Diurnal and intra-season variation of warm-season temperature in coastal zone of Qinghai Lake

摘要

The Qinghai Lake is the largest saltwater lake in the Tibetan Plateau and in mainland China. Effects of the lake on surface climate of the coastal areas, however, are not well understood. This article utilizes hourly observation data of warm season from 17 automatic weather stations to analyze the diurnal and seasonal variations in air temperature in different coastal zones of the Qinghai Lake. The EOS/MODIS data was also used to analyze the surface temperature differences between the lake and its surrounding areas. The results show a few unique characteristics of the plateau lake: (1) based on the satellite data, lake surface temperature is lower than its surrounding areas (4.925.1 degrees C and 12.235.6 degrees C respectively) in the daytime, while it is obviously higher than that in the surrounding areas (1.910.5 degrees C and - 13.16.3 degrees C respectively) at the nighttime. Daily mean water surface temperature is higher than that in the surrounding areas, which is 7.817.9 degrees C and - 2.617.9 degrees C respectively; (2) based on data of meteorological stations, coastal zones closer to the shoreline have a higher air temperature during the warm season largely due to the much warmer nighttime near the shoreline than those in deep inland zones. For the on-shore, near-shore, and far-shore zones, mean daytime air temperature is 8.79.6 degrees C, 9.511.1 degrees C, and 10.010.7 degrees C, respectively, and the mean nighttime air temperature is 2.94.1 degrees C, 1.312.3 degrees C, and - 0.20.4 degrees C respectively. The hourly mean diurnal temperature range (DTR) increases with distance to the shoreline, which is 8.6 degrees C, 10.9 degrees C, and 12.3 degrees C in the on-shore, near-shore, and far-shore zones respectively; (3) differences between maximum and minimum 5-day mean daily maximum (minimum) air temperature during the warm season are 20.3 degrees C (23.3 degrees C), 21.7 degrees C (25.6 degrees C), and 22.6 degrees C (26.7 degrees C) for the on-shore, near-shore, and far-shore zones, respectively, indicating an asymmetrical effect on daytime and nighttime air temperature in the on-shore zone; (4) daily maximum air temperature of the on-shore zone is lower before early October, but it is slightly higher afterward and occurs later; (5) daily minimum air temperature of the on-shore zone is on average higher than that of the far-shore zone, especially after the mid-September, and it also appears later in autumn than in summer.