Southwest Pacific temperatures: trends in maximum and minimum temperatures

Diurnal temperature trends are described for newly homogenised climate data sets for a large area of the South Pacific. The diurnal trends differ from those documented for Northern Hemisphere land areas, where decreases are observed in the diurnal temperature range as a result of increases principally in minimum temperature. The Southwest Pacific divides into four regions that share coherent diurnal temperature trends over the past five decades. Two regions southwest of the South Pacific Convergence Zone (SPCZ) display steady warming in mean temperature. The other two regions, located northeast of the SPCZ, cooled in the 1970ʹs and warmed in the 1980ʹs. The warming in three of the four regions can be attributed to increases in both mean daily maximum (mostly daytime) and mean daily minimum (mostly night time) temperature, with little change in the diurnal temperature range. In New Zealand, modification of the regional temperature trend occurs as atmospheric circulation interacts with the high orography, producing different local behaviour in trends of maximum and minimum temperature and diurnal temperature range. The present results come from sites where there can be no question of any urban influence. Most of the Southwest Pacific sites provide a very good climate monitoring platform for the surrounding oceans because of their island location.