Consistency Check for Trends in Surface Temperature and Upper-Level Circulation: 1950–1992

Abstract

A time series of 43 years of observed monthly mean air temperature at 109 sites in the 48 contiguous United States is compared to monthly mean air temperature specified from hemispheric gridded 700-mb heights. Because both upper-air and surface data have problems that may limit their use in climate change studies, this comparison could be considered a mutual consistency check. Cooling (by about 0.5°C) from 1951 to about 1970 and subsequent warming (also by 0.5°C) that continues through the present are found in both datasets, indicating that these interdecadal changes are probably real. In the List several years the specified temperatures were often colder than those observed. This prompted an investigation of whether the ?residual? (specified minus observed) has recently been large (and negative) compared to the earlier part of the record. It was found that for the same 700-mb height field, surface temperatures were almost a degree Celsius warmer in the last few years than they were in the early 1950s, but considering the variability of the residuals over the 1950?92 period, the recent cold residuals may not yet be strikingly unusual. By comparing the full set of 109 stations to a ?clean? subset of 24, the impact of common problems in surface data (station relocation, urbanization, etc.) was found to be quite small. The rather favorable comparison of observed surface temperatures and specified surface temperatures (which suffer from upper-air analysis / observation changes over the years) indicates that their respective data problems do not appear to invalidate their use in studies of interdecadal temperature change.