| Summary: | Tropopause polar vortices (TPVs) are upper-level cyclonic circulations that are common in high latitudes. TPVs most directly impact weather at the surface by providing baroclinic forcing for the development of Arctic cyclones (ACs), surface low-pressure systems over the Arctic Ocean and surrounding landmasses. ACs, in turn, help to drive the Arctic heat and moisture budgets via transport from the midlatitudes and govern sea ice variability on short timescales via dynamic and thermodynamic influences. Although prior studies have demonstrated and examined the link between TPVs and ACs, the exact role played by the TPV and its characteristics in the development of the surface cyclone has yet to be established. In the present study, we seek to take a step forward toward closing this gap using an idealized observing system simulation experiment (OSSE). This approach involves simulating dense dropsondes over a TPV as a surface cyclone is forming and examining the changes that the additional observations produce to the TPV and resulting surface cyclone. The ECMWF Cubic Octahedral grid Nature Run (ECO1280) is taken as the truth for the OSSE (all observations are simulated from the output of this model), and the Model for Prediction Across Scales (MPAS) is coupled with the Data Assimilation Research Testbed's (DART) ensemble adjustment Kalman filter in order to run numerical experiments. It is expected that the development of the TPV and surface cyclone will be especially sensitive to moisture observations, which influence TPV strength via diabatic processes, and that proper representation of mesoscale dynamic features along the tropopause will be key to accurate forecasts. In addition to a control in which only existing observations are simulated from ECO1280, we conduct four primary experiments assimilating additional dropsonde observations of (1) temperature, (2) humidity, (3) temperature and humidity, and (4) temperature and humidity over a broad region. All of the experiments reduce errors relative to the control ...
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