Boundary layer moisture variability at the ARM Eastern North Atlantic Observatory

• Main Authors: Cadeddu, Maria Paola, Ghate, Virendra, Turner, David, Surleta, Thomas
• Format: Text
• Language: English
• Published: 2022
• Subjects: North Atlantic
• Online Access: https://doi.org/10.5194/acp-2022-615; https://acp.copernicus.org/preprints/acp-2022-615/

Boundary layer moisture variability at the Eastern North Atlantic (ENA) site is examined at monthly and daily time scales using 5 years of ground-based observations and output from European Center for Medium range Weather Forecast (ECMWF) reanalysis model. The annual cycle of the mixed layer water budgets is presented to estimate the relative contribution of large-scale advection, local moisture tendency, entrainment, and precipitation to balance the moistening due to surface latent heat flux on monthly timescales. Advection of colder and dry air from the North acts as an important moisture sink (~ 50 % of the overall budget) during fall and winter driving the seasonality of the budget. Entrainment and precipitation contribute to the drying of the boundary layer (~25 % and ~15 % respectively) and the local change in moisture contributes to a small residual part. On a daily temporal scale, moist and dry mesoscale columns of vapor (~10 km) are analyzed during 10 selected days of precipitating stratocumulus clouds. Adjacent moist and dry columns present distinct mesoscale features that are strongly correlated with clouds and precipitation. Dry columns adjacent to moist columns have more frequent and stronger downdrafts immediately below the cloud base. Moist columns have more frequent updrafts, stronger cloud top cooling, higher liquid water path and precipitation compared to the dry columns. This study highlights the complex interaction between large-scale and local processes controlling the boundary layer moisture and the importance of vapor spatial distribution to support convection and precipitation.