Comparisons of polar processing diagnostics from 34 years of the ERA-Interim and MERRA reanalyses

Abstract

Abstract. We present a comprehensive comparison of polar processing diagnostics derived from the National Aeronautics and Space Administration (NASA) Modern Era Retrospective-analysis for Research and Applications (MERRA) and the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Reanalysis (ERAInterim). We use diagnostics that focus on meteorological conditions related to stratospheric chemical ozone loss based on temperatures, polar vortex dynamics, and air parcel trajectories to evaluate the effects these reanalyses might have on polar processing studies. Our results show that the agreement between MERRA and ERA-Interim changes significantly over the 34 years from 1979 to 2013 in both hemispheres and in many cases improves. By comparing our diagnostics during five time periods when an increasing number of higher-quality observations were brought into these reanalyses, we show how changes in the data assimilation systems (DAS) of MERRA and ERA-Interim affected their meteorological data. Many of our stratospheric temperature diagnostics show a convergence toward significantly better agreement, in both hemispheres, after 2001 when Aqua and GOES (Geostationary Operational Environmental Satellite) radiances were introduced into the DAS. Other diagnostics, such as the winter mean volume of air with temperatures below polar stratospheric cloud formation thresholds (V PSC ) and some diagnostics of polar vortex size and strength, do not show improved agreement between the two reanalyses in recent years when data inputs into the DAS were more comprehensive. The polar processing diagnostics calculated from MERRA and ERA-Interim agree much better than those calculated from earlier reanalysis data sets. We still, however, see fairly large differences in many of the diagnostics in years prior to 2002, raising the possibility that the choice of one reanalysis over another could significantly influence the results of polar processing studies. After 2002, we see overall good agreement among the diagnostics, which demonstrates that the ERA-Interim and MERRA reanalyses are equally appropriate choices for polar processing studies of recent Arctic and Antarctic winters.

Climatology and interannual variability of dynamic variables in multiple reanalyses evaluated by the SPARC Reanalysis Intercomparison Project (S-RIP)

“…There are very few observation sites in this latitude zone. Manney et al (2005) and Lawrence et al (2015) have shown that reanalyses of temperatures in the polar stratosphere can differ significantly depending on what observations are available. Differences greater than 0.5 K during the TOVS period extend to 70 hPa.…”

“…They also pointed out the difficulties of the transition from the TOVS to ATOVS observations, most notably in the upper stratosphere and lower mesosphere. Lawrence et al (2015) used polar processing diagnostics to compare the ERA-I and MERRA. They noted good agreement in the diagnostics after 2002, but cautioned that the choice of one over the other could influence the results of polar processing studies.…”

Interannual variations of early winter Antarctic polar stratospheric cloud formation and nitric acid observed by CALIOP and MLS

“…The extent to which the polar vortex distorts and wanders around the South Pole can be assessed by a dynamical diagnostic such as the vortextemperature concentricity (VTC). This hybrid temperaturevortex diagnostic (Lawrence et al, 2015, see their Eq. 1 and Fig.…”

Accuracy and precision of polar lower stratospheric temperatures from reanalyses evaluated from A-Train CALIOP and MLS, COSMIC GPS RO, and the equilibrium thermodynamics of supercooled ternary solutions and ice clouds

“…In recent decades, the augmentation of the coverage of polar regions by an increase in satellite missions, including assimilation of research satellite data, and notably the advent of GNSS RO, has dramatically improved the situation (Wang and Lin, 2007). Lawrence et al (2015) examined a 34-year record of polar processing diagnostics for MERRA and ERA-I reanalyses. They documented the introduction of new data streams and noted better agreement in the post-2001 time frame following the assimilation of Aqua Atmospheric Infrared Sounder (AIRS) and Geostationary Operational Environmental Satellite (GOES) radiances into both schemes.…”