3% during the same period. The decreasing trend in the inner-core rain rate likely results mainly from an increase in atmospheric stability.

Opposite Changes in Tropical Cyclone Rain Rate During the Recent El Niño and La Niña Years

“…(2021) to calculate the average rain rate in each 25‐km annulus from the TC center (such as 0–25, 25–50, 50–75 km, …) to obtain the radial distribution of TC rain rate (hereafter, for simplicity, the term “rain rate” will refer to TC rain rate unless otherwise stated). Then, we define the outermost radius at which the average radial rain rate >0.5 mm hr −1 (Y. Lin et al., 2015; Tu et al., 2021) as the TC rainfall radius (or rainfall size). The TC mean rainfall radii of TSs, CAT12, and CAT35 are found to be 550 km, 500 km, and 475 km respectively.…”

“…We mainly focus on those TCs generated during the peak TC season of WNP (July-October, Camargo & Sobel, 2005;Tu et al, 2018). As in Tu et al (2021), non-TC systems (such as extratropical, wave, disturbance, or others) are excluded. The monthly Niño 3.4 index is used to define the El Niño and La Niña years (see Section 2.3 for further details).…”

“…Then, we define the outermost radius at which the average radial rain rate >0.5 mm hr −1 (Y. Tu et al, 2021) as the TC rainfall radius (or rainfall size). The TC mean rainfall radii of TSs, CAT12, and CAT35 are found to be 550 km, 500 km, and 475 km respectively.…”

Exploring the Impact of Planetary Boundary Layer Schemes on Rainfall Forecasts for Typhoon Mujigae, 2015

“…On the basis of our previous study [25], the inner core of a typhoon is defined as the region between the typhoon's center and the position with the maximum radial gradient of the rain rate. According to this definition, the radius of the inner core for Typhoon Mujigae was ~150 km, and the outer region extended to 500 km.…”

“…However, the precipitation induced by a typhoon is a complicated topic, because after or near the time of its landfall, extreme weather such as rainstorms and strong winds occur, with distinct differences between the outer region and the inner core of the typhoon [22][23][24]. Recently, Tu et al used the WRF-ARW model to determine that the rain rates in the outer region and inner core of a typhoon have opposite trends, as confirmed by Tropical Rainfall Measuring Mission (TRMM) satellite observations [25]; they pointed out that the short-term prediction of the model failed in describing the circulation near the typhoon center well. Cumulus, microphysical, and PBL parameterization schemes are all sensitive to precipitation simulation; thus, a considerable amount of studies have been carried out to investigate the impact of these three parameterization schemes in simulating precipitation; among them, most of the research focuses on the performance of PBL schemes in simulating the track and intensity of typhoons, rather than precipitation, and it is unclear whether the PBL schemes have consistent performance in simulating precipitation in the inner core and outer region of typhoon.…”