Spatiotemporal pattern variations of daily precipitation concentration and their relationship with possible causes in the Yangtze River Delta, China

Understanding the spatiotemporal pattern of precipitation concentration is important in the water cycle under changing environments. In this study, the daily precipitation concentration index in the Yangtze River Delta in China is calculated based on the Lorenz curves obtained from the observed data of 36 meteorological stations from 1960 to 2017, and spatiotemporal pattern variations and their possible causes are investigated. The driving forces of elevation, SUNSPOT, El Niño-Antarctic Oscillation, Pacific Decade Oscillation, and Arctic Oscillation are detected with correlation and wavelet analysis. Results show that, the daily precipitation concentration index ranges from 0.55 to 0.62 during the study period, 22 of 36 stations (accounting for 61%) show increasing trends, while three stations increase significantly at the 95% significant level. Relationship analysis indicates that the daily precipitation concentration shows a slightly negative correlation with elevation, while the relationships with SUNSPOT, El Niño-Antarctic Oscillation, Pacific Decade Oscillation, and Arctic Oscillation are complicated and diverse, there are different correlations and significance levels in different years. Further analysis shows that SUNSPOT is significantly correlated with El Niño-Antarctic Oscillation, Pacific Decade Oscillation, and Arctic Oscillation, which suggests that SUNSPOT may be an important factor that drives the changes of the three large-scale atmosphere circulation factors and causes precipitation concentration changing indirectly. These results provide further understandings of precipitation variations, which are meaningful for regional flood risk management under climate change.

¿Es el clima de Chile un “juego de Niños”?

El Niño-South Oscillation (ENSO) is an atmospheric and oceanic phenomenon which historically shown an important relationship whit the Chilean center-southern rainfall. Thus, usually it is used for predictions mainly in newspaper articles, but it is an unsuitable approximation. Although ENSO effect is a fact, there are other indexes which mitigate ENSO impacts and they get little attention. Thus, in this work we describe the main issues related with the atmospheric phenomena remarking just the phenomena which usually are not considered in researches focused in general Public: Pacific decadal oscillation, Antarctic Oscillation and Madden-Julian Oscillation. Also, we show the general impact of these phenomenon on rainfalls in the Chilean center-southern zone. El Niño-Oscilación del Sur (ENSO) es un fenómeno atmosférico y oceánico que ha tenido históricamente una importante relación con las precipitaciones de la zona centro sur del Chile, lo que ha hecho que frecuentemente se utilice para hacer pronósticos, sobre todo en medios periodísticos, lo cual es un enfoque incorrecto. Pese a que el efecto del ENSO es innegable, hay otros índices que han recibido menos atención, y que moderan en gran medida el efecto del ENSO, por lo que merecen una atención mayor. Así, el objetivo de este artículo es mostrar los principales aspectos relacionados todos estos fenómenos atmosféricos, dando énfasis a los otros fenómenos que usualmente quedan fuera de los análisis: La Oscilación decadal del Pacífico, la Oscilación Antártica y la oscilación de Madden-Julian. De la misma manera, se mostrará el efecto que han tenido en términos generales en las precipitaciones de la zona centro-sur de Chile.

Global moisture transport and the role of major teleconnection patterns

<p>The teleconnection patterns are an important feature influencing the variability of moisture transport toward the continent. This work analyses the influence of the Arctic Oscillation, Antarctic Oscillation, Pacific North America, and ENSO on the moisture transport from major oceanic and continental moisture sources in the month of higher precipitation. The Pacific North America higher influence is observed over North America with an increased contribution to the western region from the Pacific and lower over the eastern region from the Atlantic in the positive phase. The moisture transport during Arctic Oscillation events seems to be modulated by the Mediterranean Sea and North Atlantic, increasing from the Mediterranean in the positive phase and decreasing from the Atlantic. The Antarctic Oscillation shows its most relevant influence over Australia and Eastern Africa, with increased moisture contribution from eastern regions on the positive phase. Finally, ENSO events show influence in moisture transport over different areas in the world. El Niño events are associated with increased transport from the Atlantic region over western Europe and from the Pacific over North America. In South and Central America, the moisture contribution decreased over the regions closer to the equator, while the opposite occurs over southern South America. Over eastern Africa and Southern Asia, moisture inflow from the Indian Ocean seems to be affected by the pattern. The result suggests the influence of the moisture contribution on the precipitation pattern in association with main teleconnection patterns.</p>

Impact of Boreal Autumn Antarctic Oscillation on Winter Wet and Cold Weather in East Asia

