Alternative metrics for measuring heating trends, with possible connections between the surface and troposphere

The term "global warming" has been used to describe the observed surface temperature increases during the last century. The proper use of this term, however, requires using surface heat content to monitor this aspect of the climate system. Surface observation site microclimates highlight the influence of land surface characteristics on surface heat trends. Exposure metadata should be improved. The real changes in heat content of the Earth's climate are not fully described by temperature alone. Moist enthalpy is more sensitive to surface vegetation properties and more accurately depicts surface heating than temperature. Monitoring trends in moist enthalpy, or equivalent temperature, could help explain the differences between previously observed temporal trends in surface and tropospheric temperatures. Surface heating trends have usually indicated warming with time, while tropospheric results have been mixed. Temperature and equivalent temperature trends from 1982--1997 are examined for sites in the eastern United States. Overall, surface trends show slight cooling in temperatures and slight warming in equivalent temperatures. Surface equivalent temperature trends are generally smaller in magnitude than temperature trends. Seasonally, surface trends show the most warming in winter and the most cooling in fall. Equivalent temperature trends during the winter and fall are generally identical in sign to, and larger than, temperature trends, but opposite in sign during the spring and summer. Trend patterns vary widely, however, between individual sites. Local land cover has a large influence on heating trends. Urban sites show more warming, or less cooling, than rural sites. Tropospheric temperature and thickness trends for radiosonde data and collocated reanalysis data are examined from 1979--2001. Radiosondes compare favorably to reanalysis data. The upper troposphere indicates cooling, while the lower troposphere is neutral or slightly warming. Comparisons of tropospheric and surface trends for the eastern United States show similar seasonal patterns. Lower-tropospheric trends in the eastern United States show some cooling in the fall, providing a possible connection between the surface and troposphere. Continued work with alternative heating metrics will increase understanding of microclimate influences and surface-troposphere connections.