Oral

IAMAS

M04 - Cloud-Precipitation-Aerosol Studies

Vertical Structure of Summertime Low-Level Clouds over the Western North Pacific Based on Aircraft Observations

Low-level clouds, particularly stratocumulus, play a critical role in regulating the Earth��s radiation budget and are considered one of the major sources of uncertainty in climate prediction. Although much of our understanding of stratocumulus vertical structures comes from previous studies based on observations over the subtropical eastern Pacific, comparatively little is known about such clouds in the mid-latitudes. The western North Pacific, in particular, experiences high low-level cloud cover during summer, yet direct in-situ observations there have been limited. In this study, we conducted aircraft measurements of summertime low-level clouds over the western North Pacific, specifically off the east coast of Hokkaido, from late July to early August 2022. These flights yielded vertical profiles for 95 distinct clouds by making multiple ascents and descents with instruments measuring cloud microphysical properties. We compared our findings with previously documented observations from the subtropical eastern Pacific to identify notable differences in vertical structure. Additionally, to assess how representative our 2022 measurements are for this region, we analyzed similar aircraft data collected in July 2013 over the same domain. Our analyses focused on several key parameters: (1) the degree of adiabaticity, i.e., how closely observed vertical profiles of liquid water content approach theoretical adiabatic profiles; (2) vertical coupling within the boundary layers, based on the difference in liquid water potential temperature between upper and lower levels; and (3) the strength of the temperature inversion capping the clouds. Trajectory analysis of air parcels using ERA5 reanalysis data provided insights into the moisture uptake and origin of air masses that contributed to cloud formation. Results show that low-level clouds in this region often exhibited weak inversions at their tops and boundary layers were likely to become decoupled, in contrast to many subtropical stratocumulus systems. They also tended to have lower adiabaticity. Trajectory analysis indicated that air parcels generally gained moisture near the sea surface before ascending along surfaces of constant potential temperature. Differences in parcel origins with altitude appeared to drive more complex cloud vertical structures. In the presentation, we will also discuss how these features are consistently observed over time by comparing the 2022 observations with the 2013 observations from the same domain.