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Abstract. The states of coupling between clouds andsurface or boundary layer have been investigated much more extensively formarine stratocumulus clouds than for continental low clouds, partly due tomore complex thermodynamic structures over land. A manifestation is a lackof robust remote sensing methods to identify coupled and decoupled cloudsover land. Following the idea for determining cloud coupling over the ocean,we have generalized the concept of coupling and decoupling to low cloudsover land, based on potential temperature profiles. Furthermore, by usingample measurements from lidar and a suite of surface meteorologicalinstruments at the U.S. Department of Energy's Atmospheric RadiationMeasurement Program's Southern Great Plains site from 1998 to 2019, we havedeveloped a method to simultaneously retrieve the planetary boundary layer(PBL) height (PBLH) and coupled states under cloudy conditions during thedaytime. The new lidar-based method relies on the PBLH, the liftedcondensation level, and the cloud base to diagnose the cloud coupling. Thecoupled states derived from this method are highly consistent with thosederived from radiosondes. Retrieving the PBLH under cloudy conditions, whichhas been a persistent problem in lidar remote sensing, is resolved in thisstudy. Our method can lead to high-quality retrievals of the PBLH undercloudy conditions and the determination of cloud coupling states. With thenew method, we find that coupled clouds are sensitive to changes in the PBLwith a strong diurnal cycle, whereas decoupled clouds and the PBL are weaklyrelated. Since coupled and decoupled clouds have distinct features, our newmethod offers an advanced tool to separately investigate them in climatesystems.
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Cloud‐Surface Coupling Alters the Morning Transition From Stable to Unstable Boundary Layer
Abstract Due to surface heating, the morning boundary layer transits from stable to neutral or convective conditions, exerting critical influences on low tropospheric thermodynamics. Low clouds closely interact with the boundary layer development, yet their interactions bear considerable uncertainties. Our study reveals that cloud‐surface coupling alters the morning transition from stable to unstable boundary layer and thus notably affects the diurnal variation of the boundary layer. Specifically, due to the reduction in surface fluxes, decoupled clouds can delay the process of eroding nocturnal inversion by 0.8‐hr and even prevent the transition of the boundary layer from happening for 12% of decoupled cases, keeping the boundary layer in a stable state during the noontime. On the other hand, when clouds are coupled with the surface, cloud‐top radiative cooling can directly cool the upper boundary layer to facilitate sub‐cloud convection, leading to an unstable boundary layer in the earlier morning.
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- Award ID(s):
- 2126098
- PAR ID:
- 10400823
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 50
- Issue:
- 5
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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