Abstract
Convective transport from the marine boundary layer to the upper troposphere (UT) is investigated using airborne in situ measurements of chemical species over the tropical western Pacific. Using 42 volatile organic compounds with photochemical lifetimes ranging from shorter than a day to multiple decades, we derive a transit time spectrum G(t) and the associated modal and mean transit times for the UT air mass over the convectively dominant tropical western Pacific region. G(t) describes relative contributions of air masses transported from the marine boundary layer to the UT via all transport paths with different transit times. We further demonstrate that the volatile organic compound‐derived transit time scale is broadly comparable to that estimated from convective mass flux. The observation‐based transit time spectrum not only provides insights into convective transport pathways, but also has the potential to serve as an effective diagnostic for evaluating the representation of convective transport in global models.
Plain Language Summary
Tropical deep convection is an important mechanism whereby air mass and chemical species are transported from near the surface to the upper troposphere and lower stratosphere. This transport process is difficult to quantify by observations or represent in models because of the small spatial scales and short temporal scales involved. In this study, we present a method to characterize convective transport using the framework of transit time spectrum, which describes the relative contributions of different transport paths with different transit times. We demonstrate that convective transport transit time spectrum can be derived using airborne in situ measurements of chemical species with a wide range of lifetimes, and we illustrate the wealth of information they provide for quantifying transport processes. This analysis method has the potential to serve as a unique diagnostic for evaluating the representation of convective transport in global models.
Key Points
Airborne in situ measurements of VOCs with a wide range of lifetimes are used to quantify a convective‐transport transit time spectrum
The transit time scale derived from VOC measurements is broadly comparable to that estimated from convective mass flux
The estimated transit time spectrum has the potential to serve as an effective diagnostic for evaluating convective transport in CCMs
