Abstract
Abstract. Long-term surface air temperatures at 1.5 m screen level over land are used in calculating a global average surface temperature trend. This global trend is used by the IPCC and others to monitor, assess, and describe global warming or warming hiatus. Current knowledge of near-surface temperature trends with respect to height, however, is limited and inadequately understood because surface temperature observations at different heights in the surface layer of the world are rare especially from a high-quality and long-term climate monitoring network. Here we use high-quality two-height Oklahoma Mesonet observations, synchronized in time, fixed in height, and situated in relatively flat terrain, to assess temperature trends and differentiating temperature trends with respect to heights (i.e., near-surface lapse rate trend) over the period 1997 to 2013. We show that the near-surface lapse rate has significantly decreased with a trend of −0.18 ± 0.03 °C (10 m)−1 per decade indicating that the 9 m height temperatures increased faster than temperatures at the 1.5 m screen level and/or conditions at the 1.5 m height cooled faster than at the 9 m height. However, neither of the two individual height temperature trends by themselves were statistically significant. The magnitude of lapse rate trend is greatest under lighter winds at night. Nighttime lapse rate trends were significantly more negative than daytime lapse rate trends and the average lapse rate trend was three times more negative under calm conditions than under windy conditions. Our results provide the first observational evidence of near-surface temperature changes with respect to height that could enhance the assessment of climate model predictions.
Highlights
Physical properties of the atmosphere and dynamic processes mix heat vertically and horizontally, yielding the highest temperatures, on average, at the surface with marked seasonal and spatial variations (IPCC, 2013; Karl et al, 2006)
For the period of 1997 to 2013, when trends of surface temperature anomalies are evaluated by individual surface temperatures at 1.5 m (T1.5 m) and 9.0 m (T9.0 m) from Oklahoma Mesonet stations, statistically non-significant trends of +0.065 ± 0.59 ◦C per decade and +0.281 ± 0.58 ◦C per decade, respectively were documented (Fig. 2a and b)
A greater warming at the 9 m level, or larger cooling at the 1.5 m screen level would explain such an observation. This is important as the surface temperature is used to diagnose and model global warming (IPCC, 2013)
Summary
Physical properties of the atmosphere and dynamic processes mix heat vertically and horizontally, yielding the highest temperatures, on average, at the surface with marked seasonal and spatial variations (IPCC, 2013; Karl et al, 2006). Climate models indicate a distinct height-dependent temperature response to surface temperature increases (refers to air temperature at a screen height near ground surface) (Gaffen et al, 2000; Santer et al, 2005; Karl et al, 2006; Thorne et al, 2011; Seidel et al, 2012; Mitchell et al, 2013) Most of these heightdependent temperature studies focused on tropospheric temperature trends by using radiosonde and satellite observations and climate models (Thorne et al, 2011), the Published by Copernicus Publications on behalf of the European Geosciences Union. Lin et al.: Observational evidence of temperature trends near-surface temperature lapse rate has rarely been studied in the surface layer of the atmosphere
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