The two SSWs that will be analyzed occurred on: 9 February 2010 and 7 January 2013. Calculated with NASA’s MERRA-2 dataset, both of these events had similar magnitudes of the 40-day average tropopause 45°-75°N zonal-mean meridional eddy heat flux anomaly, hereinafter heat flux anomaly, that fall in the top half of all 22 SSWs identified from 1980 to 2015. The 9 February 2010 SSW 40-day average heat flux anomaly was 4.34 K m s-1 and the 7 January 2013 40-day average heat flux anomaly was 5.13 K m s-1. Although this time-mean tropopause forcing was similar between the SSWs, the variability in the high-frequency tropospheric flow within these 40-days prior to the SSWs was different. These differences were manifest in the number of SSW-precursor tropospheric blocks: prior to the 9 February 2010 SSW there were 3 mid-tropospheric blocks while prior to the 7 January 2013 SSW there was only 1 block about a month prior.
This presentation will show the tropospheric, tropopause, and stratospheric evolution and coupling within the 40-days prior to the onset of the SSWs in NAVGEM-HA and MERRA-2 dataset. The goal is to determine how well NAVGEM-HA analyses represent the tropospheric forcing that play a role in the onset of SSWs compared to the MERRA-2 dataset, which assimilates less stratospheric satellite data and has a lower model top (i.e., ~80 km) than NAVGEM-HA. This presentation will address the questions: Does a higher model top and more middle atmosphere assimilation make a significant difference in the representation of: (1) the synoptic evolution of SSWS, (2) the tropopause forcing prior to SSWs, (3) the tropospheric evolution prior to SSWs, and/or (4) the downward propagation of anomalies from the stratosphere to the troposphere? The answers to these questions will provide a basis for future work exploring NAVGEM-HA forecasts of extreme stratospheric events.
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