Evolution of Near-Cloud Turbulence in the Upper-Level Outflow of a Tropical Cyclone Interacting with the East Asian Jet

Evolution of Near-Cloud Turbulence in the Upper-Level Outflow of a Tropical Cyclone Interacting with the East Asian Jet

Ju Heon Lee¹⁺, Jung-Hoon Kim^1*, Robert D. Sharman², Stan B. Trier², and James D. Doyle³

¹School of Earth and Environmental Sciences, Seoul National University, Seoul, South Korea

²NSF National Center for Atmospheric Research, Boulder, Colorado

³ U.S. Naval Research Laboratory, Monterey, California

A relatively high frequency of atmospheric turbulence in the Upper Troposphere and Lower Stratosphere (UTLS) was found over East Asia and the Northwestern Pacific Ocean, which attributes to upper-level jet/front dynamics related to shear, convective, and inertial instabilities around the East Asian Jet (EAJ) (Lee et al., 2023). This turbulence can be driven by the interaction between the EAJ and upper-level outflow from deep convection and Tropical Cyclones (TCs). This type of turbulence can be considered as Near Cloud Turbulence (NCT), because it occurred away from the main convective areas, and was indirectly related to the convective systems. Lee et al. (2024) found that the proximity of the mid-latitude jet and northward moving TC Hagibis played an important role to accelerate TC-induced upper-level radial outflow, which resulted in inertial and convective instability areas with localized strong turbulence responsible for the reported in situ turbulence encountered by commercial aircraft. To expand the results in Lee et al. (2024), we further examined the spatial and temporal distributions of the NCT during the entire period of TC Hagibis in 2019. In this study, the potential of NCT throughout the TC life cycle was investigated using the ECMWF Reanalysis version 5 data on native model levels with a vertical spacing of 8 hPa 300 m in the UTLS. Here, the potential of NCT dependence on various instabilities was diagnosed using Vertical Wind Shear (VWS), local Richardson number (Ri), and inertial stability (I²). Results showed that the spatial and temporal distributions of the turbulence diagnostics near the outflow of the TC changed dramatically depending on the distance between the TC and EAJ. At the early stage of the TC when Hagibis and the EAJ were located far away from each other (i.e., they did not interact), turbulence was not predicted near the TC based on these diagnostics. Some broad areas of weak inertial instability (I² ~ 0) appeared within the outflow of TC. After the recurvature stage of the TC when the TC moved northward close to the EAJ (i.e., TC-EAJ interaction existed), high frequencies of VWS and Ri < 1.0 were found, especially on the anticyclonic shear side of the EAJ. This area was found to be coincident with a maximum in the radial winds and an area of intensified inertial instability located asymmetrically at the northwestern quadrant of the TC. This implies that the TC-jet interaction strengthened the inertial instability at the northwestern quadrant of the TC, which induced stronger radial outflow from the TC, and in turn generated NCT due to shear instability at upper levels. This presentation will outline the evolution of turbulence diagnostics around the EAJ as the TC evolves.

References:

Lee, J. H., Kim, J.-H., Sharman, R. D., Kim, J., & Son, S.-W. (2023). Climatology of Clear-Air Turbulence in upper troposphere and lower stratosphere in the Northern Hemisphere using ERA5 reanalysis data. Journal of Geophysical Research: Atmospheres, 128, e2022JD037679.

Lee, J. H., Kim, J.-H., S. B. Trier, R. D. Sharman, and J. D. Doyle. (2024) Generation Mechanisms of Near-Cloud Turbulence Events in the Upper-Level Outflow of Tropical Cyclone Hagibis (in Review)

Acknowledgement: This research was performed by the Korea Meteorological Administration Research and Development Program under Grant KMI2022-00410 and by the National Research Foundation of Korea Research and Development Program (NRF-2019R1I1A2A1060035)