Diagnostics of Convective Transport Over the Tropical Western Pacific From Trajectory Analyses

Abstract

This study characterizes the representation of convective transport by a Lagrangian trajectory model driven by kinematic (pressure tendency ω) vertical velocity. Four (re)analysis wind products are used in backward trajectory calculations with the TRAJ3D model, and their representations of convective transport are analyzed. Two observation‐based diagnostics are used for the evaluation: a database of observed convective cloud tops derived from satellite measurements and a set of transit time distributions (TTDs) derived from an airborne campaign during January–February 2014 in a domain over the Tropical Western Pacific (TWP). The analysis is designed to derive trajectory‐based TTDs that can be directly evaluated using the observation‐based TTDs. The results indicate a broad consistency between two independent TTD derivations characterizing vertical transport over the TWP, with a significant portion of convective transport processes represented in trajectory experiments driven by the selected (re)analysis wind products. The convective and boundary layer source regions of upper tropospheric air parcels are shown to be consistent with the climatological flow regime within the TWP. Furthermore, contributions of convection are identified in the ω fields of the (re)analysis wind data sets, as indicated by the spatiotemporal correlation of enhanced vertical velocity and observed convection. These results demonstrate the successful application of two observation‐based diagnostics and quantify the ability for kinematic trajectory models to represent convective transport processes.

A Multimodel Investigation of Asian Summer Monsoon UTLS Transport Over the Western Pacific

“…There are two significant refinements in this approach over the previous study (Honomichl & Pan, 2020). First, the high spatial and temporal resolution of the ERA5 reanalysis winds improve the trajectory model representation of convective transport over the ERA-interim data (0.7° and 6 hourly, Dee et al, 2011) used in the earlier study, as demonstrated by Smith et al (2021). This improved representation is likely a key factor revealing the association of the primary region from which the air mass left the BL with the monsoon trough, the region known for deep convection and heavy rainfall (e.g., Krishnamurti & Bhalme, 1976).…”

“…This new result, largely owing to the much-improved representation of convective transport by using the ERA5 wind fields (Smith et al, 2021), brings clarity to results of previous studies of monsoon transport, in which the region of the southern flank of the Tibetan Plateau was shown to be the main vertical transport channel (e.g., Bergman et al, 2013;Honomichl & Pan, 2020;Pan et al, 2016). This result also provides the context for previous air mass origin studies that used tagged tracers or convective clouds which were identified using geographical regions or political boundaries (e.g., Bucci et al, 2020;Park et al, 2009;Vogel et al, 2015).…”

Variability of air mass transport from the boundary layer to the Asian monsoon anticyclone

“…With respect to the importance of convection, Wu et al (2020) showed with a free-running CCM that for the first uplift in the ASM region convection is dominant but in the UTLS the large scale dynamics are most relevant for the tracer budget. A recent study by Smith et al (2021) investigated how convective processes are captured in the vertical velocity field of (re)analysis data. They came to the conclusion that kinematic trajectories based on (re)analyses winds incorporate the effects of convection to a substantial degree.…”

The Evolutions and Large‐Scale Mechanisms of Summer Stratospheric Ozone Intrusion Across Global Hotspots

“…The stratospheric intrusion is known to be dominated by isentropic mixing near the tropopause (Holton et al., 1995), which occurs at a finer spatial and temporal resolution compared to the given daily vertical velocity. As the pure trajectory model does not incorporate parameterization for convection, mixing, and turbulence, vertical displacement should be considered with potential uncertainties (W. P. Smith et al., 2021).…”