积雪变化对中国森林凋落物分解影响研究进展

森林凋落物的分解对于维持生态系统物质循环和养分平衡具有重要意义,并受到不同积雪厚度下冻融格局的影响。冻融期（包括冻结过程期、完全冻结期、融化过程期）是冻土区凋落物分解的重要时期,该时期分解的凋落物量约占全年分解总量的一半。积雪减少通常会导致土壤温度降低、冻融循环次数增加,进而影响凋落物分解。通过综述近10年来积雪变化对我国森林凋落物分解影响的研究成果发现,积雪厚度减少在冻融期通常会抑制凋落物质量损失、碳元素释放和纤维素降解,生长季则起到促进作用,从全年来看多数表现为抑制作用。因此,冻融作用造成凋落物的物理破坏,对其分解的促进作用主要发生在后续生长季。积雪厚度减少在冻融期通常抑制氮元素释放,生长季和全年则无明显规律;磷元素和木质素目前研究还存在很大差异。最后,进一步阐述了积雪变化对凋落物分解影响研究存在的问题及未来研究发展方向。     

On the linkage between changes in cloud cover and precipitation extremes over Central India

In this study, linkage between changing characteristics of precipitation extremes and cloud covers over Central India is explored during summer monsoon period using Satellite data (1998–2015). This is a first attempt to relate the changes in cloud cover to the changes in precipitation extremes. Non-rainy cirrus clouds are excluded from this study. Results show that heavy rainfall (≥ 60 mm/day) is associated with cold cloud tops (Tb≤220 K) while moderate rainfall (<60 mm/day and ≥20 mm) occurs mostly with middle clouds (Tb>220 K and ≤245 K). Low level clouds (Tb> 245 K) are responsible for light rainfall (<20 mm/day). Increases in top 20%, 10%, 5% and 1% heavy precipitation relate well with the increases in very deep convective, deep convective and convective cloud cover. Among these relations, increase in top 5% heavy precipitation relates best with increase in very deep convective cloud cover. Decrease in bottom 30% low precipitation relates with decrease in low level cloud cover. The results reported in this study fit into the framework of how weather extremes respond to climate change.     

黄河源区多、少雪年土壤冻融特征分析

利用2011年10月至2017年12月黄河源区鄂陵湖野外观测数据,对比分析多雪年与少雪年土壤冻结与消融时间、土壤温湿度、地表能量分量的变化特征。结果表明:多雪年地表反照率偏高,净辐射偏低,地表感热输送偏低,土壤由热“源”转为热“汇”的时间晚于少雪年。积雪可减少土壤吸收辐射能量,减少地表感热通量,在土壤完全冻结期与消融期增大地表潜热通量,在完全冻结期,减少土壤向大气的热输送,在消融期,减少大气向土壤的热输送。积雪在冻结期有降温作用,使得多雪年土壤较早发生冻结,且同一时期土壤温度偏低;在完全冻结期有保温作用,使得土壤温度偏高;在消融期有保温(“凉”)作用,使得消融较晚,且同一时期土壤温度偏低。在整个积雪年内,多雪年浅层土壤湿度高于少雪年,积雪对浅层土壤有保湿作用。积雪使土壤开始冻结时间有所提前,开始消融的时间有所滞后,可延长该年土壤完全冻结持续天数。     

海南岛不同土地覆盖资料对WRF模拟的影响*

提取GLC2009土地覆盖数据,将其运用到WRF数值模式并与模式自带的MODIS、USGS土地覆盖进行对比,以海南岛做为研究区域,选择一次海风锋天气过程进行敏感性分析,结果表明：①GLC2009对海南岛农耕地、森林的划分最接近实际情况,在海南岛平原以及丘陵地带,MODIS和USGS划分的农耕地比例过高,而在山区森林比例偏低;②GLC2009、MODIS、USGS对海南岛北部的降水模拟出现了空报,但是GLC2009对东海岸的强降水模拟的较好,并避免了MODIS和USGS在海南西南部的降水空报的情况;③GLC2009模拟的10米风场清晰刻画了东海岸海风锋辐合,其相对合理的森林覆盖提高了地表粗糙度并增强了风场辐合、低反照率对地面气温的增加和海陆热力差异的增强有一定的促进作用。④GLC2009对这次海风锋过程中模拟的感热通量和潜热通量都要高于MODIS和USGS,这种陆气间的热通量交换利于强对流天气的触发,发展。     

