Response to Comment on "Contributions of Anthropogenic and Natural Forcing to Recent Tropopause Height Changes"

R. A. Pielke Sr., T. N. Chase, Science303, 1771 (2004); www.sciencemag.org/cgi/content/full/303/5665/1771b.

B. D. Santeret al., Science301, 479 (2003).

E. Kalnayet al., Bull. Am. Meteorol. Soc.77, 437 (1996).

B. D. Santeret al., J. Geophys. Res.108, 4002 (2003) (DOI 10.1029/2002JD002258).

J. R. Lanzante, S. A. Klein, D. J. Seidel, J. Clim.16, 241 (2003).

S. Pawson, M. Fiorino, Clim. Dyn.15, 241 (1999).

G. Kellyet al., Mon. Weath. Rev.119, 1866 (1991).

J. R. Eyre, Q. J. R. Meteorol. Soc.113, 279 (1987).

A. N. Basist, M. Chelliah, Bull. Am. Meteorol. Soc.7, 1431 (1997).

The NESDIS retrievals use radiances from multiple instruments: MSU, the Stratospheric Sounding Unit (SSU), and the High Resolution Infrared Radiation Sounder (HIRS). Clouds strongly affect the infrared radiances measured by HIRS, but have less impact on the microwave radiances measured by MSU. Retrievals for cloudy and partly cloudy conditions are therefore dominated by MSU-derived radiances. Temporal changes in the cloud identification algorithms used in the NESDIS retrievals may have impacted retrieval homogeneity by inducing systematic changes in the “mix” of MSU and HIRS radiances. Systematic changes in the retrievals also occurred in the late 1990s, during the transition from MSU to the Advanced MSU (AMSU) (11). The AMSU was not subject to significant cloud contamination and essentially replaced the HIRS (except for HIRS channel 12). Problems with the NESDIS retrievals are also illustrated by the fact that their assimilation into the numerical weather forecast model of the European Centre for Medium-Range Weather Forecasts (ECMWF) adversely affected forecast quality (6). This was one of the factors motivating the decision by ECMWF to assimilate satellite radiances (rather than temperature retrievals) in the ERA-15 reanalysis (14).

J. J. Bates, personal communication.

J. R. Christy, R. W. Spencer, E. S. Lobl, J. Clim.11, 2016 (1998).

B. D. Santeret al., Science301, 1047 (2003).

J. K. Gibsonet al., ERA description, ECMWF Re-Analysis Project Reports Series 1 (European Centre for Medium-Range Weather Forecasts, Reading, UK, 1997).

C. A. Mears, M. C. Schabel, F. W. Wentz, J. Clim.16, 3650 (2003).

This raises the question of why the tropopause height fingerprint from the Parallel Climate Model (PCM) is identifiable in NCEP, despite the tropospheric cooling in this data set. We attempted to explain this result in (2). NCEP's excessive stratospheric cooling, which is largely induced by biases in the NESDIS temperature retrievals (10), yields too large an increase in tropopause height. This error in stratospheric temperatures propagates into the upper troposphere, and is partly responsible for NCEP's mean tropospheric cooling, which decreases tropopause height. As noted in (2), compensating errors in stratospheric and tropospheric temperature changes must therefore influence the tropopause height detection results that we obtain with NCEP. Error compensation alone, however, cannot explain the correspondence between the detailed spatial patterns of tropopause height change in PCM and NCEP. It is far more likely that common physical mechanisms explain such similarities. We partially removed the effects of compensating errors through the “global mean removed” detection analysis and still found highly significant pattern similarities between PCM and NCEP tropopause height changes. These similarities are unlikely to be fortuitous.

We thank J. Bates (National Climatic Data Center), M. Fiorino (Lawrence Livermore National Laboratory), and S. Pawson (Goddard Space Flight Center) for valuable suggestions and comments.