Solar radiation measurements in the United States between 1916 and 1949 document widespread brightening in the mid-20th century

摘要

An analysis is presented of global radiation E-g measurements made between 1916 and 1949 at 26 sites in the continental United States. The procedures used to fill gaps in the database are described and the accuracy of the data assessed. During this period E-g averaged 172 and 41W/m(2) above the model-estimated values for the same sites during the 1960-1990 period and 7 W/m(2) below the average values estimated between 1991 and 2010; the largest changes were found at two urban sites, New York City and Pittsburgh. The major inter-annual variation found within the 1916-1949 period was a significant spike lasting a decade which reached a maximum around 1940. This episode of global brightening was attributed to reduced emissions of anthropogenic aerosols during the economic depression together with lesser cloud cover associated with the severe droughts occurring in the same decade. The widespread global brightening which occurred concurrently outside the United States is documented and a link between global brightening and global warming during the first half of the 20th century demonstrated.