Convective cold pools and attendant turbulence at the Amazon Tall Tower Observatory (ATTO)

Abstract

Deep moist convection significantly disturbs the evolution of the planetary boundary layer (PBL) through its convective cold pools (CCPs). This study investigates the statistics of CCPs and their impact on PBL turbulence as observed at the Amazon Tall Tower Observatory (ATTO) site. To obtain a large dataset of CCPs, we adapted an existing CCP-detection algorithm for use in multilevel, micrometeorological data. Application of the algorithm to ATTO observations collected from August 2021 through December 2023 resulted in a dataset consisting of 410 CCPs. CCPs occur nearly every other day at the ATTO site, although they are most common from April through September and are least common from December through March. The occurrence of CCPs is linked to the diurnal cycle of the PBL, with more events around 1800 UTC and the less events around 1100 UTC. The strength of CCP perturbations varies strongly as a function of the distance from the canopy. Above the canopy (approximately 37 m), CCPs exhibit well-defined gust fronts, marked by sharp drops in temperature and humidity, gusting winds, overturning circulations, and pressure rises. During gust front passages, sensible (latent) heat fluxes are briefly enhanced and subsequently invert sign (weaken) in the CCPs, as previously unstable (moister) PBLs become stable (drier). Turbulence is stronger and more anisotropic during gust fronts and just above the canopy due to mechanical drag. Anisotropic turbulence may be transported upward to 200 m by the gust fronts. Below the canopy, CCPs and attendant perturbations are drastically damped, except in high-end cases