豫北地区气温、降水变化的时空分布特征

利用中国国家级地面气象站均一化数据集中1971—2010年豫北地区28个测站的温度、降水资料,基于GIS技术对该地区温度和降水变化的时空分布特征进行研究。结果表明:豫北地区气温整体呈升高的趋势,其中冬春季节升温明显。气温变率空间分布表现为北中部增温明显,东部和西部增温幅度较小。降水变化各季节差异较大,春季降水整体呈现增加趋势,其他季节各地降水增减不一;空间变化分布特征为太行山沿线西部山区降水减少趋势明显,东部地区降水略有增加趋势。从整体变化情况来看,豫北地区的气候变化区域间差异加大,局地性变化趋向不稳定。文中用温度与降水的趋势比来分析豫北地区的干旱化发生趋势,结果发现太行山沿线干旱化趋势明显,沿黄河区域干旱化趋势较低,太行山脉和黄河是导致豫北地区气候变化区域性分布的主要地形因子。     

Extraction and Analysis of Land Cover Heterogeneity over China

Spatial heterogeneity exists in land surface at every scale, and it is one of key factors to bring uncertainty to land parameter retrieval from remote-sensed data. This paper proposed a methodology to use the boundary length among different land cover types to characterize and quantify land surface heterogeneity based on high-resolution land cover images. Then the heterogeneity feature at 1 kilometer scale in China was extracted from “GlobalLand30” land cover datasets with the spatial resolution of 30 m. The mixed structure, degree of fragmentation and intra-heterogeneity of eight main vegetation biomes from MODIS land cover product over heterogeneous surface in china were analyzed. Mountain area and ecotone are more heterogeneous than other regions. Savanna biome (average boundary length is 7 426 meters) is the most heterogeneous zone followed by forest, grass/crop and shrub biome with average boundary length of 4 323, 3 160, 1 779 meters, respectively.     

CLIMATOLOGICAL CHARACTERISTICS OF SPRING PRECIPITATION OVER SOUTHERN CHINA AND ITS INTRASEASONAL OSCILLATION

Based on observations and reanalysis data, the characteristics of the evolution of climatological spring precipitation over Southern China (SPSC) and the associated climatological intraseasonal oscillation (CISO) and atmospheric circulation are studied. Results show that SPSC increases in an oscillatory way. Although the evolution of SPSC is similar in different regions, there are also differences. In different regions of Southern China, the onset dates of the rain season are from the 12th to 24th pentad and the peak dates are after the 20th pentad. CISO is an important component of SPSC, which is not only statistically significant, but also accompanies a dynamically coherent structure. The peak wet/dry phase of each CISO cycle corresponds to a significant rainfall increasing/decreasing period and modulates the evolution of SPSC. The rainfall growth in the second half of March and mid-April is the result of the modulation. The wet/dry phase of CISO is accompanied by low-level convergent (upper-level divergent) and cyclonic (anti-cyclonic) circulation, which favors ascending motion to develop over Southern China.     

北欧海比容高度及其与卫星高度计海表面高度异常的比较

In this study the steric height anomaly which is calculated from the hydrological data(EN3) is compared with the sea level anomaly derived from satellite altimetry in the Nordic Seas. The overall pattern of steric height is that it is higher in the margin area and lower in the middle area. The extreme values of steric height linear change from1993 to 2010 occur in the Lofoten Basin and off the Norwegian coast, respectively. Such a distribution may be partly attributed to the freshening trend of the Nordic Seas. The correlation between SLA(sea level anomaly) and SHA(steric height anomaly) is not uniform over the Nordic Seas. The time series of SLA and SHA agree well in the Lofoten Basin and northern Norwegian Basin, and worse in the northern Norwegian Sea, implying that the baroclinic effect plays a dominant role in most areas in the Norwegian Sea and the barotropic effect plays a dominant role in the northern Norwegian Sea. The weaker correlations between SLA and SHA in the Greenland and Iceland Seas lead a conclusion that the barotropic contribution is significant in these areas. The area-mean SHA over the entire Nordic Seas has similar amplitudes compared with the SLA during 1996–2002, but SHA has become lower than SLA, being less than half of SLA since 2006.     

1996—2013年上海虹桥机场低能见度及低跑道视程特征分析

利用1996—2013年上海虹桥机场逐时地面观测资料,对影响机场正常运行的主导能见度低于800 m（低能见度）和跑道视程（RVR）低于550 m（低RVR）时次的出现次数进行统计分析,得到以下结论：1996—2013年虹桥机场除2002年低RVR时次出现较多外,其余年份均为低能见度时次出现更多;低能见度及低RVR时次出现次数分别以57次/年和26次/年的速率减少;季节变化特征显示两者均在12月出现最多,9月出现最少,11月至次年2月是两者出现的高频季节,5—9月为低频季节;一天中低能见度及低RVR多集中出现于19:00—01:00（世界时）,其中23:00达各自峰值;进入夜间后低能见度时次的出现比率首先较大,后半夜开始低RVR影响逐渐凸显。虹桥机场低能见度时次出现次数随能见度数值的降低呈先减少后增多趋势,低RVR时次则在150~200 m及0~50 m两个区间出现次数较多。     

