17:15 〜 19:15
[ACG52-P14] A case study on low-level clouds associated with low-level jet observed during MOSAiC
キーワード：混合相層状雲、下層ジェット、境界層
Arctic low-level clouds are often observed as mixed-phase clouds composed of super-cooled liquid and ice particles. These are known to modulate surface energy budgets through long-wave radiation due to their long lifetime, and therefore may play a role in formation of sea ice (cloud-sea ice feedback). The longevity can be connected to the turbulence in cloud scales, which is attributed. to buoyancy and mechanical generation. We analyzed whole period of the MOSAiC campaign to identify long-lasting Arctic mixed phase clouds, and categorized the clouds into “cell” and “roll” types based on boundary layer parameters. One of the roll types, observed on 2019 Nov 17 to 18, was found to contain low-level jets, which is the mechanical source of turbulence. In this study, we investigate relationships among synoptic conditions, depth of neutral stability layers, low level jets, and cloud distribution of the event.
The data used are radio sonde data and cloud microphysics retrievals available from ARM MOSAiC datasets, ERA5 reanalysis, CALIPSO Lida Level 2 Vertical Feature Mask (VFM), and Suomi NPP L2 cloud property products.
We found that the vertical profiles of temperature and horizontal winds are well represented in ERA5 compared to the sonde data. However, specific humidity and cloud mixing ratios were found underestimated below 3 km. The low level jet was found around 500 m above surface, reaching 25 m s-1. The low-level jet is located in the west of a surface low pressure, and relatively warm and moist air intruded into the south of the jet, forming a front. The wind speed and direction were in a good agreement with geostrophic winds. We hypothesize that the slow-moving low pressure system is the main factor for 16-hour lifetime of the mixed-phase clouds and sustained coupled state. Suomi cloud height products show good agreement with sonde moisture profiles and ground-based remote sensing data. However, the cloud phase products from CALIPSO and Suomi appear to be different from the ground-based counterparts.
The data used are radio sonde data and cloud microphysics retrievals available from ARM MOSAiC datasets, ERA5 reanalysis, CALIPSO Lida Level 2 Vertical Feature Mask (VFM), and Suomi NPP L2 cloud property products.
We found that the vertical profiles of temperature and horizontal winds are well represented in ERA5 compared to the sonde data. However, specific humidity and cloud mixing ratios were found underestimated below 3 km. The low level jet was found around 500 m above surface, reaching 25 m s-1. The low-level jet is located in the west of a surface low pressure, and relatively warm and moist air intruded into the south of the jet, forming a front. The wind speed and direction were in a good agreement with geostrophic winds. We hypothesize that the slow-moving low pressure system is the main factor for 16-hour lifetime of the mixed-phase clouds and sustained coupled state. Suomi cloud height products show good agreement with sonde moisture profiles and ground-based remote sensing data. However, the cloud phase products from CALIPSO and Suomi appear to be different from the ground-based counterparts.