| Summary: | The observed rapid changes in the Arctic are important to quantify not only for understanding the region, but also for understanding how processes between the Arctic and lower latitudes can interact to culminate in high-impact weather events. The tropopause polar vortex (TPV) is an Arctic feature that can interact with mid-latitude atmospheric flow, in which the maintenance and intensification of TPVs depends on diabatic processes. Improved knowledge and a better representation of TPV-mid-latitude interactions in numerical prediction models could extend forecast skill beyond the present-day barrier of 7-10 days. This study investigates TPVs in the Arctic and their interactions with mid-latitude atmospheric flow using a newly developed global modeling system. This modeling system couples an ensemble Kalman filter (EnKF) data assimilation software (DART) with the Model for Prediction Across Scales (MPAS) global model called MPAS-DART. This system utilizes a newly developed non-hydrostatic global model that allows for smooth transitions from coarse to fine mesh resolutions. The EnKF data assimilation technique allows for flow-dependent background error covariances within MPAS-DART, which is especially important in data sparse regions like the Arctic. Evaluation of MPAS-DART over the Arctic shows reasonable consistency between the model and observations, however, there are some notable points for improvement. There is a cold bias in the upper-troposphere and lower-stratosphere levels where TPVs are often found, which is a result of too much cooling from the model's longwave radiation scheme. This overactive longwave cooling is associated with a moisture bias found in the same layer. Assimilating special dropsonde observations from a field campaign flight mission through a TPV mitigates the moisture bias, especially in analyses. Implementing an improved moisture initialization procedure is able to alleviate the moisture bias, even in the absence of special observations. The moisture bias and associated longwave ...
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