Convective transport of biomass burning emissions over Brazil during TRACE A
Convective transport of biomass burning emissions over Brazil during TRACE A
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DOI：
10.1029/96jd00346
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发表时间：
1996-10
影响因子：
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通讯作者：
K. Pickering;A. Thompson;Yansen Wang;W. Tao;D. McNamara;V. Kirchhoff;B. Heikes;G. Sachse;J. Bradshaw;G. Gregory;D. Blake
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文献类型：
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作者：
K. Pickering;A. Thompson;Yansen Wang;W. Tao;D. McNamara;V. Kirchhoff;B. Heikes;G. Sachse;J. Bradshaw;G. Gregory;D. Blake
在GTE/TRACE A(赤道-大西洋附近的输送和大气化学)巴西阶段发生的一系列大型中尺度对流系统为观察生物质燃烧产生的微量气体的深层对流输送提供了机会。本文报告了对1992年9月27日6号航班的详细分析，该航班采样了巴西利亚以北的云和生物质燃烧扰动地区。对NASA DC-8在9-12公里处流出的云层进行的高频采样显示，CO混合比增加，通常是本底的3倍(以体积计为200-300ppbv，而不是90ppbv)，NOx和碳氢化合物显著增加。探测到了清晰的闪电产生的NO信号；我们估计，在9.5公里高度和11.3公里高度，至少40%的NOx和32%的NOx来自闪电。用四种模式分析了这一系列对流事件的动力和光化学特征。(1)利用NCAR/宾夕法尼亚州立大学中尺度模式(MM5)对这一时期进行了区域模拟，包括一氧化碳的示踪输送，并根据观测资料进行了初始化。再现了背景以上3倍的中上层对流层增强。(2)在9月26-27日期间，对一个有代表性的对流单体进行了云分辨模式(Goddard积云集合模式)。(3)光化学计算(Goddard对流层化学模式)，用在云外流中观测到的微量气体(例如，CO，NOx，碳氢化合物，03)初始化，显示出可察觉的对流后03层，最初高达7-8ppbv O_3/d。(4)云流出水平(对流后条件)的正向轨迹使巴西东部和热带大西洋的臭氧气团在2-4天内产生，大西洋、非洲和印度洋上空在6-8天内产生臭氧。事实上，在对流事件后3-4天(1992年9月30日)，纳塔尔臭氧探测的对流层上层水平与9月28日探测相比平均增加了-30ppbv(3个Dobson单位(DU))。我们模拟的云外流中的净03产生率比不受风暴干扰的空气中的产生率高出3倍或更多。在8到16公里的云流出层上整合，对流后净03产量(8天-5-6DU)占南大西洋过剩03(15-25DU)的-25%。巴西臭氧探空仪和深对流频率与气候学的比较(Kirchhoff等人，本期)表明，1992年9月下旬的条件代表了对流和对流层上层臭氧形成的异常活跃时期。
A series of large mesoscale convective systems that occurred during the Brazilian phase of GTE/TRACE A (Transport and Atmospheric Chemistry near the Equator-Atlantic) provided an opportunity to observe deep convective transport of trace gases from biomass burning. This paper reports a detailed analysis of flight 6, on September 27, 1992, which sampled cloud- and biomass-burning-perturbed regions north of Brasilia. High-frequency sampling of cloud outflow at 9-12 km from the NASA DC-8 showed enhancement of CO mixing ratios typically a factor of 3 above background (200- 300 parts per billion by volume (ppbv) versus 90 ppbv) and significant increases in NOx and hydrocarbons. Clear signals of lightning-generated NO were detected; we estimate that at least 40% of NO x at the 9.5-km level and 32% at 11.3 km originated from lightning. Four types of model studies have been performed to analyze the dynamical and photochemical characteristics of the series of convective events. (1) Regional simulations for the period have been performed with the NCAR/Penn State mesoscale model (MM5), including tracer transport of carbon monoxide, initialized with observations. Middle-upper tropospheric enhancements of a factor of 3 above background are reproduced. (2) A cloud-resolving model (the Goddard cumulus ensemble (GCE) model) has been run for one representative convective cell during the September 26-27 episode. (3) Photochemical calculations (the Goddard tropospheric chemical model), initialized with trace gas observations (e.g., CO, NO x, hydrocarbons, 03) observed in cloud outflow, show appreciable 0 3 formation postconvection, initially up to 7-8 ppbv O3/d. (4) Forward trajectories from cloud outflow levels (postconvective conditions) put the ozone-producing air masses in eastern Brazil and the tropical Atlantic within 2-4 days and over the Atlantic, Africa, and the Indian Ocean in 6-8 days. Indeed, 3-4 days after the convective episode (September 30, 1992), upper tropospheric levels in the Natal ozone sounding show an average increase of -30 ppbv (3 Dobson units (DU) integrated) compared to the September 28 sounding. Our simulated net 0 3 production rates in cloud outflow are a factor of 3 or more greater than those in air undisturbed by the storms. Integrated over the 8- to 16-km cloud outflow layer, the postconvection net 0 3 production (-5-6 DU over 8 days) accounts for -25% of the excess 03 (15-25 DU) over the South Atlantic. Comparison of TRACE A Brazilian ozonesondes and the frequency of deep convection with climatology (Kirchhoff et al., this issue) suggests that the late September 1992 conditions represented an unusually active period for both convection and upper tropospheric ozone formation.