On the temperature correlation of δ18O in modem precipitation

Reevaluation of modem precipitation, temperature, and isotope data permits reconciliation of previous disparate values for the correlation between delta(18)O of modem precipitation and surface temperature. Past analysis has used the mean surface temperature over the time interval of sample collection (e.g., mean weekly, monthly, or annual temperature) to calculate temperature coefficients, and different approaches at mid-latitudes yield different temperature coefficients (Deltadelta(18)O/DeltaT): spatial correlations among geographically distinct sites yield similar to0.55parts per thousand/K; seasonal variations at single sites yield 0.2-0.4parts per thousand/K; and 12 month running averages yield 0.5-1parts per thousand/K. However, there are systematic differences in temperature during precipitation events vs. time-averaged surface temperature means. Correction for this bias using hourly weather and monthly isotope data from U.S. sites yields a single value of similar to0.55parts per thousand/K for all three approaches. Revised temperature coefficients based on surface observations are also commensurate with coefficients obtained using cloud base temperatures and with theoretical distillation models (0.5-0.7parts per thousand/K). These coefficients provide a consistent basis for validation of general circulation models that incorporate stable isotopes of precipitation, and for comparison to independent estimators of the isotopic response to climate change. (C) 2004 Elsevier B.V All rights reserved.