青藏高原那曲中部土壤温湿分布特征

青藏高原土壤水热状况对气候变化和植被退化方面的研究具有重要意义，土壤湿度的准确刻画还会影响到数值预报模式对当地及其下游地区降水的模拟能力。为此，采用中国科学院那曲高寒气候环境观测研究站安多观测点2014年1—12月的土壤温度、土壤湿度观测资料以及同期安多气象站观测数据，分析了青藏高原那曲中部不同深度土壤温湿度的分布特征及其与气温、降水量等气象要素的关系。结果表明：土壤温度在浅层为正弦曲线，随着土壤深度的增加，曲线逐渐接近直线。土壤升温迅速而降温过程缓慢。封冻和解冻日期随土壤深度的增加而推迟，封冻期逐渐缩短。不同层次土壤湿度日内变化较小。月变化呈单峰型结构，峰值和谷值基本出现在8月和12月。土壤湿度上升速率较下降速率缓慢。区域尺度上GLDAS-NOAH资料显示出类似的变化特征。土壤温湿度在一年中的变化不一致，但土壤温湿度呈显著正相关。浅层土壤的温度梯度明显大于深层；浅层土壤湿度最大，中间层较大，深层土壤湿度最小。随着干季向湿季的转换，由于太阳辐射的增加，非绝热加热呈增加的趋势。土壤湿度与气象要素在不同时段的相关性存在一些差异，但总体上土壤湿度与气温、降水量和相对湿度呈正相关，与风速、日照时数相关性不显著。

Distribution characteristics of soil temperature and moisture in the middle region of Nagqu over the Tibetan Plateau

The soil hydrothermal condition plays a significant role on the study of climate change and vegetation degradation and so forth over the Tibetan Plateau. The accurate characterization of soil moisture will also influence the simulation capability of precipitation in local and its downstream areas. Therefore， with soil temperature and soil moisture measurements at Amdo site of Nagqu Station of Plateau Climate and Environment， Chinese Academy of Sciences， and meteorological data at Amdo Meteorological Station during January to December 2014， this paper investigated the distribution of soil temperature and soil moisture along with their relationship with meteorological factors such as air temperature and precipitation in the middle region of Nagqu over the Tibetan Plateau. Results show that： The soil temperature exhibited sinusoid variation at shallow layer， then the curve is gradually close to straight line with the depth of soil. The soil temperature rose rapidly and the cooling process was quite slow. The freezing and thawing date were delayed with the depth of the soil while the freeze-up period was gradually shortened. The intra-day variation of soil moisture was small at different depths. The monthly variation indicated the structure of single peak， and the maximum and minimum values basically appeared in August and December， respectively. The rate of soil moisture increase was much slower than the decreasing process. The regional distribution derived from GLDAS-NOAH was similar to the variation of observation. The variation tendency of soil temperature and soil moisture was not consistent in one year， though there was close positive relationship between them. The temperature gradient of the shallow layer was obviously larger than the deep layer. The soil moisture of shallow layer was largest， followed by the middle layer， and the moisture was smallest at deep layer. With the transition from dry season to wet season， non-adiabatic heating increased due to the increase of solar radiation. The relationship of soil moisture to meteorological factors varied with different periods， but generally soil moisture was positively correlated with air temperature， precipitation and relative humidity while without obvious relationship with wind speed and sunshine duration.