Hristo Chipilski-March 8

Impact of Assimilating Boundary Layer Profilers on the Prediction of Bores and Bore-Initiated Convection: A Multi-Scale Evaluation for the 6 July 2015 PECAN Case Study

Hristo Chipilski

Friday, March 8^th

3:30pm/NWC 5600

Using data from the 6 July 2015 PECAN mission, this study examines how the assimilation of novel boundary layer (BL) profilers affects the forecasts of a bore-initiated convection event. To account for the multi-scale nature of the phenomenon, data impacts are discussed separately with respect to the (i) bore environment, (ii) explicitly resolved bore and (iii) bore-initiated convection. The findings from this work suggest that BL profilers provide considerable advantages over conventional in-situ observations, especially when retrieved data are assimilated at a high temporal frequency. The clearest forecast improvements are seen in terms of the bore environment where the assimilation of both thermodynamic and kinematic BL profilers helps reduce a pre-existing bias in the structure of the low-level jet. On the other hand, the strongly nonlinear dynamics of bores produce mixed impact results with respect to the other two forecast components. While the assimilation of the Atmospheric Emitted Radiance Interferometer (AERI) instrument results in the best convective forecasts due to the addition of moisture in the lower troposphere, it also induces a positive bias in the propagation and amplitude of the convectively-generated bore. Conversely, the negative moisture increments caused by the assimilation of wind profilers help improve the characteristics of the explicitly-resoled bore at the expense of further exacerbating the lack of bore convection in the control forecasts. Finally, this paper highlights that a successful prediction of bore-initiated convection requires an accurate representation of both the explicitly resolved bore as well as the environmental conditions ahead of it.