【作者】 闭建荣；

【导师】 黄建平；

【作者基本信息】 兰州大学 ， 气象学， 2008， 硕士

【摘要】 利用兰州大学半干旱气候与环境观测站2006年4月～2008年4月的地表辐射、湍流通量和土壤等观测资料,初步分析了黄土高原半干旱区地表辐射特征、能量收支规律及地表反照率的日、季、年际变化特征,研究了雨雪天气过程对它们的影响,并讨论了土壤湿度与地表反照率的关系。同时,根据兰州大学气候灾害监测系统在景泰县兰大农场3-4月份的观测资料与同期SACOL站的辐射资料进行对比分析,得到以下主要结果:(1)地表辐射各分量月平均的日变化特征与晴天的基本一致,说明晴天条件下地表辐射的日变化具有一定的气候代表性;太阳辐射、反射辐射和净辐射日变化的位相相同,在13:00时达最大,地表长波和大气逆辐射对太阳辐射的响应时间分别为1、2小时。(2)各辐射分量日均值的年变化显著,太阳辐射、反射辐射、大气逆辐射、地表长波及净辐射的年变幅分别为:300、75、230、270、253.3 W/m~2,平均年总量分别为5916.5、1389.9、8875.2、11587.5、1813.5 MJ/m~2。净辐射在年循环中有两次方向转换期:一次是冬季辐射平衡以地表长波辐射为主时,净辐射由正值转为负值,另一次是在其他季节以太阳辐射为主要贡献项时,净辐射由负值转为正值。(3)地表反照率受雨雪天气过程影响较大,晴天表现为中午低,早晚高的“U”形结构;雪未完全融化前呈早上高,傍晚低的特点,而降水过后则呈现早上低,晚上稍高的特征。反照率月平均的日变化与晴天的一致,冬季的降雪可引起反照率的跳跃,而降水则使其减小;同时,反照率与土壤体积含水量呈指数衰减关系,即随着土壤含水量的增加,反照率逐渐减小,增加到一定程度后反照率几乎保持不变。(4)能量平衡各分量的日、季、年变化十分显著,除夏季外,感热占能量平衡的比例均高于潜热;月平均日变化中,感热通量变幅远大于潜热,只有夏季才与感热相当,甚至超过感热,这是由于降水主要集中在夏季造成的。同时,两者都呈反位相变化。(5)2008年3、4月景泰站点的太阳辐射、大气逆辐射日变化与SACOL站基本一致,3月太阳辐射的最大值达800W/m~2,4月都在800W/m~2以上,甚至还有达到1000W/m~2;从两个站看,4月平均的大气逆辐射比3月的变幅大,且景泰观测点的变幅都比榆中的强。这表明,景泰地区3、4月云量的变幅比榆中地区的大。3、4月份温度和相对湿度的日变化都呈反位相关系。(6)白天,沙尘粒子对近地面层的大气有一定的加热作用,这种作用会加热沙尘过程中带有的水汽,使其蒸发,引起相对湿度降低;而晚上,由于没有太阳辐射,沙尘粒子的加热作用就不存在,近地层大气温度一直保持负值变化,而沙尘过程附带的水汽使相对湿度有所增加,之后又有所减少。更多还原

【Abstract】 In this study, the variation of surface radiation, energy balance and albedo over Semi-Arid region of Loess Plateau are analyzed by using the land-surface radiation data, turbulence fluxes and soil data observed over Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) during April 2006 to April 2008. The daily, seasonally, yearly cycle of them are studied. The relationship between synoptic condition, soil volumetric water content and surface radiation, energy balance, albedo are discussed as well. We also discuss the difference between Jingtai and SACOL by using the land-surface radiation data observed over JingTai during March to April 2008. The main results are listed in the following:1. The mean diurnal cycle of surface radiation is close to which are under clear sky condition. It suggests, the diurnal cycle of surface radiation under clear sky condition dominate on the behalf of climatology. The phases of solar radiation, upward shortwave radiation and net radiation are similar to the surface radiation, which the maximal value is at about 13:00 (Beijing Time). However, variations of upward and downward longwave radiation lag by the solar radiation, and the response time are one hour and two hours, respectively.2. The range of annual cycle of solar radiation, upward shortwave, downwardlongwave, upward longwave and net radiation are 300, 75, 230, 270, 253.3 W/m~2, respectively. And monthly values of them are 5916.5, 1389.9, 8875.2, 11587.5, 1813.5 MJ/m~2, respectively. There are two transformed periods of net radiation in annual cycle. One is the value of net radiation change from positive to negative, when the upward longwave radiation are the main part of energy balance in wintertime. And the other one is the value of net radiation change from negative to positive, when the solar radiation are the main part of energy balance.3. The surface albedo is greatly influenced by synoptic condition. The surface albedo under clear sky condition takes on "U" shape, which is low in noon and high in nightfall. And the value of surface albedo is higher in the morning, and lower in nightfall before the snow didn’t melt completely. However, the value of surface albedo is lower in the morning, and higher in the nightfall after the rainfall. The mean diurnal cycle of surface albedo is similar to which is under the clear sky ("U" shape). The snowfall in wintertime may increase the surface albedo and rainfall may decrease the value. Furthermore, the relationship between surface albedo and soil volumetric water content (VWC) takes on exponential attenuation, that is, along with the soil VWC increases the surface albedo decreases gradually, when the soil VWC increases to some value, the value of albedo is changeless.4. The sensible heat flux is the main part of the available energy except that in the growing season over Loess Plateau area. In the growing season the latent heat flux has the same order with the sensible heat flux. And the phase variation between sensible heat flux and latent heat flux is negative.5. The diurnal cycle of solar radiation and downward longwave radiation in Jingtai are similar to SACOL during March to April 2008. And the maximum value of solar radiation is 800 W/m~2 in both March and April. The variation range of downward longwave radiation in April is higher than that in March, and the variation range of downward longwave radiation in Jingtai is more than that in SACOL. It means, the variation of cloud in Jingtai is more than that in SACOL during this period. The phase variation between air temperature and relative humidity is negative.6. The sand particles can heat up the air in near-ground layer during the daytime. And this action also can heat up the water vapor along with the sand storm and decrease the relative humidity. However, when sand storm occurs in the nighttime, because there is no solar radiation and this heating action disappear. So the air temperature in this layer decreases at all times, and the relative humidity increases to some extent and gradually decreases.更多还原