17:15 〜 19:15
[ACG43-P10] Surface air temperature adjustment over the warm ocean
キーワード：海面水温-海上気温 変動、深い積雲対流、暖水プール、現場観測ブイデータ
Sea surface temperature (SST) and surface air temperature (SAT) are closely connected through heat exchange between the ocean and the atmosphere at the sea surface. Such thermal coupling is conceptually well-known. However, few studies have quantitatively examined the precise relationship between SST and SAT. Intuitively, one might expect SST and SAT to co-vary under weak wind conditions over the tropical ocean, while atmospheric advection could disrupt this relationship in higher latitudes. But how accurate is this intuition? Are there regions or situations, even within the tropics, where the SST-SAT relationship deviates from a simple linear pattern? If so, what factors drive these deviations? This study seeks to answer these questions by analyzing daily mean data from atmospheric reanalysis and in-situ buoy observations.
A global analysis of local correlation and regression coefficients between SST and SAT, derived from daily mean ERA5 data for the period 2001–2020, challenges the previously mentioned intuition. The results reveal two distinct regimes in the SST-SAT relationship: one in which SST and SAT generally exhibit a linear relationship, predominantly in mid-to-high latitudes, and another where this relationship deviates from linearity in warm tropical ocean regions. The latter tropical regions align with areas where SST exceeds approximately 28°C and precipitation surpasses 2 mm/day. Observations from the TAO/TRITON buoy network further confirm a pronounced east-west contrast between these two regimes in the tropical Pacific.
A time series analysis of the buoy data from an equatorial site in the western equatorial Pacific reveals that when SST exceeds approximately 28°C, SAT systematically drops below SST during rain events, accompanied by increased short-term fluctuations in SAT. This feature suggests that precipitation plays a key role in the peculiar SAT suppression over the warm ocean. Further two-dimensional frequency analysis indicates that during light precipitation (<2 mm/day), the SST-SAT difference grows as precipitation intensifies. However, this difference plateaus at around 3K with further increases in precipitation. These findings support our hypothesis that the cooler SAT relative to SST in warm ocean regions is driven by latent heat cooling from raindrop evaporation and the advection of cold air outflows associated with tropical convection.
A global analysis of local correlation and regression coefficients between SST and SAT, derived from daily mean ERA5 data for the period 2001–2020, challenges the previously mentioned intuition. The results reveal two distinct regimes in the SST-SAT relationship: one in which SST and SAT generally exhibit a linear relationship, predominantly in mid-to-high latitudes, and another where this relationship deviates from linearity in warm tropical ocean regions. The latter tropical regions align with areas where SST exceeds approximately 28°C and precipitation surpasses 2 mm/day. Observations from the TAO/TRITON buoy network further confirm a pronounced east-west contrast between these two regimes in the tropical Pacific.
A time series analysis of the buoy data from an equatorial site in the western equatorial Pacific reveals that when SST exceeds approximately 28°C, SAT systematically drops below SST during rain events, accompanied by increased short-term fluctuations in SAT. This feature suggests that precipitation plays a key role in the peculiar SAT suppression over the warm ocean. Further two-dimensional frequency analysis indicates that during light precipitation (<2 mm/day), the SST-SAT difference grows as precipitation intensifies. However, this difference plateaus at around 3K with further increases in precipitation. These findings support our hypothesis that the cooler SAT relative to SST in warm ocean regions is driven by latent heat cooling from raindrop evaporation and the advection of cold air outflows associated with tropical convection.