An obvious trend shift in the annual mean and winter mixed layer depth(MLD)in the Antarctic Circumpolar Current(ACC)region was detected during the 1960–2021 period.Shallowing trends stopped in mid-1980s,followed by a...An obvious trend shift in the annual mean and winter mixed layer depth(MLD)in the Antarctic Circumpolar Current(ACC)region was detected during the 1960–2021 period.Shallowing trends stopped in mid-1980s,followed by a period of weak trends.The MLD deepening trend difference between the two periods were mainly distributed in the western areas in the Drake Passage,the areas north to Victoria Land and Wilkes Land,and the central parts of the South Indian sector.The newly formed ocean current shear due to the meridional shift of the ACC flow axis between the two periods is the dominant driver for the MLD trends shift distributed in the western areas in the Drake Passage and the central parts of the South Indian sector.The saltier trends in the regions north to Victoria Land and Wilkes Land could be responsible for the strengthening mixing processes in this region.展开更多
The main purpose of this study is to assess the climate variability and change through statistical processing tools that able to highlight annual and monthly rainfall behavior between 1970 and 2010 in six strategical ...The main purpose of this study is to assess the climate variability and change through statistical processing tools that able to highlight annual and monthly rainfall behavior between 1970 and 2010 in six strategical raingauges located in northern (Saint-Louis, Bakel), central (Dakar, Kaolack), and southern (Ziguinchor, Tambacounda) part of Senegal. Further, differences in sensitivity of statistical tests are also exhibited by applying several tests rather than a single one to check for one behavior. Dependency of results from statistical tests on studied sequence in time series is also shown comparing results of tests applied on two different periods (1970-2010 and 1960-2010). Therefore, between 1970 and 2010, exploratory data analysis is made to give in a visible manner a first idea on rainfall behavior. Then, Statistical characteristics such as the mean, variance, standard deviation, coefficient of variation, skewness and kurtosis are calculated. Subsequently, statistical tests are applied to all retained time series. Kendall and Spearman rank correlation tests allow verifying whether or not annual rainfall observations are independent. Hubert’s procedures of segmentation, Pettitt, Lee Heghinian and Buishand tests allow checking rainfall homogeneity. Trend is undertaken by first employing the annual and seasonal Mann-Kendall trend test, and in case of significance, magnitude of trend is calculated by Sen’s slope estimator tests. All statistical tests are applied in the period of 1960-2010. Explanatory analysis data indicates upwards trends for records in northern and central and trend free for southern records. Application of multiple tests shows that the Kendall and spearman ranks correlation tests lead to same conclusion. The difference in tests sensitivity was shown by outcomes of homogeneity tests giving different results either in dates of the shift occurrence or in the significance of an eventual shift. A synthesis analysis of results of tests was carried out to conclude about rainfall behaviors. Tests for homogeneity show that southern rainfall is homogeneous, while northern and central ones are not. According to trend test, upwards trends in Northern and central rainfall trend free in southern assumption in exploratory data analysis have been confirmed. The Sen’s slop estimator shows that all retained trend can be assumed to linear type. The same test over the period 1960-2010 shows independence of observations in all raingauges and exhibits neither trends nor breaks. This seems to show a return to a wet period.展开更多
Understanding precipitation variability and trends is very important for sustainable water management. In this paper, we used 65 years (1951-2016) long- term precipitation data to evaluate the precipitation variabilit...Understanding precipitation variability and trends is very important for sustainable water management. In this paper, we used 65 years (1951-2016) long- term precipitation data to evaluate the precipitation variability and trends in Quelimane, and their relation to El Ni<span style="font-size:10.0pt;font-family:;" "=""><span style="color:#4F4F4F;font-family:"font-size:14px;white-space:normal;background-color:#F7F7F7;">ñ</span></span>o Southern Oscillation (ENSO). The analysis includes annual, inter-annual inter-decadal variations, Mann-Kendall trend test, and drought frequency. The study also evaluated the relationship between Oceanic Ni<span style="font-size:10.0pt;font-family:;" "=""><span style="color:#4F4F4F;font-family:"font-size:14px;white-space:normal;background-color:#F7F7F7;">ñ</span></span>o Index (ONI) and precipitation patterns during ENSO positive, normal and negative phases. The results show two distinct seasons of precipitation in Quelimane, the wet season extending between December and April and the dry season extending from May to November. ENSO was found to influence the inter-annual variations of precipitation during the wet season, with warm ENSO (El Ni<span style="font-size:10.0pt;font-family:;" "=""><span style="color:#4F4F4F;font-family:"font-size:14px;white-space:normal;background-color:#F7F7F7;">ñ</span></span>o) and cold (La Ni<span style="font-size:10.0pt;font-family:;" "=""><span style="color:#4F4F4F;font-family:"font-size:14px;white-space:normal;background-color:#F7F7F7;">ñ</span></span>a) events tending to reduce and increase the precipitation amounts, respectively. Decreasing trends in inter-annual variations of precipitation and increase of drought frequency and severity are highlighted in this study. Both decreasing trend of inter-annual variations and increasing of drought frequency and severity have intensified after the 1970s climate shift. These intensifications seem to be associated with the strengthening of ENSO after the 1970s climate shift. The results of the present study may be useful for the design of the climate change adaptation plans in central Mozambique.展开更多
