Temporal and spatial variabilities of sea surface heights in the northeastern South China Sea

Analyses of sea surface height anomalies (SSHA) from Jan. 1993 to Dec. 2001 measured by TOPEX/Poseidon (T/P) satellite altimetry indicate that there are two energy highs of SSHA fluctuations on both sides of the Luzon Strait. The highs centered at (19.5°N, 119.5°E) and (22.0°N, 124.0°E) respectively, are separated by a low energy band in the Strait. Empirical Orthogonal Function (EOF) analysis on the "Far Field" suggests that fluctuations of these two areas are mutually independent. EOF analysis on the "Near Field" shows that SSHA oscillation in the northeastern South China Sea (SCS) is dominated by seasonal variations accompanied with significant intra-seasonal and inter-annual fluctuations. Among which, EOFI and EOF2 reflect 66.7% of the total variance. They are both seasonal but showing three months difference in phase. The basic pattern of EOFI appears to be the seasonal SSHA oscillation centered at (18.0°N, 119.0°E) northwest off Luzon Island, which shows maximums (minimums) in August/Septemb     

The strengthening East Asia summer monsoon since the early 1990s

Previous studies have documented a weakening tendency of the East Asian summer monsoon (EASM) since the end of the 1970s. In this study, we report that the EASM has been recovering since the early 1990s, although its strength is still less than in previous decades (averaged over the period 1965-1980). Following the recovery of the EASM, there has been a tendency in the last decade toward northward-moving rainbands and excessive rainfall in the Huaihe River valley (110°-120°E, 30°-35°N). There is evidence suggesting that the strengthening EASM since the early 1990s is linked to interdecadal change of land-sea thermal contrast.     

南海表层环流和热结构特征的数值模拟与影响因素分析

 采用普林斯顿海洋模式,在真实的地形数据、计算区域右边界上半部分设为开边界的条件下,对南中国海98°-126°E,3°S -26°N的范围进行了环流和温度结构的模拟。模拟从静止的海洋开始,以1月份的月平均温盐数据为初始场,在12个不同的月平均风场驱动下,模式稳定地模拟了4个模式年。从第3年开始进行数据分析。首先从数值模拟的角度给出了南海表层环流和热结构的时空演变过程,继而详细分析了气候和环境因素的影响。结果表明：冬季南海主要被一个大的气旋式环流占据,夏季主要呈大的反气旋式环流。春季和秋季是季风转换季节,南海环流在受到上一个季节影响的同时也向下一个季节的典型流态转换,并由多个涡旋组成。此外,气候和环境条件的设置,都会影响到南海的环流和热结构特征。     

Interdecadal shift in the western North Pacific Summer SST anomaly in the late 1980s

An interdecadal shift in summer (June―August) sea surface temperature (SST) variations during the period of 1968―2002 was identified in the late 1980s, which is characterized by a phase alternating from negative to positive phases of the leading mode of the empirical orthogonal function (EOF) analysis of the summer monthly mean SST in the Pacific domain 100°―180°E and 0°―40°N, accounting for 30.5% of the total variance. During the period of 1968―1987, the leading mode with a mean negative phase state (mean standard deviation = ?0.586) controlled SST variability in the western North Pacific. Correspondingly, negative SST anomalies occupied the western North Pacific south of Japan and Chinese marginal seas. During the period of 1988―2002, the leading mode shifted to its strong positive polarity (mean standard deviation = 0.781), thus positive SST anomalies appeared in the western North Pacific. Accompanied by the interdecadal shift in summer mean SST, summer mean rainfall increased in southern and southeastern China during the late period, particularly in southeastern China where increase in summer mean rainfall exceeded 40 mm, at the 0.05 significance level.     

