open access

https://hdl.handle.net/2115/78617

Convective Bursts With Gravity Waves in Tropical Cyclones : Case Study With the Himawari-8 Satellite and Idealized Numerical Study

英語

2020-02-16

American Geophysical Union

Geophysical research letters

47(3)

e2019GL086295

Convective bursts occur frequently in tropical cyclones and help their intensification by diabatic heating, but their quantitative importance has not been established. By using the high-frequency observation of infrared brightness temperature with Himawari-8, a latest-generation geostationary meteorological satellite, convective bursts in Typhoon Lan (2017) were studied. Aided with a series of numerical simulations, it was revealed that the anvil edges of many bursts are associated with finite-amplitude gravity waves consistent with internal bores, creating warm anomalies by subsidence ahead of the edges. As the edges spread, they are thinned, and their propagation speeds are often decreased. In many such instances, gravity waves, now linear, are separated from the edges to propagate away, spreading convective heating. It is proposed that by quantifying these processes with geostationary satellites, diabatic heating by convective bursts can be estimated to diagnose their impacts on tropical-cyclone intensification. Plain Language Summary Convective bursts (CBs) are intense long-lasting cumulonimbus that occur frequently in tropical cyclones (TCs). Many studies suggested that condensation heating associated with CBs is an important factor in TC intensification but to what extent they are important has not been established. The latest-generation (also known as the third-generation) geostationary meteorological satellites such as Himawari-8 provided opportunities to observe TCs at frequencies much higher than before. We studied the anvil clouds (outflow clouds near the tropopause) of CBs in Typhoon Lan (2017) by using infrared images from Himawari-8. We also conducted numerical simulations to help interpretation. It was found that the anvil of a CB frequently spreads as an internal gravity wave in such a way that the anvil edge is preceded by the subsidence and temperature increase due to an internal bore (finite-amplitude gravity wave similar to tidal bore). Since the anvil spreads circularly, its edge is thinned gradually. It was found that its expansion speed is often slowed down, and the gravity wave is separated to propagate further ahead, disseminating convective heating. It is proposed that geostationary-satellite observations can be used to estimate convective heating associated with each CB. It will help establish the impacts of CBs in TC intensification.

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Horinouchi, T., Shimada, U., & Wada, A. (2020). Convective Bursts With Gravity Waves in Tropical Cyclones: Case Study With the Himawari-8 Satellite and Idealized Numerical Study. Geophysical Research Letters, 47, e2019GL086295, DOI:10.1029/2019GL086295. To view the published open abstract, go to http://dx.doi.org and enter the DOI.

0094-8276

AA00657102