Characteristic Scales of Tropical Convection Based on the Japanese Advanced Himawari-8 Imager Observations

Convective activities play an important role in tropical weather systems. To investigate the characteristic scales of convection, a method combining a principal component (PC) analysis with Fourier decomposition is applied to brightness temperature observations from Advanced Himawari-8 Imager (AHI). Characteristic scales of different modes in tropical convective systems are obtained. The explained variance reduces rapidly from the first to the 60th PC mode by two magnitudes; the horizontal scale decreases from over 2000 km to about 100 km, and the timescale changes from more than 4 days to around 5 h. By a detailed comparison of the first, 20th, 40th, and 60th PC modes, it is found that large-scale (over 2000 km in wavelength) convective activities usually have significant nocturnal enhancement, whereas meso-scale (about 100 km in wavelength) convective activities feature short period and fast change with more intense development in regions of active large-scale convection. This study may be of some importance for the choice of AHI data assimilation cycling interval, the horizontal resolution as well as data thinning for geostationary satellite observations.

Automated summary

Convective activities play a crucial role in tropical weather systems. This study investigates the characteristic scales of convection in the tropics using a method that combines principal component analysis with Fourier decomposition. The results reveal that large-scale convective activities typically exhibit significant nocturnal enhancement, while meso-scale convective activities feature short periods and rapid changes.