Comparison between era-interim and era-40 in the tropical tropopause region

Resumen

Reanalyses are fundamental tools in climate and variability studies. Their applicability runs through a wide range of fields: from the performance of empirical analyses to their use as initial condition or validation for general circulation models (GCM). In the last years the active role of the stratosphere in the climate system has been recognized, and the necessity to accurately study its climatological characteristics and variability has arisen.  In the middle atmosphere reanalysis data are even more helpful due to the short number of observations. However, it is crucial to understand the limitations and biases in these databases, caused either by model errors, by the assimilation techniques or coming directly from observations.    With the philosophy of evaluating the current understanding and uncertainties in the stratosphere, the SPARC Project (Stratospheric Processes And their Role on Climate) brought together eleven middle-atmosphere climatologies and made detailed comparisons (Randel et al., 2004a). One of the conclusions of this intercomparison was that the best database in reproducing tropical processes in the middle-atmosphere is ERA-40 reanalysis, the last one by ECMWF at that moment.   More recently a new reanalysis, named ERAInterim, has been developed at the ECMWF (Simmons et al., 2006). This reanalysis presents several improvements in key aspects affecting the stratosphere. A brief description of these advances is given in section 2.