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土壤湿度异常对区域短期气候影响的数值模拟试验
A Numerical Study on Effects of the Soil Moisture upon the Regional Short-term Climate
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摘要: 用区域气候模式 (RegCM_NCC) 对江淮流域地区春季初始土壤湿度异常导致的区域气候效应进行了数值模拟分析, 结果表明:土壤湿度异常变化对区域降水的影响非常显著, 土壤湿度的正异常使得异常区域内降水增大, 地面空气增湿、蒸发加大, 与此相应, 地表气温迅速降低, 土壤湿度的负异常有与之相反的结果, 这种区域气候响应是通过改变地表辐射平衡及地-气系统能通量而实现的; 区域土壤湿度异常对短期气候的影响在一个月之内较明显, 它的影响可持续至以后的几个月, 但强度逐渐减弱; 区域土壤湿度异常的气候响应不仅仅局限于异常区域内部, 而且可以通过次级环流影响到其他区域的降水、温度等变化。Abstract: The feedback process between soil and atmosphere is very important in the climate system. Most researches on the interaction depend on the model outputs due to the scarce observation dataset of the soil moisture. Heavy flood event occurs in the mid-lower Yangtze basins in 1998. In winter and spring of that year, the soil moisture in Yangtze-Huaihe River basins is significantly wet. The concerned question is whether the abnormal soil moisture in prophase could provide valuable signal to summer rainfall. By using the improved regional climate model (RegCM_NCC), modeling study is undertaken to investigate the effects of the initial abnormal soil moisture in spring in Yangtze-Huaihe River basins (27°—35°N, 110°—120°E) on the regional climate. Based on the control run with climate values of soil moisture, two sensitivity experiments are carried out with "wet" and "dry" soil in the initial integration, respectively. Results indicate that varying the initial soil moisture in the key region shows significant influence on regional rainfall, wet soil results in the increase of local rainfall, humidity and evaporation near the ground, but the surface air temperature decreases rapidly, with the maximum value of 1.5 ℃. The experiment results of dry soil are converse to that of the wet soil. The regional climate response mainly depends on the changing surface radiation equivalent and land-atmosphere energy flux. The influences of initial abnormal soil moisture are remarkable in the first month, which can persist for several months, but the intensity deceases gradually. The change of air temperature is more remarkable and can persist longer time than the rainfall. In the mean time, the regional climate response to the abnormal soil moisture isn't confined in the key region, but also affects the rainfall and temperature in other regions due to the sub-circulation and large-scale advection. It can also cause the air temperature and humidity change at upper level through turbulent transfer. Thus, soil moisture has obvious effects on the regional-scale climate, but most of the present models can not describe the real-time variation of soil moisture due to the reason that only the climate virtual value of the soil moisture are used, which may be a factor of the modeling bias of the rainfall. The role of soil moisture would be attached much attention in the regional short-term climate research and prediction.
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图 1 长江中下游 (a)、华南地区 (b) 区域平均降水, 长江中下游地区 (c)、华南地区 (d) 区域平均气温的模拟与实况比较
Fig. 1 Comparison between simulation and observation of regional mean precipitation over the mid-lower Yangtze basins (a) and South China (b), regional mean temperature over the mid-lower Yangtze basins (c) and South China (d)
图 2 湿土壤试验与控制试验的降水差值图 (单位: mm·d-1)
(a) 4月, (b) 5月, (c) 6月, (d) 7月, (e) 8月, (f) 夏季平均
Fig. 2 Rainfall difference between wet soil experiment and control run (unit:mm·d-1)
(a) April, (b) May, (c) June, (d) July, (e) August, (f) summer mean
图 3 湿土壤试验与控制试验的地面气温差值图 (单位:℃)
(a) 第1时期平均, (b) 第2时期平均
Fig. 3 Temperature difference between wet soil experiment and control run (unit:℃)
(a) mean during the first period, (b) mean during the second period
图 4 试验区湿土壤试验与控制试验的平均物理量差值时间演变
(十字线为降水, 单位: mm·d-1; 空心圆圈线为地面空气湿度, 单位:g/kg; 实心圆圈线为地表径流, 单位: mm; 空心方框线为地面气温, 单位:℃)
Fig. 4 Time evolvement of average variables difference between wet soil experiment and control run
(reticle curve denotes precipitation, unit: mm·d-1; open circle curve denotes surface humidity, unit: g/kg; solid circle curve denotes surface run off, unit: mm; open pane curve denotes surface air temperature, unit:℃)
图 5 湿土壤试验中夏季平均垂直速度偏差的经向-高度剖面 (a) 和纬向-高度剖面图 (b) (单位: Pa·s-1)
Fig. 5 Meridional-height section (a) and zonal-height section (b) of vertical wind speed difference between wet soil experiment and control run (unit: Pa·s-1)
图 6 干土壤试验与控制试验的降水差值图 (单位: mm·d-1)
(a) 4月, (b) 5月, (c) 6月, (d) 7月, (e) 8月, (f) 夏季平均
Fig. 6 Rainfall difference between wet soil experiment and control run (unit: mm·d-1)
(a) April, (b) May, (c) June, (d) July, (e) August, (f) summer mean
图 7 干土壤试验与控制试验的地面气温差值图 (单位:℃) (a) 第1时期平均, (b) 第2时期平均
Fig. 7 Temperature difference between dry soil experiment and control run (unit:℃) (a) mean during the first period, (b) mean during the second period
图 8 试验区干土壤试验与控制试验的平均物理量差值时间演变
(十字线为降水, 单位: mm·d-1; 空心圆圈线为地面空气湿度, 单位: g·kg-1; 实心圆圈线为地面径流, 单位:mm; 空心方框线为地面气温, 单位:℃)
Fig. 8 Time evolvement of average variables difference between dry soil experiment and control run
(reticle curve denotes precipitation, unit: mm·d-1; open circle curve denotes surface humidity, unit: g/kg; solid circle curve denotes surface run off, unit: mm; open pane curve denotes surface air temperature, unit:℃)
图 9 试验区敏感性试验与控制试验的平均地表热平衡差值时间演变 (单位: W·m-2)
(a) 湿土壤试验, (b) 干土壤试验 (十字线为净长波辐射, 空心圆圈线为地表净短波吸收, 实心圆圈线为感热通量, 空心方框线为潜热通量)
Fig. 9 Time evolvement of surface heat fluxes difference between experiments and control run (unit: W·m-2)
(a) wet soil experiment, (b) dry soil experiment (reticle curve denotes net long wave radiation, open circle curve denotes net short wave radiation, solid circle curve denotes sensible heat flux, and open pane curve denotes latent heat flux)
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