Quality of Reanalyses in the Tropics

Abstract

Broad vertical layer-averaged temperatures from the microwave sounder unit (MSU) are used as a quasiindependent validation of temperature fields from the U.S. National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) and the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalyses. While the MSU and NCEP-NCAR temperatures show fairly good agreement overall, large discrepancies with ECMWF temperatures indicate that changes in the satellite observing system may have adversely affected the ECMWF reanalyses, especially in the Tropics. Two spurious discontinuities are present in tropical temperatures with jumps to warmer values throughout the Tropics below 500 mb in late 1986 and early 1989, and further spurious interannual variability is also present. These features are also reflected in the specific humidity fields. The temperature discrepancies have a complex vertical structure with height that is not fully understood, although it seems that the problems partly arise from positive reinforcement of biases in satellite radiances with those of the assimilating model first guess. Changes in the observing system provide a limit to the usefulness of the reanalyses in some climate studies.

A 15‐year climatology of stratosphere‐troposphere exchange with a Lagrangian particle dispersion model: 1. Methodology and validation

“…Notwithstanding this latter effect, the interannual variability has a generally lower magnitude than the respective sea- sonal cycles. No significant trends can be detected, but the series for the region north of 51°N indicates a sudden jump to higher values during 1986, which coincides with changes in the satellite observing system that were noted previously to cause a discontinuity in the ERA-15 data set [Trenberth et al, 2001;Kållberg, 1997]. Other discontinuities in the ERA-15 data (e.g., one in 1989) were found by Trenberth et al [2001], which possibly coincide with smaller discontinuities in our net STE fluxes.…”

Changes in the width of the tropical belt due to simple radiative forcing changes in the GeoMIP simulations

“…An expansion of the Hadley cells has been detected in reanalyses (Hu and Fu, 2007;Johanson and Fu, 2009;Stachnik and Schumacher, 2011;Davis and Rosenlof, 2012;Davis and Birner, 2013;Nguyen et al, 2013;Chen et al, 2014). Tropical expansion estimates based on reanalyses, however, may suffer from spurious trends and discontinuities in basic meteorological fields (Trenberth et al, 2001;Bengtsson et al, 2004). The rate of Hadley cell expansion and even the mean strength of the Hadley cells vary among the reanalyses (Stachnik and Schumacher, 2011), which could indicate that the meridional winds are not well constrained.…”

Dynamically and Kinematically Consistent Global Ocean Circulation and Ice State Estimates

“…More elaborate accounts can be found in Wunsch (2006) and among others. Within the atmospheric sciences literature itself, numerous publications exist (e.g., Trenberth et al, 1995Trenberth et al, , 2001Bengtsson et al, 2004;Bromwich and Fogt, 2004;Bromwich et al, , 2007Bromwich et al, , 2011Thorne, 2008;Nicolas and Bromwich, 2011), warning against the use of DA and the associated "reanalyses" for the study of climate change. These warnings have been widely disregarded.…”