Stratospheric Influence On The Breakdown Of A January 2009 Blocking Episode

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In previous research on atmospheric blocking the interest has primarily been on the onset of blocking. To fully understand a blocking episode, the end, or breakdown, must also be investigated. The focus of this research was to examine the dynamics of block breakdown, with special notice to the stratospheric influence. Several factors that have been previously discussed in block onset, including advection of quasi-geostrophic potential vorticity, temperature advection, and adiabatic temperature changes, were examined both at block breakdown and block onset for comparison. The calculations were done on Weather Research and Forecasting (WRF) model runs. The WRF was initialized with three different types of initial and boundary conditions from the blocking episode on 10-20 January 2009: a Global Forecast System (GFS) Final Analysis, GFS real-time 180 hour forecast, and modified GFS real-time 180 hour forecast. To perform the runs based on modified GFS forecasts, several temperature modifications were made in both the stratosphere and lower troposphere on both onset and breakdown runs of the WRF. The impact of the modifications were observed to be the greatest magnitude at block breakdown. Cooling the stratosphere had the effect of sustaining the block for up to 12 hours, and up to 24 hours longer when the troposphere was warmed. The modification at block onset did not change the timing significantly but did impact the strength. In the future, this technique will be applied to other case studies so that the results may be corroborated, as one case study does not indicate a more general pattern.

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