Sensitivity and Predictability of Mesoscale Polar Lows

Mesoscale polar lows are notoriously difficult to predict, particularly with regard to their genesis. In this study, we compare and contrast initial condition sensitivity and multi-scale predictability aspects of several polar lows with an emphasis on diabatic processes and the influence of middle- and upper-tropospheric potential vorticity (PV) anomalies. The adjoint, tangent linear, and nonlinear models for the atmospheric portion of the nonhydrostatic COAMPS system are applied using nested grids. The adjoint diagnostics indicate that the formation and intensification of severe winds in polar lows are especially sensitive to perturbations in the middle- and lower-tropospheric PV anomalies associated with upper-level PV maxima including tropopause polar vortices (TPVs). Polar lows are also sensitive to the surface flux distribution and boundary layer characteristics. The adjoint is used to quantitatively assess the sensitivity of polar lows to the fluxes relative to middle- and lower-tropospheric PV. The results of this study underscore the need for accurate observations in these regions of strong sensitivity including within the boundary layer associated with intense surface fluxes, and data assimilation systems that can adequately assimilate these observations in order to reduce the forecast uncertainties for these severe cyclones. However, given the nature of the sensitivities and the potential for rapid perturbation and error growth, the intrinsic predictability of the genesis and mesoscale characteristics of polar lows is limited.