The interannual variations in the northern hemisphere storm tracks between 1949-1999 using unassimilated radiosonde data is examined, and compared to similarly derived quantities using the NCEP/NCAR reanalysis at sonde times and locations. The effects of the temporal gaps in sonde data are also estimated by comparing results using the reanalysis data at all synoptic times and at sonde times only. This is done with the motivation of determining the extent to which the storm track variations in reanalysis data are real. Emphasis is placed on assessing previous findings, based on NCEP/NCAR reanalysis data, that both storm tracks intensified from the 1960's to the 1990's with much of the intensification occurring during the early 70's, and that the Atlantic and Pacific storm tracks are significantly correlated.
Sonde data suggests the Atlantic storm track intensified during the 1960's to 1990's, but the intensification was weaker than the reanalysis suggests. The larger trend in reanalysis is due to an overall decrease in biases with time. In the Pacific storm track entrance and exit regions sonde data shows notable decadal time scale oscillations, similar to the reanalysis, but no significant overall positive trend. Sonde does show a positive trend over Canada, consistent with a Pacific storm track intensification and north-eastward shift, but lack of data over the storm track peak prevents drawing any strong conclusions. The biases in the reanalysis are found to have a strong spatial pattern, with the largest biases being over the Pacific entrance region (Japan).
The correlation between the Atlantic and Pacific storm tracks in sonde
data (which exists over the storm track entrance and exit regions) is not
as significant as in the reanalysis, with differences being mostly due
to the decadal time scale variations of the storm tracks rather than their