1. Did we expect a disturbed stratosphere in 2009-10? QBO-EAST ? (Holton & Tan 1980) EL NINO ? (Ineson and Scaife, 2009; Bell et al 2009) SOLAR MINIMUM ? (Labitzke & Van Loon 1988; Kodera and Kuroda 2002) TREND ? (Chartlon et al 2008; Bell et al 2010)... all fit with a weaker-than-average polar vortex QBO 90N 30hPa Temperature QBO- east

2. Key features of stratospheric flow: Minor warming – early December Strong vortex until mid-January – major stratospheric sudden warming (SSW) Weak, disturbed vortex late winter – persistent easterlies over polar cap North Pole temperature at 10hPa ZMZW at 60N 10hPa Courtesy Andrew Charlton-Perez http://www.met.reading.ac.uk/research/stratclim/current/ MinorMajor

3. ZMZW 60-90N Pressure Dec-01Jan-01Feb-01Mar-01Dec-15Jan-15Feb-15 NAM index Dec-01Jan-01Feb-01Mar-01Dec-15Jan-15Feb-15 NAO Dec-01Jan-01Feb-01Mar-01Dec-15Jan-15Feb-15 ERA-40 operational analysis

4. - 08-12-2009 - lower stratospheric split Strong mid-winter (Dec – Jan) - 01-02-2010 - displacement SSW event Courtesy Andrew Charlton-Perez

5. ZMZW 60-90N Pressure Dec-01Jan-01Feb-01Mar-01Dec-15Jan-15Feb-15 NAM index Dec-01Jan-01Feb-01Mar-01Dec-15Jan-15Feb-15 NAO Dec-01Jan-01Feb-01Mar-01Dec-15Jan-15Feb-15 ERA-40 operational analysis

6. growth in vertical EP-flux is pre-blocking Was it driven by PNA-type pattern? Wave-2 confined to lower stratosphere January blocking precedes SSW Also strong PNA-like pattern, no NAO Low EP flux (10hPa) in late winter due to persistence of easterly anomalies in lower stratosphere 16 NOV16 DEC16 JAN16 FEB16 MAR16 APR EP-flux vector (10hPa, 60N) 16 NOV16 DEC16 JAN16 FEB16 MAR16 APR Vertical EP-flux (100hPa) EQ 90N Tropospheric precursors? NOV 500hPa Z’