5:15 PM - 7:15 PM
[AAS08-P05] Diurnal Variation of Precipitation and Water Vapor around Japan
Keywords:Diurnal cycle, Precipitation, Water vapor
This study aims to investigate the diurnal variations in precipitation and water vapor around Japan and understand their mechanisms. Previous research has focused on tropical regions, highlighting significant amplitudes in diurnal precipitation cycles. In the tropics, precipitation peaks are often seen in the early morning, while over land, peaks typically occur in the afternoon. Hypotheses suggest mechanisms such as radiative heating balance at cloud tops and increased relative humidity. According to Minobe and Takebayashi (2015), notable diurnal cycles are also observed in the mid-latitude areas, specifically south of Japan and along the eastern coast of the United States. However, the mechanisms of diurnal precipitation cycles around Japan remain largely unexplored, particularly concerning water vapor variations.
This study utilized the HimMet product that is based on infrared observations from the Himawari-8 satellite for air temperature and humidity and the IMERG satellite data for precipitation. HimMet is made of a supervised learning model that estimates temperature and humidity with a temporal resolution of 10 minutes and a horizontal resolution of 0.1°. The analysis focused on June 2020, examining diurnal variation in water vapor across three regions: Kyushu (130-132°E, 31-33°N), the Nansei Islands (127-129°E, 28-30°N), and the East China Sea (125-127°E, 31-33°N). The atmosphere was divided into upper (100-500 hPa), middle (500-850 hPa), and lower (850 hPa-surface) layers for analysis.
The analysis revealed several key findings regarding variations in precipitation and water vapor. The mean precipitation rate was lower in the East China Sea. In contrast, it was higher in the Nansei Islands, where a pronounced diurnal variation was observed. The relative deviation analysis of water vapor showed clear diurnal variations in the upper layer, with a notable increase in water vapor over the East China Sea starting around 9 AM local time and moving eastward by evening. This pattern is similar to the eastward movement of precipitation areas reported by Kanada et al. (2014). The standard deviation analysis of upper-layer water vapor indicated significant diurnal variations in eastern China and southwest of Kyushu. In contrast, the lower layer exhibited a diurnal cycle with nighttime peaks in Kyushu and characteristic variations in the Sea of Japan, peaking from morning to noon.
This study has clarified the existence and characteristics of diurnal variations in water vapor around Japan. Notably, the upper and lower layers exhibit different features, with eastward advection observed in the upper layer and region-specific patterns in the lower layer. Future research should explore the seasonality of these phenomena, their relationship with the Baiu front, and the mechanisms behind the differences between the upper and lower layers. Additionally, it is necessary to verify whether the findings from June 2020 can be applied to other years and months. Understanding these aspects is expected to contribute significantly to improving the accuracy of weather models.
This study utilized the HimMet product that is based on infrared observations from the Himawari-8 satellite for air temperature and humidity and the IMERG satellite data for precipitation. HimMet is made of a supervised learning model that estimates temperature and humidity with a temporal resolution of 10 minutes and a horizontal resolution of 0.1°. The analysis focused on June 2020, examining diurnal variation in water vapor across three regions: Kyushu (130-132°E, 31-33°N), the Nansei Islands (127-129°E, 28-30°N), and the East China Sea (125-127°E, 31-33°N). The atmosphere was divided into upper (100-500 hPa), middle (500-850 hPa), and lower (850 hPa-surface) layers for analysis.
The analysis revealed several key findings regarding variations in precipitation and water vapor. The mean precipitation rate was lower in the East China Sea. In contrast, it was higher in the Nansei Islands, where a pronounced diurnal variation was observed. The relative deviation analysis of water vapor showed clear diurnal variations in the upper layer, with a notable increase in water vapor over the East China Sea starting around 9 AM local time and moving eastward by evening. This pattern is similar to the eastward movement of precipitation areas reported by Kanada et al. (2014). The standard deviation analysis of upper-layer water vapor indicated significant diurnal variations in eastern China and southwest of Kyushu. In contrast, the lower layer exhibited a diurnal cycle with nighttime peaks in Kyushu and characteristic variations in the Sea of Japan, peaking from morning to noon.
This study has clarified the existence and characteristics of diurnal variations in water vapor around Japan. Notably, the upper and lower layers exhibit different features, with eastward advection observed in the upper layer and region-specific patterns in the lower layer. Future research should explore the seasonality of these phenomena, their relationship with the Baiu front, and the mechanisms behind the differences between the upper and lower layers. Additionally, it is necessary to verify whether the findings from June 2020 can be applied to other years and months. Understanding these aspects is expected to contribute significantly to improving the accuracy of weather models.