[1] The interannual Indian Ocean subtropical dipole (IOSD) event in the southern Indian Ocean is discussed using a coupled general circulation model to derive a scenario describing its complete life cycle for the first time. The positive (negative) IOSD is characterized by an anomalous warm (cool) sea surface temperature (SST) in the southwestern region of the Indian Ocean and by an anomalous cool (warm) SST in the southeastern region. The positive event brings about enhanced precipitation in the southeastern Africa during the peak phase. Composite pictures for the positive and negative IOSD clarify that an anomalous latent heat flux is the dominant factor in its formation. This flux anomaly is caused by an anomaly in the climatological wind field, which is associated with a pressure anomaly in the central region of the southern Indian Ocean. Since the flux anomaly starts during austral fall in the year previous to the event peak and develops for the next 9 months, air-sea interaction must play an active role in the formation of the IOSD. The reason the peak of the IOSD is locked to the austral summer is that the latent heat flux influences the sea surface temperature most efficiently in the austral summer when the depth of the surface mixed layer is shallowest.
Monsoonal airflow from the tropics triggers torrential rainfall over coastal regions of East Asia in summer, bringing flooding situations into areas of growing population and industries. However, impacts of rapid seasonal warming of the shallow East China Sea ECS and its pronounced future warming upon extreme summertime rainfall have not been explored. Here we show through cloudresolving atmospheric model simulations that observational tendency for torrential rainfall events over western Japan to occur most frequently in July cannot be reproduced without the rapid seasonal warming of ECS. The simulations also suggest that the future ECS warming will increase precipitation substantially in such an extreme event as observed in midJuly 2012 and also the likelihood of such an event occurring in June. A need is thus urged for reducing uncertainties in future temperature projections over ECS and other marginal seas for better projections of extreme summertime rainfall in the surrounding areas.
We investigate the impact of ENSO on the landfall characteristics of tropical cyclones (TC) over the Western North Pacific (WNP) during the summer monsoon season. During the early monsoon period (late May–late July), an increase in the numbers of TCs that make landfall in the Korean Peninsula or Japan is associated with an increase in the Niño‐3.4 SST anomalies. During the peak monsoon period (late July–mid September), the number of TCs that make landfall in the Indochinese Peninsula is greater in El Niño years than in La Niña years. Furthermore, in El Niño years, the TCs that make landfall in the Korean Peninsula or Japan tend to have longer lifespan and greater intensities. These changes can be primarily attributed to the change in the mean TC formation location as a result of ENSO.
[1] In the present study, the winter precipitation in the vicinity of Japan is simulated by the Weather Research Forecasting model by using two sets of sea surface temperature (SST) data with different spatial resolutions. On comparing the simulated mean precipitations, we found that SST resolution has a significant influence on the simulated precipitation along the northwestern coast of Japan; in this region, the coarse-resolution SST data have a systematic cold bias. In the simulation using high-resolution SST data, the moisture supply to the atmosphere increases over the relatively warm coastal SST. The increase in the moisture supply leads to an increase in the moisture convergence near the mountain ranges in Japan on the Japan Sea side, leading to an increase in precipitation amount. The result suggests that coastal SST must be carefully used for dynamic downscaling of the climate simulation, in particular, in Japan, which is surrounded by boundary currents. We also found that a small-scale SST anomaly in the Kuroshio-Oyashio Extension (KOE) region near Japan enhances the interannual variance of local precipitation in the regions downwind of the SST anomaly. The associated anomalous ascent extends to the midtroposphere and is accompanied by an increase in cloud ice, suggesting that the interannual SST variation over the KOE region may affect the free atmosphere. Moisture budget analysis indicates the influence of moisture advection by mean wind on the spatial phase difference between the SST and precipitation anomalies.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.