Dynamic control on grain-size distribution of terrigenous sediments in the western South China Sea: Implication for East Asian monsoon evolution

High-resolution oxygen isotope stratigraphy of Core MD05-2901, which is located off eastern Vietnam in the western South China Sea （SCS）, was established and indicated that the core spans a time period of the past 450 ka. Based on the bulk density, fractional porosity and lithogenic content of the sediments, terrigenous mass accumulation rate （TMAR） was obtained, which is 4.9-6.0 g cm^-2 ka^-1 on average during interglacial stages, higher than that during glacial stages, i.e. 1.9-5.0 g cm^-2 ka^-1, which is different from northern and southern SCS which show higher TMAR in glacial stages. By principle component analysis of grain size distribution of all the samples, two main control factors （F1 and F2） were obtained, which are responsible for about 80% variance of granularity. The contents of grain size population 1.26-2.66 μm% and 10.8-14.3 μm% which are sensible to F1 show high-frequency fluctuation, and correlate well with the summer insolation at 15^o N. They exhibit a distinct cyclicity with frequencies near 23 ka and 13 ka, in contrast to a strong frequency peak near 100 ka obtained in proxies 4.24-7.42 μm% and 30.1-43.7 μm% controlled mainly by F2. The sedimentary character of this part of the SCS was controlled by variations of input flux from two main source areas, namely the southwest and north SCS, which were transported by different circulations of surface current forced by East Asian summer monsoon and winter monsoon respectively. We believe that the East Asian summer monsoon has fluctuated with high frequency and been forced by changes in solar insolation in low latitude associated with precession and half precession, while ice-volume forcing is probably a primary factor in determining the strength and timing of the East Asian winter monsoon but with less important insolation forcing.     

基于CALIOP资料的中国及周边地区云出现概率时空分布特征分析

云垂直结构是影响大气辐射的重要参数,其时空分布是影响全球气候变化的关键组成部分.本文利用星载激光雷达CALIOP的1 km云层产品,计算了中国及周边地区（0-55°N,70-140°E）云的出现概率,对不同地区、不同季节、不同高度单层云的出现概率做了对比分析.结果表明：云的出现概率表现出明显的地区差异,蒙古高原和印度半岛北部少云,热带海域和中国南方多云,多数地区夜间云出现概率略高于白天;除蒙古高原和印度半岛北部以外,多数地区单层云比多层云更常见;多数地区高云占单层云的比例最大,而中国大陆南部单层的中云较常见,西太平洋北部海域常被单层的低云覆盖;夏秋两季云出现概率普遍大于春冬两季,尤其印度半岛北部的云主要出现在夏季;蒙古高原和印度半岛北部单层云少于多层云,冬季尤其明显,而中国西南地区东部全年单层云更常见;夏季单层的高云占全年单层云的比例最大,青藏高原部分地区超过35%,这与其地形特征和夏季对流活动旺盛有关.     

Rainfall retrieval over land from satellite remote sensing (SSM/I)

Composite microwave index (CMI) method is used with the satellite SSM/I data to retrieve summer rainfall rate over 96°E–127°E, 17°N–44°N. The results of verification are: the root-of-mean-square error is 0.9 mm/ h in the actual rain rate range from 2 to 2.9 mm/ h; 1.6 mm/h in that from 3 to 5 mm/h and the maximum rms error is 4.2 mm/h in that from 5.1 to 50 mm/h. Case study shows the decision tree and CMI method presented in the note are effective to the rainfall recognition and rain rate retrieval over land of East China.     

Reconstructing temperature change in Central East China during 601–920 AD

Using historical records on first and last frost and snow, spring cultivation, David peach blossom, autumn crop harvest, grade of sea freeze and change in northern citrus boundary, we reconstructed temperature change during 601–920 AD. The mean temperature of the winter half-year (October to April) over Central East China during this period was about −0.22°C higher than that of the present (1961–2000 AD mean). During 601–820 AD, mean temperature was about −0.52°C higher than the present. During 821–920 AD, the mean temperature was 0.42°C lower than the present. The temperature fluctuations were characterized by a maximum amplitude of 1.05°C at the centennial scale, 1.38°C at the 50–year scale, 2.02°C at the 30-year scale, and 2.3°C at the 20-year scale. There were four peaks warmer than today (601–620 AD, mean of 1°C higher temperature; 641–660 AD, 1.44°C; 701–720 AD, 0.88°C; 781–800 AD, 0.65°C). Three cold periods were in 741–760, 821–840, and 881–900 AD, the mean temperature of which was 0.37–0.87°C lower than the present.     

