Boundary layer moisture variability at the Atmospheric Radiation Measurement (ARM) Eastern North Atlantic observatory during marine conditions
<p>Boundary layer moisture variability at the Eastern North Atlantic (ENA) site during marine conditions is examined at monthly and daily timescales using 5 years of ground-based observations and output from the European Center for Medium range Weather Forecast (ECMWF) reanalysis model. The an...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2023-03-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/23/3453/2023/acp-23-3453-2023.pdf |
| Summary: | <p>Boundary layer moisture variability at the Eastern North Atlantic
(ENA) site during marine conditions is examined at monthly and daily timescales using 5 years of ground-based observations and output from the European
Center for Medium range Weather Forecast (ECMWF) reanalysis model. The
annual cycle of the mixed-layer total 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. When marine conditions prevail,
advection of colder and dry air from the north acts as an important moisture
sink (<span class="inline-formula">∼</span> 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 (<span class="inline-formula">∼</span> 25 % and
<span class="inline-formula">∼</span> 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 (<span class="inline-formula">∼</span> 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, and
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
spatial distribution of vapor to support convection and precipitation.</p> |
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| ISSN: | 1680-7316 1680-7324 |