The authors investigated diurnal convection peak characteristics over the eastern Indian Ocean o¤ the island of Sumatra during di¤erent phases of the Madden-Julian oscillation (MJO). During MJO phases 2 to 3 (P2 and P3) defined by Wheeler and Hendon (2004), prominent diurnal variation in convection was observed by satellites when moderate low-level westerly winds were dominant over the eastern Indian Ocean. The diurnal convection peaks were prominent over the island of Sumatra in the evening, while migrations of the convection toward the Indian Ocean were observed in the early morning. By using the Global Positioning System around the western region o¤shore of Sumatra, a significant reduction in water vapor was observed from evening until midnight, compensating for the upward motion over the island. During midnight to early morning, the water vapor increased in the western o¤shore region as the convections migrated from the island. This prominent diurnal variation confirmed the result from a numerical experiment by Miura et al. (2007) using the Nonhydrostatic ICosahedral Atmospheric Model (NICAM).During P2 to P3, the atmosphere over the eastern Indian Ocean contains abundant water vapor, while the Maritime Continent is fairly well heated by solar radiation under calm conditions. This situation should be favorable for the development of two diurnal convection peaks: the evening convection over the land induced by solar radiative heating and the midnight convection over the ocean triggered by convergence of the low-level westerly wind and the land breeze.

No abstract

A near‐future, 2‐K warming climate simulation comprising over 3,000 years of ensemble simulations was performed using 60‐km global and 20‐km regional atmospheric models. Even in the +2‐K climate, indices of extreme precipitation and dryness increased significantly in the extratropics compared with the historical climate. Mean precipitation increases in the rainy season and decreases in the dry season, indicating that the seasonal precipitation range becomes amplified with global warming. The intensification of precipitation and dryness from +2 to +4 K was also robust in the mean for climatological wet and arid regions. Around Japan, which was classified as a wet region, the regional atmospheric model predicts that the extreme hourly precipitation in the future climate becomes more extreme on hot days, but slightly weaker on cold days. This extreme precipitation has a high sensitivity to air temperature exceeding 7%/K.

Atmospheric soundings using the Vaisala RS92 radiosonde were intensively conducted during the field experiment MISMO (Mirai Indian Ocean cruise for the Study of the MJO-convection Onset) in the central and eastern equatorial Indian Ocean from October to December 2006. By comparing the RS92 relative humidity data with that from the Meteolabor Snow White (SW) chilled-mirror dew/frost-point hygrometers launched on the same ship around the local noon time, the dry bias was found to increase significantly with height. In addition, it was also revealed that the dry bias had a clear diurnal variation with its maximum at local noon and near-zero at night from the comparison of precipitable water vapor (PWV) with that derived from the shipboard Global Positioning System (GPS) data. Therefore, the dry bias of the RS92 data could be attributed to a solar radiation-induced error that was recently discussed by V omel et al. (2007).In this study, we developed a correction scheme for the MISMO RS92 humidity data as a function of pressure and local time using SW data, and then confirmed its validity with GPS-derived PWV.

This paper describes the formation mechanism of morning maximum in the diurnal cycle of precipitation, at the Strait of Malacca under a calm condition, with a nonhydrostatic mesoscale numerical model and shipbased observational data. The morning precipitation peak at the strait is induced by the convergence of two cold outflows that have been produced by the precipitation systems in the previous evening over Sumatra and the Malay Peninsula. The outflows converge at the Strait of Malacca around midnight; a new precipitation system is thus generated and reaches its peak in the early morning. Sensitivity experiments using the numerical model suggest that the timing and position of the morning precipitation peak are affected by the width of the strait. In the case of the Strait of Malacca, its width favors the formation of the morning precipitation system around the center of the strait, which explains why its diurnal cycle of precipitation can be observed much clearer than those in other coastal areas over the Maritime Continent.