Vegetation evolution and millennial-scale climatic fluctuations since Last Glacial Maximum in pollen record from northern South China Sea

A large number of paleoclimate records reveal subMilankovitch climatic fluctuations on the millennial-scalesuperimposing on the Earth orbital cycles[1], such as theHeinrich ice draft events in the Atlantic (each intervalabout 7000–10000 a)[2,3], the Dansgaard/Oeschger (D-O)events (millennial-scale) in Greenland Ice Cores and theBond cycle composed of a Heinrcih event after severalD-O events[4]. At present, most recent work on millennial-scale climatic fluctuations focuses on the high lat…     

Analysis of the ionosphere wave-motion with GPS

The periodic solar activities strongly affect the ioniza-tion of the ionosphere. Sudden enhancements in soft and hard solar X-ray and EUV radiation during solar flare can produce an immediate increase in ionospheric ionization in various degrees at different heights; altogether, they are called sudden ionospheric disturbances (SIDs), which are generally recorded as sudden increase of total electron content (SITEC), the short wave fadeout (SWF), sudden frequency deviation (SFD), sudden ph…     

近51年海河流域作物生长季干旱时空分布特征研究

基于1960-2010年海河流域及周边地区116个气象站逐月气温和降水资料,采用相对湿润度指数M作为干旱评价指标,分析海河流域作物生长季（春季至秋季）气象干旱发生的时空分布特征．结果表明：（1）春季海河流域干旱最为严重,多年平均干旱率高达56．90％;夏季较春季干旱率明显降低,多年平均干旱率为7．59％;秋季干旱率呈现出增加趋势．（2）春季干旱在1960年代最为严重,夏季干旱在1990年代最为严重,而秋季干旱在1980年代最为严重．（3）春季干旱发生概率最高,整个海河流域均在19．61％以上,干旱发生概率在50％VA上的地区面积占海河流域的3／4,河北东北部和京津一带是春季干旱发生概率最高的地区;夏季干旱发生概率较春秋低,干旱发生概率最高的地区为大同和张家口以北地区;大部分地区的秋季干旱发生概率在25％以上,发生概率最高的区域主要集中在京津唐地区．     

Climatological relationships among the tropical cyclone frequency,duration, intensity and activity regions over the Western Pacific

Climatological relationships among the tropical cyclone (TC) frequency, duration, intensity and activity regions over the Western Pacific are explored based on long-term best track data. Frequent TC occurrence does not necessarily imply a long duration of TCs in the same periods. Three types of relationship between TC number and duration in the period 1945–2007 were identified in this study: low frequency and short duration during 1945–1955 (Period I); high frequency and short duration in the 1960s (Period II); and high frequency and long duration in the 1990s (Period III). TC activity regions differed among the three periods. During Period I, the main activity regions were over the ocean east of the Philippines (120°–140°E). During period II, two prevailing storm tracks extended west-northwest between 110° and 147°E. During period III, TCs had an extensive activity region from 110° to 160°E. TC intensity is related closely to activity regions. Most strong TCs developed over the ocean far from the Philippines, and had a northwestward track. Our results also show that the relationships between TC frequency, duration and their active regions are modulated strongly by broad-scale vertical motion, geopotential height and horizontal wind anomalies.     

Seasonal features of the Sverdrup circulation in the South China Sea

Based on the Sverdrup relation, using climatological wind stress data, the basin scale Sverdrup transport in the South China Sea(SCS) is calculated and the basic seasonal features of the Sverdrup circulation are obtained. A comparison of these calculated features with observations proves that the wind-driven circulation in the SCS is very important for the formation of the SCS upper oceanic circulation in winter, summer and fall. It is shown that the non-uniform sea surface wind is one of the causes to form multi circulation centers in the basin of the SCS. The westward current at 18°N is caused by the local wind, which is stronger in fall and winter. The seasonal variation of circulation in the southern SCS is much more remarkable than that in the north. The wind in spring is helpful to the seasonal reversal of the circulation in the central SCS. The northward transport of the cyclonic circulation reaches the maximum in fall.     

