Surface diurnal cycle and boundary layer structure over Rondonia during the rainy season
Surface diurnal cycle and boundary layer structure over Rondonia during the rainy season
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DOI：
10.1029/2001jd000356
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发表时间：
2002-09-01
影响因子：
4.4
通讯作者：
Ball, JH
中科院分区：
文献类型：
--
作者：
Betts, AK;Fuentes, JD;Ball, JH
1999年1月和2月在亚马孙进行的大规模生物圈-大气试验的雨季试验期间收集了一组综合数据集，其中包括从边界层内系住的气球和从探测站上同时进行的地面观测，以支持热带降雨测量任务(TRMM)的地面验证。分析了对流层低层东风和西风条件下，地面温度、湿度、冷凝层抬升、当量位温、地面感热和潜热通量、地面热通量和净辐射的日变化周期。在东风期间，混合比的日变化表明，通过云底的水汽通量超过了地面大蒸发量。随着雨季的推进，有一种趋势是更潮湿、更凉爽的次云层。该牧场白天的地表波文比约为0.4，随着雨季的推进略有下降。通常在下午，来自对流雨带的蒸发驱动的下沉气流改变了边界层。两个区域边界层等效位温的下降趋势相似，但西风区域对流事件导致的边界层降温减少，这是因为次云层平均较浅。通过阵风锋面边缘的Tethersonde上升表明，在下沉气流到达地面之前，云下空气首先被降雨蒸发冷却和湿润。这些测量结果为验证和改进数值预报模式中浅对流和深对流的参数化提供了详细的观测基础。
An integrated data set with simultaneous observations at the surface, from tethered balloons within the boundary layer and from rawinsonde ascents, was collected during the wet season experiment of the Large-Scale Biosphere-Atmosphere (LBA) Experiment in Amazonia during January and February of 1999 in support of the ground validation for the Tropical Rainfall Measuring Mission (TRMM). We analyze the surface diurnal cycles of temperature, humidity, lifting condensation level, equivalent potential temperature, and bx64 the surface fluxes of sensible and latent heat, ground heat flux and net radiation, for easterly and westerly wind regimes in the lower troposphere. During the easterly wind regimes, the diurnal evolution of mixing ratio shows that the flux of water vapor through cloud base exceeds the large surface evaporation. There is a trend toward a wetter and cooler subcloud layer as the rainy season progresses. Daytime surface Bowen ratio for this pasture site is about 0.4, and falls slightly as the rainy season progresses. Typically in the afternoon, evaporatively driven downdrafts from convective rainbands transform the boundary layer. The fall of equivalent potential temperature in the boundary layer is similar for both regimes, but the boundary layer cooling by convective events during the westerly regimes is reduced, because the subcloud layer is shallower on average. Tethersonde ascents through the edges of gust fronts show that subcloud air is first cooled and moistened by rainfall evaporation before the arrival of downdraft air at the surface. These measurements provide a detailed observational basis for the validation and improvement of parameterizations for shallow and deep convection in numerical forecast models.