Different relationship between decadal polar temperature and eddy heat flux in the lower stratosphere in mid-winter from early spring

The lower-stratospheric polar temperatures and the eddy heat fluxes in mid-winter (January) and early spring (March) for the past 50 years were investigated based on NCEP/NCAR reanalysis data. The monthly mean polar temperatures at 70 hPa in January, February and March are compared with the eddy heat fluxes at 70 hPa averaged for the preceding two months, respectively. The eddy heat flux is divided into its stationary and transient components. Year-to-year variations of the polar temperature at 70 hPa are highly correlated with those of the stationary eddy heat flux in both mid-winter and early spring. However, the decadal components of polar temperature and eddy heat flux show different patterns. Examining the stationary and transient eddy heat fluxes separately, we show that the polar temperature variation in January is correlated with the stationary eddy heat flux from November 15 to January 15 (former period), whereas polar temperature in March is correlated with the transient eddies from January 15 to March 15 (latter period). The climatological mean values of stationary and transient eddy heat fluxes at 70 hPa for the two periods are similar, but the variance of the stationary eddies is larger in the former period and the variance of the transient eddies is larger in the latter period. The decadal variations of polar temperature in February and the corresponding eddy heat fluxes from December 15 to February 15 are much weaker than those of January and March.