LBA-ECO CD-01 SIMULATED ATMOSPHERIC CIRCULATION, CO2 VARIATION, TAPAJOS: AUGUST 2001

We have investigated mesoscale variations of atmospheric CO2 over a heterogeneous landscape of forests, pastures, and large rivers during the Santarem Mesoscale Campaign (SMC) of August 2001. The variations of atmospheric CO2 concentration were simulated using the Colorado State University (CSU) Regional Atmospheric Modeling System (RAMS) with four nested grids that included a 1-km finest grid centered on the Flona Tapajos. Surface fluxes of CO2 were prescribed in the model using idealized diurnal cycles over forest and pasture vegetation derived from flux tower observations, and over surface water using a value suggested by in situ measurements in the Amazon region. The distribution of vegetation types was derived from the 1-km International Geosphere-Biosphere Programme (IGBP) land-cover dataset version 2.0. Our simulation ran from the 1st through the 15th of August 2001, which was concurrent with the SMC. Evaluation against flux tower observations and the SMC field measurements shows that, in many respects, the model captures observed meteorological variables and CO2 concentrations reasonably well. The results also suggest that the local topography, differences in roughness length between water and land, the T shape juxtaposition of Amazon and Tapajos Rivers, and the resulting horizontal and vertical wind shears, all facilitated the generation of local mesoscale circulations. Possible mechanisms producing a lower level convergence line near the east bank of the Tapajos River during strong trade-wind conditions are also explored. Our modeling study is helping us to understand observed patterns of CO2 fluxes and concentration distribution obtained from flux towers and light aircraft.本研究针对2001年8月圣塔伦中尺度观测计划（Santarem Mesoscale Campaign, SMC）实施期间，森林、牧场与大型河流构成的异质性景观内的大气CO₂中尺度变异特征开展了分析。本研究采用科罗拉多州立大学（Colorado State University, CSU）开发的区域大气模拟系统（Regional Atmospheric Modeling System, RAMS），通过四层嵌套网格开展大气CO₂浓度变化模拟，其中最细网格分辨率达1km，中心位于塔帕若斯国家森林（Flona Tapajos）。模型中，森林与牧场植被的CO₂地表通量采用由通量塔观测数据推导得到的理想化昼夜循环模式进行赋值，而地表水体的CO₂通量则采用亚马逊地区原位测量提出的参考值。植被类型分布数据源自分辨率为1km的国际地圈生物圈计划（International Geosphere-Biosphere Programme, IGBP）2.0版土地覆盖数据集。本次模拟时段为2001年8月1日至15日，与SMC观测计划同期开展。通过与通量塔观测数据及SMC野外实测数据对比验证发现，该模型在多数场景下能够较为准确地再现观测到的气象变量与CO₂浓度分布。研究结果同时表明，局地地形、水陆下垫面粗糙度差异、亚马逊河与塔帕若斯河呈T型交汇的布局，以及由此产生的水平与垂直风切变，均对局地中尺度环流的形成起到了促进作用。本研究还探讨了强信风条件下，塔帕若斯河东侧河岸附近形成低层辐合线的潜在物理机制。本次模拟研究有助于我们理解由通量塔与轻型航空器观测得到的CO₂通量及浓度分布特征。