Changes of diurnal temperature range in taiwan and their large-scale associations: Univariate and multivariate trend analyses

By analyzing the long-term (1950-2007) variability of diurnal temperature range [DTR; daytime maximum (T_max minus nighttime minimum (T_min)] at 21 stations in Taiwan, this study applies univariate analysis, a trend-free prewhitening procedure combined with a modified Mann-Kendall test, and EOF-based multivariate trend analysis (TEOFA) to the ranked station DTR, T_max, and T_min. To reveal the large-scale associations with the local TEOFA results, this study also uses global gridded T_max, T_min, nighttime marine air temperature, and sea level pressure (SLP) datasets archived at the U.K. Meteorological Office Hadley Centre. On the basis of the signs and relative magnitudes between the annually-mean T_max and T_min trends, the stations can be classified into three types through univariate analysis. With a common increasing T_min, type-A (type-B) stations have an increasing T_min(T_max faster than T_max (T_min whereas type-C stations have a decreasing T_max. Both type-A and type-C (type-B) thus show(s) a decreasing (an increasing) DTR. For most stations, the increasing Tmin is the largest in December-February. In contrast, all type-B stations have an increasing Tmax peaking in June-August. Noticeably, six of nine type-B stations, either in the remote islands or in the seaports, are particularly influenced by the ocean. Three DTR trend modes stand out of TEOFA. The first mode, TEOF1, captures increasing DTR trends at four type-B stations and decreasing DTR trends elsewhere. The associated increasing T_min(T_max trend is consistent with the increasing (decreasing) clouds during nighttime (daytime) and is well-correlated with the largescale patterns, suggesting that it is part of the global warming scenario. Nevertheless, TEOF₁ also captures a decreasing T_max trend in Taiwan's highly developed western plains (i.e., type C) and eastern China where an increasing SLP pattern is observed, implying the anthropogenic forcings on DTR. TEOFM₂ (TEOF₃) depicts the decadal-to-interdecadal DTR variability in central (northern) Taiwan. Evolution of TEOF2 shows smaller (larger) amplitude before 1970s (after mid-1980s). The associated large-scale patterns suggest that TEOF2 (TEOF₃) captures the relationship between an intensified (weakened) East Asian winter monsoon and La Nin ̃a (El Nin ̃o)-like condition in eastern (central) equatorial Pacific. Embedded in a Pacific-Japan-like teleconnection pattern, the southwestward intrusion of Pacific subtropical anticyclone in June-August that signifies the weakened southwesterly monsoon is also depicted by TEOF₂.