This study investigated the characteristics of the rainfall associated with tropical cyclones (TCs), using the TC best-track data and daily rainfall data from 15 meteorological stations for the period 1961−2008 for the coastal region of Vietnam. In addition to investigating the TC rainfall amount, we estimated the TC rain ratio and the ratio of TC heavy rainfall days (TC_R50) and interpreted these parameters for El Niño and La Niña years. Our results show that the maximum TC rainfall occurs from July to September in the northern region, whereas the total rainfall at southern stations is mainly composed of non-TC rainfall. The TC rainfall amount is concentrated in the central region, with a peak in October-November. The TC rain ratio varies from 0 to ~25%, showing a maximum value in the region of 16°N−18°N in September. The mid-central region of Vietnam has maximum TC_R50 ratio in September-October corresponding to its highest TC frequency in the same period. During El Niño (La Niña) years, the TC rain ratio and TC_R50 ratio in the central region show a significant decrease (increase) in October-November. The La Niña phases more strongly affect TC rainfall than the El Niño phases, particularly in central Vietnam. IntroductionTropical cyclones (TCs) regularly threaten many countries, bringing dangers such as disastrously heavy rainfall and flooding. Several studies have examined the rainfall associated with TCs (hereafter called TC rainfall). For example, Rodgers et al. (2000) estimated TC rainfall in the North Pacific using Special Sensor Microwave Imager (SSM/I) observations for an 11-year period. They found that TCs contributed 12% of the climatological rainfall over the western North Pacific (WNP) from June to November. They also showed that TC rainfall increased from 12 to 18% during El Niño events. Englehart and Douglas (2001) investigated the role of tropical storms over the eastern North Pacific in the rainfall climatology of western Mexico and showed that tropical storm-associated rainfall normally constitutes 20 to 60% of rainfall along Mexico's Pacific coast. In more extreme cases, they found that such rainfall can contribute as much as 25 to 30% to seasonal rainfall totals in western interior locations. Gleason (2006) estimated the characteristics of TC rainfall in the United States between 1950 and 2004. They found that coastal and near-coastal regions received 8 to 16% and 4 to 12% of the precipitation by TCs, respectively. Ren et al. (2006) reported that the ratio of annual TC precipitation to total annual rainfall is 20 to 30% in most of Taiwan and along the coast of China south of 25°N, using rain gauge data over China during 1971−2004. Kubota and Wang (2009 investigated the effect of TCs on seasonal and interannual rainfall variability over the WNP by analyzing rainfall data at 22 rain gauge stations. They showed that along 125°E and between 18°N and 26°N, TC rain accounts for 50 to 60% of the total rainfall during the TC season from July to October. In addition, they described some cha...

The ozonesonde observations in Hanoi, Vietnam, over fourteen years since 2004 have confirmed the enhancement in lower tropospheric ozone concentration at about 3 km altitude in the spring season. We investigated the evolution of the ozone enhancement from analysis of meteorological data, backward trajectories, and model sensitivity experiments. In spring, air masses over Hanoi exhibit strong height dependence. At 3km, the high-ozone air masses originate from the land area to the west of Hanoi, while low-ozone air masses below about 1.5 km are from the oceanic area to the east. Above 4 km, the air masses are mostly traced back to the farther west area. The chemical transport model simulations revealed that precursor emissions from biomass burning in the inland Indochina Peninsula have the largest contribution to the lower tropospheric ozone enhancement, which is transported upward and eastward and overhangs the clean air intrusion from the ocean to the east of Hanoi. At this height level, the polluted air has the horizontal extent of about 20 degrees in longitude and latitude. The polluted air observed in Hanoi is transported further east and widely spread over the northern Pacific Ocean.

The ozonesonde observations in Hanoi, Vietnam, over 14 years since 2004, have confirmed an enhancement in lower tropospheric ozone concentration at about 3 km altitude in the spring season. We investigated the evolution of the ozone enhancement from analysis of meteorological data, backward trajectories, and model sensitivity experiments. In spring, air masses over Hanoi exhibit strong height dependence. At 3 km, the high‐ozone air masses originate from the land area to the west of Hanoi, while low‐ozone air masses below about 1.5 km are from the oceanic area to the east. Above 4 km, the air masses are mostly traced back to the farther west area. The chemical transport model simulations revealed that precursor emissions from biomass burning in the inland Indochina Peninsula have the largest contribution to the lower tropospheric ozone enhancement, which is transported upward and eastward and overhangs the clean air intrusion from the ocean to the east of Hanoi. At this height level, the polluted air has the horizontal extent of about 20° in longitude and latitude. The polluted air observed in Hanoi is transported further east and widely spread over the northern Pacific Ocean.

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