The change of sea surface temperature（SST） in the southern Indian Ocean（SIO） during the recent six decades has been analyzed based on oceanic reanalysis and model, as well as atmospheric data. The results show tha...The change of sea surface temperature（SST） in the southern Indian Ocean（SIO） during the recent six decades has been analyzed based on oceanic reanalysis and model, as well as atmospheric data. The results show that a thermal regime shift in SIO during the 1960 s, which is not caught enough attentions, has been of equal magnitude to the linear warming since 1970. Empirical Orthogonal Function（EOF） analyses reveal that a thermal shift is combined with atmospheric changes such as the weakening of westerly during the period of 1960–1967. Inner dynamic connections can be defined that when the westerly winds turn weak, the anticyclonic wind circulation between westerly winds and the trade winds decreases, which further reduces the SST to a negative peak in this period. It is noted that the shifts in the 1960 s are also evident for Southern Hemisphere. For example, subtropical high and the entire westerly winds belt at high latitudes both change dramatically in the 1960 s. This large-scaled process maybe link to the change of southern annular mode（SAM）.展开更多
基金The National Natural Science Foundation of China under contract No.41605052。
文摘An obvious trend shift in the annual mean and winter mixed layer depth(MLD)in the Antarctic Circumpolar Current(ACC)region was detected during the 1960–2021 period.Shallowing trends stopped in mid-1980s,followed by a period of weak trends.The MLD deepening trend difference between the two periods were mainly distributed in the western areas in the Drake Passage,the areas north to Victoria Land and Wilkes Land,and the central parts of the South Indian sector.The newly formed ocean current shear due to the meridional shift of the ACC flow axis between the two periods is the dominant driver for the MLD trends shift distributed in the western areas in the Drake Passage and the central parts of the South Indian sector.The saltier trends in the regions north to Victoria Land and Wilkes Land could be responsible for the strengthening mixing processes in this region.
文摘The main purpose of this study is to assess the climate variability and change through statistical processing tools that able to highlight annual and monthly rainfall behavior between 1970 and 2010 in six strategical raingauges located in northern (Saint-Louis, Bakel), central (Dakar, Kaolack), and southern (Ziguinchor, Tambacounda) part of Senegal. Further, differences in sensitivity of statistical tests are also exhibited by applying several tests rather than a single one to check for one behavior. Dependency of results from statistical tests on studied sequence in time series is also shown comparing results of tests applied on two different periods (1970-2010 and 1960-2010). Therefore, between 1970 and 2010, exploratory data analysis is made to give in a visible manner a first idea on rainfall behavior. Then, Statistical characteristics such as the mean, variance, standard deviation, coefficient of variation, skewness and kurtosis are calculated. Subsequently, statistical tests are applied to all retained time series. Kendall and Spearman rank correlation tests allow verifying whether or not annual rainfall observations are independent. Hubert’s procedures of segmentation, Pettitt, Lee Heghinian and Buishand tests allow checking rainfall homogeneity. Trend is undertaken by first employing the annual and seasonal Mann-Kendall trend test, and in case of significance, magnitude of trend is calculated by Sen’s slope estimator tests. All statistical tests are applied in the period of 1960-2010. Explanatory analysis data indicates upwards trends for records in northern and central and trend free for southern records. Application of multiple tests shows that the Kendall and spearman ranks correlation tests lead to same conclusion. The difference in tests sensitivity was shown by outcomes of homogeneity tests giving different results either in dates of the shift occurrence or in the significance of an eventual shift. A synthesis analysis of results of tests was carried out to conclude about rainfall behaviors. Tests for homogeneity show that southern rainfall is homogeneous, while northern and central ones are not. According to trend test, upwards trends in Northern and central rainfall trend free in southern assumption in exploratory data analysis have been confirmed. The Sen’s slop estimator shows that all retained trend can be assumed to linear type. The same test over the period 1960-2010 shows independence of observations in all raingauges and exhibits neither trends nor breaks. This seems to show a return to a wet period.
