Atsuyoshi Manda

Impacts of a warming marginal sea on torrential rainfall organized under the Asian summer monsoon.

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.

Transient and local weakening of surface winds observed above the Kuroshio front in the winter East China Sea

To confirm whether surface winds strengthen above warm waters around oceanic fronts using in situ data, a field measurement was conducted using both expendable bathythermographs and Global Positioning System sondes released concurrently across the Kuroshio front in the East China Sea in December 2010. In contrast to previous studies mainly based on satellite observations, the finding of the present field survey is the local weakening of surface winds at the northern flank of the Kuroshio front. From the above field observation in conjunction with a regional numerical model experiment, it is suggested that the northwesterly winds crossing the Kuroshio front from the cooler side first weaken at the northern flank of the front because of the onset of upward transfer of the “nonslip” condition at the sea surface. Thereafter, as the atmospheric mixed layer with warm and humid air mass develops gradually downwind over the Kuroshio region, the surface winds are gradually accelerated by the momentum mixing with strong winds aloft. The surface winds remain strong over the cool East China Sea shelf, and it is thus considered that the surface winds only weaken at the northern flank of the Kuroshio front. However, numerical modeling indicates that this local weakening of the surface winds occurs as a transient state with a short duration and such a structure has thus rarely been detected in the long-term averaged wind fields observed by satellites.

Frontogenesis and frontolysis of the subpolar front in the surface mixed layer of the Japan Sea

The frontogenesis and frontolysis processes of the subpolar front (SPF) in the surface mixed layer of the Japan Sea are investigated using state-of-the-art oceanic reanalysis data. The SPF experiences a 9 month weakening period from January to September, which shifts to a strengthening period in October. Our analysis shows that horizontal advection consistently contributes to the intensification of the SPF. After September, as the weakening effect of surface heat flux diminishes, horizontal advection becomes the dominant factor that contributes to changes in the SPF strength. Thus, the SPF enters a 3 month strengthening period. The geostrophic component of horizontal advection provides the most important contribution to strengthening the SPF, acting to intensify the SPF year-round. Ekman advection also promotes SPF strengthening with a smaller but still important contribution. During the weakening period, SPF strength is largely controlled by heat flux. The heat flux, especially the shortwave radiation component, is the primary cause of the surface front disappearance in the summer.

Oceanic influence on the Baiu frontal zone in the East China Sea

A high-resolution transect of atmospheric soundings across the Kuroshio Current in the East China Sea was conducted onboard a ship in June 2012 with the objective of analyzing the influence of the complex sea surface temperature (SST) distribution on the Baiu frontal zone (BFZ). Expendable bathythermograph castings and continuous surface meteorological observations were also examined. Two distinct mesoscale atmospheric fronts, characterized by changes of wind direction in the lower troposphere and surface air temperature, were found in the BFZ. One (northern) atmospheric front was observed around the SST front in relation to a warm water tongue extending from the Kuroshio. A high SST region around the northern atmospheric front enhances unstable near surface stratification and intensifies turbulent heat flux. They help modify the marine atmospheric boundary layer in the BFZ. The other (southern) atmospheric front was at the southern end of the BFZ. Intense evaporation over the Kuroshio and moisture transport by southerly winds were important in forming the conditionally unstable air masses in the lower troposphere of the BFZ.

Influence of the Kuroshio on Mesoscale Convective Systems in the Baiu Frontal Zone over the East China Sea

AbstractTwo mesoscale convective events in the baiu frontal zone (BFZ) were documented, based on intensive atmospheric soundings and oceanic castings in the East China Sea during May 2011, in addition to continuous surface meteorological observations, satellite products, and objective analyses. These events occurred while the BFZ was nearly stagnant and a mesolow was deepening in the zone. Near-surface southerlies associated with the low-level jet transported a warm, humid air mass from south of the BFZ. Enhanced evaporation, which was mainly attributable to the high sea surface temperature of the Kuroshio, augmented the moisture content of the air mass and helped maintain a convectively unstable stratification in the lower troposphere around the BFZ.

Atmospheric Data for Ornithology: An Introduction

Abstract This paper introduces user-friendly atmospheric data, so-called objective analysis data, for ornithological studies. The data have been interpolated onto grid points distributed at a regular interval in space and time, and are suitable for analyzing using computer data analysis software. Data assimilation techniques, which are basically the application of optimization and control theories, are utilized for producing objective analysis data in order to reduce errors as much as possible and obtain the most reliable dataset. Some examples of objective analysis data are shown and their features are described. Some cautionary notes are also given in order to avoid misinterpretation of the data.

Evaluation of CMIP5 models on sea surface salinity in the Indian Ocean

Prior to future climate assessment of the 5th Coupled Model Intercomparison (CMIP5) experiments, how well CMIP5 models simulates present climate should be examined. Sea surface salinity (sss) play important role in ocean stratification and indirectly affects air sea interaction. However, few studies have been carried out to evaluate sss in CMIP5 models. In this study, performance of CMIP5 models in simulating sss in Indian Ocean was examined with respect to the observation. Our results showed that multi model ensemble (MME) mean of CMIP5 models displayed annual and seasonal salinity bias in three regions i.e. Western Indian Ocean (WIO), Bay of Bengal (BOB) and Southeastern Indian Ocean (SEIO). CMIP5 models overestimate sss in BOB about 1.5 psu and underestimated sss in WIO and SEIO about 0.4 psu. Biases in WIO and BOB were mainly attributed to bias in precipitation. CMIP5 models overestimated (underestimated) precipitation in WIO (BOB) with greater bias found during Boreal summer to winter. Meanwhile, advection process was responsible for negative SSS bias in SEIO.