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Yale Radiosonde Analysis Project

Background

Recent analyses of radiosonde, surface, and satellite temperature trends have produced discordant results, which have caused some to question the reliability of our current estimates of global warming. Recently, some convergence seems to be occurring between the satellite and ground-based data for the period of overlap. More importantly, however, the period since 1980 or so has shown different trends in lapse rate (related to atmospheric convective instability) than the period prior to that. Theories of climate predict that tropical lapse rates should become slightly shallower with warmer surface temperatures due to pseudoadiabatic convective mixing, while extratropical lapse rates should be related to the equator-to-pole temperature difference due to slantwise eddy mixing. Anomalies from theory should decay rapidly (days in the Tropics, weeks in the extratropics). The observed changes, particularly a shift in the Tropics near 1976, seem to be at odds with these theories.

This figure shows changes in lower-troposheric lapse rate in several latitude bands from 87 radiosonde stations; red curves are prior to manual removal of estimated heterogeneities by Lanzante et al. 2003b (their Fig. 7b).

A serious impediment to accurate detection of long-term climate signals in the radiosonde network is the known presence of artificial discontinuities due to unknown changes in instrumentation and data processing. A second problem is the sporadic operation of many stations. Estimates of long-term changes are sensitive to both problems. Currently, trend estimates are quoted based on the best data available and caveats are given regarding these problems. Small subsets (<100) of the available (~1000) stations are usually used to reduce these problems, leading to suboptimal spatial coverage, but still without eliminating the problems.

The Iteratively Homogenized Dataset

We have produced a new dataset following the iterative universal Kriging procedure described in Sherwood (1999) and Sherwood (2007). The key to this approach is to estimate the climate signals, missing data, and instrument change effects synergistically, i.e., iteratively, exploiting the spatial and temporal coherence of natural variability. The resulting dataset includes temperature and wind shear at mandatory reporting levels from 527 radiosonde stations, from 1959-2005. The stations are divided into two groups: 460 A stations having substantial data at two times of day, and 67 B stations not having these (B stations are included only in the Tropics and southern hemisphere). Trends in A stations are more reliable.

The procedure appears to have been successful in eliminating systematic temperature biases in most regions, although the deep tropics appear to retain cooling biases over time that we still cannot identify; these may be due to changes that are too numerous to detect, or not step-like. A penalty paid for the elimination of systematic biases is that random errors are not reduced as effectively as other methods, so that individual stations now have trends that are about as variable as in the raw data; however, the accuracy of zonal means appears to be significantly improved. The dataset and some trend results are described more fully in Sherwood et al. (2008) .

Wind homogenization had only a small effect, so we are not proposing that our homogenized wind data are significantly better than the raw data. We interpret this as an indication that significant shifts in wind shear are isolated and not a serious problem across the network, although further studies should examine this issue more carefully. Also, this statement does not automatically apply to wind speed or direction per se, only to vertical vector wind shear, the variable that was actually homogenized.

The data are available in two NetCDF files. The 460 A stations are first, followed by the 67 B stations. In adjustment files, these two groups are contained in separate variables.

Please see the README file for further details. To obtain the files below, right-click on the name (sorry our server doesn't allow ftp so it's done w/http). I also have a page providing software for iterative universal Kriging.

COMING SOON (But not ready yet):

Some literature relevant to this project

Last updated 3/25/2008.