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Xiao-Feng Li, Jingjing Yu, and Yun Li

Abstract

Rainfall over northern Australia (NA) in austral summer is the largest water source of Australia. Previous studies have suggested a strong zonal-dipole trend pattern in austral summer rainfall since 1950, with rainfall increasing in northwest Australia (NWA) but decreasing in northeast Australia (NEA). The dynamics of rainfall increase in NWA was linked to sea surface temperature (SST) in the south Indian Ocean and the rainfall decrease in NEA was associated with SST in the northeast Indian Ocean.

This study reports that, in contrast to a zonal-dipole trend pattern, a dominant wetting pattern over NA has recently been observed in the post-1979 satellite era. The recent NA rainfall increase also manifests as the first leading mode of summer rainfall variability over the Australian continent. Further investigation reveals that SST in the tropical western Pacific (TWP) has replaced the SST in the south and northeast Indian Ocean as the controlling factor responsible for the recent NA rainfall increase. Direct thermal forcing by increasing TWP SST gives rise to an anomalous Gill-type cyclone centered around NA, leading to anomalously high rainfall. As such, the increasing SST in the TWP induces over 50% of the observed rainfall wetting trend over NA. The increased rainfall in turn induces land surface cooling in NA. This mechanism can be confirmed with results obtained from sensitivity experiments of a numerical spectral atmospheric general circulation model. Thus, increasing SST in the TWP has contributed much of the recent summer rainfall increase and consequently the surface cooling over NA.

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Xiao-Feng Li, Jianping Li, and Yun Li

Abstract

The middle–lower valley of the Yangtze River (MLY), located in the middle of eastern China, has been one of the largest economic centers of China since ancient times. Winter precipitation variability over the MLY is important for China because of its significant influence on the local economy. However, few studies have focused on the long-term variability of winter precipitation over the MLY. This study reports a significant wetting trend over the MLY in winter during the three decades since the late 1970s, forming a “mid-east-China winter wetting” pattern, which has become an important feature of precipitation change under the weakening East Asian winter monsoon. This wetting trend in the MLY also implies the poleward extension of the precipitation belts of southern China.

Further investigation reveals that the increasing sea surface temperature (SST) in the tropical Indian Ocean (TIO) is the dominant factor responsible for recent increases in precipitation over the MLY. The thermal forcing driven by warming of the TIO SST gives rise to an anomalous cyclonic circulation along the coast of eastern China. This transports more water vapor onto the Chinese mainland, shifts and causes anomalous convergence over the MLY, and generates the increase in precipitation there. As such, the increasing SST in the TIO induces over 80% of the observed wetting trend over the MLY. This mechanism was verified by results obtained from two sets of sensitivity experiments using a numerical spectral atmospheric general circulation model. Thus, increasing SST in the TIO has made a dominant contribution to the recent winter precipitation increase over the MLY.

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Xiao Feng, Renguang Wu, Jiepeng Chen, and Zhiping Wen

Abstract

The present study investigates the year-to-year variations of September–October rainfall in Hainan, China, for the period 1965–2010. The dominant circulation anomalies feature a cyclone (an anticyclone) over the Indochina Peninsula and northern South China Sea, an anticyclone (a cyclone) over subtropical western North Pacific and lower-level convergence (divergence) over the Maritime Continent in the wet (dry) years. These circulation anomalies are responses to an east–west sea surface temperature (SST) anomaly pattern with negative (positive) SST anomalies in the equatorial central Pacific and positive (negative) SST anomalies around the Maritime Continent in the wet (dry) years. Although the SST anomaly pattern is similar (but with opposite anomaly), the SST signal in the equatorial central Pacific is more significant in the dry years than in the wet years. This difference indicates a larger case-to-case variability in the wet years than in the dry years. The large variability in the wet years is attributed to contributions of tropical cyclones (TCs) and intraseasonal oscillations (ISOs). There are more TCs impinging on Hainan and the TC tracks are closer to the island in the wet years than in the dry years. The rainfall shows large intraseasonal variations with periods of 10–20 and 30–60 days during September–October in the wet years. The 10–20-day ISO originates from the Maritime Continent, whereas the 30–60-day ISO develops over tropical Indian Ocean and propagates northeastward to northern South China Sea. In contrast, the ISO signal is much weaker in the dry years.

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Jian-Sheng Ye, Yan-Hong Gong, Feng Zhang, Jiao Ren, Xiao-Ke Bai, and Yang Zheng

Abstract

Intensifying climate extremes are one of the major concerns with climate change. Using 100-yr (1911–2010) daily temperature and precipitation records worldwide, 28 indices of extreme temperature and precipitation are calculated. A similarity percentage analysis is used to identify the key indices for distinguishing how extreme warm and cold years (annual temperature above the 90th and below the 10th percentile of the 100-yr distribution, respectively) differ from one another and from average years, and how extreme wet and dry years (annual precipitation above the 90th and below the 10th percentile of the 100-yr distribution, respectively) differ from each other and from average years. The analysis suggests that extreme warm years are primarily distinguished from average and extreme cold years by higher occurrence of warm nights (annual counts when night temperature >90th percentile), which occur about six more counts in extreme warm years compared with average years. Extreme wet years are mainly distinguished from average and extreme dry years by more occurrences of heavy precipitation events (events with ≥10 mm and ≥20 mm precipitation). Compared with average years, heavy events occur 60% more in extreme wet years and 50% less in extreme dry years. These indices consistently differ between extreme and average years across terrestrial ecoregions globally. These key indices need to be considered when analyzing climate model projections and designing climate change experiments that focus on ecosystem response to climate extremes.

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Elizabeth Lewis, Hayley Fowler, Lisa Alexander, Robert Dunn, Fergus McClean, Renaud Barbero, Selma Guerreiro, Xiao-Feng Li, and Stephen Blenkinsop

Abstract

Extreme short-duration rainfall can cause devastating flooding that puts lives, infrastructure, and natural ecosystems at risk. It is therefore essential to understand how this type of extreme rainfall will change in a warmer world. A significant barrier to answering this question is the lack of sub-daily rainfall data available at the global scale. To this end, a global sub-daily rainfall dataset based on gauged observations has been collated. The dataset is highly variable in its spatial coverage, record length, completeness and, in its raw form, quality. This presents significant difficulties for many types of analyses. The dataset currently comprises 23 687 gauges with an average record length of 13 years. Apart from a few exceptions, the earliest records begin in the 1950s. The Global Sub-Daily Rainfall Dataset (GSDR) has wide applications, including improving our understanding of the nature and drivers of sub-daily rainfall extremes, improving and validating of high-resolution climate models, and developing a high-resolution gridded sub-daily rainfall dataset of indices.

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