The Antarctic Oscillation (AAO) is the dominant mode of atmospheric circulation variability over the southern hemisphere. It could not only play important roles in climate changes over southern hemisphere, but also exert lots of influences in some regions in northern hemisphere. Due to the lack of widespread instrumental records during historical periods, the understanding of the natural variability of AAO is limited. The purpose of this paper is to reconstruct an austral summer Antarctic Oscillation index (DJF-AAO) focusing on interannual-decadal variability since 1500 AD based on multiple proxies, such as tree-rings, corals, and ice-cores. A Marshall-AAO index derived from 12-station sea level pressure records since 1957 are selected as observational series for calibration. There are 263 variables retained after a series of screening criteria for proxies, to refine the major signatures contained in the proxies by applying principal component analysis, and then a series of screening criteria implemented again for the time coefficient (PC) corresponding to each eigenvector. After that, by applying multivariate regression method the observational AAO-PC relations were calibrated and cross-validated based on the period of 1957-1989, then regressions were employed to compute the DJF-AAO index in 1500-1956. In verification procedure we checked the explained variance (r2), reduction of error (RE), and the standard error (SE). The cross-validation was performed by applying a leave-one-out validation method. During the reconstruction period of 1500-1956, the mean of r2, RE, and SE are 59.9% , 0.47 and 0.67, respectively. These statistical data indicate that DJF-AAO reconstruction is relatively reasonable for the last 460 years approximately. The reconstruction is compared favorably with several existing shorter AAO indexes derived from station SLP records both on the interannual and decadal time scales. The leading periods of the DJF-AAO index are ~2.4, ~2.6, ~6.3, ~24.1, ~37.6 years during the last 500 years, which are all significant at the 95% level.
Based on long-term measurement data of weather/ecological stations over China, we calculate and produce mean annual/seasonal Photosynthetically Active Radiation (PAR) spatial data from 1961 to 2007, using climatological calculation and spatialization technique. And we analyze the spatio-temporal variation characteristics of mean annual/seasonal PAR spatial data in China in recent 50 years, by means of Mann-Kendall trend analysis method and GIS spatial analysis technique. The results show: (1) As a whole, the spatial distribution of PAR differs significantly across China, with lower PAR in the eastern and southern parts of China and higher PAR in the western part. Mean annual PAR over China ranges from 17.7 mol m-2 d-1 to 39.5 mol m-2 d-1. (2) Mean annual/seasonal PAR of every pixel over China is averaged and the mean value declines visibly with a fluctuant process, and the changing rate of mean annual PAR is -0.138 mol m-2 d-1/10a. The extents of change in different seasons are different, with the maximum dropping in summer. (3) The analysis by each pixel shows that PAR declines significantly ( α = 0.05) in most parts of China. The changing trend in the eastern part is more obvious than that in the western part, and summer and winter play more important roles in the interannual variability of PAR. North China is always a decreasing zone in four seasons, while the northwest of Qinghai-Tibet Plateau turns to be an increasing zone in four seasons. (4) The spatial distributions of the interannual variability of PAR in different periods are not the same. The interannual variability of PAR in a certain region is not only different among four seasons, but also different among different periods.
Through using monthly precipitation data of 24 meteorological stations near the Tropic of Cancer in southern Longitudinal Range-Gorge Region (LRGR) covering the period 1961-2007, this study first analyzed the main characteristics of annual precipitation at each station. Secondly, it tested the changing trend and phases of annual precipitation at 9 stations along the Tropic of Caner in the study area. Then it calculated the correlation coefficients of annual precipitation series and monthly (May to October) precipitation series between stations along the Tropic of Cancer. The results showed that in the study area, annual precipitation and its inter-annual changes are characterized by certain regional variations. On this basis, three zones are identified, i.e., western part, central part and eastern part. High similarity was found in each of the three parts and obvious variation was observed among them. Annual precipitation series at each station along the Tropic of Cancer within the study area did not present obvious “abrupt trends-phases” changes. Range-gorge landforms within the central part of the study area have certain influences upon the spatial variation of precipitation, while high correlation coefficients of annual and monthly precipitation occurred between the neighbouring stations, especially on the two sides of the Ailao Mountain within the central part, indicating that there were no obvious differences for the precipitation-driving factors in the central part. Regional inter-distributed range-gorge landforms are likely to cause local variations of precipitation.
