Intraseasonal and diurnal variations in the Indian sector
Kiyotoshi Takahashi (1)
(1) MRI/JMA
Intraseasonal variation (ISV) and diurnal one of convective activity are most dominant variabilities in the tropical monsoon region.@Revealing the relationship of both modes is considered to be important in understanding the variability in the tropical monsoon.
As you know, the Indian sector is the region where the ISV is observed most prominently. In consideration of this situation, this region is suitable for investigating the relationship between ISV and diurnal variation.
In this study, the relationship in appearance of ISV and activity of diurnal variation is investigated using geostationary satellite IR data (GMS and Meteosat-5), station data and a few sorts of reanalysis data (GAME-reanalysis, ERA40, JRA-25).
Analysis was done based with pentad data. ISV activity is monitored by accumulated precipitation observed at surface stations. Relative activity of diurnal variation is evaluated as the ratio of band-passed diurnal variance to the total variance of 3-hourly cloudiness derived from the IR observation by satellites.
The analysis results are summarized as follows.
1) Diurnal convective activity tends to be relatively enhanced in monsoon season.
2) Diurnal activity tends to be enhanced in inactive phases or just before and after rainy pentads.
3) At one month before the onset of monsoon, enhancement of diurnal activity was already started.