Resolution dependence was found in the simulated diurnal precipitation cycle over land in the tropics. We conducted a series of grid refinement experiments of the atmosphere from 14 km to 0.87 km using a global high-resolution model without any convection parameterizations. In the high-resolution experiment, the peak of the cycle was earlier and precipitation at the peak was higher. The characteristics of the simulated diurnal precipitation cycle changed at a grid spacing of around 2-3 km. The precipitation started to increase in the morning in the high-resolution experiments, suggesting that small-scale moist convection became active in the late morning. In the lower-resolution experiments, convection and precipitation began in the late afternoon. As well as the enhancement of moisture transport from the boundary layer to the middle troposphere, the rapid formation of rain can also be attributed to the difference in diurnal precipitation cycles between lower and higher resolution experiments.

This study statistically examined the relationships between the motion of a tropical cyclone (TC) and its ambient flow, stratifining the TC with reference to the longest radius (LR) and maximum sustained wind (MSW). TC motion, MSW, and LR were derived from the best track datasets compiled by the Regional Specialized Meteorological Center (RSMC) Tokyo - Typhoon Center. The environmental flow was estimated by averaging reanalyzed wind data (JRA25/JCDAS) between 1000 to 300 hPa over areas within a radius of 300, 400, and 500 km from the TC center. It was found that TCs with larger LRs or more intense MSWs are more likely to move to the northeast relative to the ambient wind. This preference for northeastward migration was confirmed when only TCs in the subtropical zone (20°N-30°N) were sampled. The bias of northeastward migration was found to be robust when components with wavelengths less than about 12° latitude–longitude were filtered from the total environmental wind field.

We describe the atmospheric features observed over the North Pacific during the summer–fall of 2014 and investigate their association with the convective activity in the intertropical convergence zone (ITCZ) and underlying oceanic conditions. During this duration, while the NINO.3 index, the area-averaged sea surface temperature anomalies (SSTAs) in the eastern equatorial Pacific, fluctuates around the threshold value for the onset of El Niño events, off-equatorial SSTAs display an equatorial antisymmetric pattern with positive (negative) anomalies north (south) of the equator. As expected from the wind–evaporation–SST feedback, the equatorial antisymmetric SSTAs accompany with anomalous southerlies, converging into a zonal belt of 5°N-10°N that induces enhanced convection in the ITCZ. Thus, the oceanic and atmospheric features in the eastern tropical Pacific are different from those in the typical El Niño events. In contrast, the observed weaker subtropical high and the shallower upper-tropospheric trough over the North Pacific are similar to the features typically found during the El Niño events. The amplitude of those anomalies, however, is much larger than that of regressed anomalies onto the NINO.3 index. A linear baroclinic model experiment indicates that the enhanced convective heating in the ITCZ contributes to sustain the anomalous atmospheric circulation.

To quantify the atmospheric iron deposition on the northern North Pacific region, we measured concentrations of iron in ice cores drilled at Mount Wrangell, Alaska, in 2003 and 2004. The iron concentration profile from 1981 to 2003 showed seasonal peaks each spring. This variation was similar to the seasonal variation in the concentration of mineral dust in the atmosphere in the North Pacific region. The annual iron fluxes calculated from the ice core records ranged from 3.2 to 27.0 mg m⁻² yr⁻¹, and the temporal variation in the iron flux was significantly correlated with the frequency of severe dust storms occurrence on the East Asian continent (r = 0.65, p < 0.05) and the total number of Kosa days observed in Japan (r = 0.64-0.66, p < 0.05), but not with the precipitation amount in Alaska. We concluded that the amount of iron deposition onto the northern North Pacific is controlled mainly by the emission of dust from the east Asian continent and not by scavenging processes in Alaska.