Based on the observed hourly precipitation data over China from 1991 to 2005, thetemporal and spatial distributions of hourly rain intensity and the recurrence periods for 50 or100 years are analyzed by using probability distribution, statistical test and extreme valueanalysis. The results show that for the purposes of the rain intensity more than 4 mmh-1, themaximum values are mainly distributed in the south coastal areas. The maximum value ofhourly rain intensity is 60-80 mm h-1 in most parts south of the Yangtze River, and 80-90 mmh-1 in the coastal areas. The diurnal variation of the rainfall intensity frequency occurred inregions are quite different. Southwest and South China are the regions featured by distinctdiurnal variation of rainfall intensity. All the test results of rain intensity more than 4 mm h-1reach 0.01 reliability. As for the estimated values of 50- and 100-year recurrence periods ofone-hour maximum rainfall intensity, it seems that spatial distribution of their patterns areconsistent. The maximum value areas are mainly distributed in coastal southeast China, wherethe maximum values of hourly rain intensity occurring once in a century and once in a halfcentury are up to 100-150 mm h-1 and 80-120 mm h-1, respectively.
Based on the citrus temperature, precipitation, sunlight and climate risk degree, the article divides subtropics of China into three types: the low risk region, the medium risk region and the high risk region. The citrus temperature risk increases with increasing latitude (except for west mountainous area of subtropics of China). The citrus precipitation risk in the central part of subtropics of China is higher than that in the northern and western parts. The distributions of citrus sunlight risk are not consistent to those of the citrus precipitation risk. The citrus climate risk is mainly influenced by temperature. There is latitudinal zonal law for the distribution of the climate risk, that is, the climate risk increases with increasing latitude. At the same time the climate risk in mountainous area is high and that in eastern plain area is low. There are differences in the temporal and spatial changes of the citrus climate. In recent 46 years, the citrus climate risk presents a gradual increasing trend in subtropics of China, especially it has been increasing fast since the 1980s. Because of the global warming, the low risk region in the eastern and southern parts has a gradual decreasing trend, however, the high risk region in the northern and western parts has an increasing trend and the high risk region has been extending eastward and southward. The article analyses the distribution of the citrus climate risk degree of reduction rates of >10%, >20% and >30% in subtropics of China, and studies their changes in different time periods. Results show that the risk is increasing from southeast to northwest.
An analysis is made about the response of Selin Co lake area change to climate change, based on RS, GIS and modern climate statistical methods with the aid of TM and CBERS remote sensing data from 1980-2008 as well as temperature, precipitation, the amount of evaporation, the biggest depth of frozen soil from 1975-2008 at the stations such as Shenzha, Bange and Anduo etc. Based on the digitized 1:100,000 topographic map in 1975 and through analyses of remote sensing data after the 1980s, it is found that water levels of Selin Co, Co'e and Yagen Co lakes present a distinct expanding trend in the past 30 years. In 2008, the water level areas of the above three lakes are 2196.23 km2, 279.24 km2, 103.07 km2, and they increase by 574.46 km2, 11.59 km2 and 68.13 km2 respectively compared to 1975. Moreover, Selin Co expands at a rate of 20%, with an average of 420 km2/10a, thus it has become the largest salty inland lake, exceeding the area of Nam Co lake in Tibet during the period 1999-2008. The main reasons for lake area expansion is the increase in snow/ice meting water under the background of global warming, followed by the increase of precipitation, decrease of the evaporation and degradation of permafrost.
A detail measurement is made for the coastal potholes on Xichong coast of Dapeng Peninsula, Guangdong. Classical and spatial statistics are used to quantitatively describe the features of the pothole shape, pothole spatial distribution and how the pothole development affect the shore platform of the coast. Results show that (1) The coastal potholes tend to form at the weaknesses appearing in coastal rock, such as joints, faults and bedding planes, and the shape and the distribution of the potholes are controlled by the weaknesses and, however, the specific position of the weakness where a pothole formed is random. (2) The result of pothole forming, deepening and expanding is to break down the second shore platforms, but the downward erosion of the potholes does not exceed the low tide level of the local coast. (3) Coastal potholes are the products of modern coastal erosion processes and can be formed at anytime, as long as the suitable conditions, such as coastal dynamic environments and rocks, are available. (4) The morphological features of marine potholes are not only related to the fluid dynamics, but also to the rock hardness and the different stages in their development. (5) Like river potholes, marine potholes can develop in all types of rocks and originate from different kinds of small pits on the rock surface. (6) The difference between coastal and river dynamics leads to the difference in marine and river pothole shapes.
