10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Aerosol Enhancement in the Tropical Tropopause Layer Controlled by Deep Convection, In Situ Production, and Mixing
SHANG LIU, Pengfei Yu, Troy Thornberry, Andrew Rollins, Yuyan Cui, Karen Rosenlof, Ru-Shan Gao, University of Colorado, Boulder
Abstract Number: 650 Working Group: Remote/Regional Atmospheric Aerosol
Abstract Aerosols in the tropical tropopause layer (TTL) are of great interest as the TTL is the main gateway for material transport from the troposphere to the stratosphere. Understanding the abundance and distribution of aerosols in this pristine region is also important for quantification of the anthropogenic influence on climate. However, our knowledge of aerosol properties in the TTL is limited. To bridge this gap, we measured vertically-resolved aerosol size distributions in the TTL over the western Pacific warm pool, an area that features deep tropical convection due to the warm sea surface. The measurements were performed using a custom-built optical particle counter onboard the NASA WB-57F as well as weather balloons based at Guam (13.5º N, 144.8° E) during the NASA POSIDON (Pacific Oxidants, Sulfur, Ice, Dehydration, and cONvection) campaign in October 2016.
From 9 research flights and 1 balloon profile, we find that the vertical distributions of aerosol in the tropical troposphere over Guam can be described by three layers, each with distinct vertical structure and properties. The first layer is from the surface to 5 km, in which the aerosol mass mixing ratio (MMR) decreased logarithmically with height from 2 ppb to 0.08 ppb. The second layer ranges from 5 km to 13.5 km, with the latter coinciding with the typical height of the tropical convective outflow. Aerosol concentrations in this layer are very low, with an average MMR of 0.07 ppb. These observations suggest that aerosols in this layer have been efficiently removed by convection, which serve as an effective aerosol sink by scavenging. The TTL constitutes the third layer, ranging from 13.5 km to 19 km. In the TTL, the aerosol MMR increases linearly with altitude from 0.07 ppb to 1.2 ppb. Good correlation of aerosol MMR with O3 in the TTL indicates that inmixing of the aerosols from the stratosphere may play a role in the rapid increase of aerosol mass. The increase of aerosol MMR could also result from particle growth due to in situ chemical production at the outflow of tropical convections. A global sectional aerosol model coupled with the Community Earth System Model has been used to examine the relative contribution of vertical mixing and local formation of the aerosol mass. In addition, a Lagrangian particle dispersion model (FLEXPART) has been used to identify the source regions of the TTL aerosols and their precursors. In summary, our results demonstrate multiple controls of the tropical deep convection in the life cycle of aerosols, acting as a sink for lower-altitude aerosols and an indirect source of aerosols in the upper troposphere and lower stratosphere.