Understanding Convective Transport Through Transit and Turnover Timescales

Deep convection plays a crucial role in atmospheric transport, yet the associated vertical transport characteristics and timescales remain insufficiently understood. This study investigates the transport dynamics of tropical deep convection by analyzing two key timescales: transit time, the average duration for chemical species to travel from the boundary layer to the upper troposphere, and turnover time, the average residence time of chemical species in the upper troposphere. The transit time considers the parcel taken through different pathways, represented mathematically by the Green function. This calculation requires integrating over all possible pathways and times, adding complexity. In contrast, the turnover time is derived from a more straightforward mass-balance approach, depending solely on the difference in mixing ratios between the upper troposphere and the boundary layer. Using observations from the CONvective TRansport of Active Species in the Tropics (CONTRAST) experiment conducted from January to February 2014, this study estimated transit and turnover times by analyzing mixing ratio differences of trace gaseous species between the boundary layer and the upper troposphere in relation to their atmospheric lifetimes. The mean transit time was determined to be 8.4 days, while the mean turnover time was 9.3 days, indicating a remarkable similarity despite their distinct physical interpretations. This close correspondence suggests a robust consistency between the efficiency of vertical transport and upper-tropospheric residence characteristics of species within deep convective systems. These findings might indicate the simpler mass-balance residence time could be applied to represent the convection processes and offer a foundation for quantifying the impact of chemical species on the warming efficiency through convective transport.