Sand hills are mainly composed of aeolian sands developed along the north shore of the Poyang Lake. The sand hill at Shaling is situated in Liaohua town of Xingzi county. The relative height of this sand hill is about 100 m and it covers an area of about 10 km2. Ridgslike landform develops on the side facing the Poyang Lake. These ridges trending to merge downwind parallel to the prevailing wind and were assumed to be the sand ridge (longitudinal dune). Although the ridge lines are relatively straight, both the space between contiguous ridges and the length of ridge are different from each other. Based on the wind data measured between 2005-10 and 2006-09, we calculate the bedform trend (132o) with maximum gross normal transport and resultant transport direction (42o) using Trend program. The result demonstrates that only transverse dunes can develop under present wind regime which might be similar to those when ridgelike landform formed because Shaling region is controlled by the funnel effect. Sand mining along the shore expose sections that reveal the sediment structure of the ridgelike landform. Some ridges are composed of two layers, i.e. the surface layer and the interior layer. The surface layer (about several tens of centimeters in thickness) shows massive structure, while the interior layer shows parallel bedding truncated by the former on both sides of the ridge. This structure indicates the slideface is absent within these ridges, and that these ridges are of erosion landform instead of accumulation landform. The erosion postdates the deposition of the interior layer and predates the deposition of the surface layer. Optically Stimulated luminescence (OSL) dating is carried out on 6 sections. 28 OSL ages show that aeolian sand deposited extensively on the sand hill about ~20 ka BP and formed the interior layer. The thicker surface layer in the downwind region only began to deposit at ~0.2 ka BP. Therefore, we conclude that the ridges on the sand hill belong to erosion landform. Since the blowout is a common erosion landform developed in sandy region, the depression between ridges is suggested to be an unusual trough blowout although it exhibits some difference compared with the typical trough blowout developed on foredunes. We think these trough blowouts were shaped during a period of the most strengthened winter monsoon (18-14 ka BP). After that time, trough blowouts were probably modified by both the erosion of the Poyang Lake since ~1 ka BP and the sand hill reactivation initiated by human activity in the past ~0.2 ka BP.
Nebkhas is a common relief type in arid and semi-arid areas, which plays an important role in the stablization of ecological environment in these areas. This paper reviews the following aspects, including formation and succession, spatial distribution, shape characteristics, surface airflow characteristics and balance between erosion and deposition, ecological and physiological characteristics of vegetation. It also focuses on its response to precipitation and underground water, soil properties as well as the protection measures. We found that there had been limited studies on nebkhas, in which succession periods were not differentiated, shape characteristics, surface airflow, soil and vegetation dynamics in different succession periods were not fully understood. So it is difficult to explain succession dynamics of nebkhas and its affecting factors.
Atmospheric heavy metals (especially Pb and Hg) from anthropogenic activities could be transported globally, resulting in tremendous negative effects on the environment. Therefore, such research has received increasing attention in recent decades. In order to evaluate the pollution status, to understand the global transport process, and to elucidate its biogeochemical cycle and ultimate fate, it is necessary to carry out related studies in remote areas. In this paper, the progress on the historical reconstruction of heavy metals through ice core and lake sediment, as well as modern long range transport process are summarized. Based on the discussion, the directions for future studies are also proposed. Due to the unique atmospheric circulation regime and clean environment, the Tibetan Plateau is an ideal region to monitor atmospheric environmental change and to evaluate various impacts caused by human activities. Nam Co, as one of the typical regions of the Tibetan Plateau, has obvious advantages for such research due to various environmental archives (ice core and lake sediment) available. The establishment of Nam Co Station (under the Institute of Tibetan Plateau Research, CAS) also makes it practicable to conduct long-term monitoring of the modern atmospheric properties.
Influenza A H1N1 has spread around the world with a horrifying speed. China has the largest population in the world, which makes China more vulnerable to Influenza A H1N1. Using the epidemiological survey data concerning 744 H1N1-infected patients in Beijing during May 13, 2009 to August 15, 2009, this paper presents the epidemiological features. Based on 94 H1N1 cluster outbreak events, we studied the pattern of spatio-temporal evolution during the early phase of Beijing 2009 H1N1 epidemic. We also compared the spatial transmission network of the early Beijing H1N1 epidemic with that of the Beijing 2003 SARS epidemic. The results indicate that both networks are consistent from the point of view of structure. The triangle zones of the city central districts (including Dongcheng, Xicheng, Chongwen and Xuanwu) - Chaoyang District - Haidian District are the key places to control H1N1 epidemic. With the limit of emergency resources, efforts should be made on public health to prevent these zones from the spread of H1N1 Influenza A H1N1 infection. The emergency control measures implemented in Beijing are effective and timely.
