Visibility and Fog Synoptic and Mesoscale Variability over Marambio Base, Antarctic Peninsula

Summertime aviation, research, and field campaigns in Marambio Base, Antarctic Peninsula (AP), and surrounding areas, are frequently affected by low visibility and fog.  Additionally, upper-air soundings in the area are launched weekly, limiting the study of the synoptic time scale variability of these hazards. A special field campaign was designed to fill this observational gap, and to examine the drivers of fog events.  A three week-long intensive observation campaign during February 2023 successfully captured the evolution and vertical structure of two multiday fog episodes that were later interrupted by westerly Foehn winds, favoring sudden warming, drying, and clear skies over eastern flank of the AP.  This dataset is also used to evaluate and assess the skill of regional climate simulations using the Global Forecasting Systems data and the Polar-WRF model.  We carried out the later modeling activities to examine the mesoscale characteristics of the interplay between the fog episodes and the Foehn winds.  This study shows the analyses of the special upper-air observations and modeling simulations, with emphasis in the description of the observable and predictable mesoscale ingredients and their relationship with synoptic forcings. We found a cycle that modulates visibility and fog: (i) low visibility ahead of the synoptic trough bringing a deep northerly moistening and warming dominating warm advection fog on the northeastern side of the AP; (ii) an enhanced mid-level inversion is formed by adiabatic warming due to westerly winds on the lee side of the AP limiting mixing; (iii) visibility increases as Foehn winds warm up and dry out the low-level atmosphere west of the AP; (iii) a meso-low (heat-low) developed on the lee side of the AP that later moved eastward with the synoptic trough, bringing cooler southerly air masses that lower visibility and favoring cold advection fog; finally (iv) cooling is maintained ahead of the synoptic ridge sustaining cold advection fog.  Polar-WRF helped us diagnose the mechanistic nature of the fog events, while providing intricate multiscale connections modulating visibility in the region.