气候变化对石羊河流域生态环境的影响分析

利用石羊河流域1959—2018年气象、水文和卫星遥感资料,采用线性倾向率、滑动t检验和相关系数(Pearson)等方法,分析石羊河流域内生态环境因素的变化事实及相互关系,得到气候变化对流域生态环境的影响程度。结果表明：石羊河流域气温呈显著上升趋势,增温速度为下游0.42℃·(10 a)^-1>中游0.36℃·(10 a)^-1>上游0.35℃·(10 a)^-1,近10 a增温最显著,较20世纪60年升高了1.67℃。四季气温均呈显著上升趋势,增温速度为冬季>秋季>春季>夏季。降水呈缓慢增加趋势,增幅为上游8.3 mm·(10 a)^-1>中游7.0 mm·(10 a)^-1>下游4.1 mm·(10 a)^-1,近10 a增加最显著,较20世纪60年代增加了17%。四季降水呈弱增加趋势,增加幅度为夏季>春季>秋季>冬季。河流流量基本持平,植被覆盖面积和归一化植被指数(NDVI)显著增大。近20 a流域气候...     

黄河流域NDVI/土地利用对蒸散发时空变化的影响

基于蒸散发(ET)、归一化植被指数(NDVI)及土地利用数据利用M-K检验、Sen趋势分析等方法,研究2001—2015年黄河流域ET时空分布及不同植被覆盖/土地利用下的ET变化规律.结果 表明:(1)黄河流域年均ET呈东南高西北低的空间分布格局,与植被覆盖和土地利用的关系具有较好的一致性;(2)黄河流域ET、NDVI...     

1961—2017年北疆初终霜日及霜期时空变化特征

利用1961—2017年北疆37个地面气象站逐日最低气温观测资料,结合常规气象统计方法,分析北疆地区初、终霜日和霜期的时空演变特征.结果表明:(1)北疆平均初霜日以2.2 d·(10a)-1速率推迟;平均终霜日以1.7 d·(10a)-1速率提前;平均霜期以3.9 d·(10a)-1速率缩短;初、终霜日和霜期的主周期均...     

Sea level induced variations in clay mineral composition in the southwestern South China Sea over the past 17,000 yr

Variations in clay mineral composition of sediment cores from the margin and continental slope of the Sunda Shelf (southern South China Sea, SE Asia) covering the past 17,000 yr reflect changing influences of sediment sources together with clay mineral partitioning processes in shallow waters. We identify the deglacial sea level rise as the principal factor driving these changes. During the late glacial, high values of kaolinite are interpreted to reflect a higher contribution of clays from soils that have formed on the exposed Sunda Shelf and in the southern archipelagos of Indonesia. At this time core sites were located in close proximity to the mouths of the Sunda Shelf palaeo-drainage systems on the emerged shelf (“Sundaland”). The progressive landward displacement of the coastline and breakdown of these vast drainage systems during deglaciation led to a decrease in influence of the kaolinite-rich southern sources. When the coastline had retreated closely to its present-day position in mid-Holocene times, the former dominance of southern sources was replaced by a stronger influence of illite-rich sources (e.g. Borneo). The overriding control of sea level changes on the clay mineral distribution patterns precludes a definite climatic interpretation of clay mineral data in terms of climatic/monsoonal changes in such highly dynamic sedimentary environment.     

Contribution of a pathway through the Arctic Ocean to the re cent reduction in the ice cover

The sea ice cover in the Arctic Ocean has been reducing and hit the low record in the summer of 2007. The anomaly was extremely large in the Pacific sector. The sea level height in the Bering Sea vs. the Greenland Sea has been analyzed and compared with the current meter data through the Bering Strait. A recent peak existed as a consequence of atmospheric circulation and is considered to contribute to inflow of the Pacific Water into the Arctic Basin. The timing of the Pacific Water inflow matched with the sea ice reduction in the Pacific sector and suggests a significant increase in heat flux. This component should be included in the model prediction for answering the question when the Arctic sea ice becomes a seasonal ice cover.     

Fresh snow chemistry from high mountain regions in central himalayas

Investigations of atmospheric composition in the Himalayas has been limited in both temporal and spatial scales, mainly due to difficult logistics. Ideal sites for monitoring atmospheric composition and its evolution should be free from local pollution and representative of the remote troposphere (HUEBERT et al., 1980). As the Himalayas are far removed from highly industrialized regions they provide suitable locations to monitor the chemistry of the remote troposphere and to study the evolu…