Low-level liquid-bearing clouds contribute to seasonal lower atmosphere stability and surface energy forcing over a high-mountain watershed environment

Abstract

Measurements of atmospheric structure and surface energy budgets distributed along a high-altitude mountain watershed environment near Crested Butte, Colorado, USA, from two separate, but coordinated, field campaigns, SAIL and SPLASH, are analyzed. This study identifies similarities and differences in how clouds influence the radiative budget over one snow-free summer season (2022) and two snow-covered seasons (2021-22; 2022-23) for this alpine location. A relationship between lower tropospheric stability stratification and longwave radiative flux from the presence or absence of clouds is identified. When low clouds persisted, often with signatures of supercooled liquid in winter, the lower troposphere experienced weaker stability, while radiatively clear skies that are less likely to be influenced by liquid droplets were associated with appreciably stronger lower tropospheric stratification. Corresponding surface turbulent heat fluxes partitioned differently based upon the cloud-stability stratification regime derived from early morning radiosounding profiles. Combined with the differences in the radiative budget largely resulting from dramatic seasonal differences in surface albedo, the lower atmosphere stratification, surface energy budget, and near-surface thermodynamics are shown to be modified by the effective longwave radiative forcing of clouds. The diurnal evolution of thermodynamics and surface energy components varied depending on early morning stratification state. Thus, the importance of quiescent versus synoptically-active large-scale meteorology is hypothesized as a critical forcing for cloud properties and associated surface energy budget variations. The physical relationships between clouds, radiation, and stratification can provide a useful suite of metrics for process-understanding and to evaluate numerical models in such an undersampled, highly complex terrain environment.