Case study of a humidity layer above Arctic stratocumulus and potential turbulent coupling with the cloud top

Abstract

Abstract. Specific humidity inversions (SHIs) above low-level cloud layers have been frequently observed in the Arctic. The formation of these SHIs is usually associated with large-scale advection of humid air masses. However, the potential coupling of SHIs with cloud layers by turbulent processes is not fully understood. In this study, we analyze a 3 d period of a persistent layer of increased specific humidity above a stratocumulus cloud observed during an Arctic field campaign in June 2017. The tethered balloon system BELUGA (Balloon-bornE moduLar Utility for profilinG the lower Atmosphere) recorded vertical profile data of meteorological, turbulence, and radiation parameters in the atmospheric boundary layer. An in-depth discussion of the problems associated with humidity measurements in cloudy environments leads to the conclusion that the observed SHIs do not result from measurement artifacts. We analyze two different scenarios for the SHI in relation to the cloud top capped by a temperature inversion: (i) the SHI coincides with the cloud top, and (ii) the SHI is vertically separated from the lowered cloud top. In the first case, the SHI and the cloud layer are coupled by turbulence that extends over the cloud top and connects the two layers by turbulent mixing. Several profiles reveal downward virtual sensible and latent heat fluxes at the cloud top, indicating entrainment of humid air supplied by the SHI into the cloud layer. For the second case, a downward moisture transport at the base of the SHI and an upward moisture flux at the cloud top is observed. Therefore, the area between the cloud top and SHI is supplied with moisture from both sides. Finally, large-eddy simulations (LESs) complement the observations by modeling a case of the first scenario. The simulations reproduce the observed downward turbulent fluxes of heat and moisture at the cloud top. The LES realizations suggest that in the presence of a SHI, the cloud layer remains thicker and the temperature inversion height is elevated.

Radiative closure and cloud effects on the radiation budget based on satellite and shipborne observations during the Arctic summer research cruise, PS106

“…5a and c). The persistent cloud structure observed from 5-7 June 2017 is studied in more detail in Egerer et al (2021), who suggest that humidity inversions supply moisture to the cloud layer, increasing the persistence of the cloud. Time periods with the largest LW CRE and cloud conditions described occurred mostly over sea ice or the marginal zone.…”

Vertical Gradient of Size-Resolved Aerosol Compositions over the Arctic Reveals Cloud Processed Aerosol in-Cloud and above Cloud

“…Alternatively, balloon-borne measurements have been applied for Arctic aerosol measurements due to their advantages in long-term observations with less cost and risk even in harsh weather conditions (e.g., extreme waves, wind, storms, currents, colder temperature, fog, etc.). Previous balloon-borne measurements in the Svalbard Islands of Arctic show vertical temperature profile measurement, turbulence and radiation measurement, , aerosol particle concentration, optical properties, black carbon (BC) profile and chemical composition measurements. ,, Recent balloon-borne measurements in the Alaskan Arctic show aerosol and thermodynamic stratification, but the aerosol composition was not investigated to understand the aerosol processes and their sources. Through this study, we are trying to fill the knowledge gap by probing the size-resolved chemistry and sources of aerosol in a vertically stratified Arctic atmosphere.…”

Case studies of the wind field around Ny-Ålesund, Svalbard, using unmanned aircraft

“…At larger scales, temperature differences between fjord water and open sea and synoptic processes play a role. Temperature and moisture inversions are common in the Arctic ABL (Egerer et al 2021). Thermal differences between frozen and open water can lead to shallow convection and the development of internal boundary layers (Svendsen et al 2002).…”