Observation of the Tropical Cyclone Diurnal Cycle Using Hyperspectral Infrared Satellite Sounding Retrievals

Abstract

Hyperspectral infrared satellite sounding retrievals are used to examine thermodynamic changes in the tropical cyclone (TC) environment associated with the diurnal cycle of radiation. Vertical profiles of temperature and moisture are retrieved from the Suomi National Polar–orbiting Partnership (S–NPP) satellite system, National Oceanic and Atmospheric Administration (NOAA)–20, and the Meteorological Operational (MetOp) A/B satellite system, leveraging both infrared and microwave sounding technologies. Vertical profiles are binned radially based on distance from the storm center and composited at 4–hr intervals to reveal the evolution of the diurnal cycle. For the three cases examined – Hurricane Dorian (2019), Hurricane Florence (2018) and Hurricane Irma (2017) – a marked diurnal signal is evident that extends through a deep layer of the troposphere. Statistically significant differences at the 95% level are observed in temperature, moisture, and lapse rate profiles, indicating a moistening and destabilization of the mid to upper troposphere that is more pronounced near the inner core of the TC at night. Observations support a favorable environment for the formation of deep convection caused by diurnal differences in radiative heating tendencies, which could partially explain why new diurnal pulses tend to form around sunset. These findings demonstrate that the diurnal cycle of radiation affects TC thermodynamics through a deep layer of the troposphere, and suggest that hyperspectral infrared satellite sounding retrievals are valuable assets in detecting thermodynamic variations in TCs.

Global and Regional Characteristics of Radially Outward Propagating Tropical Cyclone Diurnal Pulses

“…Similarly, Trabing and Bell (2021) found that three DPs in Super Typhoon Kong-rey (2018) initiated from the inner core during 15 𝐴𝐴 − 21 LT instead of the early morning, suggesting that pulsing is not diurnally "locked." Since various studies demonstrate that the environments conducive for convective development are also important to the DP Duran et al, 2021;Knaff et al, 2019), the variability of the environment may also change the phase of the diurnal cycle Ditchek et al, 2020;Stevenson et al, 2016;Trabing & Bell, 2021). Ditchek et al (2020) hypothesized that the environments of off-the-clock cooling pulses may be more favorable for deep convection and facilitate the pulse to initiate earlier.…”

“…Another diurnal variation found in TCs that could impact TC intensity is a cloud top cooling signal (the so‐called “diurnal pulse,” hereafter DP) that propagates radially outward over the course of the day (Ditchek, Corbosiero, et al., 2019; Ditchek, Molinari, et al., 2019; Ditchek et al., 2020; Duran et al., 2021; Kossin, 2002). The pulse is identified by taking 6‐hr satellite infrared (IR) brightness temperature (BT) differences, and has been found to be related to the expansion and contraction of the cirrus canopy (Dunion et al., 2019; Melhauser & Zhang, 2014; Ruppert & O'Neill, 2019; Wu & Ruan, 2016).…”

“…TCs show significant diurnal variations in many aspects related to TC convection that could impact TC intensity (e.g., Dunion et al., 2014; Kossin, 2002; Lee et al., 2020; Leppert & Cecil, 2016; Zhang et al., 2020; Zhang & Xu, 2021a, 2022). Instability, relative humidity, and low‐level inflow are all enhanced at night, likely due to the nocturnal radiation‐convection interaction and differential radiative cooling between convective and clear‐sky areas (Duran et al., 2021; Ruppert & Hohenegger, 2018; Zhang et al., 2020). This interaction could invigorate precipitation, deep convection, and lightning activity around midnight and into the early morning hours (Leppert & Cecil, 2016; Sun et al., 2021; Tang et al., 2019; Zhang & Xu, 2021a).…”

“…While the DP has been identified using cloud top brightness temperature differences, it has also been found to impact the TC's deep‐layer structure (Ditchek, Corbosiero, et al., 2019; Ditchek, Molinari, et al., 2019; Ditchek et al., 2020; Dunion et al., 2014, 2019; Duran et al., 2021). More than half of diurnal cooling pulses are coupled with surface precipitation and deep convection in TCs, including lightning and deep‐layer ice water content (Ditchek, Molinari, et al., 2019; Zhang & Xu, 2022).…”

Evaluating Satellite Sounders for Monitoring the Tropical Cyclone Environment in Operational Forecasting

“…We evaluate the NUCAPS MW-only retrieval because it may be useful for increasing the yield of successful observations near tropical cyclones. For instance, both the IR + MW and MW-only retrievals were successfully used to examine the diurnal cycle of tropical storms [17].…”