Abstract
The spatial and temporal pattern of sub-daily temperature change in mainland China was analysed for the period from 1973 to 2011 using a 3-hourly dataset based on 408 stations. The increase in surface air temperature was more significant by night between 1973 and 1992, with the fastest upward trend around local midnight being about 0.27 °C/decade, while it was more significant by day between 1992 and 2011, with the fastest upward trend being about 0.46 °C/decade in mid-late morning. The season with rapid temperature increase also shifted from winter in 1973–1992 (the largest increase happened near midnight in December, 0.75 °C/decade) to spring in 1992–2011 (the largest increase happened at in the early afternoon in March, 0.82 °C/decade). The change in the spatial distributions of the sub-daily temperature trends shows that Northeast China warmed more significantly in 1973–1992 than elsewhere, but it cooled in 1992–2011, when Southwest China was the new focus of temperature increase whereas it had previously been cooling. A preliminary analysis of the possible causes implies that changes in solar radiation, cloud cover, aerosols and the observational environments near the stations might have contributed to these observed temperature changes.
Highlights
Recent studies have shown that temperatures at different local times have had different trends
For the period 1973–2011, the temperature changes at 8, 11 and 14 Approximate Local Solar Time (ALST) were greater than those by night (Fig. 3). This result differs from the prevalent reduction of Diurnal Temperature Range (DTR) documented in the Introduction, suggesting that the forcings of surface temperature trends may have changed in recent years
The minimum daytime temperature increased at 0.56 °C/decade and the maximum nighttime temperature increased at 0.58 °C/decade. This period included the period of most rapid global warming, in which China shared. It coincided with a transition from a night maximum to a day maximum in temperature trends over China, so there was no diurnal cycle in the trends
Summary
Recent studies have shown that temperatures at different local times have had different trends. The influential factors leading to the general decrease of DTR and the varied regional trends over the global lands are unclear, though a few studies attributed them to the increasing cloudiness resulting from global climatic warming (e.g. Easterling et al 1997; Dai et al 1999; Duan and Wu 2006), the land use and land cover change Zhou and Ren (2009) and Ren and Zhou (2014) indicated that urbanization effects could explain almost all of the decreasing trends of DTR for the past five decades for the national reference climate stations and basic meteorological stations in North China. The previous studies covering China usually used daily or monthly mean temperature data from national reference climate stations and national basic meteorological stations in mainland China. The results enable us to surmise the likely forcings underlying sub-daily temperature change in a sub-continental region
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