Characterizing Near-surface Moisture Increase During the Clear-sky Afternoon-to-Evening Transition Using a Single Column Model Journal Article uri icon

Overview

abstract

  • Abstract; The afternoon-to-evening transition is the period when the atmospheric boundary layer transitions from convective to stable conditions. One noticeable feature during this transition period is the rapid increase in water vapor concentration near the surface. However, the mechanism behind the increase in water vapor remains poorly understood. This study investigated the processes contributing to the water vapor increase and the impacts of the land cover and horizontal advection on the water vapor increase using a single-column model for the clear-sky condition. Numerical experiments were conducted on three cases at the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site. Evapotranspiration was found to be the main moisture source to the water vapor increase and that change of the near-surface vertical temperature gradient from negative to positive is the trigger for this increase during the afternoon-to-evening transition. This is because the near-surface turbulence divergence term decreases due to the change in the buoyancy profile caused by vertical temperature gradient change. The impact of horizontal advection on water vapor varies, and it can either lead to an increase or decrease in water vapor, depending on the spatial horizontal water vapor gradient. This study also found that land cover can influence the timing of the water vapor increase since different land covers may have different Bowen ratios. Water vapor increases earlier under conditions with smaller Bowen ratios compared to those with larger values.

publication date

  • May 9, 2025

Date in CU Experts

  • June 18, 2025 9:15 AM

Full Author List

  • He S; Simonson JM; Turner DD; Benjamin SG; Olson JB

author count

  • 5

Other Profiles

International Standard Serial Number (ISSN)

  • 1558-8424

Electronic International Standard Serial Number (EISSN)

  • 1558-8432