Quality of reanalysis data during stratospheric vortex weakening and intensification events

Abstract

The quality of five reanalysis data (ERA, JRA-25, NASA-MERRA, NCEP/DOE and NCEP/NCAR) is evaluated for stratospheric vortex weakening (SVW) and intensification (SVI) events in the Northern Hemisphere winter. A case study is carried out for a record-breaking SVW event in 2009 whose spatio-temporal structure is well observed by the COSMIC GPS RO measurements. It is found that most reanalysis data captured this event reasonably well despite non-negligible biases are observed at 10 hPa especially in the JRA-25. Composite analysis further shows that the temporal structure of the SVW and SVI events, as measured by the Northern Annular Mode (NAM) index, is almost identical among the data sets. Remarkably good agreement is found not only in the onset but also in their downward propagation with time. These results indicate that reanalysis data are reliable for examining stratospheric extreme events and their impact on the troposphere in an intraseasonal time scale. © 2010 by the American Geophysical Union.