| Summary: | International audience The morning transition is known to break up the stable nocturnal state of the planetary boundary layer (PBL) and, by increasing shortwave downwelling radiation warms the surface developing the convective phase of the PBL. However, in arctic latitudes during winter, the cold and dark atmosphere (i.e., absence of solar radiation) prevents this mechanism from occurring. Instead, a major driver of the breakup of surface based temperature inversions (SBIs) is the direct longwave downward (LW) radiative forcing introduced by the regional changes of synoptic meteorological conditions (i.e., cyclonic advections or synoptic transients). An experimental analysis was conducted for the period from Feb 11-19, 2022 during the ALPACA field experiment where four breakup cases were recorded in the presence of transient synoptic conditions. On the basis of atmospheric soundings and vertical profiling by MPLNET backscatter Lidar, Doppler Lidar, microwave radiometer, and surface flux and radiation tower, a close examination of the PBL surface state and vertical structure changes during the breakup was conducted. Conclusions and methods to best capture this process in mesoscale modeling will be discussed in the presentation.
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