Research Catalog: CGD's Climate Analysis

	Figure 1. The hydrological cycle. Estimates of the main water reservoirs, given in plain font in 103 km3, and the flow of moisture through the system, given in slant font in103 km3/yr, equivalent to Exagrams (1018 g) per year. (Trenberth et al. 2006a). High resolution figure.
	Figure 2. Warm – cold ENSO event anomaly composites of precipitation during DJF for CAM3 (top) and CMAP (bottom). The contours are ? 0.25, 0.5, 1, 2, 4, and 8 mm day-1. High resolution figure.

The vertical temperature structure of the atmosphere

An analysis (Trenberth and Smith 2006) was performed of the full three-dimensional spatial structure of the temperature field monthly mean anomalies from ERA-40 for a core region of the tropics from 30?N to 30?S, with results projected globally using regression. The focus is on the first three empirical orthogonal functions (EOFs), two of which have primary relationships to El Niño Southern Oscillation (ENSO) and feature rather different vertical structures. The third (EOF-2) also has a weak ENSO signature but a very complex vertical structure and reflects mainly nonlinear trends, some real but also some in large part spurious and associated with problems in assimilating satellite data. The vertical coherence of all patterns suggests that they should be apparent in broad layer satellite temperature records but that stratospheric anomalies are not independent. The quite different three-dimensional structure of these different patterns highlights the need to consider the full structure outside of the Pacific and at all vertical levels in accounting for impacts of ENSO, and how they relate to the global mean.

Jim Hurrell, Jerry Meehl and Tom Wigley served as lead authors on the U.S. Climate Change Science Program (CCSP) Synthesis and Assessment Product 1.1: Temperature Trends in the Lower Atmosphere: Steps for Understanding and Reconciling Differences. Specifically, Hurrell and Meehl, with V. Ramaswamy (GFDL) coauthored the introductory chapter dealing with the basic thermal structure of the atmosphere (Ramaswamy et al. 2006), while Wigley wrote the Executive Summary of the Report (Wigley et al. 2006) as well as an Appendix describing statistical issues associated with trend estimation (Wigley 2006a), and he further contributed to another chapter (Santer et al. 2006b).

The assessment product was motivated by previously reported discrepancies between the amount of warming near the surface and higher in the atmosphere that has occurred over the past 25 years or so. These discrepancies have been used to challenge the reliability of climate models and even the reality of human-induced climate change. The major conclusion of the report is that the discrepancy no longer exists, because errors in the upper atmosphere data have been identified and corrected. New data sets have been developed that do not show such discrepancies.

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