Impact of Assimilating WindBorne Observations Following Different Parts of a TPV on the Predictability of an Arctic Cyclone during THINICE

The impact of assimilating in situ observation inside a Tropopause Polar Vortex (TPV) from a novel weather balloon system, the WindBorne, on the predictability of the TPV and the coupled Arctic Cyclone (AC) is investigated using an AC case from the 2022 THINICE filed campaign. Two WindBornes continuously sampled inside and near the center of the TPV at various vertical levels for 27 hours before the cyclogenesis. The 27 hours were divided into three phases based on the different vertical levels that the WindBornes primarily sampled. The RMSE of the forecasted cyclone at the tropopause, mid troposphere, and surface is reduced as more phases of WindBorne are assimilated from 12-hour to 36-hour forecast lead time. This period corresponds to when the surface cyclone became superimposed with the TPV and rapidly deepened. Comparing the experiment with three phases of WindBorne observations assimilated versus the control experiment with no WindBorne assimilated, the surface cyclone expands southwestwards towards the TPV and forms a stronger coupled structure. Two aspects of analysis improvement leading to the improved AC predictability are revealed. First, a stronger circulation at and below the tropopause of the TPV is observed, which leads to stronger coupling between the TPV and the surface cyclone in the forecast. Second, a mesoscale shortwave embedded in the synoptic trough was better constrained as more phases of WindBorne observations were assimilated. The northern part of the TPV, which evolved from the shortwave trough, was therefore forecasted to be stronger. The sensitivity of forecast performance to horizontal localization parameter of the WindBorne observations is also studied. Larger localization parameters (2000 km and 3000 km) results in larger RMSE reduction compared to smaller values (500 km and 1000 km).