西太平洋一、二岛链间海区声传播的季节因素分析

以分析西太平洋第一、第二岛链间海区在不同季节时的声传播情况为研究目的,利用world ocean atlas 2013(WOA13)季节平均数据和Mackenzie声速经验公式,首先分析该海区声道轴深度和表层声速值的四季分布情况;再利用BELLHOP水声学数值模型,在设定的1 000 Hz声源频率和15°～-15°掠射角情况下,仿真计算选用位置点5 m深度声源的四季声传播情况,研究其规律:四季反转深度由15°N以南的4 900 m以上,降至25°N以北的4 900 m以下,且夏季最深,春秋两季次之,冬季最浅。多数海区可形成汇聚区波导并主要存在于冬秋两季,第一汇聚区位置相对在61～64 km;通常夏季最远,春秋两季次之,冬季最近。在设定的仿真计算条件下声传播覆盖范围有限,需通过其他手段和战术行动改善。     

Three-year changes of surface albedo of degraded grassland and cropland surfaces in a semiarid area

Diurnal, seasonal and interannual variations of surface albedo of degraded grassland and cropland surfaces at a semiarid area of Tognyu have been investigated based on the continuous three years observational data from 2003 to 2005. The changes of surface albedo with solar elevation angle and soil moisture have been discussed also. It has been found that surface albedo has almost the same diurnal and seasonal variations on degraded grassland and cropland surfaces in the semiarid area, while surface albedo is large in winter and small in summer. The diurnal variation of the surface albedo has relationship with the weather condition. The diurnal cycle of the surface albedo likes the ＂U＂ shape curve in sunny day, while it is low-high after the rain, and high-low after the snow. The surface albedo has large variation in cloudy day, while it has no any variation in overcast day. The large difference of the surface albedo can be 0.04 in winter between two land surfaces, because the snow has large effects on the surface albedo in winter. The rainfall is an important factor in summer on the surface albedo, while the difference of the surface albedo is 0.01 only between two land surfaces. The differences of the surface albedo can also be 0.04 in autumn due to vegetation growing. The seasonal-average surface albeo from 2003-2005 is 0.25, 0.22, 0.24, 0.32 respectively in spring, summer, autumn and winter on the degraded grassland surface, while it is 0.25, 0.21,0.22, 0.33 respectively in spring, summer, autumn and winter on the cropland surface. The surface albedo becomes smaller with the increase of solar elevation angle. When the solar elevation angle is greater than 40°, the surface albedo changes very little and tends to be a constant. The surface albedo has negative exponent functions with soil moisture in the growing season.     

Cretaceous synfolding remagnetization components revealing tectonic rotation of the middle Yangtze fold belt

To reveal the deformation process of the middle Yangtze fold belt, we conducted a paleomagnetic study on Middle Triassic limestones and Middle to Late Jurassic sandstones from Wanzhou, Chongqing. Stepwise thermal and alternating field demagnetization were used to isolate the multi-component re-manent magnetizations. The Jurassic samples were overprinted by recent geomagnetic field, while three magnetization components were isolated from the Middle Triassic samples. A low temperature component (LTC) was isolated at temperatures below 200℃, an intermediate temperature component (ITC) at 200―360℃ and a high temperature component (HTC) at 400―460℃. The LTC is distributed around the present-day Earth magnetic field, probably a viscous component. Stepwise unfolding indi-cates that the maximum precision parameters of ITC and HTC components are achieved at 33±8% and 50±27% (with 95% confidence) unfolding, respectively. The best-clustered ITC mean direction, Dec = 11.2°, Inc = 45.2° (α₉₅ = 4.5°, N = 34), corresponding to a paleopole at 79.3°N, 219.5°E (d_p = 3.6°, d_m = 5.7°), is consistent with the Cretaceous reference direction of the South China Block (SCB). The best-clustered HTC mean direction (taking 70% unfolding), Dec = 24.2°, Inc =49.0° (α₉₅ = 3.6°, N = 23), corresponding to a paleopole at 69.2°N, 195.5°E (d_p =3.1°, d_m = 4.8°), suggests a clockwise rotation of 12.8°±3.5°. These synfolding remagnetization components clearly reveal that a clockwise rotation happened at the middle stage of folding, thus supporting that at least part of the variation in fold axis strikes is due to orocline rotation. Combined with published data, our analysis indicates that the Wan-zhou-Xiangxi segment of the middle Yangtze fold belt experienced oroclinal bending. Furthermore, a published post-folding component isolated from the Middle Triassic Puqi Formation suggests a 27.5°±5.8° clockwise rotation, confirming that at least 50% of the observed clockwise rotations in the eastern middle Yangtze fold belt can be attributed to oroclinal bending. The remagnetization data and geological evidence observed in the middle Yangtze fold belt suggest that collision between SCB and North China Block (NCB) probably lasted till the early period of Early Cretaceous.     