文摘Understanding precipitation variability and trends is very important for sustainable water management. In this paper, we used 65 years (1951-2016) long- term precipitation data to evaluate the precipitation variability and trends in Quelimane, and their relation to El Ni<span style="font-size:10.0pt;font-family:;" "=""><span style="color:#4F4F4F;font-family:"font-size:14px;white-space:normal;background-color:#F7F7F7;">ñ</span></span>o Southern Oscillation (ENSO). The analysis includes annual, inter-annual inter-decadal variations, Mann-Kendall trend test, and drought frequency. The study also evaluated the relationship between Oceanic Ni<span style="font-size:10.0pt;font-family:;" "=""><span style="color:#4F4F4F;font-family:"font-size:14px;white-space:normal;background-color:#F7F7F7;">ñ</span></span>o Index (ONI) and precipitation patterns during ENSO positive, normal and negative phases. The results show two distinct seasons of precipitation in Quelimane, the wet season extending between December and April and the dry season extending from May to November. ENSO was found to influence the inter-annual variations of precipitation during the wet season, with warm ENSO (El Ni<span style="font-size:10.0pt;font-family:;" "=""><span style="color:#4F4F4F;font-family:"font-size:14px;white-space:normal;background-color:#F7F7F7;">ñ</span></span>o) and cold (La Ni<span style="font-size:10.0pt;font-family:;" "=""><span style="color:#4F4F4F;font-family:"font-size:14px;white-space:normal;background-color:#F7F7F7;">ñ</span></span>a) events tending to reduce and increase the precipitation amounts, respectively. Decreasing trends in inter-annual variations of precipitation and increase of drought frequency and severity are highlighted in this study. Both decreasing trend of inter-annual variations and increasing of drought frequency and severity have intensified after the 1970s climate shift. These intensifications seem to be associated with the strengthening of ENSO after the 1970s climate shift. The results of the present study may be useful for the design of the climate change adaptation plans in central Mozambique.
基金The National Natural Science Foundation of China for Distinguished Young Scholars and Innovative Research Groups under contract Nos 41525019 and 41521005the Project of the State Oceanic Administration of China for Global Climate Change under contract No.GASI-IPOVAI-02the CAS/SAFEA International Partnership Program for Creative Research Teams
文摘The change of sea surface temperature（SST） in the southern Indian Ocean（SIO） during the recent six decades has been analyzed based on oceanic reanalysis and model, as well as atmospheric data. The results show that a thermal regime shift in SIO during the 1960 s, which is not caught enough attentions, has been of equal magnitude to the linear warming since 1970. Empirical Orthogonal Function（EOF） analyses reveal that a thermal shift is combined with atmospheric changes such as the weakening of westerly during the period of 1960–1967. Inner dynamic connections can be defined that when the westerly winds turn weak, the anticyclonic wind circulation between westerly winds and the trade winds decreases, which further reduces the SST to a negative peak in this period. It is noted that the shifts in the 1960 s are also evident for Southern Hemisphere. For example, subtropical high and the entire westerly winds belt at high latitudes both change dramatically in the 1960 s. This large-scaled process maybe link to the change of southern annular mode（SAM）.
