News Release

Direct/indirect effects of aerosols and their separate contributions to a tropical cyclone approaching the continent: Eyewall versus peripheral rainbands

Peer-Reviewed Publication

Science China Press

Vertical cross-sections of azimuthally averaged and time-averaged radar reflectivity (dBz) and azimuthally averaged and time-averaged hourly precipitation (mm h-1).

image: Vertical cross-sections of azimuthally averaged and time-averaged radar reflectivity (dBz) from three numerical simulations: (a) CTL, (b) CLEAN, (c) CTLARIOFF, (d) Toal=CTL-CLEAN, (e) ARI=CTL-CTLARIOFF, (f) ACI=CTLARIOFF-CLEAN. (g) Azimuthally averaged and time-averaged hourly precipitation (mm h-1). Three simulations (CTL, CLEAN, and CTLARIOFF) were designed, representing a polluted case (CTL, considering the ingestion of anthropogenic aerosols with ARI and ACI), a clean maritime case (CLEAN, mainly with sea salt aerosols), and a polluted case without aerosol radiative forcing (CTLARIOFF, as the CTL but without ARI).The time period is from 1200 UTC on October 20 to 1200 UTC on October 21. view more 

Credit: ©Science China Press

This study is led by Dr. Zhichao Liang, Dr. Juli Ding, Dr. Jianfang Fei, Dr. Xiaoping Cheng, and Dr. Xiaogang Huang (College of Meteorology and Oceanography, National University of Defense Technology, China). The convection competition between the eyewall and peripheral rainbands, and the separate contributions of direct and indirect effects of aerosols to the TC Lupit (0920) were simulated using WRF-Chem, during its process of approaching the Asian continent.

The team sought to determine what are the respective impacts of ARI and ACI on TC intensity and convection in the eyewall versus peripheral rainband? How does the importance of ARI and ACI differ, and what is the physical mechanism?

The team found that in the process of TC Lupit (0920) approaching the Asian continent, a large amount of anthropogenic aerosols accumulated in the atmospheric boundary layer, which penetrated both into the TC peripheral rainbands and the eyewall with the TC boundary-layer radial inflow.

Direct aerosol-radiation interactions (ARI) heated the distant periphery lower atmosphere at an altitude of 1–2 km by the absorbing polluted aerosols (i.e. black carbon). The heated air, driven by the radial inflow, firstly went through the periphery rainbands of the TC and invigorated convection there due to the low-level warming. Then, the enhanced periphery convection inhibited the further transport of warm moist air into the eyewall, resulting in weakening of the eyewall convection and hence typhoon intensity.

Indirect aerosol-cloud interactions (ACI) performed an opposite role compared to ARI on TC intensity, eyewall versus peripheral rainband convections, and TC precipitation distributions. Specifically, the ACI mainly enhanced the formation of ice-phase hydrometeors within the upper level of the eyewall with more freezing latent heat releases, leading to an invigoration of eyewall convection and TC intensification with dynamic feedbacks.

For the polluted scenario, as a TC approached the continent, ARI played a dominant role over ACI. Ignoring ARI effects may lead to over-forcasting of the TC intensity.

See the article:

Liang Z, Ding J, Fei J, Cheng X, Huang X. 2021. Direct/indirect effects of aerosols and their separate contributions to Typhoon Lupit (2009): Eyewall versus peripheral rainbands. Science China Earth Sciences, 64(12): 2113–2128,

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