<p>The Antarctic Oscillation (AAO) is the dominant mode of the southern extratropical atmospheric mass variability which has potential influences on the Northern Hemisphere (NH). This study reveals a significantly negative correlation between the September-October (SO) AAO index and the occurrence rate of following January-February (JF) wet and cold weather in the Middle and Lower Reaches of Yangtze River Basin (MLRY) in China. The latter is quantified by a Precipitation-Temperature (PT) Index. JF PT is modulated by both northerly air flow in the lower troposphere and southerly air flow in the lower-middle troposphere. The SO AAO stimulates Southern Ocean Dipole (SOD) pattern-like SST anomalies, which induces a North Atlantic Oscillation (NAO)-like atmospheric response in the following JF through ocean-air interaction. As for the northerly flow, the JF NAO-like pattern triggers an eastward propagating wave train, influencing the intensity of East Asian Winter Monsoon (EAWM) and subsequently the northerly cold flow to MLRY. As for southerly flow, the variation of JF SOD regulates the local meridional cell, in turn modulating the Middle East Jet Stream (MEJS) along with the NAO-like pattern, influencing the intensity of precipitation and the wet and warm flow over Southern China and the adjacent regions. In addition to the tropospheric processes, the stratospheric Quasi Biennial Oscillation (QBO) serves as the ‘bridge’ for linking SOD to NH climate, inducing the JF PT response to SOD SST. To summarize, SO AAO affects the JF PT in MLRY by modulating both cold-dry northerly air flow and warm-wet southerly air flow through ocean-atmosphere interactions and stratospheric pathway.</p>

Does Antarctic Oscillation have links and influence precipitation over the Uruguay River Drainage Basin in Southeastern South America?

This article examines the links and the influence of Antarctic Oscillation (AAO) on precipitation over the Uruguay River Drainage Basin and adjacent regions, situated in Southeastern South America. In this article, we used monthly data of AAO Index obtained from the Climate Prediction Center/National Centers for Environmental Prediction (CPC/NCEP); monthly data of 500 hPa vertical motion through omega variable (ω = Dp/Dt) and converted to vertical velocity (cm/s) from the NCEP/NCAR Reanalysis; monthly data of precipitation from the NCEP Reanalysis 2 and monthly data of precipitation rate from the CPC Merged Analysis of Precipitation (CMAP) with a latitude × longitude spatial resolution of 2.5° × 2.5°. All data are monthly means and were obtained from January 1979 to December 2008. The methodological procedures used Grid Analysis and Display System (GrADS) software to generate composites of vertical motion and precipitation rates. In the case of CMAP precipitation data, the methodology consists of applying the Aspin Welch statistical test, which verifies the statistical significance of the difference between two means using a significance level of 5%. The study region indicates a tendency to present higher (lower) mean rates of precipitation during the AAO negative (positive) phase. The vertical motion analysis results corroborate with the precipitation rates since the higher vertical motions were found during the negative phase of AAO. The statistical test showed, to some areas of Uruguay River Drainage Basin and adjacent regions, statistically significant differences between mean rates of precipitation observed in both phases of AAO.

The Impact of Preceding Spring Antarctic Oscillation on the Variations of Lake Ice Phenology over the Tibetan Plateau

ABSTRACTThe lake ice phenology response to climate change has been receiving growing concern in recent years. However, most studies have put emphasis on the spatial and temporal variability of lake ice phenology, and relatively few studies have been devoted to investigating the physical mechanisms of changes in lake ice phenology from the perspective of climatic dynamics. This study investigates the possible impact of the Antarctic Oscillation (AAO) on the variations in lake ice phenology over the Tibetan Plateau (TP). The results show that there is an intimate relationship between the AAO and the variations in break-up/ice duration during the period 2003–15. Further analysis indicates that the preceding boreal spring AAO-induced atmospheric circulation anomalies are favorable for generating tropical South Atlantic Ocean SST anomalies through air–sea interaction. Then the tropical SST anomalies strengthen the anomalous local-scale meridional–vertical circulation that projects into the Azores high and further induce the extratropical portion of the North Atlantic SST tripole. The anomalous warm core in the North Atlantic serves as the source of wave activity flux and stimulates a stationary wave train along the Eurasian continent to change the downstream atmospheric circulation. As a response, an abnormal cyclone and enhanced updraft are triggered over the TP, which are favorable for the formation of snowfall and then lower the surface air temperature according to the snow-albedo feedback mechanism, and thus result in the prolonged lake ice duration events. This study provides a new insight to link the AAO influence and climate over the TP and is helpful to understand the changes in lake ice phenology in response to climate change in recent years.