Dataset Information

Sampling biases in datasets of historical mean air temperature over land.

ABSTRACT: Global mean surface air temperature (Ta) has been reported to have risen by 0.74°C over the last 100 years. However, the definition of mean Ta is still a subject of debate. The most defensible definition might be the integral of the continuous temperature measurements over a day (Td0). However, for technological and historical reasons, mean Ta over land have been taken to be the average of the daily maximum and minimum temperature measurements (Td1). All existing principal global temperature analyses over land rely heavily on Td1. Here, I make a first quantitative assessment of the bias in the use of Td1 to estimate trends of mean Ta using hourly Ta observations at 5600 globally distributed weather stations from the 1970s to 2013. I find that the use of Td1 has a negligible impact on the global mean warming rate. However, the trend of Td1 has a substantial bias at regional and local scales, with a root mean square error of over 25% at 5° × 5° grids. Therefore, caution should be taken when using mean Ta datasets based on Td1 to examine high resolution details of warming trends.

SUBMITTER: Wang K

PROVIDER: S-EPMC3982162 | biostudies-other | 2014

REPOSITORIES: biostudies-other

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Sampling biases in datasets of historical mean air temperature over land.

Wang Kaicun K

Scientific reports 20140410

Global mean surface air temperature (Ta) has been reported to have risen by 0.74°C over the last 100 years. However, the definition of mean Ta is still a subject of debate. The most defensible definition might be the integral of the continuous temperature measurements over a day (Td0). However, for technological and historical reasons, mean Ta over land have been taken to be the average of the daily maximum and minimum temperature measurements (Td1). All existing principal global temperature ana ...[more]

PMID: 24717688

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Project description:Cyclohexene is an important intermediate during the combustion process of hydrocarbon and oxygenated fuels. In view of the lack of study on the combustion of cyclohexene in air, an experimental and modeling study is performed to investigate the chemistry of cyclohexene-air mixtures under a wide temperature range. The shock tube experiments are conducted at pressures of 2 and 10 atm with equivalence ratios of 0.5, 1.0 and 2.0 to determine the ignition delay times. The ignition data under 10 atm cover a wide temperature range varying from a low temperature of 770 K to a high temperature of 1222 K. No typical negative-temperature-coefficient is observed, but the ignition at low temperatures is shorter than the extrapolation at high temperatures. A detailed kinetic model of cyclohexene oxidation is proposed based on the low temperature mechanism of 1,3-cyclohexadiene and the existing high temperature mechanism of cyclohexene. The developed model reproduces the ignition delay times in air well, but it over predicts the ignition delays in argon conditions at higher temperatures. Sensitivity analyses under different temperatures and equivalence ratios are carried out to identify the key reactions affecting ignition. The reactions of H + O2 = O + OH and hydrogen abstraction reaction of cyclohexene with oxygen (CYHEXEN + O2 = CYHEXEN-3J + HO2) explain the change of ignition delay time of cyclohexene with equivalence ratios. Flux analysis gives the change of main reaction pathways under wide temperatures and different pressures. The retro-Diels-Alder reaction as the most important consumption channel of cyclohexene at the pressure of 2 atm and temperature of 1350 K is greatly suppressed when the pressure is increased to 10 atm, while the hydrogen abstraction reaction becomes the main consumption channel of cyclohexene at the high pressure. The proposed kinetic model for cyclohexene oxidation can be used to develop models of hydrocarbon and oxygenated fuels.

Dataset Information

Sampling biases in datasets of historical mean air temperature over land.

Publications

Sampling biases in datasets of historical mean air temperature over land.

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