CLIMATOLOGICAL LOW-FREQUENCY OSCILLATION OF OLR OVER THE MARITIME CONTINENT WITH ITS POSSIBLE LINKAGE TO SUMMER PRECIPITATION IN CHINA

Using the 1979-2009 NCEP/NACR reanalysis data and precipitation records in East China, research is performed of the climatological features of low-frequency oscillation (LFO) in OLR over the Maritime Continent (MC) as well as their associations with precipitation disturbance in the eastern part of China. Results suggest that in the MC there is significant climatological low-frequency oscillation (CLFO) in outgoing long-wave radiation (OLR), with the intraseasonal oscillation (30-60 days) being the strongest for April-September, and the MC acting as a high-value region of percentage contributions of low-frequency OLR variance. On the low-frequency time scale there occur four events of more intense active OLR during this time interval. In the January-April (May-August) phase, MC convection is relatively weak (vigorous). The CLFO makes pronounced eastward displacement at tropics, with phase propagation seen longitudinally, too. There occur low-frequency disturbance circulations similar to the EAP wavetrain or P-J teleconnection, starting from the MC via the South China Sea and the Philippines to the Yangtze valley of China. At different phases, the variation in the low-frequency circulations and heating fields shows that the rainfall disturbance in eastern China is likely to be under possible effects of the CLFO from the MC in April-September, and the low-frequency heating variation exhibits a meridional pattern as an EAP wavetrain or P-J teleconnection. As the OLR CLFO is in a peak (valley) phase the low-level divergence or convergence with the reversal at high levels over the MC is related to relatively feeble (robust) low frequency convection, thereby exciting an EAP or P-J wavetrain from the MC to the Sea of Japan. At the higher levels, the South-Asian high is eastward (westward) of normal due to effects of low-frequency cyclones (anticyclones), resulting in less (more) rainfall in the Jiangnan (areas in the middle and lower reaches of Yangtze and to the south of the river) and Hetao (the Great Bend of Yellow River) areas, and increased (decreased) rainfall in SW China, Qinghai Plateau and Gansu. At the conversion phases, low-frequency convection becomes more active in parts of the MC, consequently exciting low-frequency wavetrain of cyclones-anticyclones-cyclones at low levels, making the South-Asian high southward of the mean, so that strong convergent zones emerge in the upper and middle Yangtze basins and Jilin of NE China, responsible for plentiful precipitation there in sharp contrast to the rainfall over the band between the Yellow and Huaihe Rivers and the Yunnan-Guizhou Plateau. These results help understand in depth the climatological LFO characteristics and the phase-locked feature, thereby further improving our understanding of the causes of rainfall disturbances in different parts of the country.     

Spatiotemporal variability of drought and the potential climatological driving factors in the Liao River basin

Spatiotemporal characteristics of drought based on the Standardized Precipitation Index (SPI) in the Liao River basin (LRB) are investigated in this study. High autocorrelation in SPI seems to lend itself to drought prediction. Drought is becoming more frequent, widespread, and severe in the LRB during the past several decades. Major factors affecting drought in this basin are analysed by investigating relationship between SPI and several circulations including western Pacific Subtropical High (WPSH), East Asian Summer Monsoon (EASM) and El Niño‐Southern Oscillation (ENSO) indices. Different correlation patterns between WPSH indices and SPI are obtained. Several significant positive correlations between the area, intensity of WPSH and SPI are observed in the west and the centre of the study area, while negative correlations are observed in the east. Reverse patterns are observed in the correlation between the ridge of westward longitude of WPSH and SPI. Corresponding lag‐correlation is dominated by positive correlations between the area, intensity of WPSH and SPI, and by negative correlation between the ridge of westward longitude of WPSH and SPI. EASM is mainly negative related with drought in the east of the LRB. Significant positive correlation between ENSO and SPI is mainly located in the east while negative correlation is located in west of the basin. Lag‐correlation (with lags of 1 to 12 months) between them is also investigated and results show that significant negative correlation is located in a broad area extending from the west to the centre of the basin, while less positive correlation is observed with the increase of lags. The possibility of employing general circulation models (GCMs) for drought prediction is discussed based on the above analyses. Copyright © 2011 John Wiley & Sons, Ltd.     

西部山区总辐射气候学计算及分布

根据西部山区太阳总辐射的实测资料分析，指出，西部山区总辐射的气候学计算必须考虑日照，水汽分布及海拔高度的影响。为此研制了适宜于西部山区的总辐射气候学计算公式Ｑ＝Ｑ０（ａ＋ｂｓ１＋ｃｓ１＾２），进而讨论了西部山区总辐射的时，空分布。