In this study, daily-observed data from 481 rain gauges were used to build a new gridded rainfall dataset for Vietnam based on the Spheremap interpolation technique. The new dataset, called Vietnam Gridded Precipitation (VnGP) Dataset has the resolution of 0.25° and covers the period 1980-2010. The validation was done for VnGP by assessing the spatial distribution, correlations, mean abosolute errors, root mean square errors with gauge observations. Results showed that VnGP had a relatively better performance compared to the datasets that used different interpolation techniques or used less number of input rain gauges. VnGP is currently available at the Data Integration and Analysis System (DIAS) managed by the University of Tokyo, Japan.

In this study, we introduce a rain potential map (RPM) that globally estimates rain probabilities every hour. More specifically, we created an RPM by associating the brightness temperature (Tb) of the infrared and water vapor channels observed by five geostationary meteorological satellites (GEO) with rain probabilities observed via rain radar of the Tropical Rainfall Measuring Mission (TRMM). By using our RPM, we improved the accuracy of the Global Satellite Mapping of Precipitation (GSMaP) product, which produces global precipitation data by integrating passive microwave and infrared radiometer data. More specifically, we removed GSMaP rain areas over the ocean in which all microwave sensors were unavailable and rain probabilities according to our RPM were below 14%, which improved the “threat score” of detection in GSMaP from 0.37 to 0.41 over the ocean. Conversely, we added rain areas over land in which all microwave sensors were unavailable and rain probabilities according to our RPM were greater than 37%, which improved the “threat score” of detection from 0.27 to 0.35 over land. Given that a GSMaP “threat score” with microwave observations is approximately 0.44, our improvements here are significant.

This paper estimates marine boundary layer heights (MBLH) over the western North Pacific (WNP) using four years (2012-2015) of Global Positioning System radio occultation (GPS-RO) profiles from the FORMOSAT-3/COSMIC satellites. Four methods of auto-detecting the MBLH are evaluated against observations from nearby island radiosonde stations. The two methods that use bending angle perform significantly better than the other two, which use refractivity profiles to estimate the MBLH. The MBLH is significantly higher in the winter than summer over the WNP, because winter exhibits a larger temperature difference between the WNP ocean surface and the lower atmosphere than does summer. Moreover, many regions with high MBLHs in winter are approximately located within the paths of the Kuroshio Current and the North Equatorial Current. When these warm ocean currents flow under relatively colder air, favorable conditions for convection develop, resulting in a higher MBLH.

Warm events, periods when rising surface air temperatures can trigger surface melt, have been recorded during the austral summer at Syowa station on the East Antarctic coast. This study identifies air masses responsible for summer warm events at Syowa. Air masses arriving at Syowa are classified into marine and glacial sources based on their isotopic characteristics. Warm events are not associated with moist marine air intrusion, but with the downward flow of dry glacial air along the west side slope of the mountains in Enderby Land (EL). We use simulations from the Antarctic Mesoscale Prediction System (AMPS) to explore the atmospheric process responsible for the warmest event at Syowa. The model output illustrates several foehn-associated features such as low-level blocking, precipitation on the mountain's windward side, and mountain wave activity, with warm air ascending on the upstream slope and descending to Syowa. The foehn warming is caused by an easterly cross-mountain flow associated with a low-pressure system to the north of the EL coast. Future changes in synoptic cyclonic activity off the EL coast may have a significant impact on the frequency and intensity of foehn events at Syowa and the associated coastal warm events.

The present paper reports a sub-minute scale growth of a misocyclone and vault-like structure in a horizontal shear environment observed by a phased array weather radar (PAWR). Between 0756 and 0801 Japan Standard Time on 25 August 2013, dual radar synthesis shows a signature of significant low-level convergence at 0.6-0.8 km above sea level (ASL). PAWR data show a coincident rapid growth of a misocyclone with top altitude increasing from 1.2 to 1.8 km ASL in two minutes. A small vault-like structure with the maximum height of 1.3 km is formed following to the development of misocyclone with a delay time of about two minutes. One possible explanation is the role of vorticity stretching associated with horizontal shear instability. Fast and volumetric seamless observation of such a small spatiotemporal-scale phenomena opens up a way to progress our understanding of misocyclone that is of importance for convection initiation and severe weather phenomena.