Carbon isotopic record of foraminifers in surface sediments from the South China Sea and its significance

Since the 1990s, the papers and data involved withthe South China Sea (SCS) have been emerging in largenumbers in the world as people pay more attention to thepaleoceanography of the SCS. There have been more than100 cores mentioned in papers containing p…     

不同土地利用类型土壤动物对土壤氮矿化季节变化的影响

以苏北沿海地区3种土地利用类型(杨树人工林、农田、杨农复合林)为研究对象,通过设置不同驱除土壤动物处理(撒萘驱除所有土壤动物、撒噻唑磷驱除土壤线虫、未驱除即对照),采用顶盖埋管法测定土壤矿质N含量及净N矿化速率,研究土壤动物对N矿化季节变化的影响。结果表明:①不同土地利用类型土壤NH⁺₄-N、NO^-₃-N、土壤总矿化N(TMN)含量均呈显著的季节变化(P＜0.05),驱除线虫和所有土壤动物显著降低了不同季节的土壤NH⁺₄-N、NO^-₃-N和TMN含量,但并没有改变它们的季节变化基本趋势。3种土地利用类型土壤NH⁺₄-N含量的季节变化均表现为夏＞秋＞春＞冬; 对于NO^-₃-N和TMN含量的季节变化,杨树林和杨农复合林均表现为夏＞秋＞春＞冬,而农田则表现为秋＞夏＞春＞冬; ②不同土地利用类型净N矿化速率季节差异显著(P＜0.05),杨树林和农田的净N矿化速率最大值出现在秋季(分别为0.25、0.29 mg/(kg·d)),杨农复合林净N矿化速率最大值出现在夏季(0.45 mg/(kg·d))。驱除线虫和驱除所有土壤动物显著降低了所有土壤利用类型春、夏、秋季的土壤净N矿化速率(P＜0.05),而未改变杨农复合林净N矿化速率的季节变化趋势。驱除所有土壤动物改变了杨树林和农田的净N矿化速率的季节变化趋势,杨树林和农田驱除所有土壤动物的季节变化表现为夏＞秋＞春＞冬,而对照表现为秋＞夏＞春＞冬。重复测量方差分析表明,季节和驱除土壤动物处理对净N矿化速率有显著的交互作用(P＜0.01),表明驱除土壤动物可能会影响净N矿化速率的季节变化。     

Paleoproductivity records for the past 30 ka in the southern Nansha area, the South China Sea

This note presents productivity variations for the past 30 ka in the southern Nansha area, the South China Sea, from the gravity core 17962 (7°11′N, 112° 5′E, core length: 8 m, water depth: 1 968 m). Estimated surface productivity demonstrates that at the last glacial maximum the productivity was about 1.6 times as much as that in the Holocene, and the change may be ascribed to an increase of terrestrial nutrients as sea level lowered in the glacial time.     

New Early Triassic paleomagnetic data from Huangben section, Guangdong and its tectonic implications

Continent China is composed of several blocks of variable sizes during different geological times, inwhich South China Block is composed of three tectonic units: Yangtze Block, Jiangnan Fold Belt and Southeast China Coastal Fold Belt (Fig. 1(a)), the last…